Digital Comprehensive Summaries of Uppsala Dissertations
from the Faculty of Science and Technology 448
Diagenesis and Reservoir-Quality
Evolution of Paralic, Shallow
Marine and Fluvio-lacustrine
Deposits
Links to Depositional Facies and Sequence
Stratigraphy
OSAMA AHMED HLAL
ACTA
UNIVERSITATIS
UPSALIENSIS
UPPSALA
2008
ISSN 1651-6214
ISBN 978-91-554-7237-5
urn:nbn:se:uu:diva-8986
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Dedicated to:
Parents, brothers and sisters
And
My wife and my daughter
List of Papers
This thesis is based on the following papers, which will be referred to in the
following text by their Roman numerals.
Hlal, O., Morad, S., and El-Khoriby, E. (2008) Diagenetic
evolution of aggradational and progradational fan-delta
Arenites: Evidence from the Abu Alaqa group (Miocene), Gulf
of Suez, Egypt. Journal of Petroleum Geology, In review.
Hlal, O., Morad, S., Brazil, F., and Pereira, E. (2008)
Diagenetic and reservoir-quality evolution of shoreface sandstones in sequence stratigraphic context: The Ponta Grossa
Formation (Devonian), Paraná Basin, Brazil. Sedimentary
Geology, In review.
Hlal, O., Annersten, H., and Morad, S. (2008) Mössbauer
study of diagenetic Fe-rich minerals in Devonian clastic rocks
of the Ponta Grossa Formation, Paraná Basin, Brazil. Clay
Minerals, In review.
V Hlal, O., Morad, S., and López-Blanco, M. (2008) Linking
the distribution of carbonate cement to sequence stratigraphy
of delta complex sandstones: evidence from the Roda sandstone Formation (Eocene), South-Pyrenean Foreland Basin,
NE Spain. Sedimentary Geology, To be submitted.
V Hlal, O., Luo, J., Morad, S., Salem A., Yan, S., Zhang, X.,
and Xue, J., (2008) The diagenetic and reservoir-quality evolution of fluvial and lacustine-deltaic sandstones: evidence
from Jurassic and Triassic sandstones of the Ordos Basin,
Northwestern China, Journal of Petroleum Geology, In review.
Contents
Introduction.....................................................................................................9
Aims of the study ..........................................................................................14
Sequence Stratigraphy of Paralic, Shallow Marine and Fluvio-lacustrine
Deposits ........................................................................................................16
Parasequences and marine flooding surfaces ...........................................17
Problems with stacking patterns...............................................................18
Systems tracts...........................................................................................19
Methodology .................................................................................................23
Important eogenetic alterations linked to sequence stratigraphy ..................26
Important mesogenetic alterations linked to sequence stratigraphy .............30
Reservoir quality evolution and conceptual predictive models within
depositional facies and sequence stratigraphy ..............................................34
Model 1: summary model for distribution of diagenetic alterations and
reservoir-quality evolution of progradational and aggradational sequences
..................................................................................................................35
Figure 9: Simplified cartoons showing the most typical diagenetic features
in the aggradational and progradational fan delta sequences........................36
Model 2: summary model of the diagenetic evolution of shoreface
sandstone (paper II)..................................................................................37
Model 3: summary model of impact of diagenetic modifications on
reservoir quality of delta complex sandstone sandstones (paper IV) .......40
Model 4: summary model of impact of diagenetic modifications on
reservoir quality of Jurassic and Triassic fluvial and lacustrine deltaic
sandstones (paper V) ................................................................................42
Summary of the papers .................................................................................46
Paper I Diagenetic evolution of aggradational and progradational fandelta Arenites: Evidence from the Abu Alaqa group (Miocene), Gulf of
Suez, Egypt...............................................................................................46
Paper II Diagenetic and reservoir-quality evolution of shoreface
sandstones in sequence stratigraphic context: The Ponta Grossa
Formation (Devonian), Paraná Basin, Brazil ...........................................46
Paper III Mössbauer study of diagenetic Fe-rich minerals in Devonian
clastic rocks of the Ponta Grossa Formation, Paraná Basin, Brazil .........47
Paper IV Linking the distribution of carbonate cement to sequence
stratigraphy of delta complex sandstones: evidence from the Roda
sandstone Formation (Eocene), South-Pyrenean Foreland Basin, NE
Spain.........................................................................................................48
Paper V The diagenetic and reservoir-quality evolution of fluvial and
lacustine-deltaic sandstones: evidence from Jurassic and Triassic
sandstones of the Ordos Basin, Northwestern China ...............................49
Concluding Remarks.....................................................................................50
Summary in Swedish ....................................................................................52
Acknowledgements.......................................................................................54
References.....................................................................................................57
Introduction
Diagenesis and sequence stratigraphy have been formally treated as
isolation from each other to unravel and predict reservoir quality distribution successfully during the past three decades. Recently, it has
been demonstrated that the spatial and temporal distribution of
diagenetic alterations such as extensive calcite and dolomite cementation can be closely related to key sequence stratigraphic surfaces (Taylor et al., 1995; Morad et al., 2000; Ketzer et al., 2003a; Ketzer et al.,
2003b; Al-Ramadan et al., 2005).
The interplay between sequence stratigraphy and diagenesis enables the prediction of spatial and temporal distribution of diagenetic
alterations, and thus of post-depositional evolution of reservoir quality
of sandstones. This study approach may also provide important insight
into the formation of diagenetic baffles and barriers for fluid flow,
which can act as reservoir compartments and seals. Unraveling
diagenetic changes in a sequence stratigraphic framework has gained
significant interest in recent years and has been thoroughly applied
fairly extensively to carbonate rocks (Read and Horbury 1993; Tucker
1993; Moss and Tucker, 1996). Although the relationships between
diagenetic alterations and changes in the relative sea level in clastic
rocks are gaining increasing attention (Taylor et al., 1995, 2000;
Loomis and Crossey, 1996; South and Talbot, 2000; Ketzer et al.,
2002; Al-Ramadan et al., 2005), the linkages are less straightforward,
and thus not fully explored yet (Ketzer et al., 2003). Diagenetic alterations in clastic rocks that are relatively well constrained within sequence stratigraphy include the distribution of carbonate cements and
clay minerals (Taylor et al., 1995; Morad et al. 2000; Ketzer et al.,
2002; 2003a; Al-Ramadan et al., 2005). In these studies, extensive
early diagenetic carbonate cementation was linked to surface.
The sequence stratigraphy approach can provide useful information
on the diagenetic evolution of siliciclastic deposits which is complex
and controlled by several inter-related parameters (Fig. 1), including
9
Figure 1: Diagenesis is controlled by a complex array of interrelated parameters.
Modified after Stonecipher et al. (1984).
Figure 2: A triangular plot of extrabasinal and intrabasinal grains. The latter grains
are incorporated in sand during transgressive events. Modified after Zuffa 1980).
10
changes in:Detrital composition, particularly the proportion of
extrabasinal and intrabasinal grains (Fig. 2; Garzanti, 1991; Amorosi,
1995; Zuffa et al., 1995, Ketzer et al., 2002), which is strongly controlled primarily by the tectonic setting of the basin, paleoclimatic
conditions, source rocks, and changes in relative sea level.
(ii) Pore-water chemistry (Fig. 3), which can shift between meteoric,
marine and brackish composition (Mckay et al. 1995, Morad at al
2000). Regression may leads to subaerial exposure of at least part of
the shelf and concomitant flushing of shoreface and deltaic sediments
by meteoric waters. Conversely, transgression renders pore waters to
be dominated by marine composition.
(iii) Residence time of sediments under certain geochemical conditions (Fig. 3; Wilkinson 1989, Taylor et al 1995, Morad 2000). For
instance rapid rise in relative sea level would ensure prolonged marine
pore water diagenesis. Conversely, rapid fall in relative sea level results in meteoric-water diagenesis, which would be controlled by climatic conditions.
(iv) Abundance and type of organic matter (Cross, 1988; Fig. 4).
The depositional environments exert considerable controls on the
diagenetic evolution of sedimentary sequences. These controls are
most prominent during eodiagenesis being related to variations in pore
water chemistry, sedimentation rates, types and amounts of organicmatter, degree of bioturbation, as well as to the textural characteristics
(grain size, sorting), and architecture of the depositional facies. Facies
architecture refers mainly to the thickness, geometry of sediment bodies, and sand/mud ratio, which control in turn, the extent and pattern
of fluid flow. Variations in rates of sedimentation control the amounts
of organic matter, degree of sediment reworking by bioturbation, and
the residence time of sediments at the sediment-water or sediment-air
interface (extent of near-surface eogenetic alterations).
Pore waters in paralic and shallow marine environments have
chemical compositions that are strongly influenced by the depositional
waters, being ranging from largely meteoric, mixed marine-meteoric
(i.e., brackish), and marine compositions, variations in depositional
facies, (i.e. shoreface) have impact on the primary porosity and permeability values, and on the mass flux and rates of diagenetic reactions.
11
Figure 3: A sketch showing the influence of changes in the relative sea level (RSL)
on porewater composition in shelf and ramp sediments. A fall in RSL results in the
incursion of meteoric waters and a basinward shift of the mixing zone. The opposite
is true when a ris in RSL occurs, where porewaters in the shelf or ramp sediments
become dominantly marine and the mixing zone is shifted landward. Modified after
Morad et al. (2000) and Ketzer at al (2003b).
12
Figure 4: Growth model of carbonate (calcite or dolomite) concretion along various
hypothetical pathways related to rate of sedimentation (i.e. rate of concretion burial
below the sediment-water interface) and precipitation in the various geochemical
zones of diagenesis. Slow sedimentation rates (path A) results in more extensive
cementation (i.e. formation of continuously cemented sediment layer owing to
longer residence time below the seafloor and prolonged time span of derivation of
dissolved calcium and carbon from the overlying seawater. Modified after Wilkinson et al. (1987).
