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1 2006

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Jurassic-Cretaceous deposition-palaeogeography on the northern margin of the Dabie Orogen and its tectonic implication

Li S., Liu Y., Wang D., Li R., Meng Q., Yue S-C., Jin F-Q.

Volumina Jurassica

2006

Vol. 4, no. 1

59-60

The Jurassic-Cretaceous strata of the northern margin of the Dabie Orogen consist of terrestrial sediments comprising thirteen formations, about eight km of thickness at the southern margin of the Hefei-Huangchuan basins, and are divided into four chronosomes. The chronosome I comprises the Lower Jurassic Fanghushan Formation and the lower part of Middle-Upper Jurassic Yuantongshan Formation. The formations represent braided rivers, meandering rivers and marginal to shallow lacustrine environments, and are developed only at the east end of the Hefei Basin. The Chronosome II consists of the Middle-Upper Jurassic Sanjianpu and Zhuji formations, and the upper part of Yuantongshan Formation. The alluvial fans are recognized in the lower parts, and braided rivers in the middle and upper parts of the formations. Transverse water systems crossing the orogen were developed at an early stage, and longitudinal water systems paralleling the orogen in the late stage of sedimentation in the area of study. The East-West stretching Xinyang-Jinzhai-Shucheng Fault (XJSF) borders the sedimentation area in the south. The Chronosome III comprises lower parts of Lower Cretaceous Fenghuangtai, Duanji and Zhougongshan formations, of which the former two consist of alluvial fans and the latter formation of braided rivers and overbank deposits. Coarse-grained siliciclastic deposits prograded into the basins for a few kilometers. The transverse water system developed on the southern margin of the basins, and the longitudinal water system - in the middle of the basins. Chronosome IV comprises the late Early Cretaceous Heishidu and Chenpeng formations. The Xiaotian-Mozitan Fault (XMF) and the Tongbai-Shangcheng Fault (TSF) are placed at the southern boundary of the depositional basin, and the faults are mainly of strike-slip character. Alluvial fans to fan-deltas developed at an early stage, whereas turbidites were deposited in deep lacustrine environments at the late stage of sedimentation. The study area mostly suffered uplift and erosion during the Late Cretaceous; sedimentation was then limited to the western part of the Huangchuan Basin. Longitudinal faults such as XJSF, XMF and TSF paralleling the orogen, and more or less, East-West trending, limited the chronosomes in the south. Transverse faults such as the Tancheng-Lujiang Fault (TLF) and the Shangcheng-Macheng Fault (SMF), more or less North-East trending, controlled lateral facies changes of the chronosomes. Deposition overlapped progressively from east to west at the southern margin of Hefei-Huangchuan basins, which implies that exhumation and unroofing of the Dabie Orogen was diachronous from east toward west. The chronosomes were restricted by TLF and SMF. TLF controlled the development of the Jurassic depocenter, which implies that the fault did not become active until the Early Jurassic.