The uppermost Pleistocene–Holocene mud drape across the Marmara Sea: quantification of detrital supply from southern Marmara rivers

The Marmara Sea (area 11,350 km2; volume 3,378 km3; central basins >1100 m deep) straddles the North Anatolian Transform Fault separating the Eurasian and Aegean-Anatolian tectonic plates. Along with the shallow straits of Dardanelles and Bosphorus (depths ~63 m and ~40 m, respectively), the Marmara Sea forms the only marine connection between the Black Sea and the eastern Mediterranean. During Pleistocene glacial stages, the modern straits were subaerial valleys and the modern Marmara basin was occupied by the landlocked Propontis Lake. Previous researchers attributed major portions of a widely distributed uppermost Pleistocene–Holocene mud blanket (locally >10–25 m thick; volume 43–47 km3) to transport of suspended load through one or both of the straits, as either the Aegean Sea (at ~13.8 cal ka) or the Neoeuxine Lake (today's Black Sea, at ~11.1 cal ka) began to spill into the Marmara basin. To test these suggestions, the thicknesses and volume of the mud blanket were determined from >5000 line-km of airgun, sparker and boomer profiles and >100 cores, and compared with the contemporary supply from local rivers to decide, by difference, if the straits might have had a significant role. Volume calculations for the detrital supply from rivers rely on (1) decades of daily water- and sediment-discharge data from gauging stations, acquired before 20th century dam construction and, independently, (2) the BQART model which uses a variety of hydrological, geomorphic, geological and climate data. These calculations demonstrate that >85–90% of the detritus in the offshore mud blanket was supplied by steep rivers (Kocasu River and its tributaries) and mountainous streams draining the highlands of the southern Marmara region. Geochemistry of the