Alluvial Fans 2015
5th International Conference
on Alluvial Fans
Nov. 30 – Dec. 4
University of Canterbury
Christchurch, New Zealand
Program and Abstracts Editors: Philip Giles Saint Mary’s University, Halifax, Canada Lucy Clarke University of Gloucestershire, Cheltenham, UK Jim Driscoll Monash University, Melbourne, Australia Alluvial Fans 2015
5th International Meeting on Alluvial Fans Nov. 30 – Dec. 4, 2015 Christchurch, New Zealand SCHEDULE OVERVIEW Monday, November 30 11:00 – 18:00: Welcome reception and registration, and oral presentations Location: Erskine E031 Tuesday, December 1 8:00 – approx. 18:30: Field trip to Ryton River fan‐delta Meeting point: University Hall residence Wednesday, December 2 8:00 – approx. 18:30: Field trip to alluvial fans and fluvial systems along the SH73 freeway Meeting point: University Hall residence Thursday, December 3 8:30 – 17:00: Oral and poster presentations Location: North Arts A3 Friday, December 4 8:30 – 17:00: Oral and poster presentations Location: North Arts A3 Refreshment breaks and lunch will be provided on Monday, Thursday, and Friday Lunch will be provided on the field trips on Tuesday and Wednesday University of Canterbury Campus Map [Full colour version of this map is available at www.canterbury.ac.nz/theuni/maps/] List of Participants Phillip Abraham Christchurch, NZ Chonglong Gao Beijing, China Krzysztof Senderak Sosnowiec, Poland Shahrazad Abu Ghazleh Al Ain, U.A.E. Xiaoguang Ge Hefei, China Pradip Kumar Sikdar Kolkata, India Rupert Bainbridge Newcastle, UK Parthasarathi Ghosh Kolkata, India Syama Prasad Sinha Ray Kolkata, India David Barrell Dunedin, NZ Philip Giles Halifax, Canada Brandon Smith Toronto, Canada Lee Burbery Christchurch, NZ Mike Hall Melbourne, Australia Martin Stokes Plymouth, UK Albert Cabré Copiapó, Chile Gabriel Hunger Geneva, Switzerland Jon Tunnicliffe Auckland, NZ Frédéric Christophoul Toulouse, France Youliang Ji Beijing, China Dario Ventra Utretcht, The Netherlands Attila Çiner Istanbul, Turkey Karen Kapteinis Melbourne, Australia Gary Weissmann Albuquerque, USA Lucy Clarke Cheltenham, UK Anya Leenman Auckland, NZ Michelle Wild Christchurch, NZ Will Conley Klickitat, USA Anne Mather Plymouth, UK Richard Williams Glasgow, UK Tim Davies Christchurch, NZ Hannah Mountfrort Auckland, NZ Scott Wilson Christchurch, NZ Tjalling de Haas Utretcht, The Netherlands Mitchell O'Mara Melbourne, Australia Shenghe Wu Beijing, China Andrea Deganutti Padova, Italy Phil Richards Edinburgh, UK Cengiz Yildirim Istanbul, Turkey James Driscoll Melbourne, Australia Mehmet Akif Sarikaya Istanbul, Turkey Muhammad Aleem Zahid Huangdao, China Field Trip Descriptions Tuesday, December 1 Ryton River fan‐delta [inland Canterbury Plains] Departure at 8:00 a.m.; return by approximately 18:30 Meet at University Hall residence We depart Christchurch and cross the vast outwash fan surfaces of the Canterbury Plains, which as we approach the mountains have occasional relic moraines and older higher fan surfaces visible. We wind through the last glaciation moraines and come out to a viewpoint where the deeply incised Rakaia River is fed by streams from Mount Hutt; these have left remnants of old high‐level fan surfaces adjusted to higher Rakaia River levels. We then continue through glacial deposits, including well‐defined kettle‐hole topography, terraces and meltwater channels, and the active Porters Pass fault, to the Ryton River. Here we drive to the shore of Lake Coleridge (occupying a LGM glacial trough) where the river forms a delta occupied by a low‐key camping ground. Just upstream of the delta the Ryton River flows through the deposits of multiple rock avalanches, which have temporarily blocked the river in the past, and there is evidence of dam break flood terraces; farther upstream a huge rock avalanche ca. 500 BP completely obliterated much of the upper catchment topography. There is evidence that the river has changed course at least once to flow into Lake Coleridge at a different place, so the Ryton Delta history is certainly complex. Depending on conditions and party fitness we may be able to walk about 1 km upriver from the Ryton road bridge to look at one of the course‐change locations. Either on the way up or on the way back we can divert to the settlement of Lake Coleridge where there is one of the oldest power stations in New Zealand, and we may also be able to visit the water intake site for this power scheme on the west side of Lake Coleridge. Wednesday, December 2 Alluvial fans and fluvial systems along the SH73 freeway [inland Canterbury Plains] Departure at 8:00 a.m.; return by approximately 18:30 Meet at University Hall residence We travel up the Waimakariri fan, visiting the Waimak Gorge where the river has incised approximately 50 m into the Canterbury Plains. Then we drive up the Kowhai fan, which shows multiple uplift‐related terraces, and over Porters Pass (where the trace of the last Porters Pass fault earthquake is visible) and into Castle Hill basin, an inland basin with multiple flights of aggradation (glacial) and degradation (uplift) related terraces. Here the ubiquitous and monotonous greywacke sandstone is relieved by limestone outcrops, with the Craigieburn mountains looming above. Scattered landslides indicate past seismicity, while drastically underfit rivers suggest drainage changes related to both solution and glaciation. Both alluvial and debris‐flow fans are plentiful. If time permits we can call at the historic Bealey Hotel for refreshments before returning along the same route to Christchurch. Conference Sponsors We gratefully acknowledge funding support from our sponsors which was used to provide awards for Best Student Presentation (oral and poster) and to reduce the conference registration fee for students. A student travel grant was awarded by IAS. Schedule of Presentations Monday, November 30 Time 11:00‐12:00 Welcome reception and registration 12:00‐13:00 Lunch 13:00‐13:10 Conference organizers: Lucy Clarke, Jim Driscoll, Philip Giles, Tim Davies and Christopher Gomez Introductions and opening remarks Location: Erskine E031 Session Chair: Martin Stokes 13:10‐13:50 Lucy Clarke Keynote: The geomorphological system response to avulsions on alluvial fans 13:50‐14:15 Hannah Mountfort Fan‐river coupling dynamics in the presence of sediment overloading – the Waiorongomai fan and gully mass wasting complex, East Cape, New Zealand 14:15‐14:40 Philip Giles Mapping recent decadal‐scale patterns of channel activity on a glacier‐fed alluvial fan, Yukon, Canada 14:40‐15:00 Break Presenter and Title Session Chair: Gary Weissmann 15:00‐15:25 Tjalling de Haas Autogenic avulsion, channelization and backfilling dynamics of experimental debris‐flow fans 15:25‐15:50 Anya Leenman Deciphering historic morphologic changes in alluvial fans in response to persistent catchment‐wide disturbance 15:50‐16:15 David Barrell Characterization of alluvial fan development in the eastern sector of the South Island of New Zealand 16:15‐16:35 Refreshment break Monday, November 30 Time Presenter and Title Session Chair: Karen Kapteinis 16:35‐17:00 Scott Wilson Conceptualization of groundwater recharge from a braided river: The Wairau Fan 17:00‐17:25 Lee Burbery Smoke tracing experiment applied to examine connectivity of open framework gravel facies in the Canterbury Plains aquifer 17:25‐17:50 Will Conley Alluvial fan hydroperiod as a control on migratory fish passage, Klickitat River Subbasin, Washington State, USA 17:50‐18:00 Field trip information for Tuesday and Wednesday Thursday, December 3 Time Presenter and Title Session Chair: Richard Williams 8:30‐9:10 Anne Mather Keynote: Distributary to tributary drainage transitions 9:10‐9:35 Mehmet Akif Sarikaya Dating alluvial fans with cosmogenic isotopes: An example from Aladağlar
Mountains from Central Turkey 9:35‐10:00 Cengiz Yildirim Quaternary extension of the Central Anatolia, Turkey: Inferences from offset alluvial fans 10:00‐10:45 Refreshment break & poster session List of Poster Presentations (posters will remain on display all day Thursday and Friday) Albert Cabré Sedimentary alluvial features after 25 March rainstorm event in Huasco River catchment, Atacama Region, Chile Attila Çiner [see abstract listed under surname Üner] Fan delta evolutions under the influence of structural instability in the Miocene Aksu Basin, Southern Turkey Frédéric Christophoul Fluvial to alluvial systems of the north‐Pyrenean foothill since Miocene: From DFS to contributive drainage Lucy Clarke Investigating the impact of vegetation on alluvial fans using laboratory experiments Andrea Deganutti Numerical modelling of a debris‐flow fan in Eastern Italian Alps Tjalling de Haas Surface morphology of fans in the High Arctic periglacial environment of Svalbard: Controls and processes Tjalling de Haas Recent (< 5 MA) alluvial fans on Mars: Formative processes and climatic implications Parthasarathi Ghosh A study on the propagation of the August 2008 flood on the Kosi megafan, India Philip Giles Seasonal variations in patterns of channel activity on a glacier‐fed alluvial fan, Yukon, Canada Gabriel Hunger Sedimentary responses to tectonic and climatic forcing in a fluvial‐fan setting, central Argentinian foreland (Mendoza, Argentina) Anne Mather Cause and effect: Catastrophic floods on hyper‐arid alluvial fan systems Martin Stokes Alluvial fans as recorders of volcanic island denudation Gary Weissmann Do river channels decrease in width downstream on DFS? An evaluation of modern megafans Thursday, December 3 Time Presenter and Title Session Chair: Tjalling de Haas 10:45‐11:10 Jim Driscoll Identification of alluvial fans in the rock record: A case study from a Late Cambrian‐Early Ordovician silicilastic sequence, Northern Tasmania, Australia 11:10‐11:35 Shenghe Wu Identification of fine‐grained alluvial fans in Paleogene of Jiuxi Basin, Western China 11:35‐12:00 Chonglong Gao The characteristics of alluvial fan sedimentary microfacies: A case study of Baiyanghe modern alluvial fan, northwest China 12:00‐13:20 Lunch Session Chair: Anne Mather 13:20‐14:00 Dario Ventra Keynote: Stratigraphic records of fluvial‐fan progradation: Recent insights and a model for arid settings based on the Oligo‐Miocene of the central Argentinian foreland 14:00‐14:25 Phil Richards Controls on deposition within arid continental basin margin systems: Implications for basin‐scale fluid migration 14:25‐14:50 Xiaoguang Ge How does river water chemistry impact on formation of coal seam gas in the Yellow River alluvial fan covered area, China? 14:50‐15:25 Refreshment break & poster session Session Chair: Scott Wilson 15:25‐15:50 Jon Tunnicliffe Fan‐deltas of the Western Coromandel Peninsula: An integrated study of fluvial dynamics, fan‐delta building and marine deposition 15:50‐16:15 Albert Cabré Post LGM catchments in Huasco Valley: Re‐worked landslide barriers showing alluvial fans features, northern Chile 16:15‐16:40 16:40‐(17:00) Youliang Ji The architecture of braided flood and sheet flood deposits in gravelly alluvial fans and its formation mechanism: A case study in Poplar River profile of modern alluvial fan in Xinjiang Province of Northwest China Open discussion Friday, December 4 Time Presenter and Title Session sponsored by British Society for Geomophology Session Chair: Dario Ventra 8:30‐9:10 Tim Davies Keynote: Alluvial fans and debris‐flow fans: Processes, hazards and land‐use planning 9:10‐9:35 Richard Williams Quantifying the delivery and dispersal of sediment from Te Horo landslide: New Zealand's most active alluvial fan 9:35‐10:00 Rupert Bainbridge Rock‐avalanche distribution and censoring within the Southern Alps, New Zealand 10:00‐10:45 Refreshment break & poster session Session Chair: Phil Richards 10:45‐11:10 Krzysztof Senderak The sedimentological lesson from the geophysical surveys of the high and mid‐latitudes talus slopes 11:10‐11:35 Muhammad Zahid Stratigraphic sequence, depositional architecture and reservoir quality of Eocene thin‐bedded beach facies, southern slope of Dongying depression, East China 11:35‐12:00 Shahrazad Abu Ghazleh Geomorphology and sedimentology of the Jabal Hafit alluvial fans: Implication for paleoclimatic changes of southeast Arabia 12:00‐13:20 Lunch Session Chair: Jon Tunnicliffe 13:20‐13:45 Martin Stokes Aggradational and degradational models of Pleistocene and modern tributary‐
junction fan development (High Atlas Mountains, Morocco) 13:45‐14:10 Karen Kapteinis The megafans of the northern Victorian plains: Understanding their formation and processes 14:10‐14:35 Shyamaprasad Sinha Ray Hydrogeology of the Tista megafan in the foothills of the Darjeeling Himalaya, West Bengal, India 14:35‐15:00 Refreshment break & poster session Session Chair: Philip Giles 15:00‐15:25 Parthasarathi Ghosh Topological properties of the drainage network on the Kosi megafan, India 15:25‐16:10 Gary Weissmann Keynote: Fans in the context of sedimentary basins: Future directions of fan research 16:10‐(17:00) Open discussion, presentation of student awards, consideration of a Special Issue, and closing remarks Presentation Abstracts (in alphabetical order, by first author surname) GEOMORPHOLOGY AND SEDIMENTOLOGY OF THE JABAL HAFIT ALLUVIAL FANS:
IMPLICATIONS FOR PALEOCLIMATIC CHANGES OF SOUTHEAST ARABIA
Shahrazad Abu Ghazleh1 and Osman Abdelghany2
1
Department of Geography and Urban Planning, United Arab Emirates University, Al Ain, UAE
2
Department of Geology, United Arab Emirates University, Al Ain, UAE
[email protected]
A series of alluvial fans emanate from the western and eastern sides of Jabal Hafit on the border between Oman
and the United Arab Emirates and merged together into a distinctive bajada plain. These fans comprise almost
limestone clasts that have been eroded from Jabal Hafit and deposited in the foot of the mountain during the
Pleistocene-Holocene age (Agedi, 2005).
These fans are particularly sensitive to change in rainfall pattern and sediment supply. Therefore, their
morphology and sediments preserve an excellent record of climatic and environmental changes. In spite of the
high significance of the Jabal Hafit alluvial fans in reconstructing the climatic changes of the SE Arabia, they
have not been studied yet.
Therefore, this study aims at investigating the geomorphology and sedimentology of Jabal Hafit alluvial fans and
OSL dating of their deposits in order to understand the environmental and climatological changes of the UAE
and Oman during the Pleistocene-Holocene period. This also will help to link the paleoclimatic conditions of this
area with the regional and global paleoclimatic records.
Moreover, the result of the study will provide better understanding on the monsoon variability and its influence on
the UAE and Oman during the Pleistocene-Holocene period.
Reconstructing of the paleoclimate of the southeast Arabia could also provide environmental evidence of human
dispersal from Africa to Asia, especially the study area is situated along the proposed southern dispersal rout.
This could also help to interpret the early migration of human from Arabia to the Levant and to determine the age
of some archeological sites on the Hafit bajada plain.
Keywords: Jabal Hafit, alluvial fans, southeast Arabia, geomorphology, sedimentology, OSL dating,
paleoclimatic changes
ROCK-AVALANCHE DISTRIBUTION AND CENSORING
WITHIN THE SOUTHERN ALPS, NEW ZEALAND
Rupert Bainbridge1, Stuart Dunning2 and John Woodward1
1
Department of Geography, Northumbria University, Newcastle, UK
Department of Geography, Newcastle University, Newcastle, UK
2
[email protected]
Rock-avalanches are large (typically >106 m3) flow-like landslides of dry granular material resulting from the
disintegration of a rock mass. Internal flow conditions during material transport produces large quantities of fine
grained material which can be easily remobilised by fluvial processes. Over time, this leads to erosional
censoring as reworked landslide debris becomes fluvial sediment. Erosion of mountains by large rockavalanches is therefore likely to be under represented within our records. Here we present a new literature
based rock-avalanche inventory highlighting potential areas of deposit censoring and discuss a new method for
detecting censored rock-avalanche material within fluvial systems.
The rock-avalanche inventory is composed of 265 deposit records in the South Island, New Zealand. Clustering
of deposits appears to occur in Fiordland, Central Southern Alps and Nelson regions and also highlights
mountainous areas with little or no recorded rock-avalanche activity, such as Marlborough, despite this area
having active faults and historic earthquakes.
