The Neoproterozoic geological record contains evidence for extreme climatic change which may have profoundly influenced the course of biological evolution, particularly around the so-called Snowball Earth episodes of the Sturtian, Marinoan and Gaskiers glaciations. During the Neoproterozoic, body fossils and molecular biomarkers interpreted as being derived from multicellular animals have been reported although the radiation of basal animals is presently poorly constrained at sometime between the Sturtian and Marinoan glaciations. In this study, we aim to produce detailed temporal records of Neoproterozoic marine biogeochemistry from molecular biomarker analyses, organic and inorganic stable isotope records (including 13C, 2H and 34S) and from inorganic geochemical proxies of paleoredox for four sections in the Nanhua Basin in South China. This will allow us to investigate the effects of low-latitude Neoproterozoic glaciation on primary production, carbon cycling and redox structure applied to a shallow shelf-to-deep basinal paleoenvironmental transect.
Given the scientific interest in fossilized animal fauna and other fossils from the Doushantuo Formation in South China, it may seem surprising that no detailed molecular biomarker records currently exist for the Neoproterozic in South China. This is undoubtedly due to the high thermal maturity of some sections and due to the inherent problems of discerning low concentrations of genuine Neoproterozic biomarker signals above a significant background of petroleum-derived contaminants. A scoping study has revealed that the thermal maturity of strata in our four sections in Nanhua Basin is not problematic for preserving detectable biomarker hydrocarbon signals. The originality and principal strength of the biomarker lipid work proposed here lies in obtaining kerogen-bound biomarker records which allow us to access a high proportion of the preserved biomarker record in Nanhua Basin essentially free from contamination effects. The PI's research has demonstrated the efficacy of a continuous flow catalytic hydropyrolysis (HyPy) technique for fragmenting kerogen and releasing covalently-bound biomarker constituents to essentially ground-truth all the biomarker lipid data obtained.
We will address some fundamental questions regarding the biogeochemical history of the Neoproterozoic in South China: -Can we detect significant changes in marine redox structure in the immediate aftermath of the Sturtian and Marinon glaciations using our inorganic and biomarker proxies and, if so, is there strong evidence for concomitant fluctuations in source organism input? -Can we discern significantly different responses of shallow- versus deep-water settings to the aftermath of the glaciations in terms of their redox profiles and biota? -Can we detect specific steroid markers for basal animals (sponges) in the Nanhua Basin and, if so, when do these first appear relative to the Sturtian and Marinoan glaciations?
Broader Impacts. The research will significantly improve our understanding of the extent to which the intense climatic shock of the Sturtian and Marinoan glaciations impacted on marine microbial communities by modifying nutrient cycling, dissolved oxygen availability and creating environmental niches in low latitude marine environments. In terms of providing educational opportunities, Love and Lyons will participate during each of the project years in the UCR Mentoring Summer Research Internship Program, whereby undergraduate students from ethnic groups historically underrepresented in the sciences (particularly the earth sciences) will receive hands-on experience in the two labs. Finally, our project will benefit greatly from collaboration with Professor Xuelei Chu (Institute of Geology and Geophysics, Chinese Academy of Sciences) and his research group, who have considerable experience of studying Neoproterozoic glacial strata in South China. Chu and colleagues will visit the Southern California biogeochemical community at Caltech and UCR during the course of the project to discuss findings and to promote long-term collaborative links.
