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The Lower Cambrian (lower Toyonian) Tianheban Formation of Hubei Province, South China, includes small archaeocyath-calcimicrobial reefs that formed by combinations of archaeocyaths (e.g., Archaeocyathus yichangensis) and calcimicrobes (including Epiphyton, Renalcis, and Girvanella). The archaeocyaths provided substrates onto which the calcimicrobes became attached. In particular, Girvanella encrusts directly upon the surfaces of archaeocyaths, and bush-shaped aggregations of Epiphyton, growing downward, spread over the Girvanella. The remaining spaces among these reef framework-builders are infilled by chambered forms of Epiphyton and/or Renalcis. These calcimicrobes made a strong contribution to reinforcement of the reef frameworks. The archaeocyath-bearing reefs in South China first appeared during the Atdabanian and are last seen in the early Toyonian Tianheban Formation in Hubei Province. Subsequent reefs are purely microbial reefs without archaeocyaths. The Tianheban reefs are therefore the last representatives of archaeocyath-bearing reefs in South China. These reefs, reported herein, record the transition from archaeocyath-calcimicrobial reefs to purely microbial reefs during the Toyonian. Further studies involving integrated geobiological and geochemical analyses are needed to identify the factors that led to the demise of archaeocyath-bearing reefs and that subsequently hindered the development of skeletal-dominated reefs for 40 million years. [ABSTRACT FROM AUTHOR]

The Lower Ordovician (late Tremadocian-early Floian) Fenhsiang and the overlying Hunghuayuan Formations at the Chenjiahe section in the Three Gorges area of Hubei Province, South China, include four types of reef: microbe-dominated (lithistid sponge-stromatolite and lithistid sponge-calcimicrobial) reefs, and skeletal-dominated (lithistid sponge-bryozoan and bryozoan-pelmatozoan) reefs. The microbe-dominated reefs are characterized by the dominance of microbial sediments that encrusted and bound the surfaces of sponges to reinforce the reef frameworks. In contrast, the skeletal-dominated reefs are distinguished by bryozoans that encrusted frame-building sponges and pelmatozoans, and that grew downward to fill the open spaces available within the frameworks. A series of these reefs shows a temporal succession in reef type, with a decline in the lithistid sponge-stromatolite reefs and an increase in the lithistid sponges and receptaculitids within the lithistid sponge-calcimicrobial reefs in the Hunghuayuan Formation; the lithistid sponge-bryozoan reefs are common in both the Fenhsiang and Hunghuayuan Formations. These features of the Chenjiahe reefs are in marked contrast to other coeval reefs on the Yangtze Platform and elsewhere. Skeletal-dominated reefs first developed in the Three Gorges and adjacent areas, located on the central part of the platform. Likewise, lithistid sponges and receptaculitids first developed in the Three Gorges area and then expanded their range. In contrast, stromatolites declined over time, but remained abundant on a marginal part of the platform. The spatial-temporal distributions of these reefs on the Yangtze Platform reflect the initiation of the Great Ordovician Biodiversification Event and its consequences, although influenced by local environmental conditions. The Three Gorges area was a center for the development of skeletal-dominated reefs, which were established earlier here than elsewhere in the world. These reef types and their spatial-temporal successions provide invaluable clues to the earliest evolution of skeletal-dominated reefs and their ensuing development during the Middle-Late Ordovician. [ABSTRACT FROM AUTHOR]

Examines the relation between central Guizou and Yichang uplifts present in central Guizou to western Hubei in China. Stratigraphic evidence of the uplifts; Mechanism of the central Guizou and Yichang uplifts.

The origin of reddish nodular limestone in the Zitai Formation, a deeper-water type of marine red beds (MRBs) distributed along the marginal Yangtze Platform, South China, is enigmatic. Here we focus on the red colorations through sedimentological, mineralogical and geochemical analyses, as exemplified by the Zitai Formation at the Xiangshuidong section, Songzi City, Hubei Province and the Daling section, Shitai City, Anhui Province. Limestones studied here can be gray, green or red. The grayish limestones are generally below the reddish and/or greenish limestones, whereas the greenish layers are associated with reddish layers in forms of homogenous, banded or mottled limestone. Hematite that is fine and poorly crystalized could be the coloration mineral for the Zitai MRBs, which is largely caused by increased terrigenous iron, when the bottom seawater was oxic. Except that the irregularly banded and mottled reddish-greenish limestone are of a possible diagenetic origin, the primary greenish limestones are related to relatively reducing conditions compared with reddish limestones, as a result of eustatic changes or other fluctuating environmental factors. During this time interval, the Great Ordovician Biodiversification Event (GOBE) was facilitated by highly oxic seawater indicated by MRBs in South China, Baltica and Sibumasu, but the diachroneity of radiations in South China could be ascribed to increased terrigenous supply, emphasizing that regionally environmental factors might be critical for biological radiations at the early stage of the GOBE. • Detailed petrological analyses on the deeper-water marine red beds for the first time. • Conducting the elemental analyses on the color-alterations of the red beds. • The implications of Ordovician marine red beds for the GOBE in South China. [ABSTRACT FROM AUTHOR]