Late Quaternary co-seismic sedimentation in the Sea of Marmaras deep basinsReport as inadecuate

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1 LGCA - Laboratoire de Géodynamique des Chaines Alpines 2 GEOAZUR - Géoazur 3 EPOC - Environnements et Paléoenvironnements OCéaniques 4 GEOLOGY AND MINING DEPARTMENT - ITU 5 LDEO - Lamont-Doherty Earth Observatory 6 CEREGE - Centre européen de recherche et d-enseignement de géosciences de l-environnement 7 IPGP - Institut de Physique du Globe de Paris

Abstract : The deep, northern, part of the Sea of Marmara northwestern Turkey is composed of several aligned, actively subsiding, basins, which are the direct structural and morphological expression of the North Anatolian Fault-s northern branch. The last 20 kyr of their sedimentary fill lacustrine before 12 kyr BP have been investigated through giant piston coring onboard R-V MARION-DUFRESNE MARMACORE Cruise, 2001 and chirp subbottom profiler onboard R-V ATALANTE during MARMARASCARPS Cruise 2002. Especially during the lacustrine stage, the infilling of the deep basins Tekirda?, Central, Kumburgaz, and Çinarcic Basins; up to 1250 m depth was dominated by turbidites with coarse mixed siliciclastic and bioclastic basal part, intercalated in -hemipelagic-type- finegrained calcareous and slightly siliceous clays. Often – especially in the thickest ones – the turbidites show strong segregation and a sharp boundary between coarse part and suspendedload part. In the Central Basin, 8 m of a unique sedimentary event include a 5 to 8m-thick -homogenite- well imaged on seismic profiles. The latter is interpreted as related to a major – possibly triggered - tsunami effect, as described in the Eastern Mediterranean by Kastens and Cita 1981. In the marine Holocene upper part of the sedimentary fill, repeated to-and-from structures, affecting silt or fine sand, are evidencing seiche-like effects and, thus, earthquake triggering. Detailed correlations between two deep coring sites 1250 and 1200 m indicate more than 100 % overthickening in the deepest one; this implies specific processes of distribution of terrigenous input by dense hyperpycnal currents high kinetic energy, seiche effect, complex reflections on steep slopes. The peculiar sedimentary infilling of the Sea of Marmara-s Central Basin and, by extrapolation, of the whole set is tentatively interpreted as a direct consequence of the strong seismic activity; the imprint of the latter is more obvious prior to the base of the Holocene, as environmental conditions favoured marginal accumulation especially on the southern shelf of large amounts of erosion products available for mass wasting.

Keywords : homogenites Sea of Marmara Late Quaternary cores high resolution seismic earthquakes turbidites homogenites.

Author: Christian Beck - Bernard Mercier de Lépinay - Jean-Luc Schneider - Michel Cremer - Namik Cagatay - Evrard Wendenbaum - Sébastie



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