Amelioration of marine environments at the Smithian–Spathian boundary, Early Triassic
The protracted recovery of marine ecosystems following the Permian–Triassic mass extinction may have been caused, in part, by episodic environmental and climatic crises during the Early Triassic, among which the Smithian–Spathian boundary (SSB) event is conspicuous. Here, we investigate the SSB even...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-03-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/12/1597/2015/bg-12-1597-2015.pdf |
| Summary: | The protracted recovery of marine ecosystems following
the Permian–Triassic mass extinction may have been caused, in part, by
episodic environmental and climatic crises during the Early Triassic, among
which the Smithian–Spathian boundary (SSB) event is conspicuous. Here, we
investigate the SSB event in the Shitouzhai section, Guizhou Province, South
China, using a combination of carbonate carbon (δ<sup>13</sup>C<sub>carb</sub>)
and carbonate-associated sulfate sulfur isotopes (δ<sup>34</sup>S<sub>CAS</sub>), rare earth elements, and elemental paleoredox and
paleoproductivity proxies. The SSB at Shitouzhai is characterized by a
+4‰ shift in δ<sup>13</sup>C<sub>carb</sub> and a −10 to
−15‰ shift in δ<sup>34</sup>S<sub>CAS</sub>, recording
negative covariation that diverges from the positive δ<sup>13</sup>C<sub>carb</sub>−δ<sup>34</sup>S<sub>CAS</sub> covariation that characterizes
most of the Early Triassic. This pattern is inferred to reflect an increase
in organic carbon burial (e.g., due to elevated marine productivity)
concurrently with the oxidation of isotopically light H<sub>2</sub>S, as the result of
enhanced vertical advection of nutrient- and sulfide-rich deep waters to the
ocean-surface layer. Enhanced upwelling was likely a response to climatic
cooling and the reinvigoration of global-ocean overturning circulation at the
SSB. Coeval decreases in chemical weathering intensity and detrital sediment
flux at Shitouzhai are also consistent with climatic cooling. A decline in
marine biodiversity was probably associated with the late Smithian thermal
maximum (LSTM) rather than with the SSB per se. The SSB thus marked the
termination of the extreme hothouse conditions of the Griesbachian–Smithian
substages of the Early Triassic and is significant as a record of
accompanying climatic, environmental, and biotic changes. The ultimate cause
of the SSB event is uncertain but may have been related to a reduction in
intrusive magmatic activity in the Siberian Traps large igneous province. |
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| ISSN: | 1726-4170 1726-4189 |