2010 Vol. 28, No. 5
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Display Method:
2010, 28(5): 849-860.
Abstract:
The Tethyan tectonic zone has been always the focus of paleogeographic reconstruction financially granted by lots of oil companies, which has been promoting the global paleogeographic reconstruction. Recently, the reconstruction of the eastern Tethys, i.e., QinghaiTibetan Plateau Tethys, has been practicing. The main itinerary is summarized as: firstly, recovering the original locations of terranes or plates in QinghaiTibetan Plateau by paleomagnetism with combination of the paleotectonic and paleontology; secondly, confining the border and scale of terranes and basins on deep geophysics, surface geology and biogeography; thirdly, restoring original basins by recovering techniques of deformedshorten strata and balanced crosssection; fourthly, composing maps of biogeography and lithofacies paleogeography on the basis of the identification and classification of sedimentary and biological facies; and finalhy, exploring the prosperous hydrocarbons on paleoceanography, paleoclimate and paleogeography in Tibetan Tethys. In summary, the paleogeographic reconstruction is an integration of modern geological science. That is characterized by ways of past to future, inactive to movable, paleocontinental to paleogeographic, small to large in scale with help of 3S (simulation, information, global position) technology. It is also featured by multidisciplines of paleoenvironment, paleoclimate, paleoceanography and other geoscientific subjects, for which all kinds of geological elements, for instance, lithology, tectonics, topography, magmatism, metamorphism, can be shown in a modern palaeogeographic map. Therefore, it is suggested that the paleogeographic reconstruction would follow the new contents and techniques for the future of sedimentary geology in China.
The Tethyan tectonic zone has been always the focus of paleogeographic reconstruction financially granted by lots of oil companies, which has been promoting the global paleogeographic reconstruction. Recently, the reconstruction of the eastern Tethys, i.e., QinghaiTibetan Plateau Tethys, has been practicing. The main itinerary is summarized as: firstly, recovering the original locations of terranes or plates in QinghaiTibetan Plateau by paleomagnetism with combination of the paleotectonic and paleontology; secondly, confining the border and scale of terranes and basins on deep geophysics, surface geology and biogeography; thirdly, restoring original basins by recovering techniques of deformedshorten strata and balanced crosssection; fourthly, composing maps of biogeography and lithofacies paleogeography on the basis of the identification and classification of sedimentary and biological facies; and finalhy, exploring the prosperous hydrocarbons on paleoceanography, paleoclimate and paleogeography in Tibetan Tethys. In summary, the paleogeographic reconstruction is an integration of modern geological science. That is characterized by ways of past to future, inactive to movable, paleocontinental to paleogeographic, small to large in scale with help of 3S (simulation, information, global position) technology. It is also featured by multidisciplines of paleoenvironment, paleoclimate, paleoceanography and other geoscientific subjects, for which all kinds of geological elements, for instance, lithology, tectonics, topography, magmatism, metamorphism, can be shown in a modern palaeogeographic map. Therefore, it is suggested that the paleogeographic reconstruction would follow the new contents and techniques for the future of sedimentary geology in China.
2010, 28(5): 868-874.
Abstract:
Using twodimensional sequence stratigraphy modeling system (SSMS), we carried out a research on simulation of the formation of depositional sequences in tectonic active basins, and has revealed the control of the interplay of syndepositional fault activity, lake level change and sediment supply on the formation of the depositional sequences. The simulation shows that fast tectonic subsidence rate, relatively high lake level and abundant sediment are the necessary condition for the formation of relatively deep water fan delta, and when the sediment supply decreases or the tectonic subsidence rate increases will generate favorably the near sublacustrine fans in a rift lacustrine basin. The paleogeomorphic slopebreak zone resulting from the syndepositional faulting along the steep basin margin of a rift basin, controls obviously the distribution of the lowstand turbidite fans and the depocenter of the delta front in TST and HST. The structural slopebreak is the key control factor on variation of accommodation space. In the edge of intracontinental foreland thrusting, the alluvial fan and fluvial deposits develop in the early stage and stack back as the result of rapid tectonic subsidence rate. Later the clastic systems move into the basin and form the widely distributed river delta deposits as subsidence rate decrease in the late period of a regional depositional cycle. The simulation shows that in this sequence the distribution of the lowstand systems tracts are mainly controlled by the structural slopebreak zones resulting from the hidden thrust faults. These LST sand bodies capped with TST mudstones many form significant lithostratigraphic traps.
Using twodimensional sequence stratigraphy modeling system (SSMS), we carried out a research on simulation of the formation of depositional sequences in tectonic active basins, and has revealed the control of the interplay of syndepositional fault activity, lake level change and sediment supply on the formation of the depositional sequences. The simulation shows that fast tectonic subsidence rate, relatively high lake level and abundant sediment are the necessary condition for the formation of relatively deep water fan delta, and when the sediment supply decreases or the tectonic subsidence rate increases will generate favorably the near sublacustrine fans in a rift lacustrine basin. The paleogeomorphic slopebreak zone resulting from the syndepositional faulting along the steep basin margin of a rift basin, controls obviously the distribution of the lowstand turbidite fans and the depocenter of the delta front in TST and HST. The structural slopebreak is the key control factor on variation of accommodation space. In the edge of intracontinental foreland thrusting, the alluvial fan and fluvial deposits develop in the early stage and stack back as the result of rapid tectonic subsidence rate. Later the clastic systems move into the basin and form the widely distributed river delta deposits as subsidence rate decrease in the late period of a regional depositional cycle. The simulation shows that in this sequence the distribution of the lowstand systems tracts are mainly controlled by the structural slopebreak zones resulting from the hidden thrust faults. These LST sand bodies capped with TST mudstones many form significant lithostratigraphic traps.
2010, 28(5): 884-893.
