Paleomagnetism of early Triassic Daye Formation and its tectonic implications

The new paleomagnetic data of the early Triassic Daye Formation from Hubei Province are reported. The ChRM passes consistency test and reversal test. Two magnetic components were isolated with principal component analysis (PCA). Component B is a ChRM and component A was acquired by remagnetization during Indosinian cycle. Rock magnetic study shows that the carrier is dominantly detrital magnetite. According to the data, in conjunction with recently published Triassic paleomagnetic results, mean paleopole of the Triassic Yangtze Block is calculated as 30.3°N癗, 198.4°E, α95 = 9.2° Distribution of all Triassic declinations indicates obviously local rotation in the mid-Yangtze areas, which results in consistence of the declinations with fold axes. By comparison with Triassic paleomagnetic data in the South China Block and some of geological evidence, it is inferred that the timing of the suture between the Yangtze Block and the South China Block is earlier in western part than in eastern part in the Indosinian period.     

New paleomagnetic results from the Yangzhuang Formation of the Jixian System,North China,and tectonic implications

A paleomagnetic study was carried out on the Yangzhuang Formation （-1350 Ma） of the Jixian System in the North China Block （NCB）. Detailed stepwise thermal demagnetization isolated two components. The soft component （component A） was interpreted as a remagnetization in the recent geomagnetic field. The hard component （component B） with higher unblocking-temperatures was carried by hematite. Its site-mean direction is D/I = 77.6°/-24.3°κ= 5.4, α 95 = 18.3°, N = 15 sites） before, and D/I = 72.2°/11.5° （ κ=24.6, α95 = 7.9°） after tilt correction. It passes a fold test（Mesozoic folding） at 99% confidence level and reversal test at 95% confidence level. The corresponding pole locates at 17.3°N, 214.5°E （dp = 4.1°, dm= 8.0°）. A best fit of paleomagnetic poles from the NCB, Baltica, Siberia and the apparent polar wander path for Laurentia suggests a long-lived connection between these paleo-continents between -1800and 1350 Ma.     

华北地块沁水盆地下三叠统刘家沟组古地磁倾角浅化研究

对华北地块沁水盆地下三叠统刘家沟组红层样品进行系统的岩石磁学、磁组构和古地磁学研究, 并用E/I (elongation/inclination)方法对其进行磁倾角浅化的识别与校正, 获得刘家沟组红层磁倾角浅化因子f = 0.6。岩石磁学结果显示, 刘家沟组红层的主要载磁矿物是赤铁矿及磁铁矿, 其磁组构具有典型的静水沉积特征。经地层校正后, 15个采样点特征剩磁分量的平均方向为D_s=318.8°, I_s=30.9°(α₉₅= 6.9°), 对应的古地磁极为49.3°N, 5.5°E (A₉₅=6.7°), 磁倾角浅化校正后的古地磁极为53.5°N, 18.0°E。对包括本文数据在内的高质量的华北早三叠世古地磁极数据(Q≥4)进行平均, 得到校正前的古地磁极为55.3°N, 357.1°E (A₉₅=5.5°), 校正后的古地磁极为60.8°N, 13.4°E (A₉₅=5.8°)。经过古地磁倾角浅化校正, 华北地块早三叠世的古纬度有约10°的明显提高, 指示其东部早三叠世时与华南地块之间可能存在一定的纬度差, 但是该纬度差很可能并不代表华北地块东部早三叠世时与华南地块尚未对接, 而是指示华南地块下三叠统灰岩同样存在显著的磁倾角浅化现象。     

粤北晚三迭世一种新的木化石

本文描述了采自粤北晚三迭世艮口群下部的一种木化石,其解剖特征与原始叶枝杉型木属Protophyllocladoxylon Krausel相符,因此归入该属。但与该属已有各种均不相同,建议定为一新种:斯氏原始叶枝杉型木P.szei sp.nov,种名用以纪念中国著名古植物学家斯行健先生。     

安徽早三叠世巢湖龙前肢比较及分类学意义

由于标本少和保存情况不好等原因, 对巢湖龙(Chaohusaurus)解剖学特征缺少详细描述, 安徽地区巢湖龙的种级分异尚存争议。经过对比研究北京大学地质博物馆馆藏的采自安徽巢湖的鱼龙标本与相关模式标本, 基于骨骼形态及腕骨骨化程度等方面的差异, 将标本分为两类。将研究标本及相关模式标本等进行聚类分析, 结果表明存在两个类群。将前肢骨骼数据作图, 显示存在两条生长序列, 该结果推翻了之前的巢县陈氏龙和小巧陈氏龙均为龟山巢湖龙后出同物异名的结论。据此推断, 巢湖马家山地区的巢湖龙可能存在两个物种。厘清巢湖龙的种间关系有助于全球早三叠世原始鱼龙类的对比研究, 并对探讨鱼龙的早期演化具有十分重要的意义。     

