SHORT COMMUNICATION

The new CutSprof sampling tool and methodfor micromorphological and microfacies analyses of subsurfacesalt marsh sediments, Algarve, Portugal

João Araújo-Gomes & Ana Ramos-Pereira

Received: 25 September 2014 /Accepted: 3 November 2014# Springer-Verlag Berlin Heidelberg 2014

Abstract A new tool and method for collecting undisturbedsubsurface samples in estuarine environments by means oftrenching, timbering and sectioning is presented. Smoothingof sidewalls is achieved by a so-called cutting sediment pro-filer (CutSprof), while water draining into the trench is clearedby pumping. From smoothed sidewall sections, undisturbedthin sediment slices can then be collected for micromorpho-logical and microfacies analyses. Results demonstrating thesuccessful application of this procedure are presented for saltmarshes of the Bensafrim River estuary (Lagos, Algarve,Portugal). In addition to palaeo-reconstructions in salt marshsettings, the CutSprof would be highly suitable in var-ious other research domains as well as for environmen-tal management purposes, particularly where samplingbelow the groundwater table is desirable to explore, forexample, animal–sediment relationships in tidal-flat andmangrove ecosystems as well as the dynamics of coastalwetlands today threatened by ever-increasing anthropogenicinfluence.

Introduction

Important palaeoenviromental information critical inreconstructing environmental changes over time is commonlypreserved in estuarine and salt marsh deposits (e.g. Hindsonand Andrade 1999; Allen 2000; Boski et al. 2002; Heap et al.2004; Vis et al. 2008; Kolditz et al. 2012; Kim et al. 2013). Inaddition, micro- and macrofossils may contribute to recon-struct relative sea-level histories at high precision (e.g.

Franceschini et al. 2005; Woodroffe and Long 2009). Inter-tidal and supratidal estuarine sedimentary successions areparticularly useful in this context because they record bothsea-level fluctuations and changes which may have occurredin upstream terrestrial drainage basins (e.g. Ramos-Pereiraet al. 2011).

Traditional sampling methods in estuarine environmentsusually make use of augering and other coring techniqueswhich also allow sampling below the water table (Laneskyet al. 1979; Rapp and Hill 1998). Although these proceduresenable the extraction of long cores fromwater-saturated sandyand muddy sediments, cores from muddy substrates such assalt marsh deposits do not generally allow a full analysis ofsedimentary and post-depositional alteration processes or un-disturbed synsedimentary structures (Bullock et al. 1985),even if coring is performed with an Eijkelkamp piston sam-pler. This is because it is notoriously difficult to prepare epoxyresin peels from muddy substrates.

This short paper focuses on presenting a new trenchingprocedure and cutting device particularly useful in the recov-ery of undisturbed subsurface samples for micromorphologi-cal and microfacies analyses of salt marsh deposits. Themethod was applied in the Bensafrim River estuary nearLagos, Algarve, Portugal, within the framework of the multi-disciplinary estuarine research program FMI 5000 (Ramos-Pereira et al. 2011), one main objective being the search fortsunami deposits and associated deformations. Such seismi-cally deformed sedimentary records have previously beenidentified and analysed in a similar estuarine environmentnear Lagos (Hindson and Andrade 1999; Kortekaas and Daw-son 2007; Cunha et al. 2009), but without the additionalbenefits of the technique described in this paper. An ultimategoal is to validate thin section analyses for the purpose ofdesigning a diagnostic tool for the identification of localtsunami deposits sensu Kilfeather et al. (2007) and Bruinset al. (2008).

J. Araújo-Gomes (*) :A. Ramos-PereiraIGOT, Centre of Geographical Studies, University of Lisbon,1600214 Lisbon, Portugale-mail: joaopgomes@campus.ul.pt

Geo-Mar LettDOI 10.1007/s00367-014-0391-1

Brief outline of micromorphological approach

Micromorphological investigations are rooted inmicropedology (Kubiëna 1938; Stoops 2009). They are todaya standard technique in soil studies and have received partic-ularly strong attention in geoarchaeology over the last fewdecades (Cremaschi 2004). This geoscientific approach is anindependent research field for the study of undisturbed soils,stratifications and regoliths (Bullock et al. 1985; Stoops2003). In some cases, it has even been applied to obtain dataon soil formation in space and time, factors essential in

understanding palaeoenvironmental conditions (cf. Goldberg1979; McCarthy et al. 1998; Goldberg et al. 2003; Macphailet al. 2013).

