The Upper Ordovician Xiazhen Formation, which crops out in Zhuzhai, near the Jiangshan–Changshan–Yushan region of southeast China, consists of a variety of carbonate–siliciclastic lithofacies representing a shallow‐water platform environment. A total of eleven stromatoporoid genera in two orders, comprising three clathrodictyid genera ( Clathrodictyon , Ecclimadictyon , and Labyrinthodictyon ) and eight labechiid genera ( Cystostroma , Rosenella , Pseudostylodictyon , Aulacera , Stylostroma , Pachystylostroma , Labechia , and Labechiella ), are recognized from 18 stratigraphic units representing a wide range of depositional environments in the formation. Clathrodictyon is the most abundant stromatoporoid genus, occupying a long stratigraphic range and a wide range of lithofacies. It also occurs as a major component of patch reefs throughout the formation. The labechiids, in contrast, are highly diverse but most genera have restricted stratigraphic distributions, occurring in a narrow range of depositional environments. The size and growth form of stromatoporoids in the formation are considered to be primarily intrinsic characteristics of each genus but in some cases also seem to be related to lithofacies: clathrodictyids exhibit a wide spectrum of growth forms and have broader ecological plasticity and more flexible growth strategies than do labechiids. The Late Ordovician stromatoporoids of the Xiazhen Formation exhibit close biogeographic affinities to those of central New South Wales and the Tasmanian shelf of Australia. The discovery herein of Labyrinthodictyon and Stylostroma from the Upper Ordovician of South China further supports this close relationship. The stromatoporoids from South China exhibited one of the highest diversities of all paleocontinents during the Late Ordovician, suggesting that South China, together with Australia, was a locus of Late Ordovician stromatoporoid diversification.
Abstract Clathrodictyids are the most abundant stromatoporoids in the Upper Ordovician Xiazhen Formation (middle to upper Katian) of South China. A total of nine species belonging to four clathrodictyid genera are identified in the formation, including Clathrodictyon idense Webby and Banks, 1976, Clathrodictyon cf. Cl. microundulatum Nestor, 1964, Clathrodictyon cf. Cl . mammillatum (Schmidt, 1858), Clathrodictyon megalamellatum Jeon n. sp., Clathrodictyon plicatum Webby and Banks, 1976, Ecclimadictyon nestori Webby, 1969, Ecclimadictyon undatum Webby and Banks, 1976, Camptodictyon amzassensis (Khalfina, 1960), and Labyrinthodictyon cascum (Webby and Morris, 1976). The clathrodictyid fauna in the Xiazhen Formation is very similar to those from both New South Wales and Tasmania, although the latter two Australian regions do not share any common clathrodictyid species during the Late Ordovician. The paleobiogeographic pattern indicates that the northward drift of South China resulted in a favorable environment for the migration of clathrodictyids from other peri-Gondwanan terranes to South China. In addition, these peri-Gondwanan clathrodictyid species hosted various endobionts, representing a variety of paleoecological interactions. The high abundance and species-level diversity of clathrodictyid species presumably increased the substrate availability of suitable host taxa, judging from the diverse intergrowth associations between clathrodictyids and other benthic organisms. These paleoecological interactions between stromatoporoid and other organisms are known from the Late Ordovician and became more abundant and widespread in the Siluro–Devonian. Overall, the Late Ordovician clathrodictyid assemblage in South China demonstrates one of the highest species-level diversities among all peri-Gondwanan terranes and represents a precursor of the complex, clathrodictyid-dominated communities of later metazoan reefs during the Great Ordovician Biodiversification Event. UUID: http://zoobank.org/6063c47d-cb77-4a03-98cf-b2354656dea6
Abstract A diverse labechiid stromatoporoid assemblage that includes 16 species in 8 genera was found in the Upper Ordovician Xiazhen Formation (mid–late Katian) at Zhuzhai, Jiangxi Province of South China. The assemblage is characterized by a combination of (1) North China provincial species succeeding from their origination in the Darriwilian, including Pseudostylodictyon poshanense Ozaki, 1938, Labechia shanhsiensis Yabe and Sugiyama, 1930, Labechia variabilis Yabe and Sugiyama, 1930, and Labechiella regularis (Yabe and Sugiyama, 1930) and (2) South China endemic species, including three new species ( Labechia zhuzhainus Jeon n. sp., Labechiella beluatus Jeon n. sp., Sinabeatricea luteolus Jeon n. gen. n. sp.), and four species in open nomenclature ( Rosenella sp., Cystostroma sp., Pseudostylodictyon sp., and Labechia sp.). The finding of Labechiella gondwanense Jeon n. sp., Stylostroma bubsense Webby, 1991, Stylostroma ugbrookense Webby, 1991, and Thamnobeatricea gouldi Webby, 1991 in the formation indicates that Tasmania was closely related to South China and had a closer paleobiogeographical relation with peri-Gondwanan terranes than with Laurentia. In addition, the occurrences of Labechia altunensis Dong and Wang, 1984 and Stylostroma species support a close biogeographic link between Tarim and South China through the Middle to Late Ordovician interval, corresponding with the results from other fossil groups such as brachiopods, conodonts and chitinozoans. The diverse labechiids from the Xiazhen Formation improve our understanding of the diversity of Ordovician stromatoporoids in peri-Gondwanan terranes and the biogeographic affinities among Australia (especially Tasmania), Tarim, and South China. UUID: http://zoobank.org/4f46c91b-fa4c-4fe5-bea9-e409f1785677
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