Braided River-Fan-Delta Depositional System of the Early Cretaceous Giabulin Formation in the Xigaze Region, Xizang(Tibet)

Liu Zhifei; Wang Chengshan

The Early Cretaceous Giabulin Formation, which is distributed along the north margin of the Yarlung Zang bo ophiolite suite, is easy to distinguish in the field. It is characterized by a sequence of ter-rigenous clasticrocks, principally mottled sandstones and conglomerates. Seven types of conglomerate, seven types of sandstone, three types of shale, and one limestone may be classified according to formation and their lithofacies characteristics. They comprise foursedimentary subfacies, from bottom to top: braid-ed river subfacies, fan-delta plain subfacies, fandelt a front subfacies, and profan-delt a subfacies. This progressio n makes up a retrog radational sequence taking together the global Cretaceous transgress con-dition. Paleosalinity of the Giabulin Formation was 12.0‰-20.0‰, and its paleoenvironments were inter-mediate between semi-brackish water and salt water. The sedimentary environments of the braided river of terrestrial facies and the fan-deltas of transitional facies can be concluded from the discussion above. Sediments of the Giabulin Formation were derived chiefly from recycled subduction complexes, and from dissected transitional island arcs. Those provenances were all distributed nearby to the north of the Yarlung Zang bo River. During deposition of the Giabulin Formation, the Tectonic settings was relatively passive in the early stage and active in the late stage.

Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059

Received Date: 1997-09-24

Rev Recd Date: 1998-01-15

Publish Date: 1998-12-10

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Abstract: The Early Cretaceous Giabulin Formation, which is distributed along the north margin of the Yarlung Zang bo ophiolite suite, is easy to distinguish in the field. It is characterized by a sequence of ter-rigenous clasticrocks, principally mottled sandstones and conglomerates. Seven types of conglomerate, seven types of sandstone, three types of shale, and one limestone may be classified according to formation and their lithofacies characteristics. They comprise foursedimentary subfacies, from bottom to top: braid-ed river subfacies, fan-delta plain subfacies, fandelt a front subfacies, and profan-delt a subfacies. This progressio n makes up a retrog radational sequence taking together the global Cretaceous transgress con-dition. Paleosalinity of the Giabulin Formation was 12.0‰-20.0‰, and its paleoenvironments were inter-mediate between semi-brackish water and salt water. The sedimentary environments of the braided river of terrestrial facies and the fan-deltas of transitional facies can be concluded from the discussion above. Sediments of the Giabulin Formation were derived chiefly from recycled subduction complexes, and from dissected transitional island arcs. Those provenances were all distributed nearby to the north of the Yarlung Zang bo River. During deposition of the Giabulin Formation, the Tectonic settings was relatively passive in the early stage and active in the late stage.

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Reference (15)

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Braided River-Fan-Delta Depositional System of the Early Cretaceous Giabulin Formation in the Xigaze Region, Xizang(Tibet)

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