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The succession of ammonites of the genus Amoeboceras in the Upper Oxfordian – Kimmeridgian of the Nordvik section in northern Siberia

Rogov M., Wierzbowski A.

Volumina Jurassica

2009

Vol. 7, no. 1

147-156

A collection of ammonites of the genus Amoeboceras located carefully in the section of Nordvik Peninsula in northern Siberia has enabled recognition of the standard Boreal ammonite zones of the Upper Oxfordian and Kimmeridgian. The recognition of the standard Amoeboceras zones, well known in NW Europe and the Barents Sea area, in northern Siberia indicates the uniform character of the Late Oxfordian and Kimmeridgian ammonite faunas across the whole Boreal Province. Some comments on the occurrence of Boreal oppeliids of the genus Suboxydiscites in the studied section are also given.

Upper Oxfordian – Lower Kimmeridgian ammonite succession (Amoeboceras, Suboxydiscites) in the Nordvik section (northern Siberia)

Rogov M., Wierzbowski A.

Volumina Jurassica

2006

Vol. 4, no. 1

211-212

Nordvik Peninsula situated at the Laptiev Sea, east of Taimyr Peninsula provides one of the most fossiliferous Jurassic - Lower Cretaceous successions of northern Siberia. The succession consists of clays and mudstones with numerous levels of phosphatic and calcareous concretions. The Mesozoic deposits of the area were discovered at the beginning of XX century, but more detailed studies were undertaken by Russian geologists from sixties to eighties of the century: see Zakharov et al. (1983) and earlier papers cited therein. The present study is based on the collection of ammonites gathered during joint field-trip of the Russian (Zakharov V., Rogov M.) and Czech geologists (Kostak M., Chadima M., Slechta S., Mazuch M.) in August 2003. The collection of Upper Oxfordian - Kimmeridgian ammonites consists of about 60 specimens carefully located in the 20 meters thick section. The most abundantly represented and zonally diagnostic are representatives of the genus Amoeboceras, whereas rarely encountered but palaeogeographically important are representatives of the genus Suboxydiscites. The Amoeboceras ammonites enable recognition of the standard Boreal ammonite zones of the Upper Oxfordian and Kimmeridgian. These of the Upper Oxfordian (cf. Sykes & Callomon 1979) include: the Glosense Zone with ammonites Amoeboceras transitorium Spath, A. glosense (Bigot et Brasil); the Serratum Zone with A. serratum (Sowerby), A. koldeweyense Sykes et Callomon, A. nunningtonense Wright; the Regulare Zone with A. freboldi Spath, A. regulare Spath; the Rosenkrantzi Zone with A. rosenkrantzi Spath. The Kimmeridgian ammonite zones (cf. Wierzbowski & Smelror 1993) include: the Bauhini Zone with A. lineatum (Quenstedt); the Kitchini Zone with A. subkitchini Spath below (Subkitchini Subzone), and A. kitchini Salfeld and A. modestum Mesezhnikov et Romm above (Modestum Subzone); the Elegans Zone with A. elegans Spath and A. decipiens Spath. The Kochi Zone is the only standard zone not recognized in the succession, but the interval possibly corresponding to this zone in the Kimmeridgian unfortunately has not yielded recognizable ammonites. The recognition of the standard Amoeboceras zones in the northern Siberia well known in NW Europe and the Barents Sea area indicates the uniform character of the Late Oxfordian to Kimmeridgian ammonite faunas in the Boreal Province. The ammonites of the genus Suboxydiscites appear for the first time in the studied succession in the upper part of the Kitchini Zone of the Kimmeridgian, and do occur in the younger interval of the Kimmeridgian. The ammonites represent the group of oppeliids of the Submediterranean roots (Ochetoceras(?), see Rogov 2001) that colonized the Boreal Province during Late Kimmeridgian. In the studied section Suboxydiscites are represented by both microconchs and macroconchs, belonging to the new species.