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Status of the Black Sea flood hypothesis
Abstract and Figures
Exploration of the Black Sea shelf reveals two major shelf-crossing unconformities. The older unconformity separates mostly-barren deposits of late glacial age from overlying Neoeuxinian sediment containing fresh to brackish fauna. This unconformity can be traced over the shelf edge to depths beyond –140 m. The substrate below is dry, firm, and contains unchallenged evidence of subaerial exposure at least to depths of –110 m. The Neoeuxinian cover is present on the outer shelf and is preserved, though incompletely, in depressions on the middle and inner shelf. It is even found as subsurface valley fill in the coastal limans and Sea of Azov. The Neoeuxinian on the shelf represents a transgression leading to a highstand at ~ –20 m below today's sea surface, which was reached by 10,000 BP (uncorrected). Sediments with marine fauna lie above the Neoeuxinian and are separated from it by a sand to gravel layer that represents a younger unconformity. In the limans, the hiatus between the Neoeuxinian and overlying Bugazian is called "peririf" and on the shelf a "washout." Dune fields between –65 and –80 m and wave-truncated terraces with beach-like berms at –90 to –100 m contain shell material dated between 9500 and 8500 BP, suggesting that the younger unconformity represents a post-Younger Dryas regression that took the surface of the Black Sea's lake below the level of the global ocean. Strontium isotopes document the first arrival of saltwater at 8400 BP. Objections to the rapid flooding hypothesis in which Mediterranean water initially poured into a low-lying enclosed lake are centered on the interpretation of the younger unconformity as evidence of either (1) subaerial erosion (and thus a major early Holocene regression) or (2) underwater erosion that does not require a regression. When examined, specific criticisms appear to be based on different interpretations of observations but do not as yet present a concrete refutation of a lowstand of the lake prior to the Mediterranean connection. The flooding hypothesis is today just as vulnerable as when it was first formulated. It serves to best account for the ubiquitous nature of the younger unconformity that not only appears in sediment cores but is also widely mapped by high-resolution reflection profiling. Greater attention needs to be paid in the future to a more comprehensive investigation to find the cause of the younger unconformity.
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... Bukry et al. (1970Bukry et al. ( ), 1974 found both calcareous nannoplankton species Emiliania huxleyi and Braarudosphaera bigelowii in Unit 1, where the salinity was above 17‰ for allowing their survival; the authors proposed that the fine laminae <1 mm in thickness might represent annual blooms of E. huxleyi. A lithologic feature of Unit 3 described by Ross and Degens (1974) is the occurrence of red-brownish clays, interbedded with gray-greenish ones, in the cores of the western Black Sea (Ryan, 2007). Recent studies (Soulet et al., 2013) linked their origin to two possible provenances: (i) drainage of the Fennoscandian ice sheet through the Dnieper River, via proglacial Lake Disna into the Black Sea, or (ii) through the Danube River, supplied by glaciers from the Alps. ...
... The Bølling-Allerød CaCO 3 peak, along with a younger one, corresponding to the Pre-Boreal, were previously described as peaks C1 and C2 (Major et al., 2002;Ryan, 2007). They are separated by a significant CaCO 3 decrease of the Younger Dryas, a trend first reported by Khrischev and Georgiev (1991) in the core A96. ...
... Absolute ages after Nagavciuc et al. (2021). BA-Bølling Allerød; YD -Younger Dryas; PB-Pre-Boreal; C1 and C2 -noted after the peaks described by Major et al. (2002) and Ryan (2007) in other cores from W Black Sea. ...
We provide new data on the Black Sea evolution during the preconnection and reconnection stages with the
Mediterranean, based on sedimentology, geochemistry, calcareous nannoplankton and ostracods analysis, in 13
cores placed between 141 m and 1315 m water depths. Unit 1 – The Coccolith Mud, Unit 2 - The Sapropel Mud
and Unit 3 – The Lacustrine Lutite, including red-brownish depositional intervals, were identified in all studied
deep-water cores. These units are not present in a shallow setting, i.e., above 166.7 m water depth, being
replaced by sandy levels and shell debris. The red-brownish layers are interpreted as hyperpycnites, but some of
the red successions show turbidite features, especially the ones situated on canyon sides, at a water depth below
600 m. In the oldest intercepted Unit 3 of the Neoeuxinian lake, CaCO3 values are constantly low, but towards
the top of this unit they show two distinct peaks, interpreted as signals of Bølling–Allerød and Preboreal interstadials.
