W.B.F. Ryan et al. - An abruptdrowningof the BlackSea she/faf 7.5 Kyr B.P.

AN ABRUPT DROWNING OF THE BLACK SEA SHELF AT 7.5 KYR BP William B.F. Rvnru1, WalterC. Prrunrulll1,CandaceO. MR.loR1, KazimierasSHrurus',VladimirMoscRtrruro',GlennA. JoruEsr, Petko DrMrrRova, Naci GonURs,MehmetSRrcruqs & HiiseyinYtice SEvlR6 1 Lamont-Doheity EarthObservatory of ColumbiaUniversity, Palisades,NY 10964,USA .'Southern Branchof the P.P. ShirshovOceanology Institute,Gelendzhik-7, 353470,Russia 3 TexasA & M Universityat Galveston,Galveston,TX, USA a Bulgarian-Academy of Sciences,lnstituteof Oceanology, 9000Vama,PO Box 152, Bulgaria JeolojiB6lUmU, 80626Ayazga,lstanbul,Turkey " l.T.U.MadenFakUltesi 6 SeyirHidrografive OsinografiDairesi,81647gLiUuXtu, lstanbul,Turkey

Abstract: During latest Quaternaryglaciation,the BlackSea becamea giant freshwaterlake,The surface of this lake drew down to levels morethan 100mbelowits outlet.When the Mediterranean roseto the Bosporussill at 7.5 kyr BPl, saltwaterpouredthroughthis spiltway to refillthe and submerge,in lessthan a year,morethan 100,000Km'of its exposedcontinental shelf. Key words: continentalshelf,erosionsurface,climaticcondition, faunalsuccession,radiocarbon data,NeoeuxineLake,BlackSea

the ecology^^of the fossil molluscs2s' 32' INTRODUCTION dinoflagellatqs33 and diatoms3a'tt, from strongly The earliestwritten accountson the Bosporus negative O'o''o isotopic ratios^^inthe carbonate and DardanellesStraits,date to the Roman era'-" component of the sediments'o, and from the and chroniclea catastrophicbreakthroughof the chemistry of pore waters drawn out of the sea. The winding course of both straits, their Neoeuxine-age strata3T-3e. terraced cross-sections, and their dendritic Near-shore littoral deposits2627' 40' 41, with tributarieswere interpretedby nineteenthcentury radiocarbonages of the msllusc shells spanning geomorphologistss6 as indicative of a stream 19 to I kyr BP, have been found at depths origin.Today the channel is 9eeply submerged between -93 and -122 m. Linear steps that and pafilyfilledwith sediment'-'"toa sill depthofresemblethe profilesof beachterraceshave been 33 m". lt hosts a two-way exchange of water mapped for tens of km along the outer shelf betweenthe partly marine Black Sea and the fully between-90 to -110 m. A substantialloweringof marine MediterraneanSea11-16. In fact, the the past lake levelto at least-110 m has also been northward-flowingundercurrentlThad long ago inferredfrom the discoveryof formerlyentrenched been known to mariners who lowered baskets river valleysa2-45 which are now partlyfilled in with laden with rocks into its core to tow their vessels estuarinedepositsunderthe beds of modernrivers upstreamtowardthe BlackSea18. as they approach the coast. Boreholes in the Dated fossil coral reefs in the Caribbeanle-21Kerch Strait'o '' have recovered coarse gravel show that, at the time of the maximum expansion with fluvialfauna at -62 m in the stream bed of the of continentalice sheets around 20 kry BP, the ancient Don River > 200 km seaward of the surfaceof the globaloceanwas at -120 m. Thus present river mouth. Mud, silt and sand on the prior to the glaciers,the Black Sea was without basin plain dated between I to 7.5 kyr BPas connectionto an externalocean (Fig.1).ln the contain .A significant cgmponent of reworked absence of a saltwater inlet it had transformed molluscsae,microfossilssoand plan detritus33 23, dwarfing itself into a giant freshwater body22 washed downslope from coastal swamps. The any modernlakein areaand volume. contaminationof former proximity of wetlandsto the headsof the submarinecanyonswhich indent NEOEUXINELAKE the shelf edge and act as conduitsfor sediment Lacustrinedeposits of glacial and postglacial transportto the basinplain.The inferredrelocation age, assigned to the local Neoeuxine"-'" of the coastline in the vicinity of the current stratigraphicstage of the late Quaternary,have shelfbreak is shown in Fig.2, along with the been cored at a large numberof sites on the floor ubiquitousdistributionof loessand alluvialsoils on of the Black Sea extendinofrom the continental the broad and emerged continentalshelf south of shelf26-28 to the centerof itibasin plain26'2e-31 at a Ukraineand throughoutthe Sea of Azov27 . depth of 2.2 km. The fresheningis deducedfrom

