Organic matter type, origin and thermal maturity of Paleozoic, Mesozoic and Cenozoic successions of the New Siberian Islands, eastern Russian Arctic

Geological investigations in the offshore area of eastern Russian Arctic attracted an increased interest in the recent years. Data concerning organic and coal petrology is scarce for the shelf and offshore area of the eastern Russian Arctic. Consequently, thermal maturity and depositional environments of sedimentary fades remain less described and examined. A detailed characterisation of organic matter type and origin as well as determination of thermal maturity have been carried out on silicidastic and carbonate sedimentary samples from Paleozoic, Mesozoic and Cenozoic outcrops of the New Siberian Islands, eastern Russian Arctic. The acquired organic and coal petrological data contribute to the overall assessment of petroleum potential of the studied offshore area and the neighboring shelf area. The investigated organic matter of Silurian and Middle Devonian mudstones and siltstones contain distinct, multi-staged solid bitumen (dead oil) preserved either as fracture-, fissure-, and vein-fillings, indicating activation of migrations pathways for re-occurring crude oil-bearing fluids or in form of streaks. The examined dispersed organic matter of Triassic deposits is predominantly composed of terrestrially derived macerals followed by alginite macerals (Tasmanite and Leiosphaeridia prasinophytes). The analysed Cretaceous and Tertiary deposits reveal (i) Aptian/Albian inertinite-rich sub-bituminous coal and lignites formed in fresh water lakes and swamps to brackish near-shore depositional environments with phases of wildfires as well as (ii) Cenomanian/Turonian lignites with pollen grains and carbonised debris (pyrofusinite), indicating stages of forest/moor paleofires. The (iii) Paleocene and Eocene deposits bear mineral-rich and xylite-rich lignites characterised by the lowest coal rank stage, containing different fossil conifer species. The thermal maturity of organic matter in Silurian to Tertiary deposits obtained from random vitrinite and bitumen reflectance measurements is an important parameter in determining the petroleum generation stage at the studied localities. The calculated thermal maturities of Silurian to Middle Devonian deposits acquired from random reflectance measurements of bitumen indicate condensate-wet gas to early dry gas generation window. The thermal maturities of sedimentary organic matter in samples collected from Tertiary to Triassic successions ranges from immature to main phase of oil generation. The composition of the organic matter and thermal maturity of the analysed Triassic siliciclastic deposits suggesting mature stage for oil generation can be used among others to evaluate their hydrocarbon potential. The Cretaceous and Tertiary deposits can be described as thermally immature. In two localities, where the thermal maturity is anomalously high, the examined organic matter has been thermally altered beyond the dry gas preservation limit. (C) 2015 Published by Elsevier B.V.