1. Introduction
The WASA Project (The WAdden Sea as an Archive of landscape evolution, climate change and settlement history: exploration – analysis – predictive modelling) was designed as a new approach for a detailed palaeolandscape reconstruction and detection of potential settling surfaces in the coastal zone of the central Wadden Sea. The multidisciplinary project, combining regional expertise in geosciences, archaeology, botany and marine biology, aimed for the reconstruction of the Late Quaternary sedimentary sequences using a multi-proxy analysis, i.e. by means of in situ techniques (sediment coring) and spatial surveys (hydroacoustic subbottom data). A large core archive (ca. 30,000 cores) for the same coastal zone already exists at the Geological Survey of Lower Saxony (NIBIS® Kartenserver, 2014. Thematic maps - Boreholes and profiles), which consists of data collected mainly during the 1960s and 1970s under different purposes and interests. As a consequence, the core descriptions and the related interpretations are not always consistent, and they are mostly limited to basic sedimentological information (e.g. sediment grain size, etc.), regardless of the facies, facies transitions or erosional contacts. As a consequence, the LBEG archive does not always provide comprehensive, comparable and consistent information, which can be used for a detailed landscape reconstruction of the region. To fill this gap, the specific focus of the WASA project is on sedimentary facies (indicators of biological and sedimentological processes) and depositional environments as descriptors of potential palaeoenvironments.
More than 140 cores were collected from the sub-, inter- and supratidal settings in the back barrier tidal flat and the offshore area of Norderney (East Frisian Islands), see Fig. 1. The WASA core descriptions and catalogue used for studying those cores are mostly based on the facies classifications made by Streif (Reference Streif1990) and have been already described in detail in Karle et al. (Reference Karle, Frechen and Wehrmann2017, Reference Karle, Bungenstock and Wehrmann2021), and Schaumann et al. (Reference Schaumann, Capperucci, Bungenstock, McCann, Enters, Wehrmann and Bartholomä2021). With respect to those works, the facies characteristics were reduced and simplified to the most important and distinctive descriptors, which can be easily used in the field to recognise the local stratigraphic sequence and its related facies. As a result, this manual offers a field proven and easy to use core catalogue of facies and depositional environments for the Late Pleistocene to Holocene of the central Wadden Sea.
Position of cores in the central Wadden Sea (Norderney backbarrier and offshore) taken by the WASA project.
The WASA core catalogue has been successfully applied for re-interpreting the LBEG cores and for integrating the information into multidisciplinary studies (e.g. Scheder et al., Reference Scheder, Bungenstock, Haynert, Pint, Schlütz, Frenzel, Wehrmann, Brückner and Engel2021; Schlütz et al., Reference Schlütz, Enters and Bittmann2021). In such a sense, this manual serves as an introduction and reference for all the works, which have been published within the WASA project and made use of interpreted sedimentological facies for the description of the palaeoenvironments. Furthermore, it can be used for (i) supporting the harmonisation of existing core data sets; (ii) reviewing the scientific literature about the stratigraphic sequence of the Wadden Sea; (iii) a detailed reconstruction of the regional palaeoenvironments; (iv) a better definition in terms of stratigraphic sequences and spatial extent of the Quaternary geological evolution of the area; (v) refining the existing local Holocene sea-level curves by improving the definition of sea-level index points, and (vi) defining the preserved palaeosurfaces, where human settlements were potentially possible.
2. Middle to Late Quaternary geological evolution of the study area
The youngest geological history of the North Sea Basin is characterised by glacial and interglacial periods, which resulted – for the present-day central Wadden Sea region – in the deposition of a thick sedimentary successions including a variety of glacial, periglacial, aeolian, fluvial, and marine deposits.