The largest river catchments in the South Island drain east and have the largest numbers of rock-avalanche
deposits, as would be expected. However using rock-avalanches per km2 as a measure of deposit density it can
be seen that small west draining catchments have higher deposit densities than those in the east, particularly
catchments in the Nelson and West Coast regions. High deposit density indicates that these catchments may be
prone to higher sediment yields and river aggradation. In contrast to these catchments with high rock-avalanche
densities almost half of West Coast and Nelson region catchments have no recorded rock-avalanche activity
which could indicate that deposit censoring has taken place.
In order to detect fluvially censored rock-avalanche material a method developed to detect rock-avalanche
‘agglomerates’ in supraglacial debris has been applied to fluvial environments. Agglomerates (Reznichenko et
al., 2012) are microscopic particles, composed of smaller sub-micron particles, which are uniquely formed during
material transport in rock-avalanches. Examination of fluvially transported material from a tributary of the Buller
River, NZ, indicates for the first time that agglomerates persist through fluvial transport processes and that this
method may provide a diagnostic tool for detecting rock-avalanches within catchments with no recorded activity.
Keywords: rock-avalanche, censoring, agglomerates, sediment transport
CHARACTERIZATION OF ALLUVIAL FAN DEVELOPMENT IN THE
EASTERN SECTOR OF THE SOUTH ISLAND OF NEW ZEALAND
David J. A. Barrell
GNS Science, Dunedin, New Zealand
[email protected]
Alluvial fans are a near-ubiquitous feature at the periphery of mountain and hill terrain on the eastern side of the
South Island. Nationwide geological map coverage in New Zealand is provided at 1:250,000 scale (Quartermillion-scale). The 1st edition of this nationwide series was completed between the mid-1950s and late 1960s. A
fully revised 2nd edition of the series (‘QMAP’), compiled within a GIS environment, was published between 1996
and 2011 (Rattenbury & Isaac 2012; NZ. J. Geol. Geophys.). In most cases, the 1st edition maps did not
differentiate alluvial fan deposits from river deposits, apart from the sporadic display of form-lines depicting the
fall-line on fans. The 2nd edition maps explicitly differentiated alluvial fan deposits (as polygons) that were of
sufficiently large extent to depict clearly at 1:250 000 scale.
The QMAP digital database, including geological map polygons, is thus a valuable resource for the regionalscale evaluation and characterization of alluvial fans. For example, the QMAP polygons formed the basis for a
region-wide overview of alluvial fan hazards in Otago (Opus International Consultants 2009; report summary
accessible at www.orc.govt.nz, search words <Otago alluvial fans>). This overview report was followed by a
more detailed supplementary study which developed methodologies for characterizing alluvial fan hazards by a
three-fold physical evaluation of an alluvial fan system highlighting its three major components: (i) its catchment;
(ii) its stream and fan; and (iii) its downstream end (toe) (Barrell et al. 2009 – GNS Science Report CR2009/54;
report summary accessible at www.orc.govt.nz, search words <Otago alluvial fans>). Of particular note was the
assignation of an age parameter for fan surfaces, based on the degree of soil development. Those parts of
alluvial fan surfaces with immature soil (A-horizon on C-horizon) were taken to have experienced aggradational
activity within the past ~300 years, whereas fan surfaces displaying some degree of B-horizonation within the
surface soil were taken to have been free of aggradational activity for at least the past ~300 years. This two-fold
age distinction can readily be made from reconnaissance spade-dug test pits, or inspection of soil exposures,
and so is quick and easy to apply, and is relevant to land-use planning timeframes. The dominant factor
controlling the character of a fan was proposed to be a balance between: (i) sediment supply from its catchment;
(ii) sediment transport down a fan by its stream; and (iii) sediment removal at the toe of a fan. On this basis, four
types of fan were identified: (i) aggradational (sediment builds up on the fan); (ii) equilibrium (sediment is
transported down the fan and removed from its toe); (iii) degradational (sediment is eroded from the fan) and (iv)
terraced (repeated cycles of aggradation and degradation have terraced the fan). Recognition of these
behavioural types was promoted as a tool that can assist in identifying and assessing the nature and severity of
alluvial fan hazards. For example, an aggradational fan is the most susceptible to channel break-out and
flooding, whereas terraced fans may have areas that lie well above present flood levels.
The importance of sediment removal at a fan toe is highlighted in a study that examined the ages and
characteristics of Holocene alluvial fans in a mountain valley, the Havelock tributary of the Rangitata River, in
inland Canterbury (Forsyth et al. 2003; GNS Science Report SR2003/22). That study, using methods including
14
C dating and soil stratigraphy, found no particular temporal pattern of fan aggradation episodes, even on fans
lying adjacent to one another. This indicates that regional controls, such as climate, have been much less
important than localized, fan-specific controls. Of these, the location of the main stream of the valley’s trunk river
relative to the fan toe, was interpreted to be a key influence on fan aggradation, equilibrium or degradation in
that valley. Catchment stability is likely to also be an important influence, particularly where instability has a
stochastic character, related to occasional landslide events, or episodes of deep gully erosion and ravelling of
the catchment slopes.
Keywords: alluvial fans, geological hazards, geomorphic processes, alluvial fan classification, Otago,
Canterbury, New Zealand
SMOKE TRACING EXPERIMENT APPLIED TO EXAMINE CONNECTIVITY OF OPEN
FRAMEWORK GRAVEL FACIES IN THE CANTERBURY PLAINS AQUIFER
Lee F. Burbery1, Merren A. Jones2, Phillip Abraham1, Bronwyn Humphries1 and Murray E. Close1
1
2
Institute of Environmental Science and Research (ESR), Christchurch, New Zealand
School of Earth, Atmospheric and Environmental Sciences, University of Manchester, UK
[email protected]
The coalesced alluvial fans that make up the Canterbury Plains, New Zealand (NZ), host the country’s largest
and most valuable groundwater resource that is utilised for irrigation, industrial and potable water supply. Being
unconfined and overlain with poorly developed free-draining soils, the Canterbury Plains aquifer system is
particularly vulnerable to contamination from land-use activities. Macroporous, open-framework gravel (OFG)
facies of the alluvial outwash are known to facilitate preferential flow and contaminant transport through the
subsurface system (e.g., Dann et al., 2008), yet represent a complexity which is largely ignored in
hydrogeological models applied in resource management decision making. Difficulties in accessing and
characterising the sub-surface sediments and a lack of knowledge about how intra-fan sedimentary structure
influences the hydraulic properties of the aquifer are problematic factors.
As part of our ongoing research aimed at developing improved predictive models for groundwater resource
management in NZ, we carried out fieldwork targeted at mapping the 3-D architecture of a model section of the
Canterbury Plains, on the Rakaia fan. Using a novel vadose zone sampling unit (Close et al., 2011), we logged
the lithology in nine, 5.5 m deep bore holes drilled within an area of 100 m2, 15 m inland of the Canterbury
coastline. Lithofacies recorded in the bores were correlated with those observed in sea cliff sections. The
physiochemical properties of sediments in discrete facies were measured and a high-resolution hydrofacies map
was produced. A novel smoke tracing experiment was performed in the open bores, as was a water tracing
experiment, to study the interconnectedness and relative permeability of the OFGs.
Mapping identified four major hydrofacies: sand; sandy gravel matrix; open-framework gravel; clay-bound gravel.
The results from the water-tracing experiment demonstrated significant hydraulic connection between individual
OFG facies and potential for water to bypass low permeability clay-bound channels. The results of the smoke
tracer experiment confirmed that OFGs are truly “open” since smoke readily transported between bores along
these macroporous features. The effective travel times of smoke plumes observed from different bores
demonstrated that the permeability of an alluvial gravel aquifer system is anisotropic (Kx/Ky ≈ 6) and
heterogeneous. Heterogeneity evidenced within individual OFG facies appeared to be related to the relative
content of secondary clay infill.
The findings from the field experiments highlight the significant role interconnected OFGs play on transmission of
water and potential contaminants in alluvial outwash aquifer systems. At this stage we conclude: (i) that a smoke
tracing experiment proved useful for inferring knowledge about the connectivity of gravel facies in the
unsaturated zone (ii) alluvial gravel aquifers are highly anisotropic and heterogeneous, and most groundwater
flow (and by default, contaminant transport) is concentrated along macroporous gravel facies (iii) such facies are
hydraulically interconnected in all directions.
Our findings have implications for some of the general assumptions adopted in current water resource
management policies. Results from the field study will be used as model calibration constraints for groundwater
tracing studies we have undertaken in other portions of the Canterbury Plains and will be used in a mathematical
study of scaling issues in hydrogeological problems.
Keywords: smoke tracing experiment, Rakaia fan, Canterbury Plains aquifer, open framework gravel
hydrofacies, connectivity
POST LGM CATCHMENTS IN HUASCO VALLEY: REWORKED LANDSLIDE
BARRIERS SHOWING ALLUVIAL FAN FEATURES, NORTHERN CHILE
Albert Cabré1, 4, Germán Aguilar2, Rodrigo Riquelme3 and Enrique Bernárdez1
1
Departamento de Geología, Facultad de Ingeniería, Universidad de Atacama,
Avenida Copayapu 485, Copiapó, Chile
2
Advanced Mining Technology Center, Facultad de Ciencias Físicas y Matemáticas,
Universidad de Chile, Avenida Tupper 2007, Santiago, Chile
3
Departamento de Ciencias Geológicas, Facultad de Ingeniería y Ciencias Geológicas,
Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile
4
Programa de Doctorado en Ciencias Geológicas, Universidad Católica del Norte,
Avenida Angamos 0610, Antofagasta, Chile
[email protected]
Understanding fluvial evolution of a semi-arid drainage system after the LGM hasn’t been done yet in order to
understand the evolution of a fluvial system in the Andes Mountains. Geomorphological mapping has been
carried out showing different features such as: river terraces, alluvial fans, moraine systems, periglacial forms,
Knick- points, and so. Here we present detailed analysis of landslide barrier features.
Landslide barriers had been studied in many mountain systems around the world (Hewitt, 2006 and references
therein) and sedimentary record, and relations of them, is now clearly known. Alluvial fan features are always
related with tributary valleys which also fill the upstream lake. Classic elements of the degrading landslide
interruption complex are: rock avalanche materials reworking downstream, incision while barrier gets opened,
and gulling of the barrier deposit. Here we describe the reworking of the barrier deposit upstream showing
classical fan facies interdigitated with silty lake sediments. The nature of these features hasn’t been described in
landslide barrier deposits bibliography (Hewitt, 2006 and references therein) so we have focused on this
challenge.
Many landslides have been mapped in the main Huasco River Valley. Some of them show in their sedimentary
features layers of silty-mud upstream of the chaotic dam facies. Erosional surfaces inside massive angular clasts
layers showing massive debris flow facies and recognizable contact onlapping barrier deposit implies
contemporary formation of the alluvial fan interdigitated with fine lake facies.
We also sampled some carbonaceous sediment in order to date them with 14C AMS. It fits in the post LGM
sedimentary record in the Andes indicating age of 14 000 years B.P. for this river catchment (Cabré et al., 2015).
This dam is located >35 km from the last glacier front recorded in the Huasco high valley (Zech et al., 2006).
Keywords: LGM, semi-arid, northern Chile, Huasco River catchment, landslides, barrier deposits
SEDIMENTARY ALLUVIAL FEATURES AFTER 25 MARCH RAINSTORM EVENT
IN HUASCO RIVER CATCHMENT, ATACAMA REGION, CHILE
Albert Cabré1, 4, Germán Aguilar2, Rodrigo Riquelme3 and Enrique Bernárdez1
1
Departamento de Geología, Facultad de Ingeniería, Universidad de Atacama,
Avenida Copayapu 485, Copiapó, Chile
2
Advanced Mining Technology Center, Facultad de Ciencias Físicas y Matemáticas,
Universidad de Chile, Avenida Tupper 2007, Santiago, Chile
3
Departamento de Ciencias Geológicas, Facultad de Ingeniería y Ciencias Geológicas,
Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile
4
Programa de Doctorado en Ciencias Geológicas, Universidad Católica del Norte,
Avenida Angamos 0610, Antofagasta, Chile
[email protected]
During the extraordinary runoff event in Atacama Region (25 March 2015, northern Chile) some of the tributary
drainage basins gave a huge sedimentary input to the main Huasco River Valley. This valley infilling is mainly
controlled by the alluvial fans environment which also represents catchment features flooding huge valley areas.
In this work we describe sedimentary features in main Huasco River and tributary valleys. The study of the
present sedimentary features allows understanding past sedimentary records and geomorphological features
which have been dated by 14C. In order to estimate sediment volumes, GPS, GIS and field measures had been
done. These data allowed us to understand how erosion rates are modified by one big rain event in a semi-arid
fluvial drainage basin (Aguilar et al., in prep.).
Sedimentary analysis of the debris-flow deposits and topographic effects on the local catchment in the main river
is in course. Lateral discharge from tributary valley construct dams in floodplain areas contributing to the main
flooding event.
Mapping and stratigraphic record of some of these catchments allow us to understand past dams caused by
alluvial fans which could have affected the sediment transference down-valley after the LGM.
Keywords: semi-arid, northern Chile, Huasco River catchment, rainstorm, 25 March, floods
FLUVIAL TO ALLUVIAL SYSTEMS OF THE NORTH-PYRENEAN FOOTHILL
SINCE MIOCENE: FROM DFS TO CONTRIBUTIVE DRAINAGE
Frédéric Christophoul
Geosciences Environment Toulouse (GET), Université de Toulouse, CNRS, IRD, OMP, France
[email protected]
In the evolution of foreland basins, fluvial and alluvial deposits mainly occur in syntectonic series where they
constitute the “molasses”. The classic evolution of the fluvial systems associated to the history of foreland basins
starts with alluvial systems changing progressively to lower slope distributive fluvial systems. Grain size is
supposed to reduce progressively with time as the catchments increase in size and the transport distance from
the source area increases. During the syntectonic stage, accommodation in the basin is mainly made of tectonic
subsidence resulting from crustal bending as a result of thrust stacking in the orogenic wedge (DeCelles and
Giles, 1996). Less attention was given to the study of the post-foreland systems, when, in the history of the
foreland basin, flexural subsidence ceases to be the main origin of accommodation in the basin. In such a case,
what are the characteristics of alluvial systems and do they react to climatic forcing?
The Aquitaine basin (southwest of France) is, since the beginning of the Iberia-Europe collision, during the
Upper Cretaceous, the retro-foreland basin of the Pyrenean orogen. On a structural point of view, the Aquitaine
basin is made from north to south of: 1) the tertiary foredeep, 2) the Sub-pyrenean fold and thrust belt and 3) the
North Pyrenean Zone.
The syntectonic series includes the fluvial bearing formations from Maastrichtian to Paleocene, the marine
deposits of the north Pyrenean trough (Early Eocene), the Upper Eocene molasses (“poudingue de Palassou”
formation and the Oligocene through Lower Miocene north Pyrenean molasses. Lower Miocene to Quaternary
consists in fluvial to alluvial deposits covering the major part of the north Pyrenean piedmont. This system
exhibits a peculiar fan shape.
The post-foreland fluvial system of the north Pyrenean foothill involves several formations: Miocene consist in
randomly alternating wide and low depth channels mainly filled by sands and gravels and floodplain deposits
exhibiting numerous paleosoils with calcretes. They deposited in the foredeep of the basin. The upper part of the
formation covers the sub-pyrenean fold and thrust belt. This formation is interpreted as a braided fluvial system,
maybe ephemeral deposited in a relatively dry climatic context.
Ponto-Pliocene gravels are made of heterometric gravels (clasts up to 75cm in diametre) with sandy and muddy
matrix, interbedded with decimeter thick massive mud deposits lacking pedogenic features. Channel geometry is
difficult to evidence as it exceeds the extension of outcrops. This formation is interpreted as an interbedded
alluvial/ gravel bed braided fluvial system corresponding to the toe of and alluvial fan. This formation only
deposited ontop of the sub-pyrenean fold and thrust belt with material issued from the Pyrenees.
The Lannemezan Fm. is pliocene to low quaternary in age. It is made of matrix supported coarse to very coarse
gravels (clasts up to 2 m in diameter). Matrix is mainly muddy. The top of the formation is highly weathered. This
formation is interpreted as alluvial fans deposits.
Since Lower quaternary, the fluvial system stopped aggrading on the foothill. Quaternary deposits consist in a
network of five stepped terraces. The age of the beginning of the foothill incision started after 300 ka.
The study of the evolution of the post-foreland fluvial system of the north-pyrenean foothill shows a great change
in the structure of the fluvial systems through times. This system evolved froman aggrading fluvial system to
alluvial fans together with a retrogradation of the apexes southward. Paradoxically, grain size increased as
tectonics was quiet. This evolution may be better the result of climatic forcing and/or orogen scale tectonic
vertical movement such as isostatic readjustment in response to erosion of the Pyrenean chain.
