The systematics of the ammonite genus Kepplerites (upper Bathonian and basal Callovian, Middle Jurassic) and the proposed basal boundary stratotype (GSSP) of the Callovian Stage

摘要

In the Upper Bathonian and Lower Callovian (Middle Jurassic), the ammonite genus Kepplerites is an important guide fossil. With its help, Jurassic rocks can be correlated from North America, Greenland, Russia to Central Europe. The basis of the Callovian Stage is defined by the keppleri horizon, which occurs in more than 20 localities in Southern Germany and Switzerland, as well as in England, the Caucasus and on the Russian Platform. Probably Kepplerites keppleri or at least closely related species also occur in Greenland and Arctic Canada. In parts of the Boreal Upper Bathonian (Canada, Alaska, Greenland and Russian Platform) Cadoceras and Kepplerites are the most common ammonites. Across the territory of the present Caucasus, some species migrated to Central Europe, namely K. (Kepplerites) aigii MITTA, K. (K.) traillensis DONOVAN and K. (K.) radiatus SAKHAROV & LOMINADZE. These species are described in detail, in addition to Kepplerites keppleri and K. herscheli nov. sp., which belongs to the new subgenus Tychoites. The widespread extinction of Kepplerites soon after the beginning of the Callovian was possibly caused by an eustatic sea level fall.