Diagenetic regimes used in this summary are sensu Morad et al.
(2000; modified after Choquette and Pray, 1970), and include (i) eodiagenesis, which occurs at near-surface and shallow-burial conditions
(0-2 km of burial depth and <70ºC) and during which pore water
chemistry is controlled by surface waters, (ii) mesodiagenesis (> 2 km
and >70ºC), which is mediated by evolved formation waters, and (iii)
telodiagenesis, which occurs during uplift, erosion and incursion of
meteoric waters.
13
Aims of the study
The aims of this thesis are to: (i) unravel the impact of diagenetic alterations on the spatial and temporal distribution of reservoir quality
and heterogeneity of shallow marine, deltaic, and fluvio-lcustrine deposits, (ii) link the distribution of diagenetic alterations to the sequence stratigraphic framework, and (iii) elucidate parameters controlling the diagenetic evolution of siliciclastic and hybrid arenites. Four
siliciclastic successions representing different depositional facies have
been studied for the purpose of this work (Fig. 5), including: (i) Middle
to Upper Miocene Abu Alaqa group of aggradational and progradational fandelta deposits from Gulf of Suez, Egypt, (ii) Middle to Upper Devonian
The Ponta Grossa Formation, Paraná Basin, from Brazil (shoreface sandstones), (iii) Lower Eocene Roda sandstone Formation (delta complex)
from South-Pyrenean Foreland Basin, NE Spain, and (iv) Jurassic and
Triassic Yanchange and Yan`an Formations (fluvio-lacustrine sandstones), Yanchang oil field, Ordos Basin, China. Diagenetic studies
were conducted on sandstones samples collected from cemented and
poorly lithified sandstones within systems tracts and, when possible,
along key sequence stratigraphic surfaces in these four successions.
14
Figure 5: Location map of the studied cases.
15
Sequence Stratigraphy of Paralic, Shallow
Marine and Fluvio-lacustrine Deposits
Sequence stratigraphy is an informal chronostratigraphic methodology
that uses a hierarchy of stratal surfaces to subdivide the stratigraphic
record. This methodology allows the identification of coeval facies
and documents the time-transgressive nature of lithostratigraphic
units.
The key concept in sequence stratigraphy is that sedimentary successions are composed of two chief ingredients: sediment (preserved
as rock) and hiatus (preserved as discontinuities or stratal surfaces).
This notion is directly related to Walther`s Law, which states that genetically related facies (i.e. facies which occur in laterally adjacent
environments) will occur conformably in vertical successions. Where
a vertical succession contains transition between facies, which are not
genetically related (e.g. from upper shoreface sandstone to offshore
mudstone), Walter’s Law dictates that the transition must represent a
depositional discontinuity (i.e. a period of erosion or no deposition).
Recognition and correlation of these surfaces is the basis of sequence
stratigraphy.
The controls on sequence development are fairly simple: sediment
accumulates at a given point where there is space (accommodation)
and provided that sediment is available (e.g. Vail et al. 1977, Jervey,
1988, Posamentier et al.1988, Galloway 1989). The internal organization of sequences is also influenced by spatial variations in subsidence/uplift and the basin margin physiography, such as presence or
absence of a shelf break (sensu Van Wagoner et al. 1990). All potential controls on sequence development, such as tectonic subsidence/uplift and climate, act directly or indirectly to change one or
more of these factors (Fig. 6).
The sequence stratigraphy tool is used to correlate genetically related sedimentary successions bounded at top and base by unconformities or their stratal patterns are interpreted to form in response to the
interaction of eustatic change of sea level, compaction, sediment supply and tectonic subsidence (Van Wagoner et al., 1990). Sequence
16
stratigraphic units are recognized on a number of temporal scales from
parasequences, which may represent tens of thousands of years, to
sequences, which record timescales ranging from tens of thousands to
millions years or more.
Figure 6: Sediment accommodation space and its relationship to eustatic sea-level
and tectonic uplift and subsidence. Marine accommodation space created during a
rise in relative sea-level has been partially filled with sediment (yellow and darkgrey), whereas the non-marine accommodation space created during the rise in
relative sea level has been totally filled with sediment (yellowish-green). Modified after Angela Coe et al. (2003).
Parasequences and marine flooding surfaces
A parasequence is a relatively conformable succession of genetically
related beds bounded by marine flooding surfaces (Van Wagoner et al.
1988). Parasequences in siliciclastic systems are usually progradational being deposited when rates of sediment flux exceeds accommodation creation. Marine flooding surface, which bounds the top of the
parasequences, forms as rate sediment flux is outpaced by the addition
of accommodation. The deepening referred to in the Van Wagoner
(1988) definition is recorded by a landwards facies shift, i.e. from a
proximal to a lower energy distal depositional environment. The facies
shift is usually abrupt, but the flooding event may be represented by a
thin retrogradational interval at the top of the parasequence (Arnott
1996, 2007). Rapid and gradual landwards facies shifts are usually
accompanied by a reduction in grain size, changes in sorting, sedimentary structures, degree and type of bioturbation and bioclast concentra17
tions (e.g. Kidwell 1989, Krawinkel and Seyfried 1996). The identification of a flooding surface in prodelta or on the coastal plain is often
more difficult than in the shoreface, where there is more facies contrast (Van Wagoner et al. 1990).
Parasequences are often grouped into parasequence sets, which are
defined as successions of genetically related parasequences forming a
distinctive stacking pattern bounded by major marine flooding surfaces and their correlative surfaces (Van Wagoner et al. 1988),
Parasequences may be arranged/stacked in an overall shallowing upwards motif referred to as forestepping) or overall deepening upwards
(backstepping).
Problems with stacking patterns
The stacking pattern within sedimentary packages depends on the
rates of accommodation creation versus rate of sediment supply. Progradational, aggradational and retrogradational parasequence sets define the characteristics of systems tracts (e.g. Posamentier et al. 1988).
As a result, specific stacking patterns are linked to discrete segments
of the relative sea level curve. Recently, it has been demonstrated that
due to spatial and temporal variations in sediment flux and accommodation development, various facies stacking patterns may develop
contemporaneously. Gawthorpe et al. (1997) provided an example of
this facies variations based on field studies and computer simulation.
In a syn-rift setting, sediment flux varied by an order of magnitude
and subsidence rates by a factor of up to five, between fault segmentsan along-strike distance of around 10 km. The facies variations resulted in the contemporaneous development of progradational, aggradational and retrogradational stacking patterns (Fig. 7).
The formation of sequence boundaries and onset of forced regression occur at the same time as normal regression or even retrogradation. Designating systems tracts in such a scenario is a risky business.
However, a rapid rise in relative sea level would generally be recorded
in all parts of the basin as a landwards facies shift, since sediment flux
is likely to occur at slower rates. For this reason, major marine flooding surfaces provide a robust framework for correlation and facies
prediction.
18
Figure 7: Depositional architecture as a function of accommodation volume and
sediment supply. Modified after Galloway (1989).
Systems tracts
Systems tracts are linkage(s) of contemporaneous depositional systems (Brown and Fisher, 1977), and are the primary constituents of
sequences. Systems tracts have characteristic stratal geometries, stacking patterns, their positions relative to each other and within the sequence and their bounding surfaces.
19
Difficulties encountered in recognizing sequence boundaries and
correlative surfaces have led to the appearance of new schemes, developed from the poor genetic sequence stratigraphic model. There
exist at least two such schemes genetic stratigraphy (Galloway, 1989),
and allostratigraphy.
Systems tracts are recognized and defined by the nature of their
boundaries and by their internal geometry (Emery and Myers, 1996).
Three main systems tracts can be usually distinguished as a result of
one relative sea-level cycle (Posamentier et al. 1988).
(1) Lowstand systems tract (LST), which is formed by forced (i.e., fall
in eustatic sea level) rather than normal regression (Posamentier et al.,
1992), is comprised of: (i) deep water turbidite systems, which are
represented by basin-floor and slope fans, and (ii) lowstand wedge
comprised of fluvial deposits within incised valleys and shelf edge
deltas, which have aggradational and/or progradational parasequence
sets (Fig. 7). The LST is deposited between the lower sequence
boundary (abrupt relative sea level fall) and the beginning of relative
sea level rise, which is represented on the shelf by the first marine
transgression and formation of transgressive surface, possibly represented by a ravinement surface, which is a conglomeratic lag formed
by wave and current reworking shelf sediments (Fig. 8).
(2) Transgressive systems tract (TST), which is deposited during a
rapid rise in the relative sea level, and is bounded below by the transgressive surface and above by the maximum flooding surface (MFS).
(3) Highstand systems tract (HST), which is deposited during stable
high and slowly falling relative sea level, is bounded below by MFS
and above by the upper sequence boundary. The HST is comprised of
initial aggradational and later, as the accommodation created by rise in
the relative sea level diminishes, progradational parasequence sets
(Fig. 7). Commonly, the HST is partly preserved owing to erosion
during the next cycle of fall in relative sea level, and formation of upper sequence boundary.
20
Figure 8: The four system tracts including lowstand (LST), transgressive (TST),
highstand (HST), and forced regressive system tracts (FRST).
Two other system tracts which are not included in the original Exxon
scheme:
(1) Forced regression systems tract (FRST), which has been proposed
(Plint, 1988; and Hunt and Tucker, 1992; 1995) to be deposited during
relative sea-level fall, when incision and bypass occur on the alluvialand coastal plain, whereas deposition occurs on the submerged parts
of the shelf. FRST includes erosion based (detached), as well as
gradually based (attached) deposits. The FRST is bounded below either by a marine ravinement surface of erosion formed during regression or by a conformable surface. Above, the FRST is bounded at top
21
by a SB and/or a Transgressive surface. Therefore, LST is restricted to
the interval of lowest point of relative sea-level position to the beginning of the transgression.
