Regressions and transgressions of the Baltic basin reflected by a new high-resolution deglacial and postglacial lithostratigraphy for Arkona Basin sediments (western Baltic Sea)

Regressions and transgressions of the Baltic basin re� ected by a newhigh-resolution deglacial and postglacial lithostratigraphy for ArkonaBasin sediments (western Baltic Sea)

MATTHIAS MOROS, WOLFRAM LEMKE, ANTOON KUIJPERS, RUDOLF ENDLER, JØRN BO JENSEN, OLE BENNIKE ANDFRANZ GINGELE

Moros, M., Lemke, W., Kuijpers, A., Endler, R., Jensen, J. B., Bennike, O. & Gingele, F. 2002 (June): Regres-sions and transgression s of the Baltic basin re� ected by a new high-resolutio n deglacia l and postglacia l litho-stratigraphy for Arkona Basin sediments (western Baltic Sea). Boreas, Vol. 31, pp. 151–162. Oslo. ISSN0300-9483.

Seismoacoustic pro� les from the Arkona Basin show a late Pleistocene and Holocene succession of severaldistinct re� ectors. The physical , sedimentological , mineralogical and geochemica l properties of more than 30sediment cores were analysed in order to assign these re� ectors to speci� c sedimentary discontinuity layers.Additionally , AMS 14C data and biostratigraphi c information were gathered. Based on this multi-proxy ap-proach, seven lithostratigraphi c units (AI, AII, B to F) were distinguished . These consist of � ne-grained clay,silt and mud, and are separated from each other by thin basin-wide traceable sandy layers (Sab–Sef). The mostsensitive parameter to mark the lithostratigraphi c boundarie s is the weight percentage of the grain-size fraction>63 mm. In addition, some of the quartz-grain-dominate d sandy layers cause the strong re� ection lines re-corded in seismoacousti c pro� les. The sandy layers are interpreted to re� ect enhanced hydrodynamic energyinduced by episodes of basin-wide water-level low-stand conditions. These low stands resulted from water-level drops that occurred frequently during the Baltic Sea’s history and presumably affected the entire Balticbasin. The thick � ne-grained units AI, AII to F, in which coarser material is absent, represent water-levelhigh-stands . We conclude that the units AI and AII are Baltic Ice Lake sediments deposited before and afterthe Billingen-1 regression , respectively . We assign the most prominent sandy layer Sab to the � nal drainage ofthe Baltic Ice Lake (Billingen-2) , whereas the sandy layers between units B, C, D and E are related to the Yol-dia Sea and Ancylus Lake regressions of the Baltic Sea’s history. The uppermost � ne-grained unit F with itshigh organic carbon content contains marine sediments deposited after the Littorina Transgression . The macro-scopically well-visible sediment colour change from reddish/brown-to-grey , previously interpreted as a regio-nal stratigraphi c boundary, varies from core to core. It has been shown by our new data that this colour changehas a diagenetic origin, and thus does not represent a stratigraphi c boundary. Previous subdivisions thereforehave to be revised.

Matthias Moros (e-mail: [email protected]) , Wolfram Lemke (e-mail: [email protected]) , Rudolf Endler (e-mail: [email protected] ) and Franz Gingele (e-mail:[email protected]) , Baltic Sea Research Institute , Seestraße 15, D-18119, Rostock-Warnemunde, Germany; Antoon Kuijpers (e-mail: [email protected]) , Jørn Bo Jensen (e-mail: [email protected] ) andOle Bennike (e-mail: [email protected]) , Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400Copenhagen NV, Denmark; received 23rd August 2001, accepted 12th October 2001.

Many studies of the Late Quaternary history of theBaltic Sea have been conducted in the deeper basins ofthe Baltic Proper, i.e. the Bornholm and the Gotlandbasin (Fig. 1, inset). Only a few results have beenpublished dealing with the shallower Arkona Basin inthe SW Baltic, which forms the deeper part of theArkona Sea (>30 m water depth), (Fig. 1, inset).Nevertheless, this basin, with an average water depthof 40–45 m and a shallow depth position of theuppermost till’s surface (30–70 m b.s.l.), is well suitedfor investigations on Baltic Sea water-level changes. Inaddition, the Arkona Basin is located near to theisostatic zero line (Bjorck 1995) and to the drainagepathways of the Great Belt and Øresund. It can thereforebe expected that dramatic water-level drops, whichoccurred during the Baltic Sea’s Late Pleistocene andHolocene history (Bjorck 1995), are recorded in the

sediments of the Arkona Basin. Previous studies havefocused on deposits from the shallower south-western(Kolp 1976; Lange & Wulff 1980; Jensen et al. 1997),south-eastern (Kolp 1983, 1986) and north-easternmargins (Abelmann 1985; Schubert 1991) of theArkona Basin. Only six publications address sedimentcores from the deeper basinal part (Neumann 1981;Rother 1989a, b; Gingele & Leipe 1997, 1998;Sohlenius et al. 2001). Biostratigraphic subdivisionsof the Arkona Basin deposits are hampered by the factthat most of the pre-Littorina sediments are barren offossils. Neumann (1981) proposed to subdivide thoseparts of the sediment succession by colour. A charac-teristic change from reddish/brown-to-grey colours wasinterpreted to mark the boundary between Baltic IceLake and Ancylus Lake deposits.

The present study was initiated after seismoacoustic

# 2002 Taylor & Francis

pro� ling in the Arkona Basin in the mid-1980s and early1990s. Based on sediment physical properties, miner-alogical and geochemical studies, biostratigraphicinformation and AMS 14C dating, a new high-resolutionlithostratigraphy for Arkona Basin sediments is pre-sented here. Lithological key beds are assigned tocharacteristic re� ectors in seismoacoustic sections.Finally, an attempt is made to reconstruct the paleogeo-graphical and paleoecological changes in the ArkonaBasin during the Late Pleistocene and Early Holocene,based on the known stages and dramatic water-levelchanges of the Baltic Sea.

