This paper is a continuation from Lithofacies Palaeogeography of the Early Cambrian in China. It is based on the present writers’ achievements of study and mapping of quantitative lithofacies palaeogeography of Cambrian and Ordovician in North China, South China and Northwest China. By quantification it is meant that the delineation of each paleogeographic unit is based on quantitative data and quantitative maps. On such a basis, in combination with geological data of other areas, mainly Mongolia—Xinganling, Tibet, Hainan Island and Taiwan, through comprehensive analysis and judgment, the Lithofacies palaeogeography map of the Middle Cambrian in China is compiled and this paper is finished. Thus in this paper, the lithofacies palaeogeography map in North China, South China and Northwest China is quantitative and the description is in detail, while the lithofacies palaeogeography map in other areas is quanlitative and the description is general. In China, the lithofacies palaeogeography framework of “two troughs alternating with three platforms” in the Early Cambrian was unchanged in the Middle Cambrian. The two troughs are the Tianshan-Beishan-Mongolia-Liaoning-Jilin Trough and Kunlun-Qinling Trough. The three platforms are the Junggar-Mongolia-Xinganling Platform, Tarim-Qaidam-North China Platform and Tibet-South China Platform. The scope of these 5 paleogeographic units are basically the same with those in the Early Cambrian, but the characteristics of their second-rank palaeogeographic units are different from those of the Early Cambrian.
Abundant and well-preserved Cambrian macroalgal fossils occured in the Chengjiang Biota, Kaili Biota, Burgess Shale Biota and Siberian flora. Based on the patterns of geographic distributions of Precambrian macroalgae, and the similarities to both algae and metazoan fossils in the Kaili Biota and the Burgess Shale, the factors controlling the biogeographic provincialization of the interval of Precambrian—Middle Cambrian are discussed. Comparing algae and metazoan of the Kaili biota with those of the Burgess Shale and the Siberian flora, we discover that the regions of the same palaeolatitude present the similar bio-assemblage, while the regions of distinct different palaeolatitude present obviously different bio-assemblage. Because evolutional level of metazoan is low in the Precambrian—Middle Cambrian and biotic diversifying energy is low, the main factor controlling the provincialization of Precambrian—Middle Cambrian biogeography is palaeolatitude. Schopf's model of biogeographic region is not suitable for metazoan on the basis of the patterns of geographic distribution of metazoan in the Precambrian—Cambrian. A new model for dividing the Precambrian—Middle Cambrian biogeographic regions is established in this paper. The model could explain the similarities among the composition of the Chengjiang Biota, the Kaili Biota and the Burgess Shale Biota.
The Cambrian and Ordovician dolostones in the Bachu uplift area of Tarim Basin are investigated by means of stained thin section microscopic identification, cathodoluminescence (CL) microscopic observation, trace element analysis, carbon and oxygen isotope geochemistry, and fluid inclusion analysis. Four types of dolostones have been differentiated. The first one is composed of micritic dolomites which were formed in supratidal dolomitic flats. The micritic dolomites are characterized by the highest m(Ca)/m(Mg) ratios (averagely 3-10), higher Sr contents (>300×10-6) with a m(Sr)/m(Ba) ratio far higher than 1, higher 13C value (ranging over -1‰—+1‰ PDB) and lower 18O values (ranging between -5‰—-8‰ PDB), with an origin of penecontemporaneous supratidal sabkha dolomitization. The second one consists of fine crystalline dolomites with a cloudy center and bright rim, which were formed in an opening platform shoal setting. These dolomites have a relatively higher m(Ca)/m(Mg) ratio (ranging over 1—2), a relatively higher Sr content (ranging between100-200×10-6) with m(Sr)/m(Ba) ratios higher than 1, minus 13C value (around -2‰) and 18O value are lower(about -7‰). These dolomites were formed by seepage-reflux dolomitization during the penecontemporaneous or early diagenetic stages. The third one is calcareous dolostones with bright and clean dolomite crystals and calcareous fossil remnants. These dolostones were formed in intertidal lime flat and dolomitic flat, as well as open platform shoal environments. The dolomites are characterized by lower m(Ca)/m(Mg)ratios (about 1), lower Sr contents are (about 100×10-6) with m(Sr)/m(Ba) ratios lower than 1, lowest 13C value (between -1‰—-3‰), lower ?18O value (about -6‰). These dolomites were formed by mixing-water dolomitization during the penecontemporaneous or early diagenetic stages. The fourth type is the saccharoidal dolostones with medium to coarse euhedral dolomite crystals. Precursor of this dolostone was formed in open platform shoal environments. The dolomites have lower m(Ca)/m(Mg) ratios (ranging over 1-2), lower Sr contents (< 100×10-6) with lower m(Sr)/m(Ba) ratios (lower than 1), higher 13C values (-1‰—+3‰) and lower ?18O values (-5‰—-8‰). This kind of dolomites resulted from the burial dolomitization during the late diagenetic stages.