(2) Regressive system tract (RST), which formed between two rapid
rises in relative sea-level separated by a slow rise. The RST is
bounded below by a maximum flooding surface, and consists of prograding wedge.
Other key sequence stratigraphy surfaces, which enable us to tie
sedimentary successions into packages with genetic and chronostratigraphic significance, applied in this paper include: (1) marine flooding
surfaces (FS), which are surfaces that separate younger from older
strata, and across which there is evidence of an abrupt increase in either marine; (2) transgressive surface (TS) is the marine flooding surface marking the lower boundary of the TST deposits; (3) maximum
flooding surface (MFS), which is indicated by condensed section due
to sediment starvation, represents the point of maximum landward
advance of the strandline.
22
Methodology
Facies description was preformed for the purpose of construction of
depositional facies and sequence stratigraphic framework. Whenever
possible, samples were collected from both outcrops and subsurface
cores along, above and below key sequence stratigraphic surfaces including, amalgamated transgressive surface/sequence boundary,
maximum flooding surface and parasequence boundary and within the
highstand and transgressive systems tracts (sensu van Wagoner et al.,
1990). Thin sections were prepared for all samples subsequent to vacuum impregnation with blue epoxy. Modal analyses of the arenites
were preformed by counting 300 points in each thin section. Scanning
electron microscope (SEM) was used to study crystal habits and paragenetic relationships among diagenetic minerals in representative
samples.
The chemical composition of minerals was determined in thin
sections coated with a thin layer of carbon using a Cameca BX50 microprobe equipped with three spectrometers and a back scattered electron detector (BSE).was used to determine the chemical compositions
and paragenetic relationships of different cement types. The operations conditions were: 20 KV acceleration voltage, 5 nA (for carbonates) to 15-nA (for feldspars) measured beam current, and 10 m
beam diameter. The standard and count times used were wollastonite
(Ca, 10 s), MgO (Mg, 10 s), strontianite (Sr, 10 s), MnTiO3 (Mn, 10
s), and hematite (Fe, 10 s). Analytical precision was better than 0.1%
for all elements. Conventional petrographic examination was complemented by Cathodoluminescence (CL) petrography to study zonation in various carbonate cements (paper IV and V). The operating
conditions were 12–16 kV accelerating voltage, 300-350 μA beam
current and 0.2–0.1 Torr vacuum pressure.
Stable carbon and oxygen isotope analyses were carried out on
carbonate-cemented arenites representative of the various depositional
environments and systems tracts in order to determine the geochemical conditions, pore waters composition and temperature of precipitation. For the purpose of oxygen and carbon isotope data, bulk samples
were powdered (< 200 mesh) and reacted with 100% phosphoric acid
23
at 25ºC for one hour for calcite, at 50ºC for 24 hours for Fedolomite/ankerite and siderite-cemented samples were reacted at 50ºC
for 96 hours (e.g. Al-Aasm et al., 1990). The evolved CO2 gas was
analysed for carbon and oxygen isotopes in a SIRA-12 mass spectrometer. The phosphoric acid fractionation factors used were 1.01025
for calcite (Friedman and O`Neil, 1977), 1.01060 for Fedolomite/ankerite and 1.010454 for siderite (Rosenbaum and
Sheppard, 1986). The isotopic data are presented in the normal notation relative to V-PDB.
The ratio of 87Sr/86Sr isotopes were analysed for siderite, calcite,
and Fe-dolomite/ankerite-cemented samples using the methods of
Schulz et al. (1989). The 87Sr/86Sr isotope ratios were analyzed using
an automated Finnigan 261 mass spectrometer equipped with 9 faraday collectors. Some of calcite-cemented samples from different systems tracts were washed with distilled water and then reacted with
dilute acetic acid in order to avoid silicate leaching. Correction for
isotope fractionation during the analyses was made by normalization
to 86Sr /88Sr = 0.1194. The mean standard error of mass spectrometer
performance was ±0.00003 for standard NBS-987.
Orientated, < 2 Pm clay fractions were separated from nine samples subsequent to gentle crushing and subjected to X-ray diffraction
(XRD) analysis using SIEMENS–D5000 equipment. The samples
were analysed subsequent to air drying, saturation with ethylene glycol, and heating to 550°C for 6 hours. Total organic carbon (TOC)
was measured in Brazil paper to aid the sequence stratigraphic analyses. Mudstone samples with a regular spacing of 30 cm were collected
from all wells for the purpose of TOC analyses. Silty sandstone intervals were sampled with a spacing of 50-100 cm. All samples were
pulverized an agate mortar, heated to 1350°C and flushed with O2, and
analysed in LECO SC-444 equipment. Relative weight of organic carbon is measured from CO2 and SO2 counts in an infrared detector.
Inorganic carbon content was carefully removed from samples by repetitive addition of 0.5N HCl (under warming). Spectral gamma-ray
(uranium, potassium and thorium) measurements were carried out on
the same samples for which TOC analyses were performed. A standard duration of two minutes was selected for each measurement.
Mössbauer spectroscopy is a useful tool for studying the distribution of Fe-bearing minerals and their oxidation state in sediments and
sedimentary rocks to elucidate the diagenetic conditions (Suttill et al.,
1982; Görlich et al., 1989; Hornibrook and Longstaffe 1996: Robinson, 2000). Mössbauer spectroscopy was used (paper III) to investigate horizons containing abundant Fe-rich minerals in siliciclastic.
24
The total porosity and permeability of selected sandstones from the
transgressive and highstand systems tracts (paper II) were calculated
using image analysis software. The calculation of permeability using
this software was based obtaining the pore perimeter (pp), porosity
() and pore area (PA) and then using the equation of KozenyCarman, which was modified by Mowers and Budd (1996), as follows: K = 3/c(1- )(4pp/SPA)2. The constant c was assumed to be 5,
which is a typical value for sandstones (Mowers and Budd, 1996).
The helium porosity and air permeability were measured for core
plugs at a confining pressure of 100 and 400 psi, respectively (paper
V). Prior to measurements, the plugs were examined carefully for
hair-thin microfractures and cleaned in an oil extractor and dried in a
vacuum oven at 60°C for 24 hours.
25
Important eogenetic alterations linked to
sequence stratigraphy
The main eogenetic alterations in the paralic, shallow marine and
fluvio-lacustrine deposits are carbonates (e.g. calcite, dolomite, and
siderite), kaolinite, Pseudomatrix, grain-coating and ooidal berthierine, ooidal goethite, mechanically infiltrated clay, glauconite, and
pyrite. Calcite cement occurs commonly as coarse to poikilotopic
spar in progradational braid-delta fan sequences, particularly along
the topsets (marine flooding surfaces) (paper I), HST and TST (paper
II), along deltaic parasequence boundaries of the early HST (paper
V). Microcrystalline and equigranular mosaic calcite are more abundant in the aggradational than progradational arenites, particularly
below the marine erosional surfaces (i.e. sequence boundaries). Calcite cement occurs as syntaxial calcite overgrowths around crinoid
fragments in some of the arenites from the progradational and aggradational sequences (paper I), Vadose calcite cement was formed in
the fluvial, floodplain sediments as evidenced by the presence of
rhizocretionary calcite intraclast in the channel lag deposits. The calcite intraclasts were derived by erosion of floodplain sediments during channel migration. calcite occurred in sandstones closely associated
with organic-rich lacustrine and pro-deltaic mudstones at parasequence
boundaries of the early HST(paper V). Continuously cemented beds
occur in the upper parts of the (TST), particularly along the (PB) and
the (MFS). Conversely, incomplete carbonate cementation (i.e. nonconcretions) occurs in sandstone beds of the (RST) (paper IV).
Dolomite occurs as syntaxial overgrowth and as discrete, rhombic
crystals in arenites of the progradational fan delta sequences. Zoned
dolomite and detrital, partly dissolved dolomite, is more commonly
encountered in the progradational than aggradational sequences (paper
I) Coarse-crystalline dolomite being a more common encountered
feature in arenites from the aggradational than in the progradational
sequences. Microcrystalline dolomite (5-10 μm) occurs as pore-filling
aggregates and as grain coatings, particularly in the aggradational lags
of (MFS) (paper I)
Siderite occurs as small crystals arranged along traces of mica
cleavage planes, mainly in the fine-grained deltaic sandstones (paper
26
V) which are rich in mica and pseudomatrix. Siderite occurs also as
flattened rhombs. EMP analysis revealed that siderite is chemically zoned,
with less magnesian cores (MgCO3 = 1.3-3.7%; av. 2.3%) than rims (MgCO3
= 17.7 %). Siderite occurred in siltstones and very fine-grained sandstones
that are closely associated with organic-rich lacustrine and pro-deltaic mudstones at parasequence boundaries of the early HST (paper V). Siderite most
common in the TST deposits (paper II) occurs as scattered ooid-like spherules as discrete distorted rhombs, as aggregate of tiny, rise-like crystals that
fill the pore space locally or occurs within strongly expanded mica grains.
Euhedral siderite crystals in the silty and sandy mudrocks (paper II) occur as
scattered patches (ca 30 m across) with hollow center. the G18O V-PDB values
of siderite (-11.8‰ to -5.8‰) indicate temperatures of ca 30-65ºC BSE imaging revealed that siderite crystals are zoned mainly in terms of variations
in the Mg contents. The siderite spherules display alternating zones of Mgrich and Mg-poor siderite. Although inconsistently, the outer zones of siderite rhombs in both the TST and HST sandstones, are more enriched in Mg
than the cores. The G18O values of the siderite cements do not display systematic variation with respect to systems tracts and key sequence stratigraphic surfaces.
Kaolinite is greater extent of dissolution and kaolinitization of detrital
feldspar, mica and mud intraclasts in the HST than in the TST sandstones
(paper II) is attributed to the incursion of under-saturated meteoric waters
during fall in the relative sea level under humid climatic conditions in the
Jurassic fluvial sandstones (paper V). Kaolinite is most common in poorlylithified sandstones of RST and TST (paper IV), which occurs as scatter
patches composed of booklets and vermicular crystals that have replaced
partly to completely muscovite, K-feldspar and mud intraclasts.
