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. Although Middle Triassic reefs contain potentially reef-building organisms such as scleractinian corals, calcareous sponges, and calcareous algae, quantitative analyses of most Middle Triassic reefs indicate a limited role for macroscopic skeletal animals and algae in constructing the reefs. Instead, framework organisms of unknown biological affinities, particularly Tubiphytes, and large volumes of marine cements contribute most to the structure and volume of the reefs. We have recently completed a field season in South China during which we were able to map and sample reefs the world’s oldest Triassic reefs on an isolated and an attached carbonate platform in the Nanpanjiang Basin. Field mapping shows:
The diversity and abundance of framework-building corals, sponges, and algae increased through time from the oldest to youngest parts of the exposed reefs.
The oldest parts of the reefs are dominated by Tubiphytes and lack corals, demonstrating that the origination of corals was not required for the return of reefs.
Biodiversity was greater and cementation less important in the reef on the attached platform than on the reefs on the isolated platform.
The reef margin on the south margin of the Great Bank of Guizhou is narrower than its counterpart on the north margin, suggesting local environmental control on the structure of the reef complex likely due to differences in windward versus leeward areas.
Study sites