Reconstruction of Early Triassic ocean redox conditions based on framboidal pyrite from the Nanpanjiang Basin, South China
Authors:
Tian et al
Abstract:
Widespread oceanic anoxia has been implicated as an important factor in the PTB (Permian Triassic boundary) mass extinction and the delayed recovery of Early Triassic marine ecosystems. An investigation of framboidal pyrite in the Bianyang section (Nanpanjiang Basin, South China) suggests that euxinia/dysoxia peaked during the Induan, late Smithian to earliest Spathian and late Spathian. These anoxic episodes show a relationship, albeit imperfect, to major episodes of climatic warming during the Early Triassic that were associated with intensified oceanic stratification, reduced marine productivity and organic carbon sinking fluxes, as well as diminished burial fluxes of organic carbon and reduced sulfur. In contrast, intervals of better-oxygenated marine conditions were associated with episodes of relative climatic cooling during the early to middle Smithian and mid-Spathian. The degree of ventilation of the thermocline region, in particular, had a profound effect on marine biotas, with intervals of improved ventilation resulting in increased global diversity among ammonoids and conodonts and increased local abundance of foraminifera in the Nanpanjiang Basin. These observations suggest that oceanic redox fluctuations played an important role in the delayed recovery of Early Triassic marine ecosystems, and, specifically, that episodic expansion of oceanic oxygen-minimum zones (OMZs) resulted in repeated setbacks to the recovery process, a pattern that persisted until the late Spathian.
High temperature and low oxygen perturbations drive contrasting benthic recovery dynamics following the end-Permian mass extinction
Authors:
Pietsch et al
Abstract:
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.