Keywords: north Pyrenean foothill, fluvial, alluvial, post-foreland, DFS, contributive drainage
THE GEOMORPHOLOGICAL SYSTEM RESPONSE TO AVULSIONS ON ALLUVIAL FANS
Lucy E. Clarke
School of Natural and Social Sciences, University of Gloucestershire, UK
[email protected]
The impact and response of fluvial systems to avulsions (a dramatic change in the location of the active channel)
is a topic of ongoing debate. The majority of this research has been carried out in large river systems; however
observations on alluvial fans indicate that similar processes are operating on this smaller scale system and
present a major hazard in these environments. This presentation investigates the response of temperate gravel
alluvial fans following a major avulsion utilising image analysis of multi-date aerial photography to identify past
changes and to enable high resolution reconstruction of current fan conditions. Combining these techniques
allows detailed insight into the processes operating on the alluvial fans both prior to and following a major
avulsion.
Using study sites in Scotland and New Zealand that have experienced an avulsion event in recent history, multidate aerial photography were used to explore the system changes that occurred in response to this episode.
This included temporal analysis of the position of the channel pre- and post-avulsion, and volumetric changes of
the fan surface to identify areas of aggradation and degradation. Preliminary analysis has shown that the
position of the active channel altered continually over the observed period, with channel switching and changes
in morphology a characteristic feature of the post-avulsion alluvial fan systems. Through reconstruction of the
morphology and flow conditions pre- and post-avulsion it is hoped that better understanding can be gained of the
processes operating and driving avulsion on small-scale alluvial fans.
Keywords: alluvial fans, avulsion, geomorphology, system response
INVESTIGATING THE IMPACT OF VEGETATION ON ALLUVIAL FANS
USING LABORATORY EXPERIMENTS
Lucy E. Clarke1, Stuart McLelland2 and Tom Coulthard2
1
School of Natural and Social Sciences, University of Gloucestershire, UK
2
Geography Environment and Earth Sciences, University of Hull, UK
[email protected]
Riparian vegetation can significantly influence the geomorphology of fluvial systems, affecting channel geometry
and flow dynamics. However, there is still limited understanding of the role vegetation plays in the development
of alluvial fans, despite the large number of vegetated fans located in temperate and humid climates. An
understanding of the feedback loops between water flow, sediment dynamics and vegetation is key to
understanding the geomorphological response of alluvial fans. But it is difficult to investigate these relationships
in the natural world due to the complexity of the geomorphic and biological processes and timescales involved,
whereas the controlled conditions afforded by laboratory experiments provide the ideal opportunity to explore
these relationships.
To examine the effects of vegetation on channel form, flow dynamics and morphology during fan evolution, a
series of experiments were conducted using the Total Environment Simulator (operated by the University of
Hull). The experiments followed a ‘similarity of processes’ approach and so were not scaled to a specific field
prototype. Live vegetation (Medicago Sativa) was used to simulate the influence of vegetation on the fan
development. A range of experiments were conducted on 2x2 m fan plots, the same initial conditions and
constant water discharge and sediment feed rates were used, but the vegetation density and amount of
geomorphic time (when the sediment and water were running and there was active fan development) between
seeding / vegetation growth varied between runs.
The fan morphology was recorded at regular intervals using a laser scanner (at 1mm resolution) and high
resolution video recording and overhead photography were used to gain near-continuous data quantifying fan
topography, flow patterns, channel migration and avulsion frequency. Image analysis also monitored the spatial
extent of vegetation establishment. The use of these techniques allowed collection of high resolution spatial and
temporal data on fan development with minimal disruption to the experiments.
Results indicate that vegetation has a major influence on fan morphology and flow conditions; creating steeper
and shorter fans, whilst also reducing the number of active channels and lowering the lateral migration rate.
Vegetation also impacted avulsion behaviour by reducing the frequency of avulsion events, but increasing the
magnitude of the events that occurred.
Keywords: alluvial fans, vegetation, experimental, physical model, channel change, flow patterns
ALLUVIAL FAN HYDROPERIOD AS A CONTROL ON MIGRATORY FISH PASSAGE,
KLICKITAT RIVER SUBBASIN, WASHINGTON STATE, USA
William C. Conley, Jr, Nicolas Romero and David Lindley
Yakama Nation Fisheries Program, Klickitat Field Office, Klickitat, Washington, USA
[email protected]
The Klickitat River Subbasin is located along the margin of the Columbia River Basalt Province and Cascade
Mountains in southern Washington State, USA. Given structural influences of the Yakima Fold Belt, tributary
catchment morphology in the lower Klickitat subbasin tends to have relatively flat-lying headwaters drained by
seasonal channels that feed incised, bedrock-controlled reaches of largely seasonal and/or spatially
discontinuous hydroperiod. Alluvial fans at the interface with the moderately confined Klickitat River valley are
small (<25 ha), composed primarily of granular cobble and boulder sized materials, and largely inactive with
infrequent (decades or centuries) debris flows likely driving their form.
Salmonid fishes of various species and migratory forms (steelhead/rainbow trout (Oncorhynchus mykiss) and
coho salmon (O. kisutch)) utilize these small tributaries (typically < 20 km2) for various life-history purposes.
Surface flow seasonality, duration, and frequency across alluvial fans are key elements in the nature and
duration of fish use. Given the cultural importance of these fish species to the Yakama People, studies are
underway to increase understanding of the significance of these largely seasonal and spatially discontinuous
habitats.
Several tributaries are in their fourth year of study, inclusive of stream gages and fixed Passive Integrated
Transducer (PIT) tag interrogation stations. Stream gage data has been correlated with field mapping of
hydrographic conditions using high-resolution (1 m) GPS to determine which portions of each stream are
accessible at a given stage. PIT-tag stations permit detection and identification of unique individuals that have
been tagged both upstream in each tributary (typically juveniles), in the mainstem Klickitat River (typically
adults), and, in some cases, other tributaries. Pairing of these data have provided insights into habitat utilization
by documenting timing, frequency, and duration of fish movements which tend to be strongly correlated with
freshets.
Keywords: biogeomorphology, alluvial fans, streamflow intermittency, fish migration, fish passage Columbia
River Basin, Klickitat River
ALLUVIAL FANS AND DEBRIS-FLOW FANS:
PROCESSES, HAZARDS AND LAND-USE PLANNING
Tim Davies
Geological Sciences, University of Canterbury, Christchurch, New Zealand
[email protected]
The processes that form a fan are the processes that cause the hazards that accompany human use of the fan.
These processes and hazards are quite different for debris-flow and alluvial fans, so it is critically important that
land-use plans recognise this and zone fans for hazards accordingly. However, identifying what sort of
processes occur on what sorts of fans is difficult due to the fact that most debris-flow fans experience debrisflows relatively rarely, and in fact experience fluvial events most of the time, so the morphologies of such fans
may lack clear evidence of debris flows. In such cases catchment channel characteristics and catchment
morphometry may provide useful indicators of sites where subsurface investigations are needed to assess
debris-flow hazards as a basis for planning decisions. A New Zealand example is discussed and will be visited
on the post-conference field trip.
Keywords: alluvial fans, debris-flow fans, hazard, land-use planning
AUTOGENIC AVULSION, CHANNELIZATION AND BACKFILLING
DYNAMICS OF EXPERIMENTAL DEBRIS-FLOW FANS
Tjalling de Haas, Wilco van den Berg, Lisanne Braat and Maarten G. Kleinhans
Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
[email protected]
Alluvial fans develop their semi-conical shape by quasi-cyclic avulsions of their geomorphologically active sector
from a fixed fan apex. These cyclic avulsions have been attributed to both allogenic and autogenic forcings. On
debris-flow fans, autogenic dynamics were until now not directly observed, while physical scale experiments with
demonstrated cyclicity were exclusively on fluvial fans.
We experimentally created debris-flow fans under constant extrinsic forcings and observed cyclic autogenic
sequences of backfilling, avulsion and channelization. These cycles are governed by topographic compensation
on large spatio-temporal scales, which also drives avulsion cycles on these scales on other fan types. However,
the detailed processes that govern the autogenic dynamics are unique for debris-flow fans.
Backfilling, avulsion and channelization were gradual processes, which required multiple successive debris-flow
events. The progradational and retrogradational phases required a similar number of debris flows to complete.
Backfilling commenced when debris flows reached their maximum possible length, after which debris flows
became progressively shorter and wider until the entire channel was filled and avulsion was initiated.
Backfilling was governed by the following interactions. A shorter debris flow led to more in-channel
sedimentation. Consequently, there was more overflow in the subsequent debris flow, which led to a less
focused momentum to the flow front and therefore shorter runout. Simultaneously, the lobe deposit moves
upstream, which also forces deposition upstream as it provides a local low-gradient area, similar to the
interaction between flow and mouth bars that results in deposition in fluvial fans and fan deltas.
Debris flows avulse towards the most preferential flow path, which is defined by the balance between fan
gradient and flow inertia. In the channelization phase, debris flows become progressively longer and narrower
because momentum is increasingly focused to the flow front as flow narrows, resulting in longer runout and
deeper channels.
Keywords: debris-flow fan, debris flow, autogenic dynamics, experiment
SURFACE MORPHOLOGY OF FANS IN THE HIGH-ARCTIC PERIGLACIAL
ENVIRONMENT OF SVALBARD: CONTROLS AND PROCESSES
Tjalling de Haas1, Maarten G. Kleinhans1, Patrice E. Carbonneau2,
Lena Rubensdotter3, 4 and Ernst Hauber5
1
Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
2
Department of Geography, Durham University, Durham, UK
3
Department of Arctic Geology, University Centre in Svalbard, Longyearbyen, Norway
4
Geological Survey of Norway, Trondheim, Norway
5
Institute of Planetary Research, German Aerospace Center, Berlin, Germany
[email protected]
Fan-shaped landforms occur in all climatic regions on Earth. They have been extensively studied in many of
these regions, but there are few studies on fans in periglacial, arctic and antarctic regions. Fans in such regions
are exposed to many site-specific environmental conditions in addition to their geological and topographic
setting: there can be continuous to discontinuous permafrost and snow avalanches and freeze-thaw cycles can
be frequent.
We study fans in the high-arctic environment of Svalbard to (1) increase our fundamental knowledge on the
morphology and morphometry of fans in periglacial environments, and (2) to identify the specific influence of
periglacial conditions on fans in these environments. Snow avalanches have a large geomorphic effect on fans
on Svalbard: the morphology of colluvial fans is mainly determined by frequent snow avalanches (e.g., flattened
cross-profiles, exposed fine-grained talus on the proximal fan domain, debris horns and tails). As a result, there
are only few fans with a rockfall-dominated morphology, in contrast to most other regions on Earth. Slush
avalanches contribute significant amounts of sediment to the studied alluvial fans. The inactive surfaces of many
alluvial fans are rapidly bevelled and levelled by snow avalanches, solifluction and frost weathering. Additionally,
periglacial reworking of the fan surface often modifies the original morphology of inactive fan surfaces, for
example by the formation of ice-wedge polygons and hummocks. Permafrost lowers the precipitation threshold
for debris-flow initiation, but limits debris-flow volumes. Global warming-induced permafrost degradation will
likely increase debris-flow activity and -magnitude on fans in periglacial environments. Geomorphic activity on
snow avalanche-dominated colluvial fans will probably increase due to future increases in precipitation, but
depends locally on climate-induced changes in dominant wind direction.
Keywords: alluvial fan, colluvial fan, periglacial, snow avalanche, debris flow, Svalbard
RECENT (< 5 MA) ALLUVIAL FANS ON MARS:
FORMATIVE PROCESSES AND CLIMATIC IMPLICATIONS
Tjalling de Haas1, Susan J. Conway2, Ernst Hauber3, Dario Ventra1, Andreas Johnsson4,
Henk van Steijn1 and Maarten G. Kleinhans1
1
Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
Department of Physical Sciences, Open University, Milton Keynes, UK
3
Institute of Planetary Research, German Aerospace Center, Berlin, Germany
4
Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden
2
[email protected]
Small alluvial fans (gullies) are among the youngest landforms formed by liquid water on Mars. Some were
active in the last Ma, and therefore gullies are of critical importance in resolving the planet’s most recent
hydrologic and climatic history. Water-free sediment flows, debris flows and fluvial flows have all been identified
in gullies. These processes require very different amounts of liquid water, and therefore their relative contribution
to gully-formation is of key importance for climatic reconstructions.
We show that the formative mechanism of Martian gully-fans were previously often misinterpreted from surficial
analyses because their surface morphology is generally dominated by secondary, post-depositional, processes
including wind erosion and weathering.
For this reason we perform sedimentological analyses on outcrop exposures in gully-fans from HiRISE images
(~25 cm spatial resolution), because fan deposits are reworked at their surface but not internally. We show that
many gullies dominantly formed by debris flows. The great majority (96%) of outcrop exposures in gully-fans fed
by catchments that comprise abundant boulders contain sedimentological evidence for debris-flow formation.
These exposures contain many randomly distributed large boulders >1 m) suspended in a finer matrix and in
some cases lens-shaped and truncated layering. The inferred debris-flow origin for many gullies implies limited
and ephemeral liquid water during gully-formation.
We quantify the amount and frequency of liquid water generation in the last Ma from a bajada with pristine
debris-flow deposits in Istok crater, which is the only crater with largely unmodified morphology that is currently
found on Mars. Gully-fans are generally believed to be hydrologically active during periods of high orbital
obliquity. We determine debris-flow size, frequency and associated water volumes in Istok crater, and show that
debris flows occurred at Earth-like frequencies during short high-obliquity periods. Results further imply that local
accumulations of snow/ice within gullies were much more voluminous than currently predicted; melting must
have yielded centimeters of liquid water in catchments; and recent aqueous activity in some mid-latitude craters
was much more frequent than previously anticipated.
Keywords: alluvial fan, Mars, debris flow, sedimentology, stratigraphy, climate, return period
NUMERICAL MODELLING OF A DEBRIS-FLOW FAN IN EASTERN ITALIAN ALPS.
Andrea M. Deganutti1, Pia R. Tecca1 and Giuseppe Nigro2
1
Research Institute for Hydrological and Geological Hazard Prevention-CNR, Padova, Italy
2
Consultant geologist, Padova, Italy
[email protected]
The knowledge of flow rheology, the accurate prediction of runout distances, and velocities, can reduce the
casualties and property damage produced by debris flows, providing a means to delineate hazard areas, to
estimate hazard intensities for input into risk studies and parameters for the design of control works.
The application of models which describe the propagation and deposition of debris flow for the hazard
delineation and estimation, requires detailed topography, hydrological and rheological data that are not always
available.
In the Tolmezzo area, Eastern Italian Alps, a wide, complex shaped debris flow fan is built by a torrent and its
several tributaries. The material transported by these events invaded a very busy national road.
We compared the results of simulations carried on with two different single-phase, non-Newtonian models, the
two-dimensional FLO-2D and IDRA2D DF, in order to test the reliability to simulate the dynamic behaviour of the
design debris flow. Data from field topographic surveys and from the rain gauges of the valley are used in order
to build a trustworthy numerical model for deposition simulation.
FLO-2D model creates a more accurate representation of the hazard area in terms of flooded area, but the
results in terms of runout distances and deposits thickness are similar to the open-source IDRA2D DF results.
Parameters obtained through back-analysis with both models can be applied to predict hazard in other areas
characterized by similar geology, morphology and climate.
Keywords: debris-flow fan, debris flows, hazard, numerical modelling, IDRA2D DF, FLO-2D
IDENTIFICATION OF ALLUVIAL FANS IN THE ROCK RECORD:
A CASE STUDY FROM A LATE CAMBRIAN–EARLY ORDOVICIAN
SILICICLASTIC SEQUENCE, NORTHERN TASMANIA, AUSTRALIA
James Driscoll and Mike Hall
School of Earth, Atmosphere & Environment, Monash University, Melbourne, Australia
[email protected]
Alluvial fans and associated braided fluvial deposits typically have poor preservation potential in the geological
record since they are very high energy and dynamic subaerial systems.
Here we present a methodology for the identification of alluvial fan and low-sinuosity, multiple-channel braided
river successions in the late Cambrian–Early Ordovician siliciclastic sequence of northern Tasmania, Australia.
Four terrestrial lithofacies have been identified comprising a generally fining-up, conglomerate-dominated
(Roland Formation) through sandstone-dominated (Moina Formation) sequence. The facies architecture is
differentiated on the basis of grain size and shape, sedimentary textures and fabric, lithology, and clast
composition. Two further lithofacies representing transitional through shallow marine environments were also
identified.
