EARLIEST TRIASSIC REFUGE AT SHANGSI CHINA: A POTENTIAL ANALOG FOR MODERN MARINE CRISIS

The ocean provides food and other essential resources and yet we indirectly impact marine ecosystems through greenhouse gas emissions. In the coming century, the ocean may be faced with a series of environmental perturbations that have no recent analog. Therefore, it is important to look back in Earth’s history, to times such as the end-Permian mass extinction or EPME, when comparable environmental conditions provide a baseline for comparison with the present-day. Gathering appropriate information to model marine ecosystem changes is dependent on a high temporal resolution not normally available in deep time. The EPME is associated with acidification, anoxia and warming of the ocean. The synergistic effects of these conditions might be especially informative for understanding future changes in marine ecosystems. More importantly, understanding how marine refugia were developed and maintained following the EPME could help predict marine ecosystems that are most likely to survive and predominate in the coming centuries. Refugia are sanctuaries to which organisms migrate during times of environmental stress and are therefore essential to the survival of key species during mass extinction events. The capability of refugia to protect threatened species can be seen clearly in a large bedding surface within bed 29 at the Shangsi section, South China. This surface provides a snapshot of an oligophotic outer-shelf ocean floor during the earliest Triassic. Echinoderm groups experienced extreme bottlenecks during the EPME, with only two known families of crinoids and echinoids surviving into the Mesozoic, however bed 29 at Shangsi contains a significant echinoid community. Although the EPME is thought to have been inhospitable to metazoans, abundant microbial mats found within bed 29 could have served as a major food source and firm substrate for echinoids. Geochemical evidence indicates that anoxic conditions prevailed during this interval, but the occurrence of bivalves and trace fossils indicate that bottom water conditions were temporarily oxygenated within this isolated marine refuge, potentially due to limited biological productivity in the water column. Overall, the growth of microbial mats is the key mechanism in the development of the Shangsi refuge and can be added to a growing list of refugia mechanisms.