Material and methods

Seismoacoustic records were obtained by a DESO 25sediment echosounder (Krupp-Atlas; 15 kHz) and aGeoChirp (GEOACOUSTICS; 1.5–11.5 kHz). Thepresent study is based on data from more than 30sediment cores. Here, records of eight cores arepresented in detail (Fig. 1, Table 1). GRAPE densityand magnetic susceptibility (MS) were measured atsampling intervals of 1 cm using a GEOTEK Multi-Sensor Core Logger (MSCL; Chi 1995; Chi & Mienert1996). MS was measured with a Bartington MS2F

Fig. 1. Core locations(white dots) investigatedin the Arkona Basin anddepth (isolines in m b.s.l.)of the uppermost till,derived fromseismoacousti c data(Lemke 1998). Thelocation of the study areain the Baltic Sea isshown inset. Numbersindicate the corespresented here (see alsoTable 1). White linesindicate the position ofthe coastline after the� nal drainage of theBaltic Ice Lake derivedfrom seismoacoustic dataand magneticsusceptibility

Table 1. Locations, water depth and depth (top) of the uppermost till at the sites presented in this article (see also Fig. 1).

Core Latitude Longitude Cruise Sampling device Water depth (m)Depth of theuppermost till (m)

NAB03/93 55°6.96’N 13°29.95 ’E AvH; 08/1993 6 m GC 43.9 ¹53AB01/95 55°0.00’N 13°40.00 ’E AvH; 05/1995 6 m GC 46.6 ¹58201311 54°59.26’N 13°39.84 ’E Poseidon; 02/1996 10 m GC 46.7 ¹58202170 54°58.83’N 13°39.99 ’E AvH; 10/1996 6 m GC 46.7 ¹57201310 54°57.94’N 13°40.00 ’E Poseidon 02/1996 10 m GC 46.8 ¹66AB01/97 54°55.93’N 13°39.99 ’E AvH 04/1997 6 m GC 46.8 >70AB1114 54°54.60’N 13°40.80 ’E AvH 11/1988 6 m VC 46.8 >70AB1131 54°45.10’N 13°45.60 ’E AvH 04/1989 6 m VC 40.5 ¹51

AvH = R/V Alexander von Humboldt; GC = gravity corer; VC = vibro corer.

152 Matthias Moros et al. BOREAS 31 (2002)

Surface Scanning Point Sensor. For details concerningthe carrier of the MS signal, scanning electronmicroscope Energy Dispersive X-ray (EDX) analyseswere carried out. The GEOTEK MSCL is combinedwith a digital grey-scale line scan camera. The grey-scale images obtained were converted into grey levelsby the shareware NIH image program. The weightpercentage (wt%) of the grain-size fraction >63 mmwas determined by wet sieving. Total carbon (TC),inorganic carbon (TIC) and sulphur content weredetermined with a Carbon/Sulphur infrared analyser(ELTRA Metalyt 1000CS). The content of organiccarbon (TOC) was calculated according toTOC = TC ¡ TIC and the carbonate content accordingto CaCO3 wt% = TIC £ 8.33. Diatom and macrofossilanalyses on material of core 202170 were carried outby Professor A. Witkowski at the University ofSzczecin and at the Geological Survey of Denmarkand Greenland, respectively. AMS 14C dating ofmaterial from core AB 01/97 was undertaken at AarhusUniversity.

Results

Macroscopic description

Macroscopically (on-board descriptions) three majorunits can be distinguished in the sediments overlyingthe boulder clay in the Arkona Basin. Thesemacroscopic units are consistent with the lithostrati-graphic subdivision of Neumann (1981). At the basis,there is a reddish/brown unit with mostly clayeysediments in the deeper Arkona Basin (here, unit AIand sometimes AII, B, C). A clearly visible colourchange from reddish/brown to grey marks theboundary to the second macroscopically detectablegrey unit. This colour change was previously used asan indication of the transition between Baltic IceLake (reddish/brown) and Ancylus Lake (grey)sediments. In a few cases the reddish/brown-to-greycolour change coincides with a sandy layer, but it isgenerally not combined with a grain-size change. Thecolour shift occurs sometimes in unit AII, B, C of

Fig. 2. Wt% >63 mm distribution of six studied cores. The positions of sandy layers (Sab-Sef) marking the boundarie s between the litho-stratigraphi c units AII–F are presented by solid shaded lines. The thick dashed line indicates the position of the colour change from red-dish/brown to grey, previously regarded as the boundary between sediments deposited during Baltic Ice Lake and Ancylus Lake stages(e.g. Neumann 1981). The depth positions of Sab (*) and the uppermost till (**) at the core locations are given at the top of each core.Note different scaling on X-axis.

BOREAS 31 (2002) Sea-level � uctuations in Arkona Basin, Baltic Sea 153

the new subdivision presented here (see below). Thegrain size of the greyish unit varies strongly betweenclay and sandy silt. Macroscopically determined, thisunit may involve the new units B, C, D, E and parts

of AII. When looking carefully a dark-grey band richin organic material, accompanied by higher amountsof sandy material (here the sandy layer Sde), can befound in the greyish unit. If found, the sediments

Fig. 3A, B. (A) GRAPEdensity and (B) magneticsusceptibilit y records of � vestudied cores. Included are:the positions of thelithostratigraphi c boundaries(solid shaded lines), the depthpositions of Sab (*) and of theuppermost till (**) at the corelocations , as well as thecharacteristi c colour changefrom reddish/brown to grey(thick dashed line). Notedifferent scaling on X-axis.


between this band and the boundary to the olive-greymud (unit F) can be assigned to the new unit E.Sometimes black bands and spots are observed in thegreyish unit. The boundary to the overlying olive-grey mud is sharp. The olive-grey mud with acharacteristic H2S smell is unit F of the newsubdivision. In general, only the olive-grey mud(unit F) and mostly unit E of the new subdivisioncan be easily identi� ed by the naked eye in coresfrom the entire Arkona Basin. Further subdivisionscannot be made macroscopically or by colourchanges before further detailed studies are performedand without the knowledge of the results presentedhere.

Analytical results

Despite the different setting of the investigated cores,the general patterns of the wt% >63 mm (Fig. 2),GRAPE density (Fig. 3A), MS (Fig. 3B), grey scale(Fig. 4A), TIC (carbonate), TOC (Fig. 4C, D) and partlysulphur (Fig. 4B) show obvious similarities, whichenabled a correlation of these cores. Because of theirimportance for the sedimentary features, the positionsof the uppermost till’s surface and the water depth at thevarious locations are presented in the Figures.

Sand content. – Frequently occurring sand layers marklithostratigraphic boundaries re� ected by sharp spikesin the variation of wt% >63 mm (Fig. 2). These sandylayers were labelled Sab–ef, where for example Sab isthe sandy layer between units A and B. The sandylayer Sab overlying the clayey unit AII is the mostprominent one in all cores. The sand content of Sabwith 20–40 wt% is relatively low at sites where Sab islocated deeper than 49 m b.s.l. and the till surface isdeeper than 56 m b.s.l. The wt% of sandy materialwithin the subsequent sandy layers, from Sab to Scd,decreases steadily upwards. By contrast, at sites wherethe till surface is shallower the wt% >63 mm in Sabreaches more than 80%. Here, where Sab is the onlydetectable layer, Sbc and Scd are missing. Interest-ingly, apart from Sef, no clearly visible sedimentcolour change coincides with a special sandy layer.The colour change from reddish/brown to grey occurssometimes above sometimes below Sab (Fig. 2)

GRAPE density. – The sandy layers Sab, Sbc and Scd areclearly marked by GRAPE density peaks (Fig. 3A). Themagnitude of the peaks correlates with the wt% ofmaterial >63 mm within these layers. The boundariesbetween units D, E and F are not visible in the GRAPEdensity records. Within sub-units AI and AII, theGRAPE density pro� le re� ects the bedding. IncreasingGRAPE density values are accompanied by a coarsen-ing of the deposited material (Moros 1999). TheGRAPE density pattern of sub-unit AII is more hom-ogeneous than that of sub-unit AI. The saw-tooth

shaped, steady increase of the GRAPE density at thetransition between units AII to B occurs where thecontent of coarser material increases and the layeringbecomes more condensed (Moros 1999).

Magnetic susceptibility (MS). – The MS backgroundvalues of units AI–C are generally higher than those ofunits D–F (Fig. 3B). The carrier of the MS signal withinunits AI–C is hematite (unpublished magnetic S-ratiodata). The sandy layers Sab–Scd are re� ected by MSpeaks. The peak intensity decreases upwards. Thestrong MS signal caused by these sandy layers is dueto an enrichment of relatively coarse-grained titano-magnetite/magnetite. However, Sab displays no MSpeak at sites where Sab is situated at a depth shallowerthan 49 m b.s.l., and where it is thus the only traceablesandy layer. Here, no enrichments of titanomagnetite/magnetite grains were found. Additional MS peakswithin units D and E are not related to sandy layers.These are due to the occurrence of partly zonedsulphidic burrows and crusts. The crusts consist of amonosulphidic/greigitic core and a pyritic mantle(Moros 1999). XRD measurements performed onmaterial from the MS spike positions of units D and Eshow the existence of pyrite as well as ferrimagneticgreigite. Black bands occurring in unit C of core 201310show no higher MS values. The colour change fromreddish/brown to grey coincides with a distinct MSdecrease.

Grey scale. – The transition between units E and F canbe clearly distinguished by the grey scale record,re� ecting a sediment colour change from grey to olive(Fig. 4A). The conspicuous darker values at the unit D/Etransition (i.e. in Sde) are due to a higher organic carboncontent. Within unit A and at the boundary to unit B thegrey scale variations re� ect the thinning of the layers.Large grey scale variations within units C and D are dueto black bands and spots.

Geochemistry. – An abrupt increase of sulphur contentfrom about 1% to an average content of 2% marks theboundary between units E and F (Fig. 4B–D). Anothersharp increase of the sulphur content occurs at themacroscopically visible sediment colour change fromreddish/brown-to-grey. This colour change is accom-panied by a sharp decrease of the total iron (Fe(tot))content of the clayey sediments (Moros 1999). It hasto be emphasized, however, that this change does notcoincide with any of the sandy layers. The clays ofunit A are characterized by total organic carbon(TOC) contents of 0.7–1.5% and relatively highcarbonate (TIC) values of up to 16%. Within unitB, the TOC as well as the TIC contents arecomparatively low with 0.3% and 0.1%, respectively.Increasing values of TOC (0.9%) and TIC (8–10%)are observed within unit C. The sediments of units Dand E contain 1.4–1.6% of organic carbon with a


prominent peak at the boundary between these units.Apart from a small peak (3%) at the base of unit Dand a prominent one at the base of unit F (4–5%), thecarbonate content within the units D, E and F is close

to zero. At the transition between units E and F theTOC content increases abruptly from 2% to 4–6%.Further enrichment of TOC (up to 7%) is found in theupper part of unit F.

Fig. 4A–D. (A) Grey level, (B) sulphur and (C) carbon records of � ve investigated cores. The carbon record (C) is presented as total car-bon (curve with dots) and inorganic carbon (crosses) content. Included are the characteristi c lithostratigraphi c boundaries (solid shadedlines), the depth positions of Sab (*) as well as of the uppermost till (**) at the core locations and the characteristi c colour change fromreddish/brown to grey up sequence (thick dashed line). In (B), arrows indicate a sharp increase in the sulphur content which is consistentwith the depth position of the characteristi c colour change from reddish/brown to grey. (D) Carbonate and organic carbon records of twocores with a thick Unit F. The numbers indicate characteristi c peaks in (D). An uncorrected AMS 14C dating performed on marine benthicforaminiferas of AB01/97 is included (carbonate peak). Note different scaling on X-axis.


