On the boreal genus Buchia (Bivalvia) from the tithonian of the Lesser Caucasus

摘要

Two species of the genus Buchia, B. mosquensis (Buch) and B. ex gr. terebratuliodes (Lah.) found in the Tithonian of the Lesser Caucasus (40 degrees N) are described. Geographic distribution of the Kimmeridgian and Tithonian representatives of the genus in marginal areas of the Tethys-Panthalassa Superrealm is analyzed. Migration of buchiids into lowermost latitudes of the Northern Hemisphere coincided in time with episodes of the biota geographic homogenization. The joint occurrence of two above species facilitates correlation of the middle-upper Tithonian and middle-upper Volgian boundary beds. As is suggested, past seaways connected seas of central Russia and Transcaucasia in the relevant period of geological time.