ASGP (2007), vol. 77: 123-139
LACUSTRINE TRACE FOSSILS AND ENVIRONMENTAL CONDITIONS IN THE EARLY MIOCENE ERMENEK BASIN, SOUTHERN TURKEY
Alfred UCHMAN (1), Wojciech NEMEC (2), Ayhan ILGAR (3) & Carlo MESSINA (4)
1) Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, 30-063 Kraków, Poland, e-mail: alfred.uchman at uj.edu.pl
2) Department of Earth Science, University of Bergen, 5007 Bergen, Norway
3) General Directorate of Mineral Research and Exploration (MTA), 06520 Ankara, Turkey
4) Department of Geological Sciences, University of Catania, 95129 Catania, Italy; presently at: Statoil Research Centre, Rotvoll, 7005 Trondheim, Norway
Uchman, A., Nemec, W., Ilgar, A. & Messina, C., 2007. Lacustrine trace fossils and environmental conditions in the Early Miocene Ermenek Basin, southern Turkey. Annales Societatis Geologorum Poloniae, 77: 123-139.
Abstract: The Early Miocene lacustrine succession of the Ermenek Basin, an intramontane graben in southern Anatolia, consists of hemipelagic, variably calcareous mudstones and pelagic marlstones densely interspersed with tempestite sandstone sheets, subordinate turbidite sandstone sheets and sporadic layers of evaporitic limestone. The marly lake was hydrologically closed and mainly no deeper than 10 m, with the mean fairweather wave base at 1.5 m and storm wave base around 5 m. The deposits abound in trace fossils, including Vagorichnus cf. anyao (its second recognized occurrence), endichnial ferruginous ribbons, large tubular structures, oblique cylinders, small discontinuous ridges, undulating ridges, planar wall structures and a range of other bioturbational features. The tempestites and turbidites show both pre-and post-event trace fossils, with recognizable mixed and transitional layers similar as reported from marine tempestites and turbidites. The trace fossils constitute an impoverished Mermia ichnofacies indicating a considerable environmental stress. The lake salinity fluctuated, and the stress factor is attributed to the extreme environmental conditions (increased salinity and unusual water chemistry) caused by episodes of brackishness due to decreases in rainfall and increases in evaporation. Freshwater conditions are indicated by benthic ostracods and mollusc shells in offshore mudstones and by gastropod shells in coastal coal deposits, whereas marly layers contain only the ostracod species Miocyprideis glabra asulcata, implying mesohaline to polyhaline conditions.
