准噶尔盆地东缘中侏罗统头屯河组层序地层与沉积演化

为揭示准噶尔盆地东缘中侏罗统头屯河组(J2t)层序地层特征及其沉积充填规律,结合露头、岩心及测井资料并运用高分辨率层序地层理论,对研究区头屯河组层序地层进行划分对比,对其沉积相展布特征和沉积环境演化规律进行研究。结果表明:头屯河组可划分出个1个Ⅲ级旋回、3个Ⅳ级旋回及9个Ⅴ级旋回,沉积物岩性以砂砾岩和泥岩为主,沉积环境主要为辫状河、辫状河三角洲和滨浅湖,发育向上"变深"对称型和非对称型的两种结构类型。头屯河组沉积时期湖泊较浅,沉积基底平缓,湖泊边缘坡度小,在头屯河组下段(J2t1)时期到头屯河组上段(J2t2)段时期经历了湖侵演变过程。结合研究区的层序地层和沉积相展布特征,认为研究区中侏罗统头屯河组具有辫状河、辫状河三角洲及湖泊3种沉积环境相结合的沉积演化模式。     

Carbonate platform growth and cyclicity at a terminal Proterozoic passive margin, Infra Krol Formation and Krol Group, Lesser Himalaya, India

Abstract The Infra Krol Formation and overlying Krol Group constitute a thick (< 2 km), carbonate-rich succession of terminal Proterozoic age that crops out in a series of doubly plunging synclines in the Lesser Himalaya of northern India. The rocks include 18 carbonate and siliciclastic facies, which are grouped into eight facies associations: (1) deep subtidal; (2) shallow subtidal; (3) sand shoal; (4) peritidal carbonate complex; (5) lagoonal; (6) peritidal siliciclastic–carbonate; (7) incised valley fill; and (8) karstic fill. The stromatolite-rich, peritidal complex appears to have occupied a location seaward of a broad lagoon, an arrangement reminiscent of many Phanerozoic and Proterozoic platforms. Growth of this complex was accretionary to progradational, in response to changes in siliciclastic influx from the south-eastern side of the lagoon. Metre-scale cycles tend to be laterally discontinuous, and are interpreted as mainly autogenic. Variations in the number of both sets of cycles and component metre-scale cycles across the platform may result from differential subsidence of the interpreted passive margin. Apparently non-cyclic intervals with shallow-water features may indicate facies migration that was limited compared with the dimensions of facies belts. Correlation of these facies associations in a sequence stratigraphic framework suggests that the Infra Krol Formation and Krol Group represent a north- to north-west-facing platform with a morphology that evolved from a siliciclastic ramp, to carbonate ramp, to peritidal rimmed shelf and, finally, to open shelf. This interpretation differs significantly from the published scheme of a basin centred on the Lesser Himalaya, with virtually the entire Infra Krol–Krol succession representing sedimentation in a persistent tidal-flat environment. This study provides a detailed Neoproterozoic depositional history of northern India from rift basin to passive margin, and predicts that genetically related Neoproterozoic deposits, if they are present in the High Himalaya, are composed mainly of slope/basinal facies characterized by fine-grained siliciclastic and detrital carbonate rocks, lithologically different from those of the Lesser Himalaya.     

Allogenic and autogenic controls on facies and stratigraphic architecture of the Lower Jurassic Mashabba Formation,Gebel Al-Maghara,North Sinai,Egypt

