Field insights into sediment delivery to the northwest Black Sea: the Late Miocene fluvio-deltaic Balta Fm of the East Carpathian Foreland

The NW Black Sea contains the basin’s largest clastic system, which is currently dominated by the Danube and delivers 90 MT of sediment per year. This is 75% of the flux through the Nile and more than twice the flux through the Niger. Recent successes of the Domino and Lira wells highlight this region’s large hydrocarbon exploration potential. Our ongoing field-based research is tailored to provide better constraints on the composition of potential clastic reservoirs in both the Romanian and Ukrainian offshore. Special emphasis is placed on an understanding of the spatial, temporal and compositional evolution of the different sediment supply systems during the Late Miocene, Pliocene and Pleistocene. Key elements addressed are the timing of the arrival of the Danube, and the significance of the Balta Delta of Moldova and Ukraine; a largely underappreciated, and frequently overlooked clastic system.

In this talk, we focus on sedimentary facies analysis of the Balta Fm, which was integrated with a review of published local literature, micropalaeontological results and historical borehole information. The lowermost part of the formation is clay dominated and consists of subordinate delta front sand bodies interspersed between muds. The middle unit contains separate delta plain channels or channel belts encased in thick muds. These are overlain by a unit with amalgamated delta plain channel deposits with only minor amounts of associated mud. The abundance of upper flow regime sedimentary structures in channel sands, the absence of peats (or coals) and the presence of calcareous nodules suggest a strongly seasonal and relatively dry climate with a flashy discharge regime. The Balta Fm offers an excellent example of a largely prograding fluvio-deltaic system that came into being due to a high sediment flux from the uplifted Carpathians and was accommodated in a broad foreland basin.