2014 Vol. 32, No. 1
Display Method:
2014, 32(1): 1-7.
Abstract:
Most previous studies suggest that the lithofacies palaeogeography of northern Sichuan Basin and Qinling area is the deep-sea slopes or slopes of platform margin during the Sinian-Cambrian. However, in the process of paleogeographic mapping in this area, it was discovered that the Carbonaceous mudstone and the stone coal are deposited in the surface water or near shore shallow water, such as swamps and lagoons, rather than in the deep water or the deep sea. Therefore, based on the detailed observation , the measurement of outcrop profiles and the profound analysis of the well datas, and combined with the interpretation ofseismic profiles in the northern Sichuan Basin, the comprehensive analysisof the single section facies, cross section facies and facies mapping were made; meanwhile, by referring to the tectonic palaeogeography, quantitative palaeogeography and production palaeogeography in the area, the paleogeographic maps were drew optimally from the Sinian to Cambrian.It was concluded that the palaeogeographic framework in the area of northern Sichuan Basin to Qinling area mainly consists of tidal flats, lagoons, peat swamps, shores and restricted platform facies, rather than the facies of the deep-sea basin, slopes or margin slopes of platform during the Sinian-Cambrian.
Most previous studies suggest that the lithofacies palaeogeography of northern Sichuan Basin and Qinling area is the deep-sea slopes or slopes of platform margin during the Sinian-Cambrian. However, in the process of paleogeographic mapping in this area, it was discovered that the Carbonaceous mudstone and the stone coal are deposited in the surface water or near shore shallow water, such as swamps and lagoons, rather than in the deep water or the deep sea. Therefore, based on the detailed observation , the measurement of outcrop profiles and the profound analysis of the well datas, and combined with the interpretation ofseismic profiles in the northern Sichuan Basin, the comprehensive analysisof the single section facies, cross section facies and facies mapping were made; meanwhile, by referring to the tectonic palaeogeography, quantitative palaeogeography and production palaeogeography in the area, the paleogeographic maps were drew optimally from the Sinian to Cambrian.It was concluded that the palaeogeographic framework in the area of northern Sichuan Basin to Qinling area mainly consists of tidal flats, lagoons, peat swamps, shores and restricted platform facies, rather than the facies of the deep-sea basin, slopes or margin slopes of platform during the Sinian-Cambrian.
2014, 32(1): 19-26.
Abstract:
The obvious action from ancient landform from Wuling orogeny control the later sedimentary environment in the eastern Guizhou and adjacent area in Neoproterozoic era. Basal conglomerate lithology features reflect on the bottom of Jialu Formation: Sedimentary facies is piedmont debris flow to river in the Fanjing mountain area, river to shore in the Zhijiang area, and river to shore gravel in northern Guangxi area and Congjiang county.It determines ancient landform is highland in the Fanjing mountain area in the same time,and is lowland in northern Guangxi area and Congjiang county where accepted sedimentary filling by transgression in the first time. Calcareous rock on the upper part of Jialu Formation is ideal region for Comparison on make region sedimentary environment relative consistency from process sedimentary to filling after Wuling orogeny, indicating that sedimentary differentiation begin aggravating because of rifting in the period of Xiajiang in the same area after the period of Jialu.
The obvious action from ancient landform from Wuling orogeny control the later sedimentary environment in the eastern Guizhou and adjacent area in Neoproterozoic era. Basal conglomerate lithology features reflect on the bottom of Jialu Formation: Sedimentary facies is piedmont debris flow to river in the Fanjing mountain area, river to shore in the Zhijiang area, and river to shore gravel in northern Guangxi area and Congjiang county.It determines ancient landform is highland in the Fanjing mountain area in the same time,and is lowland in northern Guangxi area and Congjiang county where accepted sedimentary filling by transgression in the first time. Calcareous rock on the upper part of Jialu Formation is ideal region for Comparison on make region sedimentary environment relative consistency from process sedimentary to filling after Wuling orogeny, indicating that sedimentary differentiation begin aggravating because of rifting in the period of Xiajiang in the same area after the period of Jialu.
2014, 32(1): 36-43.
Abstract:
The Upper Triassic flysch Langjiexue Group is widespread in southern Tibet. It outcrops south to the river Yarlung Zangbo and east to Bailang county, confined by three thrusts: Naidong-Sangri-Langxian Fault in north, Cuona-Milin Fault in east, and Renbu-Zhangda-Longzi Fault in south. A suggestion of the coeval Nieru Formation belonging to the Langjiexue Group may have the southern boundary fault southward extended to the Renbu-Zhangda-Longzi Fault. The Upper Triassic Langjiexue Group has been classified as either a part of the northern deep sea Tethys Himalayas or a component of the melange Xiukang Group——accretionary prism within the Yarlung Zangbo suture since it was nominated. Recent geological investigation on paleocurrent flow direction and provenance analysis of clastic composition and geochemistry demonstrated a different viewpoint from the past, in which lithological distribution has not been established. A geological field investigation of the Upper Triassic flysch Langjiexue Group was in this work carried out in Shannan region, southern Tibet, south to the river Yarlung Zangbo, during which lithology and thickness of variety of terrigenous rocks were described and calculated at sixty-five outcrop observations within fourteen geological traversal profiles in almost N-S direction. Then the data of the thickness were processed as follow: 1) calculating the ratio of sandstone versus slate for every observation——response to clastic grain size distribution and source, a method for purpose of recovery of sedimentary dispersal, paleocurrent system based on the principle of finer grain size if more further transportation; 2) projecting ratio value of each observation on the scaled geological map; and 3) editing equal ratio values and draw by isoline on the map for the same formation. It is noted that sandstone in the statistic of thickness, and slate covers the silty and non-silty slate. The sum of thickness is over 50 m, in general 80 m ~ 200 m, at each observation. All the data of each observation were optimal by excluding of stratal duplicate. This is because of statistics that could be repeated at two even more observations due to folding and thrusting, etc. for overturn of strata. To avoid this shortage, relative positions of observations were examined by balance section for each profile, and results show no duplicates of observed places happened to the observed places in this work. The observation of lithology shows there are almost no conglomerates in the Upper Triassic flysch Langjiexue Group, but it is mainly composed of low grade metamorphosed flysch sandstone and slate facies. The strata are comprised by alteration of sandstone/siltstone beds and dark gray to blackish (hemi-) pelagic shale. Sandstones are dominated by medium to fine feldspar / lithic (quartz) sandstone or greywacke with angular-subangular roundness and variable sorting. Lithologies are arranged in an upward fining Bouma sequence, in which graded beddings, parallel cross-beddings, horizontal, and ripples, are common. The sedimentary strata are metamorphosed into variable degree, which is increasing eastward and toward the metamorphic core complex, with the center formed by the Cenozoic granitic pluton. Strong folding and thrusting together with metamorphism and lack of fossils makes the sequences stratigraphically difficult to restore. However, former limited biostratigraphic evidences suggest that the group is of Norian-Rhaetian age. Isolines of lithological ratios display that ratio values of sandstone vs. slate decrease from north to south in majority of formations: 1) 0.12 to 0.01 of the slaty Nieru Formation in Nagarze, 2.4 to 0.6 near Xuesa village, Lhunze, and 25.0 extremely down to 2.0 between Xuesa and Zhari villages, Lhunze, indicating an discrepancy between east and west of Shannan region and likely development of channels under water; 2) 1.0 to 0.2 of the Songre Formation in western Shannan, and 0.6 to 0.1 in mid Shannan, in which ratios are bigger in western than in eastern Shannan region; 3) 1.89 to 0.22 of the Jiangxiong Formation in western Shannan, 2.0 to 0.4 in mid Shannan, and 0.8 to 0.4 in eastern Shannan, with few exceptances, and it is also bigger in western than in eastern Shannan region; 4) 1.5 to 0.5~0.8 of the Jiedexiu Formation southeastward and southwestward in Gonggar and Zhanang. Those results above indicate a total tendency of finer and finer grain southward, implicating southward direction of terrigenous matters. This observation is quite consistent with the previously published paleocurrent data, supporting and enforcing the scientific understanding of other origination of the Langjiexue Group instead of the paleo-Indian continent (Tethys Himalaya) in south. According to lithology and the variation (tendency, isoline shape, and pattern) of ratio values of sandstone vs. slate from east to west, it is proposed that the Langjiexue Group documents the sediments of middle and outer (lobe) submarine fan without inner fan, and there are at least two even more coalescing submarine fan systems during the Late Triassic in Shannan area. Recognition of possible amount and superposition of fans remains much work in future.
