The Jianghan Basin is a typical Paleogene salt lake basin in eastern China. Micro- crystalline dolostone in the Upper Eocene salt-bearing series in the Qianjiang sag, Jianghan Basin is composed of micro-crystalline dolomite, and the dolomite is red and orange-red in cathodoluminescence images. Associated minerals are primary glauberite, halite and terrigenous mud; while calcite is absent or rare. The X-ray diffraction analysis shows that the micro-crystalline dolostone has an average CaCO3 mole content of 57.30% and an average degree of order of 0.40, revealing the characteristics of higher calcium content and lower degree of order. It is closely intergrown with glauberite, indicating that the aqueous medium in the depositional environment of micro-crystalline dolostone was hypersaline water or dilute brine. The temperature of water in the depositional environment calculated according to the oxygen isotope data averaged 30.5℃ and the minimum homogenization temperature of inclusions in primary glauberite crystals associated with micro-crystalline dolomite was 44℃. The two groups of temperature data are close, indicating that the temperature of the water in the paleolake environment during the deposition of micro-crystalline dolostone ranged from 30.5℃ to 44℃. Thus it may be inferred that the micro-crystalline dolostone in the Upper Eocene salt-bearing interval in the Qianjiang sag is peneprimary dolostone formed directly by chemical precipitation in a high-temperature, high-salinity, high-Mg/Ca ratio and perennially meromictic salt lake.
During the Suining Age of Late Jurassic, western Sichuan Province was in stable subsidence, where the tectonic movement was relatively inactive. The Suining Formation was mainly a set of fresh purple-red mudstone or shale interbedded with feldspathic fine-grained sandstone to siltites, which constituted a complete sedimentary cycle. According to the analysis of base-level cycles with different scales, the Suining Formation can be divided into one long sequence cycle, three middle sequence cycles (corresponding to the three lithologic members of the formation), and some short sequence cycles. On the basis of the rising and falling base-level phases of each middle sequence, the sedimentary facies maps of the Suining Formation has been compiled in western Sichuan Province. The maps indicated that at the Suining Age, the study area was dominated by the deposition of meandering fluvial delta system which was detached by gulfs. The relatively independent reservoir-cap associations were formed and the accumulation and hydrocarbon forming conditions were also formed. During the Suining Age, the sedimentary evolution was obviously controlled by base-level cycles, and can be inherited. During the Early Suining Age (which corresponds to the deposition of member 1 of Suining Formation), with base-level continuously rising, the sedimentation evolved from progradation to aggredation. There were some small-scale alluvial fans or zonal eroded area in front of the Longmen Mountains. At the same time, three big-scale and stable deltas were respectively developed in Fenggu, Xindu and Huilongzhen, which are located in western Sichuan. During the Middle Suining Age (corresponding to the deposition of member 2 of Suining Formation), with base-level changing from slowly rising to falling, the sedimentation evolved from aggredation to retrogradation and then to aggredation. The three deltas previously developed divided into 4-5 balancing deltas. During the Late Suining Age (corresponding to the deposition of member 3 of Suining Formation), with base-level continuously falling, the sedimentation evolved from aggredation to progradation, and the deltas was pushed to lake continuously. At the same time, the terrigenous materials supply was unbalanced, thus the development of deltas in western Sichuan changed greatly. Except for a stable delta developed in Deyang, the delta in Xindu was gradually shrinking, while in Xinjin, the sedimentary evolution was from shallow lake to a large-scale delta.
Three types of sandbodies were developed in the lower bitumen-bearing sandstone member of Silurian in Tazhong area ,i.e. shoreline sandbody , neritic sand bar and shelf sandbody. The shoreline sandbody deposited in normal conditions is characterized by cross-bedding with a low angular, a little ripply marker ,and the lithology cycle is from mudstone to siltstone to fine-grained stone, and than to middle-fine-grained stone from bottom to top. Under the storm background ,the shoreline sandbody mostly changes from muddy conglomerates to siltstones and fine-grained sandstones from bottom to top, with a few bioconstructions, while the low-angle cross-bedding in many directions, the hummocky cross-bedding are developed. The shelf sandbody and neritic sand bar deposited under normal conditions, are homogeneous in lithology, with reverse-graded bedding and cross-bedding being developed, grain size not changing obviously. The sediments are mainly siltstone and fine-grained sandstone. In the storm background, the rip-up of muddy gravels occur at the bottom of sandbody and grain size decreases from lower part to the upper part.. The erosional surface ,cross-bedding and hummocky cross-bedding are developed. The single sandbody of shoreline deposited in the storm background is relatively thick with thickness of 6-13m,width about several ten meters. The single sandbodies of neritic sand bar and shelf are thin, with thickness of 3-8m.Their sandbody scales are larger than that deposited in normal conditions. The distribution regulation of these three sandbodies is obvious in space. Vertically,sandbody types change from the shoreline sandbody to the neritic sand bar then to the shelf sandbody alternately from the bottom to top ,Horizontally from marine to continent, the evolution is from the shelf sandbody to the neritic sand bar then to the shoreline sandbody.
