Paper No. 183-24
Presentation Time: 9:00 AM-6:30 PM
ANATOMY OF A PROGRADING LOWER TRIASSIC GIANT OOID-MICROBIAL CARBONATE SHELF MARGIN, NANPANJIANG BASIN, SOUTH CHINA
WHITE, Stephanie J., Geological Sciences, University of Alabama, 201 7th Avenue, Room 2003 Bevill Building, Tuscaloosa, AL 35487-0268, MINZONI, Marcello, Geological Sciences, The University of Alabama, 1038 Bevill Building, Tuscaloosa, AL 35487, BHATTACHARJEE, Souvik, Department of Geological Sciences, The University of Alabama, 2006 Bevill Building, Box 870338, Tuscaloosa, AL 35487, LEHRMANN, Daniel J., Trinity University, Geosciences, One Trinity Place, San Antonio, TX 78212, LI, Xiaowei, Geological Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94305, KELLEY, Brian M., ExxonMobil Upstream Research Company, 22777 Springwood Village Parkway, Houston, TX 77389, LAU, Kimberly V., Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, YU, Meiyi, Resource and Environment Engineering, Guizhou University, Guiyang, 550025, China, PAYNE, Jonathan L., Department of Geological Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, CA 94305 and ENOS, Paul, University of Kansas, Department of Geology, 120 Lindley Hall, Lawrence, KS 66045
Continuous exposures of the Lower Triassic (Induan) margin of the Yangtze Platform at Zhenfeng, south China, reveal the architecture and evolution of a well-preserved oolitic-microbial carbonate system that developed after the end-Permian mass extinction and associated oceanographic perturbations. Detailed facies mapping along a faulted syncline that exposes a continuous transect through the platform interior, margin, and slope is integrated with δ16O and δ13C chemostratigraphy and analysis of concentration of redox-sensitive trace elements (e.g. V, Mo, Cr, U, I) to assess controls on carbonate factory type, facies distribution, and large-scale geometries of the platform margin and slope.
In the aftermath of the extinction that wiped out most of the calcifying metazoans, high rates of carbonate sediment production at the shelf margin and upper slope was maintained by microbialites and, principally, by abiotic production of giant ooids and early marine cements. Sediment production in the platform interior was dominated by carbonate mud, possibly abiotic, and a sparse, mostly molluscan fauna. Downslope reworking of this sediment, especially ooids, contributed to the development of steep (up to 15o), prograding clinoforms, consisting of gravity-flow deposits, including, rarely, matrix-poor breccia. By the end of the Induan the shelf margin had prograded several kilometers and had attained a relief of approximately 400 meters above a sediment-starved basin.
Preserved geometries and facies architecture of the Induan Yangtze Platform at Zhenfeng demonstrate that active carbonate sediment production occurred even in the near-total absence of calcifying metazoans and algae and that accumulation rates of the combined giant-ooids and microbial factories were sufficient to keep up with subsidence and even to prograde several kilometers. These observations should improve interpretations of analogous carbonate reservoirs, such as the Jurassic Smackover Formation of the Gulf of Mexico, and general understanding of the controls on carbonate factories and their impact on facies architecture and large-scale geometry of carbonate systems.
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