贵州西南部“法郎组”牙形石及其时代

根据近年牙形石研究,在“法郎组”中从下而上识别了３个牙形石带：１、Ｎｅｏｇｏｎｄｏｌｅｌｌａｐｏｌｙｇｎａｔｈｉｆｏｒｍｉｓ－Ｎｅｏｇｏｎｄｏｌｅｌｌａｍａａｎｔａｎｇｅｎｓｉｓ组合带;２、Ｎｅｏｇｏｎｄｏｌｅｌｌａｐｏｌｙｇｎａｔｉｆｏｒｍｉｓ－Ｎ－ｅｏｇｏｎｄｏｌｅｌｌａｔａｄｐｏｌｅ组合带;３、Ｎｅｏｇｏｎｄｏｌｅｌｌａｐｏｌｙｇｎａｔｉｆｏｒｍｉｓ带。根据牙形石Ｎ．ｅｘｃｅｌｓａ谱系演化、牙形石发展事件、牙形石分带及其与国内外的牙形石带对比,论证了“法郎组”的时代,“法郎组”可解体为瓦窑组和竹杆坡组,全属晚三叠世卡尼期,而不是拉丁期。     

贵州关岭三叠系竹杆坡组、小凹组头足类化石——兼论关岭生物群的时代

贵州关岭地区中、上三叠统竹杆坡组和小凹组产较丰富的头足类化石，计有11科19届37种，其中Enoploceras,Alloceratites,Sibyllites等属以及Trachyceras aon种系国内首次报道。自下而上可识别出(1)Xenopratrachyceras primum带；(2)Protrachyceras deprati带；(3)Protrachyceras costulatum带；(4)Trachycems multituberculatum带；(5)Sirenites cf. senticosus带等5个菊石带。讨论了每个菊石带的特征，并与国外同期菊石带进行了对比，指出(1)带与欧洲拉丁期早期R.reitzi带相当，(2)和(3)带分别与拉丁期晚期E.curionii带和P.archelaus带相当，(4)和(5)带分别与欧洲早卡尼期早期T.aon带和北美的早卡尼期晚期Sirenites nanseni带对比。关岭生物群产出层位与Trachyceras multituberculatum菊石带层位一致，时代应为早卡尼期早期。     

Strengthening Western Gondwanan correlations: A Brazilian Dicynodont (Synapsida,Anomodontia) in the Middle Triassic of Namibia

Terrestrial Middle Triassic strata occur throughout continental Africa and are particularly well exposed in South Africa, Tanzania, Zambia, and Namibia. The youngest age for all these African deposits is widely accepted as early Middle Triassic (Anisian). Fossils collected recently from the uppermost strata of the upper Omingonde Formation in Namibia highlighted the presence of Chiniquodon, a carnivorous cynodont previously only found in Ladinian-Carnian aged rocks of South America. In addition, work in progress indicates that a large archosaur, originally reported as Erythrosuchus, also discovered from levels close to the top of this unit, is in fact a rauisuchian, a group of archosaurs well known from Ladinian-Carnian beds of southern South America. Here we present the first record of the tuskless dicynodont Stahleckeria potens from the top of the upper Omingonde Formation in central Namibia. This taxon was up until now only known from the Ladinian Dinodontosaurus Assemblage Zone of the Santa Maria Formation in southern Brazil. Thus, compelling evidence for a Ladinian age for the upper levels of the upper Omingonde Formation is provided by two therapsid and one archosaur taxa. The tetrapod fauna of the upper Omingonde Formation partially fills the gap of the well-documented hiatus (Ladinian gap), prevalent throughout the Karoo basins of south and central Africa. The presence of the same therapsid taxa in the Namibian Waterberg Basin and the Paraná Basin of Brazil during Middle Triassic suggests that these basins were biogeographically linked through a series of interconnecting lowlands, with no major ecological, climatic and/or physical barriers.     

