2017 Vol. 35, No. 4
Display Method:
2017, 35(4): 649-663.
doi: 10.14027/j.cnki.cjxb.2017.04.001
Abstract:
The red beds of late Cretaceous are widely and sporadically distributed in the western Qinling Mts. At late Cretaceous, the tectono-geomorphological features in the area are critical in elucidating the structural and geomorphological situation at the end of Mesozoic and determining the beginning time of the uplifting of the northeastern Qinghai-Tibet Plateau. That is, the red beds deposited in the independent intermontane basins or unified flat basin in the intra-continental orogenesis. In this paper, a suite of brick-red sandstones of the red beds of the upper Cretaceous located in the Wushan area, northern margin of the western Qinling Mts. are studied on the sediments sequence, structure and grain size analyses. Combining the mineral compositions, microscopic and SEM surface textures of quartz of the sandstones, the rocks have been discerned to have the following features: 1) developing macroscopic eolian cross-beddings; 2) the medium-fine grained, extremely fine-grained components dominate, but the siltstone-clay components are absent, with even sizes and well-sorting; 3) quartz is well-rounded and the surface develops typical eolian-origin disc-and crescent-type pits, erosion pits, and siliceous films. Therefore, we put forward that the brick-red sandstones are the typical desert facies deposits. According to the desert deposits symbols, the sediments are further subdivided into sand dune and inter-dune deposits. It is well known that the desert deposits have two essentials, the torrid-arid climate and relatively flat topography. Combining the determination of the desert facies sediments at the Wushan area, northern margin of the western Qinling Mts. similar desert facies sediments on the mount tops at Hadapu, Xijiang of Minxian county in the interior of the western Qinling Mts., it is proposed that the western Qinling Mts. were in torrid-arid climate and flat topography in late Cretaceous. That is the large scale, flat and unified basin developed in the area at that period. This deduction is critical for re-constructing the paleo-topography and climate of the western Qinling Mts. in late Cretaceous, and for geological constraining the geological background before the uplifting of the western Qinling Mts. since the Cenozoic.
The red beds of late Cretaceous are widely and sporadically distributed in the western Qinling Mts. At late Cretaceous, the tectono-geomorphological features in the area are critical in elucidating the structural and geomorphological situation at the end of Mesozoic and determining the beginning time of the uplifting of the northeastern Qinghai-Tibet Plateau. That is, the red beds deposited in the independent intermontane basins or unified flat basin in the intra-continental orogenesis. In this paper, a suite of brick-red sandstones of the red beds of the upper Cretaceous located in the Wushan area, northern margin of the western Qinling Mts. are studied on the sediments sequence, structure and grain size analyses. Combining the mineral compositions, microscopic and SEM surface textures of quartz of the sandstones, the rocks have been discerned to have the following features: 1) developing macroscopic eolian cross-beddings; 2) the medium-fine grained, extremely fine-grained components dominate, but the siltstone-clay components are absent, with even sizes and well-sorting; 3) quartz is well-rounded and the surface develops typical eolian-origin disc-and crescent-type pits, erosion pits, and siliceous films. Therefore, we put forward that the brick-red sandstones are the typical desert facies deposits. According to the desert deposits symbols, the sediments are further subdivided into sand dune and inter-dune deposits. It is well known that the desert deposits have two essentials, the torrid-arid climate and relatively flat topography. Combining the determination of the desert facies sediments at the Wushan area, northern margin of the western Qinling Mts. similar desert facies sediments on the mount tops at Hadapu, Xijiang of Minxian county in the interior of the western Qinling Mts., it is proposed that the western Qinling Mts. were in torrid-arid climate and flat topography in late Cretaceous. That is the large scale, flat and unified basin developed in the area at that period. This deduction is critical for re-constructing the paleo-topography and climate of the western Qinling Mts. in late Cretaceous, and for geological constraining the geological background before the uplifting of the western Qinling Mts. since the Cenozoic.
2017, 35(4): 664-680.