Biyang Depression was in the stage of transition from fault depression to down-warping depression during the sedimentary time of the Member 2 of Hetaoyuan Formation. Sedimentary environment and its evolution, distribution of sedimentary facies and sand bodies are discussed on the base of the data of log, drilling and C, O isotope. Five sedimentary systems, i. e., braided river delta, fan delta, delta, inshore subaqueous fan and saline lake, were distinguished in member 2 of Hetaoyuan formation, Biyang depression. The properties and distributions of the sedimentary system are controlled by paleotopography and supplying condition of sediments. There exits fan delta sedimentary system in the west and middle of the steep slope, while inshore subaqueous fan in the east. There is braided river delta sedimentary system in the northeast of the gentle slope, while delta in the northwest. According to the calculation from the data of C, O isotope, the average paleowater temperature is 28.17 ℃, and the average paleosalinity index is 126.84, indicating its saline setting. In addition, two depositional cycles are shown according to the evolution of δ13C、δ18O、Z and t. The first cycle is from the bottom of Member 2 of Hetaoyuan Formation to the bottom of third sand group, and the second is from the bottom of third sand group to the top of Member 2 of Hetaoyuan Formation.
During the Sinian, a series of catastrophic events occurred in the eastern part of the Yangtze Gorge, including hot, cold and gravity events. In the Early Sinian, clastic sediments formed by fluvial and continental glacial actions were developed; While in late Sinian, great thickness of marine carbonate rocks formed by two transgression-regression cycles were developed. Hot event deposits occurred in Liantuo Formation of Lower Sinian, interbedded in fluvial facies sandstones and siltstones. According to the lithologic characteristics of tuff clasts, descendant tuff clasts and water-carried tuff clasts can be divided. Cold event deposits were developed in the Nantuo Formation of the Lower Sinian and should be continental glacial deposits in a low-latitude and low-altitude area. The gravity events include slumping event and turbidity- current event, and the gravity event deposits were developed in deep-water carbonate rocks in the Upper Sinian. The slumping event deposits were mainly breccia dolostone (limestone) while the turbidity current event deposits were turbidity grain limestone (dolostone).
According to the data of rock thin-section, porosity and permeability, the characteristics of low permeability reservoir and its genesis of the Jurassic in the Southern Yiqikelike tectonic zone of eastern Kuqe Depression in Tarim Basin are studied. The results show the rock types of Lower Jurassic sandstone reservoirs are mainly litharenites and feldsparthic litharenites, which are characterized by lower compositional maturity and higher textural maturity. The types of reservoir space are mainly secondary porosity-primary porosity in the eastern region and crack-secondary porosity in western region. The reservoir heterogeneity is of severity laterally. Generally, the reservoirs have low porosity, low permeability or particular low porosity and particular low permeability. The quality of reservoirs in Tugeerming area of the eastern region is superior to that of the southern region. The factors controlling the reservoir quality are by petrology, sedimentary environment, diagenesis and cracks. However, the most important factor is the combination of the burial compaction and the structural stress, which results in the particular stoniness of the reservoir compaction in the west area.