Pseudomatrix (i.e. matrix formed by pseudoplastic deformation and
squeezing of mud intraclasts between the rigid feldspar and quartz grains),
occur in the LST and HST sandstone (paper II), fluvial channel TST (paper
V).
Berthierine occurs as thin coatings around detrital grains, ooids, and grain
replacive. The grain-coating berthierine/chlorite occurs as continuous or
discontinuous, single or multiple layers that are thin (5 to 15 m) or absent at
grain-to-grain contacts. The berthierine coatings are composed of boxworklike, tiny crystals (about 1-2 m across) being, in some cases, covered by
coarser-crystalline patches that resemble rosette-like, Fe-rich chlorite (ca 5
m in size), which may extend to fill the adjacent pores. The grain-coating
berthierine/chlorite varies in abundance from scarce, being coating a small
fraction of the grains in (HST), to widespread, and being coating major portions to most grains (TST) (paper II). Berthierine ooids occur as beds showing cross bedding or are scattered in mudrocks of (TST), particularly along
TS and MFS (paper II). The ooids are overall ovoidal in shape and range in
size from ca 250 m to 1 mm, being lacking nucleus or have a nucleus com27
posed of silt- or sand-sized, framework silicate grains surrounded by a cortex
of relatively poorly-distinguishable, 5–10 m thick laminae of cryptocrystalline berthierine. Ooids in some of the sandy siltstones and mudstones, which
are extensively cemented by microcrystalline siderite, are arranged concentrically presumably owing to circular bioturbation.
Goethite occurs as cement and as ooids being most common and most
abundant in the TST sediments particularly below MFS (paper II). Porefilling goethite occurs as scattered patches (400-800 m across) and as small
circular shaped, patches with hollow center or as local, extensive cement
patches. Goethite ooids occur as concentric laminae (ca 5-15 m thick)
around silt and sand-sized goethite grains. Goethite was identified by XRD
analyses, and the EMP analyses revealed that goethite contains small
amounts of Al (Al2O3 = < 1.1 wt.%). Goethite ooids and cement were presumably formed at or immediately below the seafloor from oxygenated pore
waters, which implies that the bottom waters were oxygenated too (Claypool
and Kaplan, 1974; Irwin et al., 1977; Curtis et al., 1986; Curtis, 1987;
Postma, 1993). Dissolved iron needed for the formation of diagenetic goethite was presumably derived by diffusion of dissolved iron from the suboxic
and anoxic geochemical zones that underlie the oxic zone below the seafloor
(Gehring, 1989), in a manner similar to the formation of Fe-Mn nodules on
the modern abyssal seafloor. In some cases, the texture of diagenetic goethite, such as the tiny, circular forms, may suggest the role of bacteria in
their precipitation (Ghiorse, 1984; Konhauser, 1998).
Mechanically infiltrated clay occur nearly exclusively in the HST
sandstones (paper II), display textural properties indicative of an origin as
infiltrated clays, such as the tangential arrangement of these clay flakes and
their presence along grain-to-grain contacts (Morad and De Ros, 1994; Morad et al 2000). Clay infiltration occurs in subaerially exposed sand as a consequence of percolation of surface waters that are rich in suspended mud.
Subaerial exposure of shallow marine sand is anticipated to occur during fall
in the RSL and concomitant progradation of the HST shoreface sand (Ketzer
et al., 2003b). The original composition of the infiltrated and inherited clays
is unknown, but is commonly presumed to be dominantly smectitic in composition (De Ros et al, 1994).
Glaucony is a widespread greenish mineral in marine environments. It
occurs as grains or pellets, which are spheroidal, irregular, or lobate in shape
(Triplehorn, 1966; Jeans et al., 1982). Glaucony peloids, which are yellowish brown to deep green in color and lack internal cracks are more common
in the aggradational (i.e. sequence boundaries) than progradational sequences, being most abundant along the marine regressive surfaces (i.e. sequence boundaries) (paper I). Glaucony (light- to dark-green in color) occurs
in trace amounts (< 1%) as sand-sized, flake-like grains and, less commonly,
as pelloids (paper II). The flake-like glauconite grains have similar size,
shape and distribution pattern as the associated mica grains and commonly
28
enclose remnants of biotite. Most glauconite was formed by the replacement
of biotite grains, which is evidenced by the similar shape and size of glauconite to those of biotite as well as by the presence of biotite remnants within
the glauconite grains (Ketzer et al., 2003b).
Pyrite occurs mainly (up to ca 2%) in the carbonate-cemented sandstones
and in mudstones in the TST and MFS. (paper II). Pyrite occurs in the shoreface (paper II) as: (i) framboids (ca 10-20 m cross) and local pore-filling
aggregates of discrete (5-10 m across), euhedral crystals, and (ii) scattered,
small (ca 10-30 m in size) euhedral crystals within mica grains that have
been pervasively replaced by berthierine and/or siderite. Pyrite occurs as
framboids in trace amounts (trace to 1%; 0.2%) that are scattered within
calcite and dolomite cements (paper I) and within chambers of foraminifera.
pyrite is more common in progradational braid-delta fan sequences, particularly along the topsets MFS (paper I). Pyrite is more common in the TST
than in the RST sediments (paper IV). Pyrite in the RST and LST sediments
is often partly oxidized (Paper IV).
29
Important mesogenetic alterations linked to
sequence stratigraphy
The main mesogenetic alterations in the paralic, shallow marine and fluviolacustrine deposits are Fe-dolomite/ankerite, illite, quartz overgrowths, albite, dickite, and chlorite.
Pore-filling and grain-replacing Fe-dolomite and, less abundant, ankerite
occur as coarse, rhombic to poikilotopic crystals. These carbonates occur in
variable amounts (nil to 15%) being slightly more abundant in the HST than
in the TST shoreface sandstones (paper II). There are no systematic variations in the chemical and isotopic compositions of Fe-dolomite/ankerite in
the TST and HST sandstones (paper II). The G18O V-PDB values of bulk Fedolomite/ankerite (-10.8‰ to -9.6‰) suggest precipitation at narrow temperature range (55-70ºC) (paper II). The slightly to considerably higher
87
Sr/86Sr ratios of the Fe-dolomite/ankerite cements in the TST and HST
sandstones (0.708910 to 0.709640) than that of ambient seawater (0.70780.7083; Veizer et al., 1999) is attributed to derivation from 87Sr/86Sr from the
mesogenetic dissolution and alteration of K-feldspar and mica, which are
known to be enriched in radiogenic strontium (paper II). Ankerite occurs as
blocky saddle crystals (100-350 μm) that fill the intergranular pores and
replace detrital feldspars and pseudomatrix. Ankerite also occurs within expanded biotite grains Paper V). Ankerite is more abundant in the fluviodeltaic, Triassic sandstones than in the fluvial Jurassic sandstones (paper V).
Fe and Mg needed for ankerite cementation were possibly derived internally
from dissolution of volcanic fragments, biotite and grain coating smectitic
clays and iron-oxide pigment, and externally by diffusive transfer from adjacent mudrocks (Boles and Franks, 1979). The oxygen isotopic values of
ankerite are extremely low (av. G18O V-PDB = -15‰ and -19‰, respectively),
which indicate either precipitation from highly 18O-depleted waters of meteoric origin or at elevated temperatures. The temperature for ankerite precipitation (98-127oC) such temperatures agree well with the maximum temperatures reached during mesodiagenesis (105-124oC) (paper V). The emplacement of oil has retarded the precipitation of ankerite, which is more abundant
in the water-saturated reservoirs (paper V).
30
Illite occurs in various textural habits (mat-like, fibrous or lath-like
crystals that form rims around framework grains, platelet-like, filamentous, booklets-like and honeycomb-like) mainly in the HST shoreface sandstone (paper II), RST than in the TST sandstones (paper IV),
and in all facies of Jurassic and Triassic fluvio-lacustrine sandstones
during rapid subsidence to depths of 3700-4400 m (paper V). Illite formed
by various processes including transformation of a clay precursor, precipitation from porewaters (authigenesis), replacement kaolinite and
feldspar (e.g. Worden and Morad, 2003). Grain-coating illite that varies widely in thickness (paper II) and occurs within embayed surfaces
of sand grains are interpreted to be originally inherited clay coatings
(Pittman et al., 1992). The original composition of the infiltrated and
inherited clays is unknown, but is commonly presumed to be dominantly smectitic in composition (De Ros et al, 1994).The chemical
composition and XRD properties of illite (paper II) suggest that the
Devonian sandstone were subjected to fairly deep burial diagenesis.
Illite in the water zone (paper V) occurs; however, as better developed
than in the oil-saturated zone, filaments up to 40 μm long that are arranged perpendicular to the grain surface. The formation of considerable amounts of filamentous, permeability-deteriorating illite was retarded because of: (i) the replacement of eogenetic kaolinite by the
more stable dickite, and (ii) the resistance of detrital K-feldspars towards albitization due to the low maximum temperatures reached
(105-124°C), and to the short residence time at these temperatures.
Conversely, these burial-temperature conditions were sufficient to
cause pervasive albitization of the moderately calcic plagioclase
grains.
Quartz overgrowths are more abundant in the HST sandstones owing to the less abundant and less extensive grain-coating berthierine/chlorite than in the TST sandstones (paper II). Silica needed for
the formation of quartz overgrowths was presumably derived internally from the intergranular dissolution of quartz grains in the sandstones (Walderhaug, 1994; Walderhaug and Bjørkum, 2003). Chemical compaction of the Devonian sandstones is manifested by intergranular pressure dissolution of quartz grains, sutured and straight intergranular contacts which was frequently enhanced by the presence of
grain-coating illitic clay and muscovite grains (Oelkers et al., 1996).