Two Elsterian ice advances have been recorded in Northern Germany, producing up to 400 m deep tunnel valleys (Lutz et al., Reference Lutz, Kalka, Gaedicke, Reinhardt and Winsemann2009; Stackebrand, Reference Stackebrandt2009; Murton & Murton, Reference Murton and Murton2012). The Elsterian glaciation was followed by the Holsteinian Interglacial; during its maximum, the coastline in the East Frisian area was situated ca. 10 km north of its present-day position (Linke et al., Reference Linke, Katzenberger and Grün1985; Streif, Reference Streif1990; Schaumann, Reference Schaumann2018). In fact, Holsteinian marine deposits have not been described so far in the study area. During the Saalian glaciation, only the first (namely the ‘Main Drenthe’) of three ice advances reached the East Frisian region (Rappol et al. Reference Rappol, Haldorsen, Jørgensen, van der Meer and Stoltenberg1989; Meyer, Reference Meyer2005; Litt et al., Reference Litt, Behre, Meyer, Stephan and Wansa2007; Graham et al., Reference Graham, Stoker, Lonergan, Bradwell, Stewart, Ehlers, Gibbard and Hughes2011) as documented by initially outwash sediments and, later on, moraine-deposits (see core N14, PANGAEA-WASA). In the study area, the Saalian moraine is directly overlain by Eemian (compare core N14, PANGAEA-WASA), Weichselian or even Holocene sediments. During the Eemian Interglacial, the coastline reached up to 5 km south of the present-day coastline (Caspers et al., Reference Caspers, Merkt, Müller and Freund2002; Streif, Reference Streif2004; Schaumann, Reference Schaumann2018). Dechend & Sindowski (Reference Dechend and Sindowski1956) describe the Eemian shallow marine environment as a sandy tidal flat system for the East Frisian region (see core N14, PANGAEA-WASA). Schaumann et al. (Reference Schaumann, Capperucci, Bungenstock, McCann, Enters, Wehrmann and Bartholomä2021) even differentiate between a mixed- and sandy-tidal flat for the Eemian. Climatic cooling marked the following onset of the Weichselian glaciation when the ice extent did not reach the study area. The periglacial sands deposited during this period have been referred to as ‘brown sands’ in the literature and are related to fluvial and aeolian deposition (e.g. Streif, Reference Streif1990; Sindowski, Reference Sindowski1973; see Fig. 2 (core VVC17) and core N11, PANGAEA-WASA). During the maximum of the Weichselian glaciation, sea level dropped to 110-130 m below the present-day level (Streif, Reference Streif2004). The subsequent climate warming during the Holocene resulted in sea-level rise. Finally, the characteristic landscape elements of the recent Lower Saxony coastal region with its barrier islands, mudflats and salt marshes, were formed in the course of the last 8500 years under the influence of ongoing sea-level rise (e.g. Davis, Reference Davis1994). The so-called Geest landscape, consisting of the deposits of the last glaciations and interglaciations, was flooded, partially reshaped and disconformably covered in varying thicknesses of up to 25 m Holocene coastal deposits, which show multiple cycles of peat formation, flooding, and marine transgression over time (Fig. 2 – core VVC17). Fossil soil horizons (mostly podzols) can be occasionally found in the upper part or on top of the Pleistocene sequence (Fig. 2 – core VVC17). The presence of such horizons indicates the preservation of palaeosurfaces that have not been subject to deep erosion and, therefore, may represent surfaces which could have been potentially used for human settlement. The peatlands mostly developed as fen peat, whereas bog peat was documented only at few locations of the study area (Schlütz et al., Reference Schlütz, Enters and Bittmann2021). In most of the WASA cores, the peat beds are erosively overlain by intertidal (i.e. tidal flat) or subtidal (i.e. channel) deposits (Fig. 2 – intercalated peat in core VVC17); some cores show a slow and continuous transition from peat to salt marsh and/or brackish-lagoonal and, finally, to tidal flat depositional environments (compare Fig. 2 – core VVC17 and core N11, PANGAEA-WASA).
Example of the transfer of core description, analysis, interpretation and stratigraphical classification and subsequent sampling of the core halves of VVC17 (left) into the EasyCore template (right). The latter will be available in the PANGAEA data publisher (PANGAEA-WASA).
3. Methods and application
3.1. Coring
Three coring systems were deployed in the field in order to cover the range from subtidal to supratidal settings. The coring locations were planned based on geological maps, existing core data (LBEG) and preliminary evidence showed by the hydroacoustic subbottom data.
For the subtidal setting (mostly offshore of Norderney, the Riffgat channel (i.e., the tidal inlet), and the ferry route from Norddeich to Norderney), a modified version of the vibrocorer VKG6 (medconsultant GmbH) was used from aboard the research vessels FK SENCKENBERG (Senckenberg am Meer, SaM, Wilhelmshaven) and BURCHANA (Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz, NLWKN, Norderney). The vibrocorer was deployed in full-weight load mode (1.1 t gravity weight) and was equipped with PVC liners of 5000 mm length and 100 mm diameter.