Comparing lithostratigraphic and biostratigraphicinformation

As known from previous studies, most of the ArkonaBasin deposits are barren of fossils. However, somebiostratigraphic information is recorded in core 202170.The only lithostratigraphic boundary, also recognized inthe narrow spaced diatom record, is the one betweenunits E and F, and no diatoms were found within unitsA–E. Unit F is characterized by a marine to brackishdiatom assemblage. Few specimens of typical Littorinastage diatoms were found between 44 and 188 cm. Mostabundant taxa are Paralia sulcata, Diploneis smithii, D.didyma, Dimedramma minor, Plagiogramma stauro-phorum, Grammatophora marina, G. oceanica, G.macilenta, Pseudosolenia calcar-avis, Rhabdonemaarcuatum, Actinocyclus octonarius, Chaetoceros spp.resting spores, Opephora marina and O. paci� ca. Post-Littorina taxa were identi� ed in the upper part of unit F,above 44 cm. Typical species are Cyclotella chocta-whatcheana, Thalassiosira proschkinae, T. levanderi,Chaetoceros resting spores, which indicate brackishwater, but freshwater taxa like Amphora pediculus,Fragilaria martyi and Epithemia turgida also occur.

The typical carbonate peak at the base of unit F (in core202170 at 160–170 cm) is due to an enrichment ofmarine benthic foraminiferas (Ammonia beccarii(Linne), Elphidium incertum (Williamson)) and ostra-cods. In units D and E, above 230 cm, freshwater fossilslike Cladocera were observed.

Comparing lithostratigraphic units and seismoacousticpro� les

Based on the GEOTEK MSCL data (GRAPE densityand P-wave velocity), the acoustic impedancies andre� ection coef� cients (R) within the individual corestaken on the seismoacoustic pro� les were calculated. Toidentify the boundaries causing seismoacoustic re� ec-tions, the variations of R were compared with singleGeoChirp signals at the various locations (Moros 1999).It has been shown that in the seismoacoustic records thesandy layers Sab–Scd and the sandy layer subdividingunit A are generally detectable, whereas the boundariesbetween units D/E and E/F are not re� ected in theseismoacoustic sections. GRAPE density and/or P-wavevelocity changes, necessary prerequisites for seismo-acoustic re� ections, were not observed in connection

Fig. 5. Seismoacoustic DESO25 records (A, B) with the units marked by seismoacousti c re� ectors and the position of core NAB03/93.The sandy layer Sab on top of the lithostratigraphi c Unit AII causes the most prominent seismoacoustic re� ection. At the margin of suf� -ciently deep channels onlap structures were observed. (C) Locations of the seismoacousti c pro� les (white lines).


with the sandy layers Sde and Sef of cores from thedeeper basin. Sde forms a strong re� ector at the westernbasin margin, where it has a much higher sand contentthan in the deeper basin. Where Sab is located deeperthan 49 m b.s.l., all detectable sandy layers show typicalonlap structures (Fig. 5). As also shown by the wt%>63 mm record, Sab is the most prominent seismo-acoustic re� ector. In places where it is locatedshallower than 49 m b.s.l. it is the only re� ector.Compared to the seismostratigraphy proposed by Jensenet al. (1997), the subdivision presented here is of higherresolution. This might be due to the fact that our studywas performed in the deeper central part of the ArkonaBasin, while the data of Jensen et al. (1997) weregathered mainly in its marginal parts. Moreover, thedifference in resolution potential of the differentequipment used in these studies has to be taken intoaccount. The boomer system used by Jensen et al.(1997) allows for a deeper penetration, but has a lowerresolution compared to the relatively high frequencysediment echo-sounders applied here. Furthermore, ourlab-measured sediment physical properties allow adirect assignment of � eld detected re� ectors to seismicdiscontinuity layers in sediment cores.

Discussion

Our core studies demonstrate that the new lithostrati-graphic subdivision for Arkona Basin sediments de� nedabove is suitable for the entire basin. Especially the wt%of material >63 mm, which consists mostly of quartzgrains, can sensitively distinguish lithostratigraphicboundaries. Essential for the interpretation of seismo-acoustic records of the Arkona Basin is the fact that onlythe lithostratigraphic boundaries between units AI–Care shown by strong variations in the sediment physicalparameters GRAPE density and/or P-wave velocity,hence producing a detectable seismoacoustic re� ector(Moros 1999). The boundaries between units D, E and Fare not detectable in these records. In cores taken atpositions where the uppermost till surface is deeper than56 m b.s.l., up to seven lithostratigraphic units (AI–F)can be distinguished. With the introduction of the sandylayers (consisting mostly of quartz grains) as lithostrati-graphic boundaries, the question of their genesis andpaleoenvironmental implications arises. For this pur-pose all relevant data from the sandy layers as well asfrom the lithostratigraphic units in-between have to beconsidered. The interpretation is most obvious for theboundary between the units E and F. Although thisboundary is not always marked by a peak in the wt%>63 mm record, it is very characteristic. It marks thedramatic change from lacustrine to brackish-marineconditions in the Arkona Basin, i.e. the LittorinaTransgression (see below). All other boundaries de� nedhere are characterized by comparably high contents ofthe sand fraction. Their genesis might be interpreted in

different ways. Since they are traceable with similarproperties (relative uniform sand grain size and miner-alogical properties, � xed to a special depth position,etc.) over major parts of the basin, their interpretation asdetritus transported by icebergs can be excluded.Regarding them as tempestites, storm-induced sedi-ments, is problematic, because the wt% >63 mmvariation shows a saw-tooth pattern indicating a moregradual, long-term change rather than a short event.Furthermore, the sandy layers form the boundariesbetween thick � ne-grained clayey deposits (partly withcompletely different mineralogical, geochemical andsediment physical features) without any sand admix-tures which could be interpreted as storm-derived, i.e.formed under stronger wave action. In our opinion theonly possible interpretation of these sandy layers is thatthey were formed during regressional phases marked bylow stands and enhanced sediment dynamics due toincreased current and wave action. This is supported by� ndings in the marginal zone of the basin which clearlyshow low-stand phases during late Pleistocene and earlyHolocene (Jensen 1995; Jensen et al. 1997; Lemke et al.1998).

