滇西巍山地区上三叠统诺利阶三合洞组牙形石年代及沉积相分析*

滇西兰坪-思茅地块晚三叠世诺利期(Norian)发育一套海相碳酸盐岩沉积(三合洞组)。对巍山三合洞剖面进行了实测与采样, 分离了三合洞组碳酸盐岩中的牙形石, 经鉴定其种属为Epigondolella vialovi, Epigondolella uniformis和Epigondolella aff. triangularis, 时代为早诺利期(Lacian亚期)。通过野外剖面及室内显微薄片观察, 采用微相分析的方法对剖面三合洞组碳酸盐岩的微相类型和沉积环境进行研究, 将巍山三合洞剖面三合洞组沉积归纳为9种微相, 并根据微相特征结合野外宏观特征, 将三合洞剖面划分为3种沉积相类型, 即局限台地相、开阔台地相和台地边缘礁相。在剖面不同层位的碳酸盐岩中发现的热液矿物石榴子石及发黑的牙形石化石(CAI指数约为5), 表明该区曾遭受热液作用的影响, 可能与三合洞组沉积后大陆边缘裂谷下陷或板块拼合引起的热卤水上涌有关。     

贵州西部早三叠世浅水碎屑岩相中微康奇虫(microconchids)化石的发现及其古生态意义*

微康奇虫(microconchids)是一种主要营水生固着生活的帚形动物, 在奥陶纪至侏罗纪的地层中均有广泛记录。本文报道了产自贵州遵义市播州剖面及六盘水市六枝剖面下三叠统夜郎组泥质岩中保存的微康奇虫的钙质栖管化石及印模化石。该组内的微康奇虫化石数量丰富, 保存精美, 电镜下可观察到其壳体特有的平行纤维薄层状微晶结构。本文共鉴定出微康奇虫化石共2科2属4种, 为该门类生物在华南早三叠世浅水碎屑岩中的首次报道。古生态上, 微康奇虫群落呈现出低分异度和高丰度的特征, 为早三叠世恶劣海洋环境中具有较强适应能力的典型生态灾难分子。     

贵州西部早三叠世浅水碎屑岩相中微康奇虫(microconchids)化石的发现及其古生态意义*

微康奇虫(microconchids)是一种主要营水生固着生活的帚形动物, 在奥陶纪至侏罗纪的地层中均有广泛记录。本文报道了产自贵州遵义市播州剖面及六盘水市六枝剖面下三叠统夜郎组泥质岩中保存的微康奇虫的钙质栖管化石及印模化石。该组内的微康奇虫化石数量丰富, 保存精美, 电镜下可观察到其壳体特有的平行纤维薄层状微晶结构。本文共鉴定出微康奇虫化石共2科2属4种, 为该门类生物在华南早三叠世浅水碎屑岩中的首次报道。古生态上, 微康奇虫群落呈现出低分异度和高丰度的特征, 为早三叠世恶劣海洋环境中具有较强适应能力的典型生态灾难分子。     

四川江油马鞍塘上三叠统天井山组Glossifungites遗迹相

首次在四川江油马鞍塘天井山组顶部发现Thalassinoides suevicus,属于Glossifungites遗迹相,属滨海或潮下带在未完全石化的、处于半固结状态的沉积底质上所产生的遗迹化石组合,发育在停积面上,因受到下伏硬底构造的限制,仅产于上表面,没有向下发展,是该地区从开阔海台地相转变为局限海台地相的证据。     

中下扬子区海相三叠纪叠层石及其环境演变

中、下扬子区三叠纪叠层石大多产自中三叠统嘉陵江组白云岩中，仅少数产自下三叠统青龙组灰岩中。这些叠层石可根据各自所处环境分为下列２种类型：１）浅滩相叠层石生物丘；２）潮坪相叠层石生物层。这些叠层石及其围岩常含丰富的石膏晶痕或盐溶角砾，显示了一种干燥炎热气候中一低能水动力环境产物的特征。根据中、下扬子区三叠纪叠层石的形态及发育特点研究，结合有关沉积特征分析，发现该区由早三叠世的陆表海演变为中三叠世早期的潮坪复合体，其较深的部位转变为青盐湖，而较浅的部位则变为藻坪或萨布哈盐坪。这种转变暗示着此期间扬子地块已由主要受热带低气压控制下的赤道附近地区移至常年受副热带高气压或干燥信风控制的回归线附近地区。     