GEO-ECO-MARINA, 41997 Nationallnstituteof Maine Geologyand Geo-ecologyof Romania Prcc. lntern. Workshopon "Fluvial-Mainelnteractions"in Malnas,Romania,OcLl-7, 1996

W.B.F. Ryanet al. - An abruptdrowningaf the Black Sea she/f af 7.5 Kyr B.P.

boundary)at -120 m belowthe moderncoastline(bold 9 kyr BP shoreline(blue/green Fig.1 The BlackSea lakewith its reconstructed shelfand the Seaof Azov,therebyreducingthe regioncoveredby line).The regressionportrayedherehas exposedthe entirecontinental waterto two-thirdsof its presentextent.

stagein the BlackSeadeducedfrom the lithologiesof morethan 250 sedimentcores'u' Fig. 2 The arid landscapeof the Neoeuxine ". The soils of the emergedshelf are dominatedby wind-blownloess (wavypattern)and the alluvialdeposits(stippledpattern)of meanderingriversthat flowedhundredsof km beyondtheirpresentmouthsto shelf-edgedeltas.The ancientlittoralzone (brickpaftern) in 1993.The linewith smallcirclesextendingnorth-westfrom the survey was exploredduringtwo surveysof a jointRussiaiUS expedition and agesare portrayedin Fig.6. west of the Crimeaindicatesa transectof newcoreswhoselithr.rlogies

116

GEO.ECO.MARINA, 41997 NationalInstituteof Marine Geologyand Geo-ecologyof Romania Proe. lntern. Workshopon "Fluvial-Mainelnteractions"in Malnas,Romania,Oct"1-7, 1996

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W.B.F.Ryanet al.- An abruptdrowning stlerfaf 7.5KyrB.P. of the Blac[,Sea

1220'E

shelf edgewest of the Crimea (bold dby

I formerriverchannel(Fig.5) I'

l+\

Ii

.4

r,#tAune

fietd(Fig.5) \4'

45000'N

44050',N

Oll corelocadon scismicline(Fig.4)

in metersbelowpresentsealevel.A beltof duneslieebetween Fig.SThewestCrimeasurvey,contoured the-70and-80 m isobath. Core14at- 140 m containsan erosionsurfaceformedbyemergence of thelakebottom.

A

ttl

9

710

2ltr DP

2

of rn) ey

,/

craages

Fig.il Interpretationof selsmic profils A-A" lllustraungan erosionsurface (bold llne) which has truncated an underlyingglaolal-age deltaicdepositand which ie ubiquitousin the west Crimeasurveyeverywh€reabovethe- 156 m isobath.The cores obtainedin 1993 are proJectedontg the profile (llne6 showingthe depth of penetrationare those cores close to the profile,circled numbers are those further auny). In the bottomhalf of the figurethe reflectionprofile has been proJectedInto an age-distancespace to emphaeizethe major hiatus (outlinedin bold) formed by the regr€gsionsof the lake. The diamondsymbolslocateAMS radiooarton-dat€dlevels in the cor€s. Two transgressionsare apparent,one starlingabout 15 kyr BP and the secondat 7.5 yr lcyrBP. The latterdrowns the shelf from -123 to49 m in the diagramin an interval,which appearsto be instantaneousgiventhe resolutionof the AMS dates.

