Decimetre-scale domal to tabular patch reefs consisting of dendroid tetradiids are found in the Late Ordovician (late Katian) Xiazhen Formation, southeast China. It is intriguing to observe that siliceous sponges occur together with the tetradiids in many patch reefs, as this has not been previously reported. The tetradiid Rhabdotetradium jiangshanense are preserved in situ and the siliceous sponges, where present, as spicule networks. Calcimicrobe Ortonella encrusting tetradiid tubes and burrows filled with faecal pellets also constitute as subordinate components of the patch reef. The tetradiid tubes are regarded as frame-builders that are commonly surrounded and encrusted by the siliceous sponges. The sponges, wherever observed, form the bulk of the patch reef and are regarded as a primary constructor as well as binder of the patch reef. Burrows filled with faecal pellets often penetrate the area between tetradiids and sponge spicule networks in the boundstone and these are considered to be the loci of dweller. Where the sponges and tetradiids co-occur, the tetradiid tubes are sparsely distributed and commonly display non-quadripartite fission (i.e., bipartite or tripartite). In contrast, where the sponges are rare in the patch reef, the tetradiid tubes are densely spaced and predominantly display quadripartite fission. This indicates that the tetradiid growth was influenced by the presence of siliceous sponges. This finding of the new Late Ordovician reef association and their mutual interplay extend our understanding of the Early Palaeozoic carbonate reefs. It reaffirms the need for multidisciplinary studies of carbonate buildups where similar interactions with siliceous sponges might have been overlooked.
Bibliographical noteFunding Information:
This work was supported by a grant from the Korea Research Foundation ( KRF-2007-331-C00247 ) to S.-J. Choh and a grant from the Korea Research Foundation ( KRF-2010-0008549 ) to D.-J. Lee. We thank helpful comments from B.R. Pratt and H.M. Steele-Petrovich, which improved the manuscript considerably. We also thank S.K. Chough of the Seoul National University and J. Woo of the Korea Polar Research Institute for carefully reading the earlier manuscript. J. Hong and M. Lee of the Korea University and Y.M. Choi of the Andong National University are appreciated for their assistance during the thin section and the artwork preparation.
Copyright 2012 Elsevier B.V., All rights reserved.
- Late Ordovician
- Patch reef
- Siliceous sponge
- Xiazhen Formation
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