1. Institute of Geology and Geophysics,
Chinese Academy of
Sciences, Beijing 100029, China
2. Department of Geology, Wichita State
University, 1845 Fairmount,
Wichita, KS 67260, USA
Studies of two
Permian-Triassic boundary (PTB) sections
on top of a Changhsingian reef in Ziyun,
Guizhou Province, southwestern China
indicate that the end-Permian mass
extinction of reef ecosystems occurred
in two steps. The first step is the
extinction of all stenotropic organisms
such as calcisponges and fusulinids in
the latest Permian (in the Clarkina
yini conodont zone). The biota after
the first extinction is simple,
comprising eurytropic organisms
including microgastropods, ostracods,
and some small burrowing organisms, or
only algal mats. At the beginning of the
Early Triassic (i.e. the beginning of
the Hindeodus parvus zone), the
environments became anoxic, and the
microgastropod dominated biota or algal
mats disappeared, which constituted the
second episode of the mass extinction.
The biota after the second extinction
comprises small spherical
microproblematica, some kinds of
specialized organisms tolerant of anoxic
or oxygen-poor conditions. As the
environments became oxygenated, the
specialized biota was replaced by a
microgastropod-dominated simple biota.
When the environmental conditions
improved further, the simple biota was
replaced by a diverse biota with
normal-sized ammonoids, bivalves, and
gastropods, representing restoration of
normal oceanic conditions. Comparison
with PTB sections in Dolomites, Italy
and Meishan, Zhejiang Province shows
that non-reef ecosystems had a similar
first episode of mass extinction in the
latest Permian. In the case that oceanic
anoxia happened, non-reef ecosystems had
a second extinction episode similar to
that of reef ecosystems.
Submit Time:
2006-4-8 11:59:05
end-Permian, reef, mass
extinction, Guizhou, Permian-Triassic
boundary