The Upper Triassic flysch Langjiexue Group is widespread in southern Tibet. It outcrops south to the river Yarlung Zangbo and east to Bailang county, confined by three thrusts: Naidong-Sangri-Langxian Fault in north, Cuona-Milin Fault in east, and Renbu-Zhangda-Longzi Fault in south. A suggestion of the coeval Nieru Formation belonging to the Langjiexue Group may have the southern boundary fault southward extended to the Renbu-Zhangda-Longzi Fault. The Upper Triassic Langjiexue Group has been classified as either a part of the northern deep sea Tethys Himalayas or a component of the melange Xiukang Group——accretionary prism within the Yarlung Zangbo suture since it was nominated. Recent geological investigation on paleocurrent flow direction and provenance analysis of clastic composition and geochemistry demonstrated a different viewpoint from the past, in which lithological distribution has not been established. A geological field investigation of the Upper Triassic flysch Langjiexue Group was in this work carried out in Shannan region, southern Tibet, south to the river Yarlung Zangbo, during which lithology and thickness of variety of terrigenous rocks were described and calculated at sixty-five outcrop observations within fourteen geological traversal profiles in almost N-S direction. Then the data of the thickness were processed as follow: 1) calculating the ratio of sandstone versus slate for every observation——response to clastic grain size distribution and source, a method for purpose of recovery of sedimentary dispersal, paleocurrent system based on the principle of finer grain size if more further transportation; 2) projecting ratio value of each observation on the scaled geological map; and 3) editing equal ratio values and draw by isoline on the map for the same formation. It is noted that sandstone in the statistic of thickness, and slate covers the silty and non-silty slate. The sum of thickness is over 50 m, in general 80 m ~ 200 m, at each observation. All the data of each observation were optimal by excluding of stratal duplicate. This is because of statistics that could be repeated at two even more observations due to folding and thrusting, etc. for overturn of strata. To avoid this shortage, relative positions of observations were examined by balance section for each profile, and results show no duplicates of observed places happened to the observed places in this work. The observation of lithology shows there are almost no conglomerates in the Upper Triassic flysch Langjiexue Group, but it is mainly composed of low grade metamorphosed flysch sandstone and slate facies. The strata are comprised by alteration of sandstone/siltstone beds and dark gray to blackish (hemi-) pelagic shale. Sandstones are dominated by medium to fine feldspar / lithic (quartz) sandstone or greywacke with angular-subangular roundness and variable sorting. Lithologies are arranged in an upward fining Bouma sequence, in which graded beddings, parallel cross-beddings, horizontal, and ripples, are common. The sedimentary strata are metamorphosed into variable degree, which is increasing eastward and toward the metamorphic core complex, with the center formed by the Cenozoic granitic pluton. Strong folding and thrusting together with metamorphism and lack of fossils makes the sequences stratigraphically difficult to restore. However, former limited biostratigraphic evidences suggest that the group is of Norian-Rhaetian age. Isolines of lithological ratios display that ratio values of sandstone vs. slate decrease from north to south in majority of formations: 1) 0.12 to 0.01 of the slaty Nieru Formation in Nagarze, 2.4 to 0.6 near Xuesa village, Lhunze, and 25.0 extremely down to 2.0 between Xuesa and Zhari villages, Lhunze, indicating an discrepancy between east and west of Shannan region and likely development of channels under water; 2) 1.0 to 0.2 of the Songre Formation in western Shannan, and 0.6 to 0.1 in mid Shannan, in which ratios are bigger in western than in eastern Shannan region; 3) 1.89 to 0.22 of the Jiangxiong Formation in western Shannan, 2.0 to 0.4 in mid Shannan, and 0.8 to 0.4 in eastern Shannan, with few exceptances, and it is also bigger in western than in eastern Shannan region; 4) 1.5 to 0.5~0.8 of the Jiedexiu Formation southeastward and southwestward in Gonggar and Zhanang. Those results above indicate a total tendency of finer and finer grain southward, implicating southward direction of terrigenous matters. This observation is quite consistent with the previously published paleocurrent data, supporting and enforcing the scientific understanding of other origination of the Langjiexue Group instead of the paleo-Indian continent (Tethys Himalaya) in south. According to lithology and the variation (tendency, isoline shape, and pattern) of ratio values of sandstone vs. slate from east to west, it is proposed that the Langjiexue Group documents the sediments of middle and outer (lobe) submarine fan without inner fan, and there are at least two even more coalescing submarine fan systems during the Late Triassic in Shannan area. Recognition of possible amount and superposition of fans remains much work in future.
2014, 32(1): 61-67.
Abstract:
Combined with few well drilling and well logging data, and results of previous studies, sequence stratigraphy characteristics and coal accumulation controlling factors of Middle-Lower Jurassic coalbearing series in south margins of Junggar Basin have been analyzed on the basis of sequence stratigraphic study in outcrops. Middle-Lower Jurassic coal-bearing series in south margins of Junggar Basin can be divided into one complete 2nd order tectonic sequence, where four 3rd order sequences and twelve system tracts were developed inside. The results show that paleo-tectonic setting (weakly extensive and gentle subsidence) and paleoclimate (warm, humid, and reducing condition) were the fundamental conditions for coal-forming in Middle-Lower Jurassic. While, relative lake level changes of the 2nd order tectonic sequence and rate of relative lake level change in the 3rd order sequence were the major controlling factors for coal accumulation. Commercial recoverable coals, which were characterized by large thickness and stably lateral distribution in outcrops, were all developed in highstand system tract (HST). During the depositional period of SQ1, relative lake level of the 2nd order tectonic sequence was descending, leading a lower paleowater table, where the coals were mainly developed in the lower part of HST (ascending rate of the relative lake level in the 3rd order sequence was moderate). The depositional period of SQ3 was the maximum flooding period of Early-Middle Jurassic, when the relative lake level of the 2nd order tectonic sequence ascended to the highest point. coal beds were mainly developed in the middle-upper part of HST (descending rate of the relevant lake level in the 3rd order sequence was moderate).
Combined with few well drilling and well logging data, and results of previous studies, sequence stratigraphy characteristics and coal accumulation controlling factors of Middle-Lower Jurassic coalbearing series in south margins of Junggar Basin have been analyzed on the basis of sequence stratigraphic study in outcrops. Middle-Lower Jurassic coal-bearing series in south margins of Junggar Basin can be divided into one complete 2nd order tectonic sequence, where four 3rd order sequences and twelve system tracts were developed inside. The results show that paleo-tectonic setting (weakly extensive and gentle subsidence) and paleoclimate (warm, humid, and reducing condition) were the fundamental conditions for coal-forming in Middle-Lower Jurassic. While, relative lake level changes of the 2nd order tectonic sequence and rate of relative lake level change in the 3rd order sequence were the major controlling factors for coal accumulation. Commercial recoverable coals, which were characterized by large thickness and stably lateral distribution in outcrops, were all developed in highstand system tract (HST). During the depositional period of SQ1, relative lake level of the 2nd order tectonic sequence was descending, leading a lower paleowater table, where the coals were mainly developed in the lower part of HST (ascending rate of the relative lake level in the 3rd order sequence was moderate). The depositional period of SQ3 was the maximum flooding period of Early-Middle Jurassic, when the relative lake level of the 2nd order tectonic sequence ascended to the highest point. coal beds were mainly developed in the middle-upper part of HST (descending rate of the relevant lake level in the 3rd order sequence was moderate).
2014, 32(1): 78-84.
Abstract:
73 samples from the typical section of the "Wushan Loess" were analyzed for elemental compositions in order to obtain information about its origin and sediment source. Elemental analysis show that the major elements of the "Wushan Loess" contain SiO2, Al2O3 and TFe2O3(Fe2O3+FeO), average concentration of those is 84.8%. It is similar as the UCC (86.2%), Luochuan Loess (85.34%) and Zhenjiang Xiashu Loess (86.76%). Elemental compositions of the "Wushan Loess" were similar as the Luochuan Loess, Ganzi Loess and Xifeng Red Clay, indicating the similar sediment environment. TiO2/Al2O3 vs. K2O/Al2O3 diagram shows that the "Wushan Loess" and the Ganzi Loess had almost the same elemental compositions. Besides the UCC-normalized patterns were also similar, indicating the aeolian origin. Elemental ratios show that the "Wushan Loess" were derived from multi-provenances. Besides, the "Wushan Loess" were reworked by fluvial process.
73 samples from the typical section of the "Wushan Loess" were analyzed for elemental compositions in order to obtain information about its origin and sediment source. Elemental analysis show that the major elements of the "Wushan Loess" contain SiO2, Al2O3 and TFe2O3(Fe2O3+FeO), average concentration of those is 84.8%. It is similar as the UCC (86.2%), Luochuan Loess (85.34%) and Zhenjiang Xiashu Loess (86.76%). Elemental compositions of the "Wushan Loess" were similar as the Luochuan Loess, Ganzi Loess and Xifeng Red Clay, indicating the similar sediment environment. TiO2/Al2O3 vs. K2O/Al2O3 diagram shows that the "Wushan Loess" and the Ganzi Loess had almost the same elemental compositions. Besides the UCC-normalized patterns were also similar, indicating the aeolian origin. Elemental ratios show that the "Wushan Loess" were derived from multi-provenances. Besides, the "Wushan Loess" were reworked by fluvial process.
2014, 32(1): 93-100.
Abstract:
The authors have studied 7 profiles in Barkol Lake and surrounding areas at northern foothills of Barkol Mount in the eastern Tianshan. By means of sedimentary facies analysis, OSL dating, grain size analysis and magnetic susceptibility measurement, the Holocene environmental evolution of Barkol Lakes were reconstructed. The glaciers of the East Tianshan area expanded during Last Glacial Maximum (LGM) at 14 000 a B.P. Water sealed in the glaciers of Barkol Mount, resulting in Barkol Lake shrink to the north to the #1 profile. The glaciers of Barkol Mount were shrank during 8 000~4 000 a B.P. Barkol Lake attained to the largest lake of the expansion since the beginning of the Holocene. The lake expanded to the south of the # 1 section, the area amounted to 600 km2. East Tianshan area was warm and humid during Holocene Optimum at 8 000~4 000 a B.P. subsequently the lake was gradually shrinking. The lakes area was 470 km2 at 4 000~2 000 a B.P. and shrank to 380 km2 at 2 000~1 000 a B.P.The lakes dried up at around 1 500 a B.P. Appeared mud flat deposits in the current lake zone, subsequently Barkol Lake came into the small lake with the area changing at about 100km2 when expansion or dry. The changing of lake level of the Barkol was mainly controlled by the summer solar radiation of Northern Hemisphere, which was manifested in the expansion and shrank of the Northern Hemisphere ice sheets. the expansion of the Barkol Mount glaciers in the early Holocene and water injected into Barkol Lake by glaciers shrank in middle Holocene) . The Barkol influenced little by the East Asian summer monsoon, westerly circulation bring limited water to supple the area, which drive the Barkol to the arid environment during middle to late Holocene.
