An Abrupt Drowning of the Black Sea Shelf

Abstract

During latest Quaternary glaciation, the Black Sea became a giant freshwater lake. The surface of this lake drew down to levels more than 100 m below its outlet. When the Mediterranean rose to the Bosporus sill at 7,150 yr BP1, saltwater poured through this spillway to refill the lake and submerge, catastrophically, more than 100,000 km2 of its exposed continental shelf. The permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of Europe at that time.

Full text

W.B.F.
Ryan et al.
- An abrupt
drowning
of the Black Sea she/f
af 7.5 Kyr B.P.
AN ABRUPT DROWNING OF THE BLACK SEA SHELF AT 7.5 KYR BP
William B.F. Rvnru1, Walter C. Prrunru lll1, Candace
O. MR.loR1,
Kazimieras
SHrurus',
Vladimir MoscRtrruro', Glenn A. JoruEsr,
Petko DrMrrRova,
Naci
GonURs,
Mehmet SRrcruqs & Hiiseyin
Ytice
SEvlR6
. 1
Lamont-Doheity Earth Observatory of Columbia
University, Palisades, NY
10964,
USA
'Southern
Branch of the P.P. Shirshov Oceanology Institute, Gelendzhik-7, 353470, Russia
3
Texas
A & M University
at Galveston, Galveston, TX, USA
a
Bulgarian-Academy of Sciences, lnstitute of Oceanology,
9000 Vama, PO Box
152,
Bulgaria
" l.T.U.
Maden
FakUltesi Jeoloji
B6lUmU, 80626 Ayazga, lstanbul, Turkey
6
Seyir Hidrografi
ve Osinografi
Dairesi, 81647
gLiUuXtu,
lstanbul, Turkey
Abstract: During latest
Quaternary
glaciation,
the Black Sea became
a giant
freshwater
lake,
The surface of this lake drew down
to levels
more than
100m
below its outlet. When the Mediterranean rose to the Bosporus
sill
at 7.5 kyr BPl,
saltwater
poured
through
this spiltway
to
refill
the
and submerge, in less than a year,
more than 100,000Km'
of its exposed
continental
shelf.
Key words: continental shelf, erosion surface, climatic
condition, faunal succession, radiocarbon
data,
Neoeuxine Lake, Black
Sea
INTRODUCTION
The earliest written accounts on the Bosporus
and Dardanelles
Straits, date to the Roman
era'-"
and chronicle a catastrophic
breakthrough
of the
sea. The winding course of both straits,
their
terraced cross-sections, and their dendritic
tributaries
were interpreted by nineteenth century
geomorphologistss
6 as indicative of a stream
origin.
Today
the channel
is 9eeply
submerged
and
pafily
filled with sediment'-'"to a sill depth
of-
33 m". lt hosts a two-way exchange of water
between the partly
marine
Black
Sea and
the fully
marine Mediterranean Sea11-16. In fact, the
northward-flowing undercurrentlT had long ago
been known to mariners
who lowered baskets
laden
with rocks into its core
to tow their vessels
upstream toward the Black Sea18.
Dated fossil coral reefs in the Caribbeanle-21
show that, at the time of the maximum expansion
of continental ice sheets around
20 kry BP, the
surface
of the global
ocean
was at -120
m. Thus
prior
to the glaciers,
the Black Sea was without
connection
to an external ocean
(Fig.1).
ln the
absence of a saltwater inlet it had transformed
itself into a giant freshwater
body22
23,
dwarfing
any
modern lake
in area
and volume.
NEOEUXINE LAKE
Lacustrine
deposits of glacial
and postglacial
age, assigned to the local Neoeuxine"-'"
stratigraphic stage of the late Quaternary, have
been
cored at a large number of sites on the floor
of the Black Sea extendino
from the continental
shelf26-28 to the center of itibasin plain26'2e-31
at a
depth
of 2.2 km. The freshening is deduced
from
the ecology
^^
of the fossil molluscs2s'
32'
dinoflagellatqs33 and diatoms3a'
tt, from strongly
negative
O'o''o isotopic ratios^^in
the carbonate
component of the sediments'o, and from the
chemistry of pore waters drawn out of the
Neoeuxine-age strata3T-3e.
