Holocene source rock deposition in the Black Sea, insights from a dropcore study offshore Bulgaria
M. Fallah, J. Mayer, G. Tari, J. Baur, 2018. "Holocene source rock deposition in the Black Sea, insights from a dropcore study offshore Bulgaria", Petroleum Geology of the Black Sea, M. D. Simmons, G. C. Tari, A. I. Okay
Download citation file:
One of the main issues in source rock evaluation has always been the availability of thermally immature samples, which would represent the same source rock quality and facies as the mature source rock within the deeper parts of the basin. Forty dropcore sample locations from shallow depths beneath the present-day seafloor were selected and analysed for mineral composition and bulk geochemical parameters. The water depths of the samples range from shelfal to bathyal environments. The quartz content of the samples clearly decreases with increasing distance from sedimentary input sources (e.g. river deltas), whereas clay content increases towards the distal areas. Mass movements (e.g. slides and debris flows) along the present-day shelf are recognizable on the bathymetry, as well as in the mineral content. Bulk geochemical parameters show that currently only poor to fair gas-prone source rocks are deposited within the study area. This lack of source rock quality, as well as organic content, is attributed to the fine-grained sedimentary input from the Danube river. These fine-grained sediments decrease the organic productivity due to dulling (decrease in the thickness of the photic zone) of the water column, and dilute the currently deposited source rock with low TOC sediments. These effects decrease with distance from the Danube delta, as indicated by published data from outside the study area. Additionally mass movements along the present-day shelf rework possible source rocks. The results of this study clearly show that anoxic conditions alone are not sufficient for source rock deposition. Distance from major sedimentary input and basin geometry are of major importance, and should be considered in basin modelling.
Figures & Tables
The Black Sea remains one of the largest underexplored rift basins in the world. Future success is dependent on a better understanding of a number of geological uncertainties. These include reservoir and source rock presence and quality, and the timing of migration of hydrocarbons relative to trap formation. An appreciation of the geological history of the Black Sea basins and the surrounding orogens is therefore key. The timing of basin formation, uplift of the margins, and of facies distribution remain issues for robust debate. This Special Publication presents the results of 15 studies that relate to the tectono-stratigraphy and petroleum geology of the Black Sea. The methodologies of these studies encompass crustal structure, geodynamic evolution, stratigraphy and its regional correlation, petroleum systems, source to sink, hydrocarbon habitat and play concepts, and reviews of past exploration. They provide insight into the many ongoing controversies concerning Black Sea regional geology and provide a better understanding of the geological risks that must be considered for future hydrocarbon exploration.