广西南丹巴平石炭系中间界线剖面的碳酸盐微相特征及其沉积环境

巴平石炭系中间界线剖面位于碳酸盐台地相区和盆地相区之间的过渡带,在详细研究剖面岩石学和古生物学特征的基础上,可以区别出１０个主要的碳酸盐微相类型,形成于盆地边缘、斜坡、台地边缘和开阔台地环境,石灰系中间界线处于斜坡和台地边缘相之间。     

华北板块西缘甘肃平凉上奥陶统平凉组灰岩微相和沉积环境

甘肃平凉官庄剖面为上奥陶统平凉组的建组剖面,出露其完整的地层序列,主要由细砂、粉砂级颗粒的碎屑岩和灰岩构成。该地区在平凉组沉积时期的构造背景属华北板块西部,位于鄂尔多斯古陆西缘。对官庄剖面平凉组灰岩夹层开展的微相分析显示其中含有丰富的泥状灰岩砂屑,生屑种类含量偏低且破碎程度高,无浅海区特有的沉积构造,海水深度不利于底栖生态群落栖居。灰岩的沉积学机制指示鄂尔多斯古陆西南海区存在较陡的海底地貌,这些内碎屑不是原地或近原地沉积的,它们最初产生于浅海碳酸盐岩台地,经重力流、等深流长距离搬运后到达接近秦岭-祁连海槽的深水区沉积。     

宁强广元地区志留系宁强组灰岩的微相研究

志留纪时期在扬子地台西北缘宁强湾沉积的宁强组,是一套巨厚的泥页岩夹小型局限台地相灰岩。局限台地相灰岩的沉积类型主要有生物礁、生物层和灰泥丘三种,按岩性可分为灰泥岩、颗粒岩、障积岩、粘结岩、格架岩、漂浮岩、灰砾岩等类型。岩石的微相分析和宏观相带的识别相结合,能指示各种沉积类型不同部位的环境和形成机制。     

南京近郊早三叠世孢粉及疑源类

本文对南京东郊徐家山剖面12块样品中所发现的孢粉及疑源类进行了分析研究,共发现孢粉31属、47种,疑源类17属、41种(包括9新种)。按其所含孢粉属种及含量特征认为:下青龙组及上青龙组的地质时代属早三叠世。结合出现的菊石及牙形刺进行分析,下青龙组四段的地质时代属早三叠世Nammalian期;上青龙组的地质时代属早三叠世spathian期。按疑源类属种及含量特征自下而上明显地划分出组合带Ⅰ、Ⅱ和Ⅲ,分别与下青龙组四段、上青龙组一段及上青龙组二段相对应。根据疑源类各带特征推测:下青龙组四段为平静、近岸的海相沉积;上青龙组一段沉积时的海水较为动荡,且气候亦较温暖;上青龙组二段沉积时的海水平静,且水体较先前要深。     

新疆塔里木玉北井区早奥陶世古环境及生态组合时空分布

新疆塔里木板块玉北地区下奥陶统沉积于极浅海带碳酸盐岩沉积区,化石密度普遍很低,依据该地区6口钻井的化石碎片类型以及所赋存的围岩特征可划分出6种生态组合:三叶虫-介形类组合或介形类组合;介形类-三叶虫组合或三叶虫组合;棘屑-三叶虫组合;三叶虫-棘皮类组合;海绵-三叶虫-介形类组合和三叶虫-腕足类组合。生态组合和沉积微相分析表明,玉北地区该地质时期共有三次沉积环境变迁:蓬莱坝组顶部-鹰山组底部沉积期为局限台地潮坪环境;鹰山组下部沉积期为局限台地潮坪与潮沟交互环境;鹰山组中部沉积期为局限台地潮坪环境;鹰山组上部沉积期为局限台地潮坪与潮沟交互或者局部的局限台地潮坪环境。     

