Death,
Destruction & Dirt: Using Paleosols to
Reconstruct Environmental Changes across the Permo-Triassic
Boundary
Thomas, Stephanie1, Neil Tabor1,
Wan Yang2 (1) Southern Methodist University, Dallas, TX (2) Wichita State University, Wichita, KS
Although the Permian-Triassic Boundary
(PTB) marks the largest mass extinction of the Phanerozoic,
the cause(s) of the extinction remains largely enigmatic. Paleosols
provide a means for evaluating environmental and climatic changes across the
PTB. Terrestrial exposures of the PTB are known primarily from high-latitude Gondwana, including sections from India, South Africa, Australia, & Antarctica, and from peri-Tethyan sections in China and Russia.
During the Late Permian, the demise of
icehouse conditions led to widespread coal development in Gondwana
due to increased high-latitude humidity. In western and equatorial Pangea climate shifted towards greater aridity, although Tethyan realms remained humid until earliest Triassic time.
Paleosols
from the Turpan-Hami Basin, NW
China, show striking variations in morphology across the PTB. Paleosols
of the Permian Wutonggou fm. are characterized by
intense redoximorphy, accumulation of vascular plant
matter, accumulation of clay minerals and Fe-oxides, slickensides,
and clastic dikes, suggesting a soil moisture regime
that ranged from perennially wet to one with distinct seasonal variations in
soil moisture budget. The Lower Triassic Jiucaiyuan
fm. contains pedogenic CaCO3 accumulations
and gypsum pseudomorphs, indicating a drier
environment characterized by net soil moisture deficiency. Modern soil analogs
suggest that the Wutonggou paleosols
formed in humid environments with >1000 mm of precipitation/yr, whereas
Lower Triassic paleosols formed in environments with
<300 mm/yr. A negative shift in the δ13C values of organic
matter is observed across the PTB from ~-22‰ in the Upper Permian to ~-31‰ in
the Lower Triassic, suggesting dramatic changes in atmospheric composition and OM burial.