The alluvial fan lithofacies are represented by moderately to thickly bedded, pebbly sandstone to cobble–boulder
conglomerate, with chaotic fabrics evident in the more proximal areas and sheetflood fabrics in the more distal
portions of the fans. The transition between the alluvial fan and braided fluvial system is represented by
moderately bedded, pebble–cobble conglomerate with interbeds of lateral impersistent wedges of fine-grained to
granule channel sandstone.
Adjacent lithofacies commonly have sharp contacts or rapid transition with each other, suggesting accelerated
changes in the volume of sediment flux and/or the rate of tectonic subsidence. In addition, sediments within the
alluvial fan and braided fluvial setting typically display a strong proximal–distal grain-size relationship.
The distribution and juxtaposition of the lithofacies and the associated sedimentary features within the late
Cambrian–Early Ordovician siliciclastic sequence has allowed construction of a detailed stratigraphic
architecture. This, in turn, enabled the basin configuration and structural framework of the extensional tectonic
setting to be established. This proved vital in understanding the nature of the fault networks operating, and
allowed us to trace the transition from an active rifting succession to a post-rift system.
Keywords: rift, extensional tectonics, fluvial fans, lithofacies, fault networks, extension, braided fluvial,
conglomerate, sheetflood
THE CHARACTERISTICS OF ALLUVIAL FAN SEDIMENTARY MICROFACIES:
A CASE STUDY OF BAIYANGHE MORDEN ALLUVIAL FAN, NORTHWEST, CHINA
Chonglong Gao1, 2, Youliang Ji1, 2, Ying Ren1, 2, Dawei Liu1, 2, Xiaobing Duan1, 2 and Zhijun Huan1, 2
1
College of Geosciences, China University of Petroleum (Beijing), Beijing, China
2
State Key Laboratory of Petroleum Resource and Prospecting,
China University of Petroleum (Beijing), Beijing, China
[email protected]
Baiyanghe morden alluvial fan formed during the late quaternary period, is located in the northwest boundary of
Junggar Basin, China. It is a typical piedmont semi-conical coarse clastic sedimentary body with a maximum
horizontal width of 38 km, and longitudinal length of 27 km. Controlled by an active normal fault, present alluvial
fan is the production of superposition of multiple-phase fans. Latest three fans in the body of Baiyanghe alluvial
fan can be figured out in the field outcrop, and are analyzed to study the characteristics of alluvial fan
sedimentary microfacies. In addition, depositional differences of different parts within an alluvial fan are revealed
in the research.
In the root fan, four sedimentary microfacies can be identified, namely, debris flow, main braided river channel,
gravel bar and stream channel. Debris flow is the most coarse-grained part and the maximum gravel diameter
can reach 60cm. The lithofacies of debris flow can be divided into two types: graded bedding conglomerate and
matrix supported conglomerate. Main braided river channel can be easily figured out by scour surface, but due
to the migration of braided river channel, early deposition can be reformed in later period. There exists one
typical lithofacies in main braided river channel, named “skeleton conglomerate”, which shows gravel supported
and no fine-grained sediments among gravels. Between main braided river channels, there are gravel bars.
While, the stream channel is the most fine-grained part in root fan, it is formed during the last period of alluvial
fan, and mainly distributed on top of braided river channel or gravel bars. Lithofacies of stream channel are
sandstone and siltstone.
In the mid-fan, four sedimentary microfacies can be identified as well, namely, sheet flow, braided river channel,
gravel bar and stream channel. Compared with root fan, the scale and grain size of braided river channel, gravel
bar and stream channel become smaller. But the number of braided river channel becomes larger and the
migration frequence of braided river channel becomes more rapid, which lead to more complex relations
between braided river channels and gravel bars. The location of stream channel is still mainly on top of braided
river channel or gravel bars, but its proportion increases. Besides all these changes above, beddings of the three
microfacies sediments become clearer, more varied and more typical in mid-fan, indicating that the mechanism
of deposition transforms from turbulent current to tractive current compared with root fan. For sheet flow
deposition, it can be easily figured out by the large scale parallel bedding in conglomerate, and this microfacies
mainly distributes in the transitional zone of root fan and mid fan.
In the outer fan, where is the most fine-grained part of alluvial fan, two sedimentary microfacies can be identified,
namely, flood plain and surface runoff. The flood plain is characterized by thick mudstone or siltstone, and is the
belt where plants grow lushly. Surface runoff is the extension of braided river channel in mid fan. Due to the
decrease of water energy and volume, surface runoff is characterized by sandstone or pebbly sandstone, and
the scale of water channel becomes smaller and shallower. Moreover, surface runoff gradually disappears in the
plane, and the fixed water channel of surface runoff results in isolated sandbody among floodplain mudstone on
the section.
Keywords: Baiyanghe alluvial fan, sedimentary characteristics, sedimentary microfacies, northwest China
HOW DOES RIVER WATER CHEMISTRY IMPACT ON FORMATION OF COAL SEAM GAS
IN THE YELLOW RIVER ALLUVIAL FAN COVERED AREA, CHINA?
Xiaoguang Ge and Ni Zhou
School of Resources and Environmental Engineering, Hefei University of Technology, Hefei, China
[email protected]
A phenomenon in eastern China has been noticed that coal seam gas (CSG) abundances in the upper
Paleozoic coal fields were much less in the Yellow River alluvial fan covered areas than in the mountain areas
around the alluvial fan. Our investigation suggested that the chemistry of the groundwater infiltrating from the fan
down to the fan-covered coal-bearing strata takes a significant impact on methanogenesis in coal beds there.
About half of coal resources and more than 90% of CBM resources for scalable applications have been
discovered from the upper Paleozoic coal fields in China. It seems strange that almost all of high CSG coal fields
have been found only in the mountain areas surrounding the Yellow River alluvial fan, and most of low CSG coal
mines in the central areas of the fan. Earlier researchers believed which be caused by some geological structure
factors.
An ion comparison of 347 pit-water samples collected from 16 coal-mines shows that the groundwater
chemistries were generally characterized by high sulfate and low CSG in the fan covered coal-bearing areas,
while low sulfate, high bicarbonate and high CSG on edge or outer areas of the fan. The groundwater of CSG
coal fields in many countries, as a matter of fact, are all low SO42-, and most with types of Cl-Na or HCO3-Na,
which were regarded as the results of sulfate reduction by sulfate-reducing bacteria (SRB) in groundwater
(Taulis et al., 2007).
A widely accepted theory by Scott A R (1993) believes that CSG in shallow Buried coal beds may be produced
during a methanogenesis process caused by the anaerobic metabolism of methane producing bacteria (MPB).
According to Kehew (2001), methanogenesis is always preceded by adequate sulfate reduction, for MPB growth
needs a lower redox potential and is less resistant to H2S inhibition than SRB growth.
A group of groundwater bacterial samples have been collected from two coal-mines located at Yellow River
alluvial fan edges. The bacteria were identified by S16 rRNA gene nucleotide sequencing, which confirms the
presences of some genera of SRB such as Desulfovibrio and Desulfuromonadales, and MPB such as
Methanobacterium and Methanolobus. More notable is that groundwater samples collected from a coal-mine at
the central area of the Yellow River fan, were found containing high sulfate, little bacteria, and neither SRB nor
MPB detected.
It can be explained the reason why groundwater in the Yellow River alluvial fan contains high sulfate. The Loess
Plateau is located at the middle reaches of the Yellow River, where the loess layers were aeolian deposits
formed 2 Ma ago when the dry and cold early Pleistocene, and the loess components include such evaporite
minerals as gypsum and epsomite. Severe erosion on the Loess Plateau started since the Middle Pleistocene
has been continuously offering abundant source materials and forming a vast expanding alluvial fan, so far over
300 000 km2. It’s found that eroded gypsiferous loess promotes sulfate concentration of the river water to be 10
to 20 times higher than those of other rivers. We think that over 1 Ma of high sulfated water infiltration from the
Yellow River has been efficiently inhibiting methanogenesis, thus causing little GMS in coal-bearing strata
covered by Yellow River alluvial fan, eastern China.
Keywords: Yellow River alluvial fan, coal seam gas (CSG), methanogenesis, sulfate reduction,
hydrogeochemistry
TOPOLOGICAL PROPERTIES OF THE DRAINAGE NETWORK ON THE KOSI MEGAFAN, INDIA
Parthasarathi Ghosh
Geological Studies Unit, Indian Statistical Institute, Kolkata, India
[email protected]
The Kosi River, flowing through the north Bihar plain of India, receives its discharge from a huge upland
catchment basin lying within the Nepal Himalayas. Upon entering the Gangetic alluvial plain near Barahakshetra,
Nepal, the flow branches out into a distributary network before meeting the Ganga River system that flows
parallel to the axis of the modern foreland basin of the Himalayas and serves as the local base level for the
transverse river systems like Kosi. The topography of the region occupied by this distributary network is similar
to that of a low-gradient, large, fluvial fan - the Kosi megafan (Chakraborty et al., 2010). Kosi is well known for
recurrent floods and the associated course changes during historical time. Earlier workers have suggested that
the avulsion of the Kosi River is related to the megafan building processes. On 18 August 2008, Kosi breached
its eastern embankment close to the mountain front (near Kusaha). About 80-85% of the flow was diverted
through this breach (Sinha et al., 2013) and the diverted water took an axial path to cross the megafan. In this
work we explore the role of the topological properties of the pre-flood channel network on the megafan surface in
routing the flood flow.
The pre-flood channel network covering the entire fan surface has been represented by a collection of
connected polylines obtained by manually digitizing a Landsat image of 1999 in a GIS. This representation could
be considered as a directed, planer, acyclic graph, where the channel segments are the links and the
confluences are the nodes. The topological properties of this graph were studied with the help of network
analysis functions included in the NetworkX python library (http://networkx.github.io/index.html).
Further, we have compared the pre-flood network with the pattern visible in a Landsat image taken in 2013, i.e.,
after the flood event of 2008, to study the effects of that large flood on the megafan drainage system. It was
observe that though this very large flood made innumerable local modifications to the morphology of the preexisting channels, it had left the topological characteristics of the large-scale drainage network virtually
unchanged. Older channels persist and no new channel was formed. This would indicate that the extant channel
network has the necessary and sufficient topological characteristics to guide the flood flow through a particular
part of the fan surface.
The nodes occurring along the perimeter of this network serve either as the entry points (entrances) for the flood
water or as the exits situated along the toe of the fan. There are four main entrances, two located along the
western margin of the fan (left embankment) and the other two situated along the contact between the megafan
and the inter-megafan bajada lying in the east. The analyses show that the flow entering through one of the
entrances can access only a part of the entire network and reach only to a subset of the exit points. For
example, the entry point of the flood in 2008 had access to the central part of the net. As the configuration of the
entire channel network is not modified by the large flood event it might be more appropriate to consider the
reported course changes of the Kosi River in historical time (cf. Gole and Chitale, 1966) as changes in
partitioning of flow among the branches of this network.
However, during the time of heavy monsoonal precipitation a significant amount of water probably enters the
network through all the four entrances. When we calculated the number of paths passing through each of the
internal nodes (i.e., neither an entrance nor an exit) and connecting every pair of entrances and exits, we note
that the nodes lying in the axial part of the fan are the most visited ones. These busy nodes are all located along
the avulsion belt of the August 2008 flood in Kosi. It may be suggested that the topology of the pre-flood channel
network provided the best connectivity for routing the flood flow along the axial part of the fan surface. Further,
as the post-flood network is topologically similar this remains the preferred route for the future floods. However,
the changes in differential contribution of the sources and/or small topological changes around the busy nodes
can alter this connectivity pattern significantly.
Keywords: Kosi, megafan, India, flood routing, drainage network, graph topology
A STUDY ON THE PROPAGATION OF THE
AUGUST 2008 FLOOD ON THE KOSI MEGAFAN, INDIA
Parthasarathi Ghosh1 and Debasmita Majumder2
1
Geological Studies Unit, Indian Statistical Institute, Kolkata, India
Department of Geography, University of Madras, Chennai, India
2
[email protected]
The Kosi River is the combined flow of three smaller rivers called Tamar Kosi, Sun Kosi, and Arun Kosi, all rising
in Nepal Himalayas and from the northern side of the Greater Himalayan Range. Upon entering the Gangetic
alluvial plain Kosi splits into a distributary network of channels that constitutes the drainage of the Kosi megafan.
The river is well known for its recurrent course changes in historical time and the pattern of change is a live topic
in the alluvial fan literature. These avulsion events have led to a number of devastating floods in the north Bihar
plain, India, and are considered to actively guide the fan building process. Recently, on 18 of August, 2008, the
river breached its left embankment and flooded a large area. The inundation persisted for the next few months.
The flood caused a huge loss of life, livestock, crop and property. The media, administration and river scientists
consider this flood as one of the major catastrophes of recent times.
Availability of satellite images for the entire period of inundation, in this case, provides a unique opportunity to
study how a very large flood propagates. Here we present a series of inundation maps prepared from the
satellite images taken during that event and document how the pattern of inundation changed with time. The
mode of propagation of a large flood, like this one, might provide important clues for understanding the different
types flow processes operating at different stages as well as how the flood flow interacts with pre-existing, manmade structures and geomorphic features. In turn, this knowledge might help in devising improved flood-control
measures and better disaster management policies.
We note that immediately after breaching the embankment the flow travelled as a 15 km wide unconfined sheet
of water. The flow was not guided by a particular pre-existing channel of the drainage network but occupied the
space of a number of channels and floodplains. Initially (2nd to 5th day) the embankments for the highways and
the irrigation canal near Tribeniganj (mid-upper part of the fan) offered obstruction to the flow. Possibly due that
obstruction the flow began to widen and branched out towards east. This eastern branch (passing close to the
Purnia Town) grew and established the first connection between the flood water and the Ganges River (local
base level) for the first time on the 5th day. However, on the 6th day the main flood established a direct contact
with the Ganga River flowing through the central part of the fan and the eastern branch shrank.
Between the 6th and the 14th day the central flow became progressively narrow and non-branching soon after it
got connected with the local base level. The connections with the eastern branch(s) were severed. Between the
14th and the 28th day and after the end of monsoon, the central flow became channelized and restricted to the
pre-existing channels of the network. Even after three months the channels in the central part were found to be
actively carrying water. We note that the flood water traveled about 40km in first two days (i.e., 20 km/day),
90km in the first four days (22.5 km/day), 110 km in the first five days (22 km/day), and about 130 km in the first
six days (21 km/day).
In summary, in the initial phase of the flood the flow was unconfined and started to become channelized after the
establishment of full connectivity between the source and the base level. Though the flood started to recede
within two weeks but the inundation persisted for the next 3 months. The main flow was mostly restricted to the
axial part of the megafan surface and in no point of time affected the entire distributary network on the fan
surface. Before the flow was connected with the base level it was travelling at an average velocity of 20km/day.
Keywords: Kosi, megafan, India, flood propagation, inundation pattern, fluvial processes
MAPPING RECENT DECADAL-SCALE PATTERNS OF CHANNEL
ACTIVITY ON A GLACIER-FED ALLUVIAL FAN, YUKON, CANADA
Philip T. Giles
Department of Geography and Environmental Studies,
Saint Mary’s University, Halifax, Nova Scotia, Canada
[email protected]
Analysis of Landsat image data from the period 1984-2014 was conducted for the Disappointment River alluvial
fan in Kluane National Park, southwest Yukon, Canada. Discharge for this 6.0 km2 fluvial-dominated fan is
supplied predominantly by meltwater from Disappointment Glacier located 25 km upstream and from other
glaciers in the 580 km2 drainage basin. The fan is situated on the southern side of the Kaskawulsh River axial
valley and it is not covered by white spruce forest which occurs extensively on stable surfaces at similar
elevations in this area. Changes in the location of active channels on the fan surface, and the area covered by
active channels, occur frequently which prevents the growth of trees and development of forest habitat.
A sample of Landsat images was acquired from the USGS Earth Explorer online archive to study patterns of
channel activity over the three-decade study period. The months of June, July, August, and September were
each divided into periods consisting of the first two weeks and the second two weeks. For each of these eight
two-week periods, eight cloud-free images were downloaded and processed, thus creating a data set consisting
of 64 images distributed between 1984 and 2014. Images were collected by the Landsat 5, 7, and 8 sensors,
and the data were converted to common units of radiance using supplied calibration values. Spatial resolution of
the image data used is 30 metres.
Active channels carrying sediment are characterized by higher values of radiance in the visible portion and very
low values in the infrared portion of the electromagnetic spectrum. An index of channel activity was calculated
as the sum of three visible bands divided by one mid-infrared band of Landsat data: (ρ Blue + ρ Green + ρ Red) / ρ
MIR, where ρ is radiance. Higher values of the index correspond to channels transporting sediment. The midinfrared band used was Band 5 in Landsat 5 TM and Landsat 7 ETM images, and Band 6 in Landsat 8 OLI
images. Presence or absence of active channels was interpreted by applying a threshold value to each pixel in
the image to produce a map of channel activity on the fan surface for each selected image.