The Lower Jurassic Mashabba Formation crops out in the core of the doubly plunging Al-Maghara anticline, North Sinai, Egypt. It represents a marine to terrestrial succession deposited within a rift basin associated with the opening of the Neotethys. Despite being one of the best and the only exposed Lower Jurassic strata in Egypt, its sedimentological and sequence stratigraphic framework has not been addressed yet. The formation is subdivided informally into a lower and upper member with different depositional settings and sequence stratigraphic framework. The sedimentary facies of the lower member include shallow-marine, fluvial, tidal flat and incised valley fill deposits. In contrast, the upper member consists of strata with limited lateral extension including fossiliferous lagoonal limestones alternating with burrowed deltaic sandstones. The lower member contains three incomplete sequences (SQ1-SQ3). The depositional framework shows transgressive middle shoreface to offshore transition deposits sharply overlain by forced regressive upper shoreface sandstones (SQ1), lowstand fluvial to transgressive tidal flat and shallow subtidal sandy limestones (SQ2), and lowstand to transgressive incised valley fills and shallow subtidal sandy limestones (SQ3). In contrast, the upper member consists of eight coarsening-up depositional cycles bounded by marine flooding surfaces. The cycles are classified as carbonate-dominated, siliciclastic-dominated, and mixed siliciclastic-carbonate. The strata record rapid changes in accommodation space. The unpredictable facies stacking pattern, the remarkable rapid facies changes, and chaotic stratigraphic architecture suggest an interplay between allogenic and autogenic processes. Particularly syndepositional tectonic pulses and occasional eustatic sea-level changes controlled the rate and trends of accommodation space, the shoreline morphology, the amount and direction of siliciclastic sediment input and rapid switching and abandonment of delta systems.     

新疆乌恰中侏罗世孢粉植物群及其环境意义

基于对新疆乌恰地区中侏罗统塔尔尕组33属48种孢子花粉化石的研究,建立了该区中侏罗世晚期孢粉植物群。塔尔尕组孢粉植物群以包括掌鳞杉科、松科、罗汉松科、南美杉科和杉科的松杉目的优势和包括桫椤科、蚌壳蕨科、紫萁科、海金砂科和双扇蕨科的真蕨目的次优势为特征。根据孢粉植物群的特征,探讨了该区中侏罗世晚期古生态、古气候和古地理特征以及古环境与油源的关系。研究结果表明,乌恰地区中侏罗世晚期气候属于亚热带半湿润-半干旱型,巴通期气候相对湿润,卡洛夫期气候变干,开始趋于干旱。孢粉植物群的生物多样性和植物地理分布的分带性反映,该区中侏罗世晚期具有山峦、河流、湖泊、沼泽、三角洲等多样古地理景观。孢粉学资料显示,乌恰地区在巴通期暖热和相对湿润气候条件下的湖泊和沼泽沉积有利于石油和天然气的形成。     

伊犁盆地南缘西段中下侏罗统水西沟群沉积体系及其对铀成矿的控制作用

通过野外地质露头和钻孔岩心观察以及对大量钻孔岩心编录和测井解释资料的综合统计分析,笔者将伊犁盆地南缘西段中下侏罗统水西沟群划分出4个大的沉积体系:八道湾组(J1b)的冲积扇沉积体系、三工河组—西山窑组一段的辫状河三角洲沉积体系、西山窑组二段至三段的浅湖沼泽沉积体系和西山窑组四段至五段的曲流河三角洲沉积体系。文中详细讨论了伊犁盆地南缘西段水西沟群各沉积体系的沉积相特征,研究了水西沟群沉积体系及沉积相与砂岩型铀矿的成矿关系,指出辫状河三角洲沉积体系是砂岩型铀矿成矿最有利的沉积体系,三角洲前缘河口坝及席状砂亚相、三角洲平原辫状河流亚相、扇中-扇端亚相及三角洲平原分流河道亚相是砂岩型铀矿主要的控矿沉积相。     

藏南聂拉木北部喜马拉雅山主脊带侏罗系重解

通过野外调查和地层系统校正,认为前人在该区划分的侏罗纪地层系统存在偏差。下侏罗统在喜马拉雅山主脊带南北两侧岩相变化较大,普普嘎组可能穿时;中上侏罗统岩相变化较小;侏罗系总厚度不超过1400m。中侏罗统鲕粒铁质岩所对应的岩石地层单元按命名先后原则应为定结组,形成于外陆棚环境,可能与全球侏罗纪海泛时期洋流涌入有关,代表特提斯喜马拉雅地区中侏罗世晚巴通期一次沉积地质事件;晚侏罗世基末利期在特提斯喜马拉雅可能存在与欧洲同期的缺氧事件。     