GEO-ECO-MARINA,2/1997 Nationallnstituteof Maine Geologyand Geo-acologyof Romanla Proc. Intern. Workshapon "Fluvial-Mainglnteractions"in Malnas.Romania.Oct.1-7. 1996

W.B.F. Ryan ei al. - An abruptdrowningof tha BlackSea shelf al 7.5 Kyr B.P

NEW DATA The submerged shorelines on the northern shelfof the BlackSea were revisitedin June,1993 by a joint Russian/Us expedition.Two regions were surveyedwith more than 1,000 km of highresofutionsub-bottom reflection profiling and 24 new gravitycores (Fig.1).One surveylies southof the Kerch Strait in depths beyondthe present-45 m isobathin a regionwhere the ancientDon River would have flowed to reach the freshwaterlake. The other (Fig.3)is situatedwest of the Cfimea at depthsbelowthe -65 m isobathwhere the ancient Dneiperand DneisterRivers might have followed routeslo the lake'sedge. Widespread erosion surface An erosion surface (Fig.4) reachesacrossihe sholf to a depth of -'156 m. This unconformilyis mappable without interruption throughout both survey areas and along the track of the survey vesselto and from the port of Gelendzhik.

er osion suf face river chan:rel

dunes

\,'i"'

; *.Jf1;:' '

€f, oslon $,

;; 7m

3:'' r

suriaCE,-, ',i

It truncates strata with a clinoform geometry diagnostic of an alluvial fan, flood plains, meandenngriver beds, and deltas.The surfaceis locallycoveredwith dunes (Fig.5)attributedto the wind drift of beach sands. The erosionsurfaceis widely strewnwith a shelly gravel having a sharp top contact and gradational base. The gravel component is comprised almost entirely of bleached and abraded fragments of a freshwater molfusc (Dreissenarostiformisdistincta).The most common fragment is the robust hinge portion of the valve.At depthsbelow-95 m the shellygravel overliesa mud with sand-richlayerscontainingthe same mollusc as found pulverisedin the shelly gravel.However,herethe fragilemolluschas both valvesstill attachedand showsno sing of abrasion or transport.The exteriorof the shell is coatedwith a brown hairy scum of what appears to be fossilisedalgae,which can be easily removedwith a fingernail In five cores (Fig.6) below the -95 m isobath this shell-bearing sand restson a firm, dry clay in which one could identify desiccationcracks filled with plant detritus and surrounded by the preserved roots of plants and shrubs. The sand, rnud and clay layers contain gastropods (Viviparus viviparus) indicative of fluvial environments. The fauna in the gravel, sand and mud are characteristicof the freshwater Neoeuxinestage of the late Pleistocene Black sea25'5t.Mud cracks at -99 m , a l g a er e m a i n sa t - 1 1 0 m , roots of shrubs in olace at 123 m, and pebble gravel with neriticspeciesto -140 m are all indicatorsof a former alluvial to coastal environment during the Neoeuxineintervalin regions now deeply submergeo underwater.

450 m

erosion zurface

118

Fig.5 Seismic profilesiliustrating examplesof a burled river channel incisedinto the erosionsurface(top), asymmetricalsand dunes on the erosion surface (middle) and the marked truncation of steeply incline delta toreset deposits (bottom). In everycase, there is a uniform drapeal Holooene mud with no evidence of reworkingby surf zone of a gradually transgressing shoreline.

GEO.ECO.MARINA, 41997 Nationsllnstituteof Maine Geolagyand Geo-ecologyof Romania Proc. lntern.Wotkshopon "Fluvial-Maine lnteractions" in Mahas, Romania,Oct.1-7,1996

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W.B.F. Ryan et al. - An abruptdrowningof the Black Sea she/f al 7.5 Kyr B.P

2r12611810

leometry ptains, [rface is d to the lrface is a sharp gravel rety of shwater ]e most rtion of / gravel ringthe shelly as both brasion ed with to be $ with -95 m rearing

0 -50 -100 -9-

t

-rru . -^

o

.s -200

€ -zso -300 -350 0

Sl ! ffi

datedat 7.5 kyr BP Holocene shellygravel Neoeuxine dry clay and sand

-100 Nonhwest

Southeast

Fig.6 The transectof new coreswhoselocationsare shownin Fig.2,and which extendfrom -49 to -160 m belowpresentsea level.The base of the marineHoloceneBlackmud,where dated, 7.5 kyr BP" The freshwaterNeoeuxinesediments is everyltrhere onlap the erosionsurface and the underlyingstiff clay and have beenpartlypreservedfrom erosionbelow-90 m in the surveyare. The shelly gravel is the subaerialweatheringproduct of the Neoeuxinecoquina-richsandsand mud.

rycray lentify d with surierved 1rubs. clay lpods indivironthe I are reshrf the llack , -99 0m, atavel f0m

to -8 %o).This shift from older and more negative to youngerand more positivevalues is coincident with the first appearanceof marine molluscs.A similarshift occurs in cores from the basin plain52 where an offset of the same magnitudeslis again abruptand accompaniedby the appearanceof the marine microfossils (inclyding coccolithssO, diatoms3a and dinoflagellates33). The detritus in the shelly gravel can be artificially produced in the laboratory by a washing of the underlying moderately-agitated coquina-bearingNeoeuxine mud and sand, a process which easily pulverised the delicate molluscs.The shelly gravel is everywheredraped with a low-energymud deposit as evidenced by shells that are intact. Previous workers have invariably associatedthe manufacturingof the shellygravel with a slowly advancingshorelineof the Late-Pleistocene- Holocene transgression. However, it's desiccated nature and abundant plant debris is not indicative of a subaqueous origin and instead suggests a regressive lag deposit.

AMS radiocarbon dating The timlng of the onset of the Holocene depositionhas been determinedwith Accelerator Mass Spectrometer (AMS) radiocarbon dating Faunal successions methods.Ages have been obtainedin a suite of is a cores by samplingonly singleintactmolluscs(both erosion surface overlying the The sediment dark organic rich mud with abundant brackish valves still articulated)which were removed from (Monodacna caspia, Dreissena polymorpha) to the initial0.5 cm of the black mud on top of the more marine (Cardiumedule),molluscs.The latter shellygravel. A speciesis an emigrantfrom the Mediterranean. few cm above the shelly gravel, the briefly 2.0 flourishingbrackish-watermolluscsdisappearand o years by hundred a few with are replaced additionalmarine speciesthat prefer still higher salinity, e.9., Mytilaster lineatus, Mytilus t . 6I galloprovinaalis.The first appearance of marine species directly above the shelly gravel defines datum in the Black Sea for the the stratigraphic Thq last appearanceof D. of the Holocene2s. base depth in corc (cm) rostiformisin the gravel indicatesthe end of the Neoeuxinestageof the Late Pleistocene2a'46

'mer lstal the ions geo

Physical and chemical shifts Fig.7 Variationsin moistureand wet bulk densityin core AK24-93 Moistureand bulk densitymeasurementsmade fromthe Kerchsurveyarea.The Holocenemarinemud has a high shipboard on the fresh cores (Fig.7) show an water content and low density indicative of a subaqueous shellygraveland stiff clay has and low- sediment,whereasthe Neoeuxineexposure. abrupt change from high-water-content The watercontentis beendewateredthroughsubaerial density Holocene dark mud above the shelly measuredby a nuclearresonancemethodand its units are the gravelto significantlymore-desiccated and higher- periodof vibration. densityvalues for the underlyingNeoeuxine-age ages(Table1) are Thecalibrateds3 radiocarbon gravel,sand, mud and clay layers.The dry clay is indistinguishable from eachother(7.5-7.6kyr BP) stiff and can be cut only with difficulty using a to withinthe tabulatederrorranges(* 45 y) over knife. The stable isotopicratiosof O'o"o measure waterdepthrangefrom -49 to -123 m. Thus,the on individualmolluscvalvesin the Holoceneblack apparentmarineintrusionacrossthe continental mud are significantlymore positive (-1 to 0 %o) shelfis virtually identical in tjnlingto the onsetof 'o. The datesin the than those from the Neoeuxinesand and mud C4 anoxiathroughout the basin*o

