Problems of phytostratigraphy and the correlation of the Lower Jurassic continental sediments in West Siberia and Kuznetsk and Kansk-Achinsk basins

Paleofloral and palynological records of Lower Jurassic sediments in West Siberia, Kuznetsk (Kuzbass), and Kansk-Achinsk basins and their correlation are discussed. In a number of recent papers dedicated to the Jurassic stratigraphy of Siberia this problem is ambiguously treated. The reference palynological scale has been developed for the Jurassic West Siberian sediments and an uninterrupted succession of floral assemblages associated with it and with regional stratigraphic units has been recognized. On this basis the scheme of the correlation between the Lower Jurassic sediments of the Kansk-Achinsk and Kuznetsk basins and West Siberia permitting a better age estimate of coal-bearing deposits, is proposed.     

Paleomagnetism and magnetostratigraphy of Upper Cretaceous and Cretaceous-Paleogene boundary intervals,southern Kulunda basin (West Siberia)

The study presents new paleomagnetic data on the Upper Cretaceous and Cretaceous-Paleogene boundary intervals of the southern Kulunda basin (Alei area), which were obtained from core samples collected from a 305-m-thick section penetrated in two wells. The paleomagnetic sections of each well were compiled and correlated based on the characteristic remanent magnetization (ChRM). Paleomagnetic, geological, stratigraphic, and paleontological data were used to compile the Upper Cretaceous and Cretaceous-Paleogene magnetostratigraphic section of the southern Kulunda basin. The magnetostratigraphic section consists of five magnetozones, one normal polarity zone, and four reversed polarity zones spanning the Upper Cretaceous and Lower Paleogene. The lower part of the Gan’kino Horizon, showing normal polarity, forms a single normal polarity magnetozone N. The upper part of the Gan’kino Horizon comprises two reversed polarity magnetozones (R₁km and R₂mt). The Talitsa and Lyulinvor Formations of Lower Paleogene age correspond to two reversed polarity magnetozones (R₁zl and R₂i). The compiled Upper Cretaceous and Lower Paleogene magnetostratigraphic section was correlated with the geomagnetic polarity time scale. Two options were considered for correlating the lower normal polarity part of the section with geomagnetic polarity time scale of Gradstein.     

羌塘地块西南缘上侏罗统-下白垩统海相地层的发现

通过1:5万区域地质调查,在青藏高原羌塘地块西南缘鸡夯地区原划上三叠统日干配错群中新识别出一套上侏罗统-下白垩统地层。本文根据该套地层的岩石组合以及古生物面貌特征,初步探讨了该套地层的沉积环境和沉积相特征,对其中发育的玄武岩夹层采用锆石U-Pb (LA-ICP-MS)同位素测年方法,获得其年龄为118.3±2.1Ma。在发育的生物碎屑灰岩夹层中采集了珊瑚、双壳类、腕足、腹足类化石,化石资料显示该套地层形成于晚侏罗世-早白垩世。这是首次在南羌塘地块发现该时期海相地层,这一发现证明南羌塘地块在晚侏罗世-早白垩世时期海水并未完全退出,而是局部发育海相三角洲。     

藏南古错地区上侏罗统上部和下白垩统沉积相?

基于野外剖面和室内沉积学研究,对古错地区侏罗纪末期-早白垩世地层进行详细描述和修订,识别出6种主要岩相类型：红褐色（风化色）石英砾岩、灰色－黄绿色岩屑砾岩、灰白色石英砂岩、灰色－黄绿色岩屑砂岩、灰色－黄绿色长石岩屑砂岩、灰色、深灰色、黑色页岩。发现粒序层理、水平层理、平行层理、板状交错层理、丘状交错层理等层理构造、波痕和槽模层面构造、重荷模和砂岩岩墙变形构造以及侵蚀面构造、叠瓦状构造、硬底、结核等沉积构造和生物遗迹。识别出三角洲（包括三角洲前缘亚相和前三角洲亚相）和陆棚（包括受风暴影响的陆棚相亚相和深水陆棚相亚相）两类沉积相,其中三角洲前缘亚相进一步划分为水下分流河道、分流河口砂坝和远砂坝等微相。建立了侏罗纪末期-早白垩世沉积相序及其演化,并在此基础上分析了沉积环境变化。     

Dinocyst biostratigraphy of the Lower Cretaceous in North Siberia

The described scheme of the Lower Cretaceous (Berriasian-Barremian) stratigraphic subdivisions is elaborated based on palynological study of sections in the Khatanga depression, Ust-Yenisei region, Pur-Taz interfluve, and around the Ob River latitudinal segment, the North Siberia. Stratigraphic distribution of microphytoplankton studied in detail is used to distinguish 10 biostratigraphic units in the rank of dinocysts zones. Stratigraphic position of the zones is determined with confidence using data on the Lower Cretaceous reference sections in the Khatanga depression, which were principal ones by constructing the Boreal standard zonation. In majority, boundaries of the dinocysts beds are of a high correlation potential and can be regarded as reliable stratigraphic markers, as they are recognizable not only in Siberia, but also in northern Europe and America.     

Depositional controls on glaucony texture and composition, Upper Jurassic, West Siberian Basin

This study examines textural inhomogeneity and variable chemical composition of Upper Jurassic glaucony in relation to small‐scale synsedimentary and postsedimentary authigenic processes controlled by the palaeonvironmental and palaeogeographical context. Four glaucony types with complex textural and compositional features have been recognized in cores of the Georgiev Formation of the West Siberian Basin. Samples exclusively made of light green type 1 glaucony (K₂O < 6·5%: the less mature type, richer in glauconite–smectite mixed layer) formed under dysoxic conditions in the deepest distal marine environments of the northern sectors of the West Siberian Basin. Dark green type 2 glaucony is the most mature (richest in glauconitic mica: K₂O up to 8·5%), is sometimes associated with type 1 glaucony, and is typical of high bottom areas with a low sedimentation rate within the central sectors of the basin. Type 3 glaucony is formed by brown grains, poorer in K and Fe but richer in Al and Si than type 2 glaucony, and is only present in strongly condensed successions of the central‐eastern sectors of the West Siberian Basin. Type 4 glaucony is much richer in Fe than any other type, shows fresh yellowish green cores slightly less mature than type 2 glaucony, and brown rims and cracks with composition similar to that of type 3 grains; it was formed in western sectors of the West Siberian Basin, close to Urals. Weathering under a subtropical to temperate climate, and erosion of badly drained peneplaned lowland areas around the basin, provided Al‐rich terrigenous clays as substratum for glauconitization, which explains Al and Si enrichment in Siberian glaucony. Maturation from glauconite–smectite to glauconitic mica is monitored by a change from light to dark green colour related to decrease in Al, Si, Mg, Ca and Na, and to increase in K and Fe. Brown rims of type 4 glaucony, and brown type 3 grains formed after leaching of Fe and K from mature glauconite, with formation of clays and Fe oxyhydroxides as reaction products, as a result of free oxygen exposure related to a hydrodynamic regime and temporary sea‐level fall. Glauconitization stopped and diagenetic pyrite formed due to basin deepening and burial under black shales during the latest Jurassic–earliest Cretaceous transgression. This study demonstrates that, due to the complex nature of glaucony, the authigenesis of glauconitic minerals in the rock record cannot be correctly understood if the palaeoenvironmental context and the palaeogeographical context of glaucony‐bearing sediments are not considered.     

Biofacies analysis of Upper Cretaceous deposits in the Ust-Yenisei region: Implications of palynomorphs

The results of palynomorph biofacies analysis in the Upper Cretaceous deposits of the Ust-Yenisei region are presented. The established facies confinement and indicative features of separate palynomorph groups are used, along with identified dinocyst morphotypes and taxa, in paleogeographic reconstructions. Seven palynomorph associations characterizing continental, coastal-marine, shallow-and deep-water facies are distinguished based on quantitative proportions between morphological groupings and individual taxa. As boundaries between distinguishable biostratigraphic and facies subdivisions do not coincide, dinocysts were likely insignificantly dependent in distribution on facies in the West Siberian epicontinental basin at least. On the other hand, distribution trends of particular dinocyst morphotypes and other microphytofossils are correlative with transgressive-regressive cycles and can be used for reconstruction of paleoenvironments.     

滇中地区上侏罗统叶肢介化石及其地层学意义

在回顾似东方叶肢介科(新科)Eosestlherlopseidae Niu(fam．nov．)内各属的特征、产出层位和分布的基础上，探讨了该科与真叶肢介科的亲缘关系，该科的起源，地层间的沉积间断和该科的迁移，以及Chuanjieestheria(gen．nov．)，Eosestheriopsis，Yunnanograpta(gen．nov．)等属在滇中上侏罗统中的层位演化关系，首次提出麻地山组至安宁组和蛇店组至妥甸组的时代可能为晚侏罗世早期的意见．大体可与中国北方土城子组对比。Eosestheriopsis群和Pseudograpta群分别为中国南方特提斯区和北方太平洋区2个不同生物地理区的产物。这些成果对中国陆相侏罗纪地层划分与对比、生物地理区及其变迁、古构造研究等，都具有理论意义和实际价值。文中还描述了叶肢介的一些新属种。     

Biogeochemistry and microfossils of the Upper Jurassic and Lower Cretaceous,Anabar Bay,Laptev Sea

A detailed analysis of organic matter from the Oxfordian-Lower Valanginian interval of the Nordvik section (Anabar Bay) allows the definition of three geochemical horizons (terpane, diasterene, and hopane), which are characterized by specific geochemical compounds and their ratios. These horizons are correlated with several stages in the evolution of microfossils associated with ecological and geochemical changes in sea paleobasin. Our study shows a good correlation among the variation in many geochemical parameters, the composition of microfossil assemblages, and the transgressive-regressive phases of the paleobasin evolution. Moderately shallow-water facies was reconstructed using micropaleontological, palynological, and lithological data from the upper and lower parts of the section, where the terpane and hopane horizons were identified. Both horizons are characterized by a general dominance of hopanes over other polycyclic biomarkers, the presence of compounds with the biological configuration and organic matter of mixed terrestrial-marine origin, the presence of benzohopanes and retene, an indicator of the conifer resins. This is also reflected in the composition of palynological assemblages, which are dominated by terrestrial palynomorphs, with rare conifer pollen grains. Relatively deep-water facies were identified in the middle part of the section (diasterene horizon). A distinctive geochemical feature of this interval is high relative abundances of diasterenes and 4-methyldiasterenes. The lower subhorizon is characterized by the highest values of the pristane/n-C₁₇ ratio and relatively light δ¹³C values of noncarbonate carbon. The aromatic fractions have anomalously high concentrations of methyltrimethyltridecylchromans (MTTCs), which are interpreted to be derived mostly from chlorophyll of prasinophytes. The terpenoid distribution is marked by the presence of neohop-13(18)-enes, which probably originated from the activity of methanotrophic bacteria. The above geochemical parameters indicate high photic zone productivity (which is confirmed by the composition of palynological assemblages with abundant dinocysts and prasinophytes) that favored the accumulation of organic matter in dysaerobic conditions, which periodically occurred in the bottom of paleobasin. The alternation of dysaerobic and low-oxic bottom water conditions is easily reconstructed from the analysis of microbenthic communities. The analysis of biogeochemical, micropaleontological, paleontological, and palynological data on the Upper Volgian-lowermost Berriasian organic-rich shales revealed a very good source rock potential for this part of the section, as indicated by relatively high concentrations of organic matter of mixed bacterial-algal genesis and stagnant conditions during deposition and diagenesis. However, this potential was not realized because of the extremely “mild” thermobaric conditions that existed within the Mesozoic strata of the present-day Anabar Bay. At the same time, our results and analysis of the available data allow an optimistic assessment of the hydrocarbon potential of Jurassic-Lower Cretaceous deposits on the Laptev Sea shelf.     

羌塘盆地侏罗纪末—早白垩世沉积特征与地层问题

羌塘盆地侏罗纪末至早白垩世地层包括扎窝茸组、雪山组、白龙冰河组和索瓦组上段，目前对它们的划分、对比和相互间关系的认识不一。笔者根据各组的含义和时代依据，指出各地层组为岩石地层单元，目前资料尚不足以作进一步年代学划分。通过全面统计各组的分布情况，分析各组的沉积特征，发现白龙冰河组为陆棚相，仅见于盆地北西部；索瓦组上段为海湾泻湖相，见于盆地中部；雪山组和扎窝茸组为河流一三角洲相，见于北东部。为此，认为各地层组是盆地内同期异相沉积，作为上下关系处理是不妥的，据此又提出了新的地层对比方案，认为盆内最高海相层位应该跨入了下白垩统，海水最终是向北西方向逐步退出盆地的。     

关于鲁西侏罗纪一白垩纪岩石地层单位使用之我见

在中生代山东分为鲁东、鲁西、华北平原三个地层分区。鲁西地层分区在不同时期、不同研究者建立和使用了许多不同的岩石地层单位，使用比较混乱。本文对相关的岩石地层单位进行了讨论，提出了新的划分方案。侏罗系建议使用淄博群，划分为中、下侏罗统的坊子组和中、上侏罗统的三台组；白垩系建议使用下白垩统蒙阴组和西洼组；上白垩统固城组。其中固城组的时代根据所产化石由原来归为古新统而改为上白垩统。同时建议，废除“汶南（亚）组”和“分水岭（亚）组”，并且在鲁西地层分区不使用鲁东地层分区的“杨家庄组”、“曲格庄组”、“八亩地组”等岩石地层单位。     

关于鲁西侏罗纪-白垩纪岩石地层单位使用之我见

在中生代山东分为鲁东、鲁西、华北平原三个地层分区。鲁西地层分区在不同时期、不同研究者建立和使用了许多不同的岩石地层单位,使用比较混乱。本文对相关的岩石地层单位进行了讨论,提出了新的划分方案。侏罗系建议使用淄博群,划分为中、下侏罗统的坊子组和中、上侏罗统的三台组;白垩系建议使用下白垩统蒙阴组和西洼组;上白垩统固城组。其中固城组的时代根据所产化石由原来归为古新统而改为上白垩统。同时建议,废除“汶南(亚)组”和“分水岭(亚)组”,并且在鲁西地层分区不使用鲁东地层分区的“杨家庄组”、“曲格庄组”、“八亩地组”等岩石地层单位。     

深海相中的砂质碎屑流沉积--以西藏特提斯喜马拉雅侏罗-白垩系为例

阐述了砂质碎屑流沉积特征、研究现状及其与其他深海碎屑沉积的区别 ,认为西藏特提斯喜马拉雅上侏罗统 -下白垩统深海沉积背景下的块状砂岩具有砂质碎屑流沉积性质 ,指出深海相中的块状砂岩可以预测。     

营山地区上三叠统与中、下侏罗统油气源特征对比研究

从烃源岩特征、天然气组分、油气碳同位素、凝析油全烃和轻烃、储层沥青等方面对营山地区上三叠统和中、下侏罗统油气源特征进行了对比研究,阐明了营山地区上三叠统须家河组和中、下侏罗统油气的地球化学特征、成因和可能来源.研究表明营山地区上三叠统须家河组油气主要来自须家河组自身的煤系烃源岩,天然气以成熟腐殖型母质成因为主,而中、下侏罗统气藏产出的油气主要来自其自身的烃源岩.营山地区构造活动强烈,断层发育,使得部分井区中、下侏罗统产出的天然气特征与下伏产层极为相似 ,反映了断层对该井区附近的各层段有一定的沟通作用.中、下侏罗统地层在部分井区可能有上三叠统须家河组油气的侵入,须家河组烃源岩对中、下侏罗统油气成藏有一定贡献作用.     

Aptian (Lower Cretaceous) biostratigraphy and cephalopods from north central Tunisia

Thick Aptian deposits in north central Tunisia comprise hemipelagic lower Aptian, reflecting the sea-level rise of OAE 1a, and an upper Aptian shallow marine environment characterized by the establishment of a carbonate platform facies. Carbon stable isotope data permit recognition of the OAE 1a event in the Djebel Serdj section. Cephalopods are rare throughout these successions, but occurrences are sufficient to date the facies changes and the position of the OAE1a event. Ammonite genera include lower Aptian Deshayesites, Dufrenoyia, Pseudohaploceras, Toxoceratoides and ?Ancyloceras; and upper Aptian Zuercherella, Riedelites and Parahoplites. Correlation of carbon isotope data with those of other Tethyan sections is undertaken together with the integration of planktonic foraminiferal data.     

滇中鱼坝村组的建立及陆相侏罗系底界

滇中及相邻地区上三叠统舍资组含煤层与下侏罗统冯家河组红层之间，连续沉积了一套杂色细碎屑岩过渡层。其分布稳定，该层所含化石及磁性地层特征表明其时代属早侏罗世。因此建立下侏罗统鱼坝村组，并确定该组底界为陆相侏罗系的底界。     

对西藏岗巴上白垩统的新认识

在前人研究的基础上对岗巴地区上白垩统的划分做了厘定 ,进一步建立了晚白垩世的 1 2个浮游有孔虫化石带。根据岩性特征及化石带的研究 ,上白垩统被划分为赛诺曼期至土仑早期的冷青热组 ;土仑中期至三冬期的岗巴村口组和康潘期至马斯特里赫特期的宗山组。该区赛诺曼期与土仑期的界线位于冷青热组上部 ,以 H elvetoglobotruncana praehelvetica的初现为标志。     

New genus and species of Cerophytidae (Insecta: Coleoptera) from the Lower Cretaceous of Baissa (Siberia)

One new genus and two new species of fossil Cerophytidae, Baissophytum convexus gen. et. sp. nov. and Baissophytum amplus sp. nov. are described and illustrated from Zaza Formation (Lower Cretaceous), Eravnensky (Bauntovsky) District, Buriatskay Autonomous Republic (Transbaikalia), Russia.     

Paleomagnetic investigations of Jurassic and Lower Cretaceous sedimentary rocks of Siberia

The paper contains recent information on the history of the earth's magnetic field in the Jurassic and Lower Cretaceous, obtained in paleomagnetic exploration of the key paleontological sections of sea deposits in the Bay of Anabar and Khatanga basin. Six paleomagnetic zones in the Valanginian were found for the first time, as well as alternation of paleomagnetic zones in Middle and Lower Jurassic rocks. Comparison of paleomagnetic sections of different regions indicates inversions of the magnetic field of the earth. The pole position was calculated for the Lower Valanginian: λ = = 174° E; Φ = 63.2° N. Possibility is seen for the use of rocks possessing high magnetic viscosity and low values of Q and of the collapse field, for paleomagnetic purposes. – Authors.     

Sequence stratigraphy of the Berriassian-Lower Aptian deposits of West Siberia

The geological structure and conditions of formation of a Lower Cretaceous clinoform complex in West Siberia are examined based on sequence stratigraphy. The regional Berriasian-Hauterivian clinoforms are interpreted as third-order sequences, and their formation should be considered in terms of the Depositional Sequence III model. Productive beds of both shallow and deep marine as well as continental genesis formed mostly in a regressive basin and belong to the highstand systems tracts.