The Middle–Late Jurassic forced regression and disconformity in central Portugal: eustatic, tectonic and climatic effects on a carbonate ramp system

Abstract Successions across the Middle–Upper Jurassic disconformity in the Lusitanian Basin (west‐central Portugal) are highly varied, and were probably developed on a large westward‐inclined hangingwall of a half‐graben. The disconformity is preceded by a complex forced regression showing marked variations down the ramp, and provides an example of the effects of rapid, relative sea‐level falls on carbonate ramp systems. In the east, Middle Jurassic inner ramp carbonates (‘Candeeiros’ facies) are capped by a palaeokarstic surface veneered by ferruginous clays or thick calcretes. In the west, mid‐outer ramp marls and limestones (‘Brenha’ facies) are terminated by two contrasting successions: (1) a sharp‐based carbonate sandbody capped by a minor erosion surface, overlain by interbedded marine–lagoonal–deltaic deposits with further minor erosion/exposure surfaces; (2) a brachiopod‐rich limestone with a minor irregular surface, overlain by marls, lignitic marls with marine and reworked non‐marine fossils and charophytic limestones, with further minor irregular surfaces and capped by a higher relief ferruginous erosional surface. The age ranges from Late Bathonian in the east to Late Callovian in the west. This disconformity assemblage is succeeded by widespread lacustrine–lagoonal limestones with microbial laminites and evaporites (‘Cabaços’ facies), attributed to the Middle Oxfordian. Over the whole basin, increasingly marine facies were deposited afterwards. In Middle Jurassic inner‐ramp zones in the east, the overall regression is marked by a major exposure surface overlain by continental sediments. In Middle Jurassic outer‐ramp zones to the west, the regression is represented initially by open‐marine successions followed by either a sharp marine erosion surface overlain by a complex sandbody or minor discontinuities and marginal‐marine deposits, in both cases capped by the major lowstand surface. Reflooding led to a complex pattern of depositional conditions throughout the basin, from freshwater and brackish lagoonal to marginal‐ and shallow‐marine settings. Additional complications were produced by possible tilting of the hangingwall of the half‐graben, the input of siliciclastics from westerly sources and climate change from humid to more seasonally semi‐arid conditions. The Middle–Late Jurassic sea‐level fall in the Lusitanian Basin is also recorded elsewhere within the Iberian and other peri‐Atlantic regions and matches a transgressive to regressive change in eustatic sea‐level curves, indicating that it is related in part to a global event.     

Sequence stratigraphy of the Lower Cenomanian Bahariya Formation, Bahariya Oasis, Western Desert, Egypt

The Lower Cenomanian Bahariya Formation corresponds to a second-order depositional sequence that formed within a continental shelf setting under relatively low-rate conditions of positive accommodation (< 200 m during 3–6 My). This overall trend of base-level rise was interrupted by three episodes of base-level fall that resulted in the formation of third-order sequence boundaries. These boundaries are represented by subaerial unconformities (replaced or not by younger transgressive wave ravinement surfaces), and subdivide the Bahariya Formation into four third-order depositional sequences.

The construction of the sequence stratigraphic framework of the Bahariya Formation is based on the lateral and vertical changes between shelf, subtidal, coastal and fluvial facies, as well as on the nature of contacts that separate them. The internal (third-order) sequence boundaries are associated with incised valleys, which explain (1) significant lateral changes in the thickness of incised valley fill deposits, (2) the absence of third-order highstand and even transgressive systems tracts in particular areas, and (3) the abrupt facies shifts that may occur laterally over relatively short distances. Within each sequence, the concepts of lowstand, transgressive and highstand systems tracts are used to explain the observed lateral and vertical facies variability.

