Taizhong Duan¹, Jian Wang²

(1) Colorado School of Mines, Golden, CO
(2) Chengdu Institute of Geology and Mineral Resources, Chengdu, China

ABSTRACT: Signatures of Tectonics, Climate and Sediment Supply on Sinian-Cambrian Supersequence, Yangtze Block, South China

Sinian-Cambrian Supersequence consists of a set of landward-stepping and a set of seaward-stepping sequences. It developed during stages of rifting and passive margin of Yangtze Block, under influence of ice- to green-house climate change, and by different sediment supplies. Rifting sequences (Z1) are restricted spatially and are siliciclastics-dominated, including fluvial, volcanic, gravity-flow, and glacial deposits. Young passive margin sequences (Z2) are widespread and carbonate, shale and chert-dominated. Isolated carbonate platforms and surrounding deeper-water basins/shelves obviously corresponded to faulted-blocks and surrounding rifting/faulting zones. Matured passive margin sequences ( ) are very regular and stable regionally, carbonate-dominated with minor shale and siltstone, and seaward-stepped. In this period a single, huge carbonate platform was formed that covered almost entire Yangtze Block, and prograded steadily oceanward up to tens of kilometers. Sequences formed during ice-house climate (Z2 to 1) have larger proportion of deeper-water deposits corresponding to transgression and early highstand on tops of carbonate platforms. Corresponding platform got drowned, or its margin retrograded first. Then carbonate production resumed in late transgression or highstand. This should indicate larger amplitudes of sea-level cycles, and rapid thermal subsidence on the young passive margin. In contrast, sequences formed during green-house climate ( 2 to 3) have smaller proportion or are lack of the deeper-water deposits. Corresponding platform never got drowned, but remained prograding seaward. Platform-wide dolomitization is overwhelming. This may indicate smaller amplitudes of sea-level cycles and slower thermal subsidence on the matured passive margin. Condensed interval of the supersequence is black shale-dominated, and is high-quality source rock and regional seal.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado