The start‐up of the Dolomia Principale/Hauptdolomit carbonate platform (Upper Triassic) in the eastern Southern Alps

Wide carbonate platform environments developed on the western passive margin of the Tethys during the Late Triassic, after a major climate change (Carnian Pluvial Episode) that produced a crisis of high‐relief microbial carbonate platforms. The peritidal succession of this epicontinental platform (Dolomia Principale/Hauptdolomit, Dachstein Limestone) is widespread in the Mediterranean region. However, the start‐up stage is not fully understood. The original platform to basin depositional geometries of the system have been studied in the north‐eastern Southern Alps, close to the Italian/Slovenian boundary where they are exceptionally preserved. Sedimentological features have been investigated in detail by measuring several stratigraphic sections cropping out along an ideal depositional profile. The analysis of the facies architecture allowed reconstruction of the palaeoenvironments of the Dolomia Principale platform during its start‐up and early growth stages in the late Carnian. The carbonate platform was characterized by an outer platform area, connected northward to steep slopes facing a relatively deep basin. Southward, the outer platform was connected to inner sheltered environments by a narrow, often emerged shelf crest. Behind this zone, carbonate sedimentation occurred in shallow lagoons and tidal flats, passing inward to a siliciclastic mudflat. The Dolomia Principale platform was initially aggrading and able to keep pace with a concomitant sea‐level rise, and then prograding during the late Carnian. This stratigraphic interval was correlated with the Tuvalian succession of the Dolomites, allowing depiction of the depositional system on a wide scale of hundreds of kilometres. This large‐scale depositional system presents features in common with some Palaeozoic and Mesozoic carbonate build‐ups (for example, the Permian Capitan Reef complex, Anisian Latemar platform), both in terms of architecture and prevailing carbonate producers. A microbial‐dominated carbonate factory is found in the outer platform and upper slope. The recovery of high‐relief microbial carbonate platforms marks the end of the Carnian Pluvial Episode in the Tuvalian of Tethys.     

藏高珠穆朗玛峰地区三叠系层序地层及沉积演化：—从陆表海盆地到裂谷盆地

珠峰地区的三叠系形成于大陆拉伸背景。自下而上可划分为12个三级沉积层序和5个层序组，分属于2个中层序。发生在Induan阶初期（约250Ma)，Anisian阶早期（约239Ma),Carnian阶初期（约231Ma）和Norian早期（约223Ma)的4个海侵事件最为重要。可作跨越板块的地层对比标志。藏南地区在三叠纪经历了从泛大陆到大陆裂谷的构造演化，早一中三叠世以陆表海盆地浅水环境为主，晚三叠世以深水断陷盆地为特征。晚三叠世晚期，与长期全球海平面下降相伴随，过量的陆源碎屑输入造成该地区由深水盆地转为河流作用明显的三角洲平原环境。     

Late Triassic volcanic activity in South-East Asia: New stratigraphical,geochronological and paleontological evidence from the Luang Prabang Basin (Laos)

In South-East Asia, sedimentary basins displaying continental Permian and Triassic deposits have been poorly studied. Among these, the Luang Prabang Basin (North Laos) represents a potential key target to constrain the stratigraphic and structural evolutions of South-East Asia. A combined approach involving sedimentology, palaeontology, geochronology and structural analysis, was thus implemented to study the basin. It resulted in a new geological map, in defining new formations, and in proposing a complete revision of the Late Permian to Triassic stratigraphic succession as well as of the structural organization of the basin. Radiometric ages are used to discuss the synchronism of volcanic activity and sedimentation.The Luang Prabang Basin consists of an asymmetric NE-SW syncline with NE-SW thrusts, located at the contact between Late Permian and Late Triassic deposits. The potential stratigraphic gap at the Permian–Triassic boundary is therefore masked by deformation in the basin. The Late Triassic volcaniclastic continental deposits are representative of alluvial plain and fluvial environments. The basin was fed by several sources, varying from volcanic, carbonated to silicic (non-volcanic). U–Pb dating of euhedral zircon grains provided maximum sedimentation ages. The stratigraphic vertical succession of these ages, from ca. 225, ca. 220 to ca. 216 Ma, indicates that a long lasting volcanism was active during sedimentation and illustrates significant variations in sediment preservation rates in continental environments (from ∼100 m/Ma to ∼3 m/Ma). Anhedral inherited zircon grains gave older ages. A large number of them, at ca. 1870 Ma, imply the reworking of a Proterozoic basement and/or of sediments containing fragments of such a basement. In addition, the Late Triassic (Carnian to Norian) sediments yielded to a new dicynodont skull, attributed to the Kannemeyeriiform group family, from layers dated in between ∼225 and ∼221 Ma (Carnian).     