By combining the results of image interpretation from all 64 images, a map representing the recent decadalscale pattern of channel activity on the Disappointment River alluvial fan was created. This map shows that 4.7
km2 of the 6.0 km2 fan surface (78%) was interpreted as being pixels with an active channel in at least one of the
sample images. The central part of the fan was more frequently active than zones towards the margins, and
frequency of channel activity decreased from the apex towards the lower boundary. However, although channel
activity fluctuated and shifted to cover most of the fan surface during the study period, some principal channels
existed in which activity occurred more frequently than in adjacent locations with similar distance downfan from
the apex.
Mean daily temperatures are above 0°C in the months of May to September in the study area. Mean and
maximum values of active channel area interpreted on the fan surface in two-week periods increased slightly
from the first half of June to the first half of August and subsequently decreased rapidly to the second half of
September. Cloud-free image data had been downloaded and processed for the month of May, but the
identification of active channels was distorted by the presence of ice cover in both two-week sets of images so
these data were excluded.
Keywords: Landsat, image analysis, decadal-scale, mapping, active channels, glacier, Yukon
SEASONAL VARIATIONS IN PATTERNS OF CHANNEL ACTIVITY
ON A GLACIER-FED ALLUVIAL FAN, YUKON, CANADA
Philip T. Giles and Colin K. Werle
Department of Geography and Environmental Studies,
Saint Mary’s University, Halifax, Nova Scotia, Canada
[email protected]
Seasonal variations in patterns of channel activity on Disappointment River alluvial fan in Kluane National Park,
southwest Yukon, Canada, were interpreted from Landsat satellite images. Changes in the location and area
covered by active channels are frequent on this fluvial-dominated 6.0 km2 fan which is supplied with discharge
and sediment from Disappointment Glacier located 25 km upstream and from other glaciers in the 580 km2
drainage basin.
Landsat image data were downloaded from the USGS Earth Explorer online archive. The period of available
imagery began in 1984, and a search of the archive was conducted to determine the year in which the most
cloud-free images of the study area were available in the summer season. Mean daily temperatures are above
0°C in the months of May to September in the study area. The year 1998 had 10 suitable images, all acquired
by the Landsat 5 TM sensor between May 25 and September 28. Image data were downloaded and converted
to units of radiance using supplied calibration values. Spatial resolution of the image data used is 30 metres.
Active channels carrying sediment are characterized by higher values of radiance in the visible portion and very
low values in the infrared portion of the electromagnetic spectrum. An index of channel activity was calculated
as the sum of three visible bands divided by one mid-infrared band of Landsat data: (ρ Blue + ρ Green + ρ Red) / ρ
MIR, where ρ is radiance. Higher values of the index correspond to channels transporting sediment. The midinfrared band used was Band 5. Presence or absence of active channels was interpreted by applying a
threshold value to each pixel in the image to produce a map of channel activity on the fan surface for each date
of imagery.
The area interpreted as pixels with active channels in the 1998 sample of images ranged from a minimum of
4.85 x 105 m2 on May 25 to a maximum of 1.77 x 106 m2 on July 3. For the 10 images, the mean area with
active channels was 1.08 x 106 m2, with a standard deviation of 4.82 x 105 m2. Fluctuations occurred in the parts
of the fan that were covered by active channels, with a zone in the middle of the fan remaining active throughout
the summer season while other zones, all towards the right margin as viewed downfan from the apex, displayed
the presence and subsequent absence of active channels. In this sample of images 3.0 x 106 m2, or 50% of the
fan surface, was interpreted as pixels with an active channel in at least one image of the series.
Keywords: Landsat, image analysis, seasonal variations, map, active channels, glacier, Yukon
SEDIMENTARY RESPONSES TO TECTONIC AND CLIMATIC FORCING IN A FLUVIAL-FAN
SETTING, CENTRAL ARGENTINIAN FORELAND (MENDOZA, ARGENTINA)
Gabriel Hunger1, Andrea Moscariello1, Dario Ventra1 and Gonzalo D. Veiga2
1
Earth and Environmental Sciences, University of Geneva, rue des Maraichers 13, 1205 Geneva, Switzerland
2
Centro de Investigaciones Geológicas, Universidad Nacional de La Plata - CONICET, Argentina
[email protected]
Sediments deposited in foreland basins are accurate recorders of processes acting at different temporal and
spatial scales during orogenic uplift. The effects of allogenic forcing on foreland sedimentation are well known at
basin-scale, but uncertainties remain in deciphering and interpreting them at higher resolution, and in
differentiating them from the sedimentary changes due to autogenic processes.
Here, we present preliminary observations on the continental sedimentology and stratigraphy of the Central
Argentinian Foreland. The majority of the basin infill is comprised by the Mariño and La Pilona Formations, which
were deposited during the Miocene and cover almost 2000 m of stratigraphy. The large scale stratigraphy trend
leads to interpret the entire alluvial system as a large fluvial fan that aggraded/prograded over the proximal
margin of the foreland basin. The basin infill records a continuous sediment supply from the rising Principal
Cordillera and the first stages of the uplift of the Frontal Cordillera. The interaction of different allogenic forcing
factors, but also autogenic processes, is recorded in the compositional changes of the sedimentary infill.
This project aims to provide a detailed reconstruction of paleoenvironmental dynamics and unravel the relative
roles of climate and tectonics, using a high-resolution, integrated compositional and sedimentological analysis of
the Mariño Formation and the basal part of the La Pilona Formation. The main objectives are: (1) detect
geochemical signatures of allogenic controls; (2) track changes in sediment provenance in relation to
magmatism and exhumation of the uplifting Andes; and (3) recognize the effects of different allogenic drives on
sedimentary processes and local environmental changes; (4) testing the effectiveness of high-resolution
chemostratigraphy for correlation within fluvial-fan successions along thick stratigraphic intervals characterized
by relative architectural/ lithological homogeneity. The followed approach embodies a high-resolution
mineralogical and petrographical study, using both conventional techniques and automated QEMSCAN
technology, heavy-minerals analysis, geochemistry, radiogenic isotope analysis, and U-Pb and fission-track
dating of detrital zircons.
Preliminary geochemical and petrographic results of two 10 km distant outcrop sections show the evolution of
the sedimentary compositional signature. General trends that are common to the two sections are recognized,
reflecting the evolution of the system due to forcing factors acting at larger spatial and temporal scale (allogenic).
Isolated compositional signals, proper to each section, certainly reflecting spatially restricted process changes
(autogenic), are also identified. Quantitative measurements combined with stratigraphic correlations allow us to
constrain the relative role of the different forcing factors. Also, it will offer insights into the understanding of
comparable sedimentary complexes in the subsurface. Besides providing an extensive outcrop analogue for the
characterization and prediction of subsurface reservoirs, this project represents a significant, ground-based
assessment of mineralogical and geochemical methods for reservoir correlation and evaluation.
Keywords: Andes, foreland basin, Miocene, fluvial-fan, geochemistry, QEMSCAN, heavy minerals
THE ARCHITECTURE OF BRAIDED FLOOD AND SHEET FLOOD DEPOSITS IN GRAVELLY
ALLUVIAL FAN AND ITS FORMATION MECHANISM - A CASE STUDY IN POPLAR RIVER
PROFILE OF MODERN ALLUVIAL FAN IN XINJIANG PROVINCE OF NORTHWEST CHINA
Youliang Ji and Chonglong Gao
State Key Laboratory of Petroleum Resource and Prospecting, College of Geosciences,
China University of Petroleum, No.18, Fuxue Road, Changping, Beijing,102249, China
[email protected]
Poplar River alluvial fan located in Piedmont Zaire of northwest China, is a large gravelly modern alluvial fan,
and its radius is about 30 kilometers. Due to that the Poplar River forming alluvial fan cut down continuously,
very clear cross section of modern alluvial fans is exposed in the two sides of the river. A detailed study and
measurement are made on the Poplar River section of the modern alluvial fan, sheet flood deposits in inner fan
and braided flood deposits in middle fan are identified, the sedimentary characteristics and architecture of sheet
flood and braided flood deposits are studied, and its formation mechanism and controlling factors are analyzed.
On the Poplar River profile, it can be observed that the typical parallel bedding structure are developed in the
inner fan sheet flood deposits, and the parallel bedding is more obvious in the distal-fan direction. Gravel bar
deposits were lens-shaped in cross-section, the gravel is slightly imbricated. With increasing distance from the
proximal part of the fan, the morphology of gravel dam changed significantly, its length increases,
thickness/width ratio decreases, average gravel size is decreasing.
Braided flood channel deposits are widely distributed in the middle fan of Poplar River alluvial fan. It can be
observed from a cross-section, that the gravel deposits is interbedded with sand deposits. The gravel sediments
above scoured the sand sediments below, and cross-bedding are developed. The investigation of Poplar River
alluvial fan indicate that the deposition process of the alluvial fan is mainly braided flood, due to the frequent
diversions and erosion of braided flood, scour structure and cross-bedding are widely developed in the gravel
deposits.
The gravel in Poplar River alluvial fan are mostly rounded or sub- rounded, and are mainly grain supported, few
matrix supported, reflecting that the gravel have been transported for a long distance in the mountain rivers
before deposition.
It can be judged from the sedimentary features mentioned above, the main process that formed Poplar River
alluvial fan is a process of transport and sedimentation of sediment-rich water in high flow regime, rather than
suddenly happened landslides and rapid mud or debris flow.
Keywords: gravelly alluvial fan, sheet flood sediments, braided flood sediments, controlling factors
THE MEGAFANS OF THE NORTHERN VICTORIAN PLAINS:
UNDERSTANDING THEIR FORMATION AND PROCESSES
Karen Kapteinis1, 2, John Webb2 and Susan White2
1
2
Archaeology at Tardis Pty. Ltd.
Environmental Geoscience, Department of Ecology, Environment and Evolution,
La Trobe University, Melbourne, Australia
[email protected]
Low-angle alluvial fans occur along the northern boundaries of the Victorian highlands across the fluvial
sediments of the Murray Basin. Due to their very low angle (no more than 0.3°), these deposits were previously
classified as general channel and flood sediments of the Shepparton Formation, a Pliocene-Holocene aged
floodplain Formation on the Victorian Riverine Plain, and not as alluvial megafan deposits. By using radiometric
imagery to analyse the surficial sediments, fan-shaped structures were observed stretching north from the
Victorian uplands towards the Murray River. Three megafans are the focus of this study, and lie along the main
streams of Loddon River, Campaspe River and Bullock Creek. These fans range in length from ~110 km to ~150
km, from apex to toe, with the Loddon River and Bullock Creek fans shown to be overlapping significantly in their
middle and northern extents. The sediment profile of these megafans is a direct consequence of their formation
processes; flood events have deposited sequential layers of medium- to coarse-grained silt with interbedded
sand lenses. Coupling of the depositional mechanisms to processes upstream has shown that the likely source
of sediment for these alluvial fans is likely a combination of redeposited windblown silt, originally lain down on
the slopes of the Victorian uplands during periods of lower precipitation by prevailing winds of the time, and
weathered material from the Palaeozoic metasediment basement. Carbon 14 and relative dating techniques
have given ages for the surface sediments of the Bullock Creek and Loddon River fans. Using C14 AMS
procedures on macrocharcoal, the Bullock Creek fan was dated at ~7ka BP. The Loddon River fan was dated
indirectly using a ~1 million year old basalt flow that overlies part of the fan sediments in the southern section of
the fan. The Campaspe River fan has not been dated. Using the methods and conclusions outlined in this study,
a map can be created to identify the boundaries of other alluvial megafans in southeastern Australia, with further
inferences made to interpret the past climates and environments that contributed to their formation.
Keywords: megafans, sedimentological processes, fluvial fans, Victorian plains
DECIPHERING HISTORIC MORPHOLOGIC CHANGES IN ALLUVIAL FANS IN RESPONSE TO
PERSISTENT CATCHMENT-WIDE DISTURBANCE
Anya S. Leenman and Jon F. Tunnicliffe
School of Environment, University of Auckland, Auckland, New Zealand
[email protected]
In the Tapuaeroa River catchment in New Zealand’s East Cape region, extensive removal of the natural forest
cover between c.1880 and 1920 has resulted in catchment wide gully-initiation and pervasive, chronic
landsliding. This work examines the response of five tributary-junction alluvial fans to persistent loading by
landslide generated sediment.
Planform fan evolution has been mapped from historic aerial photography, and aggradation rates have been
determined from repeated cross-sectional surveys, both in the tributaries and mainstem channel. A dronemounted camera was used to capture high resolution photography of the five junctions in February 2015, and
converted to a 0.2 m DEM using Structure-from-Motion photogrammetry techniques. This dataset was used to
examine contemporary morphology of the fans; in particular, it allowed characterisation of the multiple
topographic levels generated during multiple “generations” of fan surfaces, formed by fan-channel incision,
aggradation, avulsion and telescoping, as well as toe-cutting by the braided mainstem channel.
We find a range of complex adjustments occurring at sub-decadal timescales, in response to the wave of
landslide generated coarse sediment. The nature of changes to fan-channel coupling (and therefore sediment
delivery) can be related to a number of factors. These include sediment calibre, mainstem rates of aggradation
and braid-channel switching, physiographic characteristics of the tributary (such as catchment size and fan
slope), and most importantly, tributary sediment loads. Ultimately, the goal of this work is to provide insights into
the role of alluvial fans in modifying the large-scale river response to the long-term, cumulative impacts of
deforestation-induced sediment loading.
Keywords: tributary-junction fan, fan coupling, sediment delivery, sediment loading, East Cape, New Zealand
DISTRIBUTARY TO TRIBUTARY DRAINAGE TRANSITIONS
Anne E. Mather1, Martin R. Stokes1 and Adrian J. Hartley2
1
2
School of Geography, Earth & Environmental Sciences, University of Plymouth, UK
Department of Geology & Petroleum Geology, School of Geosciences, University of Aberdeen, UK
[email protected]
Alluvial fan and larger, distributive fluvial systems (DFS) comprise a source catchment area with a tributary
drainage network that feeds a related sediment dispersal and accumulation area associated with a distributive
drainage network (the alluvial fan or DFS). Particularly in tectonically active terrains associated with uplift it is not
uncommon for basinal distributive drainage networks to evolve into tributary drainage networks as incision
begins to dominate in the landscape. However, in such basinal landscapes there is no continuous record of how
this transition from distributary to tributary networks occurs. At best we are left with a spatially fragmented
sedimentary record of the aggrading phases (e.g. the early, pre-incision landscape fan sediments and later,
incisional river terraces) but by its very nature, the early degradational element of the landscape change is not
preserved. Using available evidence the transformation of distributive fluvial networks into continuous fluvial
drainages has been attributed to though-fan dissection related to a range of factors. These may be ‘top down’
controls associated with catchment area changes to water and sediment supply leading to fanhead trench
development or ‘bottom up’ controls relating to basin-wide distal incision of fans related to base-level changes.
Typically the complete transformation occurs over a prolonged (Ma) time period (e.g., the Quaternary in SE
Spain reported by Harvey et al., 2012, 2014), dependent on the spatial scale and sensitivity of the system. Here
we present field examples of the role of interfan drainage in the transformation from fluvial distributary to tributary
systems using examples from tectonically active, dryland areas that preserve the transitional erosional stage
within the landscape evolution. These unique ‘snapshots’ of the degradational phase during the period of
transformation from distributary to tributary fluvial networks have been preserved as a result of catchment area
removal via tectonic activity and river capture.
Keywords: drylands, distributary fluvial systems, tributary fluvial systems, river capture, river diversion
CAUSE AND EFFECT: CATASTROPHIC FLOODS ON HYPER-ARID ALLUVIAL FAN SYSTEMS
Anne E. Mather1, Adrian J. Hartley2, Laura A. Evenstar3 and Finley M. Stuart4
1
2
School of Geography, Earth & Environmental Sciences, University of Plymouth, UK
Department of Geology & Petroleum Geology, School of Geosciences, University of Aberdeen, UK
3
School of Earth Sciences, University of Bristol, UK
4
Isotope Geoscience Unit, East Kilbride, UK
[email protected]
The Atacama Desert of Northern Chile is one of the oldest and driest deserts on Earth. As a result of its hyperaridity it preserves some of the oldest geomorphology in the world in remarkable detail. The range of flow types
preserved within Pliocene and Pleistocene alluvial fans archives cover hyperconcentrated through to cohesive
debris flow and extremely bimodal mudflows capable of transporting extreme outsize clasts over large distances
(>20 km) on low slopes (<4 degrees). Within channelized areas the hyperconcentrated flows represent
extremely high discharges of water and sediment capable of generating anti-dune bedforms in conglomerates,
reminiscent of the characteristics of outburst floods described form landslide and glacial lake outburst events.
