Timing,petrogenesis, and setting of granites from the southern Beishan late Palaeozoic granitic belt,Northwest China and implications for their tectonic evolution

Late Palaeozoic granites are widely distributed in the southeastern Beishan area, which is located in the central part of the southern Central Asian Orogenic Belt (CAOB). U–Pb zircon dates of five late Palaeozoic granitic plutons from the southeastern Beishan area yield Permian ages: 285 ± 2 Ma (Shuwojing and Western Shuwojing plutons), 269 ± 3 Ma (Jianquanzi and Jiuquandihongshan plutons), and 260 ± 1 Ma (Jiujing pluton). The early Permian Shuwojing pluton, an unfractionated calc-alkaline biotite monzogranite with slightly positive εNd(t) (+0.7 and +0.6) and low initial ⁸⁷Sr/⁸⁶Sr (0.70722 and 0.70712), and the early Permian Western Shuwojing pluton, a high-K calc-alkaline biotite granite with slightly negative εNd(t) (?0.2 and ?0.1) and low initial ⁸⁷Sr/⁸⁶Sr (0.70390 and 0.70919), are likely derived from a mixture of depleted (juvenile) mantle and upper continental crustal (or sedimentary) material. The mid-Permian Jianquanzi and Jiuquandihongshan monzogranites have highly fractionated potassium-rich calc-alkaline characteristics with negative εNd(t) (?4.3) and very high initial ⁸⁷Sr/⁸⁶Sr (0.71949), reflecting a continental crustal component. The compositionally diverse Jiujing pluton and the granodiorite and high-Sr monzogranite phases display adakite-like compositions with relatively low εNd(t) (?0.1 and ?2.2) and high initial ⁸⁷Sr/⁸⁶Sr (0.70822 and 0.70913). The Jiujing low-Sr monzogranite has higher initial ⁸⁷Sr/⁸⁶Sr (0.73464) and lower εNd(t) (?2.8), indicating a significant continental crustal component in its genesis. This work, combined with the regional geology and previous studies, suggest that the early to middle Permian southern Beishan plutons formed in a post-collisional environment, probably an intracontinental rift environment linked to asthenospheric upwelling in response to the break-off of a subducted slab. In the late Permian, the southern Beishan area was in a compressive tectonic regime and thickening of the continental crust resulted in the formation of the Jiujing adakite-like granite.     

新命名地层单位──三塘湖组

经首次全国地层多重划分对比研究，在东准噶尔地层小区建议使用新命名地层单位──三塘湖组，用以代表一套以陆相中酸性火山熔岩及火山碎屑岩为主的火山岩系（局部有基性火山岩）．时限大致为早二叠世．文中介绍了三塘湖组的定义、划分沿革。层型剖面及分布变化。     

宁镇山脉小壳化石层时代的新认识

最新研究表明，句容仑山的小壳化石层和南京幕府山的一样，其层位都相当于下寒武统沧浪铺阶Ｐａｏｋａｎｎｉａ带，为我国下寒武统层位最高的一个小壳化石组合带。句容仑山当时位于台地边缘，缺失了早寒武世早期至沧浪铺期中期的沉积。     

新疆早侏罗世植物群特征

本文根据新疆早侏罗世各组中所产的植物化石,提出了疆新早侏罗世植物群分属于毛羽叶—锥叶蕨植物群与锥叶蕨—拟刺葵植物群的过渡植物群和锥叶蕨—拟刺葵植物群.过渡植物群中苏铁类比较丰富.锥叶蕨—拟刺葵植物群以真蕨类和银杏类为主,真蕨类中锥叶蕨,托第蕨,枝脉蕨最为发育.两个植物群按照不同层位均可分出上下两个组合.本文还探讨了八道湾组时代,认为无疑属早侏罗世,塔里奇克组植物组合也应属早侏罗世(塔里奇克组的地质时代为T_(?)—J_1).早侏罗世早期新疆气侯曾一度炎热,向后转为湿暖潮湿.     