巴颜喀拉盆地岩相、相组及其演化

巴颜喀拉盆地北以东昆仑南缘蛇绿混杂岩带为界,东与龙门山-锦屏山前陆褶冲带相邻,西以甘孜-理塘结合带为界,总体呈斜三角形状展布。黄汲清(1962)称之为松潘-甘孜褶皱系,张勤文(1983)称马尼干戈-理塘残余后弧盆地,余如龙(1989)称松潘-甘孜前缘复理石推覆带。笔者认为本区是在被动边缘基础上由弧后盆地转换为前陆盆地。     

南盘江盆地早—中三叠世层序地层格架及相对海平面变化研究

南盘江盆地的早—中三叠世地层中 ,沉积相形成复杂而有序的空间变化和时间变化。二叠纪与三叠纪之交的大规模台地淹没事件之后 ,三叠纪碳酸盐台地从缓坡型演化为镶嵌陆架型 ;空间上 ,从连陆台地到浊积盆地相分异特别明显 ,而且在盆地中发育若干的孤立台地 ,特别是南宁和靖西一带 ,孤立台地上早三叠世的鲕粒滩以及连陆台地边缘的礁滩相灰岩更是引人注目。尽管不同相带的三级沉积层序相序组构千差万变 ,并且它们的形成时限也不尽相同 ,但是由其所表征的相对海平面变化则具有大致的同步性 ,因此在早—中三叠世地层中可以识别出 6个三级沉积层序。以地层记录中的两种相变面和两种穿时性为基本要素 ,可以建立南盘江盆地早—中三叠世的层序地层格架。     

Tectonic and climatic events controlling deposition in Tanzanian Karoo basins

The depositional megasequence of the Tanzanian Karoo resulted from an intracratonic phase of sedimentation prevailing during the maximum extension of Pangea in Late Palaeozoic and Triassic times. Karoo rocks are contained in a number of basins, extending from northeastern-most Tanzania to Lake Nyasa and beyond into neighbouring countries. The type section of the Tanzanian Karoo is the Songea Group of the Ruhuhu Basin, situated at the NE-shoulder of the Nyasa Rift. The succession, which reaches a thickness of more than 3000 m, is of Late Carboniferous to Mid-Triassic age. It exhibits five distinctive sequences, each commencing with rudaceous sediments and fining up towards the top. A sixth sequence of Middle to Late Triassic age is recognized in the Selous Basin, NE of the Ruhuhu Basin. The climate ranged from cold, semi-arid conditions in the Stephanian and Asselian to generally warm to hot climates, with fluctuating precipitation in the remaining Permian and Triassic. A marked peak in precipitation is evidenced in the Early Triassic. Each of the sedimentary sequences reflects tectonic movements related to the formation of non-volcanic rift systems during the Permian, and to detachment faults and crustal foundering during the Triassic. The intracratonic Karoo rifts were part of the Malagassy Trough, a large chasm emanating from the Tethyan margin of Gondwana in early Permian times. The Karoo rifts were terminated by their transformation to a pericratonic, passive margin in the Early Jurassic.     

西藏东部昌都地区三叠纪岩相古地理

昌都地区三叠纪岩相古地理演化可划分为5个阶段,各阶段的古构造与古地理格架既有继承性,又有差异性。早三叠世承袭了晚二叠世末期的古地理,古陆面积扩大,海域沉积只占据狭窄部分,并且从这个时期起,已展现出弧－盆体系中的岛、海格架雏形;中三叠世沿袭了早三叠世弧－盆体系,弧内盆地发生强烈拗陷,堆积了巨厚的多物源浊积岩与幕式弧火山岩;晚三叠世卡尼早期因东侧金沙江洋的消亡,发育磨拉石沉积,仅在局部地区表现为陆棚→斜坡→盆地沉积;晚三叠世诺利早期,全区范围内发生一次规模空前的海侵,碳酸盐沉积向东西两侧古陆超覆,弧－盆区岛海格局从此消失;晚三叠世诺利晚期以后,海水自东向西退出,海陆过渡相与滨岸陆屑沉积广泛覆盖全区。研究表明,三叠纪时昌都地区曾经存在着一个类似于现今印度尼西亚岛、海的古地理格局。     

The Triassic of the Thakkhola (Nepal). I: stratigraphy and paleoenvironment of a north-east Gondwanan rifted margin

The Mesozoic sediments of Thakkhola (central Nepal) were deposited on a broad eastern north Gondwanan passive margin at mid-latitudes (28–41 °S) facing the Southern Tethys ocean to the north. The facies is strikingly similar over a distance of several thousand kilometres from Ladakh in the west to Tibet and to the paleogeographically adjacent north-west Australian margin (Exmouth Plateau, ODP Legs 122/123) and Timor in the east. Late Paleozoic rifting led to the opening of the Neo-Tethys ocean in Early Triassic times. An almost uninterrupted about 2 km thick sequence of syn-rift sediments was deposited on a slowly subsiding shelf and slope from Early Triassic to late Valanginian times when break-up between Gondwana (north-west Australia) and Greater India formed the proto-Indian Ocean. The sedimentation is controlled by (1) global events (eustasy; climatic/oceanographic changes due to latitudinal drift; plate reorganization leading to rift-type block-faulting) and (2) local factors, such as varying fluvio-deltaic sediment input, especially during Permian and late Norian times. Sea level was extremely low in Permian, high in Carnian and low again during Rhaeto-Liassic times. Third-order sea-level cycles may have occurred in the Early Triassic and late Norian to Rhaeto-Liassic. During the Permian pure quartz sand and gravel were deposited as shallowing upward series of submarine channel or barrier island sands. The high compositional maturity is typical of a stable craton-type hinterland, uplifted during a major rifting episode. During the early Triassic a 20–30 m thick condensed sequence of nodular ‘ammonitico rosso’-type marlstone with a ‘pelagic’ fauna was deposited (Tamba Kurkur Formation). This indicates tectonic subsidence and sediment starvation during the transgression of the Neo-Tethys ocean. During Carnian times a 400 m thick sequence of fining upward, filament-rich wackestone/shale cycles was deposited in a bathyal environment (Mukut Formation). This is overlain by about 300 m of sandy shale and siltstone intercalated with quartz-rich bioclastic grain- to rudstone (Tarap Shale Formation, late Carnian-Norian). The upper Norian to (?lower) Rhaetian Quartzite Formation consists of (sub)arkosic sandstones and pure quartz arenites, indicating different sediment sources. The fluvio-deltaic sandstones are intercalated with silty shale, coal and bioclastic limestone, as well as mixed siliciclastic-bioclastic rocks. The depositional environment was marginal marine to shallow subtidal. The fluvio-deltaic influence decreased towards the overlying carbonates of Rhaeto-Liassic (?) age (Jomosom Formation correlative with the Kioto Limestone), when the region entered tropical paleolatitudes resulting in platform carbonates.     

The Triassic of the Thakkhola (Nepal). II: Paleolatitudes and comparison with other Eastern Tethyan Margins of Gondwana

During the Triassic, the Thakkhola region of the Nepal Himalaya was part of the broad continental shelf of Gondwana facing a wide Eastern Tethys ocean. This margin was continuous from Arabia to Northwest Australia and spanned tropical and temperate latitudes.A compilation of Permian, Triassic and early Jurassic paleomagnetic data from the reconstructed Gondwana blocks indicates that the margin was progressively shifting northward into more tropical latitudes. The Thakkhola region was approximately 55° S during Late Permian, 40° S during Early Triassic, 30° S during Middle Triassic and 25° S during Late Triassic. This paleolatitude change produced a general increase in the relative importance of carbonate deposition through the Triassic on the Himalaya and Australian margins. Regional tectonics were important in governing local subsidence rates and influx of terrigenous clastics to these Gondwana margins; but eustatic sea-level changes provide a regional and global correlation of major marine transgressions, prograding margin deposits and shallowing-upward successions. A general mega-cycle characterizes the Triassic beginning with a major transgression at the base of the Triassic, followed by a general shallowing-upward of facies during Middle and Late Triassic, and climaxing with a regression in the latest Triassic.     

