湘西北地区二叠-三叠系界线地层与牙形石分带  

THE PERMO-TRIASSIC BOUNDARY AND CONODONT ZONES IN NORTHWESTERN HUNAN PROVINCE

作　　者：田树刚[1] 

机构地区：[1]中国地质科学院地质研究所

出　　处：《地球学报》1993年第1期133-150,共18页Acta Geoscientica Sinica

摘　　要：本文主要从生物地层学角度探讨湘西北地区二叠-三叠系界线划分。笔者对该区上二叠世地层进行了重新划分;以牙形石地层分布、百分比丰度和演化关系为基础,将该区二叠系栖霞阶顶部至三叠系格里斯巴赫阶划分为13个牙形石带,并与区内其它门类化石带和国内外同期牙形石带做了详细对比;界线层夹有多层海底火山喷发物成因的伊利石-蒙脱石粘土岩,界线上见有“过渡层”或生物“混生层”,证明该区界线地层为连续沉积。据界线上下“二叠型”与“三叠型”生物的盛衰和演替,以菊石Hypophiceras带或“过渡层”的底部为该区二叠-三叠系界线。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.

关 键 词：牙形石 地层划分 长兴组 栖霞阶 吴家坪阶 连续沉积 龙潭组 分带 湘西北 组合带 

分 类 号：P5[天文地球—地质学]