The Maurynya section, West Siberia: a key section of the Jurassic–Cretaceous boundary deposits of shallow marine genesis

Abstract

The Maurynya section exposed on the northwestern margin of West Siberia is one of few continuous sections of the Jurassic–Cretaceous boundary deposits in Boreal regions. In the meantime, it can be considered a reference section for the transitional Volgian–Ryazanian beds formed in shallow water environments of the West Siberian sea basin. This study is a synthesis of the new data with previous results of lithologic, paleontological, biostratigraphic, and (O, C, Sr) isotope studies of the Upper Volgian–lowermost Ryazanian of the Maurynya section. It has been established that the beginning of the Cretaceous (corresponding to the middle Late Volgian) is associated with a sharp increase in species number and diversity of cephalopods and bivalve mollusks on the northwestern margin of the West Siberian sea basin. This can be explained by an increase in its depths and their stabilization at a level which appeared optimal for the habitat of nekton, nektobenthos, and benthic fauna communities, superimposed on the general trend of warming. At the same time, the percentage of phytoplankton significantly increased, indicating the onset of transgression, which affected largely coastal landscapes and type of vegetation: The forests dominated by conifers were gradually succeeded by forests mostly composed of Ginkgoaceae.

Ryazanian (Berriasian) molluscs and biostratigraphy of the Dutch and Norwegian North Sea area (south of Viking Graben)

“…4). Only in the uppermost Volgian Singularis Zone buchiids are missing on the Russian Platform (Kiselev et al, 2018, p. 231), as well as in contemporary strata of the Subpolar Urals (Dzyuba et al, 2018). All in all, compared to the before mentioned areas and especially northern Siberia and Canada (see Zakharov, 1987, p. 144-145;Grey, 2009, fig.…”

Jurassic palynoevents in the circum-Arctic region

“…The bioevents used for the definition of the boundaries of Siberian miospore zones are mainly applicable to local to sub-regional correlations. Dzyuba et al (2018) proposed the first formal biostratigraphy for the upper Volgian to lower Ryazanian of the Northern Urals, defining two miospore zones. In addition to regional correlations, the key taxa from the upper Volgian interval enabled these authors to make a biostratigraphic comparison with coeval successions of terrestrially derived palynomorphs from Australia.…”

Late Jurassic – earliest Cretaceous prolonged shelf dysoxic–anoxic event and its possible causes

“…Rising temperatures accompanied by increased productivity, together with slow ocean circulation, are considered among the factors responsible for prolonged black shale deposition in the Arctic (Georgiev et al 2017). Indeed, gradual warming during the Late Jurassic epoch in the Boreal areas is supported by palynology (Dzyuba et al 2018), clay mineralogy (Ruffell et al 2002) and oxygen stable isotope data (Price & Rogov, 2009;Zakharov et al 2014;Dzyuba et al 2018). Cold-water glendonite pseudomorphs are common in the Middle Jurassic deposits of Siberia (Morales et al 2017), but they rarely occur in the Upper Jurassic deposits.…”