The tidal flat cores were collected using a portable vibrocorer (Wacker Neuson generator with an IE high-frequency vibrator head of 20 kg) and 6000 mm long aluminium liners with a diameter of 80 mm. A hand-driven pulley-chain system, coupled with a telescopic tripod, was used for recovering the cores.
South of the dike line, on land, a Jackhammer auger corer (weight: 50 kg) was preferred, as it allows the coring of coherent but unconsolidated sediments in undrained environments. The liner in the coring extractor had a diameter of 50 mm and a length of 1000 mm.
The cores were cut into sections if necessary, sealed, labelled and moved to the lab for further processing.
3.2. Positioning and levelling
All positions for the intertidal and supratidal cores were recorded by means of a DGPS RTK-corrected system, providing a horizontal precision of 0.01–0.02 m and a vertical precision of 0.02–0.03 m. The elevation data are referred to the German standard elevation zero (Normalhöhennull, NHN).
The horizontal position of the subtidal cores was achieved using a SeaPath System (Kongsberg Maritime) with RTK corrections (SAPOS-Service). For the elevation, the cores were positioned on a multibeam-derived DTM (from 2016) kindly provided by the NLWKN with a horizontal precision of < 0.40 m and a vertical precision of 0.15–0.30 m depending on the absolute water depth (Francesco Mascioli, personal communication).
3.3. Profile types
The Holocene sedimentary succession in the coastal zone of the Central Wadden Sea is characterised by the alternation of clastic sediments and intercalated peat layers, representing the cycles of landward and seaward coastline shifts that occurred during the sea-level rise. The peat deposits are dominant on the landward side, while clastic deposits are typical in the tidal flat areas on the seaward side. These sediment sequences are determined following the lithological classification principle according to Barckhausen et al. (Reference Barckhausen, Preuss and Streif1977), Streif (Reference Streif1979, Reference Streif1998) and Hoselmann & Streif (Reference Hoselmann and Streif2004). The Holocene sediments are subdivided based on the vertical succession and lateral interfingering of siliciclastic sediments and peat deposits. Thus, this classification system reflects the depositional history of the Holocene coastal plain deposits in terms of (local) progradational and retrogradational phases and provide basic information to map former palaeogeographies as shown by Karle et al. (Reference Karle, Bungenstock and Wehrmann2021). For example, profile type x1 corresponds to solely siliciclastic deposits: in landward areas with generally thicker peat sequences, it would indicate the presence of clastic channel fill deposits.
The profile type and the related lithological sequences are provided for each of the WASA cores (see the template, Fig. 2), in order to include a relevant information, which can be used together with coring data derived from other sources or projects. For cores not reaching the Pleistocene and therefore not covering the preserved Holocene sequence, the profile type for the documented sediment sequence is given.
3.4. The WASA core catalogue: Core description, analysis, interpretation and stratigraphic classification
The cores were cut lengthwise in the lab and high-resolution digital images were taken under constant light conditions.
In a second step, the cores were macroscopically described and subdivided into depositional units, which presented significant differences from the intervals above and below. Based on its characteristics and its relative vertical stratigraphic position (i.e. in relation to specific intervals, for example, peat or moraine deposits), each of those units was assigned to a distinct depositional environment, sedimentary facies and time stage (e.g. Holocene, Weichselian, Eemian, etc., Table 1).
The WASA core catalogue displays the Late Pleistocene to Holocene coastal palaeoenvironments of the central Wadden Sea and their sedimentary facies. The depositional codes derived from the prior four columns and include series/epoch, stage/age, the depositional environment and the subenvironment/facies with 00 indicating ‘not defined’. The EasyCore template as shown in Fig. 2 is based on the depositional and colour codes of the core catalogue.
