Early Silurian Siliciclastic-Carbonate Ramp Deposits in NW Sichuan

Zhang Tingshan; Lan Guangzhi; Chen Xiaohui; Yu Jianhuaand; Bian Lizeng

The Llandoverian to Wenlockian storm-influenced siliciclastic and carbonate ramp environment has been recognized from the NW Sichuan area. The Early Silurian deposited on the NW margin of the S-China paleoplate tectonically and it has very thick sequences of shale, silty shale, mud and silty sandstone with some reefs, bioherms and stratigraphically discontinuous lenticular and irregular bioclastic tempestites, and multigenic nodular limestone beds.According to the different petrographic assemblages and paleoecology analysis, the authors have divided the sedimentary environment into littoral zone, shallow ramp, deep ramp and basin. The littoral zone is located at intertidal area with tidal flat carbonate deposits; the shallow ramp which is between the wave base and the storm wave base, has type A, B tempestites, pattern A, B nodular limestone, reef limestone and bindstone deposits; the deep ramp is below the storm wave base and above the maximal storm wave base and has type D, E tempestites, pattern C nodular limestone, dark shale deposits; the characteristics; the area below the maximal storm wave base is the basin area with black shale. From Lower Llandoverian to Lower Wenlockian, the sedimentary environment changed from basin to deep ramp, shallow ramp and littoral zone, the representative strata are Lungmachi Formation, Chuijiagou Formation, Wangjiawan Formation and Ningqian Formation, respectively.The authors also discuss the sea level change and its influence in this area. The global glaciation may be the main factor for the influence of the sea level change. Under the action of Tamadjert and Cananiri glaciation, the sea level changed from high to low in this area during the Llandoverian to Wenlockian.

1 Nanjing Univ., Nanjing 210008;

2 SW Petroleum Institute, Lanchun 937001

Received Date: 1994-11-03

Publish Date: 1995-12-10

Key words:

Abstract: The Llandoverian to Wenlockian storm-influenced siliciclastic and carbonate ramp environment has been recognized from the NW Sichuan area. The Early Silurian deposited on the NW margin of the S-China paleoplate tectonically and it has very thick sequences of shale, silty shale, mud and silty sandstone with some reefs, bioherms and stratigraphically discontinuous lenticular and irregular bioclastic tempestites, and multigenic nodular limestone beds.According to the different petrographic assemblages and paleoecology analysis, the authors have divided the sedimentary environment into littoral zone, shallow ramp, deep ramp and basin. The littoral zone is located at intertidal area with tidal flat carbonate deposits; the shallow ramp which is between the wave base and the storm wave base, has type A, B tempestites, pattern A, B nodular limestone, reef limestone and bindstone deposits; the deep ramp is below the storm wave base and above the maximal storm wave base and has type D, E tempestites, pattern C nodular limestone, dark shale deposits; the characteristics; the area below the maximal storm wave base is the basin area with black shale. From Lower Llandoverian to Lower Wenlockian, the sedimentary environment changed from basin to deep ramp, shallow ramp and littoral zone, the representative strata are Lungmachi Formation, Chuijiagou Formation, Wangjiawan Formation and Ningqian Formation, respectively.The authors also discuss the sea level change and its influence in this area. The global glaciation may be the main factor for the influence of the sea level change. Under the action of Tamadjert and Cananiri glaciation, the sea level changed from high to low in this area during the Llandoverian to Wenlockian.

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Early Silurian Siliciclastic-Carbonate Ramp Deposits in NW Sichuan

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