Cretaceous-Paleogene (K/T) boundary in the North-Eastern Caucasus (Dagestan): sedimentology, geochemistry and biota

Abstract

The Cretaceous/Paleogene (K/T) boundary interval was studied in the Okhli and Gubden sections, northeastern Caucasus. Two sediment successions represented in these sections were accumulated in different zones of the paleobasin and distinguished by their lithological and geochemical characteristics. The high-resolution study of nannofossils revealed very gradual changes in nannoplankton community at the Cretaceous/Paleogene transition. The nannofossil assemblage becomes poor from the level ca. 4 m below K/T boundary and it is very scarce in the last 2.5 m of uppermost Maastrichtian. The significant sea-level fall is evidenced in the beginning of the K/T event. It led to erosion and redeposition of Maastrichtian calcareous sediments within the thin layer of clay, covering erosional surface in the Okhli section. The clay mineral assemblage, starting from this surface contains palygorskite. The concentrations of coprolites (Decapoda?) and microspherulas (diagenetic microconcretions) with higher content of some trace elements were found within the small red lenses at the base of the clay layer overlying the Maastrichtian erosional surface. The reliable evidence of impact event are not recognized. The evolutional trends which are recorded within the Cretaceous/Paleogene transitional interval in the Okhli and Gubden sections are similar to trends recognized in studied sections of the K/T event on the adjacent territories of the North-Eastern Peri-Tethys (e.g., southern Turkmenistan and Mangyshlak Peninsula).