Basin Margin Clinoform Analysis in the Dacian Basin of the Paratethys Domain, Romania

Fongngern, Rattanaporn; Steel, Ron; Olariu, Cornel

Large scale, approximately 400 m high, upper Miocene clinoforms have been documented in 3-D seismic data of the Dacian Basin (7-4 Ma) that is a marginal basin that was occasionally connected with the Black Sea Basin. This study is the first to integrate outcrop, well log and seismic data to interpret depositional settings, filling mechanisms and eventually sediment transport to the Black Sea focusing on understanding the clinoforms in the western Dacian Basin.

3-D seismic data shows clinoform features that infer shelf-edge progradation for 20-25 km from at least two main directions: N-S and E-W. There are incised valleys and multiple slope channels, varying in size from 300 to1,500 m wide, on the clinoform foresets. These observations imply erosion on the shelf and sediment bypass to the basin floor.

A typical motif on the western Dacian Basin well logs is a thousand-meter stacking of sandy-muddy-sandy deposits that are composed of thick sandstone beds (Meotian), mudstones with rare sandstones (Pontian), and thick coarsening-upward sandstone successions (Dacian). This overall succession might represent the bottomsets-foresets-topsets of the large clinoforms that filled the basin and are observed on seismic data. The idea that Meotian-Pontia-Dacian deposits are genetically linked is departing from the conventional layer-cake stratigraphy of the basin.

From outcrop observation, Meotian deposits are interpreted to be delta front and prodelta turbidites associated with deformed remobilized bodies downdip. Pontian deposits are mud dominated with mollusk fossils occasionally interbedded with cm thick fine sandstones and rarely encase sandstone bodies representing low energy shelf to outer-shelf environments. Incised valley fills, shallow water and fluvial deposits with coal fragments and thin coal seams are characteristic of Dacian time. These observations imply that depositional environments have changed due to progressive filling up of the basin.

Study of the western Dacian Basin filling history could lead to better understanding of sediment transfer from the Carpathians into a deeper water setting. The understanding of the clinoform genesis and evolution is significant for coal and hydrocarbon exploration not only within this particular basin but also for the adjacent Black Sea Basin, which is the larger sediment sink. Additionally, we are working further with thick turbidite deposits at the clinoform toes in the western Dacian Basin

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013