The Ammonite Catacadoceras barnstoni Beds and the Problem of the Separation of the Middle and Upper Substages of the Bathonian Stage in Northern Siberia

• Published in: Stratigraphy and geological correlation Vol. 31; no. 4; pp. 275 - 298
• Main Authors: Shamonin, E. S., Knyazev, V. G., Dzyuba, O. S.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.08.2023; Springer Nature B.V
• Subjects: Age determination; Archaeology; Chronology; Correlation; Distribution; Earth and Environmental Science; Earth Sciences; Geographical distribution; Geophysics/Geodesy; Historical Geology; Jurassic; Polar environments; Sedimentology; Stratigraphy; Structural Geology; Umbilicus; Siberia; Russia; interregional correlations; Cardioceratidae; biostratigraphy; Arctic; Middle Jurassic; ammonites
• ISSN: 0869-5938; 1555-6263
• DOI: 10.1134/S0869593823040032

— The taxonomic composition of the ammonite family Cardioceratidae is studied in the Bathonian of northern Siberia in the range of distribution of the last representatives of the genus Arcticoceras and the first representatives of the genus Catacadoceras, aiming to solve the problem of the Middle-Upper Bathonian boundary. It is shown that all previous identifications of northern Siberian material as the Middle Bathonian species Arcticoceras cranocephaloide Callomon et Birkelund, 1985, were incorrect. The misidentified specimens were mainly the Late Bathonian ammonite species Catacadoceras barnstoni (Meek, 1859) or the form with a narrow umbilicus referred to herein as Cat . aff. barnstoni . An updated ammonite zonal scale of the Middle–Upper Bathonian of Siberia is proposed, which is recommended for use both in the regional stratigraphic schemes of the Jurassic deposits of Eastern (Middle) Siberia and in the Boreal (Siberian) zonal standard of the Bathonian Stage. The extreme importance of preserving an auxiliary biostratigraphic subdivision in this scale, the Cat. barnstoni Beds, is emphasized, because of the wide distribution and abundance of the index species in Siberian sections, as well as its significance for the correlation of the lower part of the Upper Bathonian of northern Canada, northern Siberia, Franz Josef Land, and East Greenland. In addition, two intervals, i.e., the interval with Cat . aff. barnstoni and interval with Cat. perrarum , are fixed as marker levels, which are useful for rapid age determination and correlation of the Upper Bathonian deposits in Arctic sections within the upper part of the Cat. barnstoni Beds.