Some of these flows were capable of transporting large (81,000 kg) boulders more than 30 km from their source
area. Of this journey the flow would have travelled some 23 km as a confined valley flow on a slope of 5% and
then more than 10 km as an unconfined flow across a fan surface with an average slope of 3.2%. The style of
deposition suggests a mixture of debris and fluvial flow behaviour. The suggested flow depths on the fan can
range from 1 - 5 m some 10 km from the apex. If we consider the possible range of fluid densities (water with
sediment to debris flow) responsible for transport, potential peak discharges of > 17 000 cumecs are suggested,
generating specific peak discharges of >23 cumecs per square km. Triggers for these events are likely to be
intense rainstorm events within a transport limited system, which in some catchments are amplified by large,
seismically generated temporary landslide blockages (individual landslide areas of up to 22 km2).
Keywords: hyper-arid, outburst flood, catastrophic flood, landslide dam
FAN-RIVER COUPLING DYNAMICS IN THE PRESENCE OF
SEDIMENT OVERLOADING - THE WAIORONGOMAI FAN AND GULLY
MASS WASTING COMPLEX, EAST CAPE, NEW ZEALAND
Hannah Mountfort and Jon Tunnicliffe
School of Environment, The University of Auckland, Auckland, New Zealand
[email protected]
The sedimentary systems of New Zealand’s East Cape are highly dynamic, due mainly to the prolific rates of
sediment yield from massive gully systems. High rates of sediment loading in the drainage network have
important repercussions for system coupling and downstream sediment transfer. The focus of this talk is the
Waiorongomai Fan and Gully Mass Wasting Complex, and the nature of fan response to high rates of sediment
delivery. Historical airphoto analysis reveals notable rates of fan growth between the 1940s and the 1980s, with
an acceleration of growth in the 1980s and 1990s. The pace of vertical aggradation in the latter 20th century is
emphasised in the inundation by fan sediments (>2 m) of an historical homestead close to the fan. The fan
extent has not changed its boundaries significantly between 2004 and present day, possibly due to a slowing of
sediment generation from the gully complex. Higher resolution (both spatial and temporal) imaging from 2014
and 2015 highlights the details of fan surface reworking and tributary channel adjustment. There are two
principal threads (north and south) that convey most of the flow; smaller scale channels develop and disappear
over the course of the airphoto time series. Grain size estimates taken from high resolution orthophotos
emphasise high silt content within the active channels, with modal pebble fractions and coarse material up to the
cobble range. A more pronounced, winnowed lag of coarser material (up to 128 mm) covers many of the older,
stable surfaces. These monthly- to decadal-scale reconstructions of the Wairongomai Fan dynamics and storage
characteristics thus provide a number of important insights into the nature of linkages between hillslope mass
wasting and fluvial response downstream.
Keywords: East Cape New Zealand, gully mass wasting complex, fan dynamics, fan morphology,
photogrammetry, airphoto time series
CONTROLS ON DEPOSITION WITHIN ARID CONTINENTAL BASIN MARGIN SYSTEMS:
IMPLICATIONS FOR BASIN-SCALE FLUID MIGRATION
Philip C. Richards1, Amy Gough2, 3, Stuart M. Clarke2 and Antoni Milodowski4
1
2
British Geological Survey, Murchison House, Edinburgh, UK
School of Geography, Geology and the Environment, Keele University, UK
3
Department of Earth Sciences, Royal Holloway University of London, UK
4
British Geological Survey, Keyworth, Nottingham, UK
[email protected]
Continental basin margins are commonly dominated by alluvial fan environments, which are long-lived
throughout basin development. Fan deposition is influenced by: 1) varied transport and depositional
mechanisms; 2) interactions between the fan and contemporaneous environments in the basin centre; 3) longterm allocyclic climatic variations; and, 4) localised autocyclic variations. Towards the distal extent of the basin,
the alluvial fan interdigitates through a zone of interaction with contemporaneous environments in the basin
centre. The sedimentology of the zone of interaction can have a significant impact upon basin-scale fluid flow by
generating or restricting fluid migration pathways between the fan and permissible reservoir or seal lithologies in
the basin centre.
This work considers a well-exposed analogue for continental basin margin systems through the examination of
the Cutler Group sediments of the Paradox Basin, western USA The work presents generalised spatial facies
models across the Cutler Group alluvial fans and the zone of interaction. Temporal facies models have been
constructed to highlight how long-term allocyclic climatic variations and short-term and localised autocyclic
variations control deposition in the Cutler Group. The identified cyclicity highlights clear horizons which can be
used to cyclostratigraphically correlate through the deposits, allowing for the further examination of basin-scale
fluid migration pathways.
The generic facies models derived from this work are applied to the basin margin sediments of the Permian
Brockram Facies, of the East Irish Sea Basin, UK. The application of the Cuter Group models provides
significant insight into the sedimentology, geometry, and flow pathway connectivity of the Brockram Facies.
This work highlights the impact of the deposits of both the alluvial fan and the zone of interaction on basin-scale
fluid migration pathways and prospectivity in continental basins. The facies models show that basin margin
sedimentation controls: 1) the connectivity of otherwise isolated potential reservoirs in the distal extent of the
basin; 2) the development of ‘thief zones’ away from distal reservoirs; 3) the creation of bypass routes to charge
distal reservoirs; and, 4) the introduction of baffles into an otherwise productive system. The net effect on fluid
flow can be examined through the generation of a climate-based cyclostratigraphical framework.
Keywords: Cutler, Brockram, alluvial fan, temporal facies models, fluid migration, basin-scale
DATING ALLUVIAL FANS WITH COSMOGENIC ISOTOPES:
AN EXAMPLE FROM ALADAĞLAR MOUNTAINS FROM CENTRAL TURKEY
M. Akif Sarıkaya1, 2, Cengiz Yıldırım1 and Attila Çiner1
1
2
Eurasian Institute of Earth Science, Istanbul Technical University, Sarıyer-Istanbul, Turkey
Kozmo-Lab, Geomorphology and Cosmogenic Nuclides Laboratory, Büyükçekmece-Istanbul, Turkey
[email protected]
Cosmogenic dating of alluvial fans relies on in-situ accumulation of cosmic ray produced nuclides in sediments,
and allows dating material independent of the more traditional radiocarbon and luminescence methods. There
are two approaches applied to date alluvial fans with single isotope; (1) surface-exposure dating of boulders, and
(2) depth-profile technique. Surface-exposure dating based on dating of multiple boulders on the surface of fan
and determining the probable exposure age from the mean of the samples. Dating individual boulders on alluvial
fans can be difficult because of the inherited component of cosmogenic nuclides at the time of deposition. This
problem can be addressed by “depth-profile dating”, which relies on collecting multiple amalgamation samples in
a 2- to 3 m deep profile.
Here, we applied both dating methods to the sequential Late Quaternary alluvial fans within the paraglacial
Ecemiş River Valley within the drainages on the Aladağlar Mountains in south central Turkey. Fans were studied
using geomorphological, sedimentological, and chlorine-36 cosmogenic nuclide dating methods to examine the
timing of alluvial fan abandonment/incision, and to understand the role of climatic and tectonic processes in the
region. These alluvial fan complexes are among the best-preserved succession of alluvial fans in Turkey and
they were offset by the major strike-slip Ecemiş Fault of the Central Anatolian Fault Zone. The alluvial fans are
mostly composed of well-lithified limestone cobbles (5 to 25 cm in size), and comprise crudely stratified thick
beds with a total thickness reaching up to about 80 m. Cosmogenic dating indicates that the oldest alluvial fan
surface (Yalak Fan) was likely formed and subsequently abandoned latest by 136.023.4 ka ago, on the
transition of the Penultimate Glaciation (Marine Isotope Stage 6, MIS 6) to the Last Interglacial (MIS 5) (i.e.
Termination II). The second set of alluvial fan (Emli Fan) was possibly developed during the Last Interglacial
(MIS 5), and incised twice by between roughly 97.013.8 and 81.213.2 ka ago. A younger alluvial fan deposit
placed on relatively older erosional terraces of the Emli Fan suggests that it may have been produced during the
Last Glacial Cycle (MIS 2). The incision times of the Ecemiş alluvial fan surfaces coincide with major climatic
shifts from the cooler glacial periods to warmer interglacial/interstadial conditions. This indicates that alluvial fans
were produced by outwash sediments of paleoglaciers during cooler conditions, and, later, when glaciers started
to retreat due to a major warming event, the excess water released from the glaciers incised the pre-existing fan
surfaces.
Keywords: cosmogenic isotopes, chlorine-36, alluvial fans, depth-profile dating, central Turkey
THE SEDIMENTOLOGICAL LESSON FROM THE GEOPHYSICAL SURVEYS
OF THE HIGH AND MID-LATITUDES TALUS SLOPES
Krzysztof Senderak1, Bogdan Gądek2, Marta Kondracka3 and Dariusz Ignatiuk2
1
Centre for Polar Studies KNOW (Leading National Research Centre),
Faculty of Earth Sciences, University of Silesia, Sosnowiec, Poland
2
Department of Geomorphology, Faculty of Earth Sciences, University of Silesia, Sosnowiec, Poland
3
Department of Applied Geology, Faculty of Earth Sciences, University of Silesia, Sosnowiec, Poland
[email protected]
The talus slopes are found in all latitudes. They are the most characteristic in the high-mountain areas and
periglacial zone, where they show the highest dynamic of the slope processes. The talus slopes are sensitive to
the changes of the climate conditions, therefore they can be used as source of information about the
paleoenvironments. Their inception and the subsequent development are often connected with the extreme
events, which influence a whole environment. In the polar and high-mountain areas this structure can determine
e.g., the end of glaciation and the beginning of deglaciation of area.
Our research was carried out on the south-western Spitsbergen and in the High Tatras (South Poland). Its aim
was to compare the talus slopes, which develop in the high and mid-latitudes. Poland was several times covered
by the Scandinavian Ice Sheet (SIS) in the Pleistocene, which contributed to inception of the mountain glaciers
in the High Tatras. The talus slopes have developed from the beginning of the Holocene. In the area of
Spitsbergen glaciation is still present. The talus slopes were developed in the conditions of periglacial zone from
the beginning of the recession of the Spitsbergen’s glaciers. In this research the talus cones from the different
latitudes were compared, but the selected forms were similar by source of detritus, size of slopes and modern
dynamic of the slope processes. For recognizing internal structure the geophysical methods were used: the
electrical resistivity tomography (ERT) and the ground penetrating radar (GPR). Data obtained from the both
methods allowed to describe cones geometry, including a thickness, a type of basement surface, and a volume
of the talus slopes as well as describing of the sedimentological structures.
The analyzed structures have a maximum thickness in an interval from 45 to 50 meters. Additionally the results
of measurements allowed to obtain the information about a depth of an active layer and the permafrost table.
The differences in the internal structure of the talus cones (from high and mid-latitude) show that in the first stage
of development of the talus slopes, various mechanisms dominated. The slopes on Spitsbergen were created by
the relaxation of basement after the rapidly deglaciation. It illustrates the more heterogeneous internal structure
and a mixed material. The talus slopes from the High Tatras are characterized by the higher textural maturity
(more sorted and smaller fraction), which indicates the activity of mechanisms connected to frozen weathering
and particle rockfall of the small rock elements. On the Spitsbergen the debris flows occur more often, which
leaves a distribution channel visible in the radargram (GPR). Application of the geophysical methods on the talus
slopes occurring in the polar environment (high-latitudes) and in the high-mountains area (mid-latitudes) in both
cases allows to read information about type of evolution and the depositional structures.
Keywords: debris cone, scree, internal structure, Spitsbergen, High Tatras, periglacial zone
HYDROGEOLOGY OF THE TISTA MEGAFAN IN THE FOOTHILLS
OF THE DARJEELING HIMALAYA, WEST BENGAL, INDIA
S.P Sinha Ray1 and P.K Sikdar2
1
Centre for Ground Water Studies, Kolkata - 700032
2
Department of Environment Management,
Indian Institute of Social Welfare and Business Management, Kolkata – 700073
[email protected]
The Tista Megafan, bounded by the River Mahananda to its west and the River Tista to the east, with the Rivers
Atrai and Karatoya flowing through its axial part covers an area of 1800 km2. This Mega Fan is broadly upward
convex with gently sloping flanks. Near its apex the surface slope is around 19o which declines to 0.01o near the
toe. The River Tista flanking the Mega fan has an average annual discharge of about 600 m3/s with higher
monthly discharge exceeding 2000 m3/s during monsoon. A radiating network of abandoned channels, forming
an intricate network of radial drainage on the Mega Fan surface has been identified in satellite images of the
Mega Fan.
The Tista Megafan is fringed on the northern side by sub-Himalayas ranges which gradually slopes downward
and merge with the alluvial plains of the Ganga, Brahmaputra river system in the south. The soils are alluvial and
predominantly coarse. The sand- gravel- boulder sequence has been encountered in the bore holes down to the
depth of 200 m. This sand- gravel- boulder sequence continues the major aquifer system, the upper part of
which contains ground water in water table condition whereas the deeper aquifer occurs under semi confined to
confined conditions. Because of high hydraulic conductivity of the aquifers, water retention capacity is low,
resulting in quick depletion of soil moisture during dry weather condition. Ground water recharging potentiality of
these aquifers has been assessed.
The ground water and the aquifer materials have excess silica which calls for suitable treatment by mixing with
dolomite dust for effective agricultural use. Iron content is quite high ranging from 2 to 10 mg/L both in shallow
and deep aquifers. Arsenic content in ground water at places is high (0.01 mg/L). Such occurrences of arsenic
have been observed in areas near the banks of the Rivers Tista and Mahananda.
The hydrogeological situation is likely to change under changed climatic projection—the rate, volume and timing
of melt run-off from the snow and glaciers are likely to be the most vulnerable component of run-off. As such it
would be prudent to incorporate possible effects of climate changes in the planning and design of management
of ground water resources in the Tista Mega Fan area.
Keywords: Tista megafan, climate change, ground water resources
AGGRADATIONAL AND DEGRADATIONAL MODELS OF PLEISTOCENE AND MODERN
TRIBUTARY-JUNCTION FAN DEVELOPMENT (HIGH ATLAS MOUNTAINS, MOROCCO)
Martin Stokes and Anne E. Mather
School of Geography, Earth and Environmental Sciences,
Plymouth University, Drake Circus, Plymouth, Devon, PL4 8AA, UK
[email protected]
Within the Dades River region of the non-glaciated south-central High Atlas Mountains of Morocco, active
modern and relict Pleistocene alluvial fans are common landscape features. The analysis of these hitherto little
studied landforms provide important spatial and temporal conceptual insights into channel coupling and climaterelated variations in sediment supply and flood regime in dryland mountain terrains.
The modern active fans that form at tributary junction settings are small features (area = <0.02 km2) and are
sourced from ephemeral tributary streams that build into the high order perennial trunk drainage of the River
Dades. The tributary catchments that generate alluvial fans possess higher relief, longer lengths, lower
gradients, and larger areas than nonfan-generating catchments. Geologically, fan-generating catchments are
underlain by folded / steeply dipping weak bedrock conducive to high sediment yield. Fans are built from debris
flow and/or fluvial processes into open or confined canyon trunk valley settings. The proximity of the perennial
trunk drainage combined with the valley morphology produces lobate or foreshortened trimmed fan forms.
Morphometric analysis of fan and catchment variables using regression and residuals reveals that tributary fans
are smaller and lower gradient than expected. This can be explained by interplay between the catchment and
trunk drainage geology, morphology, climate, and flood regime. Ephemeral tributary-junction fans develop
progressively during annual localised winter-spring storm events, attempting to build toward a morphological
equilibrium. However, the fans never reach an equilibrium morphological form as they are reset by rare (>10
year) large floods along the River Dades that are linked to regional incursions of Atlantic low pressure troughs.
Relict Pleistocene fans are less common features. They are preserved in wider trunk valley settings, possessing
large area (>0.1 km2), single level surface areas that are incised by the modern tributary channel network.
Sections through the relict fans commonly revealed >5 m aggradations of poor to moderately sorted coarse
angular gravels organised into massive or weakly stratified (<1 m thick) units that suggest debris flow and fluvial
processes. The fan sediments and surfaces grade to and bury Pleistocene river terrace levels. OSL dating of
river terrace sediments suggests climatically controlled cold stage sedimentation. Collectively, these stratigraphic
and age constraint relationships suggest coeval tributary fan building and valley floor aggradation.