Near-shore littoral deposits26
27' 40' 41,
with
radiocarbon ages of the msllusc shells
spanning
19 to I kyr BP, have been found at depths
between -93 and -122 m. Linear steps that
resemble the profiles
of beach terraces have been
mapped for tens of km along the outer shelf
between
-90 to -110 m. A substantial lowering
of
the
past
lake level to at least
-110
m has also
been
inferred from
the discovery of formerly entrenched
river valleysa2-45
which are now
partly
filled in with
estuarine deposits under the beds of modern rivers
as they approach the coast. Boreholes
in the
Kerch Strait'o '' have recovered coarse gravel
with fluvial fauna
at -62 m in the stream bed
of the
ancient Don River > 200 km seaward of the
present
river mouth. Mud, silt and sand on the
basin plain dated between I to 7.5 kyr BPas
contain .A significant cgmponent of reworked
molluscsae,
microfossilsso
and plan detritus33
washed downslope from coastal swamps. The
contamination of former proximity
of wetlands to
the heads of the submarine canyons
which indent
the shelf edge and act as conduits
for sediment
transport to the basin
plain.
The inferred relocation
of the coastline
in the vicinity of the current
shelfbreak is shown in Fig.2, along with the
ubiquitous distribution of loess
and alluvial soils on
the broad and emerged continental
shelf south of
Ukraine and throughout
the Sea of Azov27
.
GEO-ECO-MARINA, 41997
National lnstitute
of Maine Geology and Geo-ecology of Romania
Prcc. lntern.
Workshop on "Fluvial-Maine
lnteractions" in Malnas, Romania, OcLl-7, 1996

W.B.F. Ryan et al.
- An abrupt
drowning af the Black Sea she/f af 7.5 Kyr B.P.
Fig.1 The Black
Sea lake with its reconstructed
9 kyr BP shoreline
(blue/green
boundary) at
-1
20 m below
the modern
coastline
(bold
line). The regression
portrayed
here has exposed the entire continental
shelf and the Sea
of Azov, thereby reducing the region
covered
by
water to two-thirds
of its present
extent.
Fig. 2 The arid landscape
of the Neoeuxine stage in the Black Sea deduced
from the lithologies of more than 250
sediment cores'u'
". The soils of the emerged
shelf are dominated by wind-blown loess
(wavy
pattern)
and the alluvial deposits
(stippled
pattern)
of
meandering
rivers that flowed hundreds
of km beyond their
present
mouths to shelf-edge
deltas. The ancient littoral zone
(brick
paftern)
was
explored during two
surveys of a
joint
Russiai US expedition in 1993. The
line
with
small circles extending north-west from the survey
west
of the Crimea indicates a transect
of new
cores whose lithr.rlogies and ages are
portrayed
in Fig. 6.
GEO.ECO.MARINA, 41997
National Institute
of Marine Geology and Geo-ecology
of Romania
Proe.
lntern. Workshop
on "Fluvial-Maine
lnteractions"
in Malnas, Romania,
Oct"1-7, 1996
116
.L-_

W.B.F.
Ryan
et
al.
- An
abrupt
drowning of
the Blac[,Sea stlerf
af 7.5
Kyr B.P.
(bold
dby
1220'E 45000'N
44050',N
Fig.S
The
west
Crimea
survey, contoured
in meters below
present
sea level. A belt of dunes liee between the
-70
and
-80
m isobath.
Core
14
at-
1 40
m contains an erosion
surface formed
by
emergence
of
the lake bottom.