The macroscopic description (Supplementary material Table 1) includes the main sediment attributes (e.g. grain size, colour, presence of specific minerals, e.g. mica), texture (sorting, clast/matrix support, grading), stratigraphic features (e.g. lamination, cross-bedding, lenses), post-depositional structures (reworking, cryoturbation, bioturbation, erosional contacts, boreholes), macrofauna definition (presence of single shells, articulated bivalves, etc.), and presence and nature of plant organic matter (e.g. roots, peat layers, reworked peat fragments and organically enriched sediments). The sediments were tested with diluted (10%) hydrochloric acid for carbonate content, and its amount was scored on a 6-steps scale from K0 (no reaction, 0% content of CaCO3) to K5 (violent reaction, very high content of CaCO3 – Preuß et al., Reference Preuß, Vinken and Voss1991). The abundance of shells, shell fragments and shell debris was flagged using a similar scale (from S0 to S5). For specific intervals, a first assessment about the presence of environment-related organisms/remains (e.g. marine diatoms for the Pleistocene sediments, or sponge spiculae for marine deposits) was carried out.
After the macroscopic description, one core half was sampled for in-depth analysis with regard to the specific disciplines involved in the project. Samples were taken at both regular and irregular intervals, depending on the specific research questions or approaches for each discipline, namely for grain size analysis (for method see Elschner et al., Reference Elschner, Scheder, Bungenstock, Bartholomä, Becker, Capperucci, Enters, Schlütz, Wehrmann and Hoffmann2021), gravel component analysis (for method see Schaumann et al., Reference Schaumann, Capperucci, Bungenstock, McCann, Enters, Wehrmann and Bartholomä2021), C/N and TOC (Elschner et al., Reference Elschner, Scheder, Bungenstock, Bartholomä, Becker, Capperucci, Enters, Schlütz, Wehrmann and Hoffmann2021), 14C-datings (Enters et al., Reference Enters, Haynert, Wehrmann, Freund and Schlütz2021; Scheder et al., Reference Scheder, Bungenstock, Haynert, Pint, Schlütz, Frenzel, Wehrmann, Brückner and Engel2021; Schlütz et al., Reference Schlütz, Enters and Bittmann2021), palynology (Schlütz et al., Reference Schlütz, Enters and Bittmann2021), diatoms (Bulian et al., Reference Bulian, Enters, Schlütz, Scheder, Blume, Zolitschka and Bittmann2019), foraminifers and ostracods (Scheder et al., Reference Scheder, Frenzel, Bungenstock, Engel, Brueckner and Pint2019, Reference Scheder, Bungenstock, Haynert, Pint, Schlütz, Frenzel, Wehrmann, Brückner and Engel2021; Haynert et al., Reference Haynert, Gluderer, Pollierer, Scheu and Wehrmann2020), and taphonomy. Additionally, down core scanning was applied on most of the intact core halves for magnetic susceptibility, and XRF (for methods see Lee et al., Reference Lee, Enters, Titschack and Zolitschka2021). Based on the above listed analysis, some of the macroscopic core descriptions could be specified or corrected (Elschner et al., Reference Elschner, Scheder, Bungenstock, Bartholomä, Becker, Capperucci, Enters, Schlütz, Wehrmann and Hoffmann2021; Scheder et al., Reference Scheder, Bungenstock, Haynert, Pint, Schlütz, Frenzel, Wehrmann, Brückner and Engel2021).
It has to be noted that some of the aforementioned macroscopic-derived characteristics can be found in more than one depositional environment, and therefore they could not be used as standalone indicators for appointing specific facies. Thus, the coring location (e.g. offshore, in a tidal inlet or in the tidal flat nearby the present dike line) played an important role in the definition of the depositional environment, especially for recent sediments.
In comparison to the Holocene sediments, the Pleistocene deposits showed a general enrichment in mica content, due to the depletion of metamorphic rocks during the glacial and periglacial stages, lately reworked during the interglacial phases (Schaumann et al., Reference Schaumann, Capperucci, Bungenstock, McCann, Enters, Wehrmann and Bartholomä2021).
With regard to the Pleistocene sediments, the CaCO3 content and the presence/abundance of diatoms are an important function for the characterisation of the marine deposits and for distinguishing them from similar recent sediments. In fact, the Pleistocene deposits generally show content of CaCO3 = K0. The finding of marine diatoms within the fine fraction (mud) layer of the Pleistocene intervals, together with the sedimentological characteristics, supported the definition of proper intertidal facies related to the Eemian interglacial (Eemian tidal flat). Where the diatoms were not found or where no investigations were carried out, the transition to the Weichselian remains uncertain.
For moraine deposits, a specific analysis of the fine gravel fraction of cores N70, N20, N22 and Nney02 confirmed its attribution to the Main Drenthe Saalian ice advance (Schaumann et al., Reference Schaumann, Capperucci, Bungenstock, McCann, Enters, Wehrmann and Bartholomä2021).
The definition of the ages, the depositional environments and the related facies were translated into a graphical representation (colour and texture) and a unique coding, to be used for sketching the cores in EasyCore (Supplementary material Table 1). At each depositional environment (e.g. subtidal unprotected, subtidal protected, etc.) corresponds a unique colour, defined in its RGB values (so that the same colour-code could potentially be used consistently from external sources and by means of different software). The unique coding (“Depositional Code” in Table 1) is made of 8 digits, separated by underscores: ss_aa_dd_ff, where ss: Series/Epoch (e.g. ho for Holocene); aa: Age/Stage (e.g. we: Weichselian); dd: depositional environment (e.g. ip for intertidal protected) and ff: Facies (e.g. ef for eolian/fluvial). 00 stands for ‘not defined’.
3.5. Dating samples
Datings samples were collected and analysed by the WASA working groups using different calibration programs and correction factors. The results have been already published in several studies (see here in after for the details) with regard to specific cores. In order to offer a comprehensive and consistent overview of the dating outcomes, they have been harmonised using age data and the respective calibration procedures. For this manual, the datings relative to two cores (N11 and VVC17, Fig. 2 and Table 2) are presented. The remaining datings will be made available to the public on PANGAEA data publisher (PANGAEA-WASA).
14C data for cores N11 (PANGAEA-WASA) and VVC17 (Fig. 2). All data have been calibrated with the Intcal20 and Marine20 (Reimer et al. Reference Reimer, Austin, Bard, Bayliss, Blackwell, Bronk Ramsey, Butzin, Cheng, Edwards, Friedrich, Grootes, Guilderson, Hajdas, Heaton, Hogg, Hughen, Kromer, Manning, Muscheler, Palmer, Pearson, van der Plicht, Reimer, Richards, Scott, Southon, Turney, Wacker, Adolphi, Büntgen, Capano, Fahrni, Fogtmann-Schulz, Friedrich, Köhler, Kudsk, Miyake, Olsen, Reinig, Sakamoto, Sookdeo and Talamo2020; Heaton et al. Reference Heaton, Köhler, Butzin, Bard, Reimer, Austin, Bronk Ramsey, Grootes, Hughen, Kromer, Reimer, Adkins, Burke, Cook, Olsen and Skinner2020) by Oxcal (Bronk Ramsey, Reference Bronk Ramsey2009). If already published, the respective reference is given in the last column. Note that previously published age data are eventually calibrated with a former calibration curve and a different delta R value for marine samples.
The 14C age determination was performed at the Poznań Radiocarbon Laboratory (Poland) by means of accelerator mass spectrometry (AMS, see in Elschner et al., Reference Elschner, Scheder, Bungenstock, Bartholomä, Becker, Capperucci, Enters, Schlütz, Wehrmann and Hoffmann2021 for details). The results were originally calibrated with the software CALIB (Version 7.1), using the calibration curves IntCal13 and Marine13 (Reimer et al., Reference Reimer, Bard and Bayliss2013). According to the measurements of Enters et al. (Reference Enters, Haynert, Wehrmann, Freund and Schlütz2021), the ΔR value for reservoir correction of ages originating from in situ shell material was presumed 74 ± 16 14C years. During the proofreading of the latter, the ‘new’ ΔR value was recalculated to -85 ± 17 14C years (note the negative sign) when the most recent marine calibration curve, i.e. Marine20 (Heaton et al., Reference Heaton, Köhler, Butzin, Bard, Reimer, Austin, Bronk Ramsey, Grootes, Hughen, Kromer, Reimer, Adkins, Burke, Cook, Olsen and Skinner2020) was published.