At present, several regressional phases are believedto have taken place during the deglacial and postglacialhistory of the Baltic Sea. The most signi� cant water-level drop happened at the end of the Baltic Ice Lake(BIL) phase. According to Bjorck (1995) and Bjorck etal. (1996), a 25 m lowering occurred during a few yearsat about 10.0 14C ka BP. This drop caused largepaleoenvironmental changes not only in the drainagearea around Mt. Billingen in south central Sweden, butalso around the whole Baltic coast. Bjorck (1995) refersto changing foraminiferal faunas outside the Swedishwest coast, to a ¯18O anomaly in the Skagerrak andhiatuses in the clay sequences of southwestern LakeVanern. Likewise, changes in the sedimentation patternwithin the Arkona Basin must be expected as aconsequence of the large paleogeographic changes.Increased in� ux of coarse-grained material into theBaltic basin can be assumed to have characterized thisdistinct regression. Therefore, we assign the formationof the most signi� cant sandy layer Sab to this event.Doing so, it is possible to estimate the local water levelafter the � nal drainage of the BIL in the Arkona Basin.The absence of titanomagnetite/magnetite in Sab at sitesshallower than 49 m b.s.l. can be explained if these siteswere not affected by high energy hydrodynamics. Mostlikely these sites were above the water level after the� nal BIL drainage. Combining this � nding with theoccurrence of the subsequent onlapping units B and C(Fig. 5), a map of paleo-coast lines at the beginning ofthe Yoldia stage may be drawn (Fig. 1). Unfortunatelyno concrete signs for subaerial exposition have beenfound so far. Obviously, a local lake was connected withthe Bornholm Basin and was fed by freshwater inputfrom the Oder river (Kolp 1983; Lemke et al. 1998) andfrom the Darss Sill area (Jensen et al. 1997; Lemke


1998). The position of the southern Arkona Basin coastat this time as indicated by the dashed line in Fig. 1cannot be reconstructed in detail due to the presence ofshallow gas in the overlying unit F deposits, whichhampers acoustic penetration. Regarding Sab as aproduct of the � nal BIL drainage, the partly ‘varved’clay below with its relatively high carbonate contents,low TOC (Kogler & Larsen 1979, Kolp 1976; Neumann1981; Bjorck et al. 1990), its mainly reddish/browncolour (Neumann 1981; Kolp 1976), its rare freshwaterdiatoms (Blazhchishin 1976; Abelmann 1985), and itsgenerally high magnetic susceptibilities (Rother 1989a;Jager 1984; Bjorck et al. 1990; Sohlenius 1996) musthave been deposited in the BIL. In previous publica-tions, two phases of the BIL stage were concluded (e.g.Donner 1982; Synge 1982; Gluckert 1995; Bjorck1995). Both phases were separated by a low-standevent, the � rst drainage of BIL at Mt. Billingen at theend of the Allerød at 11.2 ka BP and 10.9 14C ka BPaccording to Bjorck (1995), Bjorck et al. (1996) andBoden et al. (1997), respectively. It is unlikely that thisevent had no in� uence on the sedimentation processesin the Arkona Basin. We therefore suggest that this so-called Billingen-1 drainage (according to Boden et al.1997) is re� ected by the characteristic sandy layersubdividing unit A into AI and AII in our study area.First results show that this layer is also traceable insediments from the Mecklenburg Bay and the south-western Bornholm Basin (Moros 1999). Owing to areadvance of the Scandinavian Ice Sheet, the Billingen-1 outlet was closed at c. 10.8 ka BP (Bjorck 1995;Bjorck et al. 1996). The BIL was dammed up again, thewater level rose and in the Arkona Basin the depositionof sediments with a more distal character (sub-unit AII)began. A subdivision of BIL deposits was also observed

in the marginal areas of the Arkona Basin by Jensen(1995), Bennike & Jensen (1995) and Jensen et al.(1997) on the basis of seismoacoustic data. This is ingood agreement with our observation that BIL depositsare subdivided by a sandy layer traceable all over theArkona Basin as a characteristic seismoacoustic re� ec-tor (Moros 1999).

As quoted above, the BIL stage ended with a secondout� ow at Mt. Billingen around 10.0 14C ka BP (Bodenet al. 1997 and Bjorck et al. 1996) described asBillingen-2. The abrupt regression resulted in theformation of the most prominent sandy layer Sab in theArkona Basin. However, in our records, a general changein the sediment character does not occur before the eventmarked by the sandy layer Scd. This fundamental changein the sedimentation is re� ected by the backgroundlevels of the GRAPE density, MS, TOC and carbonate(calcite and dolomite, Moros 1999) records (see Figs 3–5). Furthermore, the � rst appearance of freshwatermacrofossils is observed in unit D, whereas units A, Band C are barren of fossils. The deposits of unit D aretypically silty and show higher TOC and sulphurcontents in combination with low carbonate valueswhen compared to the sediments of units A–C (cf.Kogler & Larsen 1979; Kolp 1986; Gingele & Leipe1998; Sohlenius et al. 1996; Sternbeck & Sohlenius1997). The abrupt decrease of GRAPE density valuesfrom unit C to D is due to an absence of the � ne grain-sizefractions in unit D. This resulted in a better sortingaccompanied by coarser mean grain-size values andtherefore in higher water contents of the accumulatedsediments. In terms of microfacies analysis (Dunham1962; Flugel 1982), the grain fabric changes from a mud-supported matrix in units A–C to a grain-supported onein units D and E. In the marginal parts of the Arkona

Fig. 6. Link between the lithostratigraphi c units,the sandy layers, biostratigraphi c informationobserved in Arkona Basin sediments and theknown stages of the Baltic Sea’s history. Thesandy layers re� ect low-stand situations asresults of drainage events during the LateGlacial and Holocene development of the BalticSea. An uncorrected AMS 14C dating performedon marine benthic foraminiferas is included onthe age scale (cross, italic letters). Calendaryear ages for the drainage events were given bySvante Bjorck (pers. comm. 2001; http://www.geol.lu.se/personal/seb/shome.htm).


