Evolutions of sedimentary facies and palaeoenvironment and their controls on the development of source rocks in continental margin basins:A case study from the Qiongdongnan Basin,South China Sea

Hydrocarbon resources in the Qiongdongnan Basin have become an important exploration target in China.However,the development of high-quality source rocks in this basin,especially in its deep-water areas,are still not fully understood.In this study,evolutions of sedimentary facies and palaeoenvironment and their influences on the development of source rocks in diverse tectonic regions of the Qiongdongnan Basin were investigated.The results show that during the Oligocene and to Miocene periods,the sedimentary environment of this basin progressively varied from a semi-closed gulf to an open marine environment,which resulted in significant differences in palaeoenvironmental conditions of the water column for various tectonic regions of the basin.In shallow-water areas,the palaeoproductivity and reducibility successively decrease,and the hydrodynamic intensity gradually increases for the water columns of the Yacheng,Lingshui,and Sanya-Meishan strata.In deep-water areas,the water column of the Yacheng and Lingshui strata has a higher palaeoproductivity and a weaker hydrodynamic intensity than that of the Sanya-Meishan strata,while the reducibility gradually increases for the water columns of the Yacheng,Lingshui,and Sanya-Meishan strata.In general,the palaeoenvironmental conditions of the water column are the most favorable to the development of the Yacheng organic-rich source rocks.Meanwhile,the Miocene marine source rocks in the deep-water areas of the Qiongdongnan Basin may also have a certain hydrocarbon potential.The differences in the development models of source rocks in various tectonic regions of continental margin basins should be fully evaluated in the exploration and development of hydrocarbons.

The Loess in the Qinling Mountains and Its Records of Palaeoenvironmental Changes

The Fengzhou loess section is very typical in the Qinling Mountains. The section, which is about 82 m thick and underlain by Neogene red clays, consists of 33 layers of loess and 33 layers of palaeosol. It covers the Brunhes normal polarity zone and Matuyama reversed polarity zone, and the B / M boundary is located in the middle part of loess layer 8 (L8). The loess of the Matuyama reversed polarity zone records the Jaramillo, Olduvai and Reunion normal polarity subchrons. The boundary between the Matuyama reversed polarity zone and Gauss normal polarity zone (M / Ga) appears on the lithological boundary between loess and Neogene red clays. Loess accumulation in the Fengzhou section started before 2.48 Ma B.P. Based on the stratigraphical structure, the material composition and magnetic susceptibility curve of the Fengzhou loess section, the palaeoclimatic changes during the last 2.48 Ma in the Qinling Mountains are subdivided into 66 cold-dry and warm-humid stages, equivalent to 33 climatic cycles. The above climatic fluctuations agree very well with those of the oxygen isotopic records from deep—sea deposits.

Analytical Model for the Palaeoenvironmental Evolution of the Nihewan Beds

In this paper, the evolutional characteristics of palaeoclimate and oxidation-reduction conditions as well asacidity-alkalinity environment are discussed by means of the step-regression, cluster, optimal partitioning andcorrelation analyses of CaCO_3, C / P_2O_5, Fe^(2+) / Fe^(3+), pH and Eh values, taking the Xiaodukou section in theNihewan basin as an example. The CaCO_3, C / P_2O_5 and pH were calculated respectively using the optimalpartitioning method. Thus five cold zones and six warm zones as well as five reduction and six oxidation zoneswere distinguished. Then the inductive method was used to produce four numerical groups: 8.10, 8.3-8.4,8.6-8.7 and 8.9-8,97. The above-mentioned results are respectively based on CaCO_3 content, C/P_2O_5 andpH values. From Fig. 3, Tables 1 and 2 it can be seen that the Nihewan Beds were formed mainly under a re-duction and slightly alkaline environment of cold climate, with pH values of 8.3-8.4. Fig. 3 shows that bed 35is approximately near the boundary between the Brunhes and Matuyama polarity epochs, 0.73 Ma in age; bed26 is roughly near the Jaramillo event (base), 0.97 Ma in age; bed 18 coincides roughly with themagnetostratigraphic boundary of 2.00 Ma (?). Bed 13 may be the Pleistocene-Pliocene boundary, 2.48 Ma inage. Thus geochemical zones Ⅰ, Ⅱ, Ⅲ and Ⅳ include respectively cold zones 1; 2 and 3; 4; and 5.

A preliminary study on the element strata and palaeoenvironment of core NP95-1 from the Prydz Bay,Antarctica

This paper deals with the characteristics of element geochemistry of the core NP95 1 from the Prydz Bay, Antarctica and its palaeoenvironment implication. The results show that the sediments in this area were greatly affected by dissipation of ice cover, gushing of freshwater and terrigenous materials in the process of deposition, and the elements such as SiO 2,Al 2O 3,Fe 2O 3,CaO, MgO,P,S and C org in sediments have well recorded the changes of material source resulting from palaeoclimate change and the distribution patterns of these elements correspond to the palaeosedimentary environment of ocean and the variations of palaeoclimate. Climatically five periods can be roughly divided,such as warm, cold, hot, turning cold and turning warm since the late pleistocene. The turning points of temperature , which indicate the changes of climate, lie at 145 cm, 85 cm and 25 cm of the core NP95 1, and the sudden change of element content occurs at 85 cm of the core NP95 1, this layer indicating that an abnormal event happened and marking the beginning of Holocene.

Palaeoenvironmental Reconstruction of the Early to Middle Miocene Sequence in West Central Sinai, Egypt, as Revealed from Fossil Diatoms

A detailed analysis of the diatoms from the sedimentary sequence exposed in Abu Qada basin, west central Sinai, was used to determine the palaeoenvironmental changes during the Lower to Middle Miocene. A total of 85 diatom species and varieties belonging to 37 genera were identified from 154 samples collected throughout the stratigraphic succession. The lithological characters of the studied samples varied between sandstone, silty interbeds, sandy shales, shales, and terminated with anhydrite and limestones. These rock units are included in two lithostratigraphic formations （Rudies and Kareem）, which are separated by a marked unconformity. The distribution and preservation of fossil diatoms in the sedimentary record are examined with the aim of outlining the temporal and spatial variation in the composition of the diatom assemblages, in order to estimate the changes in depositional environments during the Lower to Middle Miocene. The distributional pattern of the recorded diatom taxa distinguished four diatom eco-zones. The environment of each eco-zone is deduced and a proposed paleobathymetric change and depositional history of the Miocene sediments in the studied area are given.

Palaeoenvironments and Taphonomy of Bird Fossils(Early Cretaceous) from Jehol Biota in Western Liaoning,China

Jehol Biota in western Liaoning and northern Hebei has been a hot topic of global concern,a large number of exquisite fossils were found in Yixian group Sihetun,such as Sinosauropteryx,Protarchaeopteryx, Caudipteryx and Confuciusornis.Scientists consider the discovering of Sinosauropteryx discovered so far as the earliest ancestor of birds.According to the dates of root layer,we can see warm and humid,lakes

Mesozoic and Cenozoic microbiotas from eastern Antarctic Peninsula: adaptation to a changing palaeoenvironment

A compiled selected literature on some groups of microfossils of the Mesozoic and Cenozoic of the James Ross Basin,eastern Antarctic Peninsula,is presented here,in order to show how the microbiota has been modified over time,triggered by environmental changes.The analyzed microfossils consist of palynomorphs(mostly pollen grains,spores,and dinoflagellate cysts),foraminifers and bryozoans.Dinoflagellate cysts and pollen-spores have been recorded in Jurassic to Pleistocene sedimentary outcrops.Dinoflagellate cysts proved to be good indicators for productivity and/or nutrient availability,surface water temperature and chemistry,the position of ancient shorelines and paleoceanographic trends.Pollen and spores allowed reconstruction of floral community and thus characterization of the climate that prevailed on the continent.Foraminifera,recovered from the Lower Cretaceous to the Pleistocene sedimentary rocks,provided information about the bathymetry,showing different marine settings(e.g.,coastal,inner neritic,outer neritic,upper bathyal)in different localities.The bryozoan record is restricted to the Cenozoic.Their colonial growth-forms reflect several environmental conditions such as shallow waters with a low rate of sedimentation,hard substrate and moderate or strong current action for the analyzed localities.The study of the Antarctic ecosystems based on the fossil microbiota and their response to the climate and the continental configuration changes,allowed understanding of the composition and dynamics of the polar environments,which have an important role in the Earth climate.

Evolution of Palaeoenvironment of the South Yellow Sea Since the Last Deglaciation

The sediments in core YS01 recovered from the South Yellow Sea mud deposit zone contain abundant benthic foraminifera,particularly shallow continental shelf species,but rare of planktonic foraminifera.The benthic foraminifera are dominated by stenohaline cold shallow-water species and euryhaline brackish-water species.In this paper,the palaeoenvironmental changes were discussed based on the grain-size compositions and benthic foraminiferal assemblages.Six different benthic foraminiferal assemblages were discriminated by species analysis from the foraminiferal fauna.According to AMS14C dating data in core YS01,we identified four main stages of marine environmental changes since the last deglaciation:a near-shore depositional stage(13.1–9.5 kyr B.P.),a transitional stage from near-shore deposition to shallow-sea deposition(9.5–5.6 kyr B.P.),a high sea level stage with shallow-sea deposition(5.6–2.9 kyr B.P.),and a stable shallow-sea depositional stage(2.9 kyr B.P.to the present).

QUATERNARY DIATOMS AND CYSTS FROM XIHU LAKE ON FILDES PENINSULA OF KING GEORGE ISLAND, ANTARCTICA AND THEIR PALAEOENVIRONMENTS

The Xihu Lake is Located on the southern Fildes Peninsula. A drill hole is 2. 6 m deep and total 102 samples were collected by Dr. Xie Youyu during 1985-1986. The samples from drill hole in the Xihu Lake contain abundant and well-preserved diatoms and Cysts (Chrysophata), 131 species and variaties of diatoms belonging to 21 genera were recognized. As a result of the detailed research on the diatom assemblages from the Xihu Lake sediments, 9 diatom assemblages were distinguished. From diatom and Cysts (Chrysophyta) data, the changes of the Palaeoenvironments and Palaeoclimate and their age are discussed.

Stratigraphy and palaeoenvironments across the Jurassic-Cretaceous boundary in the reference section (Olenek River) for eastern regions of Laptev Sea area (Arctic Siberia,Russia)

The Volgian-Valanginian succession of shallow-water deposits from the Olenek section(Anabar-Lena region,Arctic Siberia)has been studied by sedimentological and palaeontological methods.High-resolution biostratigraphy of studied interval is based on the ammonites,foraminifers,marine and terrestrial palynomorphs.Foraminiferal and palynological zones have important regional implications providing well-constrained biostratigraphy of the Anabar-Lena region.Sedimentological studies together with ecological analysis of the associations of microbenthos,microphytoplankton and terrestrial palynomorphs allow the palaeoenvironmental reconstructions for the marginal area of the Anabar-Lena palaeosea and coastal land areas.

Middle and Late Tertiary Palaeogeography and Palaeoenvironment on the Northern Continental Margin of the South China Sea

Based essentially on research results of calcareous nannofossils, combined with some other microfossil da-ta and several secondary depositional breaks, this paper discusses the criteria of division and comparison of themiddle and late Tertiary marine sediments, palaeogeographical and palaeoenvironmental evolution andpalaeoclimates on the northern continental margin of the South China Sea, comprising the Tainan basin, PearlRiver Mouth basin. Southeast Hainan basin and Beibu Gulf basin. Study shows that the upper Oligocene toPliocene strata in the whole area consist essentially of marine sediments except in the Beibu Gulf basin. Theyinclude littoral. neritic and deltaic sediments as well as carbonate rock-bioherm limestone. The sea advancedfrom southeast to northwest. During the transgression there appeared three culminations coinciding to thestages of deposition of nannofossil zones NN4-5, NN11 and 13-15.

Palynological Assemblage Age and Palaeoenvironment of the Cretaceous Salt-bearing Strata in Laos and Yunnan,China

The study of Cretaceous-Palaeogene salt-bearing strata of the Khorat Basin Laos and the Lanping-Simao Basin in Yunnan,China has an great significance not only in explaining the basin evolution and the genesis of potash

Palaeoenvironmental Evolution During the Holocene in Itapeva Lake, RS, Brazil:Palynological and Geochemical Records

Based on palynological and geochemical data (Organic Carbon-Corg and Sulphur-S) of sedimentary samples from a vibrocore, considerations about the palaeoenvironmental evolution of Itapeva Lake region during the Holocene are made. The analysed core (BOXVI) consists in its lowermost part of a fine to medium sand packet, rich in glauconitic minerals, whose upper limit is considered to be the Holocene-Pleistocene contact. Using Cluster analysis on palynomorphs combined with Corg and S data, it was possible to distinguish four zones related to the Holocene transgression-regression cycle. Variations in Corg and S data permitted the recognition of changes in palaeosalinity. Zone 1 represents the beginning of the Holocene sedimentation; palynomorphs composition reveals a marsh environment under predominating freshwater conditions. In Zone 2, the occurrence of dinoflagellate cysts and high S values, indicating brackish water, reflects Holocene sea level highstand around 5100yrs. B.P. High concentration of Cyperaceae associated with a significant increase in Corg in Zone 3 indicates a typical marsh environment influenced at least sometimes by higher saline water, reflecting a regression phase. Salvinia natans (L)All. and Cyperaceae grains are considered to be the most significant palynomorpha in Zone 4, characterising a freshwater marsh. Based on the occurrence of dinoflagellates sample 2, Operculodinium sp., related to marine to estuarine environments, a question arises regarding about the time at which Barrier Ⅳ became completely closed.

Constraints of palaeoenvironment on organic matter of Benxi Formation shale and discussion on enrichment mechanism under different facies

As a hydrocarbon-rich sedimentary basin in China,the Ordos Basin has enormous potential for shale gas resources.The shale of the Upper Carboniferous Benxi Formation is rich in organic matter,however,its palaeoenvironment and organic matter enrichment mode are yet to be revealed.In this study,the geochemical characteristics of the shale of the Benxi Formation in the east-central part of the Ordos Basin were analyzed to investigate its palaeoenvironment.At the same time,the organic matter enrichment modes in different sedimentary facies were compared and analyzed.The results indicate that:1)the shale of the Benxi Formation was mainly deposited on the continental margin and strong terrestrial clastic input;2)the deposition period of the Benxi Formation shale had a hot and humid climate with high palaeoproductivity and local volcanic hydrothermal fluid,and a high sedimentation rate with the strong stagnant environment.The bottom water was in dysoxic conditions and a semi-saline deposition environment;3)multiple factors,such as palaeoproductivity,volcanic hydrothermal,redox conditions,and palaeosalinity interact to influence the enrichment of shale organic matter in Benxi Formation;4)the organic matter enrichment modes of continental,marine-continental transitional,and marine shales can be classified into three types:“production mode”,“hybrid mode of preservation and production”,and“preservation mode”,respectively.This study provides a reference for the organic matter enrichment mode,shale gas formation conditions,and core area evaluation in these marine-continental transitional shales,and also offers new guidance for exploration ideas for shale gas in different sedimentary facies.

山东莱州湾南岸晚上新世以来(6.8~0.004 Ma)古植被演替与海平面波动

【研究目的】海岸带沉积物中的微体古生物化石保存着丰富的地质环境信息,本文的目的是重建莱州湾南岸晚上新世以来的古植被演替与海平面波动关系。【研究方法】拟通过对HLL01钻孔的孢粉、淡水藻类、海相沟鞭藻、有孔虫内衬等微体古生物化石的分析,恢复和重建莱州湾南岸及其附近地区晚上新世以来的古植被演替与海平面波动。【研究结果】(1)在晚上新世—早更新世阶段(约6.8~1.6 Ma),大量的陆生草本花粉(75.13%)指示研究区的植物群落主要以藜科、蒿属及禾本科为主的草原植被,气候温暖偏干。(2)在早更新世—中更新世阶段(约1.6~0.6 Ma),研究区的植物群落开始由草原向森林草原类型过渡;急剧增加的淡水藻类,则指示研究区可能有大的河流注入,或形成较大规模的湖泊;降水量增加,气候变得湿润。(3)在中更新世—晚全新世阶段(约0.6~0.004Ma),研究区的植物群落已经变成森林草原植被。淡水藻类含量略有降低,指示研究区的河流注入量开始减少,湖泊面积也开始萎缩。同时,海相沟鞭藻和有孔虫内衬等海相化石记录,指示研究区在该阶段出现了较为明显的大规模海侵事件。【结论】莱州湾晚上新世以来发生了3次古植被演替与海平面波动事件。

Late Eocene pollen records and palaeoenvironmental changes in northern Tibetan Plateau

The Eocene palaeovegetation landscape and palaeoclimate reconstructed from the pollen records in the Jiuquan Basin, northwest China provide some important information on the early uplift of the Tibetan Plateau and the origin and evolution of the aridification in northwest China. The records show the arid-semiarid scrubs with open forest palynofloras controlled by the subtropical high existed in northwest China during the 40.2-33.4 Ma. Four pollen assemblages are found: Nitrariadites-Cheno-podipollis-Pinaceae assemblage (40.2-37.9 Ma) is followed by Chenopodipollis-Nitrariadites assemblage (37.9-34.6 Ma), Pinuspollenites & Abietineaepollenites-Chenopodipollis assemblage (34.6-33.9 Ma), and Chenopodipollis-Nitrariadites assemblage (33.9-33.4 Ma). The percentage of thermophilic types is in anti-correlation with that of the dry types, which means the palaeoclimate is relatively warmwet or cold-dry during most of that time. Such aridity may be related to the water vapor reduction and the planetary wind system movement northward in response to the cooling caused by small-ephemeral icesheets.

Palaeolake and palaeoenvironment between 42 and 18 kaBP in Tengger Desert,NW China

Comprehensive field investigations and laboratory analyses show that palaeolakes, including fresh-mesohaline water Megalake Tengger and other semi-connected, isolated water bodies, during late Pleistocene covered an area of more than 20000 km2, which is more than half of the Tengger Desert in NW China. Stratigraphic correlation and chronological evidence indicate that before ca. 42000 aBP the area was more arid. The palaeolakes started to develop around 40000 uncal. 14C aBP but until 37000 14C aBP their scope was limited. High water levels established from 35000 14C aBP lasted until 22000 14C aBP. Lake levels regressed between 22000 and 20000 14C aBP but transgressed from 20000 to 18600 14C aBP. Subsequently, water level declined further and the Megalake Tengger finally desiccated at around 18000 14C aBP. Megalake Tengger possessed a fresh-mesohaline water property, implying that the regional precipitation increased significantly. During the period of Megalake Tengger, the climate was warmer-humid

Late Quaternary palaeoenvironmental changes documented by microfaunas and shell stable isotopes in the southern Pearl River Delta plain,South China

