|mhorn||Дата: Saturday, 04.05.2013, 18:07 | Сообщение # 1|
|Wimbledon W.A.P. (2012) A revised description of the lithostratigraphy of the Kimmeridgian-Tithonian and Kimmeridgian-Volgian boundary beds at Kimmeridge, Dorset, UK: discussion to Gallois 2011 // Geoscience in South-West England. Vol.13. P.131. |
In this brief paper Wimbledon criticized recent contribution by Gallois (2011, see), trying mainly to show methodological problems. But Wimbledon’s critical note itself is full of errors or misunderstandings. Wimbledon argued that the only Tithonian Stage could be in use for the latest Jurassic, writing “The international stratigraphic community thus knows very precisely what the Tithonian is, where it begins and where it ends, as they do for the Kimmeridgian”. But taking into account absence of GSSP for Kimmeridgian, Tithonian and Berriassian Stages and absence of any agreement concerning GSSP levels of all these stages, their boundaries became undefined yet. And among these stages Tithonian boundaries are especially unclear: two events used for recognition of the lower boundary of the Tithonian, which are mentioned in the GTS-2012 (FAD of Gravesia and FAD of Hybonoticeras hybonotum) are not coincides, with at least one subzone differences between these. The third proposal, LAD of Aulacostephanus s.l., independently proposed by Gallois (2011) and me (Rogov, 2011), is nearly coincides with FAD of the H. hybonotum, and easily traced throughout in the Subboreal Realm as well as in some Submediterranean successions. Moreover, Federico Oloriz, head of the Tithonian WG, suggesting that FAD of species within Hybonoticeras lineage could not be a good choice for boundary, and prefer to use instead FAD or LAD of the Hybonoticeras genus (discussion during the Jurassic Congress, 2010). Wimbledon also writing the following phrase, full of errors “it is true that a few Russian authors persist in using ‘Volgian’ for thin successions in the landlocked boreal basins of the Russian platform and Siberia”. Perhaps Bill thought “few hundreds” instead “few”, as the Volgian is used by nearly all exploration geologists in Arctic? And he forgot many Norwegian, Polish, Canadian, Dutch, Danish and USA colleagues, who also widely use the Volgian Stage for the terminal Jurassic of Boreal areas. Wimbledon’s knowledge on the Volgian if really out-of-date, while using of thickness as argument for completeness of succession is erroneous even at the student’s level (and, again, Wimbledon forgot the Volgian successions of NE Russia, which are than 1 km in thickness). Unfortunately, head of the Berriasian WG is not familiar with current practice of GSSP recognition, as he is writing “Biostratigraphy is much more preoccupied with appearances, not disappearances”: there are many LAD events used as GSSP markers, and few GSSPs has LADs as primary markers (i.e. Campanian, Ruppelian and Bartonian Stages).
Middle Jurassic - Lower Cretaceous ammonites & aptychi