doi: 10.14027/j.cnki.cjxb.2017.04.002
Abstract:
Middle Ordovician Majiagou Group, widely distributed in North China, was characterized by layers of marine dolomitic limestones, calcareous dolostones and dolostones in Liujiang Basin, Qinhuangdao area, North China. Four types of carbonate rocks in Majiagou Group were recognized in Liangjiashan Section, Shimenzhai area. From bottom to the top, they are type I-dolomitic wackstones; type II-fine to medium grained dolostones; type III-"wheat shaped" fine to medium grained dolostones; and type IV-calcareous microcrystalline pellets dolostones. Type I rock is mainly composed of microcrystalline calcite with fragments of trilobites and ostracods. Some fine-grained euhedral dolomites are "floating" in the pressolution stylolites and seams, rare in matrix. Petrological analysis and geochemical features of type I rocks indicate that the dolomitization occurred after the pressolution. The pressolution seams and stylolites provided pathways for dolomitizing fluids. Meanwhile, the conversion of clay minerals within the stylolites could provide part of magnesium for the dolomitization; Type II dolostone consists largely of euhedral to subhedral inequigranular (fine to medium grained) dolomites with "cloudy center and clear rim" structure. Photomicrographs of backscattered electron and cathodeluminescence of type II dolostones show that most dolomites have clear zonal structures. The variations of major elements, especially Fe ions between the rings and the intervals in a single dolomite crystal suggest that type II dolomites were formed by multi-stage dolomitizations during the burial history. The dolomite in type III dolostone reveals the feature of unidirectional extending, named as "wheat-shaped" crystals. The long axis orientation of the dolomite is fixed and perpendicular to crystal c axis. The EPMA analysis indicates that type III dolomite is Fe rich and poor with Mn and Sr. The content of MgO along the long axes is slightly higer than that along the short axes, while CaO content shows the opposite tendency. Both the geochemical and cathodeluminescence features indicate that the "wheat-shaped" dolomite was also the result of burial dolomitization. The diagenetic fluids may play an important role in the formation of the unidirectional extending dolomite crystals; Type IV is calcareous microcrystalline pellets dolostones, with pseudomorphisms of gypsum. This type is mainly composed of microcrystalline to microsparry dolomite, including pellets and algae. The dissolution pores are common in type IV rocks, but had already been filled by poor-Fe sparry calcites totally. The petrology of type IV dolostones indicates that the dolomitization occurred very early, probably formed in lagoon or tidal flat of supratidal zones. In summary, these four types of dolomite in research area are the products of different dolomitizations, varied from very early to burial dolomitizations. From the bottom to the top of this section, the dolomite degree of order declined from 0.8 to 0.47, while the dedolomitization in four types of rocks appears the reverse tendency.
Middle Ordovician Majiagou Group, widely distributed in North China, was characterized by layers of marine dolomitic limestones, calcareous dolostones and dolostones in Liujiang Basin, Qinhuangdao area, North China. Four types of carbonate rocks in Majiagou Group were recognized in Liangjiashan Section, Shimenzhai area. From bottom to the top, they are type I-dolomitic wackstones; type II-fine to medium grained dolostones; type III-"wheat shaped" fine to medium grained dolostones; and type IV-calcareous microcrystalline pellets dolostones. Type I rock is mainly composed of microcrystalline calcite with fragments of trilobites and ostracods. Some fine-grained euhedral dolomites are "floating" in the pressolution stylolites and seams, rare in matrix. Petrological analysis and geochemical features of type I rocks indicate that the dolomitization occurred after the pressolution. The pressolution seams and stylolites provided pathways for dolomitizing fluids. Meanwhile, the conversion of clay minerals within the stylolites could provide part of magnesium for the dolomitization; Type II dolostone consists largely of euhedral to subhedral inequigranular (fine to medium grained) dolomites with "cloudy center and clear rim" structure. Photomicrographs of backscattered electron and cathodeluminescence of type II dolostones show that most dolomites have clear zonal structures. The variations of major elements, especially Fe ions between the rings and the intervals in a single dolomite crystal suggest that type II dolomites were formed by multi-stage dolomitizations during the burial history. The dolomite in type III dolostone reveals the feature of unidirectional extending, named as "wheat-shaped" crystals. The long axis orientation of the dolomite is fixed and perpendicular to crystal c axis. The EPMA analysis indicates that type III dolomite is Fe rich and poor with Mn and Sr. The content of MgO along the long axes is slightly higer than that along the short axes, while CaO content shows the opposite tendency. Both the geochemical and cathodeluminescence features indicate that the "wheat-shaped" dolomite was also the result of burial dolomitization. The diagenetic fluids may play an important role in the formation of the unidirectional extending dolomite crystals; Type IV is calcareous microcrystalline pellets dolostones, with pseudomorphisms of gypsum. This type is mainly composed of microcrystalline to microsparry dolomite, including pellets and algae. The dissolution pores are common in type IV rocks, but had already been filled by poor-Fe sparry calcites totally. The petrology of type IV dolostones indicates that the dolomitization occurred very early, probably formed in lagoon or tidal flat of supratidal zones. In summary, these four types of dolomite in research area are the products of different dolomitizations, varied from very early to burial dolomitizations. From the bottom to the top of this section, the dolomite degree of order declined from 0.8 to 0.47, while the dedolomitization in four types of rocks appears the reverse tendency.