四川江油渔洞子下三叠统飞仙关组巨鲕灰岩中疑似蓝细菌及早三叠世疑似蓝细菌的双幕式爆发

二叠纪末海洋生态环境的恶化导致海洋底栖生物的大灭绝及早三叠世蓝细菌的爆发,有关这一时期我国华南蓝细菌化石的报道主要来自早三叠世早期的微生物岩。四川江油渔洞子剖面下三叠统飞仙关组下部巨鲕灰岩中首次发现有丰富的疑似蓝细菌,在种类和结构上与以往所报道的蓝细菌有着明显区别。疑似蓝细菌在巨鲕内和围岩中的富集,表明巨鲕灰岩的成因与疑似蓝细菌的活动有关,与飞仙关组底部微生物岩在成因上有着密切联系,显示早三叠世早期在这一地区发生了疑似蓝细菌的双幕式爆发,同时,暗示着这一地区二叠纪-三叠纪之交至少发生了两次海洋环境恶化及动物灭绝事件。疑似蓝细菌的爆发性生长,对于海洋生态环境的修复和海洋含氧条件的改善,进而为早三叠世末、中三叠世的生物全面复苏、辐射有着重要意义。     

Reinvestigation of conchostracans (Crustacea: Branchiopoda) from the Permian–Triassic transition in Southwest China

Sedimentary deposits of the Permian–Triassic transition are well-exposed in numerous outcrops of South China. Depending on the palaeogeographic positions of the sections, their lithofacies vary from fully marine, shallow marine, lagoonal, lacustrine, and fluvial to alluvial. In the present study, conchostracans (Crustacea: Branchiopoda) were newly collected from the continental deposits of the Kayitou and Jialingjiang formations around the Kangdian Highland elevated by the Emeishan Basalt in the southern Sichuan, western Guizhou, and northeastern Yunnan provinces. The conchostracan fauna of the Kayitou Formation is composed of Pseudestheria chatangensis, Euestheria fuyuanensis, and Euestheria sp. aff. E. gutta. These species occur in varying lithofacies types of different sections. In particular, the late Permian Pseudestheria chatangensis occurs in grey siltstones interbedded with pebbly sandstones, which are interpreted as lacustrine deposits. Euestheria fuyuanensis and Euestheria sp. aff. E. gutta were obtained from yellowish to greenish–grey clay- and siltstones, interpreted as coastal plain deposits. In comparison to other regions, occurrences of Euestheria gutta are indicative of an early Induan to Olenekian (Early Triassic) age. The fossil record of Euestheria fuyuanensis is so far restricted to a few occurrences in the Kayitou Formation of Southwest China and, therefore, using this species for long-distance biostratigraphic correlation requires further investigation. The distribution of late Permian pseudestheriid and Early Triassic euestheriid species in the respective sections possibly depends on the local lithofacies and, therefore, a diachronous age of the Kayitou Formation within the study area can be assumed. Additionally, Magniestheria sp. aff. M. mangaliensis and Magniestheria sp. aff. M. subcircularis were recorded in the Jialingjiang Formation, which represents a lithostratigraphic unit considered as late Early Triassic (Olenekian). Further investigations of both taxonomy and the real stratigraphic ranges of the conchostracan species as well as cross-correlations with other age data are recommended, in order to better constrain the position of the Permian–Triassic boundary and the specific timing of the terrestrial end-Permian mass extinction in continental deposits of Southwest China.     

The upper Shemshak Formation (Toarcian–Aalenian) of the Eastern Alborz (Iran): Biota and palaeoenvironments during a transgressive–regressive cycle

The siliciclastic, up to 4,000 m thick Upper Triassic–Bajocian Shemshak Formation is widespread across the Iran Plate, especially in the Alborz Mountains of northern Iran. In contrast to its lower, generally non-marine part, the upper part is marine. Based on the Tazareh section of the eastern Alborz, an integrated analysis of this marine interval is presented. The 1,700 m thick marine sedimentary succession records a gradual deepening from inner to mid and outer shelf environments from the Middle Toarcian to early Late Aalenian. During the Late Aalenian–Early Bajocian, the trend was reversed and infilling of the basin by a large delta system occurred. This general facies development reflects a nearly symmetrical transgressive–regressive (T–R) megacycle, terminated by the inter-regional mid-Cimmerian tectonic event. A renewed transgression in the early Late Bajocian initiated a subsequent sedimentary megacycle. The bioturbated mid and outer shelf sediments contain a low to moderately diverse benthic fauna dominated by deep burrowing bivalves, often preserved in the growth position. A hierarchy of four orders of sedimentary cycles can be recognized (parasequences, parasequence sets, unconformity-bounded third-order depositional sequences, and the 13 ma long second-order T–R megacycle). A regional correlation with the Jajarm area (200 km to the east) shows a very similar temporal facies pattern of the upper Shemshak Formation. The eastern Alborz T–R cycle is completely out-of-phase with other (eustatic) sea-level curves, suggesting regional tectonic control. Rough estimates of subsidence rates give an average value of 126 m/ma. However, much higher values for the Aalenian (230 m/ma), particularly the Late Aalenian (700 m/ma), indicate a distinct increase in subsidence rate towards the Early Bajocian mid-Cimmerian tectonic event. These high subsidence rates suggest that the sediments of the Shemshak Formation of the eastern Alborz formed in a (young) rift basin.     

