61st Annual Report on Research 2016

During the last year my students and I have completed one field season (May-July 2016) and processed date collected from our 2015 field seasons including stratigraphic sections and gamma ray log compilation, petrographic thin section description and point counting, and elemental geochemistry analysis. 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 2016 field season including detailed measured sections and sampling of the upper Permian reefs and uppermost Permian platform interior of the Great Bank of Guizhou, and detailed geological mapping of large sector collapse features in the Anlong area of the Yangtze Platform.

Field and laboratory work over the last year has involved four undergraduate students from Trinity University. The laboratory work has included thin section petrography, point counts, and plotting and analysis of stratigraphic and geochemical data. Two students completed directed study research projects research into quantification of the carbonate factories Upper Permian reefs and platform interior facies. Another two undergraduate student are currently conducting a directed studies project on the Permian-Triassic boundary sections and sector collapse features. Elemental geochemical analyses and total organic carbon analysis of samples from the Yangtze Platform were contracted to Chemostrat labs, which completed the analyses. 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. The changes in ocean chemistry resulted in a shift to predominantly abiotic carbonate factories (oolite and micrite) with extremely high production rates following the end-Permian mass extinction, and a return to greater skeletal content in carbonate factories coinciding with a shift to increased seawater oxygenation in the Middle Triassic.

The project has had the benefit of broadening the PI’s geologic background into the areas of elemental geochemistry and ocean redox chemistry and study of collapsed platform margins. 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 in the summer of 2017. 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. Additional presentations are planned for the National GSA meeting this fall and the south central GSA and National AAPG in the spring.