3D and 4D controls on carbonate depositional systems: sedimentological and sequence stratigraphic analysis of an attached carbonate platform and atoll (Miocene, Níjar Basin, SE Spain)

This study investigates the controls on three-dimensional stratigraphic geometries and facies of shallow-water carbonate depositional sequences. A 15 km² area of well-exposed Mid to Late Miocene carbonates on the margin of the Níjar Basin of SE Spain was mapped in detail. An attached carbonate platform and atoll developed from a steeply sloping basin margin over a basal topographic unconformity and an offshore dacite dome (Late Miocene). The older strata comprise prograding bioclastic (mollusc and coralline algae) dominated sediments and later Messinian Porites reefs form prograding and downstepping geometries (falling stage systems tract). Seven depositional sequences, their systems tracts and facies have been mapped and dated (using Sr isotopes) to define their morphology, stratigraphic geometries, and palaeo-environments. A relative sea-level curve and isochore maps were constructed for the three Messinian depositional sequences that precede the late Messinian evaporative drawdown of the Mediterranean. The main 3D controls on these depositional sequences are interpreted as being: (i) local, tectonically driven relative sea-level changes; (ii) the morphology of the underlying sequence boundary; (iii) the type of carbonate producers [bioclastic coralline algal and mollusc-dominated sequences accumulated in lows and on slopes of < 14° whereas the Porites reef-dominated sequence accumulated on steep slopes (up to 25°) and shallow-water highs]. Further controls were: (iv) the inherited palaeo-valleys and point-sourced clastics; (v) the amount of clastic sediments; and (vi) erosion during the following sequence boundary development. The stratigraphy is compared with that of adjacent Miocene basins in the western Mediterranean to differentiate local (tectonics, clastic supply, erosion history, carbonate-producing communities) versus regional (climatic, tectonic, palaeogeographic, sea-level) controls.     

Impact of dynamic sedimentation on facies heterogeneities in Lower Cretaceous peritidal deposits of central east Oman

This study, based in the Haushi‐Huqf area of central east Oman, aims to characterize the controls on facies distribution and geometries of some of the best preserved examples of Lower Cretaceous tidal flat facies within the Tethyan epeiric platform. Field, petrographic and geochemical data were acquired from the Barremian–Aptian Jurf and Qishn formations that crop out in a 500 × 1000 m² butte, thus allowing for pseudo three‐dimensional quantitative data acquisition of the dimensions and spatial distributions of discontinuity surfaces and sedimentary bodies. The interpretation presented here suggests that the main processes impacting sedimentation in the Lower Cretaceous peritidal environment of the Haushi‐Huqf were transport and erosion processes related to storm waves and currents. The vertical evolution of the carbonate system is organized into six types of metre‐scale depositional sequences, from subtidal dominated sequences to supratidal‐capped sequences, which are bounded by regional discontinuity surfaces. At subaerial exposure and submarine erosion surfaces associated with a base level shift, sedimentary horizons along the entire depositional profile are cut by scours possibly created by storm events. Chemostratigraphy allows correlation between the Haushi‐Huqf and the age‐equivalent sections logged in the interior of the platform in Oman. The correlation suggests that the change from subtidal to intertidal depositional sequences during the late highstand is coeval with the development of rudist dominated shoals on the shelf. This study is the first to discuss the controls on Lower Cretaceous peritidal carbonate cyclicity of the Arabian epeiric platform. The results presented here also offer a unique quantitative dataset of the distribution and dimensions of peritidal carbonate shoals and storm scours in a regional sequence stratigraphic context.     

Permian Peri‐glacial Deposits from Central Mongolia in Central Asian Orogenic Belt: A Possible Indicator of the Capitanian Cooling Event

