Sedimentary Features and Their Implications of Microdigital Stromatolites from the Mesoproterozoic Wumishan Formation at the Jixian Section in North China |
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| Authors: | MEI Mingxiang GAO Jinhan MENG Qingfen LIU Zhirong |
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| Institution: | [1]State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China [2]School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China |
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| Abstract: | The Mesoproterozoic Wumishan Formation at the Jixian section in Tianjin is a set of more than 3000-m-thick stromatolitic carbonate succession. In this succession, several lithofacies units, that is, the subtidal stromatolitic biostrome, the thrombolitic bioherm, tidal-flat micritic dolomite and lagoon dolomitic shale, make up many meter-scale cycles of the peritidal carbonate type that have been nominated as the Wumishan cycles. Importantly, many microdigital stromatolites make up the stromatolitic biostrome unit of the Wumishan cycles in the lower part of the Wumishan Formation. These microdigital stromatolites have been grouped as a stromatolitic assemblage by paleontologists, that is, "Pseudogymnosolen mopanyuensis-Scuphus-Yangzhuang columnaris"assemblage. These microdigital stromatolites had also been interpreted as the aragonite (tufa) sea-floor precipitates by sedimentologists, and has further been thought as the special products of the transitional period from the sea-floor aragonite precipitates of the Archean to the clastic and muddy carbonates of the Neoproterozoic. Although there are some restrictions for the stratigraphic meaning of the concept of the stromatolitic assemblage, detailed studies on classification by paleontologists provide an important clue to understand the sedimentological meaning of the microdigital stromatolites. Furthermore, an important and obvious horizon for the end of the microdigital stromatolites was recorded in the Mesoproterozoic Wumishan Formation at the Jixian section, which provides useful information to understand the stromatolite decline occurred at c.1250 Ma and the evolving carbonate world of the Precambrian. |
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| Keywords: | microdigital stromatolites stromatolite decline Wumishan Formation Mesoproterozoic Jixian in Tianjin |
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