2017, 35(4): 681-690.
doi: 10.14027/j.cnki.cjxb.2017.04.003
Abstract:
Calcareous concretions of different genesis have a great significance in the study of early diagenetic environment, the sedimentary water body and shale of compacted degree. By polishing, the calcareous concretion shows the interior textures including bedding, dark circles structure and tension cracks during the lower Cambrian Qiongzhusi stage in Wangcang, north of Sichuan Basin. The relationship of concretions and surrounding rock of bedding and the preservation of sedimentological micro-features in the concretion matrix point to an early diagenetic concretions and forming before compaction. Not obvious systematic geochemical variations including Al, Ti, Ca, K, Na from concretion center to edge suggests that the element distribution of concretions are affected by cracks. The rich bioclastic and forming about tens meters under the sediment-water interface suggest the concretions may primarily grow during sulfate-reduction. The two characteristics which the beddings are not deformed among the concentric circles and the move of elements reveal that the concretions are pervasive growth which the calcium crystallites of the concretions nucleated at virtually the same time across the entire concretion. The ratios of Mg/Ca and Sr/Ca indicate that the internal calcium components of concretions is magnesium-rich calcite and biogenic calcite. The large migration of calcium in the biogenic calcite of the surrounding rock lead to the rich calcium component in the concretions. Fracture morphology shows the crack is tension cracks. The rapid transportation and deposition of turbidite at the top of Qiongzhusi Formation and analogous-nodular limestone at the bottom of Canglangpu Formation may be the cause of tension cracks.
Calcareous concretions of different genesis have a great significance in the study of early diagenetic environment, the sedimentary water body and shale of compacted degree. By polishing, the calcareous concretion shows the interior textures including bedding, dark circles structure and tension cracks during the lower Cambrian Qiongzhusi stage in Wangcang, north of Sichuan Basin. The relationship of concretions and surrounding rock of bedding and the preservation of sedimentological micro-features in the concretion matrix point to an early diagenetic concretions and forming before compaction. Not obvious systematic geochemical variations including Al, Ti, Ca, K, Na from concretion center to edge suggests that the element distribution of concretions are affected by cracks. The rich bioclastic and forming about tens meters under the sediment-water interface suggest the concretions may primarily grow during sulfate-reduction. The two characteristics which the beddings are not deformed among the concentric circles and the move of elements reveal that the concretions are pervasive growth which the calcium crystallites of the concretions nucleated at virtually the same time across the entire concretion. The ratios of Mg/Ca and Sr/Ca indicate that the internal calcium components of concretions is magnesium-rich calcite and biogenic calcite. The large migration of calcium in the biogenic calcite of the surrounding rock lead to the rich calcium component in the concretions. Fracture morphology shows the crack is tension cracks. The rapid transportation and deposition of turbidite at the top of Qiongzhusi Formation and analogous-nodular limestone at the bottom of Canglangpu Formation may be the cause of tension cracks.
2017, 35(4): 691-704.
doi: 10.14027/j.cnki.cjxb.2017.04.004
Abstract:
Tuff intervals of Yangchang Formation are widespread in the south of Ordos basin, most of them are well documented at the bottom of Chang 7 segment. The geochronology and volcanic matters of tuff intervals have great significance on the formation of high quality source rock, the development time of hydrocarbon-rich sag and the occurrence of synchronous tectonic-magmatic events. This paper focuses on the tuff intervals, which are located at the bottom of Chang 7 segment in Hejiafang outcrop section, southern Ordos basin. Firstly, thin sections, scanning electron microscopy (SEM) and major and trace elements analysis methods were used to identify the petrographic and geochemical characteristics of the tuff. Then, zircon U-Pb dating method was used to study the geochronology of the tuff intervals as well as the sandstone at the same segment. The results indicate that the tuff has the characteristics of intermediate-acidic volcanic rocks with strong alteration. The weighted average ages of the dominant component in the two tuff samples are 226.5 ± 1.6 Ma (n = 24) and 229.7 ± 2.2 Ma (n = 21), respectively, while the youngest group ages of detrital zircons range from 235 ~ 243 Ma (n = 7, the weighted average age is 239.3 Ma). Combined with previous study results, it is concluded that the age of tuff intervals at the bottom of chang7 segment is around 230 Ma±, which can represent the peak period of Ordos basin's evolution and the beginning development of hydrocarbon-rich sag in Yanchang Formation. According to the characteristics of tuff intervals, the syntectonic events of Ordos Basin and Qinling Orogenic belt over this period, it can be deduced that the volcanic matters of tuff invtervals mainly derived from the Qinling area, related closely to the volcanic arc belt caused by the subduction of Mianlue oceanic crust to the south Qinling plate. The coupling process between the Qinling orogenic belt and the southern Ordos basin can be divided into three periods. The results have important indications to re-recognize the evolution of the Ordos Basin and the basin property at Chang 7 period.