Pressure dissolution has obviously acted as an internal source of silica
needed for the formation of quartz overgrowths (Worden and Morad,
2000). Quartz cement (trace to 7%; av. 2% paper V), which occurred
during rapid subsidence to depths of 3700-4400 m occurs as syntaxial
overgrowths on detrital quartz and as prismatic outgrowths when the
quartz grains are coated with thick clay layers. The outgrowths are
comprised of a single crystal or a number of blocky crystals that com31
pletely fill adjacent pore space. Trace amounts of quartz cement occur
as microcrystals that are closely associated with diagenetic illitic clays.
Quartz overgrowths are most abundant in sandstones which are poor in
carbonate cement and in grain-riming, illite or chlorite (paper V).
Quartz is also more abundant in the water-saturated than in the oilsaturated sandstones. Oil emplacement retarded cementation by quartz
and carbonate but had little influence on dickite, illite and chlorite
formation (paper V). Retardation of quartz cementation was also due
to the presence of chlorite fringes around detrital quartz grains.
The albitized grains are composed of numerous euhedral crystals
(2-10 μm) arranged parallel to each other and to traces of twinning and
cleavage planes of the detrital feldspars. Albite occurs in both the HST
and TST sandstones (paper II). Albitization of plagioclase (paper II
and V) has been inferred to commence during mesodiagenesis at temperatures greater than about 70ºC (e.g. Saigal et al., 1988; Morad et al.,
1990) and becomes more extensive with further increase in temperature (Boles, 1982). The Ca and Al released from the albitization of
plagioclase have presumably been used in the formation of carbonate
cement and clay minerals, respectively (e.g. Boles, 1982; Morad et al.,
1990). The small extent of K-feldspar albitization is probably due to
the formation of small amounts of illite, which is the typical sink of
released K+ , and hence the driving kinetic factor of the reaction (Morad et al., 1990). Some of the albitized plagioclase contains a thin layer
of euhedral albite overgrowths (paper V). There is no variation in the
amounts of albitized plagioclase grains between the water-saturated
and oil-saturated sandstones, but albitized K-feldspar grains occur almost exclusively in the water-saturated sandstones (paper V).
Dickite occurs mainly in the HST sandstones (paper II). The conversion of thin crystals of kaolinite into thicker, blocky dickite, which
is a dissolution-reprecipitation process (MackAuloy et al, 1994) occurring during mesodiagenesis (Ehrenberg et al., 1993; Morad et al.,
1994; Lanson et al., 2002), is common in the HST sandstones Thus,
this conversion process in the Devonian shoreface sandstones suggests
that eogenetic kaolinite was destabilized during burial and increase in
temperature. The conversion is suggested to be aided by incursion of
acidic fluids (MacAuly et al, 1994; Morad et al, 1994). In the fluvial
Jurassic sandstones (paper V); kaolinite is etched and replaced by
blocky dickite. Replacement of kaolinite by dickite is more extensive
in the coarser-grained, permeable sandstones than in fine-grained, less
permeable sandstones. Intercrystalline microporosity is more abundant
in the dickite (up to 70%) than in poorly- or well-crystallized kaolinite
patches (paper V).
Chlorite occurs as a grain coating which composed of boxwork-like with the chlorite crystals attached perpendicular to the grain
32
surface, platelet-like, rosettes, and honeycombs textures in the TST and
HST (paper II). The grain-coating berthierine/chlorite varies in abundance from scarce, being coating a small fraction of the grains (in
HST sandstones), to widespread, being coating major portions to most
grains (in TST sandstones) (paper II). Chlorite that covers layers of grain
coating and ooidal berthierine has presumably been formed by direct precipitation from the pore waters and not by chloritization of berthierine (paper II).
The grain-coating berthierine and chlorite have halted the precipitation of
quartz overgrowths (paper II). Mössbauer spectroscopy (paper III) re-
vealed that iron is dominated by Fe2+ (>85%). Fe2+ replaces Mg2+
whereas Fe3+ replaces Al3+ in the octahedral sites. Fe-rich chlorite
occurs as partial to extensive grain rims that are comprised of pseudohexagonal crystals arranged perpendicular to the surfaces of framework grains (paper V). Chlorite fringes are more abundant in the deltaic channel and delta front facies (trace to 16%; av. 3%) than in the
fluvial sandstones (trace to 3%; av. 1% paper V). Chlorite fringes
were formed by successive replacement of smooth layers of precursor,
grain-coating smectitic clays (paper V) through intermediate phases of
mixed-layer chlorite/smectite (C/S) that, in some cases, have the typical honeycomb texture of corrensite. Chloritization of smectite occurred most extensively in the deltaic sandstones (paper V) that were
enriched in biotite and volcanic rock fragments, which acted as
sources of Fe and Mg. Additional sources of Fe and Mg include fine
crystalline, grain coating iron-oxide pigment.
33
Reservoir quality evolution and conceptual
predictive models within depositional facies
and sequence stratigraphy
Linking the distribution of diagenetic alterations with the depositional
facies and in a sequence stratigraphic framework, i.e., at sequence and
parasequence boundaries, transgressive and maximum flooding surfaces, and within systems tracts of paralic, shallow marine, and fluviolacustrine deposits which is based on the results from this thesis is of
profound importance in deciphering the spatial and temporal distribution of diagenetic alterations and of their impact on reservoir quality
evolution. Prediction of reservoir quality in paralic and shallow marine deposits is usually complicated by the generally greater influence
of diagenetic modifications on porosity than on permeability.
The depositional environments and facies in paralic and shallow
marine exert considerable controls on the diagenetic evolution of clastic sequences. These controls are mostly take place during eodiagenesis being related to variations in pore water chemistry, degree of bioturbation, organic-matter contents, as well as to the textural and architecture of the sedimentary sequence. The sediment refers mainly to the
thickness, spatial and temporal inter-relationships (i.e., geometry of
sediment bodies) and ratio sand and mud, which in turn controls the
extent and pattern of fluid flow. Variations in sedimentation rate control sediment reworking by bioturbation and the residence time of
sediments at the sediment-water or sediment-air interface. The latter
exert profound control on the amounts of organic matter and extent of
near-surface eogenetic alterations.
34
Model 1: summary model for distribution of diagenetic
alterations and reservoir-quality evolution of
progradational and aggradational sequences
The distribution of diagenetic alterations and of their impact on reservoir-quality evolution of the coarse-grained, deltaic progradational
and aggradational sequences (Fig. 9) were controlled by: (i) the carbonate-grain rich composition of the arenites, (ii) the overall arid, paleo-climatic conditions, (iii) the shallow estimated maximum burial
depth (ca 1 km) reached by the successions, and (iv) variations in the
rates of changes in relative sea level versus rates of sediment supply,
which had an impact on changes in pore water chemistry. The carbonate grains have played a dual role in reservoir-quality evolution. These
grains were subjected to dissolution and formation of moldic pores,
which had limited impact on permeability enhancement owing to the
poorly connected nature of these pores. Dissolution of the carbonate
grains is expected to have contributed to porosity deterioration
through re-precipitation as carbonate cement. Moreover, these grains
have acted as nuclei for the precipitation of carbonate cement, which
hence induced further deterioration to reservoir quality. The arid climatic conditions resulted had resulted in the formation of gypsum/anhydrite, which was in some cases been replaced by calcite during near-surfaces diagenesis. The sulfate released from this replacement reaction was reduced into sulfide, as evidenced by the presence
of framboidal pyrite in the vicinity of calcitized gypsum.
The formation of trace amounts of syntaxial quartz and Kfeldspar overgrowths around quartz and K-feldspar grains, respectively, have had little or no impact on reservoir quality evolution of
the arenites. The origin of trace amounts of euhedral quartz overgrowths, which are engulfed by, and hence pre-date, early diagenetic
dolomite in both the progradational and aggradational sequences is
enigmatic. The only viable way to form near-surface quartz overgrowths is through the process of silcrete formation, which typically
occurs under arid to semi-arid climatic conditions (Abdel-Wahab et
al., 1998). However, the absence of opal and chalcedony suggests that
the quartz overgrowths do not likely represent part of silcrete development. The formation of burial diagenetic quartz overgrowths requires depths > ca 2 km and temperatures > 70ºC (cf. McBride, 1989;
Worden and Morad, 2000), which have not been reached by the studies sequences. However, the relatively small amounts of quartz grains
in most of the studied arenites coupled with the common presence of
35
Figure 9: Simplified cartoons showing the most typical diagenetic features
in the aggradational and progradational fan delta sequences.
abundant early diagenetic carbonate cements, may have been another
limiting factor for the formation of greater amounts of quartz overgrowths. The sources of K, Al and Si ions needed for the formation of
early diagenetic K-feldspar overgrowths are not immediately clear. K+
could have been derived from seawater, whereas K+, Al3+ and Si4+
could be derived from partial dissolution of mica and K-feldspar
grains (cf. De Ros, 1998).
Palygorskite, which covers, and hence post-dates, dolomite cement in the arenites is suggested to be of telogenetic origin. The close
association between palygorskite and dolomite suggest that dolomite
36
provided a localized source of Mg needed for the formation of palygorskite, which is enhanced by the arid climatic conditions in the Sinai
Peninsula.
Model 2: summary model of the diagenetic evolution of
shoreface sandstone (paper II)
Sandstones of the various systems tracts and below key sequence
stratigraphic surfaces have fairly characteristic, yet variable diagenetic
evolution pathways (Fig. 10), which is underlining the profound impact of the rates of changes in the relative sea level and rates of sediment supply of the distribution of eogenetic and, consequently,
mesogenetic alterations (cf. Taylor et al., 1995; Amorosi, 1995; Morad et al., 2000; Ketzer et al., 2002, 2003a). Eogenetic alterations in
the TST sediments, particularly below the TS and MFS, which are
accomplished under low sedimentation rates, include the formation of:
(i) goethite ooids and cement under oxic conditions at and immediately below the seafloor, (ii) grain-coating, grain-replacing and ooidal
berthierine, siderite spheroids, from sub-oxic pore waters, (iii) glauconite, primarily by the replacement of mica grains under weakly reducing conditions (Curtis, 1987), presumably in the suboxic, nitrate reduction zone of Froelich et al. (1979), and (iv) pyrite in the bacterialsulfate reduction, yet small amounts of siderite that engulf pyrite may
have been formed in the methanogenesis zone.
