Messinian forced regressions in the Adana Basin: a near-coincidence of tectonic and eustatic forcing

Authors: AYHAN ILGAR, WOJCIECH NEMEC, AYNUR HAKYEMEZ, ERHAN KARAKUŞ

Abstract: This sedimentological and sequence-stratigraphic study focuses on the late Miocene deposits in one of the largest peri-Mediterranean basins of southern Turkey, the Adana Basin, which formed as a Tauride foreland depression accumulating molasse deposits. The Tortonian-Messinian shallow-marine Handere Formation, previously interpreted as a regressive succession, appears to have recorded several relative sea-level changes. The formation base recorded a forced regression attributed to the end-Serravalian (Tor-1) eustatic fall in sea level. The lower to middle part of the formation is transgressive, culminating in offshore mudstones. The upper part is regressive and its 3 isolated conglomeratic members represent sharp-based Gilbert-type deltas with incised fluvial valley-fill deposits, recording a forced regression followed by marine reflooding. The time of this regression is biostratigraphically constrained to ~7.8 to 6.4 Ma B.P. on the basis of planktonic foraminifera in delta bottomset deposits. The regression is attributed to the tectonic conversion of the Adana foreland shelf into a piggyback basin, as indicated by seismic sections and compressional basin-margin deformation. The reflooding of the basin ~6.4 Ma B.P. is ascribed to a postthrusting flexural subsidence of the foreland under increased crustal load. The marine transgression brought an almost immediate evaporitic sedimentation, which suggests invasion of hypersaline Mediterranean water. The basin was subsequently emerged and its gypsiferous deposits were extensively eroded due to a second Messinian forced regression, attributed to the early evaporative drawdown in the Mediterranean Sea (~6 Ma B.P.). The postorogenic isostatic uplift of the Taurides had meanwhile elevated the basin enough to prevent its reflooding by the Zanclean regional transgression. Stratigraphic comparison with coeval peri-Mediterranean basins to the west demonstrates that interbasinal correlations are difficult, and that a superficial linking of comparable events may be quite misleading. The local timing of the late Miocene relative sea-level changes and the landward extent of the Zanclean flooding were apparently determined by the combination of eustasy, tectonics, basin topography, and sediment supply, whereby the eustatic signal was modulated and often obscured by local conditions. However, the individual basin-fill successions bear a high-resolution record of local events and give unique insights into the local role of tectonics, sediment yield, and sea-level changes.

Keywords: Sedimentology, sequence stratigraphy, Taurides, piggyback basin, Gilbert-type delta, incised valley-fill, Messinian salinity crisis, stratigraphic correlation

Full Text: PDF