伊朗珊瑚在新疆的发现

本文描述的伊朗珊瑚(Iranophyllum)是1971和1984年第一区调队在新疆南部昆仑山下二叠统黄羊岭群和叶桑岗组采集的,共4新种和1未定种,名单是:Iranophyllum xinjiangense(sp.nov).Ir.kunlunense(sp.nov.),Ir.clisiophylloides(sp.nov.),Ir.neoclisio-phylloides(sp.nov.),Ir.sp.A等.与其共生的有(?)类:Sumatrina annae,Verbeekina of.verbeeki,paraverbeekina of.umbi-lcata,Polydiexodina sp.,Yangchienia sp.,Neo-misellina sp.,parafusulina sp.,Chusenella sp.,Afghanella?sp.,腕足:Neospir-ifer sp.,Martinia sp.,Stenoscisma sp.,Waagenoconcha sp.,四射珊瑚:Amplexo-carinia sp.,Huangophyllum sp.,Lytvolasma sp.,plerophyllum sp.等.因此,含Ira-nophyllom的黄羊岭群和叶桑岗组应属同一层位,它们与新疆喀喇昆仑地区空喀山口组、西藏阿里地区龙格组及文部组是相当的.     

贵州紫云石头寨晚二叠世—中三叠世牙形石动物群及生态意义

本文所研究的贵州紫云石头寨上二叠统长兴组—中三叠统新苑组牙形石,共计5属14种,其中Hindeodus julfensis在华南系首次发现。文中对下三叠统罗楼组上部—中三叠统新苑组下部共建立了3个牙形石带,它们是Neospathodus timorensis带、Neogondolella regale带和N.constricta带。其中N.regale在华南属首次报导。此外就N.timorensis带的时代归属作了讨论,认为该带应属早三叠世晚期。而N.regale带为安尼阶最下部的牙形石带。文中还对牙形石的生态作了初步探讨。     

Early Jurassic Soft-Sediment Deformation Interpreted as Seismites in the Wuqia Pull-Apart Basin and the Strike-Slip Talas–Ferghana Fault, Xinjiang, China

The early Jurassic soft-sediment deformation occurring within lacustrine sandstone is distributed mainly in the Wuqia region of SW Tianshan Mountains, Xinjiang, western China. Triggered by earthquakes, such deformation was found to occur in three beds overlying the lower Jurassic Kangsu Formation. The main styles of deformation structures comprise load cast, ball-and-pillow, droplet, cusps, homogeneous layer, and liquefied unconformity. The deformation layers reflect a series of three strong earthquakes at the end of early Jurassic in the Wuqia region. The differences of deformation mechanisms undergone might represent the varying magnitudes of the earthquake events. During the early Jurassic, the Wuqia region was located in a pull-apart basin controlled by the significant Talas-Ferghana strike-slip fault in central Asia, which initiated the soft-sediment deformation induced by earthquakes. Our research suggests that the paleoseismic magnitudes could have ranged from Ms 6.5 to 7.     

New Schizolepis Fossils from the Early Cretaceous in Inner Mongolia, China and its Phylogenetic Position

