Geo-Mar Lett (2015) 35:69–75
DOI 10.1007/s00367-014-0391-1
SHORT COMMUNICATION
The new CutSprof sampling tool and method
for micromorphological and microfacies analyses of subsurface
salt marsh sediments, Algarve, Portugal
João Araújo-Gomes & Ana Ramos-Pereira
Received: 25 September 2014 / Accepted: 3 November 2014 / Published online: 12 November 2014
# Springer-Verlag Berlin Heidelberg 2014
Abstract A new tool and method for collecting undisturbed
subsurface samples in estuarine environments by means of
trenching, timbering and sectioning is presented. Smoothing
of sidewalls is achieved by a so-called cutting sediment profiler (CutSprof), while water draining into the trench is cleared
by pumping. From smoothed sidewall sections, undisturbed
thin sediment slices can then be collected for micromorphological and microfacies analyses. Results demonstrating the
successful application of this procedure are presented for salt
marshes of the Bensafrim River estuary (Lagos, Algarve,
Portugal). In addition to palaeo-reconstructions in salt marsh
settings, the CutSprof would be highly suitable in various other research domains as well as for environmental management purposes, particularly where sampling
below the groundwater table is desirable to explore, for
example, animal–sediment relationships in tidal-flat and
mangrove ecosystems as well as the dynamics of coastal
wetlands today threatened by ever-increasing anthropogenic
influence.
Introduction
Important palaeoenviromental information critical in
reconstructing environmental changes over time is commonly
preserved in estuarine and salt marsh deposits (e.g. Hindson
and Andrade 1999; Allen 2000; Boski et al. 2002; Heap et al.
2004; Vis et al. 2008; Kolditz et al. 2012; Kim et al. 2013). In
addition, micro- and macrofossils may contribute to reconstruct relative sea-level histories at high precision (e.g.
J. Araújo-Gomes (*) : A. Ramos-Pereira
IGOT, Centre of Geographical Studies, University of Lisbon,
1600214 Lisbon, Portugal
e-mail: [email protected]
Franceschini et al. 2005; Woodroffe and Long 2009). Intertidal and supratidal estuarine sedimentary successions are
particularly useful in this context because they record both
sea-level fluctuations and changes which may have occurred
in upstream terrestrial drainage basins (e.g. Ramos-Pereira
et al. 2011).
Traditional sampling methods in estuarine environments
usually make use of augering and other coring techniques
which also allow sampling below the water table (Lanesky
et al. 1979; Rapp and Hill 1998). Although these procedures
enable the extraction of long cores from water-saturated sandy
and muddy sediments, cores from muddy substrates such as
salt marsh deposits do not generally allow a full analysis of
sedimentary and post-depositional alteration processes or undisturbed synsedimentary structures (Bullock et al. 1985),
even if coring is performed with an Eijkelkamp piston sampler. This is because it is notoriously difficult to prepare epoxy
resin peels from muddy substrates.
This short paper focuses on presenting a new trenching
procedure and cutting device particularly useful in the recovery of undisturbed subsurface samples for micromorphological and microfacies analyses of salt marsh deposits. The
method was applied in the Bensafrim River estuary near
Lagos, Algarve, Portugal, within the framework of the multidisciplinary estuarine research program FMI 5000 (RamosPereira et al. 2011), one main objective being the search for
tsunami deposits and associated deformations. Such seismically deformed sedimentary records have previously been
identified and analysed in a similar estuarine environment
near Lagos (Hindson and Andrade 1999; Kortekaas and Dawson 2007; Cunha et al. 2009), but without the additional
benefits of the technique described in this paper. An ultimate
goal is to validate thin section analyses for the purpose of
designing a diagnostic tool for the identification of local
tsunami deposits sensu Kilfeather et al. (2007) and Bruins
et al. (2008).
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Brief outline of micromorphological approach
Micromorphological investigations are rooted in
micropedology (Kubiëna 1938; Stoops 2009). They are today
a standard technique in soil studies and have received particularly strong attention in geoarchaeology over the last few
decades (Cremaschi 2004). This geoscientific approach is an
independent research field for the study of undisturbed soils,
stratifications and regoliths (Bullock et al. 1985; Stoops
2003). In some cases, it has even been applied to obtain data
on soil formation in space and time, factors essential in
Fig. 1 a Map of Portugal and location of the study area. b Elevation
model of the Bensafrim River basin showing the lithological boundary
between the upper and lower catchment, as well as the coring and
Geo-Mar Lett (2015) 35:69–75
understanding palaeoenvironmental conditions (cf. Goldberg
1979; McCarthy et al. 1998; Goldberg et al. 2003; Macphail
et al. 2013).