西藏西部狮泉河地区二叠纪和三叠纪牙形石的发现及其意义

西藏西部阿里狮泉河地区的昂杰组、下拉组和左左组中发现牙形石化石。昂杰组的牙形石组合大致对比于中二叠世空谷期早中期Mesogondolella idahoensis-Vjalovognathus shindyensis组合带。下拉组顶部的牙形石组合大致对比于晚二叠世长兴期晚期Clarkina changxingensis带。左左组中含有早三叠世的Neospathodus sp.和Gladigondolella sp.,左左组和下拉组整合接触,左左组主体时代为三叠纪。狮泉河地区在早二叠世末期就开始由冈瓦纳相碎屑岩沉积转变为特提斯相碳酸盐岩沉积,在晚二叠世长兴期和早三叠世依然维持在海相沉积环境中。冈底斯西部在晚二叠世和三叠纪为古陆的观点有待于重新审视。     

贵州地区中三叠统垄头组沉积特征及其海平面变化意义*

为认识中三叠世拉丁期华南地区碳酸盐岩台地边缘沉积演化及其海平面变化特征,文中主要选取贵州关岭扒子场剖面,以岩石学特征研究为基础,建立中三叠统拉丁阶垄头组的沉积演化序列,来恢复其沉积时期的海平面变化特征。中三叠统垄头组按其岩石类型及组合特征可分为3段: 下段主体为核形石灰岩—叠层石沉积旋回,代表潮间带至潮上带环境。中段下亚段由核形石灰岩—泥晶灰岩—玛瑙纹层状灰岩旋回组成,最顶层的玛瑙纹层状灰岩指示地表暴露环境;中段上亚段为核形石灰岩—叠层石旋回,代表潮间带至潮上带环境。上段由代表潮间带至潮下带的核形石灰岩—似球粒灰岩旋回组成。垄头组沉积特征表明,该沉积时期黔西南地区海平面整体表现为持续上升,但在中段沉积时期发生过一次海平面下降事件,导致沉积物持续遭受地表暴露,随后海平面开始上升,又恢复到潮坪沉积环境。与国内外中三叠世拉丁期海平面变化研究结果相比,贵州地区垄头组中段沉积时期的海平面下降很可能是拉丁期大海退的产物,但自中段上亚段至上段沉积时期,海平面逐渐上升,与同时期的黔西南地区和全球海平面变化趋势一致。该结果对于认识玛瑙纹层状灰岩成因及中三叠世晚期生物复苏研究具有重要意义。     

The interpretation of cyclic successions of the Middle and Upper Triassic of the Northern and Southern Alps

Theories regarding the formation of sedimentary cycles in the 3rd, 4th and 5th order bands are reviewed with reference to the Middle and Upper Triassic of the Northern Calcareous Alps (NCA) and Southern Alps. Milankovitch, autocyclic and tectonic theories are discussed, together with an evaluation of concepts of chaotic sedimentation and a case example from the NCA. Concerning eustasy, 3rd, 4th and 5th order sea-level fluctuations were probably a low-amplitude, low-rate phenomenon caused by fluctuations in the volume of mountain glaciers and ocean water during the Triassic. The Mid and Late Triassic was a non-glacial interval in which polar regions may have been ice-free, so glacio-eustasy can not be expected. Eustatic sea-level variations in the 3rd, 4th and 5th order bands seem to have left no useful imprint on cyclic successions in the region; whatever record there may be is inextricably mixed with two other signals (tectonic activity and autocycles). The review shows how sedimentation in the Triassic of the area was strongly influenced by tectonic activity. This is as true for the Middle and Late Triassic of the NCA as it is for the Southern Alps. Tectonic activity may be responsible for large-scale cyclicity (4th to 3rd order scale). Although seismogenic structures have yet to be identified and described in carbonate successions of the Alps, candidates do exist. Slumped and microfaulted layers in laminated sediments of the Seefeld Basin (Upper Triassic, NCA) have been described as the products of fault movements. The sedimentary record from the NCA and Southern Alps also leaves little doubt that autocyclic processes were important in all environments except perhaps the deep, sediment-starved basins. Most small-scale platform cycles (5th order scale) in the region can be related to autocyclic processes and, in shallow basinal successions, to events such as storms. Previous workers have not been consistent in their interpretation of cyclic successions in the area, applying diverse theories to similar successions. So far, the Steinplatte-Hochkönig platform, with attached Kössen Basin, is the only example interpreted with reference to tectonics and autocyclicity; eustasy was probably not the most important factor in cycle generation in the Triassic of the NCA and Southern Alps. Such an approach could prove useful in future studies.     

The change from rifting to thrusting in the Northern Calcareous Alps as recorded in Jurassic sediments

Facies analysis, fossil dating, and the study of the metamorphism in the Late Triassic to Early Cretaceous sedimentary successions in the central part of the Northern Calcareous Alps allow to reconstruct the tectonic evolution in the area between the South Penninic Ocean in the northwest and the Tethys Ocean with the Hallstatt Zone in the southeast. The Triassic as well as the Early and Middle Jurassic sediments were deposited in a rifted, transtensive continental margin setting. Around the Middle/Late Jurassic boundary two trenches in front of advancing nappes formed in sequence in the central part of the Northern Calcareous Alps. The southern trench (Late Callovian to Early Oxfordian) accumulated a thick succession of gravitatively redeposited sediments derived from the sedimentary sequences of the accreted Triassic–Liassic Hallstatt Zone deposited on the outer shelf and the margin of the Late Triassic carbonate platform. During a previous stage these sediments derived from sequences deposited on the more distal shelf (Salzberg facies zone of Hallstatt unit, Meliaticum), and in a later stage from more proximal parts (Zlambach facies zone of Hallstatt unit, Late Triassic reef belt). Low temperature–high pressure metamorphism of some Hallstatt limestones before redeposition is explained by the closure of parts of the Tethys Ocean in Middle to Late Jurassic times and associated subduction. In the northern trench (Late Oxfordian to Kimmeridgian) several hundred meters of sediment accumulated including redeposited material from a nearby topographic rise. This rise is interpreted as an advancing nappe front as a result of the subduction process. The sedimentary sealing by Tithonian sediments, documented by uniform deep-water sedimentation (Oberalm Formation), gives an upper time constraint for the tectonic events. In contrast to current models, which propose an extensional regime for the central and eastern Northern Calcareous Alps in the Late Jurassic, we propose a geodynamic model with a compressional regime related to the Kimmerian orogeny.     

Anchimetamorphose im Anis und Ladin (Trias) der Nördlichen Kalkalpen zwischen Arlberg und Kaisergebirge — ihre Verbreitung und deren baugeschichtliche Bedeutung

Anisian to Ladinian sedimentary rocks of the Northern Calcareous Alps from the area between the Arlberg pass and the Kaisergebirge mountains have been sampled (more than 2500 samples) in about 50 stratigraphic profiles, recorded in great detail. The (silicate) mineral residue, fraction below 2 micron, resulting from solution in formic acid, has been investigated mineralogically. Its sheet silicate content proved to be markedly homogeneous, containing mainly di-octahedral illite minerals, their crystallinity as most prominent result found to increase in a twofold way:

1. The (Upper Austro-Alpine) Lechtal-Nappe is in its southern part characterized by increasing illite crystallinity from hanging to basal strata within the Ladinian to Anisian stratigraphic column. The source of this effect is found to be older than folding was.
2. The whole area of sedimentary rocks investigated here presents an increase in illite crystallinity data from north to south (i. e. towards the Central Alpine metamorphic units), irrespective of the presently existing tectonic structures (folding or nappe units within the Upper Austro-Alpine of the Northern Calcareous Alps). Hence the source of this effect must be younger than these events were. With this also a broad margin of “anchimetamorphic” influence has been detected within the southern part of the Northern Calcareous Alps, in the area of the Mieminger and Wetterstein mountains showing even a strong extension towards the north (reaching the location of Garmisch-Partenkirchen)

. These effects can by no means be attributed simply to sedimentary mineral distribution. Contradictionary to such an interpretation are the non-conformity of the illite crystallinity distribution within the existing tectonic setting to the original sedimentary position as well as general sedimentary data (paleo-morphology within the sedimentation area compared to homogeneous mineral distribution). Also (former or recent) sedimentary overburden cannot be quoted for as explanation, with no indication for this influence found so far in the stratigraphie profiles investigated at the thick Triassic sedimentary rock sequence in the steep descent of the Southern Karwendel mountains as well as in more than 6400 m of sedimentary rock sequence investigated in the ultradeep exploration borehole Vorderriß 1. The effects described here are attributed to very low grade metamorphic (“anchimetamorphic”) influences detected by these investigations within the Northern Calcareous Alps. A much higher influence due to increase in temperature compared to increase of pressure is indicated by experimental work done by the author. Even with a cautious attempt to incorporate these newly found temperature effects on Triassic sedimentary rocks into the geologic development of the Northern Calcareous Alps and the Alpine Orogeny, at least for the older effect the conception of “transported” metamorphism is implied, perhaps also for the younger one. This idea is furthermore supported by K/Ar — age determinations of well ordered illite minerals gained from the Schwaz Triassic occurrence, yielding data of about 110–120 mio. y. This age for the older temperature effect can be explained in terms of (starting?) subduction of Penninic units below Austro-Alpine units, long before Austro-Alpine nappes reached their present position within the Northern Calcareous Alps.     

Conodont Biostratigraphy and Age Determination of the Lower–Middle Triassic Boundary in South Guizhou Province, China

The demarcation of the Lower–Middle Triassic boundary is a disputed problem in global stratigraphic research. Lower–Middle Triassic strata of different types, from platform to basin facies, are well developed in Southwest China. This is favorable for the study of the Olenekian–Anisian boundary and establishing a stratotype for the Qingyan Stage. Based on research at the Ganheqiao section in Wangmo county and the Qingyan section in Guiyang city, Guizhou province, six conodont zones have been recognized, which can be correlated with those in other regions, in ascending order as follows: 1, Neospathodus cristagalli Interval-Zone; 2, Neospathodus pakistanensis Interval-Zone; 3, Neospathodus waageni Interval-Zone; 4, Neospathodus homeri-N. triangularis Assemblage-Zone; 5, Chiosella timorensis Interval-Zone; and 6, Neogongdolella regalis Range-Zone. An evolutionary series of the Early–Middle Triassic conodont genera Neospathodus-Chiosella-Neogongdolella discovered in the Ganheqiao and Qingyan sections has an intermediate type named Neospathodus qingyanensis that appears between Neospathodus homeri and Chiosella timorensis in the upper part of the Neospathodus homeri-N. triangularis Zone, showing an excellent evolutionary relationship of conodonts near the Lower–Middle Triassic boundary. The Lower–Middle Triassic boundary is located at 1.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Qingyan section, whereas this boundary is located 0.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Ganheqiao section. There exists one nearly 6-m thick vitric tuff bed at the bottom of the Xinyuan Formation in the Ganheqiao section, which is usually regarded as a lithologic symbol of the Lower–Middle Triassic boundary in South China. Based on the analysis of high-precision and high-sensitivity Secondary Ion Mass Spectrum data, the zircon age of this tuff has a weighted mean 206Pb/238U age of 239.0±2.9Ma (2s), which is a directly measured zircon U-Pb age of the Lower–Middle Triassic boundary. The Ganheqiao section in Wangmo county can therefore provide an excellent section through the Lower–Middle Triassic because it is continuous, the evolution of the conodonts is distinctive and the regionally stable distributed vitric tuff near the Lower–Middle Triassic boundary can be regarded as a regional key isochronal layer. This section can be regarded not only as a standard section for the establishment of the Qingyan Stage in China, but also as a reference section for the GSSP of the Lower–Middle Triassic boundary.     

Potassium-argon ages from the Ceneri Zone,Southern Swiss Alps

The Ceneri Zone is a unit of the crystalline basement of the Southern Alps. Its northern boundary is the Tonale Line segment of the Periadriatic Line, an important tectonic lineament separating the Oligocene and younger features of the Central Alps from the older metamorphic and structural trends of the Southern Alps. Unmetamorphosed Permian and younger sedimentary units lap onto the Southern Alpine basement from the south.Potassium-argon results from the Ceneri Zone define a Hercynian age pattern typical for the basement of continental Europe. This pattern extends to within at least 100 meters of the Tonale Line. Thus, amphibolite facies metamorphism in this region occurred around 325 m.y. ago. The geochronologic similarity of the Southern Alps to many other European regions must be taken into account in megatectonic theories.In detail, the Hercynian age pattern of the Ceneri Zone is complicated. Some hornblendes have apparent ages between the Hercynian and a Caledonian value (430 m.y.). They probably retained some radiogenic argon during the Hercynian upper amphibolite facies metamorphism. In addition, mica results between 200 and 300 m.y. have a strong geographic correlation. Apparently, the northwestern portion of the Ceneri Zone was reheated or mildly metamorphosed during the Upper Triassic to Lower Jurassic. A relationship between these ages and 170–180 m.y. ages from the neighboring Ivrea-Verbano Zone seems likely. No geologic evidence for any post-Hercynian event has been noted as yet in the Ceneri Zone.     

Stratigraphy and ammonite fauna of the upper Shemshak Formation (Toarcian–Aalenian) at Tazareh, eastern Alborz, Iran

With a thickness of 3900 m, the Tazareh section is one of the thickest developments of the Shemshak Formation in the Alborz range. It overlies with sharp and disconformable contact the limestones and dolomites of the Lower–Middle Triassic Elikah Formation and is topped, again with a disconformable contact, by the marls and limestones of the Middle Jurassic Dalichai Formation. The nearly exclusively siliciclastic succession represents a range of environments, from fluvial channels, flood plains, swamps and lake systems to storm-dominated shelf, and a comparatively deep marine and partly dysoxic basin. The segment of the section between 2300 and 3500 m is exclusively marine and contains a moderately diverse ammonite fauna, ranging from the Middle Toarcian to the Upper Aalenian. The ammonite fauna comprises 21 taxa, among them the new genus Shahrudites with two new species, Shahrudites asseretoi and S. stoecklini from the Middle Aalenian Bradfordensis Zone. The other ammonites from the Shemshak Formation at Tazareh (as elsewhere in North and Central Iran) are exclusively Tethyan in character and closely related to faunas from western and central Europe. An ammonite-based correlation of Toarcian–Aalenian successions of the eastern Alborz with time-equivalent strata of the Lut Block, part of the Central-East Iranian Microcontinent (ca. 500 km to the south), suggests a strong influence of synsedimentary tectonics during the deposition of the upper Shemshak Formation.     

滇东南法郎组含锰地层沉积相分析

滇东南中三叠统法郎组是重要的含锰地层,前人对其沉积环境的认识却存在着深水浊流沉积和浅水潮坪沉积的争议。本文通过对建水-开远地区典型剖面的研究,认为法郎组为浊积扇沉积。法郎组底部为碳酸盐滑塌沉积、碎眉流沉积与泥岩粉砂岩互层,中上部逐渐由外扇渐变为中扇辫状水道和辫状水道间沉积,顶部为内扇补给水道和溢岸沉积。相对海水深度总体表现为在拉丁早期逐渐加深,到拉丁中晚期有逐渐变浅。锰矿层主要发育在底部的碎屑流沉积中,其彤成可能与拉丁早期相对水深的增高有关。     

The Triassic of Timor: Lithostratigraphy, chronostratigraphy and palaeogeography

The palaeontologically rich and lithologically diverse Triassic successions of Timor provide a key stratigraphic and palaeontological link between northwestern Australia and other terranes of former eastern Gondwana (present-day Southeast Asia). Timor is now located in the zone of collision between the northern margin of the Australian continent and island arc terranes bordering the Eurasian plate, with the Triassic successions exposed in a fold-and-thrust belt and an extensive mélange complex. Three formal lithostratigraphic units have been defined previously within the main Triassic succession in Timor (Niof, Aitutu and Babulu formations), with a fourth, the Wai Luli Formation, primarily Jurassic in age but extending down into the Triassic. The Niof Formation (Anisian to Ladinian, possibly also Early Triassic) is a fine-grained deepwater succession, succeeded conformably by the Aitutu and Babulu formations (Ladinian to Norian/Rhaetian), which were deposited contemporaneously, with the Aitutu Formation continuing locally into the Lower Jurassic. The Aitutu Formation consists of deep shelf limestones interbedded with shales and marls, while the Babulu Formation is a deltaic to turbiditic siliciclastic succession. The Late Triassic to Jurassic Wai Luli Formation is characterised by marine shales and marls.Informal stratigraphic units include the Cephalopod Limestone Facies, a Rosso Ammonitico-type deposit, which contains an extremely rich fossil fauna (particularly ammonoids) and ranges through the entire Triassic; and the Fatu Limestone and Pualaca Facies which consists of shallow to marginal marine carbonates (mud mounds, oolitic limestones and reefs) restricted to the Late Triassic. Facies diversity was low during the Early Triassic and Anisian, but became more pronounced from the Ladinian and continuing through the Late Triassic, probably as a consequence of renewed tectonic extension. Triassic extension was not associated with major volcanism, unlike a previous phase of extension in the Early Permian.The Cablac Limestone Formation, originally defined as a Miocene stratigraphic element, is now recognised to be at least partly Late Triassic–Early Jurassic in age, with lithologies comparable to parts of the Fatu Limestone. The stratigraphy of these shallow marine carbonate sequences is clearly in need of rigorous revision, but it is not yet possible to suggest appropriate redefined formations.     

贵州边阳地区中三叠世的六射珊瑚化石

本文描述了贵州边阳地区中三叠统拉丁尼克期的六射珊瑚4属6种，其中1个已知种，1个亲近种，2个新种和2个未定种：Pinacophyllum spizzensis(Tornquist)，P．aff．yunnanense Wu，P．bianyangense sp．nov，Retiophyllia bianyangensis sp．nov．，Procydolites sp．，Margarosmilia sp．，丰富了世界中三叠世六射珊瑚研究的资料。迄今全世界缺乏早三叠世珊瑚，研究中三叠世珊瑚，对探讨中生代开始出现的六射珊瑚的发生和系统演化，古生代四射珊瑚与中生代珊瑚之间存在的关系，都有很重要的意义。     

The Middle Jurassic radiolarites and pelagic limestones of the Nieves unit (Rondaide Complex, Betic Cordillera): basin starvation in a rifted marginal slope of the western Tethys

Middle Jurassic radiolarites and associated pelagic limestones occur in the Rondaide Nieves unit of the Betic Cordillera, southern Spain. The Rondaide Mesozoic includes: (a) a thick succession of Triassic platform carbonates, comparable to the Alpine Hauptdolomit and Kössen facies; (b) Lower Jurassic pelagic limestones comparable to the Alpine Hierlatz and Adnet facies; (c) the Middle Jurassic Parauta Radiolarite Formation, described herein; and (d) a thin Upper Jurassic-Cretaceous condensed limestone succession. The Parauta Radiolarite Formation and associated limestones were studied with respect to stratigraphy, petrography, micropalaeontology (radiolarians, calcareous nanno- and microfossils) and facies. Radiolarite sedimentation occurred in the Middle Bathonian in a restricted and dysoxic deep Nieves basin, perched in the distal zone of a continental margin fringing the Tethyan ocean. This margin was adjacent to a young narrow oceanic basin between the South-Iberian margin and a continental block called Mesomediterranean Terrane. The Nieves basin was part of a marine corridor between the Proto-Atlantic and Piedmont-Ligurian basins of the Alpine Tethys. The regional tectonic position, the stratigraphical evolution since the Triassic, the age and the nature of the Mesozoic facies and the palaeogeographic relations to adjacent domains show striking analogies between the Betic Rondaide margin and coeval units of the Alps.     

The Jurassic Prehodavci Formation of the Julian Alps: easternmost outcrops of Rosso Ammonitico in the Southern Alps (NW Slovenia)

The Julian Alps are located in NW Slovenia and structurally belong to the Julian Nappe where the Southern Alps intersect with the Dinarides. In the Jurassic, the area was a part of the southern Tethyan continental margin and experienced extensional faulting and differential subsidence during rifting of the future margin. The Mesozoic succession in the Julian Alps is characterized by a thick pile of Upper Triassic to Lower Jurassic platform limestones of the Julian Carbonate Platform, unconformably overlain by Bajocian to Tithonian strongly condensed limestones of the Prehodavci Formation of the Julian High. The Prehodavci Formation is up to 15 m thick, consists of Rosso Ammonitico type limestone and is subdivided into three members. The Lower Member consists of a condensed red, well-bedded bioclastic limestone with Fe–Mn nodules, passing into light-grey, faintly nodular limestone. The Middle Member occurs discontinuously and consists of thin-bedded micritic limestone. The Upper Member unconformably overlies the Lower or Middle Members. It is represented by red nodular limestone, and by red-marly limestone with abundant Saccocoma sp. The Prehodavci Formation unconformably overlies the Upper Triassic to Lower Jurassic platform limestone of the Julian Carbonate Platform; the contact is marked by a very irregular unconformity. It is overlain by the upper Tithonian pelagic Biancone (Maiolica) limestone. The sedimentary evolution of the Julian High is similar to that of Trento Plateau in the west and records: (1) emergence and karstification of part of the Julian Carbonate Platform in the Pliensbachian, or alternatively drowning of the platform and development of the surface by sea-floor dissolution; (2) accelerated subsidence and drowning in the Bajocian, and onset of the condensed pelagic sedimentation (Prehodavci Formation) on the Julian High; (3) beginning of sedimentation of the Biancone limestone in the late Tithonian.     

