Carbon and oxygen isotopic composition of Jurassic foraminifers in the Unzha River basin

Study of the carbon and oxygen isotopic composition of the foraminifera shells of different species from the Callovian-Oxfordian undershale rocks in the Unzha River basin near the town of Makar’ev (Central Volga region) has shown that the δ¹⁸O values of the epistomina shells correspond to relatively low temperatures and their δ¹³C values indicate the high productivity of the basin in this period. The Lenticulina tumida shells register low δ¹³C and δ¹⁸O values, which probably reflect the biological effect of fractionation during their formation. The Jurassic lagenids (Lenticulina tumida and Citharina chanika) were characterized by a wider habitat areal or ecological niche. We established the importance of isotopic studies of foraminifers of the same genus, and even better of the same species. Most likely, the foraminifera shells may be applied for study of Mesozoic sedimentation conditions.