Abstract:
The newlydiscovered paleoweathering crust sediments are developed beneath the continental volcanic rocks, sedimentaryvolcaniclastic rocks, and alluvialdiluvial sandstones and conglomerates from the Upper Triassic Nadigangri Formation, and diachronously overlapped upon the Upper Triassic(?) Xiaochaka Formation and its underlying strata including the CarboniferousPermian strata in the Qiangtang Basin, indicating a sedimentary gap between the Nadigangri Formation and its underlying strata. These volcanic rocks, sedimentaryvolcaniclastic rocks and alluvialdiluvial sandstones and conglomerates from the Nadigangri Formation deposited above the paleoweathering crust represent the onset of the Qiangtang Basin sediments during the Mesozoic. The SHRIMP zircon UPb isotopic dating gives the ages of 219.5±2.1 Ma and 219±2 Ma for the basalt and granodiorite from central Qiangtang, and 216.8±2.1 Ma and 217.3±2.5 Ma for the vitric tuff and crystal tuff from the Nadigangri Formation in the Shenglihe and Wanghuling areas in the Qiangtang Basin. All these age determinations imply that the onset of the Mesozoic Qiangtang Basin should be traced back to the Late Triassic. The deposition went through the continental to marine sedimentary overlap during the early evolution of the Mesozoic Qiangtang Basin. The sedimentary overlap started from the alluvialdiluvial facies and accompanied by magma intrusion, volcanic eruption and pyroclastic deposition. On the whole, the deposition displays a deepeningupward transgressive sequence, characteristic of a passive marginal rift basin.
The newlydiscovered paleoweathering crust sediments are developed beneath the continental volcanic rocks, sedimentaryvolcaniclastic rocks, and alluvialdiluvial sandstones and conglomerates from the Upper Triassic Nadigangri Formation, and diachronously overlapped upon the Upper Triassic(?) Xiaochaka Formation and its underlying strata including the CarboniferousPermian strata in the Qiangtang Basin, indicating a sedimentary gap between the Nadigangri Formation and its underlying strata. These volcanic rocks, sedimentaryvolcaniclastic rocks and alluvialdiluvial sandstones and conglomerates from the Nadigangri Formation deposited above the paleoweathering crust represent the onset of the Qiangtang Basin sediments during the Mesozoic. The SHRIMP zircon UPb isotopic dating gives the ages of 219.5±2.1 Ma and 219±2 Ma for the basalt and granodiorite from central Qiangtang, and 216.8±2.1 Ma and 217.3±2.5 Ma for the vitric tuff and crystal tuff from the Nadigangri Formation in the Shenglihe and Wanghuling areas in the Qiangtang Basin. All these age determinations imply that the onset of the Mesozoic Qiangtang Basin should be traced back to the Late Triassic. The deposition went through the continental to marine sedimentary overlap during the early evolution of the Mesozoic Qiangtang Basin. The sedimentary overlap started from the alluvialdiluvial facies and accompanied by magma intrusion, volcanic eruption and pyroclastic deposition. On the whole, the deposition displays a deepeningupward transgressive sequence, characteristic of a passive marginal rift basin.
2010, 28(5): 906-916.
Abstract:
Retreating Shelf Break occurred from Oligocene to Miocene in deep water area of Baiyun depression, South China Sea, which controlled the development and distribution of sedimentation in the study area. And, to some extent, effective reserves are formed. Based on the latest drilling data, detailed sedimentary analysis and meticulous interpretation of long cable, high quality, three dimensional seismic data, research of sedimentary responses of retreating shelf break is carried out, meanwhile integrating the theories of shelfmargin delta, which indicates that the responses of shelf break is shelfmargin delta progradational system of Zhuhai Formation in Oligocene and growth faults complicating shelfmargin delta and deepwater fan system of Zhujiang Formation. This discovery will be favorable for oil and gas exploration of Baiyun Depression.
Retreating Shelf Break occurred from Oligocene to Miocene in deep water area of Baiyun depression, South China Sea, which controlled the development and distribution of sedimentation in the study area. And, to some extent, effective reserves are formed. Based on the latest drilling data, detailed sedimentary analysis and meticulous interpretation of long cable, high quality, three dimensional seismic data, research of sedimentary responses of retreating shelf break is carried out, meanwhile integrating the theories of shelfmargin delta, which indicates that the responses of shelf break is shelfmargin delta progradational system of Zhuhai Formation in Oligocene and growth faults complicating shelfmargin delta and deepwater fan system of Zhujiang Formation. This discovery will be favorable for oil and gas exploration of Baiyun Depression.
2010, 28(5): 926-932.
Abstract:
An extremely shallow water environment is defined as an environment where the water depth is much smaller than the thickness of a fully developed benthic boundary layer. The intertidal flat and tidal creeks represent examples of such environments. Observations from the Jiangsu coast show that, towards the end of an ebb tide phase, the bed surface and tidal creeks are subjected to water flows with a low speed (0.1 m/s in magnitude) and a very small water depth (1 cm in magnitude). As a result, flattopped ripples and plane bed are formed on the lower parts of the intertidal zone, whilst smallscale secondary creeks develop at the bottom of major creeks over the upper part of the intertidal zone. In these cases, the flow structure within the boundary appears to be maintained, with the u100 value derived being applicable to the calculation of sediment transport rates. Tidal surges occurring over the middle part of the intertidal flat are another type of behavior for the small flow depth boundary layer, representing destruction to the Von Kárm ánPrandtl flow structure; the height of the tidal surge is equivalent to the critical water depth associated with the system collapse, which can be expressed quantitatively as Hb=4 z0. Thus, the processes of the small flow depth boundary layer play a unique role in influencing the sedimentological and morphological patterns of intertidal flats.
An extremely shallow water environment is defined as an environment where the water depth is much smaller than the thickness of a fully developed benthic boundary layer. The intertidal flat and tidal creeks represent examples of such environments. Observations from the Jiangsu coast show that, towards the end of an ebb tide phase, the bed surface and tidal creeks are subjected to water flows with a low speed (0.1 m/s in magnitude) and a very small water depth (1 cm in magnitude). As a result, flattopped ripples and plane bed are formed on the lower parts of the intertidal zone, whilst smallscale secondary creeks develop at the bottom of major creeks over the upper part of the intertidal zone. In these cases, the flow structure within the boundary appears to be maintained, with the u100 value derived being applicable to the calculation of sediment transport rates. Tidal surges occurring over the middle part of the intertidal flat are another type of behavior for the small flow depth boundary layer, representing destruction to the Von Kárm ánPrandtl flow structure; the height of the tidal surge is equivalent to the critical water depth associated with the system collapse, which can be expressed quantitatively as Hb=4 z0. Thus, the processes of the small flow depth boundary layer play a unique role in influencing the sedimentological and morphological patterns of intertidal flats.
2010, 28(5): 945-952.
Abstract:
Unayzah Formation is one of the most important exploration target in Rub Al Khali Basin Saudi Arabia. The depositional facies analysis based on the studies of field investigation and well cores and thin section research shows the dune, seasonal river, playa and paleosol environments. The rocks are mainly quartzite which has the high porosity and fair permeability. The sandstone diagenesis of Unayzah Formation has experienced the mechanic infiltration, concreation, dissolution, cementation and compaction. The diagenesis has relatively less influenced the quality of sandstone reservoirs because of the weak compaction and cementation. The pore types are mainly intergranular pores maintainning the good reservoir space.
Unayzah Formation is one of the most important exploration target in Rub Al Khali Basin Saudi Arabia. The depositional facies analysis based on the studies of field investigation and well cores and thin section research shows the dune, seasonal river, playa and paleosol environments. The rocks are mainly quartzite which has the high porosity and fair permeability. The sandstone diagenesis of Unayzah Formation has experienced the mechanic infiltration, concreation, dissolution, cementation and compaction. The diagenesis has relatively less influenced the quality of sandstone reservoirs because of the weak compaction and cementation. The pore types are mainly intergranular pores maintainning the good reservoir space.
2010, 28(5): 962-968.
Abstract:
Permian is the important oil layer and reservoir in the northwestern margin of Junggar Basin. By means of observing cores, analyzing sections and well logging data, we studied on the sedimentary environment and characteristics of the Permian glutenite which stored in the downdip block of KeBai fault in the northwestern margin of Junggar Basin. The result shows that some glutenites pertained to alluvial fan deposit, the other pertained to front fan delta deposit. The former was brown, wealthy of argillaceous matrix, poorly rounded and sorted and poor reservoir physical property; the later was poor of argillaceous matrix, Supermature calcitic or zeolitic cementation, well rounded and sorted with good reservoir physical property. So, we have established the combined sedimentation model of alluvial fan and delta fan. This model emphasized the importance of lake strandline and deemphasized the boundary of alluvial fan and delta fan. We summarized the lithologic characteristics and depositional texture and sequence of each subfacies of alluvial fan, and delta fan and provided the ideas of enplorating the Permian high quality reservoirs in the northwestern margin of Junggar Basin.
Permian is the important oil layer and reservoir in the northwestern margin of Junggar Basin. By means of observing cores, analyzing sections and well logging data, we studied on the sedimentary environment and characteristics of the Permian glutenite which stored in the downdip block of KeBai fault in the northwestern margin of Junggar Basin. The result shows that some glutenites pertained to alluvial fan deposit, the other pertained to front fan delta deposit. The former was brown, wealthy of argillaceous matrix, poorly rounded and sorted and poor reservoir physical property; the later was poor of argillaceous matrix, Supermature calcitic or zeolitic cementation, well rounded and sorted with good reservoir physical property. So, we have established the combined sedimentation model of alluvial fan and delta fan. This model emphasized the importance of lake strandline and deemphasized the boundary of alluvial fan and delta fan. We summarized the lithologic characteristics and depositional texture and sequence of each subfacies of alluvial fan, and delta fan and provided the ideas of enplorating the Permian high quality reservoirs in the northwestern margin of Junggar Basin.
2010, 28(5): 980-986.
Abstract:
Minor saddle dolomite cements are identified in the Upper Ordovician Yeoman carbonate rocks in southeastern Saskatchewan, Canada. These saddle dolomite cements are restricted to upper part of the Yeoman Formation, in a 20~30 m zone of dolomite rocks, and they are conspicuously absent both in the overlying and underlain carbonate strata, suggesting their precipitation in a relatively closed system. These Ordovician saddle dolomite cements are characterized by δ13C values (0.2‰ to 0.9 ‰ PDB) and Sr isotopic ratios (0.7082 to 0.7090) similar to those of their host replacement dolomites, indicating the sources of carbon and strontium for the saddle dolomite cements were mostly from precursor host dolomite rocks via pressure dissolution. In addition, the measured homogenization temperatures from the saddle dolomite cements vary from 99 to 105℃, which could be accounted for by the normal burial temperatures in the region. Based on these data and observations, the saddle dolomite cements in the Upper Ordovician Yeoman Formation in southeastern Saskatchewan are interpreted to be related to cannibalization of earlier replacement dolomite through chemical compaction in a relatively closed system during burial, rather than related to hydrothermal activities documented elsewhere in the Western Canada Sedimentary Basin. The occurrences of saddle dolomite, therefore, are not necessarily indicative of hydrothermal activity or fluids; nor are all saddle dolomites definitely related to hydrothermal fluids.
Minor saddle dolomite cements are identified in the Upper Ordovician Yeoman carbonate rocks in southeastern Saskatchewan, Canada. These saddle dolomite cements are restricted to upper part of the Yeoman Formation, in a 20~30 m zone of dolomite rocks, and they are conspicuously absent both in the overlying and underlain carbonate strata, suggesting their precipitation in a relatively closed system. These Ordovician saddle dolomite cements are characterized by δ13C values (0.2‰ to 0.9 ‰ PDB) and Sr isotopic ratios (0.7082 to 0.7090) similar to those of their host replacement dolomites, indicating the sources of carbon and strontium for the saddle dolomite cements were mostly from precursor host dolomite rocks via pressure dissolution. In addition, the measured homogenization temperatures from the saddle dolomite cements vary from 99 to 105℃, which could be accounted for by the normal burial temperatures in the region. Based on these data and observations, the saddle dolomite cements in the Upper Ordovician Yeoman Formation in southeastern Saskatchewan are interpreted to be related to cannibalization of earlier replacement dolomite through chemical compaction in a relatively closed system during burial, rather than related to hydrothermal activities documented elsewhere in the Western Canada Sedimentary Basin. The occurrences of saddle dolomite, therefore, are not necessarily indicative of hydrothermal activity or fluids; nor are all saddle dolomites definitely related to hydrothermal fluids.
2010, 28(5): 1006-1011.
