EVOLUTION AND STEPWISE DROWNING OF A RAMP-TYPE CARBONATE PLATFORM IN THRACE BASIN, NW TURKEY (LATE MIDDLE EOCENE –OLIGOCENE)

The Sogucak Limestone is an Eocene shallow marine carbonate unit in the Thrace basin in northwest Turkey. The Formation has been studied in Pinarhisar, Catalca, Kirklareli, Karaburun and Samlar areas in the north, and Mecidiye, Pirnar, Murefte, Besyol in the south of the basin. The studied successions display a transgressive character including siliciclastic near shore and fluvial deposits on the basement rocks and platform carbonates and patch reefs at the top. The patch reefs display back and fore reef facies with limited extension.

Inner ramp is characterized by dasyclad algae, pecten, gastrapoda, miliolid foraminifera association and display bioturbated silty mudstone, bioturbated calcareous bioclastic sandstones, dasyclad algal, miliolid foraminiferal wakestones/packstones. In the inner ramp, lagoonal facies with limited extension characterized by ostracoda, gastrapoda, miliolid foraminifera association display dark colored mudstones and wakestones. Siliciclastic fluvial and beach facies have been observed in inner ramp environment in association with poorly sorted polygenic sandstone and cross-bedded conglomerate and well-sorted quartz sandstones.

Middle ramp is characterized by association of nummulitids, orthophragmines, and red algae. Coral patches and nummulite banks are observed as discontinuous features. Path reefs are composed of reef core, back and fore reef facies. Reef cores are composed of bufflestones, framestones, and bindstones. Back reefs display red algal, foraminiferal packstones, grainstones, wackestones. Fore reefs are composed of poorly sorted red algal, coral debris and poorly sorted polygenic carbonate breccia.

Outer ramp is characterized by association of rhodoid nodules, bryozoa, red algae, orthophragmines and display pelagic marls, porous chalks and fore reef talus in some places.

Patch reefs in the Thrace basin present a transgressive distribution from south (Early Bartonian) to north (Priabonian) and increase in abundance in the north.

Transgression of platform carbonates over the elevated basement metamorphics (paleohighs) without basal clastics in the north take place in the Early Priabonian and infill the Neptunian dykes.

In the Late Priabonian/Early Oligocene, drowning of the platform took place and characterized by bryozoan accumulations, iron and glauconite bearing surfaces on bioturbated bioclastic limestones with planktonic foraminifera, echinid, orthophragminid fragments and overlying pelagic marls with planktonic foraminifera and glauconite.

In the Oligocene, in some places, local unconformities overlie the platform carbonates. This may imply sudden uplift and tilting of blocks after drowning event, and abundance of dissolution porosities in platform carbonates take place beneath the unconformity surface.