In
between,
a
significant
decrease
in
CaCO3
values, linked to the setting of the Younger Dryas, is
coincident in the deep cores with diatom blooms and high frequency of ostracods related to cooler waters. The
scarce but continuous occurrence of Emiliania huxleyi nannoplankton species from the top of Unit 3 indicates that
the salinity was at least 10–11‰ prior the Sapropel Mud deposition and increase at a least 17‰ within the lower
part of Unit. 2. In the same interval, the Ponto-Caspian ostracods are still present. The Mediterranean ostracods
consistently occur from the top of Unit 2, when bottom water salinity reached values for allowing their survival.
The first bloom of E. huxleyi is placed at the base of Unit 2, where coccolith laminae occur, while the second
bloom is placed in Unit 1 that contains exclusively Mediterranean ostracods and consistent assemblages of
benthonic foraminifers, similar with the ones present today.
... Bukry et al. (1970Bukry et al. ( ), 1974 found both calcareous nannoplankton species Emiliania huxleyi and Braarudosphaera bigelowii in Unit 1, where the salinity was above 17‰ for allowing their survival; the authors proposed that the fine laminae <1 mm in thickness might represent annual blooms of E. huxleyi. A lithologic feature of Unit 3 described by Ross and Degens (1974) is the occurrence of red-brownish clays, interbedded with gray-greenish ones, in the cores of the western Black Sea (Ryan, 2007). Recent studies (Soulet et al., 2013) linked their origin to two possible provenances: (i) drainage of the Fennoscandian ice sheet through the Dnieper River, via proglacial Lake Disna into the Black Sea, or (ii) through the Danube River, supplied by glaciers from the Alps. ...
... The Bølling-Allerød CaCO 3 peak, along with a younger one, corresponding to the Pre-Boreal, were previously described as peaks C1 and C2 (Major et al., 2002;Ryan, 2007). They are separated by a significant CaCO 3 decrease of the Younger Dryas, a trend first reported by Khrischev and Georgiev (1991) in the core A96. ...
... Absolute ages after Nagavciuc et al. (2021). BA-Bølling Allerød; YD -Younger Dryas; PB-Pre-Boreal; C1 and C2 -noted after the peaks described by Major et al. (2002) and Ryan (2007) in other cores from W Black Sea. ...
We provide new data on the Black Sea evolution during the preconnection and reconnection stages with the Mediterranean, based on sedimentology, geochemistry, calcareous nannoplankton and ostracods analysis, in 13 cores placed between 141 m and 1315 m water depths. Unit 1 – The Coccolith Mud, Unit 2 - The Sapropel Mud and Unit 3 – The Lacustrine Lutite, including red-brownish depositional intervals, were identified in all studied deep-water cores. These units are not present in a shallow setting, i.e., above 166.7 m water depth, being replaced by sandy levels and shell debris. The red-brownish layers are interpreted as hyperpycnites, but some of the red successions show turbidite features, especially the ones situated on canyon sides, at a water depth below 600 m. In the oldest intercepted Unit 3 of the Neoeuxinian lake, CaCO3 values are constantly low, but towards the top of this unit they show two distinct peaks, interpreted as signals of Bølling–Allerød and Preboreal interstadials. In between, a significant decrease in CaCO3 values, linked to the setting of the Younger Dryas, is coincident in the deep cores with diatom blooms and high frequency of ostracods related to cooler waters. The scarce but continuous occurrence of Emiliania huxleyi nannoplankton species from the top of Unit 3 indicates that the salinity was at least 10–11‰ prior the Sapropel Mud deposition and increase at a least 17‰ within the lower part of Unit. 2. In the same interval, the Ponto-Caspian ostracods are still present. The Mediterranean ostracods consistently occur from the top of Unit 2, when bottom water salinity reached values for allowing their survival. The first bloom of E. huxleyi is placed at the base of Unit 2, where coccolith laminae occur, while the second bloom is placed in Unit 1 that contains exclusively Mediterranean ostracods and consistent assemblages of benthonic foraminifers, similar with the ones present today.