Late Permian–early Middle Triassic back-arc basin development in West Qinling,China

The Late Permian–early Middle Triassic strata of the northern West Qinling area, northeastern Tibetan Plateau, are composed of sediment gravity flow deposits. Detailed sedimentary facies analysis indicates these strata were deposited in three successive deep-marine environments. The Late Permian–early Early Triassic strata of the Maomaolong Formation and the lowest part of the Longwuhe Formation define a NW–SE trending proximal slope environment. Facies of the Early Triassic strata composing the middle and upper Longwuhe Formation are consistent with deposition in a base-of-slope apron environment, whereas facies of the Middle Triassic Anisian age Gulangdi Formation are more closely associated with a base-of-slope fan depositional environment. The lithofacies and the spatial–temporal changes in paleocurrent data from these strata suggest the opening of a continental margin back-arc basin system during Late Permian to early Middle Triassic time in the northern West Qinling. U–Pb zircon ages for geochemically varied igneous rocks with diabasic through granitic compositions intruded into these deep-marine strata range from 250 to 234 Ma. These observations are consistent with extensional back-arc basin development and rifting between the Permian–Triassic Eastern Kunlun arc and North China block during the continent–continent collision and underthrusting of the South China block northward beneath the Qinling terrane of the North China block. Deep-marine sedimentation ended in the northern West Qinling by the Middle Triassic Ladinian age, but started in the southern West Qinling and Songpan-Ganzi to the south. We attribute these observations to southward directed rollback of Paleo-Tethys oceanic lithosphere, continued attenuation of the West Qinling on the upper plate, local post-rift isostatic compensation in the northern West Qinling area, and continued opening of a back-arc basin in the southern West Qinling and Songpan-Ganzi. Rollback and back-arc basin development during Late Permian to early Middle Triassic time in the West Qinling area explains: the truncated map pattern of the Eastern Kunlun arc, the age difference of deep-marine sediment gravity flow deposits between the Late Permian–early Middle Triassic northern West Qinling and the late Middle Triassic–Late Triassic southern West Qinling and Songpan-Ganzi, and the discontinuous trace of ophiolitic rocks associated with the Anyemaqen-Kunlun suture.     

川西松潘地区中三叠统拉丁阶的再认识

<正> 川西高原是否存在中三叠统拉丁阶?一直是人们所关心的问题。朱占祥等对拉丁阶的一些零星发现作过初步报导。松潘地区安壁村拉丁期瓣鳃类Daonella lommeli和牙形石 Neogondolella excelsa等也作了分析。殷鸿福也讨论了中国的拉丁阶问题。 在松潘以北、岷江以西8—12km范围内,曾做过初期阶段的地质填图,西部香腊台—花山—黄胜关—则哈一带的石灰岩和砂板岩,被定为泥盆系、石炭系和下二叠统。东部     

秦岭三叠系分带及印支期发展史

秦岭及共邻区的三叠系自北而南可分为四带.北秦岭三叠系具有富含植物化石的陆相上三叠统,其下的优地槽型细碧角斑岩系时代未定.中秦岭下三叠统为复理石夹多层砾状灰岩,后者系斜坡沉积,物源可能来自北方,安尼期为复理石.南秦岭北带在二叠纪晚期已裂陷接受复理石及以砾状灰岩为代表的斜坡沉积.早三叠世至安尼期为深水相黑色板岩、薄层灰岩、复理石并夹火山岩.南秦岭南带及巴顿喀喇从早三叠世至安尼期为扬子地台的一部分,岩相及化百群与之一致,具有发育良好的安尼期陆棚边缘生物滩.从拉丁期开始裂陷．出现鱼鳞蛤页岩、砾状灰岩及巨厚复理石,后者延续至晚三叠世,有放射虫为证.整个中,南秦岭呈现一个由二叠纪晚期开始,延续于印支期的裂陷槽发育史.它的北部—中秦岭和南秦岭北带于二叠纪末及三叠纪初先后裂陷,并于拉丁期褶皱回返.它的南部—南秦岭南带及巴颜喀喇于拉丁期裂陷,并于三叠纪末回返.这个裂陷槽是否构成印支期秦岭的主体,抑或它仅是“北秦岭小洋盆”在扬子大陆边缘的弧后扩张盆地,取决于北秦岭是否存在早、中三叠世优地槽沉积.后者尚未证实.