Silurian black shales in Russia

The Silurian interval is characterised by the wide distribution of oil-prone rocks. Together, they generate ~9% of the world’s conventional petroleum reserves. These rocks are also an important source of unconventional oil and gas. However, despite their global importance there is still much basic information lacking in many parts of the world, nowhere more so than in Russia. As part of the CASP ongoing research on Silurian organic-rich source rocks, a database of Silurian black shales in Russia is being compiled from the literature with a complementary data set provided by original fieldwork and associated samples.

Silurian black graptolitic shales are well developed in Russia. They are recorded in the Kaliningrad area, the Caucasus, along the Urals Mountains including Vaigach and Pai-Khoi, Novaya Zemlya, Severnaya Zemlya, East Siberia including Taimyr, Altai-Sayan, New Siberian Islands, Kolyma and Chukotka. In some areas as much as 1500 m of black graptolitic shales are reported. In north-western parts of East Siberia, the source rock quality of the basal Silurian black shale is so good that it was mined and used as a fuel, since it generally burns without any processing. For all of the regions reviewed, we present stratigraphic charts from Llandovery to Pridoli with information on sediment thickness, biostratigraphy and depositional settings.

Our field studies cover Severnaya Zemlya, Taimyr, northern East Siberia and Kotel’ny Island of the New Siberian islands, where the Silurian sequences contain black graptolitic shale and bituminous limestone intervals. Field and analytical studies have been undertaken to map the rocks, document their stratigraphy, identify the fossils, establish and describe facies, reconstruct the palaeogeography, determine palaeoenvironmental conditions, to obtain independent parameters on organic matter source, composition, thermal history and to investigate their possible oil-oil and oil-source correlation. Combined Rock-Eval and other geochemistry analyses on the Silurian samples from Severnaya Zemlya reveal the presence of early Silurian source rocks. The Llandovery Sredny Formation yields organically rich black shale with good source potential and a Type II oil and gas prone bulk source rock quality. The Rock Eval Tmax value suggests that the organic matter is early mature for oil generation.