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, the relative timing of appearance among these taxa and their relative contributions to overall reef structure remain poorly constrained. We have recently completed a detailed analysis of the stratigraphic and environmental distributions of reef-building organisms at two localities on the Great Bank of Guizhou in southwest China. Our research shows:
Tubiphytes was the dominant framework-builder throughout the Middle Triassic reefs and the only framework builder in the oldest parts of the reefs.
Calcareous algae and calcareous sponges reappear at similar stratigraphic levels, a few hundred meters above the base of the reef complexes.
Scleractinian corals are rare and occur exclusively in the youngest parts of the reefs (late Anisian or early Ladinian).
Reef diversity increased gradually through Anisian time.
Geological map illustrating the distribution of reef-building taxa within the reef complex at Bianyang, on the Great Bank of Guizhou. Strata dip 60 degrees toward the top of the figure. Oldest strata are at the bottom of the figure, youngest at the top. Platform interior is toward the left and platform margin toward the right.