Fig.il Interpretation
of selsmic profils
A-A" lllustraung an erosion
surface (bold llne) which has truncated an underlying
glaolal-age
deltaic deposit and which ie ubiquitous
in the west Crimea survey
everywh€re above the- 156 m isobath. The cores obtained
in 1993
are
proJected
ontg
the profile
(llne6 showing
the depth of penetration
are those cores close to the profile,
circled numbers
are those further
auny). In the bottom half of the figure
the reflection
profile
has been
proJected
Into an age-distance space to emphaeize
the major hiatus
(outlined
in bold) formed by the regr€gsions of the lake. The diamond symbols locate
AMS radiooarton-dat€d levels in the cor€s. Two
transgressions
are apparent,
one starling
about
15 kyr BP and
the second
at 7.5 yr lcyr BP. The latter drowns
the shelf from -123 to49 m
in the diagram in an interval, which appears to be instantaneous
given
the resolution
of the AMS dates.
G EO-ECO-
MARINA, 2/1 997
National lnstitute of Maine Geology and Geo-acology
of Romanla
Proc. Intern.
Workshap on "Fluvial-Maing
lnteractions"
in Malnas.
Romania.
Oct.1-7. 1996
of
rn)
ey
shelf
edge
west
of the
Crimea
I former
river
channel
(Fig.
5) I' Oll core
locadon
l+\
i .4
I r,#tAune fietd
(Fig.5) \4' scismic
line
(Fig.4)
ttl
A 9 710
2
ltr DP
2 ,/ cra ages

W.B.F. Ryan
ei al.
- An abrupt drowning
of tha Black Sea shelf al 7.5
Kyr B.P
NEW DATA
The submerged
shorelines on the northern
shelf of the Black Sea were
revisited
in June,
1993
by a joint Russian/Us
expedition. Two regions
were surveyed with more than 1,000
km of high-
resofution
sub-bottom reflection profiling and 24
new
gravity
cores
(Fig.1).
One survey lies south of
the Kerch Strait
in depths
beyond
the present
-45
m isobath in a region
where
the ancient Don River
would have flowed to reach the freshwater
lake.
The other
(Fig.3)
is situated
west of the Cfimea at
depths below the -65 m isobath
where the ancient
Dneiper
and Dneister
Rivers might
have followed
routes
lo the lake's
edge.
Widespread erosion surface
An erosion
surface
(Fig.4)
reaches across
ihe
sholf
to a depth of -'156
m. This unconformily is
mappable without interruption throughout both
survey areas and along the track of the survey
vessel
to and from
the port
of Gelendzhik.
er osion suf
face
river
chan:rel
\,'i"' ;
*.Jf1;:'
' 3:'' r;; 7m
suriaCE,-,',i
It truncates
strata with a clinoform geometry
diagnostic
of an alluvial fan, flood plains,
meandenng river beds,
and deltas.
The surface is
locally
covered with
dunes
(Fig.5)
attributed to the
wind drift of beach
sands. The erosion
surface
is
widely strewn with 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
molf usc (Dreissena
rostiformis
distincta).
The most
common
fragment is the robust
hinge portion
of
the
valve.
At depths
below
-95 m the shelly
gravel
overlies
a mud
with sand-rich layers
containing the
same mollusc as found pulverised
in the shelly
gravel.
However, here the
fragile
mollusc has both
valves
still
attached
and
shows
no sing of abrasion
or transport.
The exterior of the shell
is coated
with
a brown hairy scum of what appears to be
fossilised
algae, which can
be easily
removed with
a fingernail
In five cores
(Fig.6)
below the -95 m
isobath this shell-bearing
sand rests on a firm, dry clay
in which one could identify
desiccation cracks
filled with
plant detritus and sur-
rounded by the preserved
roots of plants and shrubs.
The sand, rnud and clay
layers contain gastropods
(Viviparus viviparus) indi-
cative of fluvial environ-
ments. The fauna in the
gravel, sand and mud are
characteristic of the fresh-
water Neoeuxine stage
of the
late Pleistocene Black
sea25'5t.
Mud cracks at -99
m, algae remains at
-110
m,
roots of shrubs
in olace at -
123 m, and pebble gravel
with neritic species
to -140
m
are all indicators of a former
alluvial to coastal
environment during the
Neoeuxine
interval
in regions
now deeply submergeo
under
water.