Tuff intervals of Yangchang Formation are widespread in the south of Ordos basin, most of them are well documented at the bottom of Chang 7 segment. The geochronology and volcanic matters of tuff intervals have great significance on the formation of high quality source rock, the development time of hydrocarbon-rich sag and the occurrence of synchronous tectonic-magmatic events. This paper focuses on the tuff intervals, which are located at the bottom of Chang 7 segment in Hejiafang outcrop section, southern Ordos basin. Firstly, thin sections, scanning electron microscopy (SEM) and major and trace elements analysis methods were used to identify the petrographic and geochemical characteristics of the tuff. Then, zircon U-Pb dating method was used to study the geochronology of the tuff intervals as well as the sandstone at the same segment. The results indicate that the tuff has the characteristics of intermediate-acidic volcanic rocks with strong alteration. The weighted average ages of the dominant component in the two tuff samples are 226.5 ± 1.6 Ma (n = 24) and 229.7 ± 2.2 Ma (n = 21), respectively, while the youngest group ages of detrital zircons range from 235 ~ 243 Ma (n = 7, the weighted average age is 239.3 Ma). Combined with previous study results, it is concluded that the age of tuff intervals at the bottom of chang7 segment is around 230 Ma±, which can represent the peak period of Ordos basin's evolution and the beginning development of hydrocarbon-rich sag in Yanchang Formation. According to the characteristics of tuff intervals, the syntectonic events of Ordos Basin and Qinling Orogenic belt over this period, it can be deduced that the volcanic matters of tuff invtervals mainly derived from the Qinling area, related closely to the volcanic arc belt caused by the subduction of Mianlue oceanic crust to the south Qinling plate. The coupling process between the Qinling orogenic belt and the southern Ordos basin can be divided into three periods. The results have important indications to re-recognize the evolution of the Ordos Basin and the basin property at Chang 7 period.
2017, 35(4): 705-713.
doi: 10.14027/j.cnki.cjxb.2017.04.005
Abstract:
With the technologies of field outcrop section description, identification of thin sections, whole rock X-ray diffraction(XRD)analysis and trace element analysis, researchers have studied mineral components, sedimentary structures, rock types and sedimentary environment of fine-grained sedimentary rocks in Taerlang Formation, Daheyan Area. The results reveal that fine-grained sedimentary rocks are mainly composed of quartz and calcite, and still contain a small amount of feldspar and clay minerals. The types of sedimentary structures contain normal graded bedding, flaser bedding, cross-beddings structure under the strong hydrodynamic and laminated structures under static water environment. It develops carbonate rocks, felsic rocks and fine-grained mixed rocks, and it is divided into 5 types of lithofacies based on factors of color, mineral composition and sedimentary structure, including grey thin-layered mixed fine-grained lithofacies, deep-black laminated clay lithofacies, grey laminated mixed fine-grained lithofacies, grey thin-layered siltstone lithofacies, and off-white laminated limestone lithofacies. The period of fine-grained sedimentary rocks was warm and humid, which belong to quiet, reductive, semi-salt and salt basin.
With the technologies of field outcrop section description, identification of thin sections, whole rock X-ray diffraction(XRD)analysis and trace element analysis, researchers have studied mineral components, sedimentary structures, rock types and sedimentary environment of fine-grained sedimentary rocks in Taerlang Formation, Daheyan Area. The results reveal that fine-grained sedimentary rocks are mainly composed of quartz and calcite, and still contain a small amount of feldspar and clay minerals. The types of sedimentary structures contain normal graded bedding, flaser bedding, cross-beddings structure under the strong hydrodynamic and laminated structures under static water environment. It develops carbonate rocks, felsic rocks and fine-grained mixed rocks, and it is divided into 5 types of lithofacies based on factors of color, mineral composition and sedimentary structure, including grey thin-layered mixed fine-grained lithofacies, deep-black laminated clay lithofacies, grey laminated mixed fine-grained lithofacies, grey thin-layered siltstone lithofacies, and off-white laminated limestone lithofacies. The period of fine-grained sedimentary rocks was warm and humid, which belong to quiet, reductive, semi-salt and salt basin.
2017, 35(4): 714-729.
doi: 10.14027/j.cnki.cjxb.2017.04.006
Abstract:
Various trace-makers have been found in the soft ground of intertidal zone in Andong area, Hangzhou Bay. The trace-makers discovered in the study area include Bullacta exarata(Philippi), Cerithidea cingulata (Gmelin), Periophthalmus cantonensis(Osbeck), Ilyoplax ningpoensis, Nereis succinea, Solen strictus, Moerella iridescens, Sea anemone, as well as birds and plants. They can be classed as 8 genus, belonging to 5 categories including mollusca, arthropod, annelida, chordate, and Coelenterate. The traces made by these animals include repichnia(crawling, creeping, trails, trcaceways), domichnia, fodinichnia, augerisignia, cubichnia, digestisignia, fugichnia, avipedia and root traces. Based on the analysis of these traces, it is showed that their main types, spatial distribution, abundance and diversity and makers are different in various subenvironments of the intertidal zone. 1) The types and the distribution characteristics of trace-makers and their traces are obviously different in various subenvironments of the intertidal zone in the study area. In the upper tidal zone, the sediments mainly are sandy mud containing abundant organic material, the traces discovered in the area include trails, cubichnia and augerisignia made by Cerithidea cingulata (Gmelin), trails and cubichnia made by Bullacta exaratas(Philippi), fodinichnia, domichnia and trackways made by Ilyoplax ningpoensis, trails, fodinichnia, domichnia and digestisignia made by Nereis succinea,trails and domichnia made by Periophthalmus cantonensis(Osbeck),as well as avipidia made by birds and root traces. Among these traces, the trails and fodinichnia made by Cerithidea cingulata and Nereis succinea are the most abundant on the bedding plane. However, in the substrate, the most abundant traces are dwelling burrows made by Nereis succinea, and their distribution is also quite extensive, showing intensive disturbed structures. Meanwhile, the root traces (up to 50~60 cm in depth) and dwelling burrows made by Ilyoplax ningpoensis concentrate locally. These traces always coexist with parrallel ripple marks and interference ripple marks. In the middle tidal zone, the sediments are made up of gray silt or silt mixed with sand, with high water content and sparser vegetation. The higher abundance traces in the flat zone mainly consist the dwelling burrows made by Moerella iridescens and dwelling burrows and fodinichnia made by Solen strictus, containing a small amount trails made by Bullacta exarata (Philippi) as well as root traces and birds' traces. Along both sides of the tidal channels, the sediment is finer, trails made by Cerithidea cingulatas, domichnia and traceways made by Ilyoplax ningpoensis, and repichnia made by Periophthalmus cantonensis are commonly discovered. On the bedding plane of the middle tidal zone, linguoid ripple marks are very common, and biogenic traces always coexist with linguoid ripple marks. In the lower tidal zone, the sediments are made up of gray silt or silty sand, with high water content, most of them are soup ground and no vegetation in the area, the traces mainly are domichnia made by Moerella iridescens and Solen strictus, along with a few dwelling burrows made by sea anemone's. 2)The clearness of the traces was influenced by the grain size and the water content in the substrate sediments. 3)Because of the scouring of the tidal current and the wave, the epichnial on the bedding plane may be destroyed easily, the preservation rate of traces is extremely low, however, the domichnia made by the endogeny animals in the soft ground can be preserved easily. This study provides not only a lot of new information of modern biogenic traces in order to the sedimentary environment research in the intertidal area of Hanzhou Bay, but also use for reference to paleoichnology study in ancient similar intertidal flats.
Various trace-makers have been found in the soft ground of intertidal zone in Andong area, Hangzhou Bay. The trace-makers discovered in the study area include Bullacta exarata(Philippi), Cerithidea cingulata (Gmelin), Periophthalmus cantonensis(Osbeck), Ilyoplax ningpoensis, Nereis succinea, Solen strictus, Moerella iridescens, Sea anemone, as well as birds and plants. They can be classed as 8 genus, belonging to 5 categories including mollusca, arthropod, annelida, chordate, and Coelenterate. The traces made by these animals include repichnia(crawling, creeping, trails, trcaceways), domichnia, fodinichnia, augerisignia, cubichnia, digestisignia, fugichnia, avipedia and root traces. Based on the analysis of these traces, it is showed that their main types, spatial distribution, abundance and diversity and makers are different in various subenvironments of the intertidal zone. 1) The types and the distribution characteristics of trace-makers and their traces are obviously different in various subenvironments of the intertidal zone in the study area. In the upper tidal zone, the sediments mainly are sandy mud containing abundant organic material, the traces discovered in the area include trails, cubichnia and augerisignia made by Cerithidea cingulata (Gmelin), trails and cubichnia made by Bullacta exaratas(Philippi), fodinichnia, domichnia and trackways made by Ilyoplax ningpoensis, trails, fodinichnia, domichnia and digestisignia made by Nereis succinea,trails and domichnia made by Periophthalmus cantonensis(Osbeck),as well as avipidia made by birds and root traces. Among these traces, the trails and fodinichnia made by Cerithidea cingulata and Nereis succinea are the most abundant on the bedding plane. However, in the substrate, the most abundant traces are dwelling burrows made by Nereis succinea, and their distribution is also quite extensive, showing intensive disturbed structures. Meanwhile, the root traces (up to 50~60 cm in depth) and dwelling burrows made by Ilyoplax ningpoensis concentrate locally. These traces always coexist with parrallel ripple marks and interference ripple marks. In the middle tidal zone, the sediments are made up of gray silt or silt mixed with sand, with high water content and sparser vegetation. The higher abundance traces in the flat zone mainly consist the dwelling burrows made by Moerella iridescens and dwelling burrows and fodinichnia made by Solen strictus, containing a small amount trails made by Bullacta exarata (Philippi) as well as root traces and birds' traces. Along both sides of the tidal channels, the sediment is finer, trails made by Cerithidea cingulatas, domichnia and traceways made by Ilyoplax ningpoensis, and repichnia made by Periophthalmus cantonensis are commonly discovered. On the bedding plane of the middle tidal zone, linguoid ripple marks are very common, and biogenic traces always coexist with linguoid ripple marks. In the lower tidal zone, the sediments are made up of gray silt or silty sand, with high water content, most of them are soup ground and no vegetation in the area, the traces mainly are domichnia made by Moerella iridescens and Solen strictus, along with a few dwelling burrows made by sea anemone's. 2)The clearness of the traces was influenced by the grain size and the water content in the substrate sediments. 3)Because of the scouring of the tidal current and the wave, the epichnial on the bedding plane may be destroyed easily, the preservation rate of traces is extremely low, however, the domichnia made by the endogeny animals in the soft ground can be preserved easily. This study provides not only a lot of new information of modern biogenic traces in order to the sedimentary environment research in the intertidal area of Hanzhou Bay, but also use for reference to paleoichnology study in ancient similar intertidal flats.
