Early Cretaceous Belemnites of the Anabar Area (Northern Eastern Siberia): Taxonomic Composition, Paleoecology and Biodiversity

The ideas about the taxonomic composition and stratigraphic distribution of belemnites in the Lower Cretaceous deposits of the northern Eastern Siberia have been significantly refined based on the study of a representative collection of Cylindroteuthididae rostra from the Ryazanian–Lower Hauterivian deposits of the Anabar area (Nordvik Peninsula, Anabar River, eastern shore of the Anabar Estuary). Analysis of taxonomic and paleoecological rearrangements with an assessment of the impact of environmental factors has shown a noticeable influence of changes in the depth of the paleobasin, both on belemnite taxonomic diversity and on the ecological structure of their communities. According to the results of studying the biodiversity curves constructed for separate sections, the influence of the climatic factor is not obvious for every time intervals. At the end of the Berriasian–beginning of the Valanginian, influences of intensive migrations of nektobenthic forms of belemnites of low-boreal European origin are recorded. This leads to a significant change in the taxonomic and ecological structure of belemnite communities in the Anabar area. In this regard, the Berriasian and Valanginian stages of their development are clearly distinguished, but at the same time, a transitional stage is recognized—the second half of the Late Berriasian.