The gold-bearing quartz vein developed in the Xiajiang Group of Neoproterozoic in southwestern Guizhou Province and western Hunan Province has a great potential. The Xiajiang Group with an abundant gold-bearing quartz vein is named as a set of flysch assemblage containing thickly-bedded sandy-slate, volcanic taffaceous slate, and a few marble, and belongs to a turbidite deposition. In the paper, the authors mainly study the sediment characteristics, lithologic characteristics and geochemical background value of gold of the turbidites in Tianzhu and Jinping counties, Guizhou Province. On the basis of the palaeogeographic pattern of the Neoproterozoic Qingbaikouan (1000Ma-850Ma) in South China, the palaeogeographic evolution and geochemical background of gold-bearing in the stratigraphical units of the Neoproterozoic in southeastern Guizhou Province are analyzed, and the results show that the ore-bearing quartz vein is not only controlled by the shearing zones along the anticline axis, but also the turbidite units containing volcanic taffaceous slate.
Based on the study of outcrop sequence stratigraphy and sedimentology, according to the“single factor analysis and comprehensive mapping method”, various quantitative single factor maps and lithofacies paleogeography maps of the Buqu Age and Xiali Age of Jurassic in Qiangtang Basin have been compiled. The Buqu Age was dominated by carbonate rock deposit, and from north to south, the restricted platform (lagoon, tidal flat), open platform (platform basin, shallow beach, spot reef), platform edge shallow beach (or reef), platform foreslope, and deep sea basin were respectively developed. In the Xiali Age, the sediments were mainly terrigenous materials, deposited in the environments of lagoon, tidal flat, and shoreline and shelf. The marlite and micritic limestones of lagoon and platform basin facies are good source rocks, and the carbonate rocks of platform beach and edge reef facies are good reservoir rocks in the Buqu Formation.The mudstone and gypsum of lagoon and tidal flat facies in the overlying Xiali Formation are good seal rocks. The source-reservoir-seal combination above is mostly covered by the overlying Upper Jurassic, Cretaceous and Tertiary, and thus the Buqu Formation is the best oil-gas exploration target strata in the Qiangtang Basin. The best oil-gas exploration belt is along both sides of the central upheaval belt and the belt from Pipa Lake to Bandaohu Lake.
Calcareous incrustation in the sand-mud interface of lenticular sandbody is the production of interacting process of mudstone (hydrocarbon source rock), liquid (oil, gas and water) and sandstone (reservoir rock) in petroliferous basins. The interaction of hydrocarbon source rocks and formation water produces organic acid that can dissolve minerals, especially carbonate minerals. Hydrocarbon liquid which is produced in hydrocarbon source rock and formation water, transfer to the lenticular sandbody in the vicinity under the effect of impetus. The organic acid bearing carbonates also migrates with them. The liquid which is produced after the interaction of hydrocarbon source rocks and aqueous solution will enter a new reservoir rock. In the new physicochemical environment, it will react with the reservoir rock again. The direct result of interaction of liquid and reservoir rock is the precipitation of calcite and dolomite, which will occupy some pore space of the source rocks and create cements, then the calcareous incrustation will be formed. The carbonate cements, mainly consisting of ferroan calcite and ankerite, are telogenetic cements. The content of carbonate cements in lenticular sandbody has a negative correlation with porosity, permeability and hydrocarbon saturation of lenticular sandbody. The existence of calcareous incrustation causes the change of pore structure: the primary pores are infilled by carbonate cements, the secondary pores being developed are intercrystal and intracrystal micropore; mercury-injection curves are steep, displacement pressure and median pressure are high; pore interconnections are too small and sediments are poorly sorted. Refined analysis on the anatomization of six sand-bed groups in 2 939~3 003 m of Well Niu 35 of the middle part of Member 3 of Shahejie Formation of Paleogene in the Dongying Sag indicates that calcareous incrustation in sand-mud interface is an important factor to control the hydrocarbon accumulation of lenticular sandbody.
The Tournaisian productoid brachiopods, discovered from the base of the Luzhai Formation on the Jinzishan Section,Xing’an county, Guangxi of South China, including a new, a conformis and 6 indeterminate species, plus two forms described in open nomenclature, were described in this paper. These productoids are dominated by the forms of the families Productellidae and Productidae, and have only a few representatives of the echinoconchids and monticuliferids. All of the productoids belong to thin-shelled types dwelling in a low-energic environment and none has been recorded in other places of South China. The difference on the productoid brachiopod composition between the Jinzishan Section and other places in South China probably resulted from their different environmental conditions’ controlling . The productoids from Xing’an and the data recently discovered from the Nanbiancun of Guilin and Muhua of south Guizhou revealed that the Tournaisian brachiopod fauna in the slope margin to basinal facies of South China has an exceptionally high taxonomic diversity. It not only has abundant forms that characterizes the Tournaisian brachiopod faunas out of South China, but also contains many taxa that are new or previously considered to be stratigraphically restricted in horizons higher than the Tournaisian Stage. It is suggested that the slope margin to basinal facies of South China not only has a close biogeographical relationship with other places of the world, but also is one of the important origination and radiation centers of the brachiopods during the Tournaisian, from which many new genera and species are originated and then migrated to spread all over the world.