... According to the fossil content and lithology, unit 5 was deposited under fluviatile-lacustrine conditions during the last glacial-late glacial lowstands, when the Tarabya Considering that the last Mediterranean connection of the Black Sea via the Bosphorus is known to have taken place at 8.4 14 C ka BP (c. 9 cal ka BP) (Major et al. 2006;Ryan 2007;Soulet et al. 2011), a time lag of 3.1 kyr exists between the initial marine connection of the Black Sea and the first sediment accumulation with the euryhaline Mediterranean fauna at this location in the central Bosphorus sedimentary sequence. This time gap, represented by the disconformity between units 5 and 4 in the Bosphorus succession, is most likely to have been caused by erosion and or non-deposition after the initiation of a strong Mediterranean current towards the Black Sea (Fig. 7). ...
... With regard to the formation of the channel-levee fan complex in the Bosphorus outlet area of the Black Sea shelf, the seismic and core data have been interpreted differently by different studies. According to Flood et al. (2009), the anastomosed channel network complex was formed under subaqueous conditions by the saline Mediterranean underflow when the Black Sea 'lake' was in an outflow mode via the Bosphorus, implying that the surface of the 'lake' was above the elevation of the outflow sill, as opposed to the earlier suggestion of other studies that the 'lake' level was near the shelf edge at a depth of c. 100 m (Ryan et al. 1997(Ryan et al. , 2014Ryan and Pitman 1998;Ryan 2007;Lericolais et al. 2019). To explain the α unconformity and the overlying chaotic unit, Algan et al. (2007), Ryan et al. (2014) and Lericolais et al., (2019) have suggested that the fan system was initiated by an abrupt inflow of Mediterranean waters that rapidly submerged the subaerial Black Sea 'lake' shelf. ...
The Bosphorus (Istanbul Strait) is natural strait that connects the Black Sea with the Aegean Sea via the Sea of Marmara and Dardanelles Strait. It is a 31 km long and 3.5 km wide winding channel, with an irregular bottom morphology. It has depressions up to -110 m deep, and two sills with depths of -35 and -58 m in the south and north, respectively.
Presently, a two-layer water exchange exists through the strait, with the Mediterranean and Black Sea waters forming the lower and upper layers, respectively. The Bosphorus channel extends as shelf valleys on the Black Sea and Sea of Marmara shelves. However, it operated as a river valley or an estuary during the stadial low-stand periods.
The infill sedimentary succession of the Bosphorus channel is up to ∼100 m thick above the Palaeozoic-Cretaceous basement with an irregular topography. The oldest sediments are sandy to muddy fluvial-lacustrine facies of late Pleistocene age, which are preserved only in up to -160 m-deep scoured depressions of the basement. They are overlain by mid-late Holocene estuarine-marine shelly sandy to muddy sediments with patches of bioherms and shelly lag deposits.
The Bosphorus outlet areas of the Black Sea and Sea of Marmara are characterized by a submarine fan and a shelf valley, respectively. The fan system in the Black Sea started depositing ∼900 yr after the initial vigorous marine water incursion at ∼8.4 ¹⁴ C kyr BP. On the Marmara shelf, extension of the Bosphorus channel is a sinuous shelf valley with a channel-leveé complex, which was deposited by the Black Sea outflow during the 11-10 ¹⁴ C kyr BP. Catastrophic floodings of the Sea of Marmara by torrential Black Sea outflows during the Greenland Interstadial melt water pulses, as well as the strong Mediterranean current towards the Black Sea during the interglacial periods, were responsible for carving the Bosphorus channel and the shelf valleys, as well as removing the sediments belonging to the earlier periods.
... Material and methods 14 C dating was performed on shells in BLKS9810 and C10 cores ( Table 2). The results are given in years BP, but were not calibrated because of the difficulties involved in attributing reasonable radiocarbon reservoir ages in the Black Sea and Marmara Sea basins (Ryan 2007;Fontugne et al. 2009;Soulet et al. 2011;Çağatay et al. 2015). ...
... The second central point of discussion about human exploitation of the Dniester-Dnieper area during the Boreal period is connected with our understanding of the mode of life, system of occupation, and procurement as a response to environmental changes in the northwestern Pontic region at the Pleistocene-Holocene boundary. Proponents of the so-called 'catastrophic flood' scenario of the northwestern Black Sea shelf suggest that a rapid rise in the level of the Black Sea practically desolated the local population that had settled there living on agriculture and cattle breeding which they brought from the west (Ryan, 2007;Zalizniak, 2005). ...
