Tephrostratigraphy of Jurassic-Cretaceous boundary beds of Western Siberia

The age of tuffaceous interlayers, represented by tuffs and tuffites, which are common in the Upper Jurassic-Lower Cretaceous deposits Western Siberia (the Bazhenovo, Tutleim Frolov Formations), is discussed. nature these interlayers associated with subglobal (transfer more than 1--2 thousand km) spread volcanic ash (0.001--0.1 mm) its sedimentation burial a vast epicontinental marine basin during episodes low rates, weak hydrodynamic activity absence bioturbation. Despite extremely thickness pyroclastic layers (<1 mm -- first cm), they systematically noted drill core at certain stratigraphic levels. Tuffs tuffites clearly recognized due to sharp boundaries contrasting color mineral composition comparing host rocks. Moreover, often demonstrate exceptionally bright luminescence yellow orange tones ultraviolet. Some can be traced over area (more 700,000 sq hence used as isochronous markers.
 Considering importance information about distal pyroclastics sedimentary strata, we have summarized data on boreholes Siberia, containing Jurassic - Lower Cretaceous. Detailed linking drilling depth geophysical logging was performed. findings 370 tuff tuffite 136 wells been catalogued. justified combination lithostratigraphic biostratigraphic methods, logging. key ammonite taxa recovered from tuff-bearing figured. A brief description zones Ryazanian stage principles their identification given. We suggest replace type index Surites analogus zone S. subanalogus. described sequence combined into 8 sub-regional levels throughout central part Middle Volgian (4 levels), (3 levels) Valanginian (1 level) intervals. trace elements content characterized. enrichment rare earth direction oldest youngest ones revealed, ratios Gd/Yb, Ho/Yb, Yb/Lu, Zr/Hf, Nd/Sm determine correspondence interlayer subregional level. Our results tephrostratigraphic scale for Jurassic-Cretaceous boundary beds. Catalog finds [<a href="https://doi.org/10.2205/2022ES000817-data">https://doi.org/10.2205/2022ES000817-data</a>] text format available website Earth Sciences Database Repository (BDNS) href="http://esdb.wdcb.ru/">http://esdb.wdcb.ru/</a>], located Geophysical Center Russian Academy Sciences.