Sedimentology, cyclostratigraphy, sequence stratigraphy and geochemistry of the middle eocene lacustrine-marine oil-shales transition, Mudurnu Göynük basin, NW Anatolia, Turkey

Afridi, Bakht Zamir
Continuous studied successions of the Middle Eocene, Mudurnu-Göynük basin, in the NW Anatolia indicate a transition from marine-influence lacustrine to marine environment due to the relative rise in sea-level, which was separated by barrier deposits. Different lithofacies are identified in the studied sections, including limestone, marl, oil-shale, calcareous sandstone, conglomeratic and bio-calcirudite. Number of fossil assemblages are recorded including ostracods, charophyte gyrogonites, gastropods, bivalve and b enthic foraminifera, rare fish-teeth-scale, echinoderms, algal filamentous and plant fragments. The recorded ostracod interprets Oligo-Mesohaline lacustrine environment, which is overlain by marine environment. Based on the detailed facies analysis, the depositional environment is characterized as relatively marginal to deep lacustrine- marine deposits, floodplain to paralic-marine deposits, from south to north. The lacustrine deposits indicate balanced-fill type lake setting within the regime in foreland setting in relation to İzmir-Ankara suture. The centimeter-meter scale order cycles show symmetrical to asymmetrical transgressive-regressive cycles, which is due to repetitive change in the water-depth and/or fluctuating sediments influx. The cm-m scale cycles correspond to Milankovitch obliquity band and indicate climatic control linked with the earth`s orbital forces and local tectonics. In the sequence framework, the successions indicate marine transgression onto lacustrine en vironment in the region. The studied sections indicate a change from TST to HST in lacustrine-marine deposits. Lacustrine and Marine oil-shales in the studied area are interpreted that they have a possible source rock potential in the central and north, and in the south of the basin.