Basin, unit D consists of peat or gyttja (Moros 1999;Lemke 1998). AMS 14C datings made on material fromthese sediments gave ages between 9.7 and 9.36 14C kaBP. With this information it is justi� able to correlate theboundary between units C and D with the transition fromthe Yoldia to the Ancylus Lake stages. This correlationimplies that the formation of units B and C has to beascribed to the Yoldia stage. The two units within thisstage thus demonstrate the occurrence of a majorenvironmental change during the Yoldia stage in theArkona Basin. Such a subdivision of the Yoldia stage isin good agreement with observations reported fromSweden (Bjorck 1995; Morner 1995; Westegard et al.1995). Indications of marine in� uence as recorded inparts of the Baltic Proper during the Yoldia stage werenot found in the Arkona Basin (Bennike & Lemke 2001).In contrast to the isostatically uplifted areas to the north,the sedimentation in the deeper parts of the study arearather re� ects stagnant or slightly rising water levelsduring the deposition of units B and C but with agenerally low level. Black spots and layers found withinunits B and C have been described elsewhere as typicalfor Yoldia deposits (e.g. Svensson 1991; Sohlenius et al.1996). Generally, the thickness of units B and Cincreases northeastward, re� ecting more proximal con-ditions in this direction to the main source areas of thesediments. Unit C is signi� cantly thicker than unit B.The sandy layer Sbc is less distinct than Scd. The latter istherefore proposed to re� ect the Yoldia regression, asdescribed by Gluckert (1995) and Bjorck (1995).

The sediments of units D and E are assumed to havebeen deposited during the Ancylus Lake (AL) stage.Besides the features described above, MS peaks aretypical here. Previously, they have been reported byAbrahamsen (1995), Sohlenius (1996) and Rother(1989a) to occur in AL or AY (according to Kogler &Larsen 1979) sediments. Unit D is suggested to havebeen deposited in the � rst transgressional phase of theAL prior to the Ancylus Lake regression at 9.3 14C kaBP (Svensson 1991), or 9.2 14C ka BP according toBjorck (1995). During the latter regression, parts of thehumous unit D deposits were transported into the deeperareas of the Arkona Basin and re-deposited togetherwith coarser material, thus forming the sandy layer Sde.¯13C values of the organic material support a land-derived origin. This fact has to be taken into accountwhen performing bulk AMS 14C datings on this materialas Sohlenius et al. (2001) did on core 201310. The TOCcontent within this layer as well as its thicknessdecrease gradually from the western margin of theArkona Basin to the east. The same applies to thefraction >63 mm. For these reasons, the sandy layer Sdeforms a distinct seismoacoustic re� ector only at thewestern margin of the Arkona Basin. After the regres-sion, a water level rise is likely to have occurred, whichis re� ected by the � ne-grained deposits of unit E, i.e. asecond Ancylus Lake type phase.

The abrupt increase in TOC and sulphur contents, as

well as in the TOC/S ratio, combined with the � rstoccurrence of marine diatom taxa, clearly demonstratesthe change from lacustrine to brackish-marine condi-tions, the onset of the Littorina Transgression, at thetransition between units E and F. This is supported bythe distinct basal carbonate-rich layer consisting ofmarine benthic foraminifera and ostracods. It indicateshigh salinities, which are believed to re� ect theculmination of the marine Littorina Transgression.Interestingly, an AMS 14C dating of foraminiferas ofthis layer (core AB 01/97) gave an uncorrected age of6475 § 50 14C yr BP (AAR-4131). That age is muchyounger than most of the published datings of thebeginning Littorina Transgression. However, Lemke(1998) showed, by new AMS 14C datings on macro-fossils from Mecklenburg Bay and Darss Sill, that the� rst major ingression of brackish marine waters was notbefore 7500 14C yr BP. This age is still younger than sofar existing 14C datings made on peat and/or bulksediment (e.g. Sohlenius et al. 2001). It is noteworthythat in the marginal areas of the Arkona Basin thestratigraphic level of the carbonate spike is slightlyshallower than the depth of the unit E/F boundary(Moros 1999). This difference does not exist in coresfrom the deeper basinal parts. Whether this time-lagobserved at shallower water depth might be linked tothe transitional Mastogloia Phase has to be addressed infurther investigations. Thick deposits of the MastogloiaPhase have been found in the Mecklenburg Bay inchannel-like structures (Lemke 1998).

It is noteworthy that the clearly visible sedimentcolour change from reddish/brown-to-grey previouslypostulated as the boundary between the Baltic Ice Lakeand Ancylus Lake stage sediments in the Arkona Basin(e.g. Neumann 1981; Rother 1989a) does not coincidewith any of the lithostratigraphic boundaries describedabove. It is therefore concluded to re� ect diageneticprocesses rather than synsedimentary lithologicalchanges. This is supported by the � nding that the colourchange is related to an abrupt increase of the sulphur, adecrease of the Fe(tot) content (Moros 1999), to stronglydecreased MS and higher S-ratio (indicates lowerhematite content, unpublished data) values in the greysediments as described above. A similar observationwas made by Neumann (1981), who found highcarbonate contents, typical for unit A deposits as shownhere, in grey clays. The position of the colour changeseems to be linked to the sulphide formation in thesediments. Iron sulphide formation is well known forBaltic Sea sediments (e.g. Boesen & Postma 1988;Sohlenius et al.1996; Sternbeck & Sohlenius 1997;Lepland 1998). According to these authors, the forma-tion of iron sulphides under the Yoldia and Ancylusstage freshwater conditions was sulphate limited, thusmonosulphides and also greigites (the carrier of a strongMS signal) were formed. Iron sulphide formation underthe Littorina stage marine/brackish conditions was Fe-limited, hence pyrites were formed. Because of the