rBng nnel lop), the the t,ne ln eol of ally

GEO-ECO-MARINA, 41997 Nationallnstituteof Maine Geologyand Geo-ecologyof Romania Proc. lntern. Workshopon "Fluvial-Mainelnteractions"in Malnas,Romania,Oct.1-7, 1996

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W.B.F. Ryan et al. - An abruptdrowningof the Black Sea shelf af 7.5 Kyr B.P.

Neoeuxine sandsand mud (Table2) rangefrom 10.8to 8.3 kyr BP as mightbe expectedin a lag 14.7to 10.0kyr BP. Thosein the shellygravel deposit. invertedagesin the rangeof havestratigraphically Table 1 AMS radiocarbon dateslof Holocenefaunadirectlyabovethe shellygravel.

Core

AK3-2-93 AKl-93 AK12-93 AK8-93 AK9-93

Water Depth(m) 49 68 78 99

1?3

Depthin Core(cm) 49 134 144 104 92

Species Analysed

M.caspia M"caspia C.edule C.edule C.edule

Conventional CalenderAge (yr.BP) Ase (yr.BP) 7 , 1 3 Q* 4 0 7 , 5 0 0+ 1 1 5 7 , 2 2 4+ 4 0 7 5 8 0+ 1 1 5 7 , 1 4 0+ 4 0 7 , 5 1 0* 1 1 5 7 , 1 4 0* 4 0 7 , 5 1 0+ 1 1 5 7JjAL40 7 , 4 7 4* 1 1 5

Accession Number

os-2321 os-2357 os-2325 as-2322 os-2323

Tabte 2 AMS radiocarbon datesifromfaunain the Neoeuxine shellgravel*,the underlying Neoeuxinesandand mud lavers*andthe stiff clavtruncatedbv the erosionalsurface=.

Core AK10-93 AK7-93 AK7-93 AK7-93 AK14-93 AK'14-93

Water m '106 'l0B '108 108

Depthin Core(cm 145

D.rostriformis

215=

D.rostriformis D.rostriformis

The documentationof Neoeuxine shorelines alongthe shelf edge of the BlackSea bringsinto doubt the scenario, proposed by many researchers55-5e, of a flow-through giacial-age freshwater lake with a continuous outlet. For steadydischargethe floor of this outlet is required to have been as far belowtlp presentsea surface as the ancient shorelines"".However a major problemgeneratedby hypothesisinga deep sill is the observed long delay betlueen the rise of eustaticsea level of the external ocean above 120 m isobathat 18 kyr BP and the first entry of marine fauna from the Mediterraneansome ten thousandyears later when the outlet would have been a hundredmeter deep channel.Furthermore a Black Sea with a deep outlet should have experienced a post-glacialtransgressionof its margins in synchroneitywith the external ocean, therebyleavingthe sedimentaryand faunal record of a progressivelandwardadvanceof its coastline across the shelf. lnstead, one observesonly the abrupt appearance7.5 kyr BP age black mud on top of the severely desiccatedNeoeuxineshelly gravel. Arid ClimaticConditions However, if one considersthat the lake level might..have dropped upon occasion below its o would outlet"'rv . the rise and fall of its shoreline not need to be coupledwith the externalocean. Such a drawdownrequiresa negativehydrologic balance comparableto neighbouringpresent-day CaspianSea. Given adequatetime and sufficient 120

