RADIOLARIAN BIOSTRATIGRAPHY OF THE MAASTRICHTIAN IN THE EASTERN TAJIK DEPRESSION

Abstract

New data on the Maastrichtian stratigraphy in the eastern Tajik depression are discussed. Scarce remains of macrofauna and significant facies variability are main impediments to precise correlations between deposits of Afghanistan and Tajikistan. Coexisting ammonoids, larger foraminifers, and radiolarians enable age determination of the Maastrichtian limestone sequences in the eastern Tajik depression, where occurrence of the lower Maastrichtian sediments is confirmed. The early Maastrichtian age of the radiolarian Hemicryptocapsa djalilovi assemblage corresponding to the ammonoid Nostoceras hyatti Zone is substantiated. Based on changes in radiolarian assemblages, the identification of the upper Campanian-lower Maastrichtian boundary is proved to be possible in the east of the region, where ammonoids are missing. The lower-upper Maastrichtian boundary corresponds to the level, where the radiolarian Hemicryptocapsa djalilovi assemblage is replaced by larger foraminifers of the Siderolites calcitrapoides-Orbitoides apiculata assemblage. The base of the Maastrichtian is displaced down in accord with the ammonoid and radiolarian records.