The chronological framework in Scheder et al. (Reference Scheder, Bungenstock, Haynert, Pint, Schlütz, Frenzel, Wehrmann, Brückner and Engel2021) is based on AMS-14C dating of peat (see also Bulian et al., Reference Bulian, Enters, Schlütz, Scheder, Blume, Zolitschka and Bittmann2019), in situ bivalves and foraminifera tests. 14C dating was performed at the Poznań Radiocarbon Laboratory (Poland) and the Beta Analytic Inc (USA). Calibration and age-depth modelling were accomplished using the R software (rbacon, v. 2.3.9.1, Blaauw & Christen, Reference Blaauw and Christen2019), calibration curves IntCal13 and Marine13 (Reimer et al., Reference Reimer, Bard and Bayliss2013) of CALIB 7.1 with the respective reservoir correction (74 ± 16 14C years) after Enters et al. (Reference Enters, Haynert, Wehrmann, Freund and Schlütz2021). The available age data were used by R to interpolate an age model up until the sediment surface, where necessary layer boundaries were integrated into the modelling process to account for different possible sedimentation rates.
Dating of the peat samples (Schlütz et al., Reference Schlütz, Enters and Bittmann2021) was also carried out at the Poznań Radiocarbon Laboratory (Goslar & Czernik, Reference Goslar and Czernik2000). Calibration was done with OxCal v.4.3 (Bronk Ramsey, Reference Bronk Ramsey2009) including deposition models (Bronk Ramsey, Reference Bronk Ramsey2008; Bronk Ramsey & Lee, Reference Bronk Ramsey and Lee2013). Data in the text refer to mean ages with 2σ intervals (Bronk Ramsey, Reference Bronk Ramsey2009).
3.6. The EasyCore template
One of the major duties listed in the proposal of the WASA Project was the transfer of the sediment core information into an open access data repository (PANGAEA-WASA) for making them available to future research in earth and environmental science. A specific WASA template was therefore designed using the software package EasyCore, which offers in a single page all the relevant information for each core, such as the core metadata (e.g. core name, position, etc.), a core photo, a lithological sketch (colour- and texture-based for each of the facies), a graphical overview of all the samples taken for different purposes (e.g. grain size, pollen, etc.), and the macroscopic description of each sedimentary unit.
Metadata are noted in the header and includes the core operators (collectors and descriptors), the elevation of the top and bottom of the core (NHN referred), the logbook name (which provides information about the location, coring date and station; Fig. 2), the core name (field name), the coring date (day/month/year), the geographic coordinates, the tidal setting (sub-, inter, supratidal), the core sketching team, the coring system, the profile type, and the list of hydroacustic subbottom transects corresponding to the coring location (where present).
All data generated, processed and published in the frame of WASA will successively be stored in the open access data repository PANGAEA under the project title WASA (PANGAEA-WASA). This will assure access to these data for further research initiatives, organisations and public. For this manual, a first batch (cores N11, N14 and VVC17) of the WASA cores is presented (see the supplementary material).
Supplementary material
To view supplementary material for this article, please visit https://doi.org/10.1017/njg.2022.1
Acknowledgements
The WASA Project was founded by the Ministry for Science and Culture of Lower Saxony (Niedersächsisches Ministerium für Wissenschaft und Kultur) and was financed by the Niedersächsisches Vorab of the Volkswagen Stiftung (under ZN3197), within the initiative Küsten- und Meeresforschung Niedersachsen. We are grateful to the Wadden Sea National Park administration for fieldwork permissions. EasyCopy is acknowledged for providing the core sketching software EasyCore and for the permanent support: we especially thank Helene Hoijberg for her assistance. We thank the Landesamt für Bergbau, Energie und Geologie (LBEG) for providing the archive core data. Thanks to Francesco Mascioli, Tina Kunde and Andreas Wurpts (all Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz – NLWKN) for the friendly and professional logistic support during the several surveys. Our special appreciation goes to Francesco Mascioli for the positive collaboration in sharing ideas and finding optimal solutions while planning and collecting the cores. Thanks to our colleagues Kristin Haynert, Torsten Janßen, Maik Wilsenack (all SaM), Frank Schlütz, Thorsten Becker (both Niedersächsisches Institut für historische Küstenforschung, NIhK), the captains and crews of BURCHANA and FK SENCKENBERG and to all of the students who helped during the fieldwork. Thanks to our technicians for the professional support in sampling and analysing the samples. We also thank Annette Siegmüller and Felix Bittmann (both NIhK) for their advice during the core describing process.
Open access
