Выпуск: 6 , Том: 34 , Год издания: 2026

New data on early cretaceous belemnites from northern eastern Siberia are presented. these data are based on a study of a large collection of cylindroteuthididae rostra from the ryazanian-lower hauterivian deposits along the Boyarka river (kheta river basin), formed in the coastal zones of a marine paleobasin. the taxonomic composition of belemnites in the kheta area is revised and expanded. detailed information on the distribution of taxa across the Boyarka section is provided. as in the anabar area, the influence of low-boreal european migrants in the kheta area is most noticeable during the initial stage of the Siberian seas' regression. as a result, by the early Valanginian, a major transformation in the ecological and taxonomic structure of cylindroteuthidid communities occurs: the most actively swimming forms disappear, and nektobenthic forms predominate. in the middle of the early Valanginian, a sharp decline in belemnite abundance is observed, accompanied by a drop in their taxonomic diversity. this is associated with the emergence of lagoonal or lagoon-like environments in the kheta area against the backdrop of global sea level decline. Some recovery in belemnite abundance and biodiversity occurs at the end of the early Valanginian during a transgressive episode and under conditions of relatively high environmental temperatures. Subsequent biodiversity dynamics depended on the adaptation of cylindroteuthidids to changes in paleoenvironments associated with the spread and development of sand barriers (primarily underwater sand ridges), which to varying degrees fenced off the coastal area of the sea basin. these dynamics were accordingly controlled by the degree of influence of the marine regime; belemnite abundance (when they appeared) was low. Belemnite rostra are present in sandy and silty deposits of open lagoons (bays) and are absent in clayey (? lagoonal) deposits of the coastal sea, which is presumably related to the peculiarities of salinity distribution and aeration of the waters. in the early hauterivian, benthopelagic and nektobenthic belemnite species inhabited the kheta area in roughly equal numbers.