Sequence Stratigraphy and Lithofacial Palaeogeography of the Tremadocian of the Latest Cambrian to Early Ordovician) in the Hunan and Hubei region
Zhang Junming Sun Xiaowen Li Guoxiang Yuan Wenwei Zhang Yunbai Zhou Chuanming
1 Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008
2 National Centre for Petroleum Geology and Geophysics, The University of Adelade, Australia 5005
Four third-order orthosequences have been recognised in the latest Cambrian to Early Ordovician Tremadocian ( from the Cordylodus intermedus to Serratognathus zones) successions in the Hunan and Hubei parts of the Yangtze platform. These four orthosequences could be well subcorrelated with each other in different depositional settings of the Yangtze platform, indicating four third-order transgression-regression cycles. Among them , the transgression systems tract in sequence 3 ( the lower and middle Paltodus deltifer Zone ) represents the maximum transgression event of the lower-order cycle of the Tremadocian, and the major regression events occurred during early Tremadocian Glyptoconus quadraplicatus Zone and late Tremadocian Serratognathus Zone ( middle and upper part ), respectively.Integrated sequence stratigraphy and facies analysis has improved our understanding of lithofacies palaeogeographical evolution in the region. At the beginning of the early Tremadocian ( C.lindstromi to lower C. angulatus Zone) the depositional facies from the northwestern Hubei to central Hunan change successively from tidal flat, tidal lagoon dolomite facies through restricted carbonate platform, open carbonate platform , platform margin shoal complex, to platform marginal slope and the black carbonaceous shale basin . During the early stage of Tremadocian (Glyptoconus quadraplicatus Zone ), relative sea level fall caused gradual regression from north to south, resulting in depositional environments varying from tidal flat, tidal lagoon dolomite facies, restricted carbonate platform, to platform margin shoal and outer shelf. During the middle Tremadocian, a new transgression resulted in onlapping of the bioclastic limestone and shale towards the Qingfeng-Xiangguang fault zone to the north. At this stage, the shallow-water carbonate domain evolved into an open carbonate platform, the mixed carbonate and siliciclastic zone evolved into a deep-water outer shelf, and the central Hunan region became a lower outer shelf. During the late Tremadocian, another relative sea level fall caused a further slow regression, and the open carbonate platform in Hubei and northwestern Hunan was developed with the bioclastic shoal of inner shelf and platform margin shoal complex. On these platform margin bioclastic shoals, sponge and bryozoan reefs were well developed. The mixed sedimentary realm evoled into an upper outer shelf, and the central Hunan area became a deep muddy outer shelf.
About author: Zhang Junming, born in 1938, graduated from the Department of Geology, Nanjing University in 1963. He is currently a professor at the Nanjing Institute of Geology & Paleontology, Academia Sinica, undertaking sedimentological research.
Cite this article:
. Sequence Stratigraphy and Lithofacial Palaeogeography of the Tremadocian of the Latest Cambrian to Early Ordovician) in the Hunan and Hubei region[J]. JOURNAL OF PALAEOGEOGRAPHY, 2000, 2(3): 15-26.
. Sequence Stratigraphy and Lithofacial Palaeogeography of the Tremadocian of the Latest Cambrian to Early Ordovician) in the Hunan and Hubei region[J]. JOPC, 2000, 2(3): 15-26.
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