Lacustrine trace fossils and environmental conditions in the Early Miocene Ermenek Basin, southern Turkey

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.