Fig.5 Seismic
profiles
iliustrating
examples
of a burled river channel
incised
into the erosion surface
(top),
asymmetrical
sand dunes on the
erosion surface (middle) and the
marked truncation of steeply incline
delta toreset deposits (bottom). In
every case, there is a uniform drape
al
Holooene mud with no evidence of
reworking
by surf zone of a gradually
transgressing
shoreline.
€f,
oslon
$, 450 m
erosion zurface
dunes
GEO.ECO.MARINA,
41997
Nationsl lnstitute
of Maine Geolagy
and Geo-ecology of Romania
Proc. lntern.
Wotkshop
on "Fluvial-Maine
lnteractions"
in Mahas,
Romania,
Oct.1-7, 1996
118
^\-_

W.B.F. Ryan et al.
- An abrupt
drowning of the Black Sea
she/f al 7.5 Kyr B.P
leometry
ptains,
[rface is
d to the
lrface is
a sharp
gravel
rety of
shwater
]e most
rtion of
/ gravel
ring
the
shelly
as
both
brasion
ed
with
to be
$ with
-95 m
rearing
ry
cray
lentify
d with
sur-
ierved
1rubs.
clay
lpods
indi-
viron-
the
I are
resh-
rf
the
llack
, -99
0m,
at-
avel
f0m
2r12611810
-100
-9- . -^
t -rru
o
.s -200
€ -zso
-300
-350
0
-100
Nonhwest Southeast
Fig.6
The transect of new cores whose
locations
are shown in
Fig.2, and which extend from -49 to -160 m below
present
sea
level.
The base of the marine Holocene
Black mud,
where dated,
is everyltrhere
7.5 kyr BP" The freshwater
Neoeuxine
sediments
onlap the erosion
surface and the underlying
stiff clay and have
been
partly preserved
from
erosion below
-90 m in the survey are.
The shelly gravel is the subaerial
weathering
product
of the
Neoeuxine
coquina-rich sands
and mud.
Faunal
successions
The sediment
overlying the erosion surface
is a
dark organic rich mud with abundant
brackish
(Monodacna caspia, Dreissena polymorpha) to
more
marine
(Cardium
edule), molluscs.
The latter
species
is an emigrant
from the Mediterranean.
A
few cm above the shelly gravel, the briefly
flourishing
brackish-water
molluscs
disappear and
are replaced with a few hundred years by
additional
marine
species that prefer
still higher
salinity, e.9., Mytilaster lineatus, Mytilus
galloprovinaalis.
The first appearance
of marine
species
directly
above the shelly
gravel defines
the stratigraphic
datum in the Black Sea for the
base
of the Holocene2s.
Thq last appearance
of D.
rostiformis
in the gravel indicates the end of the
Neoeuxine
stage of the Late
Pleistocene2a'46
Physical
and chemical
shifts
Moisture
and
bulk density measurements
made
shipboard
on the fresh cores (Fig.7) show an
abrupt change from high-water-content
and low-
density Holocene dark mud above the shelly
gravel
to significantly
more-desiccated and
higher-
density
values for the underlying
Neoeuxine-age
gravel,
sand, mud and
clay layers.
The dry clay is
stiff and can be cut only with difficulty using
a
knife.
The stable isotopic ratios
of O'o"o measure
on individual
mollusc valves in
the
Holocene black
mud are significantly
more positive (-1 to 0 %o)
than those
from the Neoeuxine sand and mud
C4
to -8 %o). This shift
from older and more negative
to younger
and
more
positive
values is coincident
with the first appearance
of marine molluscs.
A
similar shift occurs in cores from the basin
plain52
where an offset of the same magnitudesl is again
abrupt
and accompanied by the appearance of the
marine microfossils (inclyding coccolithssO,
diatoms3a and dinoflagellates33).
