Ecology, Biofacies, Biogeography and Systematics of Micromorphic Lingulate Brachiopods from the Ordovician (Darriwilian to Sandbian) of South—Central China
1 Institute of Earth Sciences, Palaeobiology, Uppsala University, SE-752 36 Uppsala, Sweden; lars.holmer@pal.uu.se;2 Department of Geology, Faculty of Sciences, Golestan University, Gorgan, Iran; mghobadipour@yahoo.co.uk;
3 Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, United Kingdom; leonid.popov@museumwales.ac.uk;
4 Early Life Institute, State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China;zhangtensor@hotmail.com, elizf@nwu.edu.cn.
Ordovician (Darriwilian to Sandbian) micromorphic linguliform lingulate brachiopods are described from the Fenxiang section in Hubei Province and the Maocaopu and Cili sections in Hunan Province of South—Central China, situated on the Yangtze Platform. A total of 7560 specimens from 155 limestone samples(within the interval of the Lenodus variabilis to Pygodus anserinus biozones)are assigned to 22 species,representing a low-taxonomic-diversity and low-abundance fauna. The fauna is predominantly dominated by the Acrotretoidea, specifically species of the Torynelasmatidae, with Torynelasma being numerically most abundant (more than 40% of the total number of specimens); the Eoconulidae (including Eoconulus) (18% of the total) being the second most common type. Species of the Ephippelasmatidae are also common (16% of the total), and include representatives of Myotreta and Numericoma, as well as Ephippelasma, whereas species of the Scaphelasmatidae are somewhat less common (13% of the total). All 3 investigated sections represent outer-shelf environments, but the Maocaopu section is situated in a relatively deeper position, in proximity to the south—eastern outer margin of the upper Yangtze Platform, close to its boundary with the Jiangnan Slope. A quantitative analysis of the relative abundance data was carried out in order to investigate the biofacies distribution of the micromorphic brachiopod communities across the Yangtze Platform, something that has not been attempted before with Palaeozoic linguliforms. Six lingulate microbrachiopod communities could be recognized in the sections. It is presently difficult to tie the shifts in microbrachiopod biofacies to environmental changes without detailed sedimentological studies, which were outwith the scope of the present paper. However, the major biofacies shift that occurred in the Cili section in the upper part of the Microzarkodina ozarkodella Zone at the time of the onset and initial raise of the Mid-Darriwilian Isotopic Carbon Excursion (MDICE) suggests that these biofacies may have been depth-controlled.