Diversity and palaeoecology of a highly diverse Late Triassic marine biota from the Cassian Formation of north Italy

A sample of marine invertebrates from the Late Triassic Cassian Formation (north Italy) yielded one of the most diverse Early Mesozoic fossil assemblages ever reported (c. 170 species). The assemblage was found in basin clays, but was transported from nearby carbonate platforms as indicated by fragmentation, microbial encrustation and the presence of coated grains and ooids. Most of the specimens are small (< 1 cm) reflecting both, small adult sizes and size sorting during transport. Rarefaction analysis suggests that diversity of surface collection and bulk sampling is the same. However, rank abundance, species richness and taxonomic composition differ strongly according to sampling method. Low‐grade lithification of the sediments is the main reason that high diversity can be recognized, because it facilitates disaggregation and finding of small molluscs. Sample standardization shows that the studied assemblage is much more diverse than known Early Triassic assemblages. However, its diversity is similar to that of Anisian assemblages. This suggests that recovery from the end‐Permian mass‐extinction was quite advanced in the Middle Triassic and alpha‐diversity remained high until the Late Triassic. According to current models, Early Triassic and Anisian faunas match the niche overlap phase of recovery during which diversity is built up by increasing alpha‐diversity, whereas beta‐diversity rises slowly. Subsequently, habitat width of species contracts because of increasing competition, making beta‐diversity the principal drive of overall diversity increase. The diversity pattern of various Late Triassic Cassian associations meets the predictions for the transition from the niche overlap to the habitat contraction phase.: Triassic, Cassian Formation, palaeoecology, diversity, mollusc dominance.     

北羌塘盆地中南部侏罗纪布曲组古生物特征与沉积环境

本文通过对北羌塘盆地北坳陷中南部胜利河、东湖及毛毛山等地区侏罗纪布曲组6条剖面及其中丰富的腕足类、双壳类等古生物资料和岩石组合特征的研究,将布曲组地质时代划为中侏罗世巴通期(Bathonian)至早卡洛夫期(Callovian),还可能跨入早巴柔期(Bajocian)。通过本文研究和区域对比,认为布曲组的沉积时代在北羌塘盆地存在穿时性。依据岩石组合特征,布曲组沉积充填物三分性明显,下部和上部为一套以微晶结构、粒泥结构为主的低能碳酸盐岩,中部为一套以高能的亮晶粒屑灰岩为主的碳酸盐岩。结合古生物生态习性,布曲组沉积环境总体为近岸浅水开阔台地–台地边缘碳酸盐岩沉积体系,构成多个沉积旋回。这一基础资料对下一步分析北羌塘盆地坳陷中南部布曲组岩相古地理提供了支撑。     

Triassic temnospondyl biostratigraphy, biochronology and correlation of the German Buntsandstein and North American Moenkopi Formation

Based on temnospondyl distributions, we propose a correlation of the non-marine Lower and Middle Triassic strata of Germany and the western United States. This correlation relies principally on the presence of two genera, Nonesian (late Early Triassic) Parotosuchus and Perovkan (early Middle Triassic) Eocyclotosaurus . The distribution of Parotosuchus helgolandicus indicates that the Torrey Member of the Moenkopi Formation in Utah, USA is equivalent to the Volpriehausen Formation of the German Buntsandstein of Nonesian age. Magnetostratigraphy and the distribution of Eocyclotosaurus indicate that the Perovkan Holbrook Member of the Moenkopi Formation in Arizona corresponds to a short interval of Anisian time, as does the German Upper Buntsandstein. The Buntsandstein and Moenkopi biostratigraphic schemes agree with a recently proposed biochronology of Triassic terrestrial tetrapods.     