Abstract:
A FeMn crust sample (CB14) from a seamount in the central Pacific Ocean was studied in detail. According to the microtexture of the growth profile of the crust, its outer layer (18.7mm in thickness) can be divided into 5 sublayers, no hiatus observed between the adjacent sublayers. Using the technique of digital image processing, the graylevel variation series of the reflectivity of the growth pattern were obtained. The power spectral analysis revealed that most of the prominent cycles identified from graylevel series are corresponding to Milankovitch cycles (eccentricity, obliquity and precession). Through matching and tuning to the Milankovitch cycles, we obtained that the growth rates of sublayer 1 through sublayer 5 are 2.15, 2.70, 2.43, 2.75 and 2.67 mm/Ma, respectively. Their corresponding ages are 1.3, 2.5, 5.9, 6.7 and 7.5 Ma, respectively. Our results show that since late Micocene, the growth rates of FeMn crust changed alternatively, since recent 1.3 Ma, the growth rate of the FeMn crust slowed down significantly. It is considered that the graylevel series of the growth profile of FeMn crusts can be used as a paleoenvironmental indicator, and the application of orbital pacing method on graylevel series is an effective approach to determine the high resolution growth rates of FeMn crust and hence provide important information on paleoenvironmental change.
A FeMn crust sample (CB14) from a seamount in the central Pacific Ocean was studied in detail. According to the microtexture of the growth profile of the crust, its outer layer (18.7mm in thickness) can be divided into 5 sublayers, no hiatus observed between the adjacent sublayers. Using the technique of digital image processing, the graylevel variation series of the reflectivity of the growth pattern were obtained. The power spectral analysis revealed that most of the prominent cycles identified from graylevel series are corresponding to Milankovitch cycles (eccentricity, obliquity and precession). Through matching and tuning to the Milankovitch cycles, we obtained that the growth rates of sublayer 1 through sublayer 5 are 2.15, 2.70, 2.43, 2.75 and 2.67 mm/Ma, respectively. Their corresponding ages are 1.3, 2.5, 5.9, 6.7 and 7.5 Ma, respectively. Our results show that since late Micocene, the growth rates of FeMn crust changed alternatively, since recent 1.3 Ma, the growth rate of the FeMn crust slowed down significantly. It is considered that the graylevel series of the growth profile of FeMn crusts can be used as a paleoenvironmental indicator, and the application of orbital pacing method on graylevel series is an effective approach to determine the high resolution growth rates of FeMn crust and hence provide important information on paleoenvironmental change.
2010, 28(5): 1020-1036.
Abstract:
Based on the sedimentary microfacies study, four sedimentary facies and ten microfacies were identified in the MiddlePermian Maokou Formation and UpperPermian Wujiaping Formation at the Tieqiao section, Laibin, Guangxi. The four sedimentary facies are: basin, including microfacies 1a (bedded chert) and 1b (bedded chert with lensoid limestone); lower slope, including microfacies 2a (bedded chert with limestone intercalation), 2b (limestone intercalated with bedded chert), and 2c (limestone turbidite); upper slope, including microfacies 3a (limestone intercalated by bedded chert), 3b (limestone intercalated by lensoid or nodular chert), 3c (thicklayered limestone) and 3d (limestone of gravityflows); and platform margin, including microfacies 4 (calcareous spongereef limestone). Both Maokou Foramtion and Wujiaping Formation represent a shallowingupward sedimentary cycle, however, they are different in cycle evolution. The Maokou Formation is characterized by evolution from basin to slope, with turbidite and debris flow, while the Wujiaping Formation by evolution from basin to platform, with frequent microfacies alternation. Sea level changes recorded by microfacies alternation are characterized by continuous falling in the Moukou period, but rapid rising, followed by gradual falling then rising in the Wujiaping period.
Based on the sedimentary microfacies study, four sedimentary facies and ten microfacies were identified in the MiddlePermian Maokou Formation and UpperPermian Wujiaping Formation at the Tieqiao section, Laibin, Guangxi. The four sedimentary facies are: basin, including microfacies 1a (bedded chert) and 1b (bedded chert with lensoid limestone); lower slope, including microfacies 2a (bedded chert with limestone intercalation), 2b (limestone intercalated with bedded chert), and 2c (limestone turbidite); upper slope, including microfacies 3a (limestone intercalated by bedded chert), 3b (limestone intercalated by lensoid or nodular chert), 3c (thicklayered limestone) and 3d (limestone of gravityflows); and platform margin, including microfacies 4 (calcareous spongereef limestone). Both Maokou Foramtion and Wujiaping Formation represent a shallowingupward sedimentary cycle, however, they are different in cycle evolution. The Maokou Formation is characterized by evolution from basin to slope, with turbidite and debris flow, while the Wujiaping Formation by evolution from basin to platform, with frequent microfacies alternation. Sea level changes recorded by microfacies alternation are characterized by continuous falling in the Moukou period, but rapid rising, followed by gradual falling then rising in the Wujiaping period.
2010, 28(5): 861-867.
Abstract:
Late Carboniferous to Early Permian was an important period of tectonic changes and oceancontinent transformation in northern Xinjiang area. Several approximately eastwest intracontinental rifts occurred,such as Santanghu basin, where abundant basic, intermediate, and acidic volcanic rocks are present. Deposition of moderately deep lacustrine sediments of the Lucaogou Formation occurred during Middle Permian in Northern Xinjiang. The sediments include thick dark colored shale, tuffaceous shale, and dolomite shale, intercalated with dolomitic micritic limestone, tuff, dolomite, and volcanic rocks. They contain Turfania, bivalve, conchostracans, and ostracoda. The dolomite is composed of interlaminated ankerite,cryptocrystalline quartz and organic matter including algae, and analcime laminae as annalcite.The analcites were cenmented and replaced by ankerite. In addition, hydrothermal minerals like albite, illite, anhydrite,and pyrite are present. These hydrothermal minerals were firstly recognized in the Lucaogou,and the distribution of dolomite is consistent with that of the underlying Upper Carboniferous volcanic rocks, which occur in fractures and point sources. The networklike and branchlike fractures in volcanic rocks with a brecciated structure are filled with hydrothermal minerals indicating deposition around a hydrothermal vent. Preliminary analysis indicateds that dolomites were related to magmatism and mantle hydrothermal fluid, and formed as lacustrine eruptive hydrothermal dolomites.
Late Carboniferous to Early Permian was an important period of tectonic changes and oceancontinent transformation in northern Xinjiang area. Several approximately eastwest intracontinental rifts occurred,such as Santanghu basin, where abundant basic, intermediate, and acidic volcanic rocks are present. Deposition of moderately deep lacustrine sediments of the Lucaogou Formation occurred during Middle Permian in Northern Xinjiang. The sediments include thick dark colored shale, tuffaceous shale, and dolomite shale, intercalated with dolomitic micritic limestone, tuff, dolomite, and volcanic rocks. They contain Turfania, bivalve, conchostracans, and ostracoda. The dolomite is composed of interlaminated ankerite,cryptocrystalline quartz and organic matter including algae, and analcime laminae as annalcite.The analcites were cenmented and replaced by ankerite. In addition, hydrothermal minerals like albite, illite, anhydrite,and pyrite are present. These hydrothermal minerals were firstly recognized in the Lucaogou,and the distribution of dolomite is consistent with that of the underlying Upper Carboniferous volcanic rocks, which occur in fractures and point sources. The networklike and branchlike fractures in volcanic rocks with a brecciated structure are filled with hydrothermal minerals indicating deposition around a hydrothermal vent. Preliminary analysis indicateds that dolomites were related to magmatism and mantle hydrothermal fluid, and formed as lacustrine eruptive hydrothermal dolomites.
2010, 28(5): 875-883.
Abstract:
The PreMesozoic in China are dominated by marine deposits with multiplelayer series and multipletype source rocks, indicating the huge potential for oil/gas exploration in the marine sequences of China. However, the differential control of tectonic setting and sedimentary background results in significant differences in the quality and distribution of source rocks, thus controls the exploration potential of the marine sequences. During SinianEarly Paleozoic（Z－O2）, the main plates in China were in a tectonicsedimentary period with ocean basin extending and landmass dispersing. Source rocks of passive continental margin slope facies were developed in the peripheries of main landmasses such as Huabei, Yangtze and Tarim. These source rocks feature in wide zonal distribution, extensive distribution, high quality and longterm inheritance development. In the late of Early Paleozoic（O3－S）, ocean basins subducted and China Ancient Land converged and took shape. Under the constraint of uplifts on plate margin, source rocks were mainly developed in intraplatform sags. They are characterized by planar distribution and small thickness. In Late Paleozoicearly Mesozoic（D－T）, North of China was dominated by cratonic tectonic setting where coal measure source rocks of transitional facies were developed. These source rocks feature in planar distribution, large area and gas predominance. In contrast, South of China was dominated by divergent tectonic setting and the Huanan platform split into a tectonic framework of "basin surrounding platform". Source rocks were deposited in the interior of deep faulted depression and are characterized by narrow zonal distribution, high quality and small area.
The PreMesozoic in China are dominated by marine deposits with multiplelayer series and multipletype source rocks, indicating the huge potential for oil/gas exploration in the marine sequences of China. However, the differential control of tectonic setting and sedimentary background results in significant differences in the quality and distribution of source rocks, thus controls the exploration potential of the marine sequences. During SinianEarly Paleozoic（Z－O2）, the main plates in China were in a tectonicsedimentary period with ocean basin extending and landmass dispersing. Source rocks of passive continental margin slope facies were developed in the peripheries of main landmasses such as Huabei, Yangtze and Tarim. These source rocks feature in wide zonal distribution, extensive distribution, high quality and longterm inheritance development. In the late of Early Paleozoic（O3－S）, ocean basins subducted and China Ancient Land converged and took shape. Under the constraint of uplifts on plate margin, source rocks were mainly developed in intraplatform sags. They are characterized by planar distribution and small thickness. In Late Paleozoicearly Mesozoic（D－T）, North of China was dominated by cratonic tectonic setting where coal measure source rocks of transitional facies were developed. These source rocks feature in planar distribution, large area and gas predominance. In contrast, South of China was dominated by divergent tectonic setting and the Huanan platform split into a tectonic framework of "basin surrounding platform". Source rocks were deposited in the interior of deep faulted depression and are characterized by narrow zonal distribution, high quality and small area.
2010, 28(5): 894-905.
Abstract:
Drawing paleogeography is an important method to reconstruct paleogeography of different geological history. Sedimentary sequence often manifests the cycle characteristic of different temporal and spatial distribution, which is coupled by the interaction of tectonic movement of diverse scale, global eustasy or base level cycle of different period or order, sedimentation and climate. Sedimentary sequence of different order and scale responds differently to varying driving mechanism. To link with hydrocarbon exploration closely, usually selecting the secondorder, thirdorder and mediumterm base level phases as compilation unit, to draw sequence lithofacies paleogeographic of small scale , medium scale and large scale on large plot , basin or large area inside basin, and important block. They are marked by the advantages, such as isochronisms, succession of the sedimentation process and practicability. The sequence lithofacies paleogeographic can manifest detailedly paleogeography in varying degrees and represent the combination and distribution regulation of material from diverse scale. And they can provide the theoretical and practical proofs for selecting exploration target area, predicting favorable zone and ascertaining reservoir, then provide service for every stage of hydrocarbon exploration.
Drawing paleogeography is an important method to reconstruct paleogeography of different geological history. Sedimentary sequence often manifests the cycle characteristic of different temporal and spatial distribution, which is coupled by the interaction of tectonic movement of diverse scale, global eustasy or base level cycle of different period or order, sedimentation and climate. Sedimentary sequence of different order and scale responds differently to varying driving mechanism. To link with hydrocarbon exploration closely, usually selecting the secondorder, thirdorder and mediumterm base level phases as compilation unit, to draw sequence lithofacies paleogeographic of small scale , medium scale and large scale on large plot , basin or large area inside basin, and important block. They are marked by the advantages, such as isochronisms, succession of the sedimentation process and practicability. The sequence lithofacies paleogeographic can manifest detailedly paleogeography in varying degrees and represent the combination and distribution regulation of material from diverse scale. And they can provide the theoretical and practical proofs for selecting exploration target area, predicting favorable zone and ascertaining reservoir, then provide service for every stage of hydrocarbon exploration.
2010, 28(5): 917-925.
