Internal structure and paleoecology of the lower Permian Uzunbulak reef complex of the Tarim Basin,Northwest China |
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Authors: | Zhong-Qiang Chen Guang R. Shi Wan-Rong Yang |
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Affiliation: | (1) Institute of Geology and Paleontology, Tohoku University, Aoba, Armake, 980-8578 Sendai, Japan;(2) School of Ecology and Environment, Deakin University, Melbourne Campus, 221 Burwood Highway, 3125 Burwood, Victoria, Australia;(3) Nanjing Institute of Geology and Palcontology, Chinese Academy of Sciences, 39 Beijing East Road, 210008 Nanjing, China |
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Abstract: | Summary The internal construction and biotic communities of the Uzunbulak reef of the northwestern Tarim Basin are studied for the first time. The reef was built during the Sakmarian, while the reef substrate and capping beds are of latest Asselian and earliest Artinskian ages, respectively. The reef substrate beds are composed of skeletal and oncoid grainstone. Those fusulinid-dominated skeletal shoals and oncoid banks indicate a high-energy environment and produced local topographic highs on which the reef grew. Reef framework consists mainly of calcisponge bafflestone, calcisponge-Thartharella framestone, and Tubiphytes, Archaeolithoporella and Girvanella boundstones. Calcisponges were the primary frameconstructors that baffled high-energy currents. Archaeolithoporella, Tubiphytes, Girvanella and possibly microbes acted as the primary binders for the boundstone framework. Fusulinids and brachiopods were common reef dwellers. The interreef facies sediments are composed of skeletal-crinoid wackestone-packstone. Most of bioclasts have thick, micritized envelopes. The back-reef facies deposits consist of alternating skeletal packstone to wackestone and black shale. Sea-level fluctuations were probably accountable for the reef growth and demise. Of the reefal dwellers, brachiopods are extraordinarily abundant in Uzunbulak. They are assignable to five distinctive associations, one each from the reef substrate, framework and inter-reef facies, respectively, and two from the reef capping facies. The brachiopods in the substrate beds were mostly attached to hard substrates by a pedicle, while a few species rested on soft substrates by support of halteroid spines. Cementation of the ventral valve on hard substrates characterizes attachment of the reef framework brachiopods. All inter-reef species were anchored into the substratum comprising hard material by a strong pedicle. Back-reef brachiopods dominantly rested on the soft substrates by support of halteroid spines. the framework brachiopods had the strongest wave-resistant capability;those from both substrate and inter-reef facies were moderately capable of withstanding agitation; and the backreef species preferred to live in calmwater, organic-rich muddy environments. |
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Keywords: | Uzunbulak Reef Framework calcisponges Tubiphytes Dwelling Brachiopods Tarim Basin (Northwest China) Permian |
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