The authors have studied 7 profiles in Barkol Lake and surrounding areas at northern foothills of Barkol Mount in the eastern Tianshan. By means of sedimentary facies analysis, OSL dating, grain size analysis and magnetic susceptibility measurement, the Holocene environmental evolution of Barkol Lakes were reconstructed. The glaciers of the East Tianshan area expanded during Last Glacial Maximum (LGM) at 14 000 a B.P. Water sealed in the glaciers of Barkol Mount, resulting in Barkol Lake shrink to the north to the #1 profile. The glaciers of Barkol Mount were shrank during 8 000~4 000 a B.P. Barkol Lake attained to the largest lake of the expansion since the beginning of the Holocene. The lake expanded to the south of the # 1 section, the area amounted to 600 km2. East Tianshan area was warm and humid during Holocene Optimum at 8 000~4 000 a B.P. subsequently the lake was gradually shrinking. The lakes area was 470 km2 at 4 000~2 000 a B.P. and shrank to 380 km2 at 2 000~1 000 a B.P.The lakes dried up at around 1 500 a B.P. Appeared mud flat deposits in the current lake zone, subsequently Barkol Lake came into the small lake with the area changing at about 100km2 when expansion or dry. The changing of lake level of the Barkol was mainly controlled by the summer solar radiation of Northern Hemisphere, which was manifested in the expansion and shrank of the Northern Hemisphere ice sheets. the expansion of the Barkol Mount glaciers in the early Holocene and water injected into Barkol Lake by glaciers shrank in middle Holocene) . The Barkol influenced little by the East Asian summer monsoon, westerly circulation bring limited water to supple the area, which drive the Barkol to the arid environment during middle to late Holocene.
2014, 32(1): 110-117.
Abstract:
In Jingbian platform, Ordovician Majiagou 5 member is an important natural gas reservoir in Changqing oilfield. But there exists a long argument about its dolomitization type. This issue has been discussed on the basis of Majiagou 54 sub-member. In this paper, after researching the sedimentary and geochemical characteristics of different rock types, the authors draw a conclusion that penecontemporaneous, reflux and burial dolomitization are main dolomitization types in this region. (1) Micritic and silt-sized crystal dolomite which is always associated with anhydrite, deposited in restricted and evaporative tidal flat with high salinity, and formed by penecontemporaneous dolomitization. (2) Coarser silt-sized crystal dolomite is distributed among the layers of micritic and silt-sized crystal dolomite with anhydrite, and its coarser crystal grain, lower degree of order and slightly richer calcium show that this type dolomite is formed by reflux dolomitization. (3) Much secondary calcite is spread in karst layer, and the metasomasis residual texture shows that the grain size of the dolomite before dedolomitization is mainly fine crystal, partially with euhedral-subhedral texture, zonal structure, and bright border with vague center. Their inclusion temperature span is from 52.30 ℃ to 78.05℃, and the characteristics of carbon and oxygen isotopes are more similar to typical burial dolomites. All these indicate that the dolomite before dedolomitization is formed in shallow and middle-depth burial diagenetic environment. Clarifying the dolomitization type of Majiagou 54 sub-member is very important to rebuild lithofacies palaeogeographic, research the reservoir formation mechanism, and improve the success possibility of exploration.
In Jingbian platform, Ordovician Majiagou 5 member is an important natural gas reservoir in Changqing oilfield. But there exists a long argument about its dolomitization type. This issue has been discussed on the basis of Majiagou 54 sub-member. In this paper, after researching the sedimentary and geochemical characteristics of different rock types, the authors draw a conclusion that penecontemporaneous, reflux and burial dolomitization are main dolomitization types in this region. (1) Micritic and silt-sized crystal dolomite which is always associated with anhydrite, deposited in restricted and evaporative tidal flat with high salinity, and formed by penecontemporaneous dolomitization. (2) Coarser silt-sized crystal dolomite is distributed among the layers of micritic and silt-sized crystal dolomite with anhydrite, and its coarser crystal grain, lower degree of order and slightly richer calcium show that this type dolomite is formed by reflux dolomitization. (3) Much secondary calcite is spread in karst layer, and the metasomasis residual texture shows that the grain size of the dolomite before dedolomitization is mainly fine crystal, partially with euhedral-subhedral texture, zonal structure, and bright border with vague center. Their inclusion temperature span is from 52.30 ℃ to 78.05℃, and the characteristics of carbon and oxygen isotopes are more similar to typical burial dolomites. All these indicate that the dolomite before dedolomitization is formed in shallow and middle-depth burial diagenetic environment. Clarifying the dolomitization type of Majiagou 54 sub-member is very important to rebuild lithofacies palaeogeographic, research the reservoir formation mechanism, and improve the success possibility of exploration.
2014, 32(1): 126-137.
Abstract:
Dongpu depression is located in southeastern Bohai Bay Basin, five sets of gypsum-salt rock developed, and the maximum cumulative thickness can be up to 950 m. The lithologic variation of gypsum-salt layer can be divided into three zones including gypsum-salt zone, gypsum-salt and sand-mudstone transition zone, sand-mudstone zone. Exploration practice confirmed that gypsum-salt rock on hydrocarbon enrichment in vertical or in horizontal has an important controlling role, performing for nearly 93.7 % of oil and nearly 80% of gas in Dongpu depression distribution in the north part, and most oil and gas distributes among gypsum-salt layers. Controls of gypsum-salt rock on pool forming elements were systematically analyzed, and the results show that the source rock in gypsum-salt and sand-mudstone transition zone has the highest organic matter abundance because of its advantage for high quality source rock accumulation and preservation, the next is that in gypsum-salt zone, and that in sand-mudstone zone have relative lower organic matter abundance. Meanwhile, the farther source rock away from gypsum-salt rock, the lower organic matter abundance it has, and when the distance between source rock and gypsum-salt rock exceeds 30 or 40 meters, the influence on organic matter abundance by gypsum-salt rock decreases significantly. For high water salinity, many halophilic bacteria and algae adapted to high salt environments thrive and become a major source of sedimentary organic matter, which is conducive to the formation of sapropelic organic matter. For the gypsum-salt rock has high thermal conductivity and low heat generation rate, it can transmit ground temperature easily from deep stratum to shallow stratum, which could result in source rock in the upper part of gypsum-salt stratum has lower temperature gradient and abnormal high temperature than that of no gypsum-salt stratum, to the contrary, source rock in the lower part of gypsum-salt stratum has higher temperature gradient and abnormal low temperature than that of no gypsum-salt stratum. The anomal temperatures in the upper and lower part of gypsum-salt stratum result in reducing the generation threshold depth and increasing the postmaturity threshold depth of source rocks, this can effectively expand the scope of hydrocarbon generation window. The relationship between reservoir porosity and its depth shows that the porosity of reservoir covered by gypsum-salt rock has 2～10 percent larger than that of normal sediment stratums, it firstly increases and then decreases with increasing depth, and the maximum porosity appears within a certain distance from gypsum-salt rock. Statistical results on the distribution of gypsum-salt rock and the height of hydrocarbon bearing strata show that most reservoirs in gypsum-salt area distribute below 0～50 meters thickness of gypsum-salt strata, only 50 meters thickness gypsum-salt strata could seal 500 meters height of hydrocarbon, and gypsum-salt layers plugging maximum oil height is to be significantly greater than that of gas. Gypsum-salt rock has strong plasticity, which is apt to form kinds of traps under sypsum-salt, inter sypsum-salt, upper sypsum-salt and at the edge of gypsum-salt. Under the similar structural conditions, the abnormal formation presssure under the thicker gypsum-salt rock is significantly greater than that at the edge of gypsum-salt rock, so the oil and gas is easier to be filled and preserved in the traps at the edge of gypsum-salt rock. Even there has oil and gas migrating towards gypsum-salt rocks, mostly will be affected by abnormal pressure at the edge of gypsum-salt rock and accumulated. The strong vertical packer role of gypsum-salt rock on oil and gas is conducive to its lateral migration in the sandbody below gypsum-salt layer. Synthetical analysis lead to that hydrocarbon in northern Dongpu depression shows ring or semi-ring shaped distribution around the thickness center of gypsum-salt layer. At the edge area of gypsum-salt rock not only has good source rock and good trap conditions, but also has proper hydrocarbon charging pathway and dynamics, so it becomes the most favourable area for oil and gas accumulation.