Conventional CalenderAge \ge (yl€!) .BP

95-97* D.rostriformis 100-104" D.rostriformis 140-145- D.rostriformis

tau

140

Species

11 , 3 5 *0 4 5 1 0 , 4 0r0 5 5 8,250+ 35 10800* 65 1 0 , 0 0*0 5 0 1 4 , 7 0+0 6 5

1 2 , 8 0+0 5 0 1 1 , 4 0*01 6 0 8 , 6 1 7+ 8 0 * 120 12,20A 1 0 , 8 0+01 0 0 1 7 , 1 0*09 5

Access. Number

os-2324 os-2357 os-2358 os-2359 os-2326 os-2360

evaporation,the lake'scontentof bi-carbonatewill increase.The mollusc Didacna moribunda, lound in the Neoeuxinedeposits is thought to be an indicatorof such increasingalkalinity"'.A negative waterbalancecould occur if the river supplyto the Black Sea had diminishedfor reasonsother than local precipitation.Radiometricdates of moraines of the Barents and Scandinaviancontinentalice sheetsrecordtheir retreatbetween15 and 10 kyr BP62'63. Their peri-glaciallakes did not maintain drainageto the south. Beginning12-13 kyr BP these lakes found alternateoutlets, either to the west where they fed a large lake in the Baltic regionwith a spillwayto the North Sea, or to the Arctic via gaps between the ice sheets. The YoungerDryas (12-11 kyr BP) is an intervalin Europe.ard the Near East of marked coolingand aridityo"-o'. Elevatedlevelsof wind blowndust from Asia and Europe are^found as far away as the Greenlandice capoo-'u. In the CaspianSea the Younger Dryas coincides with the Mangyshlak regressionto -133 m during which the Caspian shrank to 3Ao/oits present surface area""' ' ) transformingthe exposed northern shelf into a desert landscapewith wind-blownsand dunes. A belt of semi-deseftterrain extendedto the west along the northern and southern sides of the Crimea, blanketing the exposed Caspian and Black Sea shelves with loess deposits. The parchedconditionsreached into Romania where fossilsand dunesqre still preservedon terracesof the DanubeRiver''. In Syria,the materialremains of humansedentaryoccupation duringthe

GEO-ECO-MARINA, 21997 NationalInstituteof Maine Geologyand Geo-ecologyof Romania Proc. lntern Workshopon "Fluvial-Mainelnteractions"in Malnas,Romania,act.1-7, 1996

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W.B.F. Ryan et al. - An abrupt drowningof the Black Seashelf at 7.5 Kyr B.P

