59th Annual Report on Research 2014

During the last year my students and I have processed data collected from our summer 2013 field season including stratigraphic section and gamma ray log compilation, petrographic thin section description, elemental geochemistry analysis, and compilation of databases in GIS. The central hypothesis we are testing is that that long-term changes in ocean redox chemistry and consequent changes in carbonate saturation state affect the distribution of carbonate factory types (abiotic, microbial, and skeletal) across the shelf-to-basin profile and thereby shape overall architecture of carbonate platforms in the Nanpanjiang Basin of south China. 

Field work during the summer of 2013 (preceding the grant period) included measuring, describing, sampling and spectral gamma ray measurements in four new sections in of the drowning sequence of the Yangtze Platform in the Hongyan and Zhenfeng area, resampling and spectral gamma ray measurements of the Hongyan section, and reconnaissance mapping of the Hongyan margin of the Yangtze platform and Pingguo platform. An additional field season, which will involve an undergraduate student in fieldwork, is planned for December 2014.

Laboratory work over the last year has involved three undergraduate students from Trinity University. The majority of this work was done at Lehrmann’s lab at Trinity. The laboratory work has included thin section petrography, conodont biostratigraphy, and plotting and analysis of stratigraphic and geochemical data. An undergraduate student completed a thesis on his research into the termination of the Yangtze Platform and presented results at AAPG. Another undergraduate student completed a directed studies project on the conodont biostratigraphy and presented her results at SC-GSA. A third undergraduate student is currently conducting petrographic study and point counts of thin sections for her thesis project on the Hongyan margin of the Yangtze Platform. Elemental geochemical analyses and total organic carbon analysis of samples from the Yangtze Platform were contracted to Chemostrat labs, which completed the analyses. High-resolution satellite images were acquired for the Hongyang margin of the Yangtze Platform and the Xiliang margin of the Great Bank of Guizhou. Detailed geologic maps of the margin architecture, geochemical and petrographic data were compiled into GIS databases for each locality in ARC Map.

Preliminary results indicate long term shifts in basin redox from oxygenated conditions in the Late Permian to anoxia following the end-Permian mass extinction and a return to oxygenated conditions in the Middle Triassic. Local areas of high nutrient-influx and anoxia contributed to the termination and drowning of the Yangtze Platform during the Late Triassic, Carnian.

The project has had the benefit of broadening the PI’s geologic background into the areas of elemental geochemistry and ocean redox chemistry. Results from the research have been integrated into an on-campus basin analysis course and into a summer field geology course to be taught in south China. The project has formed the basis for two undergraduate senior thesis projects and for an undergraduate directed study project. Students have presented results of their projects at a university student research symposium, at a south central section meeting of the GSA and at the national meeting of the AAPG.