A dropstone‐bearing, Middle Permian to Early Triassic peri‐glacial sedimentary unit was first discovered from the Khangai–Khentei Belt in Mongolia, Central Asian Orogenic Belt. The unit, Urmegtei Formation, is assumed to cover the early Carboniferous Khangai–Khentei accretionary complex, and is an upward‐fining sequence, consisting of conglomerates, sandstones, and varved sandstone and mudstone beds with granite dropstones in ascending order. The formation was cut by a felsic dike, and was deformed and metamorphosed together with the felsic dike. An undeformed porphyritic granite batholith finally cut all the deformed and metamorphosed rocks. LA‐ICP‐MS, U–Pb zircon dating has revealed the following ²⁰⁶Pb/²³⁸U weighted mean igneous ages: (i) a granite dropstone in the Urmegtei Formation is 273 ± 5 Ma (Kungurian of Early Permian); (ii) the deformed felsic dike is 247 ± 4 Ma (Olenekian of Early Triassic); and (iii) the undeformed granite batholith is 218 ± 9 Ma (Carnian of Late Triassic). From these data, the age of sedimentation of the Urmegtei Formation is constrained between the Kungurian and the Olenekian (273–247 Ma), and the age of deformation and metamorphism is constrained between the Olenekian and the Carnian (247–218 Ma). In Permian and Triassic times, the global climate was in a warming trend from the Serpukhovian (early Late Carboniferous) to the Kungurian long and severe cool mode (328–271 Ma) to the Roadian to Bajocian (Middle Jurassic) warm mode (271–168 Ma), with an interruption with the Capitanian Kamura cooling event (266–260 Ma). The dropstone‐bearing strata of the Urmegtei Formation, together with the glacier‐related deposits in the Verkhoyansk, Kolyma, and Omolon areas of northeastern Siberia (said to be of Middle to Late Permian age), must be products of the Capitanian cooling event. Although further study is needed, the dropstone‐bearing strata we found can be explained in two ways: (i) the Urmegtei Formation is an autochthonous formation indicating a short‐term expansion of land glacier to the central part of Siberia in Capitanian age; or (ii) the Urmegtei Formation was deposited in or around a limited ice‐covered continent in northeast Siberia in the Capitanian and was displaced to the present position by the Carnian.     

Depositional facies,environments and sequence stratigraphic interpretation of the Middle Triassic–Lower Cretaceous (pre-Late Albian) succession in Arif El-Naga anticline,northeast Sinai,Egypt

The Middle Triassic–Lower Cretaceous (pre-Late Albian) succession of Arif El-Naga anticline comprises various distinctive facies and environments that are connected with eustatic relative sea-level changes, local/regional tectonism, variable sediment influx and base-level changes. It displays six unconformity-bounded depositional sequences. The Triassic deposits are divided into a lower clastic facies (early Middle Triassic sequence) and an upper carbonate unit (late Middle- and latest Middle/early Late Triassic sequences). The early Middle Triassic sequence consists of sandstone with shale/mudstone interbeds that formed under variable regimes, ranging from braided fluvial, lower shoreface to beach foreshore. The marine part of this sequence marks retrogradational and progradational parasequences of transgressive- and highstand systems tract deposits respectively. Deposition has taken place under warm semi-arid climate and a steady supply of clastics. The late Middle- and latest Middle/early Late Triassic sequences are carbonate facies developed on an extensive shallow marine shelf under dry-warm climate. The late Middle Triassic sequence includes retrogradational shallow subtidal oyster rudstone and progradational lower intertidal lime-mudstone parasequences that define the transgressive- and highstand systems tracts respectively. It terminates with upper intertidal oncolitic packstone with bored upper surface. The next latest Middle/early Late Triassic sequence is marked by lime-mudstone, packstone/grainstone and algal stromatolitic bindstone with minor shale/mudstone. These lower intertidal/shallow subtidal deposits of a transgressive-systems tract are followed upward by progradational highstand lower intertidal lime-mudstone deposits. The overlying Jurassic deposits encompass two different sequences. The Lower Jurassic sequence is made up of intercalating lower intertidal lime-mudstone and wave-dominated beach foreshore sandstone which formed during a short period of rising sea-level with a relative increase in clastic supply. The Middle-Upper Jurassic sequence is represented by cycles of cross-bedded sandstone topped with thin mudstone that accumulated by northerly flowing braided-streams accompanying regional uplift of the Arabo–Nubian shield. It is succeeded by another regressive fluvial sequence of Early Cretaceous age due to a major eustatic sea-level fall. The Lower Cretaceous sequence is dominated by sandy braided-river deposits with minor overbank fines and basal debris flow conglomerate.     

The sandstone memory of the evolution of a Triassic volcanic arc in the Southern Alps, Italy