The detritus in the shelly gravel can be
artificially produced in the laboratory by a
moderately-agitated
washing of the underlying
coquina-bearing Neoeuxine
mud and sand, a
process which easily pulverised the delicate
molluscs. The shelly
gravel
is everywhere
draped
with a low-energy mud deposit as evidenced
by
shells that are intact. Previous workers have
invariably associated
the manufacturing
of the
shelly
gravel
with a slowly advancing shoreline
of
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
deposition
has been determined
with Accelerator
Mass Spectrometer
(AMS) radiocarbon
dating
methods.
Ages have been obtained
in a suite of
cores by sampling
only single intact molluscs
(both
valves
still articulated) which
were removed
from
the initial
0.5 cm of the black mud on top of the
shelly
gravel.
Fig.7 Variations
in moisture
and wet bulk
density in core AK24-93
from the Kerch
survey area.
The Holocene marine
mud
has a high
water content and low density indicative
of a subaqueous
sediment, whereas
the Neoeuxine
shelly
gravel
and stiff
clay has
been dewatered
through subaerial
exposure. The
water content
is
measured
by a nuclear
resonance method
and its units are the
period
of vibration.
The calibrateds3 radiocarbon
ages
(Table
1)
are
indistinguishable
from
each other
(7.5-7.6
kyr BP)
to within the
tabulated
error ranges
(* 45 y) over
water
depth range
from
-49
to -123
m. Thus, the
apparent marine
intrusion
across the continental
shelf
is
virtually
identical in tjnling
to
the onset of
anoxia throughout
the
basin*o
'o.
The dates
in the
0
-50
2.0
o
t.6
I
'mer
lstal
the
ions
geo
rBng
nnel
lop),
the
the
t,ne
ln
eol
of
ally
dated
at
7.5 kyr BP
Holocene
Sl shelly
gravel
! Neoeuxine
ffi dry clay
and
sand
depth in corc
(cm)
GEO-ECO-MARINA, 41997
National lnstitute
of Maine Geology and Geo-ecology
of Romania
Proc.
lntern. Workshop
on "Fluvial-Maine
lnteractions" in Malnas,
Romania, Oct.1-7, 1996
)
I tY

W.B.F. Ryan et al.
- An abrupt drowning of the Black
Sea shelf
af 7.5
Kyr B.P.
Neoeuxine sands and mud
(Table
2) range from
14.7
to 10.0 kyr
BP.
Those in the shelly
gravel
have stratigraphically
inverted
ages
in
the
range of
10.8
to 8.3 kyr BP as might be expected in a lag
deposit.
Table 1 AMS
radiocarbon
datesl
of Holocene
fauna directly above the
shelly
gravel.
Core Water Depth in Species
Depth(m) Core(cm) Analysed Conventional CalenderAge Accession
Ase
(yr.BP) (yr.BP) Number
AK3-2-93
AKl-93
AK12-93
AK8-93
AK9-93
49
68
78
99
1?3
49
134
144
104
92
M.caspia
M"caspia
C.edule
C.edule
C.edule
7,13Q
* 40
7,224
+ 40
7,140
+
40
7,140
* 40
7JjAL40
7,500
+ 115
7 580
+
115
7,510
* 115
7,510
+ 115
7,474
* 115
os-2321
os-2357
os-2325
as-2322
os-2323
Tabte
2 AMS radiocarbon datesi from fauna in
the Neoeuxine
shell
gravel*,
the underlying
Neoeuxine
sand and mud
lavers* and the
stiff clav truncated bv the erosional surface=.
Core Water Depth in
Core(cm Species Conventional Calender Age Access.
NumbermD.rostriformis
D.rostriformis
D.rostriformis
D.rostriformis
D.rostriformis
D.rostriformis
\ge (yl€!)