Eogenetic alterations in the HST sandstones, which were accomplished during fall in the relative sea level (i.e. progradation), include
the notable formation of: (i) limited amounts of discontinuous, graincoating berthierine, presumably owing to the short residence time of
the sediment to form the precursor Fe-rich clay minerals, such as odinite, and (ii) dissolution and kaolinitization of feldspars and, to
smaller extent, mica, which is attributed to the flux of under-saturated
meteoric waters during fall in the relative sea level. Eogenetic kaolinite is engulfed by siderite, Fe-dolomite and quartz overgrowths. Calcite, Fe-dolomite/ankerite and siderite cementation has occurred at
various temperatures in the TST and HST sandstones.
Mesogenetic alterations in the HST sandstones are similar to those in
the TST sandstones, except for the extensive and widespread conversion of kaolinite into dickite and formation of considerable amounts of
quartz overgrowths in the former sandstones. Silica needed for the
formation of quartz overgrowths was presumably derived internally
37
Figure 10: Simplified cartoons showing the most typical diagenetic features in
sandstones from the highstand systems tracts (HST), transgressive systems tracts
(TST), and along the amalgamated transgressive surface/sequence boundary
(TS/SB) and the maximum flooding surfaces (MFS). The HST sandstones are, overall, characterized by larger amounts of kaolin, illitic clays and syntaxial quartz overgrowths than the other sandstones. The latter sandstones are characterized by larger
amounts of berthierine and siderite. Glauconite, which is mostly restricted to the
MFS, was formed by the replacement of mica grains.
38
from the intergranular dissolution of quartz grains in the sandstones.
Eogenetic grain-coating berthierine, which was subjected to partial
chloritization during mesodiagenesis, retarded the precipitation of
quartz overgrowths (cf. Ehrenberg, 1993; Bloch et al., 2002). Other
mesogenetic alterations include: (i) further cementation of the sandstones by grain-replacing, poikilotopic calcite, which post-dates mechanical and chemical compaction as well as by quartz overgrowths,
and (ii) albitization of plagioclase grains.
Telogenetic alterations in the TST and HST sandstones include the
dissolution and kaolinitization of framework silicates, primarily feldspars. In contrast to eogenetic kaolinite, the telogenetic kaolinite does
not display evidence of conversion into dickite. The distinction between intragranular and moldic porosity of telo- and mesogenetic origins is difficult. However, moldic pores partly filled with diagenetic
quartz or Fe-dolomite cements are considered to be of mesogenetic
origin.
39
Model 3: summary model of impact of diagenetic
modifications on reservoir quality of delta complex
sandstone sandstones (paper IV)
A summary model of the various systems tracts and below
key sequence stratigraphic surfaces and related reservoir-quality evolution of spatial and temporal variations in the provenance and
changes in the relative sea level have had strong impact on the detrital
composition and rates of sediment supply, which were, in turn, the
main parameters controlling the distribution of diagenetic alterations.
Calcite cement occurs as concretions along the PB of the RST
and lower part of the TST, being more and more coalesced into continuously cemented layers towards the MFS, and below the TS (Fig.
11, 12, and 13).
Figure 11: Photograph showing that cement occurs as concretions, which are coalesced into continuously cemented layers particularly at PB.
40
Figure 12: Photograph showing that cement occurs as concretions, which are coalesced into continuously cemented layers particularly at MFS.
Figure 13: Photograph showing scattered concretions below SB and within the RST.
41
The concretions show no systematic variations in the texture
of calcite cement. Formation of microcrystalline calcite cement at
shallow depths below the seafloor is suggested to be sourced by diffusion of Mg2+, Ca2+ and HCO3- from the overlying seawater. Cementation was enhanced by the residence time of the sediments near the
seafloor. Sandstones display various degree of mechanical compaction, which is evidenced by fracturing of bioclasts and bending of the
mica grains and low-grade, micaceous metamorphic rock fragments.
Evidence of chemical compaction includes intergranular pressure dissolution of quartz grains and rare stylolites in sandstones that contain
small amounts of carbonate cements. Mechanical and chemical compaction has, in most of the arenites, been more important than cementation in the destruction of intergranular porosity. Secondary porosity
is rare in the studied arenites and has resulted mainly from the dissolution of coarse-crystalline calcite. Calcite cement dissolution and pressure dissolution of carbonate grains indicate that the diagenetic evolution of the studied arenites has involved considerable cement redistribution. Most porosity and permeability in the Roda sandstones are
anticipated to be related to tectonic fracturing.
Model 4: summary model of impact of diagenetic
modifications on reservoir quality of Jurassic and
Triassic fluvial and lacustrine deltaic sandstones (paper
V)
In addition to the impact of facies, the porosity and permeability of the
Triassic and Jurassic reservoirs are controlled to variable extents by:
(i) chemical and mechanical compaction, (ii) type, abundance and
distribution pattern of the cementing minerals, (iii) the extent of telogenetic dissolution of framework grains and calcite cement, (iv) the
amount as well as the degree of alteration and compaction pattern of
micas, particularly biotite, mud intraclast and rock fragments, and (v)
oil emplacement. Permeability and, to a smaller extent, porosity increase with increase in grain size However, the correlation of porosity
and permeability with grain size, and hence depositional facies, is
overprinted by the various diagenetic alterations induced to the sandstones during various stages of burial and uplift. Thus, the wide range
of permeability encountered for each porosity value is attributed to
variations in grain size as well as in the amounts and distribution pat42
tern of interstitial clay minerals (chlorite, kaolin, illite and pseudomatrix). Clay minerals are rich in micro-pores (Hurst and Nadeau, 1995),
and thus induce a smaller lowering of porosity compared to permeability. Variations in the amounts of intragranular pores that are
poorly connected to the open, intergranular pore system, have induced
an increase in porosity but do not enhance permeability of the sandstones.
The overall small amounts of eogenetic cements rendered compaction to be more important than cementation in reducing porosity and
permeability. Determination of the depositional intergranular porosity
is difficult (Bloch and McGowen, 1994), but assuming a value of
40%, the average porosity loss due to compaction is about 22% (430%) in the fluvial sandstones and 25% (4-34%) in the deltaic sandstones. This accounts partly for the lower porosity, and permeability in
the deltaic sandstones than in the fluvial sandstones. The slightly
greater loss of porosity and permeability due to compaction in the deltaic compared to the fluvial sandstones is partly attributed to the
higher content of ductile grains such as mica, argillaceous rock fragments and mud intraclast. However, the Triassic sandstones also have
an average higher TTI index, and thus a greater diagenetic loss of porosity and permeability than the Jurassic sandstones. Overall, sandstones that contained evenly distributed patches of eogenetic carbonate cement suffered relatively little compaction compared to sandstones that were poor in such cement.
The intergranular pressure dissolution (enhanced by mica and illitic
clay coatings) and concomitant local precipitation of dissolved silica
as quartz overgrowths induced an additional loss of porosity and permeability. The expansion of abundant biotite grains, particularly in the
deltaic sandstones, due to their eogenetic alteration into smectite
and/or precipitation of microcrystalline carbonate along traces of its
cleavage planes caused efficient choking of adjacent pore throats.
Hence, detrital mica induced partial deterioration to both porosity and
permeability by alteration and expansion and by the enhancement of
intergranular pressure dissolution of quartz grains.
The average original porosity loss due to cementation is similar in
the fluvial and deltaic sandstone (8%; range 2-26%). However, the
precise role of cementation on reservoir quality is fairly complex due
to the presence of several types of cements with various textural properties and occurrence habits. Carbonates are the most important cements that caused deterioration of both permeability and porosity and,
to a less extent, quartz overgrowths. Eogenetic carbonate cementation,
43
particularly in the Triassic sequence; tend to occurs along parasequence boundaries in the deltaic facies of the early HST. The formation of laterally cemented layers, and thus potential reservoir barriers
in field scale, is possibly favored in the late TST and early HST toward the MFS. Mesogenetic carbonates occur as less pervasive cement than the eogenetic type I calcite, but are more frequent, more
homogeneously distributed, and hence have a greater influence on
porosity-permeability loss in the sandstones. Carbonate cements are
more abundant, and, hence, have a greater control on porosity and,
particularly permeability of the deltaic sandstones than of the fluvial
sandstones. A higher overall content of carbonate cement accounts
partly for the considerably lower reservoir quality of the delta-front
and pro-delta sandstones compared to the delta-plain sandstones.
Chlorite rims around quartz grains retarded the precipitation of
quartz overgrowths and hence prevented a greater loss of primary intergranular porosity. However, extensive chlorite rims in the finegrained sandstones caused a local blockage of the pore throats, and by
virtue a permeability reduction. The clay minerals induced an increase
in microporosity, which is verified by the high values of water saturation in the oil zone (av. 26%). In the absence of quartz overgrowths,
the intergranular pores that are lined by chlorite were, particularly in
some of the water-saturated sandstones, filled partially to extensively
by mesogenetic ankerite. The illitization of intergranular kaolinite, and
hence further deterioration of permeability, was inhibited due to the
earlier transformation of kaolinite into dickite which is more resistant
to illitization, due to its better ordered crystal structure (Morad et al.,
1994). The retardation of kaolinite illitization was also due to the only
small degree of albitization of K-feldspar grains, which usually are the
most important sources of potassium ions (Morad et al., 1990).
