HR: 10:50h
AN: PP32A-03    [Abstracts]
TI: Megafloods in Marginal Basins: New Data from the Black Sea
AU: * Giosan, L
EM: lgiosan@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Mart, Y
EM: y.mart@research.haifa.ac.il
AF: Recanati Institute for Marine Studies, University of Haifa, Mount Carmel, Haifa, ISR 31905 Israel
AU: McHugh, C M
EM: cecilia@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W , Palisades, NY 10964 United States
AU: McHugh, C M
EM: cecilia@ldeo.columbia.edu
AF: Queens College, City University of New York, 65-30 Kissena Blvd., Flushing, New York, NY 11367 United States
AU: Vachtman, D
EM: vachtman@bgu.ac.il
AF: Ben-Gurion University of the Negev, Department of Geography and Environmental Development, Beer Sheva, 84105 Israel
AU: Cagatay, N M
EM: cagatay@itu.edu.tr
AF: Istanbul Technical University, Ayazaga, Istanbul, 80626 Turkey
AU: Kadir, E K
EM: keris@itu.edu.tr
AF: Istanbul Technical University, Ayazaga, Istanbul, 80626 Turkey
AU: Ryan, W B
EM: billr@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W , Palisades, NY 10964 United States
AB: One of Jim Kennett's long-standing scientific interests has been the study of abrupt events ranging from destabilization of the gas hydrate reservoir, to volcanism, to megafloods. In appreciation to his contribution to the study of catastrophes in paleoceanography, we present new data on the Holocene reconnection of the Black Sea basin to the ocean, resulting from a July 2005 survey aboard the R/V Mediterranean Explorer of the EcoOcean Foundation. The survey included tightly-spaced Chirp subbottom profiling on the outer shelf northwest of the Bosporus outlet (Istanbul Bogazi), combined with precisely targeted gravity coring. Subbottom horizons are calibrated by radiocarbon and optical luminescence ages on cores. Chirp profiles reveal channels and ridges nearly transversal to the bathymetric contours. Ridges have grown on a seaward-dipping erosion surface that truncates the top of older prograding clinoforms. The ridges are up 12 m in height and have an asymmetrical cross-section, gentler on the west and steeper on the east. Sediment drifting is apparent on the gentler side. In the interiors of the ridges we found highly reflective mounds that are rooted directly on the erosion surface. The mounds organize in both elongated and circular to oval features. Shell-bearing marine mud drapes the mounds. Between the ridges and mounds the drape rests directly on the erosion surface that can be traced seaward to beyond -120 m. High abundance of exceptionally large shells of Mytilus sp. at the base of the drape suggests that bedforms were seeded by a colonization of mollusks building bioherms right on top of the erosion surface beginning at the time of the Mediterranean connection. The Black Sea lacustrine stage experienced an evaporative drawdown below its outlet and has only tracked the global sea level rise since 8.4 ky bp. The saltwater megaflood from the Mediterranean led to dramatic morphologic reorganization of the shelf sea-floor close to the Bosporus and exceptional preservation of shorelines and coastal bedforms elsewhere. The continued input of Mediterranean water has cut a network of channels through the ridges. Presumably the bioherm explosion was shut down by changes in salinity, nutrient budget, or nepheloid layer activity or it was soon terminated by anoxia. Sediment bodies formerly interpreted as lagoons are mud drifts in the lee of the bioherm ridges and mounds.
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 1817 Extreme events
DE: 1824 Geomorphology: general (1625)
DE: 3002 Continental shelf and slope processes (4219)
DE: 4999 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005