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通过对新疆吉木萨尔大龙口背斜南翼剖面,陆相二叠系—三叠系界线层段锅底坑组介形虫生物地层的研究,发现介形虫化石非常丰富,计有3属51种,可明显地划分为两个组合带,即①Panxiania reticulata -Darwinuloides circulosa-Darwinula parallela 组合带和② Darwinula rotundata-Darwinula gloria-Darwinula pseudooblonga 组合带。第一组合带的化石由3属27种组成,分布在锅底坑组下段和上段底部(大龙口剖面的2～54层), 该组合带显示了我国贵州和华北上二叠统宣威组、孙家沟组(狭义的石千峰组)及俄罗斯上二叠统鞑靼阶的特征,其时代无疑应归为晚二叠世。第二组合带的化石包含2属24种,发现在锅底坑组上段(大龙口剖面的 55～85层),该组合带显示了我国华北和新疆准噶尔盆地下三叠统和尚沟组、韭菜园组和俄罗斯下三叠统马尔采夫组、维特卢日组及哈萨克斯坦下三叠统阿克柯尔卡恩组的特征,其时代应归属为早三叠世的早期。因此,在该界线层段出现早三叠世的第二介形虫组合带,即以早三叠世 Darwinula rotundata,D.gloria 等的始现,作为早三叠世的开始。根据介形虫化石的研究,二叠系—三叠系的界线应置于第一组合带与第二组合带之间,即在锅底坑组上段下部,大龙口背斜南翼剖面的54层和55层之间,距韭菜园组底界之下约90.27 m。
Based on the study of the ichthyosporium bio-stratum in the pan-bottom pit of the continental Permian-Triassic boundary line in the south wing of the Jimsal alluvial anticline in the Jimusar area of Xinjiang, it is found that there are three genera 51 species, can be clearly divided into two combinations, namely ① Panxiania reticulata - Darwinuloides circulosa-Darwinula parallela combination band and ② Darwinula rotundata-Darwinula gloria-Darwinula pseudooblonga combination band. The first assemblage of fossils is composed of 3 genera and 27 species distributed in the lower part of the pot bottom pit group and the bottom of the upper part (2-54 layers in the section of Dalongkou section). The assemblage shows the Upper Permian Xuanwei Formation in Guizhou and North China , The Sunjiagou Formation (Shiqianfeng Formation in the narrow sense), and the characteristics of the Upper Permian Tatar in Russia. Its era undoubtedly belongs to Late Permian. The second assemblage of fossils contains 24 genera and 2 genera and is found in the upper part of the pot pit group (55 ~ 85th layer in the section of Dalongkou). The assemblage shows that the Lower Triassic and Wuxigou Group in North China and Junggar Basin in Xinjiang, The characteristics of the Yuan Group and the Lower Triassic Maltshev Formation, the Vitrulu Formation in Russia and the Lower Triassic Akekelkarn Formation in Kazakhstan should belong to the early Early Triassic. As a result, the second Triassic second ichnoformer assemblage occurred in the boundary layer, that is, the beginning of the Early Triassic with the appearance of the Early Triassic Darwinula rotundata and D.gloria et al. According to the study of ostracod fossils, the Permian-Triassic boundary should be placed between the first and second assemblages, that is, at the lower part of the upper part of the pot bottom pit group, Between the 55th and 55th floors, about 90.27 m below the bottom of the Chive Garden Group.