| mhorn | Дата: Thursday, 19.09.2013, 19:00 | Сообщение # 1 |
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| Nikitenko B.L., Shurygin B.N., Knyazev V.G., Meledina S.V., Dzyuba O.S., Lebedeva N.K., Peshchevitskaya E.B., Glinskikh L.A., Goryacheva A.A., Khafaeva S.N. (2013) Jurassic and Cretaceous stratigraphy of the Anabar area (Arctic Siberia, Laptev Sea coast) and the Boreal zonal standard // Russian Geology and Geophysics. Vol.54. P.808–837.
http://rogov.zwz.ru/Nikitenko%20et%20al.,2013_en.pdf
Recent integrated studies of Mesozoic reference sections of the Anabar area (northern Middle Siberia, Laptev Sea coast) and the reinterpretation of all the previous data on a modern stratigraphic basis permit considerable improvement of the bio- and lithostratigraphic division and facies zoning of Jurassic and Cretaceous sediments in the region. Analysis of abundant paleontological data allows the development or considerable improvement of zonal scales for ammonites, belemnites, bivalves, foraminifers, ostracods, dinocysts, and terrestrial palynomorphs from several Jurassic and Cretaceous intervals. All the zonal scales have been calibrated against one another and against regional ammonite scale. Reference levels of different scales useful for interregional correlation have been defined and substantiated based on the analysis of lateral distribution of fossils in different regions of the Northern Hemisphere. It provides the possibilities to propose and consider parallel zonal scales within the Boreal zonal standard for the Jurassic and Cretaceous periods. A combination of these scales forms an integrated biostratigraphic basis for a detailed division of Boreal-type sediments regardless of the place of their formation and for the comparison with the international stratigraphic standard as far as a possible use of a set of reference levels for correlation. Some remarks should be done on ammonite zonation and correlation proposed in this paper. In opinion of Meledina, Oxycerites jugatus, the Lower Subzone of the Arctocephalites arcticus Zone, can be a good interregional reference as it characterized by Arctocephalites arcticus and pilaeformis, which are very similar to the North pacific species Megasphaeroceras rotundum from the rotundum Zone, while Oxycerites from the jugatus Subzone resembling Oxycerites. Thus after Meledina Arctocephalites arcticus Zone should be placed in the Upper Bajocian and O. jugatus Subzone nearly corresponding to Strenoceras niortense (“subfurcatum”) Zone. However, such correlation based on similarities only (which could be caused by homoeomorphism) contradicts with strong difference of type of dimorphism in Megasphaeroceras and Arcticoceras as well as with strontium isotope correlation, which is supports nearly coincidence of the base of Upper Bathonian with FAD of Cardioceratidae. Changes of the position of the Arcticoceras ishmae zone against the NW European scale to Lower Bathonian (while correlation of Upper Bathonian boreal zones which were correlated with European indirectly remains unchanged) lead authors to conclusion about absence of Middle Bathonian ammonites in Siberia and even in the whole Panboreal Superrealm, which is nonsense. Following the traditional determination of the base of the Kimmeridgian by FAD of the ammonite genus Amoebites, authors criticized usage of the Bauhini zone as the base of this stage. They suggesting unclear stratigraphic range of Plasmatites and problems with identification of the species P. bauhini and P. lineatum. It should be noted, however, that during the last decade range of Plasmatites has been well-indicated and FAD of this genus is clearly coincides with FAD of Pictonia (Pictonia) and thus base of the Kimmeridgian. Plasmatites also marked base of the Kimmertidgian in many Submediterranean successions, while Amoebites albeit presents here (Schweigert, 2000) are very uncommon and cannot provide good background for correlation.
Middle Jurassic - Lower Cretaceous ammonites & aptychi
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