lag

vill nd an ve 'le

an 3S

]e yr in P re ic re e n d n e e K tl

1

t t t

i ) ) I

and in the formation of a density stratificationin the water column that quickly tume_dthe sea anoxic everywhere below -200 m"4. A fast submergenceof the landscapewould explain the preservationof shelf-edgeriver channelsand sand dunes from the destructive processes of the surf zone. The migrationof the coast far inland would also have caused the observed simultaneous shutdownin the deliveryof detritalcarbonateand reworkedmaterialsto the shelf and the basin plain at the time of the marineinvasionand for the, That the inundationwas by water with an already increasedsalinityis corroboratedby the fact that, unlike the deep-basinsediments,there is only a very slight depletion of interstitialchloride with depth in the subsurfaceof the shelf76.Apparently the transgressingsea percolateddirectly into the open pore space of the highly permeableand dry Neoeuxineshellygravel and sands". A catastrophicdelugethroughthe cataractsof a narrow inlet is fully capable of cutting into the bedrockof the Bosporusand DardanellesStraits (Fig.8). Where drilled and sampled in the Bosporus Strait, the initial fill on the eroded bedrockin the bottomof this gorge containslarge blocksand bouldersof the adjacentDevonianand Carbotrjferousbedrock'" floating in a gravel matrix" with Holocene-age euryhaline benthic foraminifera (Ammonia beccarii, Elphidium crispum)'" and brackish water molluscs (Corbula gibba, Cerithidea insulaemaris;7e dated at 7.4+1.9 Fig,8 Interpreted seismic reflection profiles across the Dardanellesand B.osporus.Straits showing the erosionof the kyr BP in ageo'. Paleozoicbedrock'" and its subsequent cover with inferred Suddeninundationof depressed,enclosedbasins Holocenedeposits as calibratedbv drillins in the axis of the Tssos6. Bosporusnear lstanbule Th; base-ofthe bedrockgorge are rare but real events. At the beginningof the Pliocenethe drasticallydesiccatedMediterranean deepensin the directionofthe BlackSea and reaches-110 m in the BosporusStrait. Sea81 filled via a gigantic Gibraltar waterfall. Common to oceanicwaterfallsis the fixed head of Natufian stage of the late Palaeolithiccarry a the supplying water body.As erosiondeepensthe recordof a severe impoverishmentin diet leading upstream cataract, the flow throughthe conduit is to an abandoned of sedentary villages on the positive feedback. A through amplified banks of the EuphratesRiveroo.Pollen studiesin based on turbulent conservative calculation cares from Lake Huleh in the Levant indicatean fluidss2 with boundary conditionss3 adaptedto the episodeof post YoungerDryas ariditylastingto at Bosporus-Marmara-Dardanelles flume system least 10 kyr BP''. Loess accumulatedin the yields an inflow of water of 50 to 100 km"/day. southernUkraineto 9.0 kyr BP7a.Cores from the greaterthan Black Sea shelf east of Bulgaria have an This flux rate, several hundredtimes the world's largest waterfall and times a thousand abundance of herbaceous pollen of steppe presentundercurrent,is sufficientto the exceeding communities with Chenopodiaceqg and the sagebrush Artemisain proliferation''right up to have raisedthe level of the Black Sea 30 to 60 cm year the first appearance of marine molluscs. The each day or to have topped up the basin in a (Fig.9).On flat regionsof the shelf and in the river synchronousdepositionof mud with marinefauna directly on top of the low-moistureshelly gravel valleysthe sea might have advancedlandwardat per day. The roar of the waterfall, over a documentedminimumelevationchange74 almost1 to 2 km ground waves, would have radiated by air and m impliesa rapid submergenceof the type which enormity of its cascade to any broadcast the would have occurredif the Mediterranean Sea had humans settled or wandering within100 km of the brokenits way intothe BlackSea via the Bosporus inlet. at 7.5 kyr BP. A massive input of saltwateris expressedin the abrupt shift positiveshift with q magnitudeof 4 to 6 7ooin the oxygen isotopes"' GEA-ECO-M AR|NA.,A1 997 Nationallnstituteof Maine Geologyand Geo-ecologyof Romania Prcc. lntern. Workshopon "Fluvial-Mainelnteractions"in Malnas,Romania,OcL1-7. 1996

W.B,F

of the Black Sea shelfat 7.5

17kyr BP

14kvr BP

one year latter

Fig.9 Reconstructedlake and sea levelsin ihe Aegean (A), Sea of Marmara (M), and Black Seas (BS), and their connections/isolatiorrs via the Dardanelles(D) and Bosporus(B) Straits. An entrenchedsiream bed of the ancient Don River Passes though the Kerch Strait (K$) Sea level in the Aegean tracksthe rise of ihe globaiocean''"'. The sedimentaryrecordof the BlackSea revealstwo intervalsof isolation,duringwhichmuch of its vast continentalshelf r,vasemergedland.A brief Neoeuxine takes placebetween15 and 12 kyr BP, triggeredby transgression largeflux of melt.water,.guppliedfrcrmthe retreatingEarentsand ice sheets"'and deliveredbv the Don and Dneiper Scanclinavian 50'71 Riversand by an overflowfrom the CaspianSea3!' This tinre of high lake level coinodes with lt/elt-WaterPulse'l of ref (18). The floodingof marinewater into the Black Sea at 7.5 kyr BP is catastrophic,and is accompanledby the erosionof a gorgealong the inlet.ln the span of a year,the EiackSeeis toppedup the level of the Aegeanand is launchedon its way from a freshwateriaketo an anoxicbrackishsea.

