Eirik Larsen¹, T. Dreyer², W. Nemec¹, T.-R. Ellingsen¹

(1) University of Bergen, 5007 Bergen, Norway
(2) Norsk Hydro Research Centre, N-5020 Bergen

ABSTRACT: The Geometry and Facies Anatomy of Regressive Fan-Deltaic Wedges in an Open-Marine Graben: the Neogene Köprü Basin, Southwestern Turkey

The Köprü Basin was an asymmetric graben ~30km wide, open to south, with a submerged eastern margin and large fan deltas prograding from the north and obliquely from the western margin. The basin-fill pattern is exemplified by Altinkaya fan delta, which prograded southeastward in Serravallian-Tortonian time, is ~700m thick and consists of a series of regressive wedges (gentle clinothems) separated by transgressive deposits. The normal-regressive wedges have a gravelly part (10-11km radius) comprised of alluvium fringed with prominent beach facies, underlain by and passing seaward into sandy tempestitic shoreface and muddy offshore-transition facies. These wedges are lobate, up to 20m thick, and show little shore-parallel variation. The forced-regressive wedges have a longer gravelly part (13-15km) comprised of relatively thin (2-7m) erosive beach deposits underlain by lower shoreface or offshore-transition facies, and including one or two incised fluvial valleys, up to 30m deep and several hundred meter wide. The beach facies has a minor sandy fringe passing into offshore-transition deposits, whereas the gravel-filled valley passes into a submarine channel, up to 10-12m deep, filled with gravel-bearing sandy deposits of high-density turbidity currents. The currents were generated by powerful river effluent heavily charged with sediment, and their channeling may have been enhanced by syndepositional basin-floor faults. The southward extent of these paleochannels is uncertain, but the basin's deeper southern part abounds in sheet-like turbidites with southerly paleocurrents. The contrast between the tempestite-prone 2D wedges and turbidite-prone 3D wedges reflects the different behaviors of a wave-dominated fan delta during normal and forced regressions.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado