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1.
Measured lithostratigraphic sections of the classic Permian–Triassic non-marine transitional sequences covering the upper Quanzijie, Wutonggou, Guodikeng and lower Jiucaiyuan Formations at Dalongkou and Lucaogou, Xinjiang Province, China are presented. These measured sections form the framework and reference sections for a range of multi-disciplinary studies of the P–T transition in this large ancient lake basin, including palynostratigraphy, vertebrate biostratigraphy, chemostratigraphy and magnetostratigraphy. The 121 m thick Wutonggou Formation at Dalongkou includes 12 sandstone units ranging in thickness from 0.5 to 10.5 m that represent cyclical coarse terrigenous input to the lake basin during the Late Permian. The rhythmically-bedded, mudstone-dominated Guodikeng Formation is 197 m and 209 m thick on the north and south limbs of the Dalongkou anticline, respectively, and 129 m thick at Lucaogou. Based on limited palynological data, the Permian–Triassic boundary was previously placed approximately 50 m below the top of this formation at Dalongkou. This boundary does not coincide with any mappable lithologic unit, such as the basal sandstones of the overlying Jiucaiyuan Formation, assigned to the Early Triassic. The presence of multiple organic δ13C-isotope excursions, mutant pollen, and multiple algal and conchostracan blooms in this formation, together with Late Permian palynomorphs, suggests that the Guodikeng Formation records multiple climatic perturbation signals representing environmental stress during the late Permian mass extinction interval. The overlap between the vertebrates Dicynodon and Lystrosaurus in the upper part of this formation, and the occurrence of late Permian spores and the latest Permian to earliest Triassic megaspore Otynisporites eotriassicus is consistent with a latest Permian age for at least part of the Guodikeng Formation. Palynostratigrahic placement of the Permian–Triassic boundary in the Junggar Basin remains problematic because key miospore taxa, such as Aratrisporites spp. are not present. Palynomorphs from the Guodikeng are assigned to two assemblages; the youngest, from the upper 100 m of the formation (and the overlying Jiucaiyuan Formation), contains both typical Permian elements and distinctive taxa that elsewhere are known from the Early Triassic of Canada, Greenland, Norway, and Russia. The latter include spores assigned to Pechorosporites disertus, Lundbladispora foveota, Naumovaspora striata, Decussatisporites mulstrigatus and Leptolepidites jonkerii. While the presence of Devonian and Carboniferous spores and Early Permian pollen demonstrate reworking is occurring in the Guodikeng assemblages, the sometimes common occurrence of Scutasporites sp. cf. Scutasporites unicus, and other pollen, suggests that the Late Permian elements are in place, and that the upper assemblage derives from a genuine transitional flora of Early Triassic aspect. In the Junggar Basin, biostratigraphic data and magnetostratigraphic data indicate that the Permian–Triassic boundary (GSSP Level) is in the middle to upper Guodikeng Formation and perhaps as high as the formational contact with the overlying Jiucaiyuan Formation.  相似文献   

2.
中国非海相二叠—三叠系界线层型剖面研究   总被引：4，自引：1，他引：4  
吉木萨尔三台大龙口剖面已被推荐为国际非海相二叠─三叠系界线层型侯选剖面。该剖面是世界上研究非海相二叠─三叠系界线最理想的剖面之一，也是我国非海相二叠─三叠系界线研究程度最高的剖面。准噶尔南缘上二叠统─下三叠统统称仓房沟群，下分5个组（自下而上）：泉子街组、梧桐沟组、锅底坑组、韭菜园组、烧房沟组，除烧房沟组与下伏韭菜园组间有显著冲刷面外，各组间均为整合接触关系。仓房沟群中生物化石丰富，可以划分出植物、孢粉、双壳类、叶肢介、介形虫、脊椎动物等不同的生物组合，尤其重要的是在锅底坑组上部发育晚三叠世与早三叠世生物混生的过渡层。这个过渡层揭示了生物演变的连续性，即脊椎动物Jimusaria与Lystrosaurus共生，孢粉Lueckisporitesvirkkiae与Lundbladisporawatangensis共生，以及二叠纪型的植物、双壳、介形虫与三叠纪型的叶肢介之间的混生。即在这个过渡层中既含晚二叠世型的孑遗分子，也含早三叠世型的新生分子，因而可以确定二叠系与三叠系界线就在锅底坑组内，置于大龙口背斜南翼剖面第36层，北翼剖面第34层之底，即在锅底坑组与韭菜园组传统岩组界线之下约50m（北翼）～60m（南翼）处。古地磁反映的正负极性与生物地层界线基本一致。  相似文献   

3.
Marine and non-marine facies of the Permian–Triassic boundary stratigraphic set (PTBST) are well developed in South China. Palynological assemblages enable subdivision and correlation of the Permian–Triassic boundary (PTB) rocks. Three palynological assemblages are recognized across the PTBST in two terrestrial PTB sections in western Guizhou and eastern Yunnan, South China. Assemblage 1 (Xuanwei Formation) is a Late Permian palynological assemblage dominated by ferns and pteridosperms, with minor gymnosperms. Most taxa are typical long-ranging Paleozoic forms, but the appearance of Lueckisporites confirms a Late Permian age for this assemblage. Assemblage 2 (PTBST) is marked by an abrupt decrease in palynomorph abundance and diversity, and thriving fungal/algal(?) spores. Assemblage 2 is still dominated by ferns and pteridosperms, with a few gymnosperms, but is characterized by a mixed palynoflora containing both Late Permian and Early Triassic elements. Most taxa are typical Late Permian ones also found in Assemblage 1, however, some taxa of Early Triassic aspect, e.g. Lundbladispora and Taeniaesporites, appeared for the first time. In Assemblage 3 (top Xuanwei Formation and Kayitou Formation), the proportion of gymnosperm pollen increases rapidly, exceeding that of ferns and pteridosperms, but the abundance of palynomorphs is still low. Typical Early Triassic taxa (such as Lundbladispora, Aratrisporites and Taeniaesporites) are present in greater abundance and confirms an Early Triassic age for this assemblage.  相似文献   

4.
通过对吉木萨尔县大龙口非海相二叠系-三叠系界线上下地层磁性特征的研究,在梧桐沟组-锅底坑组共发现78个极性异常,其中以负极性为主,间隔了一系列的正极性和过渡极性.梧桐沟组上部以负极性为主,间隔了2个正极性和过渡极性.这可与巴基斯坦盐岭和四川广元上寺的大隆组下部对比,即相当于Da段.梧桐沟组顶部和锅底坑组底部,正、负极性变化频繁,极性特征可与巴基斯坦盐岭和四川广元上寺大隆组中部对比,即相当于Db段.锅底坑组下部以负极性为主,间隔了2个正极性段,可与四川广元上寺大隆组中上部对比,即相当于Dc段.锅底坑组中下部以负极性为主,上部夹1个正极性段,可与四川广元上寺大隆组上部磁性特征对比,即相当于Dd段.锅底坑组中上部以负极性为主,间隔了4个正极性段,可与四川广元上寺飞仙关组下部对比,即相当于Fa段.根据磁性段的划分对比,将二叠系三叠系界线置于Fa和Dd之间,即本次研究测制剖面的41层和42层之间.根据各岩组的古地磁特征求得岩组形成时的古地磁极:梧桐沟组79.1°N,238.1°;锅底坑组72.3°N,322.2°;下三叠统77.5°N,320.8°.古纬度基本一致,为32°～35°N.  相似文献   

5.
ABSTRACT

This study investigates three Lopingian (upper Permian)-Lower Triassic terrestrial successions in northwest China, namely the Urumqi and Jimsar sections in the southern Junggar Basin (SJB), and the Taodonggou section in the Turpan Basin (TB). Stratigraphy studies suggest that, in all three sections, the Lopingian-Lower Triassic strata are represented by mixed fluvial and lacustrine deposits. The lithofacies and geochemical indicators (CIA, PIA) suggest that, in all three sections, the Wutonggou Formation (Wuchiapingian) was deposited under subhumid conditions. The Guodikeng Formation (Changhsingian-early Induan) represents subhumid to semiarid conditions. The Jiucaiyuan and Shaofanggou formations (mid-to-late Induan to Olenekian) in the SJB show highly variable subhumid-semiarid conditions, while the two formations in the TB display early episode of fluctuating subhumid-semiarid and later semiarid-arid conditions. Within each section, all four formations display similar petrographic and geochemical characteristics, suggesting consistency in provenance during deposition. However, the provenance characteristics of the Urumqi and Jimsar sections differ from those of the Taodonggou section. Relative to the Taogonggou section, the two sections in the SJB contain more felsic and recycled sedimentary components. This suggests that the greater Junggar-Turpan Basin was in a partitioned setting during the Lopingian-Early Triassic, when different subbasins have relatively independent provenance systems.  相似文献   

6.
吐哈盆地北缘二叠系与三叠系界线   总被引：5，自引：1，他引：4  
刘兆生 《地层学杂志》2000,24(4):310-314
对吐哈盆地北缘锅底坑组中部和上部孢粉组合研究后发现 ,中部组合见有晚二叠世的重要分子 L uecki-sporites及二叠纪的重要分子 H amiapollenites,以具肋双囊粉含量明显较高为特征 ;上部组合出现了具有一定含量的早三叠世的典型分子 L undbladispora,三叠纪的常见分子 Chasmatosporites,以及以 Taeniaesporites的含量较高为特征。两个组合既具有明显的不同 ,但共有分子又在 2 0种以上 ,占各自组合孢粉种总数的一半以上 ,这说明二者又具有连续过渡的性质。因此 ,桃东沟剖面二叠系 -三叠系生物地层界线应划在锅底坑组上部 ,位于锅底坑组与韭菜园组岩石地层界线以下约 40 .49m处 (即第 12层与第 11层之间 )  相似文献   

7.
内蒙古阿鲁科尔沁旗陶海营子剖面 林西组化石新发现   总被引：4，自引：1，他引：3  
大兴安岭地区上二叠统林西组一直笼统地被划归为上二叠统,目前仍旧缺少更进一步的划分对比意见.阿鲁科尔沁旗陶海营子剖面是林西组的典型剖面之一.剖面实测过程中,在多个层位均发现有孢粉、植物、叶肢介、双壳化石,其中孢粉化石为首次发现.孢粉化石为Kraeuselisporites spinulosus-Alisporites communis组合,叶肢介化石为Palae olimnadia-C yc lotunguzites组合.综合研究孢粉、叶肢介等门类化石的组合特征,认为该剖面林西组可与新疆吉木萨尔大龙口剖面的梧桐沟组—锅底坑组中下部进行对比,时代为晚二叠世晚期.  相似文献   

8.
A section 300 m thick across the Permian—Triassic boundary has been sampled in the Southern Coalfield of the Sydney Basin, New South Wales. 55 samples, mainly grey to drab sandstones, were collected from 9 diamond drill holes which penetrated the entire Narrabeen Group and the upper part of the conformably underlying Illawarra Coal Measures, as well as a sill emplaced into the coal measures. The samples included fully oriented cores. Additional reconnaissance samples from two further drill holes were also studied.Partial alternating field demagnetization and petrography indicate the magnetic remanence to be a stable DRM. Partial thermal demagnetization above 300°C or 400°C caused large increases in magnetic susceptibility. Partial chemical demagnetization did not cause significant changes in remanence directions.For the Coal Cliff Sandstone (basal Narrabeen Group, Triassic) the palaeomagnetic pole position (Normal) was calculated to be at 59°N 322°E (dp = 27°, dm = 29°), which agrees with previously published data. For the uppermost coal measures (Permian) the pole position was calculated as 58°N 340°E (dp = 09°, dm = 10°). Data for samples from the lower to middle coal measures yield a pole position which is between the new Permian—Triassic pole position and that for the underlying Middle Permian igneous rocks. The top of the Reversed “Kiaman Magnetic Interval” (Permian) may be near the Tongarra coal and Appin Formation boundary — (early) Late Permian.  相似文献   

9.
Analyses of Lower Permian or older basalts and associated dykes of the Juchatengo sequence indicate that they are rift tholeiites that formed in a continental rift or back-arc tectonic setting. Age constraints include a Middle Permian fossil recovered from the tectonically overlying sediments and a cross-cutting, post-tectonic pluton dated by K/Ar on hornblende at 282±6 Ma. A location adjacent to the Oaxacan Complex or other old continental crust is suggested by (1) an Ndi isotopic value of −8.95 and a TDM age of 1487 Ma in the overlying sediments, which are similar to the Oaxacan Complex; (2) enrichment of incompatible elements in the lavas, suggesting old crustal contamination; and (3) the presence of Permian–Triassic calc-alkaline plutons that stitch the Juchatengo–Oaxaca boundary. The possible tectonic models depend on the age of the Juchatengo basalts, which requires future geochronological work. If the Juchatengo basalts are Permo-Carboniferous, they could have formed near the eastern edge of a back-arc basin: the contemporaneous arc would have rifted away to the west. Eastward migration of the arc magmatism indicated by the Permian–Triassic calc-alkaline plutonism may reflect shallowing of the dip of the subduction zone, which probably also produced the deformation of the Juchatengo sequence.  相似文献   

10.
Samples collected from folded carbonate rocks of the Early Permian Copacabana Group exposed in the Peruvian Subandean Zone have been subjected to detailed palaeomagnetic analysis. Thermal demagnetisation of most samples yield stable high unblocking temperature directions dominantly carried by titanomagnetite minerals. This remanence, identified in 32 samples (43 specimens), is exclusively of reverse polarity consistent with the Permian–Carboniferous Reversal Superchron (PCRS). The overall directions pass the fold test at the 99% confidence level and are considered as being a pre-folding remanence acquired in Early Permian times. The Copacabana Group yields an overall mean direction of D = 166°, I = +49° (α95 = 4.5°, k = 131.5, N = 9 sites) in stratigraphic coordinates and a corresponding palaeosouth pole position situated at λ = 68°S,  = 321°E (A95 = 5.2°, K = 100). Combining this pole with the coeval high quality data from South America, Africa and Australia results in a mean pole for Gondwana situated at λ = 34.4°S,  = 065.6°E (A95 = 4.9°, K = 73.6, N = 13 studies) in African coordinates. This pole position supports a Pangaea B palaeogeography in Early Permian times. In contrast, the combined pole for Gondwana diverges from the coeval Laurasian mean pole when assuming the Pangaea A-type configuration. Poor quality of the Gondwana dataset and inclination shallowing in sediments seem to play no role in the misfit between the Permian–Triassic poles from Gondwana and Laurasia in Pangaea A reconstruction.  相似文献   

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