Abstract:
Paleolimnology is a science to study the historical evolution of lake systems, which belongs to highly comprehensive geosciences. This paper presents a review on the definitions, research status and commonlyused research methods in paleolimnology, and takes the Paleogene oil shale bearing lake in Huadian basin, Jilin Province, as a case study. Huadian Basin is a smallscale halfgraben basin, and F1 fault in the southern margin of the basin controls the Palaogene lake evolution. Huadian Basin that is rich in oil shale resources has unique advantages for paleolimnological studies. Huadian oil shale shows characteristics of doublelayered structure, which consists of alternatively white and black thin layers. The organic and terrestrial mineral detritus layers rhythmically alternate each other the organic layers show black or brown, while the other ones of quartz, feldspar and clay minerals show white. According to the vertical variations of TOC content, we interpret that the paleoproductivity of Huadian Basin varies as Middle Member(oilbearing) > Upper Member (coalbearing) > Lower Member (pyritebearing). Such a variation indicates that paleoproductivity was the highest when the oil shale was forming. From the petrography and mineral features of oil shale, the ratios of V/V＋N, Sr/Ba and B/Ga, we conclude that the paleowater characterizes as alternatively variation of fresh to brackishsaline water, which was a preferment environment for the lake stratified. The organism was well preserved because of the stratifyingcaused anoxic in the bottom water. With the development of paleolimnology, it is acting as an important role in the fields of hydrocarbon exploration and the studies for global environment and climate changes. However, challenges in theories and methods show up in front of paleolimnologists which are waiting for continuous endeavor and exploration.
Paleolimnology is a science to study the historical evolution of lake systems, which belongs to highly comprehensive geosciences. This paper presents a review on the definitions, research status and commonlyused research methods in paleolimnology, and takes the Paleogene oil shale bearing lake in Huadian basin, Jilin Province, as a case study. Huadian Basin is a smallscale halfgraben basin, and F1 fault in the southern margin of the basin controls the Palaogene lake evolution. Huadian Basin that is rich in oil shale resources has unique advantages for paleolimnological studies. Huadian oil shale shows characteristics of doublelayered structure, which consists of alternatively white and black thin layers. The organic and terrestrial mineral detritus layers rhythmically alternate each other the organic layers show black or brown, while the other ones of quartz, feldspar and clay minerals show white. According to the vertical variations of TOC content, we interpret that the paleoproductivity of Huadian Basin varies as Middle Member(oilbearing) > Upper Member (coalbearing) > Lower Member (pyritebearing). Such a variation indicates that paleoproductivity was the highest when the oil shale was forming. From the petrography and mineral features of oil shale, the ratios of V/V＋N, Sr/Ba and B/Ga, we conclude that the paleowater characterizes as alternatively variation of fresh to brackishsaline water, which was a preferment environment for the lake stratified. The organism was well preserved because of the stratifyingcaused anoxic in the bottom water. With the development of paleolimnology, it is acting as an important role in the fields of hydrocarbon exploration and the studies for global environment and climate changes. However, challenges in theories and methods show up in front of paleolimnologists which are waiting for continuous endeavor and exploration.
2010, 28(5): 933-944.
Abstract:
Deltas in shallow water is very different from that formed in deeper water. Through modern deposits survey in Dongting and Poyong lacustrine, detailed correlation of sandstone in mature oil field (Gasi N1-N12) and seismic attributes analysis of BZ28 in Bohai Bay, two types of shallow water deltas were recognized according to the sandbody type and distibution. Sand framework is mainly made of distributary channel in the first one and the other one is mainly made of distributary bar. Sandstones are narrow and isolated in the delta mainly made of distributary channel, while sandstones are widespread and continuous in the delta made of distributary bar.
Deltas in shallow water is very different from that formed in deeper water. Through modern deposits survey in Dongting and Poyong lacustrine, detailed correlation of sandstone in mature oil field (Gasi N1-N12) and seismic attributes analysis of BZ28 in Bohai Bay, two types of shallow water deltas were recognized according to the sandbody type and distibution. Sand framework is mainly made of distributary channel in the first one and the other one is mainly made of distributary bar. Sandstones are narrow and isolated in the delta mainly made of distributary channel, while sandstones are widespread and continuous in the delta made of distributary bar.
2010, 28(5): 953-961.
Abstract:
Based on data from core samples, thin section, and physical property, we have investigated petrological characteristics and reservoir properties of dolomite reserviors in the Cambrian of the eastern Tarim Basin. The dolomites in eastern Tarim basin can be subdivided into two categories, replacement dolomite and crackcavityfilled dolomite. The replacement dolomite can be further subdivided into mudsiltsized dolomite, fine and midium crystal dolomite, coarse crystal dolomite, and breccia dolomite. The reservoir space in dolomites is predominated by intercrystal pore, dissolved pore, stylolite pore and cracks and fractures. Cracks and fractures mainly play the role of connecting the pores. The most common reservoir space is mainly the overlapped complex of cracks and cavities. The replacement dolomites show an obvious faciescontrolled feature, with the dolomite of the YingdongLuoxi region being developed in the marginal shoal, and tidal flat facies belts of the inner ramp setting, and the dolomite in the vicinity of Well Gucheng 4 being developed in the forereef slope facies belt of the rimmed shelf setting. Thin section identification and geochemical analysis indicate that the genesis of dolomite in the study area includes the seepagereflux, burial, and hydrothermal dolomitization. The distribution of the dolomite reservoirs were controlled by the sedimentary facies, diagenesis (dolomitization, cementation, disolution), and fractures. Higher quality reservoirs are those shaolfacies dolomite overprinted with interaction of seepagereflux dolomitization, burial dolomitization and/or hydrothermal dolomitization.
Based on data from core samples, thin section, and physical property, we have investigated petrological characteristics and reservoir properties of dolomite reserviors in the Cambrian of the eastern Tarim Basin. The dolomites in eastern Tarim basin can be subdivided into two categories, replacement dolomite and crackcavityfilled dolomite. The replacement dolomite can be further subdivided into mudsiltsized dolomite, fine and midium crystal dolomite, coarse crystal dolomite, and breccia dolomite. The reservoir space in dolomites is predominated by intercrystal pore, dissolved pore, stylolite pore and cracks and fractures. Cracks and fractures mainly play the role of connecting the pores. The most common reservoir space is mainly the overlapped complex of cracks and cavities. The replacement dolomites show an obvious faciescontrolled feature, with the dolomite of the YingdongLuoxi region being developed in the marginal shoal, and tidal flat facies belts of the inner ramp setting, and the dolomite in the vicinity of Well Gucheng 4 being developed in the forereef slope facies belt of the rimmed shelf setting. Thin section identification and geochemical analysis indicate that the genesis of dolomite in the study area includes the seepagereflux, burial, and hydrothermal dolomitization. The distribution of the dolomite reservoirs were controlled by the sedimentary facies, diagenesis (dolomitization, cementation, disolution), and fractures. Higher quality reservoirs are those shaolfacies dolomite overprinted with interaction of seepagereflux dolomitization, burial dolomitization and/or hydrothermal dolomitization.
2010, 28(5): 969-979.
Abstract:
The understanding for layered weathering crust model once sustained oil and gas exploration of the Lower Paleozoic deepburied carbonate in the Tarim Basin. However, strong heterogeneous characteristics of the carbonate reservoir types increases exploration risk in the study area. As a case study, The MiddleLower Ordovician carbonate reservoirs of Tahe area, Tarim basin, are studied in this paper, with focuses on superposition effect of burial diagenesis and structurally controlled thermalfluid, on reservoir formation. Finally, combined with other elements including epigenetic karst process and so on, a comprehensive explanation on reservoir distribution is given in this research. The main recognition includes: ① Normal deepburied diagenesis of Ordovician carbonates mainly resulted in precipitation rather than dissolution, and constructive modification primarily related to the epigenetic karstification (paleokarst) or structurally controlled thermalfluid flow and led to strong heterogeneity of carbonate reservoirs. ② From the Lower Ordovician to Upper Ordovician, thermal fluid flow evidence in the lower carbonate strata is stronger than that of the upper carbonate strata. ③ The constructive modification of structuralthermal fluid flow in Ordovician carbonate mainly occurred in structural intersection of superimposed faults developed during MiddleLate Devonian and Permian, respectively, and the strong preexisted epigenetic karstification area formed at MiddleLate Ordovician and preCarboniferous periods. The most efficient carbonate reservoirs have limited genetic relation with highenergy depositional facies in the study area. This paper puts forward a conceptual model about structuralgeofluid processes and related reservoir formation for the Ordovician carbonates in Tahe area, which provides a new clue for further understanding formation and distribution of the studied reservoirs.
The understanding for layered weathering crust model once sustained oil and gas exploration of the Lower Paleozoic deepburied carbonate in the Tarim Basin. However, strong heterogeneous characteristics of the carbonate reservoir types increases exploration risk in the study area. As a case study, The MiddleLower Ordovician carbonate reservoirs of Tahe area, Tarim basin, are studied in this paper, with focuses on superposition effect of burial diagenesis and structurally controlled thermalfluid, on reservoir formation. Finally, combined with other elements including epigenetic karst process and so on, a comprehensive explanation on reservoir distribution is given in this research. The main recognition includes: ① Normal deepburied diagenesis of Ordovician carbonates mainly resulted in precipitation rather than dissolution, and constructive modification primarily related to the epigenetic karstification (paleokarst) or structurally controlled thermalfluid flow and led to strong heterogeneity of carbonate reservoirs. ② From the Lower Ordovician to Upper Ordovician, thermal fluid flow evidence in the lower carbonate strata is stronger than that of the upper carbonate strata. ③ The constructive modification of structuralthermal fluid flow in Ordovician carbonate mainly occurred in structural intersection of superimposed faults developed during MiddleLate Devonian and Permian, respectively, and the strong preexisted epigenetic karstification area formed at MiddleLate Ordovician and preCarboniferous periods. The most efficient carbonate reservoirs have limited genetic relation with highenergy depositional facies in the study area. This paper puts forward a conceptual model about structuralgeofluid processes and related reservoir formation for the Ordovician carbonates in Tahe area, which provides a new clue for further understanding formation and distribution of the studied reservoirs.
2010, 28(5): 987-1005.
Abstract:
After experiencing threephase tectonic evolution in the Cenozoic, respectively Indiananhai rift period, intercontinent rift period and regional subsidence stage, the South China Sea (in short the SCS) possesses of three tectonic units, respectively continental shelf, continental slope and ocean crust. Surrounding the ocean crust, the distribution of the continental shelf and the continental slope is approximate to ringzone. The sedimentary basins are mainly located in the continental shelf and the continental slope. The basins surround to the center ocean crust zone, too. In the SCS, the action of the petroleum exploration flourished from the end of the 60s in last century and the hundreds hydrocarbon fields, located in the south\\north\\west continental margin, have been discovered so far. Those hydrocarbon fields character as the outsideoil and the insidegas. The oil fields locate mainly in the continental shelf or the area near the land. The gas fields locate mainly in the continental slope or the area near the ocean. In the sags which located in the outsideoil belts, the middledeep lake face mud and Ⅰ&Ⅱ1 types kerogen are dominated in the source rocks. In those sags, the crust is relatively thick and the heat flow is relatively lower. The source rocks are in the oilwindow and produce the crude oil. In the sags which located in the innersidegas belts, the marine facies mud & the onshoreoffshore mud and Ⅱ2Ⅲ types kerogen are dominated in the source rocks. In those sags, the crust is relatively thin and the heat flow is relatively higher. The source rocks produce mainly the gas. In the outsideoil zone, there are several petroleum plays. The sandstone, which formed in the environment of the lake and the shallow marine, is the main reservoir. In the innersidegas zone, there are two petroleum plays, respectively the shallow water sediments and the deep water sediments. The deepwater fan and the reef are the main reservoir. The seal is mainly the marinefacies mud stone. According to the 300m depth, the outsideoil zone, with high exploration, locates mainly in shallow water. The insidegas zone, with lower exploration, locates mainly in the bottom of the continental shelf and the continental slope. Nowadays, in the SCS, the exploration is transferring from the shallow water area to the deepwater area. With the development of petroleum exploration, the SCS, with the enormous hydrocarbon resource that is comparative to that in the rift area in the eastern China or in the Bohai gulf basins, would be the significant potential hydrocarbon area.