1 1,350
* 45 .BP
12,800
+
50
11,400
* 160
8,617
+
80
12,20A
* 120
10,800
+
100
17,100
* 95
AK10-93
AK7-93
AK7-93
AK7-93
AK14-93
AK'14-93
145
95-97*
1 00-1 04"
140-145-
215=
'106
'l0B
'108
108
tau
140
10,400
r 55
8,250
+
35
10 800
* 65
10,000
* 50
14,700
+
65
os-2324
os-2357
os-2358
os-2359
os-2326
os-2360
The documentation
of Neoeuxine
shorelines
along the shelf edge of the Black Sea
brings into
doubt the scenario, proposed by many
researchers55-5e, of a flow-through giacial-age
freshwater lake with a continuous outlet. For
steady discharge the floor of this outlet is required
to have been as far below tlp present
sea surface
as the ancient shorelines"". However a major
problem generated
by hypothesising
a deep sill is
the observed long delay betlueen the rise of
eustatic sea level of the external ocean above
-
120 m isobath
at 18 kyr BP and the first entry of
marine fauna from the Mediterranean some ten
thousand
years later when the outlet would
have
been a hundred meter deep
channel. Furthermore
a Black Sea with a deep outlet should have
experienced a post-glacial
transgression
of its
margins in synchroneity
with the external ocean,
thereby
leaving
the sedimentary
and
faunal
record
of a progressive
landward advance
of its coastline
across
the shelf. lnstead,
one observes
only the
abrupt
appearance 7.5 kyr BP age black mud on
top of the severely desiccated
Neoeuxine shelly
gravel.
Arid Climatic Conditions
However, if one considers that the lake level
might..have dropped upon occasion below its
outlet"'rv
o .
the
rise and fall of its shoreline
would
not need to be coupled with the external ocean.
Such a drawdown requires
a negative hydrologic
balance
comparable
to neighbouring
present-day
Caspian Sea. Given adequate time and sufficient
evaporation, the lake's
content
of bi-carbonate
will
increase.
The mollusc Didacna moribunda, lound
in the Neoeuxine deposits is thought to be an
indicator of such increasing alkalinity"'.
A negative
water balance could occur if the river
supply to the
Black Sea had diminished
for reasons
other than
local
precipitation.
Radiometric dates
of moraines
of the Barents and Scandinavian continental ice
sheets record their retreat between 15 and 10 kyr
BP62'63.
Their peri-glacial
lakes did not maintain
drainage
to the south. Beginning 12-13 kyr BP
these lakes found alternate outlets, either to the
west where they fed a large lake in the Baltic
region with a spillway to the North
Sea, or to the
Arctic via gaps between the ice sheets. The
Younger Dryas
(12-11
kyr BP) is an interval in
Europe. ard the Near East of marked cooling and
aridityo"-o'. Elevated levels of wind blown
dust from
Asia and Europe are^found
as far away as the
Greenland ice capoo-'u. In the Caspian Sea the
Younger Dryas coincides with the Mangyshlak
regression to -133 m during which the Caspian
shrank to 3Ao/o its present surface area""' ' )
transforming the exposed northern shelf into a
desert landscape with wind-blown sand dunes. A
belt of semi-deseft terrain extended to the west
along the northern and southern sides of the
Crimea, blanketing the exposed Caspian and
Black Sea shelves with loess deposits. The
parched
conditions
reached into Romania where
fossil sand
dunes qre
still
preserved
on terraces
of
the Danube River''. In Syria, the material remains
of human sedentary occupation during the
GEO-ECO-MARINA,
21997
National Institute of Maine Geology and Geo-ecology of Romania
Proc. lntern Workshop
on "Fluvial-Maine
lnteractions" in Malnas, Romania, act.1-7, 1996
120
L-_

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
W.B.F.
Ryan et al.
- An abrupt drowning
of the Black Sea shelf at 7.5 Kyr B.P
Fig,8 Interpreted seismic reflection profiles across the
Dardanelles and B.osporus.
Straits showing the erosion of the
Paleozoic
bedrock'" and its subsequent
cover with inferred
Holocene
deposits
as calibrated bv drillins
in the axis of the
Bosporus
near lstanbule
Ts sos6.
Th; base-of the bedrock
gorge
deepens in
the
direction ofthe Black Sea and
reaches
-110
m in
the Bosporus
Strait.
Natufian
stage of the late Palaeolithic carry a
record of a severe impoverishment
in diet leading
to an abandoned of sedentary villages on the
banks of the Euphrates Riveroo.