The precise role of telogenetic dissolution of detrital grains and
carbonate cement on porosity and permeability is difficult to quantify.
The dissolution of feldspar (mainly plagioclase) is, however, more
common in the coarse-grained Jurassic fluvial sandstones than in the
finer-grained deltaic sandstones. As there is no telogenetic precipitation of quartz, plagioclase kaolinitization is accompanied by a 50%
molar volume reduction, and hence induces a maximum increase in
average porosity by about 2%. Obviously, these telogenetic modifications on reservoir quality were only important for the second migration phase, which occurred during the Miocene (Zhao et al., 1996),
since the initial oil generation and migration occurred much earlier.
44
45
Summary of the papers
Paper I Diagenetic evolution of aggradational and
progradational fan-delta Arenites: Evidence from the
Abu Alaqa group (Miocene), Gulf of Suez, Egypt
Progradational (braid delta) and aggradational (fan delta) arenites of
the coarse-grained fan sequences of the Abu Alaqa Group (Miocene),
the Gulf of Suez, Egypt are extensively cemented by early-diagenetic
calcite (micro-, equant, coarse to poikilotopic spar) and dolomite
rhombs (grain-replacing and pore/void-filling). Minor amounts of
diagenetic pyrite, quartz and K-feldspar overgrowths, and glaucony
occur too. The 18OV-PDB (dolomite = -2.2‰ to +1.7‰; calcite = 7.0‰ to +3.3‰) and 13CV-PDB (dolomite = -4.5‰ to +0.6‰; calcite =
-4.5‰ to +1.4‰) values suggest precipitation from pore waters that
ranged from marine to meteoric in composition. Carbonate cement,
pyrite and glaucony are most abundant in the progradational braiddelta fan sequences, particularly along the topsets (marine flooding
surfaces), where dominate over coarse spar and poikilotopic calcite.
Cementation by the latter calcite and the formation of moldic porosity
by the dissolution of framework carbonate grains are most abundant in
the aggradational fan deltas sequences, which are being attributed to
the incursion of meteoric waters during sea-level lowstand.
Paper II Diagenetic and reservoir-quality evolution of
shoreface sandstones in sequence stratigraphic context:
The Ponta Grossa Formation (Devonian), Paraná Basin,
Brazil
This petrographic and geochemical study aims at linking the distribution of diagenetic alterations to sequence stratigraphic framework
of shoreface sandstones of the Ponta Grossa Formation (Devonian),
46
Paraná Basin, Brazil, in order to achieve better elucidation and prediction of diagenetic- and reservoir-quality evolution pathways. Early,
near-surface, grain-coating and ooidal berthierine, ooidal goethite,
grain-coating micro-quartz, glauconite, pyrite and siderite are most
abundant in the transgressive system tracts (TST), particularly below
the transgressive (TS) and maximum flooding surface (MFS). Nearsurface diagenetic alterations in the highstand systems tract (HST)
sandstones include, in addition to the formation of berthierine and
siderite, the formation of grain-coating, infiltrated illitic clays as well
as dissolution and kaolinitization of feldspars, which are attributed to
meteoric waters percolation during fall in the relative sea level.
Petrographic observations and the wide ranges of 18OV-PDB values
of siderite (-11.9‰ to -5.8‰), calcite (-11.5‰ to -5.4‰) and to,
smaller extent, of Fe-dolomite/ankerite (-10.8‰ to -9.6‰) in the TST
and HST deposits suggest that carbonate cementation occurred: (i) at
various temperatures ranging from near surface to burial diagenesis,
and (ii) from pore waters ranging from dominantly marine composition to evolved basinal brines. Other burial diagenetic alterations in
the sandstones include chemical compaction, cementation by quartz
overgrowths, albitization of plagioclase, and transformation of kaolinite into dickite (mainly in the HST sandstones). The formation of
grain-coating berthierine has inhibited the formation of extensive
quartz overgrowths, and hence contributed to reservoir-quality preservation. Telogenetic alterations include dissolution and kaolinitization
of framework silicates.
This study demonstrates that the spatial and temporal distribution
of diagenetic alterations is better elucidated when linked to the sequence stratigraphic framework of the shoreface sandstones.
Paper III Mössbauer study of diagenetic Fe-rich
minerals in Devonian clastic rocks of the Ponta Grossa
Formation, Paraná Basin, Brazil
Redox potential of pore waters exerts prime control on the formation
of diagenetic Fe-rich minerals in sediment, and thus has profound impact of the geochemistry of sediments and sedimentary rocks. This
study aims to utilize the Mössbauer analytical techniques to highlight
the oxidation states of the diagenetic Fe-rich minerals (primarily siderite, berthierine/chlorite, and goethite) and of bulk host Devonian,
shoreface-offshore siliciclastic deposits of the Ponta Grossa Forma47
tion, the Parana Basin, Brazil. The distribution pattern and redox
states of the Fe-rich minerals and of bulk host rocks are linked to sequence stratigraphic framework of the succession. Minerals that form
in contrasting redox pore waters conditions, such as goethite and siderite may coexist, reflecting progressive but incomplete reduction of
Fe3+ during shallow sediment burial below the seafloor. The redox
reactions between mineral and pore waters in the Devonain succession
were influenced by sedimentations rates and organic-matter content,
which were in turn controlled by rates of changes in the relative sea
level. Chlortization of berthierine, which is known to occur during
burial diagenesis, did not involve noticeable changes to the Fe2+/Fe3+
ratio.
Paper IV Linking the distribution of carbonate cement
to sequence stratigraphy of delta complex sandstones:
evidence from the Roda sandstone Formation (Eocene),
South-Pyrenean Foreland Basin, NE Spain
Calcite cementation in delta complex sandstones of the Roda Sandstone Formation (Eocene), which was promoted by the presence of
abundant carbonate grains, displays various patterns, including: (i)
continuously cemented layers, (ii) stratabound concretions, and (iii)
concretions scattered throughout the sandstone beds. Variations in the
cement-distribution pattern are attributed to variations in the rates of
changes in the relative sea level relative to the rates of sediment supply (i.e. the sequence stratigraphic context). Continuously cemented
sandstone beds occur in the upper parts of the transgressive systems
tract (TST), particularly along the parasequences boundaries (PB) and
below the maximum flooding surfaces (MFS) and was presumably
enhanced by prolonged residence time of the sediment below the seafloor. Such carbonate cemented horizons can act as baffles for fluid
flow, and may hence induce reservoir compartmentalization and regional seals to sandstone successions. Conversely, concretionary calcite cementation occurs in sandstone beds of the regressive systems
tract (RST) and is attributed to the short residence time below the seafloor owing to high rates of sediment supply relative to the rates of
accommodation creation.
48
Paper V The diagenetic and reservoir-quality evolution
of fluvial and lacustine-deltaic sandstones: evidence
from Jurassic and Triassic sandstones of the Ordos
Basin, Northwestern China
The reservoir quality of Jurassic and Triassic fluvial and lacustrine
deltaic sandstones of the intracratonic Ordos Basin (NW China) is
strongly influenced by facies and various types of diagenetic modifications. The fluvial sandstones have higher average He-porosity and
air permeability (14.8% and 12.7 mD, respectively) than the deltaic
sandstones (9.8% and 5.8 mD, respectively). In addition to extensive
mechanical compaction, eodiagenesis (220-97 Ma; depth d 2000 m; T
< 70oC) resulted in silicate dissolution and kaolinite formation in the
Jurassic fluvial sandstones, and in smectite infiltration and minor calcite and siderite cementation in the Triassic fluvio-deltaic sandstones.
Pervasive eogenetic carbonate cementation (> 20 vol. %) in the deltaic
facies occurred along parasequence boundaries. Mesodiagenesis (9765 Ma), which occurred during rapid subsidence to depths of 37004400 m, resulted in the albitization of plagioclase and crystallization
13
of dickite, quartz overgrowths, chlorite, illite, ankerite (G C V-PDB = 13
2.4‰ to +2.6‰; G18O V-PDB = -21.5‰ to -10‰) and calcite (G C V-PDB
= -4.7‰ to +3.7‰; G18O V-PDB = -21.8‰ to -13.4‰). Oil emplacement
retarded cementation by quartz and carbonate but had little influence
on dickite, illite and chlorite formation. Retardation of quartz cementation was also due to the presence of chlorite fringes around detrital
quartz grains. Dickitization of eogenetic kaolinite together with the
short residence time at maximum burial temperatures (105-124oC),
have retarded the albitization of K-feldspars and illite formation, and
hence prevented severe permeability destruction. Meteoric-water telodiagenesis, which occurred subsequent to uplift (Eocene to the end of
Neogene) to depths shallower than 2 km (T < 70oC), has resulted in
slight dissolution of carbonate and feldspars, and in the formation of
kaolinite.
49
Concluding Remarks
Constraining the distribution of diagenetic alterations in a sequence
stratigraphic context allows a better elucidation and prediction of the
spatial and temporal distribution of reservoir quality and heterogeneity. Linking diagenetic alterations and their impact on reservoir quality
to depositional facies and sequence stratigraphy in four basins have
revealed that:
.
The diagenetic alterations and related reservoir quality evolution
pathways of paralic and shallow marine sandstones are closely
linked to sequence stratigraphy, depositional facies, paleo-climatic
conditions, and burial history of the sandstones.
. Carbonate cement (micro-crystalline and equant calcite spars
dominate over poikilotopic calcite), pyrite and glaucony are most
abundant in progradational braid-delta fan sequences, particularly
along the topsets (MFS). Cementation by coarse spar calcite and
dolomite, and the formation of moldic porosity by the dissolution of
framework carbonate grains are most common in the aggradational
fan deltas sequences.
. Eogenetic kaolinitization of framework silicates is largely restricted to the HST sandstones, whereas telogenetic kaolinite occurs
in the HST and TST paralic sandstones.