After experiencing threephase tectonic evolution in the Cenozoic, respectively Indiananhai rift period, intercontinent rift period and regional subsidence stage, the South China Sea (in short the SCS) possesses of three tectonic units, respectively continental shelf, continental slope and ocean crust. Surrounding the ocean crust, the distribution of the continental shelf and the continental slope is approximate to ringzone. The sedimentary basins are mainly located in the continental shelf and the continental slope. The basins surround to the center ocean crust zone, too. In the SCS, the action of the petroleum exploration flourished from the end of the 60s in last century and the hundreds hydrocarbon fields, located in the south\\north\\west continental margin, have been discovered so far. Those hydrocarbon fields character as the outsideoil and the insidegas. The oil fields locate mainly in the continental shelf or the area near the land. The gas fields locate mainly in the continental slope or the area near the ocean. In the sags which located in the outsideoil belts, the middledeep lake face mud and Ⅰ&Ⅱ1 types kerogen are dominated in the source rocks. In those sags, the crust is relatively thick and the heat flow is relatively lower. The source rocks are in the oilwindow and produce the crude oil. In the sags which located in the innersidegas belts, the marine facies mud & the onshoreoffshore mud and Ⅱ2Ⅲ types kerogen are dominated in the source rocks. In those sags, the crust is relatively thin and the heat flow is relatively higher. The source rocks produce mainly the gas. In the outsideoil zone, there are several petroleum plays. The sandstone, which formed in the environment of the lake and the shallow marine, is the main reservoir. In the innersidegas zone, there are two petroleum plays, respectively the shallow water sediments and the deep water sediments. The deepwater fan and the reef are the main reservoir. The seal is mainly the marinefacies mud stone. According to the 300m depth, the outsideoil zone, with high exploration, locates mainly in shallow water. The insidegas zone, with lower exploration, locates mainly in the bottom of the continental shelf and the continental slope. Nowadays, in the SCS, the exploration is transferring from the shallow water area to the deepwater area. With the development of petroleum exploration, the SCS, with the enormous hydrocarbon resource that is comparative to that in the rift area in the eastern China or in the Bohai gulf basins, would be the significant potential hydrocarbon area.
2010, 28(5): 1012-1019.
Abstract:
Clay minerals can be used to track oceanic current variations and to reveal contemporaneous paleoclimatic changes prevailing in continental source areas, and have played a significant role in sedimentation and paleoenvironment studies of the South China Sea. However, it is quite debatable whether clay minerals in the South China Sea can directly indicate the East Asian monsoon evolution. This study reports that the clay mineral assemblage in the South China Sea is mainly controlled by provenance supply and current transport, and that the clay minerals themselves do not bear the contemporaneous paleoclimatic characteristics. For example, as three major provenances of terrigenous clastics, the Pearl River, Taiwan, and Luzon provide similar the clay mineral assemblages, respectively, regardless of glacial or interglacial stages. Once entering the South China Sea, these clay minerals are transported by different oceanic currents. Therefore, the implication of late Quaternary clay mineral assemblages in the South China Sea for proxies of the East Asian monsoon evolution is realized through the current transport processes with various results in different parts of the South China Sea.
Clay minerals can be used to track oceanic current variations and to reveal contemporaneous paleoclimatic changes prevailing in continental source areas, and have played a significant role in sedimentation and paleoenvironment studies of the South China Sea. However, it is quite debatable whether clay minerals in the South China Sea can directly indicate the East Asian monsoon evolution. This study reports that the clay mineral assemblage in the South China Sea is mainly controlled by provenance supply and current transport, and that the clay minerals themselves do not bear the contemporaneous paleoclimatic characteristics. For example, as three major provenances of terrigenous clastics, the Pearl River, Taiwan, and Luzon provide similar the clay mineral assemblages, respectively, regardless of glacial or interglacial stages. Once entering the South China Sea, these clay minerals are transported by different oceanic currents. Therefore, the implication of late Quaternary clay mineral assemblages in the South China Sea for proxies of the East Asian monsoon evolution is realized through the current transport processes with various results in different parts of the South China Sea.
2010, 28(5): 1037-1045.
Abstract:
Because of the strong diagenesis, sandstone in Upper Triassic Xujiahe Formation is thick and tight, reservoir heterogeneity is very strong, various types of gas reservoirs are developed. Major developed eight conventional gas reservoirs and two unconventional gas reservoirs. The lithological gas reservoir, structurelithological reservoir having large scale and abundant reserves, are important gas reservoirs and mainly developed in the MidSichuan area; Water soluble gas reservoir with high yield and great potential is also developed, widely distributed in the gentle slope and the Depression in the centralwest Sichuan region, is the important development direction in Sichuan Basin. The Xujiahe Formation gas reservoirs adjacent the source, have high pressure, contain condensate oil and water, distributed widely, and their scale is large and relationship between water and gas is complex. As different areas have different characters of deposition, diagenesis and structure, the main controlling factors in gas accumulation are quite different. Therefore, the distribution of reservoir, tectonic background and the degree of fracture development are the major three controlling factors of the gas accumulation in Xujiahe Formation gas reservoirs, the main control factor of accumulation and high productivity is the effective combination of the three elements.
Because of the strong diagenesis, sandstone in Upper Triassic Xujiahe Formation is thick and tight, reservoir heterogeneity is very strong, various types of gas reservoirs are developed. Major developed eight conventional gas reservoirs and two unconventional gas reservoirs. The lithological gas reservoir, structurelithological reservoir having large scale and abundant reserves, are important gas reservoirs and mainly developed in the MidSichuan area; Water soluble gas reservoir with high yield and great potential is also developed, widely distributed in the gentle slope and the Depression in the centralwest Sichuan region, is the important development direction in Sichuan Basin. The Xujiahe Formation gas reservoirs adjacent the source, have high pressure, contain condensate oil and water, distributed widely, and their scale is large and relationship between water and gas is complex. As different areas have different characters of deposition, diagenesis and structure, the main controlling factors in gas accumulation are quite different. Therefore, the distribution of reservoir, tectonic background and the degree of fracture development are the major three controlling factors of the gas accumulation in Xujiahe Formation gas reservoirs, the main control factor of accumulation and high productivity is the effective combination of the three elements.
