Cenomanian–Campanian (Late Cretaceous) planktonic assemblages of the Crimea–Caucasus area: Palaeoceanography, palaeoclimate and sea level changes

Abstract

During the Cretaceous, the Crimea–Caucasus area occupied a position in the Peri-Tethys which was transitional between the Boreal and Tethyan realms. The evolution and stratigraphic distribution of planktonic foraminifera and radiolarians in the Upper Cretaceous sediments of the region are described. The specialized, morphologically complex keeled taxa evolved in the latest Albian and persisted until the end of the Cretaceous. These overall evolutionary trends are punctuated by a series of bioevents, one of the most important being the Cenomanian–Turonian boundary. This is marked by a series of organic-rich sediments, that are related to an Oceanic Anoxic Event. The Turonian–Coniacian interval was marked by a further development of keeled taxa. A major change in the assemblage is described near the Santonian–Campanian boundary, when marginotruncanids were replaced by globotruncanids.The Albian is marked by the diversification of the radiolarian genus Crolanium, the last occurrence of which is typical of the Albian–Cenomanian boundary. The Upper Coniacian to Lower Santonian strata are characterized by the high taxonomic diversity of the Quinquecapsulariidae and the Neosciadiocapsidae. A marked change in the radiolarian assemblage occurred at the Santonian–Campanian boundary: the Late Santonian, warmer-water assemblage dominated by the Pseudoaulophacidae being replaced in the earliest Campanian by cooler-water assemblages characterized by the Prunobrachidae. The changes in the assemblages of planktonic foraminifera and radiolarians at the Santonian–Campanian boundary are attributed to changes in palaeoceanography and the influence of more Boreal-like conditions.Three significant episodes of sea level change can be identified in the Cenomanian–Campanian of the Crimea–Caucasus area. The first is associated with the Albian–Cenomanian boundary, the second at the base of OAE2, and the third in the Mid–Early Late Turonian. This latter event had different durations in the Crimea and Caucasus regions and this could be related to more local tectonic processes.