Original paper
Refined ammonite and bivalve biostratigraphy of the Agardhfjellet and lowermost Rurikfjellet formations (Bathonian–Ryazanian) of the Longyearbyen area, Spitsbergen
Rogov, Mikhail; Zakharov, Victor; Kiselev, Dmitry
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 309 Heft 2 (2023), p. 169 - 198
64 references
published: Aug 31, 2023
manuscript accepted: Aug 1, 2023
manuscript received: May 10, 2023
ArtNo. ESP155030902007, Price: 29.00 €
Abstract
We consider the Upper Jurassic and lowermost Cretaceous deposits (Adventdalen Group) of Spitsbergen, a key region for understanding Mesozoic connection between the Arctic and NW Europe and for interpretation of coeval strata of Norwegian and Barents Sea shelves. The Adventdalen Group is characterized by its diverse fossil assemblages. However, precise ages of lithostratigraphic units and regional gaps in the Bathonian–Ryazanian intervals of Spitsbergen are still poorly understood. In this article, we provide new data about ammonite and bivalve specimens, recovered from the Agardhfjellet Formation and lower part of the Rurikfjellet Formation (Bathonian–Ryazanian). Studied molluscs were recorded in three boreholes named DH2, DH4 and DH5R, which were drilled near to Longyearbyen. In spite of a small core diameter, numerous age-indicative ammonites and buchiid bivalves were found in all boreholes. Analysis of the recorded ammonite succession along with review of specimens previously reported from outcrops in Spitsbergen allow us to update the zonal and infrazonal ammonite-based stratigraphic scale and re-consider the age of regional hiatuses. The studied core contains molluscan specimens preserved both in concretions and black shales. In addition to stratigraphic intervals of the middle-upper Jurassic, which existence in Spitsbergen is well-known, here we also recorded Middle and Upper Oxfordian, Middle Callovian and Lower Volgian fossils, which are rare in this area. All boreholes are characterized by a non-fossiliferous interval in the ammonite succession, spanning uppermost Kimmeridgian and part or the whole lower Volgian, which can be named as ‘Kimmeridgian–Volgian ammonite gap’. It suggests the presence of a Bathonian–Callovian transitional gap, which spanning uppermost Bathonian to lower part of the lower Callovian, while the Oxfordian and the Volgian–Ryazanian successions seem to be complete in terms of ammonite zones. The base of the Rurikfjellet Formation is lower Ryazanian, while the uppermost Agardhfjellet Formation is either uppermost Volgian or lowermost Ryazanian.
Keywords
Jurassic • Cretaceous • Arctic • mollusks • stratigraphy • boreholes • hiatuses • correlation