This case study demonstrates the usefulness of sequence stratigraphic analysis in understanding the architecture and stacking patterns of the preserved rock record, and helps to identify 13 stages in the history of base-level changes that marked the evolution of the Bahariya Oasis region during the Early Cenomanian.     

Biostratigraphy,sequence stratigraphy,and paleoecology of the Lower–Middle Miocene of Northern Bandar Abbas,Southeast Zagros basin in south of Iran

The Guri Member is a limestone interval at the base of the calcareous marls of the Mishan Formation. It is the youngest hydrocarbon reservoir of the southeast part of the Zagros sedimentary basin. This Member overlaid siliciclastic rocks of Razak Formation and is overlain by green and gray marls of the Mishan Formation. In order to consider the paleoecology and paleoenvironments of the Lower–Middle Miocene (Guri Member), we have studied biostratigraphy and sequence stratigraphy of the Guri Member based on foraminifer and microfacies in two stratigraphic sections including Dorahi–Homag and Chahestan. A total of 33 genera and 56 species of benthic and planktonic foraminifera were identified in two studied stratigraphic sections. Benthic and planktonic foraminifera demonstrate Aquitanian to Langhian age (Early–Middle Miocene) for this Member at the study area. Studied interval has deposited in four facies association including supratidal, lagoon, coral reef, and open sea on a carbonate ramp. Carbonate rocks of the Guri Member have precipitated in two and three depositional sequences at Chahestan and Dorahi–Homag sections, respectively. Sedimentation of marine carbonates of the Guri Member on siliciclastic deposits reflects a major transgression of sea level at Lower to Middle Miocene that led to creating a new sea in the Zagros basin at that age. Increasing siliciclastic influx along with a sea level fall finally caused burying of the carbonate ramp. Except for the beginning of sedimentation of carbonate at the base of both stratigraphic sections (depositional sequence 1), most of the system tracts are not matched to global sea level curve that reflect local effects of the basin. Distribution of foraminifera suggests precipitation in tropical to subtropical in mesotrophic to oligotrophic and eutrophic to oligotrophic conditions. Based on large benthic foraminifera (porcelaneous large benthic foraminifera and hyaline larger benthic foraminifera), water temperature average was determined between 25 and 30 °C that was confirmed by analyzing oxygen and carbon stable isotopes. Finally, we have utilized achieved data to reconstruction and modeling of paleoecology, paleoenvironments, and sea level changes in the southeast part of the Zagros basin.     

Jurassic sediments in the Irkut basin and southwestern Transbaikalia: correlations based on paleobotanical and geochronological data

The Jurassic growth of mountain ranges along the southern edge of the Siberian platform occurred in an active tectonic setting related to the closure of the Mongol-Okhotsk Ocean. The oceanic subduction and subsequent continent collision events induced compressive deformations at the platform boundary. Understanding the paleogeography related to the Mesozoic closure of the Mongol-Okhotsk Ocean requires dating and correlation of the Jurassic Prisayan Formation in the Irkut basin and Tugnuyskaya Formation in southwestern Transbaikalia. This work presents structural and paleobotanic results within both formations. ⁴⁰Ar/³⁹Ar dating of underlying volcanics from the upper member of the Ichetuyskaya Formation is used to refine the age of the sediment series and provide probable correlation. The results show that the Tugnuyskaya Formation initiated at the end of the Middle Jurassic-beginning of the Late Jurassic and was not coeval with the Prisayan Formation, whose upper fine-grained members were deposited in the early Middle Jurassic. ⁴⁰Ar/³⁹Ar dating of volcanics from the upper member of the Ichetuyskaya Formation yielded a Middle Jurassic age of 167.7 ± 1.2 Ma (Bajocian to Bathonian). The paleogeographic data analysis based on facies and mineralogical composition of sediments and on a study of source areas from Sm-Nd data and the U-Pb ages of detrital zircons from the deposits in the southern Irkut basin indicates that the deposition of the Prisayan Formation was followed by the intensification of relief building along the southern edge of the Siberian Platform. Our geochronological data show that active tectonic deformations in southwestern Transbaikalia evidenced in the volcanoclastic Ichetuyskaya Formation in the Tugnuy basin also occurred during the Middle Jurassic. The uppermost sediments of the Tugnuy basin were deposited at the end of the Middle Jurassic-Late Jurassic in a quiet tectonic setting with low relief and lacustrine-boggy depositional environments.     

First direct age determination from the Jurassic radiolarian-bearing siliceous series (Jédidi Formation) of northwestern Tunisia

Our study presents preliminary biostratigraphic results from the Jurassic siliceous series of northwestern Tunisia. For the first time, radiolarians are extracted from the Jédidi formation and provide a direct age determination. They are the first radiolarian fauna documented from Tunisia. Two age assignments are comprised within the following intervals: (1) Late Bathonian–Early Callovian, (2) Late Bathonian–Early Oxfordian. These ages are compatible with recent stratigraphic synthesis proposed for the Jurassic series of Tunisia. The data suggest the correlation of the Jédidi formation with siliceous series of Middle–Late Jurassic age from the external zone of the Maghrebides belt rather than with true oceanic units from the Maghrebian flyschs or the internal zones of western Tethys. To cite this article: F. Cordey et al., C. R. Geoscience 337 (2005).     

羌塘雁石坪中侏罗统雀莫错组地层及沉积环境

本文详细描述了雁石坪附近一段地层剖面,并根据地层的岩石组合特征将其归入雀莫错组;依据古生物化石特征,将其时代划为侏罗纪早巴通期。沉积环境分析表明,雁石坪剖面为一套海侵的半咸水潮坪相沉积。     

Late Ordovician to early Silurian calc-alkaline magmatism in the Xiemisitai Mountains,northern West Junggar: a response to the subduction of the Junggar-Balkhash Ocean

Basement exposed in the Placer de Guadalupe–Plomosas uplift in northern Mexico provides important clues for the geologic evolution of the region. The stratigraphic units form stacked thrust sheets of psammitic and calcareous formations, interlayered with magmatic rock. The eastern calcareous and quartzite formations exhibit structures associated with ductile deformation, whereas the upper stratigraphic units only contain structures formed via younger brittle deformation. Porphyry interlayered in the upper Plomosas Formation has a U-Pb zircon age of 171 ± 1 Ma. This age is consistent with its stratigraphic position, interbedded quartzarenites with a maximum depositional age of ~168 Ma. Granite flakes within the Horquilla Formation are dated at 209 ± 3 Ma, and the La Viñata quartzite exhibits a maximum age of ~193 Ma. The Upper Plomosas Formation correlates well with the arc-related Middle Jurassic Nazas Formation of northeastern Mexico, constituting the first report of a Jurassic continental margin arc outcrop in the ‘Central Mexican Gap zone’. We document Late Norian to Bajocian ages for the stratigraphic units cropping out in the Placer de Guadalupe area. The Jurassic age cluster indicates that the Nazas Arc magmatism in the region occurred during the Late Triassic and ended in the Middle Jurassic times. Permian ages previously assigned to these rocks and the occurrence of a Permo–Triassic deformation event have to be dismissed.     