... Material and methods 14 C dating was performed on shells in BLKS9810 and C10 cores ( Table 2). The results are given in years BP, but were not calibrated because of the difficulties involved in attributing reasonable radiocarbon reservoir ages in the Black Sea and Marmara Sea basins (Ryan 2007;Fontugne et al. 2009;Soulet et al. 2011;Çağatay et al. 2015). ...
High-resolution pollen analyses were performed on two cores from the western Black Sea and one core from the Marmara Sea, covering the Late Glacial-Holocene transition using 14C chronology. Particular effort was invested in the botanical identification of pollen grains thereby significantly improving our knowledge of regional flora. When interpreted with respect to modern vegetation, pollen records revealed all the major changes caused by climatic fluctuations over the last 20,000 years. The results of this study provide evidence for the occurrence of relict thermophilous-hygrophilous trees (papillate Cupressaceae, Carya, Liquidambar, Zelkova) in certain refugia up to the Holocene. Vegetation dynamics is specified for some taxa (e.g. Cupressus–Juniperus, Fagus, Cedrus) and some ecosystems (e.g. mesophilous forests, Mediterranean sclerophyllous populations, steppes). Pollen data enabled palaeoclimatic reconstructions which were compared with available estimates in the region. The use of a powerful pollen ratio between ‘thermophilous and steppe taxa’ led to fruitful climatostratigraphic relationships with the oxygen isotope curve from the NGRIP core. The Younger Dryas and cooling at 8.2 ka are among the most obvious climatic phases identified in the three cores studied here.
This review and synthesis weaves various multiproxy data into a single coherent narrative for the latest Pleistocene–Holocene paleoclimatic and paleoceanographic evolution of the Black Sea, Marmara Sea and the Aegean Sea. This narrative, referred to as the “Outflow Hypothesis” rests on several key observations and interpretations which are incompatible with the suggestion that the post-LGM reconnection of the Black Sea basin to the global ocean occurred as a catastrophic flood. The widespread occurrence of sub-storm-wavebase uppermost Pleistocene to lower Holocene sediments across the southwestern Black Sea shelf at elevations as shallow as −78 m shows that the level of the Neoeuxine Lake (today's Black Sea) between 12.3 cal ka and 9.5 cal ka was high enough to spill outward into the Marmara Sea over the shallow sill in the southern Strait of Bosphorus (−37 m today). Southwest-prograded clinoforms immediately south of the strait in the northeastern Marmara Sea record the development of an early Holocene (11.1–10.2 cal ka) mid-shelf delta (Δ1) showing ~3.3 km of aggressive progradation while its topset-to-foreset break climbed 8–9 m into a rising Marmara Sea. A streamlined south-prograded barform in the throat of the strait and giant megaflutes along its thalweg confirm the vigorous outflow from the early Holocene Neoeuxine Lake required to explain the climbing Δ1 lobe. Multiproxy data from the northeastern Marmara Sea and southwestern Black Sea shelves indicate that the post-Last Glacial Maximum (LGM) reconnection of the Black Sea with the eastern Mediterranean occurred in a gradual fashion: first, at ~10.2 cal ka, a salt wedge lifted the brackish outflow off the floor of the Strait of Bosphorus terminating Δ1 progradation; second, a more persistent density underflow introduced enough seawater strontium into the Black Sea to be taken up in mollusc shells by ~9.5 cal ka, and finally a range of euryhaline marine organisms replaced lacustrine faunas when salinity levels became favourable by ~7.5 cal ka. The onset of sapropel M1 deposition across the Marmara Sea followed the breach of the Strait of Dardanelles at 13.8 cal ka when, as originally suggested by other researchers, nutrient-rich highly saline Mediterranean waters forced lower density relict lacustrine waters to the surface and then out through the Strait of Dardanelles, initiating water-column stratification. Once the low-salinity cap was expelled, the deep waters of the fully saline Marmara Sea remained stagnant and sapropel accumulation continued. The onset of outflow from the Neoeuxine Lake at 11.1 cal ka re-established water-column stratification, induced effective deep circulation across the Marmara Sea, and created a low salinity lid across the northern Aegean Sea, initiating sapropel S1 deposition in that area.