Paleomagnetic result of the Cenozoic volcanic rocks from the Tuoyun Basin, southwest Tien Shan of China and its tectonic implications

In the present decades, lots of Mesozoic and Ceno-zoic paleomagnetic data have been obtained from westernChina and adjacent areas[1—19], however, these results are still not enough to reconstruct a postcollisional kinematic model for each block of the Tibetan Plateau and Central Asia. As a result, it is very difficult to paleomagnetically depict the postcollisional interaction within blocks of Ti- bet and Central Asia in detail. On the other hand, shal- lower inclinations have been repeat…     

安徽巢湖早三叠世原始鱼龙类的结构和行为特征及其对鱼龙类起源研究的启示

鱼龙类(Ichthyosaurs)起源于早三叠世晚期, 以往发现的鱼龙类已高度适应水生生活, 其身体结构无任何能将其与可能的陆地祖先相联系的陆生适应特征。针对近年在安徽巢湖下三叠统奥伦尼克阶采集的柔腕短吻龙(Cartorhynchus)和含胚胎巢湖龙两件鱼龙类标本, 通过对柔腕短吻龙的荐前椎数目(31节)、吻长与头骨长之比(0.35)、前肢长与荐前椎长之比(0.45)的研究以及与后期鱼龙类相关数据和骨骼形态学的对比, 认为柔腕短吻龙结构更为原始, 可两栖生活。结合对早三叠世含胚胎巢湖龙、侏罗纪含胚胎狭翼鱼龙幼体保存情况的对比分析, 认为巢湖龙虽比柔腕短吻龙身体结构更进化, 且完全适应水生生活, 但其生殖行为仍然保持陆生爬行动物头位胎生的特征。鱼龙类在其陆地祖先逐渐演化至适应水生生活的过程中, 结构的适应性特征(如肢体的鳍状化、吻部的增长等)和行为特征(如生产方式的变化)的变化不同步, 前者的改变更早。     

巢湖地区早三叠世晚斯密斯亚期含鱼化石碳酸盐岩结核的地球化学特征及其地质意义

以安徽省巢湖地区下三叠统和龙山组顶部的黑色泥页岩段及其产出的含鱼化石碳酸盐岩结核为研究对象, 综合岩相学、地球化学(主微量元素和碳、氧同位素)和环境矿物学等分析手段, 探讨富有机质页岩中含鱼化石碳酸盐岩结核的形成机制及可能的地质环境指示意义。结核中心三维保存的鱼化石和较高的碳酸盐含量(80%)表明结核形成于早期成岩阶段, 结核内部呈同心环状结构, 从中心至边缘, 碳酸盐矿物含量降低, 硅质碎屑矿物增多并逐渐出现纹层, Fe和S含量升高、δ¹³C值增高、δ¹⁸O值降低和TOC含量逐渐增多等特征均表明结核为同心生长模式。对围岩中草莓状黄铁矿的粒径分析结果表明, 结核形成于硫化还原环境。结核出现在斯密斯亚阶与斯帕斯亚阶界线(SSB)之下1 m处, 与界线层有机碳埋藏增加、碳同位素组成快速正漂移(δ¹³C = -1.3‰~1.9‰)和水体硫化还原事件吻合, 有潜力作为华南地区SSB的辅助识别标志。     

New primitive ichthyosaurian （Reptilia,Diapsida） from the Middle Triassic of Panxian,Guizhou, southwestern China and its position in the Triassic biotic recovery

A new primitive ichthyopterygian Xinminosaurus catactes gen. et. sp. nov. is erected based on a complete skeleton from the Middle Triassic Upper Member of the Guanling Formation at Panxian, Guizhou, southwestern China. It has a suite of uniquely derived char- acters in its dentition, ulna, carpals and tarsals. It is similar to primitive ichthyopterygians in retaining elongated limb bones. The new taxon and a diversity of marine reptiles in Panxian Fauna are the physical markers of the Middle Triassic Biotic radiation. Detailed studies of this fauna will supply essential knowledge on the diversity, migration and paleobiogeographic affinity of Middle Triassic ichthyopterygians.     