The erosion of a southern volcanic belt provided the bulk of the fine-grained and moderately sorted siliciclastic detritus in the whole deltaic to lagoonal Carnian (Upper Triassic) sequence of the Bergamasc Alps. Volcanic input began in the Early Carnian (Calcare Metallifero Bergamasco) and became prominent in Early-Middle (Val Sabbia Sandstone) and Late Carnian times (S. Giovanni Bianco Fm.), after an intervening period of diminished supply (Gorno Fm.). The mineralogical and chemical composition of the sandstones compares closely with that of siliciclastics derived from modern, Pacific-type magmatic arcs and it testifies to an evolution of the source rocks from andesites and dacites during the deposition of the Val Sabbia Sandstone, towards rhyodacitic ignimbrites for the S. Giovanni Bianco Fm. The marked reduction in feldspars at the top of the sequence contrasts with the classical trend from Undissected to Dissected Magmatic Arc provenance and is ascribed to the progressive deepening of erosion into Middle Triassic felsic volcanics. An increase in undulatory and polycrystalline quartz grains in the Late Carnian shows that the erosion did reach deeper into the crystalline roots of the arc, although non-volcanic detritus never exceeded 10%. After a terminal pyroclastic event in Middle-Late Carnian times, suggested by the sudden appearance of pumiceous vitric clasts at the top of the Val Sabbia Sandstone, the mid-Triassic orogenic magmatism ended and was followed by the tensional stage which led to the birth of Neotethys.     

西藏措勤盆地的上古生界-下中生界：潜在的油气沉积建造

新的地层和古生物学研究结果表明,措勤盆地在晚古生代一早中生代不存在长达75Ma以上的沉积间断．其中,晚二叠世-晚三叠世诺利期都是海相碳酸盐岩地层,晚三叠世瑞替期-早中侏罗世为陆缘碎屑岩地层．两者之间为角度不整合接触．措勤盆地在晚二叠世-晚三叠世诺利期一直处于海相碳酸盐岩盆地中．晚三叠世瑞替期-早中侏罗世仍然是接受巨厚沉积的低洼地区。从宏观的油气勘探的战略评价角度看．措勤盆地在中二叠世栖霞期-晚三叠世诺利期的海相碳酸盐岩地层具有生油层的性质,上三叠统瑞替阶-中下侏罗统具有盖层的性质,两者之间的角度不整合具有储集层的性质。措勤盆地中二叠统-下侏罗统构成一个油气的有利勘探层系．称为古格层系。     

西藏措勤盆地的上古生界—下中生界：潜在的油气沉积建造

新的地层和古生物学研究结果表明,措勤盆地在晚古生代—早中生代不存在长达75Ma以上的沉积间断,其中,晚二叠世—晚三叠世诺利期都是海相碳酸盐岩地层,晚三叠世瑞替期—早中侏罗世为陆缘碎屑岩地层,两者之间为角度不整合接触。措勤盆地在晚二叠世—晚三叠世诺利期一直处于海相碳酸盐岩盆地中,晚三叠世瑞替期—早中侏罗世仍然是接受巨厚沉积的低洼地区。从宏观的油气勘探的战略评价角度看,措勤盆地在中二叠世栖霞期—晚三叠世诺利期的海相碳酸盐岩地层具有生油层的性质,上三叠统瑞替阶—中下侏罗统具有盖层的性质,两者之间的角度不整合具有储集层的性质。措勤盆地中二叠统—下侏罗统构成一个油气的有利勘探层系,称为古格层系。     

Sedimentary Facies Architectures of Third-Order Sequences from Early to Middle Triassic in Nanpanjiang Basin

There are complex and regular changes on sedimentary facies from the Early to the Middle Triassic in the Nanpanjiang basin. After the obvious drowned event of carbonate platforms in the transitional period between Permian and Triassic, carbonate platforms have evolved into the ramp type from the rimmed-shelf type. The differentiation of sedimentary facies becomes dearer in space, which are marked by the changes from an attached platform to a turbidity basin and several isolated platforms in the basin. The striking characteristics are the development of oolitic banks on isolated platforms in Nanning and Jingxi and the reef- and bank-limestones in the margin of the attached platform in the Early Triassic. Despite the difference of the time-span and the architectnre of fades succession of third-order sedimentary sequences, the process of the third-order relative sea-level changes reflected by the sedimentary facies succession of the third-order sequences is generally synchronous. Therefore, six third-order sequences could be discerned in the strata from the Early to the Middle Triassic in the Nanpanjiang basin. Using two types of facies changing surfaces and two types of diachronisms in stratigraphic records as the key elements, the sedimentary facies architectures of the third-order sequences that represent sequence stratigraphic frameworks from the Early to the Middle Triassic in the Nanpanjiang basin could be constructed.     