Pleuromeia discovered from the Middle Triassic Linjia Formation of Benxi,Northeast China

A new species Pleuromeia shaolinii Zhang et Wang n. sp. was established under the family Pleuromeiaceae, based on eight specimens of stems and leaves, cones, rhizophores, and adventitious roots that were recently collected from the Middle Triassic Linjia Formation in Benxi, Northeast China. P. shaolinii n. sp. is similar to the type species P. sternbergii, in the morphology of the stem and rhizophore, but differs from it by the transversely rounded sporophylls organized in a heterosporous cone, and the two conspicuous triangular scars present on both sides of the vascular bundle scar. The Linjia flora, an only reliable Middle Triassic flora in Northeast China, was discovered 40 years ago. Although the Linjia Formation can be compared with the Middle Triassic Ermaying Formation from another area of the North China plate, its age was questionable due to the absence of the Early to Middle Triassic index fossil Pleuromeia. Based on the flora similarity, the zircon dating, lithologic characteristics, presence of a disconformity, and the occurrence of the Middle Triassic–Early Cretaceous insect fossil Sogdoblatta, the age of the Linjia Formation can be confirmed as Middle Triassic. The new species not only supplements our knowledge in biology and taxonomy of Pleuromeia, but also supports the Middle Triassic age assignment of the Linjia flora.     

Middle Miocene carbonates from the Northern Plateau of the Western Desert (Egypt): Petrography and geochemistry

Summary An extensive carbonate platform of predominately Middle Miocene age (Marmarica Formation) occupies the larger part of the northern plateau of the Western Desert of Egypt. The Marmarica Formation (up to 150m thick) exposed on the cliffs facing the Mediterranean coast consists mainly of alternating limestones and dolostones. Deposition took place in a shallow and normal marine environment. The limestones are dominated by algal boundstone, crossbedded packstone and bioturbated wackestone facies. The occurrence of the crossbedded packstone facies throughout the Marmarica Formation indicates that a shallow marine environment prevailed. Lithification of the precursor carbonates took place mainly in a meteoric environment. Replacement dolomitization ranged from fabric destructive to retentative and from fabric selective to pervasive. The presence of an abundant open marine fauna, the lack of evaporites, coupled with the contents of Sr and Na suggests that dolomitization took place in solutions more dilute than normal sea water. The limestone and dolostone facies cannot be separated into distinct types based on their major or trace element chemistry. Only Mn and Sr seem to be facially controlled. Both elements are particularly enriched in the lagoonal facies compared with the organic buildup facies. The difference in the Mn content is attributed to their proximity to continental areas at the time of deposition. The differences in Sr values are interpreted by an originally differing mineralogy (calcite versus aragonite) and different rates of diagenesis. Dolomitization did not appear to influence the Mn content as substantially as the Sr content. The amount of the acid insoluble residue is controlled by the distribution of Si, Ti, Al, Fe, k, Rb and Zr.     

云南墨江上三叠统歪古村组燧石质砾石中的晚古生代放射虫化石及其地质意义

云南哀牢山缝合带由于长期未找到晚石炭世至二叠纪深海环境的化石及沉积地层记录,对哀牢山古特提斯盆地演化历史存在着不同认识。文中报道了采自云南墨江坝留地区上三叠统歪古村组底砾岩中的早石炭世和中二叠世放射虫化石,所有放射虫化石发现于4件燧石质砾石中,共计11属9种和7未定种及1属种未定放射虫。其中,3件砾石含有Albaillella deflandrei Gourmelon,Albaillella sinuosa Won and Seo等早石炭世放射虫化石组合,另1件砾石含有Pseudoalbaillella spp.,Quadricaulis scalae Caridroit and De Wever,Cauletella sp.和Ishigaum sp.等中二叠世放射虫化石组合。由此表明,哀牢山缝合带存在着早石炭世和中二叠世深海盆地沉积地层记录,哀牢山深海盆地应该在中二叠世之后封闭。该成果为探讨哀牢山古特提斯盆地演化提供了放射虫古生物学证据,进而说明哀牢山缝合带与金沙江缝合带一样,也存在石炭纪和二叠纪深水洋盆沉积地层记录,指示其演化历史是相同的。