Ahigh resolution study of sediments,microfaunas(ostracods and foraminifers),and stable isotopes of ostracod shells from core PRD05,sampled from the Da’ao plain of the Pearl River Delta,provides new data about palaeoenvironmental changes during the Late Quaternary.The basal fluvial gravelly sediments of the core,representing the lowest deposits of the Quaternary at the core site,were possibly formed prior to the transgression associated with the last interglacial stage.This fluvial setting changed into a marginal marine setting during the last interglacial stage,any record of calcareous fossils were destroyed by subsequent dissolution during the last glacial phase,when the upper part of the deltaic sediments experienced subaerial oxidation,indicated by a mottled clay layer in the core.The postglacial sealevel rise in the South China Sea began at16,700 cal yr B.P.During the first phase of sea-level rise(from ~16,700 to 10,100 cal yr B.P.),a swamp environment developed at the core site.At ~10,100 cal yr B.P.,marine waters intruded onto the Da’ao plain and reached the core site through the Modaomen channel.This timing was earlier than in other parts of the Pearl River Delta.Since then,a semi-enclosed estuarine environment developed and was maintained until ~5560 cal yr B.P.During this transgressive interval,short-term environmental fluctuations can be recognized based on microfauna and shell geochemical data.From ~10,100 to 8630 cal yr B.P.,the sea-level rose,which was followed by a fall from ~8630 to 8520 cal yr B.P.An expanded transgression occurred between ~8520 and 7900 cal yr B.P.The time intervals from ~8520 to 8200 cal yr B.P.and from ~8080 to 7900 cal yr B.P.were marked by peak transgression.From ~7900 to 5560 cal yr B.P.,the core site generally showed a reduced marine influence and enhanced freshwater input.A fluvial environment developed from ~5560 to 3100 cal yr B.P.,and was succeeded by an alluvial plain setting.

Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation,Anambra Basin,southeastern Nigeria

Biostratigraphy investigation of Nsukka Formation was carried out by subjecting weLt cutting samples obtained from Nzam-1 weLL to patynotogicat studies with the view towards determining the relative geologic age and pataeoenvironment of deposition of the sediments. SampLes were treated in the Laboratory through digestion with hydrofluoric acid, sieving with 5 μm, oxidation with Nitric acid and mounting of the sLides into sections with DPX mountant. A fairLy high abundance and diversity of miospores were recovered, white the interval （847-1372 m） contains distinctive and diagnostic patynomorphs which are stratigraphicatty important. A Spinizonocolpites baculatus assemblage zone was established based on the basal occurrence of S. baculatus, Spinizonocolpites echinatus, Constructipollenites ineffectus, Periretisyncolpites sp. Periretisyncolpites giganteus, Monocolpites sp 1, Foveotriletes margaritae, Syncolporites marginatus, and Longapertites marginatus. The upper part of the intervat is marked by association of Anacolosidites luidonisis （at top）, Mauritiidites crassibaculatus, Retistephanocolpites williamsi, Proteacidites dehaani, Echitriporites trianguliformis, Proxapertites cursus, Retidiporites magdalenensis, S. baculatus, Retitricolpites gigeonetti, F. margaritae and Araucariadtes sp. The Nsukka Formation is dated as Late Maastrichtian based on the cooccurrence of recovered index fossits. Importantly, Cretaceous-Tertiary （K/T） boundary is marked by high fossil content in the Maastrichtian sediments compared to paucity in patynomorph that characterises the overtying Pateocene facies. Pataeoenvironment of the anatyzed section varies atternatety from marginaL marine to continental setting based on the presence of land-derived miospores and dinoflagettates.

The vegetation feature and palaeoenvironment significance in the mountainous interior of southern China from the Last Glacial Maximum

Palynological records were selected from the profiles of three research sites in the mountainous interior of southern China(Dajiuhu at Shennongjia in the western part of Hubei Province, Dahu in the Nanling Mountains, and Gantang in the northern part of Fujian Province). It can be inferred that the forest vegetation growing in the south of the Qinling Mountains-Huaihe River was luxuriant during the late glaciation. The species succession with ecological significance in palaeoflora(Abies sp., Fagus sp. and Alnus sp.) revealed that there was a certain amount of precipitation and effective humidity in the mountain lands between Qinling Mountains-Huaihe River and Nanling Mountains. This ecological environment favored the zonal distribution of mountainous forest vegetation. The late glacial maximum featured a cold, wet climate that completely differed from the cold-dry climate on the Loess Plateau, and on the steppe and desert steppe of the Qinghai-Tibet Plateau. Besides being influenced by the predominant factors driving the Northern Hemisphere climate, the cold-wet climate feature of the mountainous interior of southern China was closely associated with some geographical factors such as the latitudinal position, proximity to the ocean, and the topography and landforms.