Strontium isotope evolution of Late Permian and Triassic seawater

The ⁸⁷Sr/⁸⁶Sr values based on brachiopods and conodonts define a nearly continuous record for the Late Permian and Triassic intervals. Minor gaps in measurements exist only for the uppermost Brahmanian, lower part of the Upper Olenekian, and Middle Norian, and only sparse data are available for the Late Permian. These 219 measurements include 67 brachiopods and 114 conodont samples from the Tethyan realm as well as 37 brachiopods and one conodont sample from the mid-European Middle Triassic Muschelkalk Sea. The Late Permian/Lower Triassic interval is characterized by a steep 1.3 × 10⁻³ rise, from 0.7070 at the base of the Dzhulfian to 0.7082 in the late Olenekian, a rate of change comparable to that in the Cenozoic. In the mid-Triassic (Anisian and Ladinian), the isotope values fall to 0.7075, followed again by a rise to 0.7081 in the Middle/Late Norian. The ⁸⁷Sr/⁸⁶Sr values decline again in the Late Norian (Sevatian) and Rhaetian to 0.7076.The sharp rise in the ⁸⁷Sr/⁸⁶Sr values during the Late Permian/Early Triassic was coincident with widespread clastic sedimentation. Because of the paucity of tectonic uplifts, the enhanced erosion may have been due to intermittent humid phases, during mainly an arid interval, coupled with the absence of a dense protective land plant cover following the mass extinction during the latest Permian. The apex of the ⁸⁷Sr/⁸⁶Sr curve at the Olenekian/Anisian boundary coincides with cessation of the large-scale clastic sedimentation and also marks the final recovery of land vegetation, as indicated by the renewed onset of coal formation in the Middle Triassic. The rising ⁸⁷Sr/⁸⁶Sr values from the Middle Carnian to the Late Norian coincide with the uplift and erosion of the Cimmeride-Indosinian orogens marking the closure of the Palaeotethys. The subsequent Rhaetian decline that continues into Jurassic (Pliensbachian/Toarcian boundary), on the other hand, coincides with the opening of the Vardar Ocean and its eastern continuation in the Izmir-Ankara Ophiolitic Belt.Samples from the Upper Muschelkalk are more radiogenic than the global trend. This may reflect separation of the basin from the open ocean. Due to strong meteoric influx from a large land mass in the north, the Germanic Basin became increasing brackish up section in the north and east, but because of the high evaporation rates, the salt content was not much reduced in the southern and central basin where a rich, but increasingly endemic, marine fauna survived.     

西藏波密地区晚古生代地层层序及盆地演化分析

西藏波密及邻区松宗、然乌一带,下石炭统诺错组与中上泥盆统松宗组之间的层序不整合界线是藏东南地区冈瓦纳北缘晚古生代盆地性质转变的重要界面。界线之下的松宗组为稳定的碳酸盐岩台地沉积;界线之上,以大规模的火山活动、盆地裂解为标志,伴随着沉积盆地的持续沉陷和相对海平面的上升,沉积了以石炭系诺错组和来姑组为代表的向上变深序列,相对海平面在晚石炭世达到了顶点,以来姑组上部的含铁质板岩和大套的浊积岩为标志。其后,以洛巴堆组为代表的晚石炭世末期-二叠纪的沉积记录,则代表了一个缓慢的向上变浅的沉积层序。在这个向上变深再变浅的沉积盆地演化过程中,火山活动呈现了明显的由强转弱的变化轨迹。中侏罗统马里组陆相红色磨拉石不整合堆积于下伏地层之上,表明本区在晚三叠世-早侏罗世经历了一次规模宏大的褶皱造山事件。     

西藏荣玛地区上三叠统日干配错组沉积环境及其构造意义

西藏荣玛地区上三叠统日干配错组发育厚度较大的碳酸盐岩夹少量碎屑岩沉积,在野外剖面实测的基础上,对这套碳酸盐岩进行了岩相与微相分析。通过对碳酸盐岩样品显微薄片观察分析,共识别出13个微相。根据岩石特征及其组合类型划分出6个沉积相:陆源碎屑滨岸相、局限台地相、开阔台地相、台地边缘浅滩相、台地边缘礁相和斜坡相。分析结果表明,晚三叠世荣玛地区主要为陆源碎屑滨岸-浅海碳酸盐台地环境,夹有较深水的斜坡相沉积,共发生了4次海侵-海退旋回,并间隔有若干次小规模的海平面升降变化。区域上,班公湖—怒江洋北缘晚三叠世的沉积环境大体一致,且广泛发育晚二叠世—晚三叠世之间的区域不整合,故认为班公湖—怒江洋的开启时间为晚三叠世之前,且东西段呈准同时开启模式打开。