1. Environmental and evolutionary controls on Triassic reef recovery
Case studies from isolated and attached carbonate platforms in South China
Jonathan L. Payne, Department of Geological & Environmental Sciences, Stanford University
The re-establishment of platform-margin reef complexes during the Middle Triassic, nearly 5 million years after end-Permian mass extinction (252.6 Ma), has been viewed as an important sign of biotic recovery from the end-Permian event. However, the timing of reef initiation of carbonate platform margins and its relationship to coeval environmental amelioration remain poorly constrained. We have used an exceptionally-exposed reef in south China to obtained detailed information on the timing and environmental context of reef initiation and on the spatial and temporal distribution of reef builders within a Middle Triassic reef complex. Our research shows:
Reef recovery began in early Anisian time, as indicated by heavy carbon isotope values in the stratigraphically lowest parts of the reef.
Reef recovery coincided with a reduction in the carbon isotope gradient from shallow to deep water, suggesting shallow-marine anoxia and its associated effects on the composition of primary producers may have inhibited recovery prior to Middle Triassic time.
Following reef initiation, the diversity and abundance of framework-building organisms increased gradually. However, Tubiphytes and early marine cements continued to form the vast majority of the reef framework throughout the Middle Triassic.