Cenomanian ammonites from German Democratic Republic, Poland, and the Soviet Union

Abstract

The Cenomanian ammonites from selected sections in German Democratic Republic (Subhercynian Basin and Saxony), Central Poland (Holy Cross Mts), and the Soviet Union (Podolia, Crimea, Caucasus, and Mangyshlak) are assigned to 98 species and subspecies of 27 genera. A great majority of the species show a wide geographic distribution which permits inter correlation of the investigated sections, as well as a correlation of the regional stratigraphic zonation patterns used in German Democratic Republic, Poland, and the Soviet Union with that used in northwestern Europe (southern England and northern France). There is a considerable variation in composition of ammonite faunules and only a small one in facies among the investigated sections, which indicates that bathymetry was insignificant in controls of ammonite distribution at that time. The phylloceratids, tetragonitids, and gaudryceratids are almost entirely confined to Crimea and Caucasus. The two regions share also most of the species with northwestern Europe, with typical Boreal forms representative of the genera Schloenbachia and Hyphoplites included, which demonstrates a mixing of Boreal and Mediterranean ammonite faunas in that area. Bareal aspects of the Cenomanian ammonites faunas are recognizable also in Mangyshlak and Kopet-Dag in the Soviet Union and in Esfahan area in Iran. The southern boundary of the Boreal province must therefore have been south of the present-day position of Crimea Highland, Caucasus, and Kopet-Dag at the Cenomanian time. The Lower and Middle Cenomanian are very well documented with ammonites in the investigated sections as a rule, whereas the abundance of ammonites is considerably decreased in the Upper Cenomanian all over the investigated area (Upper Cenomanian ammonites have not been recorded in some sections) although there is no significant change in facies. A similar phenomenon can be observed in northwestern Europe, North Atlantic drillings, and also in the Pacific, which is suggestive of its pan-regional cause. In paleontological description of the investigated ammonite taxa, good preservation state and large number of the specimens permitted recognition of micro- and macroconchs among representatives of the genera Sciponoceras, Scaphites, and Puzosia. A peculiar sexual dimorphism has been noted in Sciponoceras baculoide (Mantell), in which species the micro- and macroconchs differ from each other in the aperture type but not in the shell size or ornamentation.