Dongpu depression is located in southeastern Bohai Bay Basin, five sets of gypsum-salt rock developed, and the maximum cumulative thickness can be up to 950 m. The lithologic variation of gypsum-salt layer can be divided into three zones including gypsum-salt zone, gypsum-salt and sand-mudstone transition zone, sand-mudstone zone. Exploration practice confirmed that gypsum-salt rock on hydrocarbon enrichment in vertical or in horizontal has an important controlling role, performing for nearly 93.7 % of oil and nearly 80% of gas in Dongpu depression distribution in the north part, and most oil and gas distributes among gypsum-salt layers. Controls of gypsum-salt rock on pool forming elements were systematically analyzed, and the results show that the source rock in gypsum-salt and sand-mudstone transition zone has the highest organic matter abundance because of its advantage for high quality source rock accumulation and preservation, the next is that in gypsum-salt zone, and that in sand-mudstone zone have relative lower organic matter abundance. Meanwhile, the farther source rock away from gypsum-salt rock, the lower organic matter abundance it has, and when the distance between source rock and gypsum-salt rock exceeds 30 or 40 meters, the influence on organic matter abundance by gypsum-salt rock decreases significantly. For high water salinity, many halophilic bacteria and algae adapted to high salt environments thrive and become a major source of sedimentary organic matter, which is conducive to the formation of sapropelic organic matter. For the gypsum-salt rock has high thermal conductivity and low heat generation rate, it can transmit ground temperature easily from deep stratum to shallow stratum, which could result in source rock in the upper part of gypsum-salt stratum has lower temperature gradient and abnormal high temperature than that of no gypsum-salt stratum, to the contrary, source rock in the lower part of gypsum-salt stratum has higher temperature gradient and abnormal low temperature than that of no gypsum-salt stratum. The anomal temperatures in the upper and lower part of gypsum-salt stratum result in reducing the generation threshold depth and increasing the postmaturity threshold depth of source rocks, this can effectively expand the scope of hydrocarbon generation window. The relationship between reservoir porosity and its depth shows that the porosity of reservoir covered by gypsum-salt rock has 2～10 percent larger than that of normal sediment stratums, it firstly increases and then decreases with increasing depth, and the maximum porosity appears within a certain distance from gypsum-salt rock. Statistical results on the distribution of gypsum-salt rock and the height of hydrocarbon bearing strata show that most reservoirs in gypsum-salt area distribute below 0～50 meters thickness of gypsum-salt strata, only 50 meters thickness gypsum-salt strata could seal 500 meters height of hydrocarbon, and gypsum-salt layers plugging maximum oil height is to be significantly greater than that of gas. Gypsum-salt rock has strong plasticity, which is apt to form kinds of traps under sypsum-salt, inter sypsum-salt, upper sypsum-salt and at the edge of gypsum-salt. Under the similar structural conditions, the abnormal formation presssure under the thicker gypsum-salt rock is significantly greater than that at the edge of gypsum-salt rock, so the oil and gas is easier to be filled and preserved in the traps at the edge of gypsum-salt rock. Even there has oil and gas migrating towards gypsum-salt rocks, mostly will be affected by abnormal pressure at the edge of gypsum-salt rock and accumulated. The strong vertical packer role of gypsum-salt rock on oil and gas is conducive to its lateral migration in the sandbody below gypsum-salt layer. Synthetical analysis lead to that hydrocarbon in northern Dongpu depression shows ring or semi-ring shaped distribution around the thickness center of gypsum-salt layer. At the edge area of gypsum-salt rock not only has good source rock and good trap conditions, but also has proper hydrocarbon charging pathway and dynamics, so it becomes the most favourable area for oil and gas accumulation.
2014, 32(1): 148-158.
Abstract:
Paleozoic clastic sedimentary strata of the Tarim Basin are important oil and gas exploration zones. Permian volcanic rocks are widely distributed in the Tarim Basin, and the abundant, long-term and multistage volcanicmagmatic activities can inevitably and strongly influence the underlying strata and oil and gas generating and storing conditions. However, this influence law is not clear. Based on 3-D seismic interpretation of Tazhong 47 well area, Gas Chromatography-Mass Spectrometry analysis of Silurian-Carboniferous oil sands, as well as detailed observation and thin section porosity evaluation of sandstone casting thin sections of three crucial wells in Tazhong 47 well area, this paper investigated the influence law of volcanic-magmatic activities on Paleozoic oil and gas generating and storing conditions from organic matter, reservoir and accumulation aspects. The results show that a large volcanic edifice was drilled by Well Tazhong 47. Permian volcanic-magmatic activities enhanced the maturity of organic matter in underlying sedimentary strata, boosted the dissolution of the calcareous cements in the reservoir by acidic fluid and promoted pore formation and the development of high quality reservoir. The improvement of reservoir properties can be notable with intenser volcanic activities influences and influence scope of reservoir improvement is within about 6km from the volcanic edifice. From volcanic edifice to outside, good reservoir, poor reservoir and reservoir of background are laterally distributed respectively. Reservoir evolution and integrated accumulation has some correspondence and correlation of Permian volcanic-magmatic activities, which can directly contribute to hydrocarbon migration and oil and gas reservoir forming and can be favorable for hydrocarbon accumulation.
Paleozoic clastic sedimentary strata of the Tarim Basin are important oil and gas exploration zones. Permian volcanic rocks are widely distributed in the Tarim Basin, and the abundant, long-term and multistage volcanicmagmatic activities can inevitably and strongly influence the underlying strata and oil and gas generating and storing conditions. However, this influence law is not clear. Based on 3-D seismic interpretation of Tazhong 47 well area, Gas Chromatography-Mass Spectrometry analysis of Silurian-Carboniferous oil sands, as well as detailed observation and thin section porosity evaluation of sandstone casting thin sections of three crucial wells in Tazhong 47 well area, this paper investigated the influence law of volcanic-magmatic activities on Paleozoic oil and gas generating and storing conditions from organic matter, reservoir and accumulation aspects. The results show that a large volcanic edifice was drilled by Well Tazhong 47. Permian volcanic-magmatic activities enhanced the maturity of organic matter in underlying sedimentary strata, boosted the dissolution of the calcareous cements in the reservoir by acidic fluid and promoted pore formation and the development of high quality reservoir. The improvement of reservoir properties can be notable with intenser volcanic activities influences and influence scope of reservoir improvement is within about 6km from the volcanic edifice. From volcanic edifice to outside, good reservoir, poor reservoir and reservoir of background are laterally distributed respectively. Reservoir evolution and integrated accumulation has some correspondence and correlation of Permian volcanic-magmatic activities, which can directly contribute to hydrocarbon migration and oil and gas reservoir forming and can be favorable for hydrocarbon accumulation.
2014, 32(1): 166-173.
Abstract:
Through geochemical analysis, physical analysis and mercury intrusion analysis of conventional shale core and sealing drilling shale core, combining with the production oil test, this paper discussed the oil-bearing property of Lucaogou Formation shale oil reservoirs in Malang sag. It also studied the accumulation mechanism of shale oil, and the characteristics favorable reservoir development and distribution. The results show that the oil-bearing property of Lucaogou Formation shale is under the control of the richness of organic matter and porosity of the shale reservoirs. The TOC (%) of the shale reservoirs enriched oil should be more than 4%, and the porosity should be more than 3%. Volume-oil-bearing rate (Po, %) can reflect the oil-bearing property of the shale reservoirs more accurate than the oil saturation. For shale reservoir enrichment in oil, the volume-oil-bearing rate should be more than 1%. Mercury injection data indicate that oil enrichment mechanism of shale reservoir is different from conventional sandstone reservoirs. Oil entering the shale reservoirs includes two processes, one is that hydrocarbon was stranded in source rock without migration, the other is that oil moved into poorsource rock system near high quality source rock by short distance primary migration. Beneficial lithologic association is the main influence factor for shale oil enrichment. The configuration relation of mudstone interbedded by argillaceous limestone, argillaceous dolomite or in calcareous mudstone and dolomitic mudstone is primarily the optimal lithologic association, and has the best oil-bearing property, which is deposited in sedimentary environment of deep lake and semi-deep lake.
Through geochemical analysis, physical analysis and mercury intrusion analysis of conventional shale core and sealing drilling shale core, combining with the production oil test, this paper discussed the oil-bearing property of Lucaogou Formation shale oil reservoirs in Malang sag. It also studied the accumulation mechanism of shale oil, and the characteristics favorable reservoir development and distribution. The results show that the oil-bearing property of Lucaogou Formation shale is under the control of the richness of organic matter and porosity of the shale reservoirs. The TOC (%) of the shale reservoirs enriched oil should be more than 4%, and the porosity should be more than 3%. Volume-oil-bearing rate (Po, %) can reflect the oil-bearing property of the shale reservoirs more accurate than the oil saturation. For shale reservoir enrichment in oil, the volume-oil-bearing rate should be more than 1%. Mercury injection data indicate that oil enrichment mechanism of shale reservoir is different from conventional sandstone reservoirs. Oil entering the shale reservoirs includes two processes, one is that hydrocarbon was stranded in source rock without migration, the other is that oil moved into poorsource rock system near high quality source rock by short distance primary migration. Beneficial lithologic association is the main influence factor for shale oil enrichment. The configuration relation of mudstone interbedded by argillaceous limestone, argillaceous dolomite or in calcareous mudstone and dolomitic mudstone is primarily the optimal lithologic association, and has the best oil-bearing property, which is deposited in sedimentary environment of deep lake and semi-deep lake.
2014, 32(1): 182-188.