2017, 35(4): 730-739.
doi: 10.14027/j.cnki.cjxb.2017.04.007
Abstract:
The ocean sediments are formed in surface water and finally preserved in sea floor. During this process, the sedimentary environment always changed. In this paper, the change characteristics of TOC(%), TOC flux and δ18O and δ13C values from Globigerinoides ruber during the deposition process had been discussed in detail, basing on analyzing the relationships among particulate matter, surface sediment and core sediment in Southern of South China Sea(SCS). Here, the results shown that:1) The different proxies, such as TOC(%), TOC flux and δ18O,δ13C, have different changes during the deposition process. Specially, all the values of TOC(%), TOC flux and δ18O,δ13C descended visibly during the deposition satge from deep water layers to sea floor. The value of TOC% and TOC flux descend from 4.20%, 0.38 g/(cm2·ka) to 1.182%, 0.039 g/(cm2·ka), respectively. The value of δ18O,δ13C descend from 3.298‰ and 0.431‰ to 2.923‰ and 1.461‰, respectively. Reversely, when the core sediment formed in sea floor, the value of δ18O,δ13C would become stable except TOC(%) and TOC flux; 2) The relationship between TOC(%) change and value of δ18O, δ13C become visibly when the core sediment formed. Specially, there are clearer coherence between TOC(%) and value of δ18O in core sediments than other sediment types. In other hand, the change of relationship between TOC(%) and value of δ18O and δ13C indicate that the dissolution of TOC might be one of important factors leads to change of δ18O and δ13C value. In one word, the change characteristics of TOC(%), TOC flux and δ18O, δ13C during different sedimentary stages must be considered when reconstruct the palaeoenvironment evolution history based on these proxies.
The ocean sediments are formed in surface water and finally preserved in sea floor. During this process, the sedimentary environment always changed. In this paper, the change characteristics of TOC(%), TOC flux and δ18O and δ13C values from Globigerinoides ruber during the deposition process had been discussed in detail, basing on analyzing the relationships among particulate matter, surface sediment and core sediment in Southern of South China Sea(SCS). Here, the results shown that:1) The different proxies, such as TOC(%), TOC flux and δ18O,δ13C, have different changes during the deposition process. Specially, all the values of TOC(%), TOC flux and δ18O,δ13C descended visibly during the deposition satge from deep water layers to sea floor. The value of TOC% and TOC flux descend from 4.20%, 0.38 g/(cm2·ka) to 1.182%, 0.039 g/(cm2·ka), respectively. The value of δ18O,δ13C descend from 3.298‰ and 0.431‰ to 2.923‰ and 1.461‰, respectively. Reversely, when the core sediment formed in sea floor, the value of δ18O,δ13C would become stable except TOC(%) and TOC flux; 2) The relationship between TOC(%) change and value of δ18O, δ13C become visibly when the core sediment formed. Specially, there are clearer coherence between TOC(%) and value of δ18O in core sediments than other sediment types. In other hand, the change of relationship between TOC(%) and value of δ18O and δ13C indicate that the dissolution of TOC might be one of important factors leads to change of δ18O and δ13C value. In one word, the change characteristics of TOC(%), TOC flux and δ18O, δ13C during different sedimentary stages must be considered when reconstruct the palaeoenvironment evolution history based on these proxies.
