| 湘西北地区二叠-三叠系界线地层与牙形石分带 |
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| THE PERMO-TRIASSIC BOUNDARY AND CONODONT ZONES IN NORTHWESTERN HUNAN PROVINCE |
| Northwestern Hunan Province is one of the best areas for studying Permo-Triassic boundary. Ten thousand and more conodont specimens have been obtained from five sections which belong to two kind of facies in this area. Based on the study of the distribution and. the evolutionary relationships, 13 conodont zones have been recognized from the uppermost Qixiaian of the Lower Permian to the Griesbachian of the Lower Triassic. These zones are identical with the zones of ammonoids, brachiopods, bivalves and fusulinids in this area, and. entirely correctable with the conodont zones of other areas in South China and other regions. The zones are listed as follows:1-Neogondolella idahoensis-N. serrata A. Z., 2-N. postserrata-N. aserrata A. Z., 3-N. babcocki-N. wilcoxi A. Z., 4-N. liangshanensis-N. bitteri A. Z., 5-N. leveni A. Z., 6- 2V. orientalis A. Z., 7-N. subcarinata-N. wangi A. Z., 8-N. postwangi-N. changxingensis A. Z., 9-N. xiangxiensis-N. changxingensis A. Z., 10-Unnamed Zone, 11-Hindeodus parvus Z., 12-Isarcicella isarcica Z., 13-Neogondolella carinata-N. planata A. Z.Stratigraphical continuity through the boundary has been confirmed in the area. The clay layers above and below the boundary are all made up of illite-montmorillonite mixed-layer clay rock with some erupting structures, which contains some minerals formed at high temperatures, such as albites, β-quartzes, biotites etc. The result above shows that the clay rock originated from volcanic materials deposited in an ancient ocean. "Transitional bed" and its "mixed-fauna" at the bottom of the Triassic are considered as continuous marks of the sedimentation and animal evolution. The "transitional beds" in this area are 0.79m-4m thick and the "mixed-fauna" includes 15 genera and 18 species of brachiopods, ammonoids, bivalves and conodonts.The Permo-Triassic boundary is set at the bottom of ammonoid Hypo-phiceras Zone or "transitional bed" in this paper. The limit is defined by the replacing peak of "Permian type" and "Triassic type" organisms. |
| TIAN Shu-gang.1993.THE PERMO-TRIASSIC BOUNDARY AND CONODONT ZONES IN NORTHWESTERN HUNAN PROVINCE[J].Acta Geoscientica Sinica,14(1):133-150. |
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