extreme Fe-limitation excess, H2S diffused downwardinto the freshwater sediments, caused a partly pyritiza-tion of the monosulphides/greigites and zoned sulphidiccrusts were formed (Moros 1999). In that way themagnetic signal survived. The necessary iron wasleached from the clayey originally reddish/brown(hematite) sediments and hence the sediment colourchanged from reddish/brown to grey. The hematitic Feof unit A is most likely � xed in the zoned sulphides. Theposition of the colour change is obviously linked to thethickness of the overlying unit D and E sediments. Thus,in marginal parts of the Arkona Basin, where D and Eare thin, the colour change occurs far below Sab (up to¡70 cm unpublished data; here ¡20 cm in NAB03/93).By contrast, in cores from the central part with thickunits D and E, the colour change occurs above Sab(‡150 cm in core 201310).

Conclusions

Based on a multi-proxy approach performed at highresolution on more than 30 sediment cores, a newlithostratighraphy has been developed for the ArkonaBasin sediments. Former subdivisions could be revisedaccording to the data presented here. The new subdivi-sion is supported by biostratigraphic and seismostrati-graphic studies. The lithostratigraphic boundaries of the7 units form characteristic sandy layers. These seem tohave been formed as a result of well-known regressionevents during the Baltic Sea’s history under low-standconditions. A general scheme of the link between thelithostratigraphic units, the sandy layers observed inArkona Basin sediments and the known stages of theBaltic Sea’s history is presented in Fig. 6. Some of thesandy layers, but not all, cause the strong re� ectionsrecorded in seismoacoustic records. Therefore theresults are of high relevance for the interpretation ofseismoacoustic data in the Western Baltic. Based on thisknowledge the former coast-line after the dramaticBillingen-2 regression might be traceable in detail infuture studies. Furthermore, � rst studies on cores fromthe Mecklenburg Bay and the southwestern BornholmBasin have shown that the lithostratigraphic approachpresented here is applicable to sediment successions ofthese Baltic Sea regions as well.

Acknowledgements . – We are grateful to Andrzej Witkowski andJan Heinemeier, who performed the diatom analyses and AMS14C-dating, respectively . We thank Svante Bjorck and an anony-mous reviewer for their helpful comments on an earlier version ofthe manuscript . This study was supported and funded (M. Moros)by the German Deutsche Forschungsgemeinschaf t (Project GI324/1-1).

ReferencesAbelmann, A. 1985: Palokologische und okostratigraphisch e Unter-

suchungen von Diatomeenassoziatione n an holozanen Sedimen-ten der zentralen Ostsee. Berichte-Reports , Geologisch–Palaon-tologisches Institut der Universitat Kiel 9. 200 pp.

Abrahamsen, N. 1995: Paleomagnetic investigations . AarhusGeoscience 5, 55–63.

Bennike, O. & Jensen, J. B. 1995: Near-shore Baltic Ice Lakedeposits in Fakse Bugt, southeast Denmark. Boreas 24, 185–195.

Bennike, O. & Lemke, W. 2001: Late glacial and early Postglacial� nds of Ancylus � uviatilis from the south-western Baltic sea.Geologiska foreningens i Stockholm forhandlinga r 123, 81–84.

Bjorck, S. 1995: A review of the history of the Baltic Sea, 13.0–8.0 ka BP. Quaternary Internationa l 27, 19–40.

Bjorck, S., Kromer, B., Johnsen, S., Bennike, O., Hammarlund, D.,Lemdahl, G., Possnert, G., Lander Rasmussen, T., Wohlfarth,B., Hammer, C. U. & Spurk, M. 1996: Synchronized terrestrial–atmospheric deglacial records around the North Atlantic. Science274, 1155–1160.

Bjorck, S., Dennegard, B. & Sandgren, P. 1990: The marine strati-graphy of the Hano Bay SE Schweden, based on different sedi-ment stratigraphic methods. Geologiska foreningens i Stockholmforhandlinga r 112, 265–280.

Blazhchishin, A. J. 1976: Zur Stratigraphie spatquartarer Boden-ablagerunge n der mittleren Ostsee. Beitrage zur Meereskunde38, 49–59.

Boden, P., Fairbanks, R. G., Wright, J. D. & Burckle, L. H. 1997:High-resolutio n stable isotope records from southwest Sweden:the drainage of the Baltic Ice Lake and Younger Dryas ice mar-ginal oscillations . Paleoceanograph y 12, 39–49.

Boesen, C. & Postma, D. 1988: Pyrite formation in anoxic environ-ments of the Baltic. American Journal of Science 288, 575–603.

Chi, J. 1995: Multi-Sensor-Kernlogging-Methode n zur Bestim-mung von physikalischen Sedimenteigenschaften . Berichte Son-derforschungsbereic h 313 no. 58. 125 pp.

Chi, J. & Mienert, J. 1996: Linking physical property records ofQuaternary sediments to Heinrich events. Marine Geology 131,57–73.

Donner, J. 1982: Fluctuations in water level of the Baltic Ice Lake.Annales Academiae Scientiarium . Fennicae A III. 134, 13–28.

Dunham, R. J. 1962: Classi� cation of carbonate rocks according todepositiona l texture. In Ham, W. E. (ed.): Classi� cation of car-bonate rocks. American Association of Petroleum GeologistsMemoir 1, 108–121.

Flugel, E. 1982: Microfacies Analysis of Limestones. 633 pp.Springer-Verlag, Berlin.