2017, 35(4): 740-751.
doi: 10.14027/j.cnki.cjxb.2017.04.008
Abstract:
With promotion of shale oil and gas development on intensive studies on depositional mechanisms of mudstone and shales, transportation and deposition of fine-grained sediment have currently become hot topics in both sedimentoligical studies and petroleum industries. However, muddy gravity flow deposits in the Cenozoic lacustrine environment have not yet arisen attentions of geologists, although literatures of gravity flow-generated muddy deposits in marine environments extensively existed. Based on extensive literature researches, detailed core examinations and thin section observations, this paper analyzes characteristics of gravity flow-generated fine-grained deposits in the 3rd oil-member of the Paleogene Shahejie Formation (E2s3), Dongying Sag, Bohai Bay Basin. Discussions on their forming mechanisms have theoretical significances on lacustrine sedimentary environment study and have practical meanings on developments of shale oil and gas. Results: 1) there are various gravity flow deposits, including muddy mass flows, muddy debris flows, muddy turbidity currents and muddy hyperpycnal flows exist in E2s3 in the Dongying Sag; 2) muddy slumps, muddy debrites, muddy turbidites and muddy hyperpycnites co-generate and co-exist in spatio-temporal extents. Conclusions: 1) muddy sediments can deposit in turbulent waterbody and high hydrodynamic conditions; 2) muddy gravity flow deposits play an important role in deep water sedimentary regions; 3) muddy gravity flows are of great importance to transportation and deposition of coarse grains and organic matters, and so to preservation of organic matters; 4) muddy gravity flow deposits have important geological significances on unconventional oil and gas.
With promotion of shale oil and gas development on intensive studies on depositional mechanisms of mudstone and shales, transportation and deposition of fine-grained sediment have currently become hot topics in both sedimentoligical studies and petroleum industries. However, muddy gravity flow deposits in the Cenozoic lacustrine environment have not yet arisen attentions of geologists, although literatures of gravity flow-generated muddy deposits in marine environments extensively existed. Based on extensive literature researches, detailed core examinations and thin section observations, this paper analyzes characteristics of gravity flow-generated fine-grained deposits in the 3rd oil-member of the Paleogene Shahejie Formation (E2s3), Dongying Sag, Bohai Bay Basin. Discussions on their forming mechanisms have theoretical significances on lacustrine sedimentary environment study and have practical meanings on developments of shale oil and gas. Results: 1) there are various gravity flow deposits, including muddy mass flows, muddy debris flows, muddy turbidity currents and muddy hyperpycnal flows exist in E2s3 in the Dongying Sag; 2) muddy slumps, muddy debrites, muddy turbidites and muddy hyperpycnites co-generate and co-exist in spatio-temporal extents. Conclusions: 1) muddy sediments can deposit in turbulent waterbody and high hydrodynamic conditions; 2) muddy gravity flow deposits play an important role in deep water sedimentary regions; 3) muddy gravity flows are of great importance to transportation and deposition of coarse grains and organic matters, and so to preservation of organic matters; 4) muddy gravity flow deposits have important geological significances on unconventional oil and gas.
2017, 35(4): 752-762.
doi: 10.14027/j.cnki.cjxb.2017.04.009
Abstract:
The Precambrian sedimentary strata in the southern margin of the North China Craton are well developed, and widely exposed, it has a high value to study further. But no unambiguous biogenic criteria exist to discriminate Precambrian ancient sedimentary strata, the judgement of sedimentary environment is often based on the tectonic background, geographical environment, rock types and sedimentary structure, resulting in previous research have some controversies. This paper takes Bingmagou Formation in the Ruyang Group in the southern margin of the north China craton as an example, through the analysis of rock features, paleocurrent and sedimentary facies, combined with the regional comparison of relevant strata and the reconstruction of ancient landform, to explain the depositional genesis and the environmental transition of Bingmagou Formation. The sedimentary strata of the Ruyang Group unconformably onlaps Archean crystalline basement or Proterozoic Xionger Group, the Bingmagou Formation as the bottom unit of the Ruyang Group, obviously controlled by topography and fracture, accepted the rich fragment deposition, was a very particular "bilayer superimposition" sedimentary strata, represented an alluvial fan to coastal transition, and it also was the beginning of marine deposition in the southern margin of the North China Craton.
The Precambrian sedimentary strata in the southern margin of the North China Craton are well developed, and widely exposed, it has a high value to study further. But no unambiguous biogenic criteria exist to discriminate Precambrian ancient sedimentary strata, the judgement of sedimentary environment is often based on the tectonic background, geographical environment, rock types and sedimentary structure, resulting in previous research have some controversies. This paper takes Bingmagou Formation in the Ruyang Group in the southern margin of the north China craton as an example, through the analysis of rock features, paleocurrent and sedimentary facies, combined with the regional comparison of relevant strata and the reconstruction of ancient landform, to explain the depositional genesis and the environmental transition of Bingmagou Formation. The sedimentary strata of the Ruyang Group unconformably onlaps Archean crystalline basement or Proterozoic Xionger Group, the Bingmagou Formation as the bottom unit of the Ruyang Group, obviously controlled by topography and fracture, accepted the rich fragment deposition, was a very particular "bilayer superimposition" sedimentary strata, represented an alluvial fan to coastal transition, and it also was the beginning of marine deposition in the southern margin of the North China Craton.