Comparison of the modern and Pleistocene fan formation illustrates pronounced spatial and temporal controls
on climate-related sediment supply and flood regime behaviour, with significant interplay between the tributary
streams and the trunk valley drainage. The modern tributary fans are in a degradational or erosion mode where
tributary fans progressively build but are routinely trimmed or even completely eroded and removed (reset) by
the perennial trunk drainage (a build and reset model). In contrast, the Pleistocene fans operate in conjunction
with the trunk drainage in build mode, resulting in extensive and coeval tributary and trunk channel aggradation
to the point where sediment yield is sufficiently high to backfill tributary catchments (a build-build model). A key
difference in these fan behaviours relates to climate. The modern fans illustrate a highly complex climate pattern,
where the desert mountain climate is strongly seasonal and has a marked spatial and temporal variability that
results in a dominance of valley floor erosion. In contrast, the Pleistocene fans illustrate a much simpler climate
control where seasonality is less marked and the cold climate conditions have a regional impact with widespread
valley floor aggradation.
Keywords: tributary-junction fans, High Atlas mountains, Morocco
ALLUVIAL FANS AS RECORDERS OF VOLCANIC ISLAND DENUDATION
Martin Stokes1, Alberto Gomes2, Ana Carracedo Plumed3, Fin Stuart3 and Rosa Rocha2
1
School of Geography, Earth and Environmental Sciences, Plymouth University, Devon, UK
2
Departamento de Geografia, Faculdade de Letras do Porto, Porto, Portugal
3
Scottish Universities Environmental Research Centre, East Kilbride, Scotland, UK
[email protected]
Volcanic islands are important subaerial geomorphological features of the world’s oceans, forming from plate
motion over mantle hotspots. They have received considerable attention from geologists interested in magmatic
processes, and their potential to generate destructive tsunami. However, geomorphological research is restricted
to landslides associated with volcanic edifice collapse and marine terraces that develop around island margins.
Alluvial fans are common volcanic island features and yet little studied by the geomorphology community. The
fans can record climate-related erosion of volcanic edifices, including lava mantled slopes and landsliding
regions, and base-level changes driven by island tectonic activity or from climate-related sea-level changes.
Here we report some preliminary findings of field mapping / survey and geochronological investigations into
Quaternary alluvial fan development on two adjacent volcanic islands of the arid Cape Verde archipelago,
offshore west Africa. The Cape Verde islands have developed from Miocene to recent volcanic activity linked to
slow plate movement over a mantle hotspot. Santo Antão and São Vicente are the most northwestern islands.
Santo Antão retains a clear geomorphological expression of a volcanic caldera complex. São Vicente is highly
denuded. Both islands comprise numerous alluvial fans that appear to be recording different stages of volcanic
island erosion driven by variations in sediment supply and base-level variations. The islands are considered to
be tectonically inactive and thus landscape development is likely to be controlled primarily by climate, climaterelated sea-level change and the passive geological configuration of the volcanic island products (lava flows
etc.).
Santo Antão comprises a limited number of coalescent coastal alluvial fans restricted to the south side of the
island. This distribution is climatically controlled due to a pronounced sub-tropical (north) to arid (south side)
precipitation gradient. The largest fan (Pedrinha) is ~6 km long and up to ~4 km wide, covering an area of ~10
km2. It comprises an expansive single surface (Qf0), with a gradient of 0.03. In proximal fan areas the surface is
mantled by the Cao Grande tephra dated to ~106ka (the CAII: Eiselle et al., 2015) that forms an important
regional onshore and offshore stratigraphic marker. We have sampled the Qf0 surface for cosmogenic 3He
exposure dating on large (>0.5 m) transported basalt boulders. The fan surface is dissected by a series of
ephemeral channels, revealing poorly sorted fluvial fan sediments interbedded with lava flows and the CAII
tephra. Borehole logs reveal a 180m thick fan sediment-lava sequence suggesting prolonged coarse clastic fan
sedimentation and volcanic activity along the southern island flanks. The fan surface is dissected by ephemeral
channels. The main channel, the Ribeira das Patas, dissects the entire fan surface from the coast (~4 m deep,
~200 m wide distal fan; ~60 m deep and 10m wide proximal incision) and continues into a backfilled flank margin
catchment area (30 km2; 1500 m relief) with incision increasing up to 110 m. The catchment infill reveals a series
of inset terrace surfaces and lava flow infilling the incised channel. Collectively these suggest a complex
catchment erosion-aggradation history and highly variable fan sediment supply.
São Vicente comprises extensive coastal and inland fans. These fans are small (up to 1.2 km2 and 1.8 km long)
and steep gradient (<0.08) forms that are fed from small (<1.3 km2) and low relief (<500 m) backfilled catchment
areas. Fans comprise up to two inset surfaces (Qf0 and Qf1) that show altitude, desert varnish, soils and
sedimentological variability and relationships. Incision between fan surfaces displays proximal-distal variability
but is typically <7 m. Sections through the fan sediments reveal a dominance of debris flow processes. We have
surveyed and mapped a selection of coastal and interior fans from different base level and caldera geology
contexts to illustrate variations in fan form and development. Sampling for cosmogenic 3He exposure dating has
targeted the Qf0 surface of the largest Santa Luzia coastal fan which builds over a <0.3 Ma marine terrace
record (Ramalho, 2011) in distal fan areas.
Keywords: cosmogenic dating, base level, lava flows, climate, sea level
FAN-DELTAS OF THE WESTERN COROMANDEL PENINSULA: AN INTEGRATED STUDY
OF FLUVIAL DYNAMICS, FAN-DELTA BUILDING AND MARINE DEPOSITION
Jon Tunnicliffe, Mark Dickson and Lorna Strachan
School of Environment, Auckland, New Zealand
[email protected]
The Holocene record of sediment delivery from the major catchments of the Western steepland catchments of
the Coromandel Peninsula is recorded in the stratigraphy of several small gravel fan-deltas that have built out
into the Firth of Thames. These landforms preserve a record of long-term adjustments amongst fluvial
sedimentation from floods and debris flows, long-shore and cross-shore coastal processes. The base-level
history of these catchment systems is complex, owing to sea incursion in the early Holocene, and fluctuations in
sea-level thereafter. Using a combination of sub-bottom profiling, ground-penetrating radar, and sonic coring, we
have developed a chronology of fan-delta building and volumes of yield at the outlet of one of the larger
catchments. The record clearly reveals the timing of major geomorphic events, including the onset of marine
sedimentation following sea incursion of the Firth at roughly 6500 years BP. The semi-enclosed Firth effectively
provides a ‘sink’ term for a Holocene fluvial-coastal sediment budget: average late Holocene rates of
accumulation at the Te Puru fan-delta are roughly 76 t km-2 yr-1. Finally, we employ a 1-dimensional surfacebased sediment transport model to explore the effects of fluvial and swash abrasion on the delivery of coarse
fluvial material to the coast. Fan archives such as these are important for calibrating our models of sediment
delivery, and for providing guidance to managers and engineers who are working to minimize risk in these
important and sensitive coastal environments.
Keywords: fan-delta, Firth of Thames, fluvial-coastal interface, sediment budget, fan sedimentology
FAN DELTA EVOLUTIONS UNDER THE INFLUENCE OF STRUCTURAL
INSTABILITY IN THE MIOCENE AKSU BASIN, SOUTHERN TURKEY
Serkan Üner1, Erman Özsayın2, Kadir Dirik2, Attila Çiner3 and Mustafa Karabıyıkoğlu4
1
Yüzüncü Yıl University, Dept. of Geological Engineering, Van, Turkey
Hacettepe University, Dept. of Geological Engineering, Beytepe-Ankara, Turkey
3
Eurasia Institute of Earth Sciences, Istanbul Technical University, Sarıyer-İstanbul, Turkey
4
Ardahan University, Dept. of Geography, Ardahan, Turkey
2
[email protected]
The Aksu Basin in southern Turkey is dominantly represented by an alluvial fan and five fan deltas (FD)
developed along the tectonically controlled margins of the basin during the Miocene. Four alternating
compressional and tensional tectonic phases have influenced the basin since its formation. Strong tectonic
movements caused high sedimentation rates and progradation of large debris-flow and mass-flow dominated fan
deltas. Here we describe two fan deltas (Karadağ and Kargı FDs) in detail. The Karadağ FD began to develop
under the control of a compressional regime and evolved under a tensional regime. The same tensional regime
caused the separation of the Karadağ FD from its source and the deposition of the Kargı FD into the newly
formed accommodation area. The alternating tectonic regimes and sea level oscillations in the Aksu Basin
allowed the development of coral colonies on the shallow delta fronts, forming patch reefs despite the large
amounts of conglomerates supplied by fan deltaic processes.
Keywords: fan delta, tectonics, sedimentology, eastern Mediterranean, Antalya, Aksu Basin
STRATIGRAPHIC RECORDS OF FLUVIAL-FAN PROGRADATION:
RECENT INSIGHTS AND A MODEL FOR ARID SETTINGS BASED ON THE
OLIGO-MIOCENE OF THE CENTRAL ARGENTINIAN FORELAND
Dario Ventra1, Andrea Moscariello1, Gabriel Hunger1 and Gonzalo Veiga2
1
2
Department of Earth and Environmental Sciences, University of Geneva, Switzerland
Centro de Investigaciones Geológicas, Universidad Nacional de La Plata, Argentina
[email protected]
Recent debates on the importance of fluvial (mega)fans for the infill of continental sedimentary basins are
leading to a reconsideration of genetic relationships between stratigraphic units previously interpreted to result
from generic changes in allogenic forcing. Hypotheses on the dominance of fluvial-fan deposits in continental
records are followed by the inference that very thick facies successions of dominantly alluvial origin (but
frequently including facies associations from different depositional systems) may relate to long-term fan
aggradation / progradation, ideally reflected by vertical stacking of relatively coarse clastic facies associations
from proximal, high-energy fluvial environments over relatively fine-grained facies associations representing
distal, low-energy alluvial environments. The progressive downfan decrease in runoff competence and channel /
overbank surface ratios implies enhanced preservation for climatically controlled sedimentary and pedogenic
signatures over the distal domain.
Results are presented here from an ongoing study of continental deposits of the central sector of the Argentinian
foreland (Mendoza Province). The studied interval, ~1300 m thick, comprises superbly exposed lithostratigraphic
units dating from the latest Oligocene to the late Miocene, aggraded as an almost uninterrupted succession in an
arid to semiarid climate during uplift of the Cordillera Principal and Cordillera Frontal sectors of the Andean
orogen. The basal Divisadero Largo Formation and the lower member of the overlying Mariño Formation offer
only sparse outcrops, presenting a vertical transition from playa deposits enriched by evaporitic minerals up into
thick mudstones encasing rare coarse-clastic channel fills and overprinted by incipient pedogenic cycles,
probably controlled by orbital forcing. The middle member of the Mariño Formation represents abrupt interruption
of alluvial deposition and local establishment of a highly aggradational erg environment, with development of an
extensive dune system locally disrupted by fluvial interference. The topmost member of the Mariño Formation
features a gradual coarsening-upward trend over hundreds of metres in stratigraphy, includes isolated pods of
aeolian deposits at its base, and consists of vertically stacked, alternating, laterally extensive, amalgamated,
weakly erosive, sandy to gravelly channel fills and mud-rich units from overbank environments. Facies
associations and architectural elements indicate deposition in shallow, laterally mobile, braided channels subject
to episodic, rapid aggradation by flash-flood events. A gentle angular unconformity separates this unit from
overlying conglomerates of the La Pilona Formation, which represent highly amalgamated infills from relatively
deep channels with more sustained and competent discharge.
The vertical transition of facies associations and architectures through the stratigraphic column can be
interpreted as relatively continuous aggradation of a large fluvial fan supplied by active thrust fronts. The most
distal alluvial environments comprise rare channel fills and their modification by incipient pedogenic cycles
indicates relatively low aggradation rates and persistently scarce reworking by higher-energy drainage. The
gradual textural coarsening and increasing relative volume of channel fills vs. overbank deposits match with a
transition to proximal fan settings, with increased reworking by avulsive, energetic channels and lower
preservation of floodbasin deposits. However, this general stratigraphic trend is overprinted by elements strongly
controlled by climate aridity, such as: 1) playa basins established in the most distal domain; 2) temporary
establishment of (and interference by) aeolian systems during early stages of fan aggradation, probably
coincident with an early phase of underfilled foreland subsidence; 3) dominance of ephemeral fluvial facies
associations; 4) a lack of hydromorphic pedogenic overprinting within overbank units. This set of characteristics
informs the proposal for a modified stratigraphic / sedimentological model of fluvial-fan development and
progradation in dryland environments.
Keywords: fluvial fan, distributive fluvial system, fluvio-aeolian interactions, foreland basin, Andes
FANS IN THE CONTEXT OF SEDIMENTARY BASINS:
FUTURE DIRECTIONS FOR FAN RESEARCH
Gary S. Weissmann
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
[email protected]
In recent work, distributive fluvial systems (DFS, aka alluvial fans, fluvial fans, and fluvial megafans) have been
shown to cover more surface area (>85%) in modern sedimentary basins than tributary streams, thus we expect
DFS deposits to comprise a significant portion of the fluvial rock record. However, most facies models used by
sedimentologists are based on tributary rivers in degradational settings. A new focus on aggradational systems
is necessary in order to better interpret the fluvial rock record. Therefore, studies focused on geomorphic
processes, channel form and morphology, and facies geometries and distributions on modern DFS are needed.
Evaluations of processes and geomorphology of fans, or DFS, as presented at this meeting, are examples of the
types of studies needed to understand the rock record. Specifically, focused studies on DFS that are needed
may include:

Geomorphic analysis of catchments that feed DFS, assessing the influence of climatic and tectonic
change in the catchment on sediment supply and stream discharge and how this is linked to aggradation
or degradation on the DFS;

Evaluation of controls, timing, and processes associated with channel avulsions and channel bifurcation;

Controls on DFS lobe development, and potentially the fractal nature of distributive deposits;

Evaluation of controls on channel and floodplain morphology on the spectrum of DFS types, and
evaluation of variability that exists between different DFS in the same sedimentary basin;

Assessment of the geomorphology of the distributive to tributary transition in the inter-megafan and other
areas in sedimentary basins;

Mapping and assessment of soil formation processes on DFS;

Studies of facies distributions that are found with different termination types (e.g., axial tributary rivers,
playa, lacustrine, or marine terminations) and the influence of base-level change on fluvial facies;

Models of groundwater influences on sedimentologic character (e.g., spring line and drainage patterns);
and

Development of holistic modeling approaches (systems analysis) to better represent the complexity of
how components of the landscape are related and interact.
Additionally, many numerical models commonly used in geomorphic analysis assume a tributary nature of the
system, thus these may not be applicable for distributive systems and new models are needed. For example,
many rivers on DFS decrease in size down-DFS, thus models that estimate channel geometry relative to the
drainage basin properties will not work unless diminishing flows downfan are estimated. Additionally, drainage
network analyses that use digital elevation models typically won’t work on distributive systems since they
assume contributory networks.
Finally, modern geomorphic systems have been significantly influenced by high-amplitude climate change during
the Quaternary and Holocene. We must build predictive models that help us understand how these systems
may have responded under more subtle conditions of changing climate that existed in the past.
In the discussion that ensues after my presentation, I hope we can develop ideas for future studies that will
improve our understandings of processes on fan systems and the resulting distributions of facies on these fans.
This could provide a springboard for collaborative work focused on building a more holistic understanding of the
complex fluvial systems that may be preserved into the rock record.
Keywords: distributive fluvial systems, megafans, alluvial fans, fluvial sedimentology, fluvial geomorphology
DO RIVER CHANNELS DECREASE IN WIDTH DOWNSTREAM ON DISTRIBUTIVE
FLUVIAL SYSTEMS? AN EVALUATION OF MODERN MEGAFANS
Gary S. Weissmann1, Louis A. Scuderi1, Adrian J. Hartley2 and Björn Nyberg3
1
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
2
Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen, UK
3
UniCIPR (Centre for Integrated Petroleum Research), Bergen, Norway
[email protected]
Distributive fluvial systems (DFS) form the dominant fluvial landforms in modern continental sedimentary basins
(in terms of aerial coverage in the basin), thus we expect DFS deposits to comprise much of the fluvial rock
record. Understanding geometries and form of channels on modern DFS may provide valuable information on
expected patterns of channel belt sandstones in fluvial rocks. In our previous work, we hypothesized that rivers
on DFS commonly decrease in size downstream. We test this hypothesis through evaluation of LANDSAT
images of large DFS.