This volume honors Eldridge Moores, one of the most accomplished geologists of his generation. The volume starts with a summary of Moores’ achievements, along with personal dedications and memories from people who knew him. Leading off the volume’s 12 chapters of original scientific contributions is Moores’ last published paper that presents an example of the Historical Contingency concept, which suggested that earlier subduction history may result in supra-subduction zone geochemical signatures for some magmas formed in non-subduction environments. Other chapters highlight the societal significance of geology, the petrogenesis of ophiolites, subduction zone processes, orogenic belt evolution, and other topics, covering the globe and intersecting with Moores’ interests and influences.
Outbursts from impounded water bodies produce large, hazardous, and geomorphically significant floods affecting the Earth as well as other planetary surfaces. Two broad classes of impoundments are: (1) valleys blocked by ice, landslides, constructed dams, and volcanic materials; and (2) closed basins such as tectonic depressions, calderas, meteor craters, and those rimmed by glaciers and moraines. In some environments, floods emanate from subglacial and subterranean sources. Outburst floods are geomorphically important over geologic time because large flows achieve exceptional shear stress and stream power values, thus forming some of the most spectacular landscapes in the solar system.
A series of case studies, derived from Holocene palaeoenvironmental investigations, archaeology, and history, are used to analyze ancient natural hazards and their impact on societies. The evolution of societies is inscribed in geomorphology, as a close relationship exists between the landscape and humans. Four factors underpin disasters: time, space, type of society, and type of event. In some cases, disasters apparently caused civilization to collapse, but, in other cases, they have spawned innovations and led to more resilient societies. In the face of landscape change, our modern society should not be lured by technology and globalization, as these could become more sources of vulnerability than of prevention and mitigation. Changes always have a cost. Civilizations have always had difficulties coping with the element of surprise in a hazard; this will remain uncontrollable. If a natural hazard occurs in a restricted area of the planet, its impact may be felt worldwide due to our current great interconnectedness.
The radiocarbon method for determining the absolute age acquired wide application in marine geological research as well.
In the 1977-1980 period analysis was made of 28 specimens taken from seven drillings of bottom sediments from the periphery of the shelf.
The results obtained show that Holocene sediments, stratigraphically identified according to mollusks fauna, are distributed in the following age range: Upper Holocene — between 0 and 4 thousand years; Middle Holocene — between 4 and 7 thousand years; Lower Holocene — between 7 and 9 thousand years.
Upper Pleistocene (Novoeuxine) deposits have an age range between 9 and more than 31 thousand years. According to the analyses obtained, the boundary between Holocene and Pleistocene is dated to about 9 thousand years.
The deposits containing Chaudinian fauna have absolute age exceeding 50 thousand years.
The absolute datings obtained make possible to solve a number of problems in the sphere of sedimentology, e. g. determination of the sedimentation rate, absolute masses and a number of paleographic problems.
The peripheral area of the shelf represents an area of 5 to 25 km width which reaches downwards to 80-120 m and comprises the peripheral depression, the zone of accumulated ramparts and the peripheral terrace. The thickness of the Quaternary deposits of the ramparts is greatly reduced. The older Lower Pleistocene coastline in the region of the ramparts is probably an inherited old lagoon. The Holocene deposits in the peripheral depression and between the ramparts reach a thickness of over 300 cm while they are very thin or lacking on the ramparts. -from Abstracts of Bulgarian Scientific Literature.
Based on analysis of the molluscan fauna and the associations of spores and pollen, collected from three sections in the marginal part of the shelf and the upper part of the continental slope, a stratigraphical subdivision is made and 3 spore-pollen zones are distinguished: 1) with Tschaudinian fauna marks the Mindel glaciation; 2) with a Neo-Euxinian fauna corresponds to the late glaciation period; 3) contains faunistic complexes of Bugasian, Vitjazevian and Calamitian layers. It was formed in humid, warm climate during the Holocene. The boundaries between the zones are water-worn. -from Abstracts of Bulgarian Scientific Literature
Presents a map of the paleogeography of the Black Sea at 18 000 yr BP and describes the ways in which the evidence was collected and interpreted. -K.Clayton