In terms of geophysical, geochemical and drilling data etc., from the shelf of the East China Sea, this paper analyzes the stratigraphic structure and tectonic features of the shelf and indicates the stack and composite property possessed by the shelf basin. It can be inferred, through the research on stratigraphic structure and the geophysical properties of Pretertiary, that there exist very thick strata of Pretertiary under the Cenozoic Basin of the East China Sea, which provides material basis for superimposition basins. Geochemical data of exploration such as fluorescence, Acid—extracted hydrocarbon and methane all indicate that some tectonic heights, for example, Haijiao Uplift appears as positive abnormal, which shows oil and gas may exist in the Pretertiary. Drilling data prove that there are bumpy oil and gas in Jurassic strata and hydrocarbon traces in the Prepileozoic located in the East Side of Oujiang Depression (also named as Lishui Depression). To sum up the above analysis, we make sure that the Pretertiary of Haijiao Uplift, Yushan Uplift and East Flank in Oujiang Depression (also named as Lishui Depression) and the transitional zone between Changjiang Depression and Xihu Depression is a new prospect of time and space for hydrocarbon exploration in the shelf basin of the East China Sea.
The methane carbon isotope of natural gas, fliud inclusion homogeneous temperature and Kalium—Argon isotope of autogenetic illite of sandstone reservoir are studied. The time and process of Jurassic gas pool formation of Yinan Well 2 trap are determined. It is put forward that the gas pool formation of Yinan Well 2 is a continuos process and underwent two main stages of the inclusion formation in earlier period and gas pool formation in late period. The natural gas began to charge from Jidike to Kangcun stage that was the main time of inclusion formation. The gas reservoir was mainly formed after the middle Kangcun period. The natural gas migrates from the source rock into the sandstone by direct expulsion. Research shows that the gas pool of Yinan Well 2 is formed due to many factors of short migrating distance, little dessipating, excellent caps and good preserving condition. In conclusion, the time and the process of pool formation in Yinan 2 trap are advantageous to the primary gas reservoir in Kuche Depression. The crucial factor of gas reservoir is the properties of reservoirs.
Ten genera of calcareous nanofossils (Coccolithus,Reticulofenestra, Cyclicargolithus, Quadrum,Discoaster,Gephyrocapsa,Calcidiscus, Umbilicasphaera, Cotonocyclus, Watznaueria) have been found in 38 samples collected from 15 locations in Cenozoic—Recent sediments of terrestrial salinized lakes in northwest and northeast China by analysing 433 samples from 36 places. It was found that most of them were sedentary deposits and a few of them resediment ones. Hence, it is not appropriate to regard all the appearance of calcareous nanofossils as the evidence of marine faces or transgression. More evidences are needed. Characteristics of calcareous nanofossils in sediments of salinized lakes are as follows: low abundance and less smalquantity; low species and generic diversity; coexistence with terrestrial saline hydrobioses. Calcareous nanofossils found in Quaternary and present terrestrial salinized lakes are generally the common kinds in modern oceans. Reticulofenestra bisecta, which is an index fossil of marine faces in Middle Eocene—Oligocene, was found in core of Qixin Well 1 in upper part of Lower Ganchaigou formation (Middle –Upper Eocene) in Qigequan structure in Qaidm Basin. Some progresses have been achieved in correlation between marine and terrestrial strata, but it is far from correlation among series units.
The dominance diversity not only indicates genura and species of fossil taxa, but also shows that the number of every species distributed evenly or oddly. The dominance diversity has an important indicative significance to division of community and discovery of deposition environment. The concept of dominance diversity is discussed, and the entropy of information function is selected as a calculation method. The data of Ostracoda are analyzed and counted, and the dominance diversities are calculated in the first, the second and the third Member of the Shahejie Formation of Depression in the Dongying Sag Jiyang. Contour maps are drawn. In all 11 communities are divided according to the data of diversity and dominance species, including Limnocythere armata, Phacocypris huiminensis, Pseudocandona boxingsis, Camarocypris elliptica, Huabeinia unispinata, Camarocypris ovata, Huabeinia chinensis, Camarocypris ovata, Huabeinia chinensis, Cyprois mina, Huabeinia obscura. The data of paleoautoecology and dominance diversity play a very important role in the division of biofacies and environments. So the environments of different periods in the Dongying Sag are divided with the help of above communities.