Micromorphology is a widely used approach in many types
of research and in different environmental contexts (e.g. van
der Meer 1993, 1997; Harris 1998; Kemp 1999; Goldberg and
Byrd 1999; Carr 2001; Theler 2004; Stephens et al. 2005;
Stolt and Lindbo 2010; Kilfeather et al. 2010; van der Meer
and Menzies 2011). Excellent results have been achieved in
coastal research (e.g. Macphail et al. 2010), hydropedology
(e.g. Kutílek and Nielsen 2007) and archaeology (e.g.
trenching sites (M marina). c Simplified log of the core recovered in
2013 (extracted from Araújo-Gomes 2013)
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Macphail 2012). In spite of this, there are very few published
papers specifically dealing with sampling methods and strategies for micromorphological research in general (cf. Goldberg and Macphail 2003), let alone for salt marsh
environments.
In practice, micromorphological investigations always begin with the extraction of blocks of undisturbed sediment
along a vertical stratigraphic profile, which are then impregnated with an epoxy resin, polished and ground into thin
sections for microscopic inspection (e.g. Bouma 1968; Courty
et al. 1989). This procedure preserves sedimentary structures
and is thus fundamental to environmental interpretation. Being undisturbed and precisely oriented in space, the epoxy
peels and thin sections allow compositional and orientational
analyses of the sample material (van der Meer and Menzies
2011).
Physical setting
The study was carried out in the estuarine section of the
Bensafrim River along the southwest coast of Portugal
(Fig. 1). At present, this estuary is a restricted mouth-bar
estuary (cf. Cameron and Pritchard 1963; Dyer 1997) which
has recently been transformed into a marina. The western
margin is higher than the eastern one, being a Miocene limestone spur which forms the Ponta da Piedade. The eastern
margin, located in a more rearward position, is formed by a
fossil cliff carved into a sedimentary formation of probable
Pliocene age, which is essentially composed of incoherent red
sandstone (Ramos-Pereira 1990; Ramos-Pereira et al. 1994).
Previous coring performed in the salt marsh upstream of the
marina (Araújo-Gomes 2013) indicates that this estuary had
once been an open estuary.
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The drainage basin of the Bensafrim River can be
subdivided into two distinct geological formations: (1)
Palaeozoic turbidites, essentially composed of schists and
greywackes, which occupy the upper half of the basin; and
(2) carbonate and detrital formations, mainly composed of
dolomitic limestones, sandstones (“Grés de Silves”; RamosPereira 1990) and marls forming the lower half of the basin
(Fig. 1b).
Earlier core analyses by Araújo-Gomes (2013) showed
different sedimentary successions related to variable energy
conditions, the upper units being the less energetic (Fig. 1c).
From bottom to top the sedimentary succession comprises: (1)
a >63-cm-thick silty sand bed; (2) a 47-cm-thick sandy clay
bed; (3) a 51-cm-thick clayey silt bed with thin layers of fine
sand intercalated; and (4) a 30-cm-thick surficial silty sand
bed (sediment classification after Flemming 2000). In general
terms it was concluded that (1) the silts and clays were
probably derived from upstream turbidite deposits, whereas
(2) the “Grés de Silves” (Silves Sandstone) is the main source
of the sandy terrigenous sediments in the estuary; (3) based on
AMS dating, the change from an open estuary to a bar-built
one occurred at about 3 ka (Fig. 1c).
Materials and methods
As trenching was to be carried out to a depth below the water
table, the application of a particular technique and procedure
was required to avoid the collapse of trench sidewalls while
allowing the recovery of undisturbed sediment samples (cf.
Rapp and Hill 1998, p. 192). In the present case the study was
confronted with a number of major issues: (1) insufficient
information on the micromorphological and microfacies evolution of the estuarine infill; (2) the known existence of
Fig. 2 Schematic diagrams of a trench (a), the design of the CutSprof cutting tool (b), and the sampling procedure (c)
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seismically deformed sediments elsewhere in the Algarve
(Schneider et al. 2009); and (3) the lack of a technical solution
to overcome the problem of unstable trench sidewalls in
water-logged sediments, which is probably the reason for the
dearth of micromorphological and microfacies information in
the first place. On the other hand, for simply describing the
vertical stratigraphic sequence of the salt marsh deposits,
exhaustive profile sampling was not required (e.g. Bullock
et al. 1985; Courty et al. 1989).
With these issues in mind, a suitable technique for the
recovery of undisturbed subsurface samples in water-logged
sediments was developed. The procedure and technique is
schematically illustrated in Fig. 2. At first, a trench of suitable
dimensions (length, width, depth) is excavated (Fig. 2a). To
avoid the trench from flooding, it is drained by means of a
submersible dirt-water pump powered by a portable generator.
Fig. 3 a Trenching and timbering
procedure before water pumping:
strict safety measures are
advised—always wear a helmet,
firm shoes, and a rope around the
waist in case of partial bogging.
Adjustment and smoothing of
trench sidewalls by means of
CutSprof: b before cutting, c
during cutting, d after cutting.