. Formation of grain-coating, infiltrated illitic clays as well as dissolution and kaolinitization of feldspars are attributed to meteoric
waters percolation during fall in the relative sea level.
. Formation of goethite ooids in the TST sediments, being presumably aided by low sedimentation rate, is concluded to be encountered
during marine transgression.
.
Formation of glaucony, siderite spherules, and extensive grain
coatings, grain-replacing and ooidal berthierine is more common in
the TST than in the HST sediments, particularly below the TS and
MFS, being enhanced by low sedimentation rates.
50
. The formation of grain-coating berthierine has inhibited the formation of extensive quartz overgrowths, and hence contributed to
reservoir-quality preservation.
. Grain coating chlorite in fluvio-lacustrine sandstones is attributed
to chloritization of infiltrated smectitic clays.
. Cementation by mesogenetic calcite and Fe-dolomite/ankerite occur in both TST and HST sandstones by nucleation around eogenetic
carbonate cements.
. Syntaxial quartz overgrowths are most extensive in the HST sandstones owing to the absence of extensive, grain coating berthierine.
. The greater amounts of micro-porosity in the TST sandstones than
in the HST sandstones are related to the greater amounts of berthierine/chlorite in sandstones.
. Mössbauer spectroscopy study revealed that there is little or no
changes encountered in the Fe2+/ Fe3+ ratio during conversion of
berthierine into chlorite.
In summary, this study shows that the distribution of diagenetic alterations in siliciclastic deposits is controlled by complex array of
inter-related parameters. Nevertheless, linking diagenesis to depositional facies and sequence stratigraphy of paralic, shallow marine
and fluvio-lacustrine deposits has important implications for better
prediction of the reservoir quality ahead of exploration drilling in
aquifers and oil reservoirs as well as recovery, and should applied to
other depositional settings and basins.
51
Summary in Swedish
Diagenes och utveckling av reservoarkvaliteten hos
paraliska, grundhavs-, och fluviolakustrina avsättningar:
Kopplingar till avsättningsfacies och sekvensstratigrafi
Sammanfattning
Att koppla avsättningsfacies med sekvensstratigrafi hos sandstenar ger
möjlighet till bättre förutsägelser vad gäller den rumsliga och
temporala fördelningen av diagenetiska förändringar, och därmed
utvecklingen av reservoarkvaliteten. Den här avhandligen visar att
detta tillvägagångssätt är möjligt eftersom avsättningsfacies och
sekvensstratigrafi innehåller användbar information om parametrar
som kontrollerar ytnära diagenes, såsom förändringar i: (i)
porvattenkemin, (ii) residenstiden hos sediment under vissa
geokemiska villkor, (iii) detritisk sammansättning och andel extraoch intrabassängkorn, samt (iv) typ och mängd av organiskt material.
Bevis från fyra fallstudier har möjliggjort utvecklingen av
konceptuella modeller för fördelningen av diagenetiska förändringar
och för deras påverkan på utvecklingen av reservoarkvaliteten hos
sandstenar avsatta i paraliska, grundhavs-, och fluviolakustrina
miljöer. Diagenetiska förändringar kan i en kontext begränsad till
avsättningsfacies och sekvensstratigrafi diskuteras enligt följande: (i)
karbonatcement (mikrokristallin och jämnstor kalcit dominerar över
poikilotopisk), pyrit och glaukonit är vanligast i prograderande
braided-fan deltasekvenser, särskilt längs maximum flooding surface
(MFS) och parasekvensgränser i highstand systems tracts (HST) hos
deltafacies, (ii) cementering med grovkristallin kalcit, dolomit och
bildning av moldisk porositet genom upplösning av karbonatkorn är
vanligast i de ytligt aggregerade fan-deltasekvenserna, (iii) eogenetisk
kaolinitisering av silikater är huvudsakligen begränsad till de fluviala
och paraliska HST-sandstenarna, medan teleogenetisk kaolinit också
återfinns i transgressive systems tracts (TST)-sandstenarna, (iv)
52
bildning av götit-ooider i TST-sedimenten, (v) bildning av glaukonit,
siderit-sfärer, samt omfattande bertierit, mer i TST- än i HSTsedimenten, särskilt under den transgressiva havsytan (TS) och MFS,
(vi) kalcit- och Fe-dolomit/ankerit-cementering förekommer både i
TST- och HST-sandstenarna, (vii) syntaxiella kvartsöverväxningar är
mest omfattande i HST-sandstenarna på grund av ofullständig
kornpåväxt av bertierit/klorit, (viii) en större andel mikroporositet hos
TST-sandstenarna jämfört med HST-sandstenarna kan relateras till
den större mängden bertierit/klorit i de ursprungliga sedimenten, samt
(ix) kloritmantlar runt kvartskornen motverkade avsättningen av
kvartsöverväxning och hindrade därmed en större förlust av primär
intergranulär porositet hos de fluviolakustrina sandstenarna.
Att reducera fördelningen av diagenetiska förändringar till en kontext
av avsättningsfacies och sekvensstratigrafi utgör med andra ord ett
kraftfullt hjälpmedel vid prospektering efter gas och olja.
53
Acknowledgements
First, I would like to thank my supervisor professor Sadoon Morad. I
am deeply grateful for having been introduced to such an inspiring
field as Diagenesis and Sequence Stratigraphy. Professor Morad is
thanked for his patient endless revisions of my manuscripts and for
being a good and very encouraging supervisor who has the ability to
be both critical and positive at the same time. He taught me the arduous work of science and encouraged me to explore ideas and new lines
of work, which I will always carry with me.
I would also like to thank the Libyan Government represented by
the Higher Education section for granting a postgraduate studies at
Uppsala University. I also acknowledge the NordForsk for granting
some courses in Norway. I gratefully acknowledge Vale do Rio Doce
Company, Brazil for providing us with drill core samples. The
Yanchang Petroleum Exploration Academic Institute thanked for providing part of the petrophysical data and formation-water isotopic
data. Zhidan Petroleum Exploration and Development Headquarters
also thanked for kindly provided access to the cores. I would like to
express my gratitude to the European Science Foundation for financial
supports related to traveling and accommodation for the EGU (European Geosciences Union) that I attended in Vienna 2007 and also to
Wallenbergstiftelsen for their financial supports to attend the EGU
2008.
I would like to thank Dr De Ros (Federal University of Rio Grande
Sul, Porto Alegre, Brazil) for his help and kind support during the
entire period of this work. I would like to extend my thanks to Professor Wojtek Nemec, Dr David Gomez, Dr Alaa Salem, Dr Essam Elkurabi, Fatima Brazil, Dr Egberto, Dr Miguel Lopez, Dr Miguel Caca,
and Dr William Halland.
I also thank staff members of the Department of Earth Sciences, Uppsala University for providing inspiring working environment. Drs.
Hemin Koyi, Ala Aldahan, Örjan Amcoff, Per Nysten, Peter Lazor,
Håkan Sjöström, Tore Eriksson, and Christopher Talbot. Special
thanks go to Kersti Gløersen for many administrative help and to Hans
Harryson for help with the EMP analysis. I would like thank Dr. J.D.
54
Martín-Martín for help with the interpretation of XRD of clay minerals.
Thanks are also to the staff of the Library of the Department of
Earth Sciences, Uppsala University for being so co-operative in matters related to literature. I am also very grateful to Anna, Taher, Johan,
and Leif for all the help with printing and technical issues.
Sincere thanks go to all my colleagues and friends at the department Ashour Abouessa, Muftah Khalifa, Sebastian Willman, Yasser
Abdu, Mohamed El-ghali, Khalid Al-Ramadan, Howri Mansubeg,
Masoumeh Kordi, Faramarz Nilfouroushan, Zurab Chemia, Hesam
Kazemeini, Ismail Nazli, Sofia Winell, Tuna Eken, Zuzana Konopkova, Peter Dahlin, Kristina Zarins, Sara Sundberg, Erik Ogenhall,
Anna Ladenberger, Farag Elkhutari, Lijam Hagos, Zemichael, Alireza
Malemir and Mattias Lindman.
I have many wonderful friends outside the academia, who helped
me, supported me and made me feel at home in Uppsala. In particular
I would like to thank Emin Poljarevic, Usama Hegazy, Akram Bassam, Yousry Abdelrahman, Giorgis Isaac, Mohamed Ramadan, and
Mohamed Issa, for sharing good time, continuous support, and for
their interest in my research work.
At Al- Fath University, there were many professors from whom I
learned a lot including Dr. Abdalla Attiqa, the former chairman of
Geology Department, Dr. Ali El-Makhrouf, Dr. Omar Hammuda, and
Dr. Ali Sbeta for their concern and support. Also I acknowledge Dr.
Mabrouk Busrewil, Dr. Khalid Oun, Dr. Zuhair Hafi, Dr. Salem
Lagha, Dr. Abd-Alatef Al-Najjar, and, my friend Dr. Amer Borgan for
all good time we spend together when I was as a teacher assistant and
interesting talks, although the times when the topic concerned geology
were, as I recall, very few. Thanks to you all.
Many thanks go to Khairi Abogassa, Ahmed Agded, Mohamed
Elrutab, Hakeem Mugber, Osama Elalij, Najib Elrutab, Rabee Hlal,
Milad Sraab, Adel Elrjbani, Fathi Alsaadi, Bashir Hlal, Khalid Alsudani, Abobaker Tnesha, Milad Ben Rhuma, Ali Elrutab, Aiad AlZetreni, Salah Abdelgaleel, Mohseen Elrutab, Hisham Elosta, Adel
Elrabiea, and so many others, in Libya and thus, too many to list, for
their support, friendship and their help in many things.
Finally, I wish to thank my very dear family for the enormous support and sympathy that you all have provided during this time. I am
especially grateful to my wife Amira Elalij and my little daughter Emtenan for their patience and giving me a full and rich life outside office hours.
55
56
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