Gingele, F. X. & Leipe, T. 1997: Clay mineral assemblages in thewestern Baltic Sea: recent distribution and relation to sedimen-tary units. Marine Geology 140, 97–115.

Gingele, F. X. & Leipe, T. 1998: Distribution and enrichment ofredox-sensitiv e metals in Baltic Sea sediments. Baltica 11, 5–17.

Gluckert, G. 1995: The Baltic Ice Lake in South Finland and itsoutlets. Quaternary Internationa l 27, 47–51.

Jager, W. 1984: Petrophysikalisch e Untersuchunge n an spatglazia-len und holozanen Sedimenten der Lubecker und MecklenburgerBucht. Ph.D. dissertation , Institut fur Meereskunde, Warne-munde. 107 pp.

Jensen, J. B. 1995: A Baltic Ice Lake transgressio n in the south-western Baltic: evidence from Fakse Bugt, Denmark. Quatern-ary Internationa l 27, 59–68.

Jensen, J. B., Bennike, O., Witkowski, A., Lemke, W. & Kuijpers,A. 1997: The Baltic Ice Lake in the southern Baltic: sequence-,chrono- and biostratigraphy . Boreas 26, 217–236.

Kogler, F. C. & Larsen, B. 1979: The West Bornholm Basin in theBaltic Sea: geologica l structure and Quaternary sediments. Bor-eas 8, 1–22.

Kolp, O. 1976: Die submarinen Uferterrassen der sudlichen Ostseeund Nordsee und ihre Beziehung zum eustatischen Meeres-spiegelanstieg. Beitrage zur Meereskunde 35, 6–47.

Kolp, O. 1983: Die schrittweise Verlagerung der Odermundungvon der Bornholmmulde bis in die Oderbucht infolge holozaner


Wasserstands anderungen im sudlichen Ostseeraum. PetermannsGeographische Mitteilungen 127, 73–87.

Kolp, O. 1986: Entwicklungsphase n des Ancylus Sees. PetermannsGeographische Mitteilungen 130, 79–94.

Lange, D. & Wulff, B. 1980: Diatomeenuntersuchunge n am Stech-rohrkern AB 3 vom Westrand des Arkona-Beckens . Beitrage zurMeereskunde 44/45, 75–88.

Lemke, W. 1998: Sedimentation und palaogeographisch e Entwick-lung im westlichen Ostseeraum (Mecklenburge r Bucht bis Arko-nabecken) vom Ende der Weichselvereisun g bis zur Litorina-transgression. Meereswissenschaftlich e Berichte 31. Baltic SeaResearch Institute , Warnemunde. 156 pp.

Lemke, W., Jensen, J. B., Bennike, O., Wikowski, A. & Kuijpers,A. 1999: No indication of a deeply incised Dana River betweenArkona Basin and Mecklenburg Bay. Baltica 12, 66–70.

Lepland, A. (1998): The pre-Littorina diatom stratigraphy andsediment sulphidisatio n record from the west-centra l Baltic Sea:implications of the water column salinity variations . Ph.D. dis-sertation , Department of Geology, Earth Sciences Centre, Gote-borg, 95 pp.

Morner, N.-A. 1995: The Baltic Ice Lake – Yoldia Sea transition .Quaternary Internationa l 27, 95–98.

Moros, M. 1999: Spatquartare Sedimentation am ReykjanesRucken und in der Westlichen Ostsee – Rekonstruktion anhandhochau� osender sedimentphysikalische r Eigenschaften . Ph.D.dissertation , Baltic Sea Research Institute, Warnemunde, 100 pp.

Neumann, G. 1981: Lagerungsverhaltnisse spat- und postglazialerSedimente im Arkona-Becken . Ph.D. dissertation , Institut furMeereskunde , Warnemunde, 164 pp.

Rother, K. 1989a: Petro- und palaomagnetische Untersuchunge n an

jungquart aren Sedimenten der Ostsee. Veroffentlichungen desZentralinstitut s fur Physik der Erde 109. 230 pp.

Rother, K. 1989b: Magnetostratigraphi c correlation of youngerQuaternary sediment pro� les in the southern Baltic Sea. Zeit-schrift fur geologische Wissenschafte n 17, 713–717.

Schubert, C. J. 1991: Organischer Kohlenstof f und Schwermetall -gehalte in jungquart aren Ostseesedimenten . M.Sc. thesis, Justus-Liebig-University , 96 pp.

Sohlenius, G. 1996: Mineral magnetic properties of Late Weichse-lian–Holocene sediments from the northwestern Baltic Proper.Boreas 25, 79–88.

Sohlenius, G., Sternbeck, J., Andren, E. & Westman, P. 1996:Holocene history of the Baltic Sea as recorded in a sedimentcore from the Gotland Deep. Marine Geology 134, 183–201.

Sohlenius, G., Emeis, K. C., Andren, E., Andren, T. & Kohly. A.2001: Development of anoxia during the Holocene fresh-brack-ish water transition in the Baltic Sea. Marine Geology 177, 221–242.

Sternbeck, J. & Sohlenius, G. 1997: Authigenic sul� de and carbo-nate mineral formation in Holocene sediments of the Baltic Sea.Chemical Geology 135, 55–73.

Svensson, N.-O. 1991: Late Weichselian and Early Holocene shoredisplacemen t in the central Baltic Sea. Quaternary Internationa l9, 7–26.

Synge, F. M. 1982: A new shoreline chronology for the Salpaus-selkas. Annales Academiae Scientiarium . Fennicae A III. 134,29–60.

Westegard, S., Andren, T., Sohlenius, G. & Ekman, I. 1995: Dif-ferent phases of the Yoldia Sea in the North-Western BalticProper. Quaternary Internationa l 27, 121–129.


Documents

Regressions and transgressions of the Baltic basin reflected by a new high-resolution deglacial and postglacial lithostratigraphy for Arkona Basin sediments (western Baltic Sea)