Eocene – Oligocene source rock organic geochemistry, micro-facies and basin connectivity in Paratethys

A Paleogene to early Neogene succession, including the Maykop Series type locality, is exposed on the Belaya River, south-west Russia. Exposed here are the Kuma Formation (Eocene) and the Maykop Series (Oligocene – Early Miocene) deposited in a marginal marine setting within the Paratethys Sea. Organic material is abundant in these hydrocarbon-producing strata that are now exposed around the periphery of the Black Sea. It is hypothesised that the preservation of this organic matter occurred due to the episodic restriction of the Paratethys Sea as a result of the collision of Africa and Arabia with Eurasia.

Detailed sedimentary logging and sampling (approximately every 50 cm) through 250 m of stratigraphy has been completed along the Belaya River. RockEval pyrolysis was conducted on the Eocene portion of these samples and then combined with data previously obtained by Reinhard Sachsenhofer to examine the source potential of the Kuma Formation (Eocene) and lower Maykop formations (Oligocene). The Kuma Formation is characterised by total organic carbon (TOC) values of 1-5.5% over approximately 43 m compared to values of between 1-3% in the lower Maykop Series throughout the lowermost 130 m. Detailed thin section analysis of the same samples reveals a range of facies including calcareous laminated marls with abundant, well-preserved foraminifera (Kuma Formation) to dark heterogeneous mudstones with occasional lenses and sporadic very-fine to fine sand-sized quartz grains and fish remains (Maykop Series). Within the Kuma Formation facies of dark fine-grained matrix interlaminated with parallel concentrated organic matter correlate with higher TOC values. In samples with lower TOC values the matrix is much lighter and distinctly lacks laminae of concentrated organic material supporting the hypothesis of a link between facies and TOC content.

Strontium isotope analysis is technique also being incorporated in this project to determine the connectivity of Paratethys during Early Cenozoic times. Comparing global ocean 87/86Sr ratios to the signature of those obtained from the Belaya River samples will provide insights into the apartment ‘restriction’ of Paratethys through time. If the acquired data is coincident with the global ocean curve it is assumed there was full marine connectivity at that time. Most of the facies found in the Eocene portion of the succession are abundant in foraminifera which are used in strontium isotope analysis. Facies with a lack of calcareous micro-fauna (majority of the Maykop Series) are unable to be analysed at this time.

The characterisation of Black Sea organic-rich mudstones and associated basin connectivity will provide new insights into the processes and controls on source rock development in marginal marine settings in tectonically active regions.