Journal of Earth Science, Vol. 21, Special Issue, p. 174–175, June 2010 ISSN 1674-487X Printed in China

Calcareous Tube-Worm Fossils in Microbialites after End-Permian

Mass Extinction and Their Paleoenvironmental Implications

Yang Hao* (杨浩), Liu Hao (刘浩), Wang Yongbiao (王永标)

Key Laboratory of Biogeology and Environmental Geology of Ministry of Education,

China University of Geosciences, Wuhan 430074, China

Calcareous tube-worm fossils, forming dense ag-

gregations, are very common in the Permian–Triassic

microbialites and laminated, micritic limestone in

South China. They usually have the closed, elliptical

to kidney-shaped outlines in cross sections, 50–200

μm in diameters. The walls are composed of micritic

calcites. Worm tubes appear various outlines in verti-

cal sections, but micritic tube walls are always pro-

nounced and don’t have any optic change under the

crossed polarization of microscope.

Previously, small, spirally-coid worm tubes were

assigned to the polychaete Spirorbis in the Phanero-

zoic. However, the modern Spirorbis is a polychaete

annelid. In contrast, tube wall microstructure in the

pre-Cretaceous ‘Spirorbis’ suggests affinities with the

Microconchida, an extinct order of possible lopho-

phorates (Taylor and Vinn, 2006). Most aspects of

microconchid paleoecology are believed to be closely

similar to modern spirorbid polychaetes (Taylor and

Vinn, 2006). Various morphological characteristics of

This study was supported by the National Natural Science

Foundation of China (Nos. 40730209, 40572002), and the 111

Project (No. B08030).

*Corresponding author: 2003yanghao@163.com

© China University of Geosciences and Springer-Verlag Berlin

Heidelberg 2010

Manuscript received December 22, 2009.

Manuscript accepted January 10, 2010.

both spirorbid and microconchid tubes are usually in-

terpreted as adaptation to environmental conditions,

especially depositional conditions (Rzhavsky, 1994;

Tyson and Pearson, 1991) or competition with other

organisms living on the same substrate (Rzhavsky,

1994; Brönnimann and Zaninetti, 1972).

After the end-Permian mass extinction, the ma-

rine environments have been severely devastated and

the deleterious seawater prevailed in the Early Triassic

oceans (Bottjer, 2004). Thus, the marine ecosystems

have been degraded to the pre-Cambrian level (Knoll

et al., 2007). On one hand, these tube-worms at-

tempted to change their living behaviors to adapt to

the stressed environments. Their morphological fea-

tures therefore highly varied. On the other hand, the

ecospace hospitable for organisms to inhabit was lim-

ited in the post-extinction oceans and thus facilitated

biotic competition among organisms dwelling in the

same habitat. The tube-worms also need to change

morphology and living styles to win the competition.

Accordingly, proliferation of tube-worms in the

Permian–Triassic microbialites is interpreted as the

consequence of the stressed environment in the after-

math of the end-Permian mass extinction.

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