The palaeo-Volga is a major hydrocarbon play in the Pliocene Productive Series of the South Caspian region. Extensive palynological analyses have been carried out on core from the BP / AOIC operated ACG (Azeri-Chirag-Gunashli) and Shah Deniz oil and gas fields, offshore Azerbaijan. These data have helped understand sediment distribution in the Productive Series, mainly in terms of environment of deposition and regional facies variation. The palynological analyses identified 3 main “palynofacies types”, referred to as “Caspian Lake”, “Delta Front” and “Lake Margin”, which occur in the Pereriv and Balakhany reservoir sandstones and associated mudstones and siltstones. In order to assess the extent to which the modern (Holocene) Volga delta could be an analogue for the Pliocene Productive Series, a detailed study of the modern delta was undertaken, involving seismic surveys, shallow coring, radiocarbon dating and detailed palynology. The study was carried out in collaboration between Moscow State University, the Technical University of Delft, BP, KrA Stratigraphic Ltd. and others, with surveys carried out in the Damchik region of the Astrakhan Biosphere Reserve in the Russian Federation.

The present day Volga delta is a low-gradient, mud-dominated delta with numerous distributaries and more than 800 outlets into the northern Caspian Sea. The pollen records in the modern delta sediments are sourced from the huge and varied Volga catchment, with pollen originating from boreal and temperate forests, steppe, saltmarsh, semi-desert and desert, as well the from the wetland vegetation on the delta itself. Aquatic derived palynomorphs include various microplankton types, notably brackish dinocysts (e.g. Spiniferites cruciformis and Caspidinium rugosum) and freshwater algae. Samples with frequent Pediastrum in the modern delta occur in highstand, fluvio-lacustrine deposits and are a potential equivalent for the “Delta Front” Pliocene palynofacies type. Samples with frequent brackish dinocysts are a potential equivalent for the “Caspian Lake” Pliocene palynofacies type and samples with frequent fungal bodies are interpreted broadly as lowstand, sub-aerial deposits and are a potential equivalent for the “Lake Margin” Pliocene palynofacies type. Similar depositional trends and palynofacies associations are therefore present in both the modern delta and Pliocene delta. The main difference is that warm temperate tree pollen types are more prevalent in the Pliocene sediments, which reflects the warmer climate and the more southerly position of the delta at that time.

The palynological and other results from the survey of the modern Volga delta have been incorporated into the reservoir models for the Pliocene Productive Series. Although differences do occur, there are many features in common between the two deltas and the resultant lithofacies and palynofacies. Both can be interpreted broadly in terms of progradational deposition in response to lake level fall, and aggradational deposition in response to lake level rise. The modern Volga delta is therefore a good analogue for at least part of the Pliocene depositional system in the offshore area, even though the present day delta occurs c.500km to the north of its Pliocene position. A key difference is that the modern delta is a low gradient ramp delta with minimal incision, whereas major river incision occurred in the palaeo-Volga, mainly at the end of the Miocene (Messinian), resulting in formation of an extensive canyon which can be traced northwards through the north Caspian basin and into the Russian hinterland.