Abstract:
The Pr/Ph ratio has been used widely as a significant biomarker. Except for the sources and palaeosedimentary environments, the Pr/Ph ratio is also affected by the maturity. In this paper, the terrestrial source rocks of different organic phases, taken from the western Pearl River Mouth Basin, were thermally simulated by the hydrocarbon generation-expulsion experiments and the soluble organic matters were obtained, then the tendency of the Pr/Ph ratio following the maturity was relatively systematically researched in the generated oils/extracts and the samples from strata. The results showed that, from Ro=0.6％ to Ro=1.8％, the Pr/Ph ratios in both the medium-deep (terrestrial kerogen of type Ⅱ) and the shallow lacustrine (terrestrial kerogen of type Ⅲ) source rocks were decreasing with the increase of maturity and the latter decreased more obviously than the former; However, the Pr/Ph ratios in the two source rocks were almost similar in high maturity phases. This research indicated that the effects of maturity on the Pr/Ph ratio should be considered in identifying palaeosedimentary environments and the correlations of oil-oil and oil-source rocks and it was necessary to combine with other geochemical parameters for the applications of the Pr/Ph ratio to the basins containing terrestrial Ⅲ source rocks.
The Pr/Ph ratio has been used widely as a significant biomarker. Except for the sources and palaeosedimentary environments, the Pr/Ph ratio is also affected by the maturity. In this paper, the terrestrial source rocks of different organic phases, taken from the western Pearl River Mouth Basin, were thermally simulated by the hydrocarbon generation-expulsion experiments and the soluble organic matters were obtained, then the tendency of the Pr/Ph ratio following the maturity was relatively systematically researched in the generated oils/extracts and the samples from strata. The results showed that, from Ro=0.6％ to Ro=1.8％, the Pr/Ph ratios in both the medium-deep (terrestrial kerogen of type Ⅱ) and the shallow lacustrine (terrestrial kerogen of type Ⅲ) source rocks were decreasing with the increase of maturity and the latter decreased more obviously than the former; However, the Pr/Ph ratios in the two source rocks were almost similar in high maturity phases. This research indicated that the effects of maturity on the Pr/Ph ratio should be considered in identifying palaeosedimentary environments and the correlations of oil-oil and oil-source rocks and it was necessary to combine with other geochemical parameters for the applications of the Pr/Ph ratio to the basins containing terrestrial Ⅲ source rocks.
2014, 32(1): 8-18.
Abstract:
During the Late Katian-Hirnantian Age of Late Ordovician, it were deposited Wufeng and Guanyinqiao Formations in the Northwestern Hunan, Wufeng Formation in the central Hunan, Tianmashan and Sushuichong formations in the southern Hunan. According to the lithological characters, sedimentary structures and paleontological features, Hunan can be divided into restricted shallow marine facies, tidal-flat facies, deep-water basin facies and shelf-margin-slope facies. In the Late-Katian, As a result of the continuous extrusion and collision between Yangtze and Cathaysia blocks, the area of the central Sichuan and central Guizhou uplifts gradually increased and the sea level relatively rise, the northwestern Hunan were changed into restricted shallow marine with black carbonaceous, siliceous shales and marlstones surrounded by ancient uplifts, the central Hunan was a deep-water basin with black carbonaceous, siliceous and sility shales, whereas the southern Hunan deposited the interbeds of sandstones and shales in the shelf-margin-slope facies. In the Hirnantian age of Late Ordovician, as the global glacier event occurred, large scale of retrogression had begun in the south area, the north area of the Yongshun-Zhangjiajie-Cili line were lifted to be Hunan-Hubei uplift, and the south of the front line deposited marlstones with more than 10 centimeters in thickness, but the depositional pattern of southern and central Hunan did not change.
During the Late Katian-Hirnantian Age of Late Ordovician, it were deposited Wufeng and Guanyinqiao Formations in the Northwestern Hunan, Wufeng Formation in the central Hunan, Tianmashan and Sushuichong formations in the southern Hunan. According to the lithological characters, sedimentary structures and paleontological features, Hunan can be divided into restricted shallow marine facies, tidal-flat facies, deep-water basin facies and shelf-margin-slope facies. In the Late-Katian, As a result of the continuous extrusion and collision between Yangtze and Cathaysia blocks, the area of the central Sichuan and central Guizhou uplifts gradually increased and the sea level relatively rise, the northwestern Hunan were changed into restricted shallow marine with black carbonaceous, siliceous shales and marlstones surrounded by ancient uplifts, the central Hunan was a deep-water basin with black carbonaceous, siliceous and sility shales, whereas the southern Hunan deposited the interbeds of sandstones and shales in the shelf-margin-slope facies. In the Hirnantian age of Late Ordovician, as the global glacier event occurred, large scale of retrogression had begun in the south area, the north area of the Yongshun-Zhangjiajie-Cili line were lifted to be Hunan-Hubei uplift, and the south of the front line deposited marlstones with more than 10 centimeters in thickness, but the depositional pattern of southern and central Hunan did not change.
2014, 32(1): 27-35.
Abstract:
Suoxian and Baqing county are located in the south side of Tangula mountain and belong to the Qiangtang stratigraphic area. However, Liuwan Formation of Suoxian and Buqu Formation of Baqing are especially characterized by a lot of organic reefs. Reef-building organisms are chiefly hexacorals Schizosmilia, Stromatoproids Parastromatopora and Bivalve Liostrea. The reef-building organisms mentioned above are majority preserved at the original growth state, which all require warm, clean and normal shallow water environment with abundant light and better circulation. Through the study of individual ecology and analysis of assembled of reef-building organisms, five reef-building communities are recognized, namely Schizosmilia-Parastromatopor，Parastromatopora， Schizosmilia，Liostrea and Cyanobacteria-Liostrea community. Among these five reef-building communities，First three communities formed reef-building community evolutionary sequence of Suoxian county area, while, Liostrea and Cyanobacteria-Liostrea community made up reef-building community evolutionary sequence of Baqing county area. Community evolution research indicates that it exists two kinds of community evolution in the studying areas, the first one is community succession that mainly developed in reefs of Liuwan Formation at Suoxian county, the second one is community replacement that developed in reefs of Buqu Formation in Baqing county. The developing characteristic of biological-baffling. Among these three reef-building, frame-making, baffling are developed in reefs of Liuwan Formation at Suoxian county, baffling and bind-baffling are seen in reefs of Buqu Formation in Baqing county. The authors hold that the existenc of reef communities is of great significance for further study of merging time of Bangongcuo-Nujiang River suture zone. The authors consider that oceanic crust subduction time of middle-east Bangongcuo-Nujiang River suture zone(ie. Suoxian and Baqing county region) should be in early age of Middle Jurassic or before the deposition of Liuwan Formation of Middle Jurassic. The existence of reef communities of Middle Jurassic showed that the study area may belong to a part of shallow continental shelf of the remaining back-arc basin after Bangongcuo-Nujiang River oceanic crust subduction.
Suoxian and Baqing county are located in the south side of Tangula mountain and belong to the Qiangtang stratigraphic area. However, Liuwan Formation of Suoxian and Buqu Formation of Baqing are especially characterized by a lot of organic reefs. Reef-building organisms are chiefly hexacorals Schizosmilia, Stromatoproids Parastromatopora and Bivalve Liostrea. The reef-building organisms mentioned above are majority preserved at the original growth state, which all require warm, clean and normal shallow water environment with abundant light and better circulation. Through the study of individual ecology and analysis of assembled of reef-building organisms, five reef-building communities are recognized, namely Schizosmilia-Parastromatopor，Parastromatopora， Schizosmilia，Liostrea and Cyanobacteria-Liostrea community. Among these five reef-building communities，First three communities formed reef-building community evolutionary sequence of Suoxian county area, while, Liostrea and Cyanobacteria-Liostrea community made up reef-building community evolutionary sequence of Baqing county area. Community evolution research indicates that it exists two kinds of community evolution in the studying areas, the first one is community succession that mainly developed in reefs of Liuwan Formation at Suoxian county, the second one is community replacement that developed in reefs of Buqu Formation in Baqing county. The developing characteristic of biological-baffling. Among these three reef-building, frame-making, baffling are developed in reefs of Liuwan Formation at Suoxian county, baffling and bind-baffling are seen in reefs of Buqu Formation in Baqing county. The authors hold that the existenc of reef communities is of great significance for further study of merging time of Bangongcuo-Nujiang River suture zone. The authors consider that oceanic crust subduction time of middle-east Bangongcuo-Nujiang River suture zone(ie. Suoxian and Baqing county region) should be in early age of Middle Jurassic or before the deposition of Liuwan Formation of Middle Jurassic. The existence of reef communities of Middle Jurassic showed that the study area may belong to a part of shallow continental shelf of the remaining back-arc basin after Bangongcuo-Nujiang River oceanic crust subduction.
2014, 32(1): 44-60.