Note the smooth vertical cut
revealing undisturbed sediments
Geo-Mar Lett (2015) 35:69–75
The collapse of the trench is prevented by supporting the
sidewalls with wooden (or metal) boards held in place
by adjustable steel struts (timbering procedure), but
leaving narrow wall sections non-timbered for the purpose of sampling (Fig. 2a). Once the sidewalls have been
stabilized and percolating water is under control, the trench
can be safely entered.
In a next step, the non-timbered sidewalls are vertically
smoothed by means of a so-called CutSprof tool, a cutting
sediment profiler specially designed for this purpose (Fig. 2b).
It comprises a thin, spade-like, concave-shaped steel cutting
edge supported by two or three vertical steel arms ending in a
horizontal round steel or wooden handle. This cutting tool
proved to be essential for producing perfectly smooth vertical
surfaces required for the extraction of undeformed sediment
samples. Spades and trowels were found to be inferior for this
Geo-Mar Lett (2015) 35:69–75
purpose. After smoothing, thin soil slices can be removed by
means of suitably sized plastic boxes and a normal spatula
(Fig. 2c). After recovery, the boxes are sealed to avoid desiccation. In the laboratory, the samples can be X-rayed, impregnated with epoxy resin and ground into thin sections for
microscopic analysis.
Results
In the case of the Bensafrim River estuary, the sidewalls of
trenches excavated into the salt marsh are prone to collapse
due to groundwater seepage from water-logged sediment
layers. Figure 3a shows an excavated trench supported by
steel boards held in place by an adjustable steel strut. The
non-timbered sidewalls were then cut into vertical smooth
surfaces by means of the CutSprof cutting tool as illustrated
in Fig. 3b–d.
For the recovery of undisturbed samples, simple plastic food boxes with clamp lids were used as sampling
devices (Fig. 4a). The plastic is hard enough to endure
extraction and transportation but soft enough to be
pierced for later drying procedures. Although this type
of container is rarely used because it is less resistant
than other plastic boxes, they are relatively cheap, easily
obtained in any supermarket, and their clamp lids provide perfect seals optimal for the preservation of sedimentary structures and water content. As shown in Fig. 4b,
the thin section produced from such a box sample is well
suited for micromorphological and microfacies analyses under
a microscope.
Fig. 4 a Sampling with a plastic
food container box; b
corresponding thin section
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Discussion and conclusions
A new procedure and particularly a tool were developed for
this study because the poor stability of excavated trenches in
water-saturated salt marsh deposits of the Bensafrim River
estuary prohibited the use of standard techniques. Indeed, van
der Meer and Menzies (2011) encouraged the adaptation of
the micromorphological approach and techniques to suit the
needs of a wider range of environments, providing specific
examples where this had already been successfully achieved
(e.g. Borchert 1968; Kooistra 1978; Johnson 1982; Kilfeather
et al. 2007).
In the present case, the sidewalls of the trenches were
stabilized by adapting a form of timbering commonly used
in street excavations. This involved the lining of the trench
sidewalls with steel boards which were then held in position
by an adjustable steel strut wedged between them. Seepage
water collecting in the trench was drained by means of a
submersible dirt-water pump. To obtain smooth vertical trench
sections, a specially designed cutting tool, the CutSprof, was
constructed. This new tool makes use of a concave cutting
blade which is especially effective in ductile and watersaturated soils. It allows the adjustment and smoothing of
vertical trench profiles, the pendulum shape and concave base
facilitating lateral tilting motions to penetrate resistant or
compacted soils.
In addition to palaeo-reconstructions of, for example, tsunamis in salt marsh settings, the CutSprof would be highly
suitable in various other research domains as well as for
environmental management purposes. These include animal–sediment relationships in tidal-flat and mangrove ecosystems and the dynamics of coastal wetlands in general,
74
particularly where sampling below the groundwater table is
desirable and also where anthropogenic impacts today pose
ever-increasing challenges in coastal restoration (e.g. Perillo
et al. 2005; Araújo et al. 2012; Lo et al. 2014).
In conclusion, the findings convincingly demonstrate that
the tools and the procedure developed for this work enable the
recovery of undisturbed subsurface samples from excavated
trench sidewalls even in water-saturated salt marsh environments below the groundwater table. The mechanical
trenching, water pumping and profile timbering applied in
the present study greatly reduce the risk of injury commonly
associated with trenching.
Acknowledgements The authors wish to thank the Portuguese Science
and Technology Foundation (FCT-MCTES) for the financial support of
this ongoing investigation within the research project PTDC/CTEGIX/
104035/2008 - FMI 5000: Environmental changes: Fluvio-marine interactions over the last 5000 yrs. The assistance of the SLIF (Littoral and
Fluvial Systems) team of the Centre for Geographical Studies, IGOT,
University of Lisbon is also gratefully acknowledged. The editors of GeoMarine Letters and an anonymous reviewer are thanked for their considerable help in improving the manuscript.
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