The forest-fire is a special composition in the natural ecosystem. It could be triggered by different factors repeatedly. The frequency and intensity of its occurrence depended on the behaviors of eco-factors, the forest-fire, however, affected the environmental events deeply on the contrary. It takes an important part in the development of vegetation system, i.e. a special kind of frequency and intensity of the forest fire are helpful to develop a special vegetation type, the higher frequency could lead to the formation of grass marshland and tropical rainforest could develop if without the influence of forest-fire. The forest fire happened universally in geology history and left a lot of remains. The fossil charcoal was one of the remains. The charcoal distributed widely and the cell structure was preserved very well when being covered by earth. Furthermore, the fossil charcoal provided more important information of the frequency and intensity of ancient forest-fire without any artificial interfering factor. The amount of fossil charcoal showed close relation to the climate factor, vegetation type and geographical features. The arid climate such as short of rainfall or the vegetation composed of combustible species of plants could raise the frequency of forest fire, the amount of fossil charcoal would increased; whereas wet climate and the vegetation with apyrous species led the amount decrease. Besides, terrestrial environment is favorable to induce the occurring of forest fire. The important rule of forest-fire is helpful to conjecture the development of climate, vegetation and geographical features in long historical period. The fossil charcoal, not only provided the important evidence of paleoflora, palaeobiotope and palaeogeography, but provided an important measure to use forest fire in improving the ecological environment also. The research on the fossil charcoal offers the chance to understand palaeoecology, palaeoclimatology and palaeogeography and lay the theory basis of using forest fire and improving nature environment, because under various conditions, presented or controlled burning is used to maintain or develop grassland, shrub-land or forest.
Based on the basement features, the unique sedimento-igneous formation and deformation of the Sinian—Mesozoic, and the exclusive chatacters for regional mineralization and tectono-thermal events, as well as the paleomagnetic data, the Su—Wan (an abbreviation for Jiangsu and Anhui Provinces) Block might be considered as an independent tectonic unit during the period of Tethyan evolution. The Su—Lu (an abbreviation for Jiangsu and Shandong Provinces) Ocean, which once separated the Su—Wan Block from the North China Craton, finally closed in Late Jurassic and Early Cretaceous, and the Su—Lu Orogen was a part of the East Asian Yanshanides. The Early Precambrian of the Su—Wan Block might be a part of the North China Craton. It drifted away, and correspondingly, the Su—Lu Ocean opened in Middle-Late Proterozoic. The Su—Wan Block attached to the Yangtze tectonic domain during the Sinan and Early Paleozoic, and its sedimento-volcanic formation and deformation had some differences from that of the Yangtze Craton. The global tectonic framework changed greatly from Devonian when the Paleotethyan oceanic basins opened. Glacial activity and cold water faunas characterized the Gondwana in Permian, while a mantle plume recorded by eruption of the Emeishan basalt featured the Yangtze Craton. During that time the Su—Wan Block, not affected by the mantle plume, might be a median block in the Paleotethyan marine, which was evidenced by the sediments being affected by the glacial activity and the mixed faunas (although no cold water faunas discovered). In other words, The Su—Wan Block must have been independent away from the Yangtze Craton since the latest Carboniferous. The Su—Lu Ocean once subducted in Triassic, but not closed, so the Late Triassic plant fossils in Su—Wan Block differed from that of the Yangtze Craton. The remained ocean subducted and closed in Late Jurassic and Early Cretaceous, indicated by the widely occurred Andean-type arc magmatism. From then on the Su—Wan Block collided with the North China Craton and became a part of the embryonic Asia continent.