Micromorphology is a widely used approach inmany typesof research and in different environmental contexts (e.g. vander Meer 1993, 1997; Harris 1998; Kemp 1999; Goldberg andByrd 1999; Carr 2001; Theler 2004; Stephens et al. 2005;Stolt and Lindbo 2010; Kilfeather et al. 2010; van der Meerand Menzies 2011). Excellent results have been achieved incoastal research (e.g. Macphail et al. 2010), hydropedology(e.g. Kutílek and Nielsen 2007) and archaeology (e.g.

Fig. 1 a Map of Portugal and location of the study area. b Elevationmodel of the Bensafrim River basin showing the lithological boundarybetween the upper and lower catchment, as well as the coring and

trenching sites (M marina). c Simplified log of the core recovered in2013 (extracted from Araújo-Gomes 2013)

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Macphail 2012). In spite of this, there are very few publishedpapers specifically dealing with sampling methods and strat-egies for micromorphological research in general (cf. Gold-berg and Macphail 2003), let alone for salt marshenvironments.

In practice, micromorphological investigations always be-gin with the extraction of blocks of undisturbed sedimentalong a vertical stratigraphic profile, which are then impreg-nated with an epoxy resin, polished and ground into thinsections for microscopic inspection (e.g. Bouma 1968; Courtyet al. 1989). This procedure preserves sedimentary structuresand is thus fundamental to environmental interpretation. Be-ing undisturbed and precisely oriented in space, the epoxypeels and thin sections allow compositional and orientationalanalyses of the sample material (van der Meer and Menzies2011).

Physical setting

The study was carried out in the estuarine section of theBensafrim River along the southwest coast of Portugal(Fig. 1). At present, this estuary is a restricted mouth-barestuary (cf. Cameron and Pritchard 1963; Dyer 1997) whichhas recently been transformed into a marina. The westernmargin is higher than the eastern one, being a Miocene lime-stone spur which forms the Ponta da Piedade. The easternmargin, located in a more rearward position, is formed by afossil cliff carved into a sedimentary formation of probablePliocene age, which is essentially composed of incoherent redsandstone (Ramos-Pereira 1990; Ramos-Pereira et al. 1994).Previous coring performed in the salt marsh upstream of themarina (Araújo-Gomes 2013) indicates that this estuary hadonce been an open estuary.

The drainage basin of the Bensafrim River can besubdivided into two distinct geological formations: (1)Palaeozoic turbidites, essentially composed of schists andgreywackes, which occupy the upper half of the basin; and(2) carbonate and detrital formations, mainly composed ofdolomitic limestones, sandstones (“Grés de Silves”; Ramos-Pereira 1990) and marls forming the lower half of the basin(Fig. 1b).

Earlier core analyses by Araújo-Gomes (2013) showeddifferent sedimentary successions related to variable energyconditions, 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 claybed; (3) a 51-cm-thick clayey silt bed with thin layers of finesand intercalated; and (4) a 30-cm-thick surficial silty sandbed (sediment classification after Flemming 2000). In generalterms it was concluded that (1) the silts and clays wereprobably derived from upstream turbidite deposits, whereas(2) the “Grés de Silves” (Silves Sandstone) is the main sourceof the sandy terrigenous sediments in the estuary; (3) based onAMS dating, the change from an open estuary to a bar-builtone occurred at about 3 ka (Fig. 1c).

Materials and methods

As trenching was to be carried out to a depth below the watertable, the application of a particular technique and procedurewas required to avoid the collapse of trench sidewalls whileallowing the recovery of undisturbed sediment samples (cf.Rapp and Hill 1998, p. 192). In the present case the study wasconfronted with a number of major issues: (1) insufficientinformation on the micromorphological and microfacies evo-lution 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 solutionto overcome the problem of unstable trench sidewalls inwater-logged sediments, which is probably the reason for thedearth of micromorphological and microfacies information inthe first place. On the other hand, for simply describing thevertical stratigraphic sequence of the salt marsh deposits,exhaustive profile sampling was not required (e.g. Bullocket al. 1985; Courty et al. 1989).

With these issues in mind, a suitable technique for therecovery of undisturbed subsurface samples in water-loggedsediments was developed. The procedure and technique isschematically illustrated in Fig. 2. At first, a trench of suitabledimensions (length, width, depth) is excavated (Fig. 2a). Toavoid the trench from flooding, it is drained by means of asubmersible dirt-water pump powered by a portable generator.

The collapse of the trench is prevented by supporting thesidewalls with wooden (or metal) boards held in placeby adjustable steel struts (timbering procedure), butleaving narrow wall sections non-timbered for the pur-pose of sampling (Fig. 2a). Once the sidewalls have beenstabilized and percolating water is under control, the trenchcan be safely entered.

