Friday, February 21, 2014

Anoxia, High Temperatures Effected Benthic Biotic Recovery During Scythian Triassic

High temperature and low oxygen perturbations drive contrasting benthic recovery dynamics following the end-Permian mass extinction


Pietsch et al


The end-Permian mass extinction event was the greatest loss of biodiversity ever experienced on the planet. The event is thought to have been triggered by the initiation of the volcanic eruptions of the Siberian Traps. The five million year recovery interval that followed the extinction event was strongly influenced by the environmental effects of sustained volcanic eruptions including extreme temperature events and persistent global and regional oxygen minimum zones. The effects of these environmental perturbations on the paleoecological recovery of the benthic marine fauna were studied in two depositional units from the Southwestern United States representing two substages during the Early Triassic recovery. The Smithian Sinbad Limestone was influenced by high sea surface temperatures and contains a relatively high diversity fauna that exhibits extremely small body size. Gastropods that lived in this environment were size-limited, a possible result of metabolic stress due to extreme temperatures. These microgastropods were able to become dominate components of the benthic fauna by occupying niche space vacated by other taxa that were excluded by high temperatures. The Spathian Virgin Limestone shows evidence for low oxygen conditions. The resulting low diversity benthic fauna had a more ecologically complex community structure than the Smithian Sinbad Limestone including the occupation of epifaunal tiering space by crinoids. As the prevalence of aerobic facies increased through time, diversity, body size, and the complexity of faunal interactions also increased suggesting that low oxygen conditions were the limiting factor for the benthic recovery in that region. The differences in diversity and community structure between the two units highlight the importance of environmental and temporal differences in driving the recovery patterns of the benthic fauna following the extinction event. High temperature events and low oxygen conditions restricted the benthic fauna in different ways but both contributed to the delay in recovery from the end-Permian mass extinction.

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