On Lacustrine Depositional Systems and Coal Accumulation in Baise Basin

Baise basin is a semi-graben type , pan-shaped faulted basin of Early Tertiary , in which carbonate lacustrine deposits and elastic lacustrine deposits developed . The assemblages of Gilbert-type delta-lakes ,littoral ,shallow and deep water fades are recognized . Based on grain size , the clastic lacustrine deposit systems can be grouped in three kinds of depositional sequences of progressive deposition : (1)from coarse to fine , (2)from fine to coarse and (3) from fine to coarse and then to fine agan . This was controlled mainly by hydrodynamic factor of lake bottom type .Lake shore was an important place for coal accumulation and peatmoor development . It had long time for coal accumulation and there was a very little amount of minerals into the basin ,and the thick coal layer and high quality coal developed m the zone where initial lake bottom was plan-like and the surface stream flow was weak .Peat accumulation advanced from the margin to the center of basin .Carbonate lakes contained much water ,very high preponderant contenis of coagel ,low inert contents and no fusinite in the coal .

Investigation of the Petrological and Geochemical Characteristics of Siderite in the Early Cretaceous Sandstone of Lacustrine Sedimentary Sequence in the Erlian Basin from Northeastern China

Siderite is a prevalent authigenic mineral in siliciclastic rocks, which usually occurred in eodiagensis period and could be used as an indicator of sedimentary environment. Some siderite precipitated in burial depth with geochemical information of basin fluid evolution. The crystal morphology, geochemical composition, and isotope values are influenced by physical and geochemical environment of precipitation. In this study, samples from the Early Cretaceous of Erlian basin in the northwestern China were collected, and mineralogy, bulk and in-situ geochemistry, C and O isotopes were analyzed to comprehensively investigate the sedimentary and diagenetic environment that the sediments experienced. Six lithofaices with three types of crystal habits were recognized in the siderite-rich sandstone, bundle crystal in spherical forms, blocky rhombs in intergranular pore and cleavage of muscovite, and micro bundle and mosaic crystals aggregates in nodular. The siderite growth proceeds through micro bundle and mosaic crystals to bundle siderite aggregates and then into blocky rhombs. The crystal evolution is also reflected by geochemical composition. The micro bundle and mosaic crystals are Casiderite. The spheritic shaped bundle aggregates are Ca-Mn-siderite. The blocky rhomb siderite shows gray part and bight part with Ca, Mg and Mn varies. Increase of Ca in block rhomb siderite suggests burial and mesodiagenesis, the high content of Mn may have linkage with eogenetic effects. The relatively positive and slightly negative δ13C value indicates meteoric water domination and influence of organic matter evolution in shallow buried time. The narrow ranges negative δ18O value suggest a small span of temperature of siderite formation.

Discovery of lacustrine shale deposits in the Yanshan Orogenic Belt,China: Implications for hydrocarbon exploration

The mechanism of formation of lacustrine deposits within stable orogenic belts and their potential for shale oil and gas exploration are frontier themes of challenge in the fields of sedimentology and petroleum exploration. Orogenic belts witness strong tectonic activities and normally cannot host stable lacustrine basins and deep shale formations. Therefore, basins in orogenic belts are considered to have no potential to form shale hydrocarbon reservoirs. Here we investigate the Luanping Basin located in the Yanshan orogenic belt where previous studies regarded rivers and fan deltas as the major main Mesozoic deposits. Based on detailed field exploration and scientific drilling, we report the finding of a large number of lacustrine shale continental deep-water deposits in the Mesozoic strata. Our finding of the occurrence of active shale oil and gas also in this basin also subvert the previous perceptions.We report SHRIMP zircon U-Pb age that define the bottom boundary of the target interval as 127.6 ± 1.7 Ma belonging to the early Cretaceous strata. Tectonics and climate are considered to be the main factors that controlled the deep-water sedimentation during this period. The drill cores revealed evidence of shale gas and the TOC of shale is 0.33%–3.60%, with an average value of 1.39% and Ro is 0.84%–1.21%, with an average value of 1.002%. The brittleness index of shale is between 52.7% and 100%. After vertical well fracturing, the daily gas production is more than 1000 m^(3). Our findings show that the basin has considerable potential for shale oil and gas. The geological resources of the shale gas in the Xiguayuan Fm. are estimated as 1110.12 × 10^(8) m^(3), with shale oil geological resources of 3340.152 × 10^(4) t. Our findings indicate that the Yanshan orogenic belt has potential exploration prospect. This work not only redefines the Luanping Basin as a rift deep-water Mesozoic Lake Basin, but also rules out the previous notion that the basin is dominated by shallow water sediments. The discovery of shale oil and gas also provides an important reference for subsequent petroleum exploration and development in this basin. Our study shows that shale oil and gas reservoirs can be found in the lacustrine basins of orogenic belts which were strongly influenced by volcanism. These results have significant implications for the sedimentology and oil exploration in the Qinling and Xingmeng Orogenic Belts of China, as well as those in other terranes of the world including the New England Orogenic Belt in Australia.

Characteristics of the mineral phase constituents of lacustrine deposits from the Fildes Peninsula of King George Island,Antarctica and their environmental implication

Based on analytical data of mineral phase constituents at three sections from Tern Lake, West Lake and Kitezh Lake in the Fildes Peninsula of King George Island, Antarctica, the characteristics of mineral phase constituents, material source and their environmental implication have been discussed. Research results indicate that lacustrine deposits came primarily from widespread volcanic rocks at the peninsula. Under cold and dry condition in Antarctica, the weathering process of the parent rocks in some area is mainly physical weathering with a weak chemical one. The relation curves of abundance of kaolinite and calcite against deposition age change steeply at the boundary between lacustrine and glacial deposits, indicating that the corresponding environment changes are abrupt, which may be related to different transportation fashion of both different deposits and the protection of glacial deposits.

The Formation Conditions and Distribution Regularities of Lithologic Reservoirs in the Songliao Basin

The geological background of the fluvial and lacustrine depository system in the large mid-shallow layered depressed lake in the Songliao Basin has been proven to have the geological conditions for the formation of lithologic reservoirs over a large area. Because the rise and fall of the base level caused considerable differences in the space at different periods, the types of sand bodies varied in different geologic periods; but at the same time, because of the differences in burial depths and the relative differences in positions of the siltstones and source rocks, the formation conditions and distributive regularities for oil-bearing groups of subtle reservoirs also vary accordingly. In view of the reality of the thinly-interbedded lithologic reservoir in the deltaic frontal facies belt, we have conducted a series of research to study the thinly-interbedded subtle reservoirs with the help of high resolution sequence stratigraphy, pattern recognition and the geophysical recognition and prediction techniques for thinly-interbedded subtle reservoirs, thus achieving a better effect and optimizing several exploration target areas, each of which has an oil reserve of about 100 million tons. This has shed light on further exploration of new subtle reservoirs.

Tectonics and Topography of the Tibetan Plateau in Early Miocene

Early Miocene stratigraphy,major structural systems,magmatic emplacement,volcanic eruption,vegetation change and paleo-elevation were analyzed for the Tibetan Plateau after regional geological mapping at a scale of 1：250,000 and related researches,revealing much more information for tectonic evolution and topographic change of the high plateau caused by Indian-Asian continental collision.Lacustrine deposits of dolostone,dolomite limestone,limestone,marl,sandstone and conglomerate of weak deformation formed extensively in the central Tibetan Plateau,indicating that vast lake complexes as large as 100,000-120,000 km2 existed in the central plateau during Early Miocene.Sporopoilen assemblages contained in the lacustrine strata indicate the disappearance of most tropical-subtropical broad-leaved trees since Early Miocene and the flourishing of dark needle-leaved trees during Early Miocene.Such vegetation changes adjusted for latitude and global climate variations demonstrate that the central Tibetan Plateau rose to ca.4,000-4,500 m and the northeastern plateau uplifted to ca.3,500-4,000 m before the Early Miocene.Intensive thrust and crustal thickening occurred in the areas surrounding central Tibetan Plateau in Early Miocene,formed Gangdise Thrust System （GTS） in the southern Lhasa block,Zedong-Renbu Thrust （ZRT） in the northern Himalaya block,Main Central Thrust （MCT） and Main Boundary Thrust （MBT） in the southern Himalaya block,and regional thrust systems in the Qaidam,Qilian,West Kunlun and Songpan-Ganzi blocks.Foreland basins formed in Early Miocene along major thrust systems,e.g.the Siwalik basin along MCT,Yalung-Zangbu Basin along GTS and ZRT,southwestern Tarim depression along West Kunlun Thrust,and large foreland basins along major thrust systems in the northeastern margin of the plateau.Intensive volcanic eruptions formed in the Qiangtang,Hoh-Xil and Kunlun blocks,porphyry granites and volcanic eruptions formed in the Nainqentanglha and Gangdise Mts.,and leucogranites and granites formed in the Himalaya and Longmenshan Mts.in Early Miocene.The K2O weight percentages of Early Miocene magmatic rocks in the Gangdise and Himlayan Mts.are found to increase with distance from the MBT,indicating the genetic relationship between regional magmatism and subduction of Indian continental plate in Early Miocene.

Regional Environmental Differentiation in China Sincethe Mid-Pleistocene Inferred from Lake Recordsand Its Relation with East Asian Monsoons

Abstract: Comparative study of long lake records in different regions in China can provide some significant information about the regional differentiation of the environment and Asian monsoon activities. However, intensively studied lacustrine cores with a span of a few hundred thousand years are very rare in China. The available examples are only three long cores from the Zoigê basin in the eastern Qinghai-Tibet plateau, the Qaidam basin in the northern Qinghai-Tibet plateau and the Dianchi basin in the Yunnan plateau respectively. The results show that the regional environmental differentiation since the Mid-Pleistocene involved three stages, i.e. 780–480, 480–160, 160–0 ka B.P. In each of the three stages different regions of China had their own distinctive environmental characteristics, indicating that the uplift of the Qinghai-Tibet plateau played a major role in the environmental differentiation process.

A study on historical location and evolution of Lop Nor in China with maps and DEM

Lop Sea,located at the east end of the Tarim Basin,Northwest China,dried up permanently,which is the terminal lake of the Tarim River.Lop Sea was considered as the lake basin of Lop Nor since Quaternary.However,the possibility that Lop Nor was away from the Lop Sea in historical time is crucial to be discussed to interpret the proxy records in sediment profiles.To obtain a general view of the evolution of Lop Nor and Lop Sea in a historical period,several approaches were adopted in this paper.First,the Qianlong Thirteen-Row Atlas,an ancient imperial atlas of the Qing Dynasty,which was completed around 1760,indicated that the Tarim River formed a relatively large lake at its modern upstream region.Second,a Digital Elevation Model(DEM)with a 10-m spatial resolution and a relative precision of 0.42 m was derived from TanDEM-X/Terra SAR-X satellite image pairs using the interferometry method,which was verified using ICESat-GLAS laser footprints and a local DEM acquired by a drone.Finally,based on the spatial analysis of historical documents,expedition reports,sediment profiles and archaeological evidence,it can be deduced that the lacustrine deposition was discontinued in the Lop Sea.Six episodes in the evolutionary history of the drainage system in eastern Tarim Basin were summarized.The proved depositional condition variations could be used for future interpretation of proxy records in sediment.The high-accurate DEM provided a reference for the location of further fieldwork in the Lop Sea.The method proposed in this paper may be efficient for the research of inland lakes or rivers in global arid regions.

The elemental geochemical characteristics of Late Quaternary rock core from Yanwo Lake in the Great Wall Station area， King George Island， Southwest Antarctica

This paper is manily to treat the change regularity of the contens,distributions, enrich coefficients and correlative coefficients of some trace and constant elements in the sediments of Late Quaternary rock core from Yanwo Lake in the Great Wall Station area, King George Island and to discuss the sedimentary sources in Yanwo Lake and the periodical changes of Late Quaternary climate and the environment in the area. It is concluded that the elastic sedimentary rocks, including volcanic sedimentary rocks, around Yanwo Lake are the major sources of Yanwo Lake sedimentsi the mantle material is also one of its sources and what is more, the continent-sourced materials are transported by the Antarctic glacier.

Reconstruction Paleoclimate Dased on Sporopollen Record of Re'nacuo Lake,Tibet

The sedimentary sequences since 33 ka B.P. to 10 ka B.P. have been established in the Re＇nacuo-Lake, Gaize area of north Tibet, through a study of a lacustrine section. The climate since 33 ka B.P. to 10 ka B.P. may be divided into two cycle include 5 dry phases and 5 moist phases from reconstructing the paleoclimate through a study of sporopollen analysis. It mainly reflects the general regularity of global climatic change through contrasting with the pale environment in northern hemisphere. Our pollen record reveals a regional climate history similar to those from the neighboring sites, including the GISP2, the Guliya ice core and core RM in Zoige, and thus supports the notion that the Qinghai-Tibetan Plateau acts as an important link between climatic events in the North Atlantic realm and the Asian monsoon domain. The response of the Qinghai-Tibet Plateau to the global climatic change is relatively sensitive.

Research status of lacustrine mudrock deposition constrained from astronomical forcing

The sources,transportation and depositional processes of lacustrine mudrock are still poorly understood.Existing studies have demonstrated the controlling effect of astronomical forcing on lacustrine mudrock deposition,but its depositional mechanism and evolution are still not systematically investigated.Most research related to astronomical forcing exclusively highlights the sedimentation of carbonate rocks in deep-water lacustrine setting,with insufficient attention paid to the thick organic-rich,deep-lake mudrock.With the increasing interest in exploration and development of shale oil and gas accumulations,it is urgent to deeply understand depositional rules of lacustrine mudrock.This study reviews sediment sources,depositional mechanism and evolution process of mudrock through expounding the correlations between the periodic changes of astronomical forces,the parameters of Earth orbital and mudrock compositions.By investigating the existing literature and using some actual data of Jiyang Depression,Bohai Bay Basin in East China,this study expounds on the influence of astronomical cycles on the deposition of lacustrine mudrock.Moreover,efforts are made to analyze the effects of various orbital parameters(e.g.,precession,obliquity,and eccentricity with the periods ranging from tens of thousands years to million years)on the deposition of mudrock from small-scale(decimeters to meters)to large-scale(10s to 100s meters).Further,it is feasible to apply the high-precision isochronous stratigraphic correlation into clarifying the distribution of favorable shale oil and gas reservoirs.To conclude,this study enunciates the sedimentation of mudrock from a new perspective(astronomical forcing)and provides a direction for the research on sedimentation of fine-grained sedimentary rocks.