In this study, we report on channel width for DFS in the Chaco Plain of the Andean Foreland Basin. We use
ArcGIS to: (1) isolate regions that correspond to the active channel (e.g., exposed sand and water), and (2)
measure the active channel width every ~1000 m successively downstream from the DFS apex. We also
measure the sinuosity and gradient of the active channel. For most rivers on DFS in the Chaco Plain, active
channel width decreases down-DFS, thus supporting the hypothesis for this region. Several of the rivers (e.g.,
Rio Grande, Parapeti, and Pilcomayo) diminish in width to the point of termination in wetlands distal on the
megafan. This decrease in width occurs primarily within 100 km of the DFS apex, most likely due to infiltration
into amalgamated channel belt deposits in the proximal areas. Sinuosity also tends to increase proximally to
distally, where proximal channels tend to display low sinuosity and a more braided morphology and distally these
channels become more sinuous. In the case of the Bermejo River DFS, the channel width decreases until about
140-km from the apex, then remains relatively constant downstream of this point. A marked sinuosity increase
occurs coincident with this width stabilization. Interestingly, no coincident change in gradient is observed with
the change in sinuosity.
Not all channels on DFS decrease in size down-DFS. The Paraguay and Paraña rivers enter the basin from the
east, forming large DFS (e.g., the Brazilian Shield). These rivers display a relatively constant width down-DFS
and then become the axial rivers in the basin (increasing in width downstream in this axial position). The Beni
River, located north of the Chaco Plain, also displays a relatively constant width down-DFS. The reasons for this
lack of channel decrease are unclear; however, amalgamated abandoned channel belts are not clearly apparent
on imagery. Therefore, these systems may lack a coarse-grained substrate for infiltration. Alternatively (or
additionally), the water table may be relatively high across these systems, thus limiting infiltration and stream
loss to groundwater. For the Beni system, the distal portion DFS is being uplifted on the Fitzcarron Arch;
therefore river form may be partially controlled by this uplift.
Though this method only shows widths and sinuosity of active channels and does not completely capture the
channel-belt character, we are developing tools to evaluate the active channel belt. Our results indicate that
channel-belt sandstones may decrease in width distally basinward, and that observed sinuosity increases in
these sandstones may be coincident with discharge loss down-DFS.
Keywords: distributive fluvial systems, megafans, fluvial channel morphology, fluvial channel width
QUANTIFYING THE DELIVERY AND DISPERSAL OF SEDIMENT FROM
TE HORO LANDSLIDE: NEW ZEALAND’S MOST ACTIVE ALLUVIAL FAN
Richard D. Williams1, James Brasington2, Simon C. Cox3 and Dart River Research Team
1
School of Geographical and Earth Sciences, University of Glasgow, UK
2
School of Geography, Queen Mary, University of London, UK
3
GNS Science – Te Pu Ao, Dunedin, New Zealand
[email protected]
Alluvial fans are temporary stores of sediment, positioned within sediment transfer systems that are likely to be
responding to a range of input/output geomorphological processes. To date, monitoring the morphodynamics of
alluvial fans within their sediment system context, to enable the quantification of three-dimensional morphology
and sedimentology, has proved challenging. However, contemporary terrestrial, airborne and satellite geomatics
and imaging technologies, together with in-situ monitoring of water levels, offer new opportunities to quantify
spatial and temporal patterns in sediment disturbance at the system scale.
An ongoing monitoring project is quantifying the delivery and dispersal of sediment from the Te Horo landslide an active compound rock and debris slide in Dart Valley, Otago. The landslide feeds 105-106 m3 sediment
annually to a debris-flow fan, connected to the right bank of the Dart River. At present this is arguably New
Zealand’s most active ‘alluvial fan’. Debris flows increased in activity during 2013 and 2014. An event in January
2014 crossed the fan, entered and impeded flow of Dart River, where it impounded a 6 million cumec lake
covering 1.5 km2. Subsequently, there has been a complex, inter-connected relationship between water and
sediment flows throughout the system, including: (i) transport of sediment across the fan through fluvial and
debris flows, (ii) remobilization of sediment from the fan surface during rain; (iii) reworking of the impoundment
level and thus adjustments to the lake level; (iv) erosion by the Dart River of material from the toe of the fan and
the hillslope opposite; (v) downstream delivery and dispersal of sediment and associated reworking; and (vi)
deposition of sediment onto the slopes of a prograding delta in Lake Wakatipu.
A sediment budget for the Dart River has been reconstructed to gain insight into the morphodynamics of the
system. The budget relies upon two system-scale topographic surveys that were undertaken in April 2014 and
May 2015. These surveys stretch from the upstream end of the new lake, across the landslide and alluvial fan
surface, and extend 40 km downstream to Lake Wakatipu. Each survey combined aerial image acquisition for
Structure-from-Motion photogrammetric reconstruction, terrestrial laser scanning and bathymetric surveying.
Differencing the two Digital Elevation Models, sheds light on the morphodynamics throughout the system. In
addition to these surveys, morphodynamics have also been monitored at a finer temporal resolution using
satellite remote sensing. Analagous processes are present throughout the Southern Alps and might be
widespread following landscape disturbance generated by a major Alpine Fault earthquake. Insights from
system scale quantification of source to sink morphodynamics therefore provides insight into the hazards
associated with sediment delivery and morphological change. The high-resolution, repeat surveys also provide a
baseline dataset for testing hypotheses associated with sediment delivery and dispersal at the system scale.
Keywords: alluvial fan, debris flow, landslide, braided river, morphodynamics, sediment cascade, DEM
differencing, Structure-from-Motion photogrammetry, terrestrial laser scanning, bathymetric survey
CONCEPTUALIZATION OF GROUNDWATER RECHARGE FROM A BRAIDED RIVER:
THE WAIRAU FAN
Scott R. Wilson1, Peter Davidson24 and Thomas Wöhling1, 3
1
Lincoln Agritech, Lincoln University, Christchurch, New Zealand
2
Marlborough District Council, Blenheim, New Zealand
3
Technische Universität Dresden, Institute of Hydrology, Dresden, Germany
[email protected]
The braided Wairau River is the main source of recharge to the highly productive Wairau Aquifer. Concurrent
flow gauging measurements at low flow indicate that a 7 cumec loss occurs as the river traverses the Wairau
alluvial fan, a distance over 15 km. Half of this loss occurs in the upper to middle 4 km of the fan, although the
nature of this loss is not well understood. Theoretically, the relationship between a river and groundwater can be
considered as being hydraulically connected (gaining or losing), disconnected (perched), or transitional (Brunner
et al. 2011). A disconnected river is distinguished from a hydraulically connected river by the presence of a
partially saturated zone between the river bed and the aquifer. The aim of this study is to improve our conceptual
understanding of how flow losses occur, and to test a new hypothesis that much of the river is perched above
the aquifer.
It is practically difficult to make direct observations beneath a river bed. However, indirect methodologies can be
employed to characterize the nature of the river-aquifer exchange, and we have employed a number of these
approaches. LiDAR imaging across the Wairau River has enabled the inclusion of representative river level
elevations in piezometric surveys. Tracer data can also be used to understand fluxes adjacent to the river. For
example, radon analyses (Close, 2014) indicate that the groundwater flux is higher in the upper fan. We have
reviewed existing 18O samples from the river and adjacent aquifer (Stewart, 2008) to understand the various
recharge sources within the aquifer. Temperature loggers have also been installed in bores adjacent to the river.
The available observational data have been used to develop a new numerical model of the Wairau Aquifer so
that we can better understand river-aquifer exchange dynamics.
Revised piezometric surfaces that include river elevations show a consistent sharp disjuncture between the river
surface and the water table in the upper half of the fan. Water levels in recently drilled riparian bores support this
observation. Streams on the north bank of the river also lose flow and may be ephemeral in the vicinity of the
Wairau River, indicating that the water table may dip southwards beneath the river. 18O data for the upper fan
show high values considering the proximity of wells to the river, and the abundance of river recharge expected.
This suggests that river recharge signature may be diluted by north bank groundwater flowing underneath the
river. Temperature data from riparian bores show a response to individual flow events in the uppermost gravels,
with only a seasonal cycle being evident at greater depths.
The combined evidence from all data sources supports the hypothesis that the dominant recharge reach of the
river may be hydraulically disconnected from the aquifer. Results from aquifer tests indicate that the hydraulic
conductivity of the alluvial gravels is highly anisotropic. We suggest that this anisotropy inherently creates a
perched river setting. The numerical model confirms our hypothesis, as we have found that the aquifer cannot be
simulated without a hydraulically disconnected river and strong anisotropy (Wilson and Wöhling, 2015).
Keywords: fluvial fans, braided river, hydrogeology, groundwater-surface water interaction
IDENTIFICATION OF FINE-GRAINED ALLUVIAL FANS IN PALEOGENE OF
JIUXI BASIN, WESTERN CHINA
Shenghe Wu1, 2 and Chen Yu1
1
2
College of Geosciences, China University of Petroleum, Beijing, China
State key laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China
[email protected]
Different from most coarse-grained alluvial fans, the fine-grained alluvial fans characterized by fan-shaped
sandstone bodies developed in the Paleogene of Jiuxi basin, western China. Identification of the fine-grained
alluvial fans is made by the integration of core, well-logging and 3D seismic data.
The core analysis shows that the lithology is mainly reddish–brown gravel-bearing medium-coarse sandstones
and anisometric sandstones. The gravel content is lower than 5 percent, and size 2 to 3 mm. The clastic
particles are mainly sub-angular, and the sorting is poor. Silty and muddy matrix ranges from 5-50 percent in
sandstone. The main types of sedimentary structures are graded bedding and massive structure. The rock color,
texture and sedimentary structures show that these are the subaerial sandy debris flow deposits.
3D seismic data interpretation constrained by wells (cored wells and well loggings) shows that the deposits are
fan-shaped planely and convex-shaped in cross section, and an incised valley developed in the root of fanshaped deposits. It can be concluded that the subaerial sandy debris flow deposits with fan-shape are the
results of fine-grained alluvial fans. The individual fan is about 5 to 10 km in width, 12 to 15 km in length, and 15
to 25 m in thickness. The width of incised valley ranges from 2 to 4 km, whose incised depth varies from 20 to 25
m.
The formation of the fine-grained alluvial fans in the studying area is controlled by three main factors, including
geomorphology, source rocks and climate. Open topography at the bases of mountain slope provides inducible
landform for the generation of alluvial fan through incised valley. The provenance is mainly composed of
mudstone and sandstone of Cretaceous as source rocks, which weathered in arid climate, providing the finegrained debris for alluvial fan.
Keywords: fine-grained alluvial fan, identification, controlling factors, Jiuxi basin, western China
QUATERNARY EXTENSION OF THE CENTRAL ANATOLIA, TURKEY:
INFERENCES FROM OFFSET ALLUVIAL FANS
Cengiz Yıldırım1, M. Akif Sarıkaya1, 2 and Attila Çiner1
1
2
Eurasia Institute of Earth Science, Istanbul Technical University, Sarıyer-Istanbul, Turkey
Kozmo-Lab, Geomorphology and Cosmogenic Nuclides Laboratory, Büyükçekmece-Istanbul, Turkey
[email protected]
Quaternary slip-rate of the Ecemiş Fault Zone within the Central Anatolian Plateau of Turkey has been
challenging to determine due to the difficulty of dating offset markers. Our study focuses on the excellent
exposures of offset alluvial fan surfaces in the Yalak River, originating from the Aladağlar, a Late Quaternary
glaciated mountain. Using high-precision offset measurements and 36Cl cosmogenic nuclide dating of offset
alluvial fans, we present the geochronologically determined Late Quaternary slip-rate for the fault. Analysis of
airborne orthophotogrametry and GNSS (Global Navigation Satellite System) surveys indicates 168±2 m of left
lateral and 31±1 m vertical displacement on the fault. In-situ terrestrial cosmogenic 36Cl geochronology obtained
from eleven surface boulders provide a minimum abandonment/incision age of 104.2±16.5 ka for the oldest
offset alluvial fan surface. Our geomorphic observations together with Self-potential geophysical surveys
revealed the presence of an unfaulted alluvial fan terrace, which allows us to constrain the timing of deformation.
The abandonment/incision age of this fan is 64.5±5.6 ka based on thirteen 36Cl depth profile samples.
Accordingly, we obtained a geologic fault slip-rate of 4.2±1.9 mm a-1 horizontally and 0.8±0.3 mm a-1 vertically
for the time frame between 104.2±16.5 ka and 64.5±5.6 ka (39.7±17.4 ka). Our analysis indicates that the EF
has not been producing a major surface-breaking earthquake at least since 64.5±5.6 ka (mid-Late Pleistocene),
at least on the main strand.
Activity of the Ecemiş Fault Zone is integrally tied to ongoing intraplate crustal deformation in the Central
Anatolian Plateau. We also document the vertical displacement, slip rate, extension rate, and geochronology of
normal faults within a narrow strip along the main strand of the fault zone. The Kartal, Cevizlik and Lorut faults
are normal faults that have evident surface expression within the strip. Terrestrial cosmogenic nuclide
geochronology reveals that the Kartal Fault deformed a 104.2 ± 16.5 ka alluvial fan surface and the Cevizlik
Fault deformed 21.9 ± 1.8 ka glacial moraine surfaces. Topographic surveys indicate 105 ± 10 m and 13.1 ± 1.4
m surface breaking vertical displacements along the Kartal and Cevizlik faults, respectively. Accordingly, we
suggest a 1.01 ± 0.19 mm a-1 slip rate and 0.58 ± 0.11 mm a-1 extension rate for the last 104.2 ± 16.5 ka on the
Kartal Fault and a 0.60 ± 0.08 mm a-1 slip rate and 0.35 ± 0.05 mm a-1 extension rate for the last 21.9 ± 1.8 ka on
the Cevizlik Fault. Taken together with other structural observations in the region, we believe that these
structures are an integral part of intraplate crustal deformation in Central Anatolia. They imply that intraplate
structures such as the Ecemiş Fault Zone may change their mode through time; presently, the Ecemiş Fault
Zone has been deformed predominantly by normal faults. The presence of steep preserved fault scarps along
the Kartal, Cevizlik and Lorut faults point to surface breaking normal faulting away from the main strand and
particularly signify that these structures need to be taken into account for regional seismic hazard assessments.
Keywords: slip-rate, cosmogenic isotopes, extension, offset alluvial fans, central Turkey
STRATIGRAPHIC SEQUENCE, DEPOSITIONAL ARCHITECTURE AND
RESERVOIR QUALITY OF EOCENE THIN-BEDDED BEACH FACIES,
SOUTHERN SLOPE OF DONGYING DEPRESSION, EAST CHINA
Muhammad A. Zahid1, 2, Dong. Chunmei2, Chengyan Lin2 and Muhmmad J. Munawar2
1
School of Geosciences, China University of Petroleum (Qingdao), P.R China, 266580
2
Faculty of Marine Sciences, LUAWMS, Pakistan, 90250
[email protected]
Thin-bedded beach-bar sand reservoir is widely deposited in the upper fourth member of Eocene Shahejie
Formation (Es4s) of Niuzhuang Sag, along the southern gentle slope of Dongying depression. The objective of
this paper is to establish a linkage between sequence stratigraphy, sedimentary facies and diagenetic effects on
reservoir quality. Seismic, wireline logs, core observations and analyses are used to interpret depositional
settings and sequence stratigraphic framework. Petrographic study based on microscopic observation of optical,
cathodoluminescence (CL), confocal laser scanning (LSCM) and scanning electron microscope (SEM) along
with X-ray diffraction (XRD) is used to discuss the fabric, texture, allogenic and authigenic mineralogy of highly
heterogenic beach-bar sand reservoir.
Es4s is interpreted as third-order sequence, composed of lowstand systems tract (LST), transgressive systems
tract (TST) and highstand systems tract (HST). On fourth order, twenty-nine parasequences and seven
parasequence sets have been identified. Sand bodies of Es4s are mainly deposited in the shore shallow lake
beach-bar (clastic beach-bar), semi-deep lake (carbonate beach-bar) and the shallow water channel. Fine grain
size, poor sorting, continuous thin interbedded mud layers with siltstone/fine-sandstone having argillaceous
layers in regular intervals and low sedimentological maturity are main causes of depositional heterogeneity.
Despite of the dissolution of grains and numerous fractures, destruction of porosity by cementation and
compaction are main causes of diagenetic heterogeneity. Secondary pores are developed with the increasing
effect of diagenesis causing the dissolution of feldspar grains. Grain coating smectite clays destruct primary
porosity at places while dominating pore filling authigenic illite and illite/smectite clays reduced permeability.
Due to high degree of heterogeneity in beach-bar, it is characterized as middle to low permeable reservoir. The
current study reflects significant insight to understand properties of beach-bar sands and can lead for the
comprehensive reservoir characterization and overall reservoir bed quality.
Keywords: Dongying depression, beach-bar sand, sequence stratigraphy, sedimentary facies, heterogeneity,
reservoir quality