PARALLEL BIOSTRATIGRAPHIC SCALES OF THE BOREAL BATHONIAN AND CALLOVIAN IN THE NORTH PECHORA REGION AS A TOOL FOR INTERREGIONAL CORRELATIONS

Abstract

Investigation results on ammonites, belemnites, and dinoflagellate cysts from Bathonian and Callovian deposits in the North Pechora region are used to elaborate the detailed stratigraphy and to correlate these deposits in the northern West Europe and Siberia. The Pechora basin, which was located in Jurassic time at the boundary between the Arctic and Boreal Atlantic paleobiogeographic provinces, incorporates faunas typical of neighboring regions and thus is an intermediate province linking Siberia with West Europe. The bed-by-bed study of sections exposed along tributaries of the Pechora River provided grounds to elaborate the Bathonian-Callovian biozonation of ammonites, belemnites, and dinoflagellate cysts. The ammonite zonation consisting of eleven units is correlated with the West European standard and East Siberian local zonations. The identified common species suggest that Pechora sections include the standard zigzag, herveyi, calloviense, athleta, and lamberti zones. Other units bearing only the arctic species are correlated with Bathonian and Callovian ammonite zones established in eastern and western Siberia. The revealed belemnite zonation includes five biostratigraphic units spanning the middle Bathonian and entire Callovian intervals. It is correlated with the regional ammonite scale and also with the East Siberian belemnite zonation. The Bathonian-Callovian succession of dinocysts assemblages is shown to include seven units ranked as zones or dinocyst beds. The dinocyst assemblages from Bathonian and Callovian deposits of the North Pechora and other regions of the Russian platform, along with similar assemblages from northern Siberia, are calibrated by comparison with dinoflagellale zonations in northwestern Europe and Arctic Canada. The mutually coordinated Bathonian-Callovian zonation of ammonite, belemnite, and dinocyst fossils is suggested to be a reliable biostratigraphic scale for interregional correlations in a vast area of northern Eurasia, Arctic regions, and America. The paper also includes description of Cadoceras pishmae Meledina, C. variabile Spath (ammonites), and Belemnopsis sp. ind.