Abstract:
Through comprehensive analysis of various outcrops, drilling and seismic sequence stratigraphy, Ordovician sequence stratigraphic framework in Ordos Basin has been established. In view of poor quality of Ordovician seismic data in the basin, a set of suitable sequence stratigraphic analysis method is very necessary. So,we meticulously researched Ordovician sequence stratigraphy of Ordos Basin in the eleventh five-year plan, and put forword "the five elements analysis method of carbonate strata sequence stratigraphic classification and correlation". Using the analysis method, 3 secondary sequence interface and 6 tertiary sequence interface have been identified in the Ordovician, and the Ordovician can be divided into 2 secondary sequences and 8 tertiary sequences. OMsq1 including Osq1 (equivalent to Yeli Group), Osq2 (equivalent to Liangjiashan Group), Osq3 (LST: equivalent to Majiagou 1 Formation；TST: equivalent to Majiagou 2 Formation；HST: equivalent to Majiagou 3 Formation), Osq4 (TST: equivalent to Majiagou 4 Formation；HST: equivalent to Majiagou 5 Formation) and Osq5 (equivalent to Majiagou 6 Formation /Kelimoli Group)；OMsq2 including Osq6 (equivalent to lower Pingliang Group/Wulalike Group + Lower Lashizhong Group), Osq7 (equivalent to Upper Pingliang Group/Upper Lashizhong Group + Gongwusu Group) and Osq8 (equivalent to Baiguoshan Group). Different basin tectonic environment formed different sequence stratigraphic framework. Ordovician of the northern portion of western narrow continental margin in the basin can be divided into Osq3-Osq7 of sequence stratigraphy of which geologic time is from the Floian of Early Ordovician to the Sandbian of Late Ordovician. Ordovician of the southern portion of western narrow continental margin in the basin can be divided into Osq1-Osq7 of sequence stratigraphy of which geologic time is from the Tremadocian of Early Ordovician to the Sandbian of Late Ordovician, The sequence stratigraphy's thickness is 0~1 600 m which exhibit a bolt in shape extend in a north-south ward direction on the norrow edge which is sloped gently toward west and overlapping and pinching out to Yimen-Qingyang Ancient Uplift . In the southern wide continental margin of the basin, we have discoved eight sequence stratigraphy in Ordovician of which geologic time is from the Floian of Early Ordovician to the Early Katian of Late Ordovician. The sequence stratigraphy's thickness is 0~1 800 m which exhibit a bolt in shape extend in a west-east ward direction on the wide edge which is sloped gently toward south and overlapping and pinching out to Qingyang Ancient Uplift. In the eastern platform inner sag of the middle-eastern Ordos Basin, we only divided Ordovician into three sequence stratigraphies (Osq 3-Osq5 TST) which thickness is 800m in the east of the depression and overlapping and pinching out to Qingyang Ancient Uplift. Northem Yimeng Ancient Uplift and Qingyang Ancient Uplift have been uplifted in eroding state, which developed the only Osq4 TST ,and show that the Qilian Sea in western Ordos Basin and the North China Sea in Eastern Ordos Basin have been fleetingly connected in the late of Middle Ordovician.
Through comprehensive analysis of various outcrops, drilling and seismic sequence stratigraphy, Ordovician sequence stratigraphic framework in Ordos Basin has been established. In view of poor quality of Ordovician seismic data in the basin, a set of suitable sequence stratigraphic analysis method is very necessary. So,we meticulously researched Ordovician sequence stratigraphy of Ordos Basin in the eleventh five-year plan, and put forword "the five elements analysis method of carbonate strata sequence stratigraphic classification and correlation". Using the analysis method, 3 secondary sequence interface and 6 tertiary sequence interface have been identified in the Ordovician, and the Ordovician can be divided into 2 secondary sequences and 8 tertiary sequences. OMsq1 including Osq1 (equivalent to Yeli Group), Osq2 (equivalent to Liangjiashan Group), Osq3 (LST: equivalent to Majiagou 1 Formation；TST: equivalent to Majiagou 2 Formation；HST: equivalent to Majiagou 3 Formation), Osq4 (TST: equivalent to Majiagou 4 Formation；HST: equivalent to Majiagou 5 Formation) and Osq5 (equivalent to Majiagou 6 Formation /Kelimoli Group)；OMsq2 including Osq6 (equivalent to lower Pingliang Group/Wulalike Group + Lower Lashizhong Group), Osq7 (equivalent to Upper Pingliang Group/Upper Lashizhong Group + Gongwusu Group) and Osq8 (equivalent to Baiguoshan Group). Different basin tectonic environment formed different sequence stratigraphic framework. Ordovician of the northern portion of western narrow continental margin in the basin can be divided into Osq3-Osq7 of sequence stratigraphy of which geologic time is from the Floian of Early Ordovician to the Sandbian of Late Ordovician. Ordovician of the southern portion of western narrow continental margin in the basin can be divided into Osq1-Osq7 of sequence stratigraphy of which geologic time is from the Tremadocian of Early Ordovician to the Sandbian of Late Ordovician, The sequence stratigraphy's thickness is 0~1 600 m which exhibit a bolt in shape extend in a north-south ward direction on the norrow edge which is sloped gently toward west and overlapping and pinching out to Yimen-Qingyang Ancient Uplift . In the southern wide continental margin of the basin, we have discoved eight sequence stratigraphy in Ordovician of which geologic time is from the Floian of Early Ordovician to the Early Katian of Late Ordovician. The sequence stratigraphy's thickness is 0~1 800 m which exhibit a bolt in shape extend in a west-east ward direction on the wide edge which is sloped gently toward south and overlapping and pinching out to Qingyang Ancient Uplift. In the eastern platform inner sag of the middle-eastern Ordos Basin, we only divided Ordovician into three sequence stratigraphies (Osq 3-Osq5 TST) which thickness is 800m in the east of the depression and overlapping and pinching out to Qingyang Ancient Uplift. Northem Yimeng Ancient Uplift and Qingyang Ancient Uplift have been uplifted in eroding state, which developed the only Osq4 TST ,and show that the Qilian Sea in western Ordos Basin and the North China Sea in Eastern Ordos Basin have been fleetingly connected in the late of Middle Ordovician.
2014, 32(1): 68-77.
Abstract:
It established an analytical method to elucidate the relationship between sediment sources and tectonic evolution by the analyses on heavy minerals type and their assemblages and the characteristics of sandstone detrital component in Kuqa foreland basin, it shows the relationship of response to tectonic movement on the characteristics of heavy mineral assemblage. Meanwhile, it also shows that there are five periods tectogenesis during Triassic-Neogene, that are Middle-Late Triassic, Late Jurassic-Early Cretaceous, Late Cretaceous, Paleogene and Miocene. Different heavy minerals assemblages and increasing of unstable heavy minerals during Late Jurassic-Early Cretaceous, Late Cretaceous and Miocene might indicate tectonic activity during these three periods. By analyzing the color, content and their assemblages characteristics of the heavy mineral and sandstone detrital composition of the Kuqa foreland basin, there mainly existed three provenance channel that is the Tuzi-Dina, Dabei and Kela sediment sources areas in the northern piedmont zone of Kuqa depression and one that is the Quele sediment sources areas in the Wensu uplift. The Triassic-Neogene tectonic activities and evolution of the basin-orogen pattern in the Kuqa basin should be related to the heavy minerals' assemblages characteristics.
It established an analytical method to elucidate the relationship between sediment sources and tectonic evolution by the analyses on heavy minerals type and their assemblages and the characteristics of sandstone detrital component in Kuqa foreland basin, it shows the relationship of response to tectonic movement on the characteristics of heavy mineral assemblage. Meanwhile, it also shows that there are five periods tectogenesis during Triassic-Neogene, that are Middle-Late Triassic, Late Jurassic-Early Cretaceous, Late Cretaceous, Paleogene and Miocene. Different heavy minerals assemblages and increasing of unstable heavy minerals during Late Jurassic-Early Cretaceous, Late Cretaceous and Miocene might indicate tectonic activity during these three periods. By analyzing the color, content and their assemblages characteristics of the heavy mineral and sandstone detrital composition of the Kuqa foreland basin, there mainly existed three provenance channel that is the Tuzi-Dina, Dabei and Kela sediment sources areas in the northern piedmont zone of Kuqa depression and one that is the Quele sediment sources areas in the Wensu uplift. The Triassic-Neogene tectonic activities and evolution of the basin-orogen pattern in the Kuqa basin should be related to the heavy minerals' assemblages characteristics.
2014, 32(1): 85-92.
Abstract:
Qaidam Basin develops nearly continuous, integrative and ultra-thick Quaternary sediment sequences. Saline lake deposits are the product of the physic-geographical and geological environments. This paper discussed the sedimentary characteristics of Gasikule Salt Lake where located in the northwestern margin of Qaidam Basin. Brine in the lake belong to magnesium sulphate subtype and halite was the mainly chemical sedimentation. From the studies on cores from 6 boreholes which distributed in the east playa area by the on-the-spot documentation and indoor studies，the lithological features, salinization periods，sedimentary type，sedimentary structure and sedimentary amplitude have been studied. The research work will be of great importance to study the evolution process of Qaidam basin and Gasikule Salt Lake. The results revealed that the sedimentary sequences of silt-bearing medium and coarse halite and silt-bearing mud and clay were the main lithological features and sedimentary rhythm changes frequently in Gasikule Salt Lake. The overall trend is that detrital sediment ratio gradually increased from top to bottom，and evaporate salt layer decreased in boreholes. Sedimentary characteristics showed obvious difference in the non-salinization phase and salinization phase. These represent two different sedimentary environments, and also indicate the result of long-term salt lake evolution with gradually becoming dry climate conditions. The sedimentary types can be divided into three kinds of silt clastic sediments, clay and silt deposition, and evaporates of epsomite gypsum halite respectively. The detrital sediments in Gasikule Salt Lake district showed relatively simple in lithologic features with mainly silt sandstone distributed in the upper portion of the core. Clay and mud-bearing sediments were widespread in the middle-lower portion of the core and mostly occurred in interstratified layers with evaporate deposition. But evaporate deposition was widely distributed at the top of each boreholes. The evaporite deposition was mainly halite while gypsum and epsomite were occurred as associated component in sedimentation sequence in Gasikule Salt Lake area. Therefore, there exist not obvious variations between evaporite layer and clay-silt layers. The sedimentary amplitude of Gasikure Salt Lake was completely consistent with geosynclines-polycyclic sedimentary characteristics in western Qaidam basin. According to the salt lake sedimentary amplitude and duration of salinization time, the salinization deposition period had been divided into seven stage of saline deposition and seven relative humid epoch since Late Pleistocene. Average deposition rate in each period of saline sedimentation had little variation and retained in around 2.5mm/a. It is thus evident that Gasikule Salt Lake deposition rate on average is about 5 times than that of Xinjiang region, and 2.5 times of Inner Mongolia region. The difference of the deposition rate may be contributed by the dry climate and desertification in Western Qaidam Basin than that of in Inner Mongolia and Xinjiang region since Late Pleistocene.