New record of <Emphasis Type="Italic">Plectoidothyris</Emphasis> from the Middle Jurassic Sequence of Jaisalmer Basin,Western India: Implications on the easterly brachiopod migrations

The Bathonian sediments of the Jaisalmer Basin, India host a terebratulide brachiopod Plectoidothyris which has been previously known from the Bajocian rocks of the Boreal Province. The sharp and prominent plication of the anterior commissure and increased length of costae separates the Jaisalmer specimens from other known species of the genus and the population represents an endemic species — Plectoidothyris jaisalmerensis. The population was only cursorily described earlier lacking in details of precise stratigraphic control and was wrongly assigned to a different genus. The present study is based on a large number of specimens from different localities with precise stratigraphic data, coupled with this some recent findings of time-diagnostic ammonites have helped determine the Plectoidothyris jaisalmerensis duration in the Jaisalmer Basin as the Late Bathonian. Presence of lower Jurassic Boreal brachiopod genera in the Middle Jurassic rocks of Ethiopian and Indo — Madagascan biogeographic provinces has been noticed earlier whereto Plectoidothyris is a new addition while it is also the first report of the genus from the Jurassic of India. The brachiopod migrations from the north to south of the Tethys provide evidences for opening of shallow water routes in the Tethyan seaway and are probably indicative of warmer water conditions in the Indo-Madagascan and African areas during the Middle Jurassic.     

Sequence stratigraphic controls on reservoir characterization and architecture: case study of the Messinian Abu Madi incised-valley fill, Egypt

Understanding sequence stratigraphy architecture in the incised-valley is a crucial step to understanding the effect of relative sea level changes on reservoir characterization and architecture. This paper presents a sequence stratigraphic framework of the incised-valley strata within the late Messinian Abu Madi Formation based on seismic and borehole data. Analysis of sand-body distribution reveals that fluvial channel sandstones in the Abu Madi Formation in the Baltim Fields, offshore Nile Delta, Egypt, are not randomly distributed but are predictable in their spatial and stratigraphic position. Elucidation of the distribution of sandstones in the Abu Madi incised-valley fill within a sequence stratigraphic framework allows a better understanding of their characterization and architecture during burial. Strata of the Abu Madi Formation are interpreted to comprise two sequences, which are the most complex stratigraphically; their deposits comprise a complex incised valley fill. The lower sequence (SQ1) consists of a thick incised valley-fill of a Lowstand Systems Tract (LST1)) overlain by a Transgressive Systems Tract (TST1) and Highstand Systems Tract (HST1). The upper sequence (SQ2) contains channel-fill and is interpreted as a LST2 which has a thin sandstone channel deposits. Above this, channel-fill sandstone and related strata with tidal influence delineates the base of TST2, which is overlain by a HST2. Gas reservoirs of the Abu Madi Formation (present-day depth ～3552 m), the Baltim Fields, Egypt, consist of fluvial lowstand systems tract (LST) sandstones deposited in an incised valley. LST sandstones have a wide range of porosity (15 to 28%) and permeability (1 to 5080mD), which reflect both depositional facies and diagenetic controls. This work demonstrates the value of constraining and evaluating the impact of sequence stratigraphic distribution on reservoir characterization and architecture in incised-valley deposits, and thus has an important impact on reservoir quality evolution in hydrocarbon exploration in such settings.     

柴北缘鱼卡地区侏罗纪含煤地层层序地层学研究

运用钻井岩心、测井及层序地层学有关理论、方法,对青海柴北缘鱼卡地区侏罗纪含煤地层进行了层序地层学研究。共识别出4个层序界面,将侏罗系含煤地层划分为3个三级层序,分别对应于中侏罗统大煤沟组、石门沟组下段和石门沟组上段;研究区层序界面主要包括区域不整合面(古风化壳)、三角洲平原分流河道下切谷、河道间古土壤和盆地内基准面下降—暴露—上升旋回的转折点;与海相含煤盆地不同,厚煤层在层序格架内的发育具有多样性。在古隆起和盆地内部,厚煤层常靠近初始湖泛面发育(煤7);在盆地边缘河流—三角洲平原,厚煤层常靠近最大湖泛面发育(煤5)。总体来看,陆相含煤盆地三级层序中,湖侵体系域聚煤最好。      

Timing of the initiation of the Jurassic Yanshan movement on the North China Craton: evidence from sedimentary cycles,heavy minerals,geochemistry, and zircon U–Pb geochronology