Three Schizolepis species collected from the Lower Cretaceous layer of the Huolinhe Basin,Inner Mongolia,China are described.These fossils are Schizolepis longipetiolus Xu XH et Sun BN sp.nov.,which is a new species,Schizolepis cf.heilongjiangensis Zheng et Zhang,and Schizolepis neimengensis Deng.The new species is a well-preserved female cone,slender and cylindrical in shape.The seed–scale complexes have long petioles and are arranged on the cone axis loosely and helically.The seed scales are divided into two lobes from the base.Each lobe is semicircular or elongate ligulate in shape,widest at the middle or the lower middle part,with an obtuse or bluntly pointed apex.The inner margin is almost straight and the outer margin is strongly arched.On the surface of the lobe,there are longitudinal and somewhat radial striations from the base to the margin.The seed is borne on the adaxial surface at the base or middle of each lobe.Schizolepis was established in 1847,and,although more than twenty species have been discovered and reported,its phylogenetic position is controversial because of the imperfection of fossils.Most authors have considered there to be a close evolutionary relationship between Schizolepis and extant Pinaceae.Here,we analyze characteristics and compare Schizolepis with Picea crassifolia Kom,which is morphologically most similar to Schizolepis.The results indicate that the genus probably has a distant evolutionary relationship with extant Pinaceae.A detailed statistical analysis of the global paleogeographic distribution of Schizolepis showed that all the fossils of this genus appeared in strata ranging from the Upper Triassic to the Lower Cretaceous in the North Hemisphere,being rare in the Upper Triassic and Lower Jurassic,but being very common from the Middle Jurassic to the Lower Cretaceous,and particularly abundant in the Lower Cretaceous.According to the statistical results,we speculate that the genus originated in Europe in the Late Triassic then spread from Europe to Asia between the Late Triassic and the Late Jurassic.In the Early Cretaceous most species existed in China’s three northeastern Provinces and the Inner Mongolia Autonomous Region and adjacent areas.Combining the paleogeographic distribution of the genus with ancient climatic factors,we deduced that Schizolepis began to decline and became extinct in the Early Cretaceous,and the reason for its extinction is closely related to the icehouse climate during the Early Cretaceous.     

Early Ordovician CA-IDTIMS U–Pb zircon dating and conodont biostratigraphy,Canning Basin,Western Australia

A continuously cored section of more than 300 m through the Nambeet Formation and the basal part of the conformably overlying Willara Formation in the Olympic 1 petroleum well, drilled in the Canning Basin of northern Western Australia, yields valuable information that increases by more than 40% the number of precise isotopic ages available to constrain the Ordovician Period. New CA-IDTIMS U–Pb zircon ages for seven bentonite layers in the Olympic 1 core are integrated into a new conodont biostratigraphic framework for the Early Ordovician comprising four biozones recognised in this well. The weighted mean U–Pb dates range from 479.37 ± 0.16 Ma within the late Tremadocian Paroistodus proteus conodont Biozone, to 470.18 ± 0.13 Ma near the boundary between the Floian and Dapingian stages within the Jumudontus gananda conodont Biozone. The intervening Prioniodus oepiki–Serratognathus bilobatus conodont Biozone (early Floian) and succeeding Oepikodus communis conodont Biozone (middle Floian) are similarly well constrained by isotopic dates centred on ca 477 Ma for the early Floian and by three ages of 473–471 Ma for the middle Floian. The seven new isotopic dates significantly increase the precision of dating for the Early Ordovician, where previously only two ages with limited or imprecise biostratigraphic control were known globally.     

The Geological Significance of a Tuffite Interlayer in the Cretaceous Port Island Formation in Northeastern Hong Kong

The Port Island Formation(PIF), a typical Cretaceous red bed in Hong Kong, is dominated by non-fossiliferous, reddish clastic rocks, making it difficult to determine the sedimentary age of PIF precisely. Previous studies assigned the PIF to Late Cretaceous provisionally only on the basis of its stratigraphic sequence and lithology. This study identified a tuffite interlayer in the PIF and a zircon UPb age of 128.2±2.7 Ma by LA-ICP-MS method was obtained. It's the first time to date the depositional age of the PIF with a reliable chronological constraint. With the support of stratigraphic evidence, we concluded that the geological age of PIF should be Early Cretaceous rather than Late Cretaceous. Based on the volcanic history of Hong Kong and Southeast China and the distribution of the PIF in Mirs Bay, it is believed that there was no volcanic activity in Hong Kong in ca. 128 Ma. The tuffite interlayer discovered in PIF was formed by the deposition of volcanic ash, which might originate from remote region outside Hong Kong, in an aquatic environment on Port Island. The identification of the tuffite interlayer, as the response to a volcanic event, has great significance not only to the studies of establishment and regional correlation of the strata system and the geological evolution in Hong Kong,but also to the study of volcanic activities in Southeast China.