Qaidam Basin develops nearly continuous, integrative and ultra-thick Quaternary sediment sequences. Saline lake deposits are the product of the physic-geographical and geological environments. This paper discussed the sedimentary characteristics of Gasikule Salt Lake where located in the northwestern margin of Qaidam Basin. Brine in the lake belong to magnesium sulphate subtype and halite was the mainly chemical sedimentation. From the studies on cores from 6 boreholes which distributed in the east playa area by the on-the-spot documentation and indoor studies，the lithological features, salinization periods，sedimentary type，sedimentary structure and sedimentary amplitude have been studied. The research work will be of great importance to study the evolution process of Qaidam basin and Gasikule Salt Lake. The results revealed that the sedimentary sequences of silt-bearing medium and coarse halite and silt-bearing mud and clay were the main lithological features and sedimentary rhythm changes frequently in Gasikule Salt Lake. The overall trend is that detrital sediment ratio gradually increased from top to bottom，and evaporate salt layer decreased in boreholes. Sedimentary characteristics showed obvious difference in the non-salinization phase and salinization phase. These represent two different sedimentary environments, and also indicate the result of long-term salt lake evolution with gradually becoming dry climate conditions. The sedimentary types can be divided into three kinds of silt clastic sediments, clay and silt deposition, and evaporates of epsomite gypsum halite respectively. The detrital sediments in Gasikule Salt Lake district showed relatively simple in lithologic features with mainly silt sandstone distributed in the upper portion of the core. Clay and mud-bearing sediments were widespread in the middle-lower portion of the core and mostly occurred in interstratified layers with evaporate deposition. But evaporate deposition was widely distributed at the top of each boreholes. The evaporite deposition was mainly halite while gypsum and epsomite were occurred as associated component in sedimentation sequence in Gasikule Salt Lake area. Therefore, there exist not obvious variations between evaporite layer and clay-silt layers. The sedimentary amplitude of Gasikure Salt Lake was completely consistent with geosynclines-polycyclic sedimentary characteristics in western Qaidam basin. According to the salt lake sedimentary amplitude and duration of salinization time, the salinization deposition period had been divided into seven stage of saline deposition and seven relative humid epoch since Late Pleistocene. Average deposition rate in each period of saline sedimentation had little variation and retained in around 2.5mm/a. It is thus evident that Gasikule Salt Lake deposition rate on average is about 5 times than that of Xinjiang region, and 2.5 times of Inner Mongolia region. The difference of the deposition rate may be contributed by the dry climate and desertification in Western Qaidam Basin than that of in Inner Mongolia and Xinjiang region since Late Pleistocene.
2014, 32(1): 101-109.
Abstract:
It is significant for using China inland basins deposition to obtain the Cenozoic continental climate change records that we appropriately acquire paleoenvironmental proxies and examining their validity for a long-term scale. Water dissolved salts, as a paleoenvironmental proxy, has widely applied to the field of inland lake sediments with stable sedimentation. However, it is required to examine when this proxy has been used to the lake sediments with significant sedimentary facies alternation. In this study, we focus on a set of strata of inland lake sediments consisting of mudstones/gypsum alternations in Xiejia section, Xining Basin, age ranging from Eocene to Miocene. The investigation of water dissolved salts in Xiejia Section sediments shows the strong control of lithology alternations on variations of water dissolved salts concentrations. Specifically, the gypsum and mudstone layers correspond to the high/low concentrations of Ca2+, SO2-4 and Sr2+, respectively. The lower part of this section sediments with widely spread gypsum layers has low concentrations of Na+ and Cl- and high concentrations of Ca 2+, SO2-4 and Sr2+ ; The upper part of this section sediments lack of gypsum layers has slight high concentrations of Na+ and Cl- and low concentrations of Ca2+, SO2-4 and Sr2+. Based on the sedimentary facies analysis, the gypsum and red mudstones layers are corresponding to shallow playa lake and distal alluvial fan, respectively. The evolution from distal alluvial fan and shallow playa lake alternations in the lower part of this section to distal alluvial fan in the upper part indicates a regional aridification process. The water dissolved salts in Xiejia section, strongly controlled by sedimentary facies alternations, clearly indicate a dry trend occurred at about 33 Ma. Hence, for the inland lake sediments with significant sedimentary facies alternations, not only the solubility limit control on the carbonate-sulfate-halide sequences in the d inland lake water, but the differences of water dissolved salts occurrence and activity between different sedimentary environment, of solute types provided by the source area, should be taken into account.
It is significant for using China inland basins deposition to obtain the Cenozoic continental climate change records that we appropriately acquire paleoenvironmental proxies and examining their validity for a long-term scale. Water dissolved salts, as a paleoenvironmental proxy, has widely applied to the field of inland lake sediments with stable sedimentation. However, it is required to examine when this proxy has been used to the lake sediments with significant sedimentary facies alternation. In this study, we focus on a set of strata of inland lake sediments consisting of mudstones/gypsum alternations in Xiejia section, Xining Basin, age ranging from Eocene to Miocene. The investigation of water dissolved salts in Xiejia Section sediments shows the strong control of lithology alternations on variations of water dissolved salts concentrations. Specifically, the gypsum and mudstone layers correspond to the high/low concentrations of Ca2+, SO2-4 and Sr2+, respectively. The lower part of this section sediments with widely spread gypsum layers has low concentrations of Na+ and Cl- and high concentrations of Ca 2+, SO2-4 and Sr2+ ; The upper part of this section sediments lack of gypsum layers has slight high concentrations of Na+ and Cl- and low concentrations of Ca2+, SO2-4 and Sr2+. Based on the sedimentary facies analysis, the gypsum and red mudstones layers are corresponding to shallow playa lake and distal alluvial fan, respectively. The evolution from distal alluvial fan and shallow playa lake alternations in the lower part of this section to distal alluvial fan in the upper part indicates a regional aridification process. The water dissolved salts in Xiejia section, strongly controlled by sedimentary facies alternations, clearly indicate a dry trend occurred at about 33 Ma. Hence, for the inland lake sediments with significant sedimentary facies alternations, not only the solubility limit control on the carbonate-sulfate-halide sequences in the d inland lake water, but the differences of water dissolved salts occurrence and activity between different sedimentary environment, of solute types provided by the source area, should be taken into account.
2014, 32(1): 118-125.
Abstract:
The dolomite of Carboniferous in Baizuo Formation in Huize, Yunnan was studied by several methods such as petrological analysis, geochemistry analysis and isotope, in order to understand its geochemical characteristics and genesis. The study area is located in central Yunnan (Kunming) Mesozoic uplift zone, which belongs to the Yangtze micro-continent of the South China block group. The dolomite rock is mainly characterized by colors in gray-white gray, flesh red, beige, and coarse-grained dolomite, and it has the subhedral-euhedral structure. The analysis based on MgO—CaO indicates that the formation of the dolomite is due to the accountable or recrystallization, and is not due to the sedimentation. The trace elements analysis shows that the content of Sr in the dolomite rock is low. It indicates that the dolomite may be formed in post-burial genesis and the time of dolomitization is late,Therefore, Sr had been an abundant loss, consequently, the Sr/Ba ratio is relatively high.The result indicates that the medium of water is high in salinity when the dolomite is under diagenesis in deep burial. The distribution pattern of rare earth elements shows a negative anomaly of Ce and Eu. Ce3+ ions is negative anomaly because Ce3+ was oxidized to the soluble Ce4+ ions. Eu is negative anomaly because it was brought out in priority in the chemical weathering process. According to the carbon and oxygen isotope, a relatively higher salinity index(121～125) and diagenetic temperature (52.40℃～69.44℃) were observed. It indicates that the illumincited dolostones were formed under the high concentrated salinity and high temperature. We inferred that the dolomite in the region was in deep burial environment. According to the report of the regional stratigraphy investigation and regional tectonic evolution, We speculated that the time of the dolomitization may occur in the Permian, and it should belong to the epigenetic dolomite. We concluded that the dolomite in Huizhe was formed under deep burial conditions. Due to the structure function and the influence of the earth's crust uplift, the Baizuo Formation was raised to the earth surface and the dolomite in this formation experienced the chemical weathering,then created the negative anomalies of Eu. This may be related to the tensile and vertical lifting movements of Indo-China-Hercynian stage in the Northeast Yunnan.
