Permian-triassic global change [electronic resource] : the strontium cycle and body size evolution in marine clades

Immediately following the most severe extinction in the history of animal life, the Early Triassic was a time of major changes in ocean chemistry and delayed biotic recovery. Many hypotheses for the cause of the end-Permian extinction invoke the environmental consequences of Siberian Traps flood basalt eruption. However, the precise relationship between volcanism, ocean chemistry, and the tempo and mode of biotic recovery remain incompletely understood. I present four studies that investigate the relationship between environmental change and biological evolution during this unique time interval, using carbonate and conodont samples from south China and literature-based fossil and geochemical data from around the globe. (1) I test strontium isotopic constraints on Permian-Triassic global change with a new high-resolution seawater 87Sr/86Sr record and a numerical model of the strontium cycle. Strontium isotope data reveal a rapid radiogenic excursion occurred during the first two million years of Early Triassic time. Model results show that the magnitude of CO2 release during Siberian Traps volcanism is sufficient to account for much of the observed increase in seawater 87Sr/86Sr through CO2 enhancement of continental weathering rates. (2) The small size of Early Triassic marine organisms has important implications for the ecological and environmental pressures operating during and after the end-Permian mass extinction. I quantify Permian-Triassic body size trends in eight marine clades and find widespread size decrease after the extinction in ecologically and physiologically disparate clades. Nektonic habitat or physiological buffering capacity may explain the contrast of Early Triassic size increase and diversification in ammonoids versus size reduction and slow recovery in benthic clades. (3) I compare size evolution in conodonts at the end-Permian extinction to their entire evolutionary history. Quantifying size trends reveals a long-term pattern of size increase during the early Paleozoic followed by size decrease until conodonts went extinct at the end of Triassic. Conodont size change during intervals of mass extinction and rapid environmental change appears small compared to long-term trends. (4) Finally, I review the constraints on Permian-Triassic ocean redox chemistry provided by lithological and geochemical proxy records. Paleoredox records show a rapid shift from relatively well-ventilated Late Permian oceans to widespread anoxic and euxinic conditions coincident with the end-Permian extinction horizon. Earth system models and geological observations support the eruption of the Siberian Traps as a mechanism for the expansion of anoxia at the Permian-Triassic boundary. Taken together, these results suggest that the physical environment has a large impact on biological evolution during intervals of rapid environmental change, but long-term evolutionary trends may be primarily driven by ecology.

Keywords: Geological and Environmental Sciences.
Advisor: Payne Jonathan L. primary advisor. Thesis advisor
Boyce C. Kevin advisor. Thesis advisor
Hilley George E. advisor. Thesis advisor
Lowe Donald R.