A series of significant geological changes indicated by deformation, magmatic–metallogenic systems, and the climate and environment occurred in East Asia during Late Jurassic to Early Cretaceous time, but the timing and development of the ‘Yanshan movement’ on the north margin of the North China Craton has not been well-established. Based on the evidence of tectonic deformation and magmatic activity, previous studies resulted in two views of the beginning of the Yanshan movement: Early Jurassic vs. late Middle Jurassic. In this work, the timing of the initial Yanshan movement was investigated by examining the Jurassic Chenjiabangou section in the Ningwu–Jingle basin overlying the north-central part of the North China Craton. The timing of the initial Yanshan movement was constrained by restoration of stream flow directions, determination of boundaries of sedimentary cycles, identification of heavy mineral assemblages in clastic rocks, quantification of changes in chemical compositions, and zircon U–Pb isotope dating. The results indicate that the basal conglomerates of the Middle Jurassic Yungang Formation (Bathonian) mark the beginning of the Yanshan movements. Evidence supporting this conclusion includes the following. (1) The switch from transgressive lacustrine deposition to regressive lacustrine deposition in the Yungang Formation sedimentary succession indicates a change from extension to compression, possibly reflecting uplift. (2) Early-stage clastic rocks rich in quartz and feldspar are replaced by feldspar detritus in late-stage clastic rocks; the heavy mineral assemblage dominated by zircon at the early stages changed to garnet-dominated assemblage upsection. Moreover, the concentrations of CaO, MgO, CO_2, and Fe₂O₃ + FeO and the Fe₂O₃/FeO ratio changed abruptly near the basal conglomerates of the Middle Jurassic Yungang Formation, suggesting increased denudation. (3) Conglomerates at the bottom of the Middle Jurassic Yungang Formation were deposited approximately 168 million years ago, as inferred from the age of zircons in tuffaceous micrite (160.6 ± 0.55 Ma) at the bottom of the Upper Jurassic Tianchihe Formation (Oxfordian) and the age of zircons in pyroclastic rocks (179.2 ± 0.79 Ma) in the Lower Jurassic Yongdingzhuang Formation (Toarcian). These lines of evidence indicate that initial Jurassic Yanshan movement began 168 million years ago during Middle Jurassic time.     

民和盆地侏罗系地层划分与对比

民和盆地是一个油、煤、气伴生的中新生代陆相盆地,侏罗系地层层序自下而上划分为下侏罗统炭洞沟组(大西沟组)、中侏罗统窑街组、红沟组、上侏罗统享堂组。中侏罗世早、中期气候温暖湿润,形成了以沼泽相煤系地层和湖相暗色泥岩、油页岩为主的生油建造,晚侏罗世至白垩纪气候较为干燥,形成了以河流相为主的砂砾岩储集建造。根据古生物、岩性、电性、含煤性、构造、古气候等地层划分对比标志,重新确立了盆地的地层系统,建立了盆地中新生界地层标准剖面,为盆地石油勘探奠定了坚实的基础。     

Lytoceratid ammonites from the Inferior Oolite Formation (Middle Jurassic,Aalenian and Bajocian) of Dorset (United Kingdom)

Ammonites of the family Lytoceratidae from the Middle Jurassic Inferior Oolite Formation, Aalenian to lowermost Bathonian, of Dorset are rarely described, perhaps because the macroconchs are often very large and difficult to collect intact and the microconchs are very small and easily overlooked. Detailed stratigraphical collecting over several years has shown them to be a minor part of the ammonite fauna but more common at certain horizons. Four genera, Lytoceras, Megalytoceras Nannolytoceras and Pleurolytoceras have been shown to have different stratigraphical ranges and abundances in the Aalenian and Bajocian but they have not been found in the Lower Bathonian of Dorset. The taxonomic basis of several of the well-known species is poorly described in the literature and is remedied here.