Flabellariopteris,a new aquatic fern leaf from the Late Triassic of western Liaoning,China

An aquatic fern leaf, Flabellariopteris mii Sun gen. et sp. nov. from the Late Triassic of Western Liaoning, China, is described and proposed as the type species of the new morphortaxon of the Marsileaceae. The fossil leaves are preserved as impression. No fertile and rhizomatic materials are found. The leaves attached at a common point on the top of the petiole are composed of two leaflets joined basally in an opposite arrangement. The petiole is slender. The leaflet is fan-shaped or semi-circular, and commonly divided into four wedge-shaped lobes. Terminal margin of lobes is usually incised, incisions shallow or deep, with bluntly rounded or notched apex. The veins are conspicu- ously dichotomous, but anastomoses and marginal vein are absent. The unique morphological features, including two- parted thin leaflets, size, shape, veins and slender petiole, indicate that the present specimen represents an aquatic fern, which is the oldest fossil record and the first megafossil evidence assignable to Marsileaceae from the Triassic floras.     

浙西北地区二叠系和三叠系的构造变形样式及其大地构造意义初步研究

浙西下三叠系统政棠组(T_1zh)发育有典型的鲍马序列,是一套深水相浊积岩建造;区域构造环境初步分析表明浙西北地区具被动大陆边缘沉积楔特征。下三叠系统政棠组(T_1zh)与二叠系协调变形,其构造变形样式总体上以向西北逆冲的冲褶席(duplex)~ 为特征,变形强度自南东向北西呈递减趋势。上三叠统乌灶组(T_3w)为含煤陆相磨拉石盆地建造,变形样式以宽缓褶皱和逆断层组合为主。该区大地构造相主要为前陆褶皱冲断带相,而土三叠统乌灶组(T_3w)为前陆磨拉石盆地相,二者对浙西北地区早中生代造山作用的研究具重要意义。     

New discovery on dinosaur fossils from Early Jurassic, Sichuan, China

An early and primitive sauropod dinosaur, Gongxianosaurus shibeiensis (gen. et sp. nov.), from Lower Jurassic Dongyuemiao Member of Ziliujing Formation in Shibei Village, Gongxian County, Sichuan Province, China is described, which is among Gongxian dinosaur fossils discovered in 1997. Except for skull incomplete, fossils were well-preserved. It has concurrently some features of both sauropod and prosauropds. It is an intermediate type of evolution from prosauropod to sauropod, provides practical materials for studying of origin and evolution of sauropod dinosaur fauna, and a favourable way for stratigraphic correlation between Early Jurassic Ziliujing Formation and Lower Lufeng Formation, in the Sichuan Basin and the Central Yunnan Basin that lies to its southwest.     

Sponge fossil assemblage from the Early Cambrian Hetang Formation in southern Anhui

Abundant well-preserved large articulated sponge fossils and isolated spicules have been reported from the Early Cambrian Hetang Formation, southern Anhui Province. This unique epifaunal fossil assemblage dominated by articulated sponge fossils is called the Xidi Sponge Fauna. The sponge fauna lived in a quiet oxygenic environment below the storm wave base. Bloom of phytoplankton and rapid sedimentation rate resulted in the deposition of the black shales. Sufficient food supply, lack of other competitors, abundant ecological niches, and demand for oxygen during early Cambrian were in favor of the diversification and evolution of large sponges in the Early Cambrian.     

鄂尔多斯盆地上三叠统延长组沉积体系特征及演化

在野外剖面观察、岩心描述及测井、测试资料分析的基础上,综合前人研究成果,对鄂尔多斯盆地上三叠统延长组沉积体系的类型、特征进行了详细分析,并深入讨论了鄂尔多斯盆地延长组沉积体系垂向上的演化规律.结果表明: 鄂尔多斯盆地延长组主要发育冲积扇、扇三角洲、河流、河流三角洲、湖泊和湖泊浊积扇六大类沉积体系.长8期湖盆开始形成,主要发育神木-乌审旗、安塞和正宁-合水等三角洲沉积体系;长7期湖盆进一步扩展,三角洲规模萎缩;长6期湖水大面积退缩,三角洲前缘连片,面积最大,东北三角洲前缘已推进至吴旗-甘泉一线,西南缘推进至华池-庆阳一带;长4 5期以浅湖亚相为主;长3、长2期以三角洲平原沉积为主;长1期湖盆继续萎缩至消亡,局部出现沼泽环境.盆地沉积体系的演化,在纵向上构成了五套储盖组合.     