In a next step, the non-timbered sidewalls are verticallysmoothed by means of a so-called CutSprof tool, a cuttingsediment profiler specially designed for this purpose (Fig. 2b).It comprises a thin, spade-like, concave-shaped steel cuttingedge supported by two or three vertical steel arms ending in ahorizontal round steel or wooden handle. This cutting toolproved to be essential for producing perfectly smooth verticalsurfaces required for the extraction of undeformed sedimentsamples. Spades and trowels were found to be inferior for this

Fig. 3 a Trenching and timberingprocedure before water pumping:strict safety measures areadvised—always wear a helmet,firm shoes, and a rope around thewaist in case of partial bogging.Adjustment and smoothing oftrench sidewalls by means ofCutSprof: b before cutting, cduring cutting, d after cutting.Note the smooth vertical cutrevealing undisturbed sediments

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purpose. After smoothing, thin soil slices can be removed bymeans of suitably sized plastic boxes and a normal spatula(Fig. 2c). After recovery, the boxes are sealed to avoid desic-cation. In the laboratory, the samples can be X-rayed, impreg-nated with epoxy resin and ground into thin sections formicroscopic analysis.

Results

In the case of the Bensafrim River estuary, the sidewalls oftrenches excavated into the salt marsh are prone to collapsedue to groundwater seepage from water-logged sedimentlayers. Figure 3a shows an excavated trench supported bysteel boards held in place by an adjustable steel strut. Thenon-timbered sidewalls were then cut into vertical smoothsurfaces by means of the CutSprof cutting tool as illustratedin Fig. 3b–d.

For the recovery of undisturbed samples, simple plas-tic food boxes with clamp lids were used as samplingdevices (Fig. 4a). The plastic is hard enough to endureextraction and transportation but soft enough to bepierced for later drying procedures. Although this typeof container is rarely used because it is less resistantthan other plastic boxes, they are relatively cheap, easilyobtained in any supermarket, and their clamp lids pro-vide perfect seals optimal for the preservation of sedi-mentary structures and water content. As shown in Fig. 4b,the thin section produced from such a box sample is wellsuited for micromorphological andmicrofacies analyses undera microscope.

Discussion and conclusions

A new procedure and particularly a tool were developed forthis study because the poor stability of excavated trenches inwater-saturated salt marsh deposits of the Bensafrim Riverestuary prohibited the use of standard techniques. Indeed, vander Meer and Menzies (2011) encouraged the adaptation ofthe micromorphological approach and techniques to suit theneeds of a wider range of environments, providing specificexamples where this had already been successfully achieved(e.g. Borchert 1968; Kooistra 1978; Johnson 1982; Kilfeatheret al. 2007).

In the present case, the sidewalls of the trenches werestabilized by adapting a form of timbering commonly usedin street excavations. This involved the lining of the trenchsidewalls with steel boards which were then held in positionby an adjustable steel strut wedged between them. Seepagewater collecting in the trench was drained by means of asubmersible dirt-water pump. To obtain smooth vertical trenchsections, a specially designed cutting tool, the CutSprof, wasconstructed. This new tool makes use of a concave cuttingblade which is especially effective in ductile and water-saturated soils. It allows the adjustment and smoothing ofvertical trench profiles, the pendulum shape and concave basefacilitating lateral tilting motions to penetrate resistant orcompacted soils.

In addition to palaeo-reconstructions of, for example, tsu-namis in salt marsh settings, the CutSprof would be highlysuitable in various other research domains as well as forenvironmental management purposes. These include ani-mal–sediment relationships in tidal-flat and mangrove ecosys-tems and the dynamics of coastal wetlands in general,

Fig. 4 a Sampling with a plasticfood container box; bcorresponding thin section

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particularly where sampling below the groundwater table isdesirable and also where anthropogenic impacts today poseever-increasing challenges in coastal restoration (e.g. Perilloet al. 2005; Araújo et al. 2012; Lo et al. 2014).

In conclusion, the findings convincingly demonstrate thatthe tools and the procedure developed for this work enable therecovery of undisturbed subsurface samples from excavatedtrench sidewalls even in water-saturated salt marsh environ-ments below the groundwater table. The mechanicaltrenching, water pumping and profile timbering applied inthe present study greatly reduce the risk of injury commonlyassociated with trenching.

Acknowledgements The authors wish to thank the Portuguese Scienceand Technology Foundation (FCT-MCTES) for the financial support ofthis ongoing investigation within the research project PTDC/CTEGIX/104035/2008 - FMI 5000: Environmental changes: Fluvio-marine inter-actions over the last 5000 yrs. The assistance of the SLIF (Littoral andFluvial Systems) team of the Centre for Geographical Studies, IGOT,University of Lisbon is also gratefully acknowledged. The editors of Geo-Marine Letters and an anonymous reviewer are thanked for their consid-erable help in improving the manuscript.

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