The dolomite of Carboniferous in Baizuo Formation in Huize, Yunnan was studied by several methods such as petrological analysis, geochemistry analysis and isotope, in order to understand its geochemical characteristics and genesis. The study area is located in central Yunnan (Kunming) Mesozoic uplift zone, which belongs to the Yangtze micro-continent of the South China block group. The dolomite rock is mainly characterized by colors in gray-white gray, flesh red, beige, and coarse-grained dolomite, and it has the subhedral-euhedral structure. The analysis based on MgO—CaO indicates that the formation of the dolomite is due to the accountable or recrystallization, and is not due to the sedimentation. The trace elements analysis shows that the content of Sr in the dolomite rock is low. It indicates that the dolomite may be formed in post-burial genesis and the time of dolomitization is late,Therefore, Sr had been an abundant loss, consequently, the Sr/Ba ratio is relatively high.The result indicates that the medium of water is high in salinity when the dolomite is under diagenesis in deep burial. The distribution pattern of rare earth elements shows a negative anomaly of Ce and Eu. Ce3+ ions is negative anomaly because Ce3+ was oxidized to the soluble Ce4+ ions. Eu is negative anomaly because it was brought out in priority in the chemical weathering process. According to the carbon and oxygen isotope, a relatively higher salinity index(121～125) and diagenetic temperature (52.40℃～69.44℃) were observed. It indicates that the illumincited dolostones were formed under the high concentrated salinity and high temperature. We inferred that the dolomite in the region was in deep burial environment. According to the report of the regional stratigraphy investigation and regional tectonic evolution, We speculated that the time of the dolomitization may occur in the Permian, and it should belong to the epigenetic dolomite. We concluded that the dolomite in Huizhe was formed under deep burial conditions. Due to the structure function and the influence of the earth's crust uplift, the Baizuo Formation was raised to the earth surface and the dolomite in this formation experienced the chemical weathering,then created the negative anomalies of Eu. This may be related to the tensile and vertical lifting movements of Indo-China-Hercynian stage in the Northeast Yunnan.
2014, 32(1): 138-147.
Abstract:
A large number of secondary porosity due to quartz overgrowths dissolution, at the top of the Lower Sandstone the bituminous sandstone near the unconformity in Kepingtag Formation, in the Silurian marine clastic reservoirs in the central of Tarim Basin. By microscopic and SEM observation, dissolutions of SiO2 of sandstone reservoirs can be divided into 3 types, in which the reservoir constructive roles include quartz siliceous particles edge of dissolution and overgrowths dissolution, while carbonate replacement of quartz and silicon has little constructive. The path of the SiO2 dissolution path can be divided into the alkaline environment and acidic environment, statistics show that SiO2 dissolution generally in the alkaline environment of development, but the low level, dissolved in the acidic environment of the type of organic acids, the number of fluid properties, dissolved in fluid ability, as well as the formation temperature requirements are more demanding. Quartz dissolution under acidic fluid medium conditions in the study is the ancient reservoirs destruction process by microbial degradation of hydrocarbons releasing large amounts of oxalic acid plays a major role, because it reduces the surface of the quartz grains activation energy of the dissolving reaction, and formation water alkali metal ion salt effect role, which greatly improve the dissolution rate of SiO2 lysate spread into the ground water was taken away, resulting in a strong quartz dissolution phenomena, research also shows that the dissolution degree of strong but has a strong limitations. Dissolution of SiO2(solution) role is to provide a certain amount of space for oil and gas, and important significance to the deep clastic rocks in the Tarim Basin.
A large number of secondary porosity due to quartz overgrowths dissolution, at the top of the Lower Sandstone the bituminous sandstone near the unconformity in Kepingtag Formation, in the Silurian marine clastic reservoirs in the central of Tarim Basin. By microscopic and SEM observation, dissolutions of SiO2 of sandstone reservoirs can be divided into 3 types, in which the reservoir constructive roles include quartz siliceous particles edge of dissolution and overgrowths dissolution, while carbonate replacement of quartz and silicon has little constructive. The path of the SiO2 dissolution path can be divided into the alkaline environment and acidic environment, statistics show that SiO2 dissolution generally in the alkaline environment of development, but the low level, dissolved in the acidic environment of the type of organic acids, the number of fluid properties, dissolved in fluid ability, as well as the formation temperature requirements are more demanding. Quartz dissolution under acidic fluid medium conditions in the study is the ancient reservoirs destruction process by microbial degradation of hydrocarbons releasing large amounts of oxalic acid plays a major role, because it reduces the surface of the quartz grains activation energy of the dissolving reaction, and formation water alkali metal ion salt effect role, which greatly improve the dissolution rate of SiO2 lysate spread into the ground water was taken away, resulting in a strong quartz dissolution phenomena, research also shows that the dissolution degree of strong but has a strong limitations. Dissolution of SiO2(solution) role is to provide a certain amount of space for oil and gas, and important significance to the deep clastic rocks in the Tarim Basin.
2014, 32(1): 159-165.
Abstract:
On the basis of clay mineral X-ray diffraction analysis and trace element analysis, the lake basin paleosalinity of the deposition of Chang 9 reservoir in Longdong area, Ordos Basin has been recovered according to Couch formula and Adams formula. We discover that they are affected by diagenesis, the value of the paleosalinity which calculate by the Couch formula is lower than the actual value, and Adams formula calculation results reflect the nature of the ancient body of water salinity is more reliable. Studies have shown that, the lake water of Ordos Basin is brackish during the Chang 9 deposition period. Paleosalinity was gradually increased from northeast, northwest and southwest to the central lake basin. The salinity of the late Chang 9 deposition period is lower than the early that reflect the transgressive lake level rise. The salinity high value area was relatively isolated bays or lake centers which belongs half deep lake. The paleosalinity gradually decrease from the lake center to the river estuary direction. The variation of paleosalinity provides a foundation for restoring the ancient geography. The reservoir is closely to lake water salinity, and high salinity water is conducive to the formation of early diagenetic stage chlorite ring edge cement and laumontite. The chlorite ring edge cement formatted in early diagenetic stage is favourable for intergranular porosity preservation. The laumontite is more likely to be dissolved and formed abundant secondary dissolved pores.
On the basis of clay mineral X-ray diffraction analysis and trace element analysis, the lake basin paleosalinity of the deposition of Chang 9 reservoir in Longdong area, Ordos Basin has been recovered according to Couch formula and Adams formula. We discover that they are affected by diagenesis, the value of the paleosalinity which calculate by the Couch formula is lower than the actual value, and Adams formula calculation results reflect the nature of the ancient body of water salinity is more reliable. Studies have shown that, the lake water of Ordos Basin is brackish during the Chang 9 deposition period. Paleosalinity was gradually increased from northeast, northwest and southwest to the central lake basin. The salinity of the late Chang 9 deposition period is lower than the early that reflect the transgressive lake level rise. The salinity high value area was relatively isolated bays or lake centers which belongs half deep lake. The paleosalinity gradually decrease from the lake center to the river estuary direction. The variation of paleosalinity provides a foundation for restoring the ancient geography. The reservoir is closely to lake water salinity, and high salinity water is conducive to the formation of early diagenetic stage chlorite ring edge cement and laumontite. The chlorite ring edge cement formatted in early diagenetic stage is favourable for intergranular porosity preservation. The laumontite is more likely to be dissolved and formed abundant secondary dissolved pores.
2014, 32(1): 174-181.
Abstract:
Research indicates that focus merely on the organic carbon content can not meet exploration needs because the characteristics of the shale formation. The most important issue of the exploration is to evaluate the free hydrocarbon content in shale formation. The relationship between porosity and oil volume in per cubic meter of rock and the relationship between porosity and water volume in per cubic meter of rock have been studied. The result shows that in the oil source rock, the characteristics of oil-bearing is increasing with the increasing of rock porosity. On basis of the analysis of closed cored laboratory data such as the porosity and oil saturation in Shengli Oil field, an new evaluation model is constructed to reflect the free hydrocarbon content. And the logging interpretation model has also been established by using the deep resistivity curve response value, porosity and the organic matter maturity to calculate it. The ratio of organic carbon content from free hydrocarbon and total organic carbon content can directly reflect the vertical variation regulation of the free hydrocarbon content, which also indicates the favorable oil and gas exploration section. An example from Luojia area in Zhanhua sag has been reprocessed . A new model of the organic matter maturity was derived based on the experimental data and the depth. The calculating result shows a good application of this method. The indicator of free hydrocarbon enrichment zone can be derived by combining two parameter. One is the absolute value of organic carbon from free hydrocarbon, the other is the value between absolute value of organic carbon content from free hydrocarbon and the total organic carbon content. The section with high ratio will be the exploration targets of shale oil reservoir. This idea can provide reference for today’s shale oil and gas exploration.
Research indicates that focus merely on the organic carbon content can not meet exploration needs because the characteristics of the shale formation. The most important issue of the exploration is to evaluate the free hydrocarbon content in shale formation. The relationship between porosity and oil volume in per cubic meter of rock and the relationship between porosity and water volume in per cubic meter of rock have been studied. The result shows that in the oil source rock, the characteristics of oil-bearing is increasing with the increasing of rock porosity. On basis of the analysis of closed cored laboratory data such as the porosity and oil saturation in Shengli Oil field, an new evaluation model is constructed to reflect the free hydrocarbon content. And the logging interpretation model has also been established by using the deep resistivity curve response value, porosity and the organic matter maturity to calculate it. The ratio of organic carbon content from free hydrocarbon and total organic carbon content can directly reflect the vertical variation regulation of the free hydrocarbon content, which also indicates the favorable oil and gas exploration section. An example from Luojia area in Zhanhua sag has been reprocessed . A new model of the organic matter maturity was derived based on the experimental data and the depth. The calculating result shows a good application of this method. The indicator of free hydrocarbon enrichment zone can be derived by combining two parameter. One is the absolute value of organic carbon from free hydrocarbon, the other is the value between absolute value of organic carbon content from free hydrocarbon and the total organic carbon content. The section with high ratio will be the exploration targets of shale oil reservoir. This idea can provide reference for today’s shale oil and gas exploration.