四川盆地中部嘉二段储层特征及成因

通过钻井、录井、测井及岩心等大量资料的综合分析,系统识别出鲕粒灰岩储层、砂屑云岩储层和粉晶云岩储层是四川盆地中部地区下三叠统嘉陵江组嘉第二段主要的碳酸盐岩储层。鲕粒灰岩储层以孤立的粒内溶孔和铸模孔为主要储集空间,孔隙间喉道欠发育,以微喉为主,中孔微喉的配置关系导致储层多表现为中孔低渗、渗透率偏低的特征;砂屑云岩储层以残余粒间孔和粒间溶孔为主要储集空间,孔隙间喉道发育,以缩颈喉道为主,较好的孔喉配置关系使储层多表现为中孔中渗、储渗能力较好的特征;粉晶云岩储层以晶间孔和晶间溶孔为主要储集空间,孔隙间喉道以片状喉道为主,孔喉配置关系较好,储层多表现为中孔中渗的特征。储层成因分析结果表明,沉积微相是储层形成的沉积基础,分别形成于鲕滩微相、砂屑滩微相和云坪微相中的鲕粒灰岩、砂屑云岩和粉晶云岩为储层的形成提供了早期物质基础;台地内次一级微地貌高地为储层形成提供了有益的微地貌条件;同生期大气淡水淋溶、原生粒间孔保存和白云岩化作用分别是鲕粒灰岩储层、砂屑云岩储层和粉晶云岩储层形成的关键。     

A new pterosaur (Pterodactyloidea,Tapejaridae) from the Early Cretaceous Jiufotang Formation of western Liaoning,China and its implications for biostratigraphy

In this article we describe a new and exceptionally weel-preserved pterodactyloid pterosaur,Sinopterus dong gen.et sp.nov.from the Jiufotang Formation in western Liaoning Province of northeast China,The new species is referred to the family Tapejaridae,representing its first record outside Brazil.It also represents the earliest occurrence as well as the most complete sketeton of the famil.Some revisions are made about the family according to the mophological observations of the postcranial bones of Sinopterus.Two pterosaur assemblages appear to have existed in the Jehol Group,represented by the lower Yixian Formation and upper Jiufotang Formation,respectively,The lower pterosaur assemblage shows some resembalance to that of the Late Jurassic in Solnhofen (Tithonian)by sharing members of the Pterodactylidae and Anurognathidae.The upper one shows more resemblance to that to the Early Cretaceous Santana Formation (Aptian/Albian) by comprising only pterodactyloids such as the Tapejaridae,The age of the Yixian Formation is younger than that of the Solnhofen lihographic limestone ,and the age of the Jiufotang Formation (Aptian )is slightly older than the Santana Formation.     

SHRIMP zircon U-Pb dating for volcanic rocks of the Dasi Formation in southeast Hubei Province, middle-lower reaches of the Yangtze River and its implications

The Jinniu Basin in southeast Hubei,located at the westernmost part of middle-lower val-ley of the Yangtze River,is one of the important vol-canic basins in East China. Volcanic rocks in the Jin-niu Basin are distributed mainly in the Majiashan Formation,the Lingxiang Formation and the Dasi Formation,consisting of rhyolite,basalt and basaltic andesite,(trachy)-basalt and basaltic trachy-andesite and (trachy)-andesite and (trachy)-dacite and rhyolite respectively,in which the Dasi volcanism is volumet-rically dominant and widespread. The Dasi volcanic rocks were selected for SHRIMP zircon U-Pb dating to confirm the timing of volcanism. The results indi-cate that there exist a large amount of magmatic zir-cons characterized by high U and Th contents in the volcanic rocks. The concordia ages for 13 points are 128 ± 1Ma (MSWD = 3.0). On account of the shape of zircons and Th/U ratios,this age is considered to represent the crystallization time of the Dasi volcan-ism. The volcanic rocks in the Dasi,Majiashan and Lingxiang Formations share similar trace elementand REE partition patterns as well as Sr-Nd isotopic compositions. In combination with the regional geol-ogy,it is proposed that the southeast Hubei volcanic rocks were formed mainly during the Early Creta-ceous,just like other volcanic basins in middle-lower Yangtze valley. A lithospheric extension is also sug-gested for tectonic regime in this region in the Cre-taceous Period.     

Triassic U-Pb age for zircon from granites in the Tonghua area and its response to the Dabie-Sulu ultrahigh-pressure collisional orogenesis

Single-grain zircon U-Pb dating was carried out to constrain the emplacement timing of granitic plutons at Chaxinzi, Xiaoweishahe and Longtou in the Tonghua area, south of Jilin Province. The results show that these plutons formed in the Triassic with ages of 203—217 Ma. Geological and geochemical characteristics indicate that the plutons are composed of quartz diorite and granite. The former was derived from partial melting of mafic lower crust, whereas the latter originated from thickened crust with garnet as the residue in the source. It appears that protoliths of these two types of granitits are different although they have the same emplacement age. Considering that these plutons are petrologically different from the coeval granites in the Xingmeng (Xing‘an-Mongolian) to Jihei (Jilin-Heilongjiang) orogenic belt in the north, it is suggested that their formation was related to the Dabie-Sulu ultrahigh-pressure collisional orogenesis since their ages are only 10—20 Ma younger than timing of the ultrahigh-pressure metamorphism, but comparable to that of the first rapid exhumation of the ultra-high-pressure metamorphic rocks and the emplacement of the post-collisional granites.