Pollen studies in
cares from Lake Huleh in the Levant
indicate
an
episode of post
Younger Dryas aridity
lasting to at
least 10 kyr BP''. Loess accumulated in the
southern Ukraine to 9.0 kyr BP7a. Cores from the
Black Sea shelf east of Bulgaria have an
abundance of herbaceous pollen of steppe
communities with Chenopodiaceqg and the
sagebrush Artemisa in proliferation''
right up to
the first appearance of marine molluscs. The
synchronous deposition
of mud with marine fauna
directly on top of the low-moisture shelly
gravel
over a documented minimum elevation change 74
m implies
a rapid submergence
of the type which
would have occurred
if the Mediterranean Sea had
broken
its
way into
the Black Sea via
the Bosporus
at 7.5 kyr BP. A massive input of saltwater is
expressed
in the abrupt shift positive
shift with q
magnitude of 4 to 6 7oo in the oxygen isotopes"'
and in the formation of a density
stratification in
the water column that quickly tume_d the sea
anoxic everywhere below -200 m"4. A fast
submergence of the landscape
would explain
the
preservation
of shelf-edge
river
channels
and sand
dunes from the destructive
processes
of the surf
zone.
The migration of the coast
far inland
would
also have caused the observed simultaneous
shutdown
in the delivery of detrital carbonate
and
reworked materials to the shelf
and the basin
plain
at the
time
of the marine
invasion and for
the,
That
the inundation was by water with an already
increased
salinity
is corroborated by the fact that,
unlike
the deep-basin sediments,
there is only a
very slight depletion of interstitial
chloride with
depth in the subsurface of the shelf76. Apparently
the transgressing sea percolated
directly
into the
open
pore
space
of the highly
permeable
and dry
Neoeuxine
shelly
gravel
and sands".
A catastrophic deluge through
the cataracts of
a narrow inlet is fully capable
of cutting into the
bedrock of the Bosporus and Dardanelles Straits
(Fig.8). Where drilled and sampled in the
Bosporus
Strait, the initial fill on the eroded
bedrock
in the bottom of this
gorge
contains large
blocks and boulders of the adjacent
Devonian and
Carbotrjferous
bedrock'" 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
kyr BP in
ageo'.
Sudden inundation of depressed, enclosed basins
are rare but real events.
At the beginning
of the
Pliocene
the drastically desiccated
Mediterranean
Sea81 filled via a gigantic Gibraltar waterfall.
Common to oceanic waterfalls is the fixed head of
the supplying water body.
As erosion deepens the
upstream cataract, the flow
through
the conduit is
amplified through positive feedback. A
conservative calculation based on turbulent
fluidss2 with boundary conditionss3 adapted to the
Bosporus-Marmara-Dardanelles flume system
yields
an inflow
of water of 50 to 100 km"/day.
This flux rate,
several
hundred
times
greater
than
the world's largest waterfall and a thousand
times
exceeding
the present
undercurrent,
is sufficient
to
have
raised
the level of
the Black Sea 30 to 60 cm
each day or to have topped up the basin
in a year
(Fig.9).
On flat regions of the shelf
and in the river
valleys the sea might have advanced
landward
at
almost 1 to 2 km per
day.
The roar
of the waterfall,
radiated by air and ground waves, would have
broadcast the enormity of its cascade to any
humans settled or wandering within 100 km of the
inlet.
G EA-ECO-
M AR|NA., A1 997
National lnstitute of Maine Geology and Geo-ecology of Romania
Prcc. lntern. Workshop on "Fluvial-Maine
lnteractions"
in Malnas, Romania, OcL1-7. 1996

W.B,F
Fig.9 Reconstructed
lake and sea levels
in ihe Aegean
(A),
Sea of Marmara (M), and Black Seas (BS), and their
connections/isolatiorrs via the Dardanelles
(D) and Bosporus
(B)
Straits.