orifice. The Black Sea flood took place when farming villages had already been establishedin Greece and southern Bulgariao",in ^lhe lower feachesof the modernDanubeRivero"oo,nearthe coast of the Sea of MarmarasTand in the Fertile Crescentss. At 7.5 kyr BP advancedfarming,with the possible use of the light plow and simple irrigation techniques, blossomed in the Trans Causasusits suddenintrojuctioninterpretedas an intrusionfrom the outside"". Ar^o-und 7.4 kyr BP and within the span of 100 yearso"farming villages spread along the major river valleysof Germany,Austriq^Czechoslovakia, Poland and the Low Countrieso''o' Due to the remarkable homogeneity of these cultural deposits,archaeologists have considereda "wave. of-advance"model for the assumed population movementsn'.The immigrants had an obvious preference for the flood plains of rivers and lakes"' They settled throughout most of southeastern Europe amo^qg^a mysteriously sparse indigenouspcpulation'"o" Althoughthe migration model has been challengedand replacedby one of diffusion of skills rather than peopleo', the permanentfloodingof the expansiveshelf of the Black Sea could have been and impetusto expel into Europe and the Near East communitiesof farmers which had adapted to the natural resoufcesof the late NeoeuxineBlack Sea, i.e.,its arable loess soils, the seasonal irrigation of its entrenchingrivers,and the fresh moist loam along the retreatingshorelineof its vast freshwaterlake potentiallyexploitablefor the springtimegrowing of domesticatedfood crops.

Acknowledgements The 1993 expeditionmaterializedthough the generous assistance of the officersandcrewof the RA/ Aquanaut, the Datasonics Corporation, Falmouth,MA, and R, Kosyanand E Kontarof the P.P Shirshov Oceanology InstituteM, Bruckner,R, Fairbanks,T. B. Hatau,W. Haxby,B. lf ina, S. Klimley, Guilderson, W. Menke,L. Nevesskaya, and J Weisselprovided crucialtechnicaland analyticalhelp, D. Harris,l. Possible human response . Hodder, A Moore,J. Oates,C. Renfrew, J. Mellaaft, J. A Renfrew and Sherratt have contributed substantially The geological evidence of an injection of to our understandrng of possiblearchaeological saltwaterinto a depressedNeoeuxinelake via a implications of the Black Sea connections with the Bosporuscataract lends credenceto the ancient Mediterranean accounts of a bursting of the sea though this REFERENCESAND NOTES dates are nonnalisedto a C-13 1. All radiocarbon ages have value of -25 per mil. The conventional been reservoir corrected by 460 years based on measurementof rnolluscscollectedin 1931.The ages reportedas kyr BP have been convertedto calendar years using the calibrationprogram of Stuiverand Braziunas(1993)for ages< 10 kyr BP 122

ancl by the u-Th calibrationof Bard et al. (1990) for ages> 10 kyr BP. 2. Pliny.BooklV and Vl (70 AD). 3. Strabo.Bookl, Chapter3 (19 AD) . 4. Sicily,D. o. . N.1.,Akad.NaukSt.Petersburg 5. AtrtoRusov, Bull,, N.S.,3, 437-448(1893). 6. SoKoLov, N., Geol. Komitet St.Petersburg T r u d y1 0 ( 1 8 9 5 ) .

GEO.ECO.MARINA, 41997 Nationallnstltuteof Maine Geologyand Geo-ecologyof Romania Proc. lntefn. Workshopan "Fluvial-Mainelnteractions"in Malnas,Romania,Oct-1-7, 1996

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