Early and Middle Triassic trends in diversity, evenness, and size of foraminifers on a carbonate platform in south China: implications for tempo and mode of biotic recovery from the end-Permian mass extinction

—Delayed biotic recovery from the end-Permian mass extinction has long been interpreted to result from environmental inhibition. Recently, evidence of more rapid recovery has begun to emerge, suggesting the role of environmental inhibition was previously overestimated. However, there have been few high-resolution taxonomic and ecological studies spanning the full Early and Middle Triassic recovery interval, leaving the precise pattern of recovery and underlying mechanisms poorly constrained. In this study, we document Early and Middle Triassic trends in taxonomic diversity, assemblage evenness, and size distribution of benthic foraminifers on an exceptionally exposed carbonate platform in south China. We observe gradual increases in all metrics through Early Triassic and earliest Middle Triassic time, with stable values reached early in the Anisian. There is little support in our data set for a substantial Early Triassic lag interval during the recovery of foraminifers or for a stepwise recovery pattern. The recovery pattern of foraminifers on the GBG corresponds well with available global data for this taxon and appears to parallel that of many benthic invertebrate clades. Early Triassic diversity increase in foraminifers was more gradual than in ammonoids and conodonts. However, foraminifers continued to increase in diversity, size, and evenness into Middle Triassic time, whereas diversity of ammonoids and conodonts declined. These contrasts suggest decoupling of recovery between benthic and pelagic environments; it is unclear whether these discrepancies reflect inherent contrasts in their evolutionary dynamics or the differential impact of Early Triassic ocean anoxia or associated environmental parameters on benthic ecosystems. Jonathan L. Payne, Mindi Summers,* and Brianna L. Rego. Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305. E-mail: [email protected]. *Present address: Scripps Institution of Oceanography, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093 Demir Altiner. Department of Geological Engineering, Middle East Technical University, Ankara 06531, Turkey Jiayong Wei. Guizhou Geological Survey, Bagongli, Guiyang 550011, Guizhou Province, China Meiyi Yu. College of Resource and Environment Engineering, Guizhou University, Caijiaguan, Guiyang 550003, Guizhou Province, China Daniel J. Lehrmann. Department of Geology, University of Wisconsin-Oshkosh, 800 Algoma Boulevard, Oshkosh, Wisconsin 54901. Present address: Department of Geosciences, Trinity University, One Trinity Place, San Antonio, Texas 78212 Accepted: 5 October 2010