An entrenched siream bed of the ancient Don River
Passes
though the Kerch Strait
(K$) Sea level in the Aegean
tracks the rise of ihe globai
ocean''"'.
The sedimentary
record
of
the
Black Sea
reveals
two intervals of isolation, during which
much
of its vast
continental shelf
r,vas
emerged
land. A brief Neoeuxine
transgression
takes
place
between
15 and 12
kyr BP, triggered by
large
flux
of melt.water,
.gupplied
frcrm the retreating Earents and
Scanclinavian
ice sheets"'and delivered
bv the Don and Dneiper
Rivers and
by an overflow
from the Caspian Sea3!'
50'71
This tinre
of high lake level
coinodes
with lt/elt-Water Pulse'l of ref (18).
The flooding
of marine
water
into the Black Sea at 7.5 kyr BP is
catastrophic,
and is accompanled by
the erosion of a gorge
along
the
inlet. ln the
span
of a year,
the
Eiack See is topped up the level
of the
Aegean
and is launched on its way
from
a freshwater
iake
to
an anoxic
brackish
sea.
Possible human response .
The geological evidence of an injection
of
saltwater
into a depressed
Neoeuxine
lake via a
Bosporus
cataract
lends credence
to the ancient
accounts
of a bursting of the sea though this
REFERENCES AND NOTES
1. All radiocarbon
dates are nonnalised
to a C-13
value
of -25
per
mil. The conventional
ages have
been reservoir corrected by 460 years based on
measurement
of rnolluscs collected in 1931. The
ages reported as kyr BP have been
converted
to
calendar
years using the calibration
program
of
Stuiver and
Braziunas
(1993)
for
ages
< 10 kyr BP
orifice. The Black Sea flood took place when
farming villages had already been established
in
Greece and southern Bulgariao",
in ^lhe lower
feaches
of the modern Danube
Rivero"
oo,
near the
coast of the Sea of MarmarasT
and in the Fertile
Crescentss.
At 7.5 kyr BP advanced farming,
with
the possible
use of the light plow and simple
irrigation techniques,
blossomed
in the Trans
Causasus
its sudden
introjuction
interpreted
as an
intrusion from the outside"".
Ar^o-und 7.4 kyr BP and within the span
of 100
yearso"
farming villages
spread along the major
river valleys of Germany, Austriq^ Czechoslovakia,
Poland
and the Low Countrieso''
o' Due to the
remarkable homogeneity of these cultural
deposits, archaeologists
have considered
a "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 south-
eastern Europe amo^qg^-
a mysteriously sparse
indigenous
pcpulation'"
o" Although the migration
model
has been challenged
and replaced
by one
of diffusion of skills rather than peopleo',
the
permanent
flooding of the expansive
shelf of the
Black Sea could have been and impetus to expel
into Europe and the Near East communities
of
farmers which had adapted to the natural
resoufces
of
the late Neoeuxine Black Sea, i.e.,
its
arable loess soils, the seasonal irrigation
of its
entrenching
rivers, and the fresh
moist loam
along
the retreating
shoreline
of its vast freshwater
lake
potentially
exploitable
for the springtime
growing
of
domesticated food crops.
Acknowledgements
The 1993 expedition
materialized though the
generous
assistance of the
officers
and crew
of the
RA/
Aquanaut, the Datasonics Corporation,
Falmouth, MA,
and R, Kosyan and E Kontar
of the P.P Shirshov
Oceanology Institute
M, Bruckner, R, Fairbanks,
T.
Guilderson,
B. Hatau, W. Haxby,
B. lf
ina,
S. Klimley,
W. Menke, L. Nevesskaya, and
J Weissel
provided
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D. Harris, l.
Hodder,
J.
Mellaaft, A Moore, J. Oates, C.
Renfrew, J.
Renfrew and
A Sherratt have
substantially
contributed
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archaeological
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with the
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41997
National
lnstltute
of Maine Geology
and Geo-ecology of Romania
Proc. lntefn. Workshop
an "Fluvial-Maine
lnteractions"
in Malnas, Romania,
Oct-1-7,
1996
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