THE FIRST RECORD OF A REPRESENTATIVE OF THE TOARCIAN-EARLY AALENIAN BELEMNITES IN KIMBERLITES OF THE OBNAZHENNAYA PIPE (NORTHEASTERN SIBERIAN PLATFORM)

Abstract

Berlites of the Obnazhennaya pipe of the Kuoika kimberlite field (northeastern Siberian Platform, Olenyok uplift), a rostrum fragment of a representative of Toarcian–Early Aalenian (latest Early Jurassic–earliest Middle Jurassic) belemnites was found for the first time, namely Arcobelus cf. krimholzi (Sachs, 1970). It is shown that belemnite records previously known from here and dated to the Late Jurassic or Early Cretaceous, may be of Bajocian–Bathonian (Middle Jurassic) age. The stage of kimberlite magmatism of 177 ± 1.5 Ma, recently established in the northeastern part of the Siberian craton according to U–Pb geochronological data, falls on the time of the existence of belemnites of the genus Arcobelus. The estimated Late Bajocian–Early Bathonian age of the representative of the genus Pachyteuthis previously found in kimberlites of the Obnazhennaya pipe is consistent with the 40Ar/39Ar age (167 Ma) as well as with the age based on some paleomagnetic data (168 ± 11 Ma) reported for the pipe. In the paleogeographic schemes of the northeastern part of the Siberian Platform during the Toarcian–Early Bathonian interval, the inner part of the shelf should be extended to the territory of the Kuoika kimberlite field, taking into account the new data on belemnites.