60th Annual Report on Research 2015

During the last year my students and I have completed two field seasons (Dec 2014-Jan 2015, and June-July 2015) and processed date collected from our Dec 2014-Jan 2015 field season including stratigraphic section 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 Dec 2014-Jan 2015 included detailed measurement, description and sampling of three stratigraphic sections spanning the upper slope to distal basin margin of the Yangtze Platform in the Guanling area. Field work during June-July 2015 focused on reconnaissance mapping and measuring and sampling a long stratigraphic section of the Upper Permian southern margin of the Great Bank of Guizhou and mapping and measuring sections in the Lower Triassic northern margin of the Great Bank of Guizhou

Field and laboratory work over the last year has involved two undergraduate students from Trinity University. The laboratory work has included thin section petrography, point counts, and plotting and analysis of stratigraphic and geochemical data. An undergraduate student completed a thesis on her research into quantification of the carbonate factories of the margin of the Yangtze Platform in the Guanling area. Another undergraduate student is currently conducting a directed studies project on the Upper Permian margin facies of the Great Bank of Guizhou. 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. 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.