2017, 35(4): 763-771.
doi: 10.14027/j.cnki.cjxb.2017.04.010
Abstract:
Research of coarse-grained turbidite sediment waves in submarine channel-lobe system can deepen the geological understanding of deep-water transporting process. The special sedimentary bodies, which are easy to be reworked later found in a submarine channel-lobe system of the Ruvuma Basin, East Africa, are identified and explained through the use of advanced geophysical imaging technologies and the analysis of the seismic relief. The causes and influencing factors are discussed by describing the shape, scale, migration style, thickness variations, and distribution of the coarse sediment waves. The coarse-grained turbidite sediment waves which are found in submarine channel-lobe system in Ruvuma Basin have various morphology and antidune bedforms. The small scale sediment waves with limited extension are mainly developed in the channel. While, large inclusive sediment waves distributes in channel-lobe transition zone, wave heights are in the region of 45~110 m, and wavelengths are up to over one thousand meters. The overall scale is larger than the coarse-grained sediment waves that have been identified in worldwide other regions. The coarse-grained turbidite sediments waves in the Ruvuma Basin were mainly controlled by tectonic deformation, hydraulic jumps of the supercritical flow, topography and bottom current activities.
Research of coarse-grained turbidite sediment waves in submarine channel-lobe system can deepen the geological understanding of deep-water transporting process. The special sedimentary bodies, which are easy to be reworked later found in a submarine channel-lobe system of the Ruvuma Basin, East Africa, are identified and explained through the use of advanced geophysical imaging technologies and the analysis of the seismic relief. The causes and influencing factors are discussed by describing the shape, scale, migration style, thickness variations, and distribution of the coarse sediment waves. The coarse-grained turbidite sediment waves which are found in submarine channel-lobe system in Ruvuma Basin have various morphology and antidune bedforms. The small scale sediment waves with limited extension are mainly developed in the channel. While, large inclusive sediment waves distributes in channel-lobe transition zone, wave heights are in the region of 45~110 m, and wavelengths are up to over one thousand meters. The overall scale is larger than the coarse-grained sediment waves that have been identified in worldwide other regions. The coarse-grained turbidite sediments waves in the Ruvuma Basin were mainly controlled by tectonic deformation, hydraulic jumps of the supercritical flow, topography and bottom current activities.
2017, 35(4): 772-780.
doi: 10.14027/j.cnki.cjxb.2017.04.011
Abstract:
Shale samples are from Wufeng-Longmaxi Formation of Tianba area in northeast of Chongqing. The results showed that major components of the Wufeng-Longmaxi Formation mud shale were composed of quartz, clay minerals and feldspar. In addition, other mineral components include Sulfide mineral like pyrite, gypsum and few carbonate. The mineral assemblage revealed that the Wufeng-Longmaxi Formation was composed of neritic shelf deposits that was in favor of the preservation and enrichment of organic matter and provided a good depositional condition for the shale gas reservoirs. Shale reservoir contained much quartz, and brittleness index was high that were conductive to form crack. Comparing adjacent Fuling area and Tianba area, we would find they were similar and the quartz and brittleness mineral content of Tianba shale was greater that of than the Fuling area, however, the clay minerals content and carbonate mineral content of Tianba shale was less than that of the Fuling area. Clay mineral compositions characterization reflected that Wufeng-Longmaxi Formation had already been in a phyllomorphic stage and that was corresponding to a highly mature or postmature evolutionary stage of hydrocarbons and provided with a suitable maturity condition for shale gas formation. Moreover, the Wufeng Formation and Longmaxi Formation were highly poriferous and which provided a better place for the shale gas reservoirs.
Shale samples are from Wufeng-Longmaxi Formation of Tianba area in northeast of Chongqing. The results showed that major components of the Wufeng-Longmaxi Formation mud shale were composed of quartz, clay minerals and feldspar. In addition, other mineral components include Sulfide mineral like pyrite, gypsum and few carbonate. The mineral assemblage revealed that the Wufeng-Longmaxi Formation was composed of neritic shelf deposits that was in favor of the preservation and enrichment of organic matter and provided a good depositional condition for the shale gas reservoirs. Shale reservoir contained much quartz, and brittleness index was high that were conductive to form crack. Comparing adjacent Fuling area and Tianba area, we would find they were similar and the quartz and brittleness mineral content of Tianba shale was greater that of than the Fuling area, however, the clay minerals content and carbonate mineral content of Tianba shale was less than that of the Fuling area. Clay mineral compositions characterization reflected that Wufeng-Longmaxi Formation had already been in a phyllomorphic stage and that was corresponding to a highly mature or postmature evolutionary stage of hydrocarbons and provided with a suitable maturity condition for shale gas formation. Moreover, the Wufeng Formation and Longmaxi Formation were highly poriferous and which provided a better place for the shale gas reservoirs.
2017, 35(4): 781-788.
doi: 10.14027/j.cnki.cjxb.2017.04.012
Abstract:
The shale in Chang 7 oil-bearing formation of the upper Triassic Yanchang Formation, Ordos Basin, have always been considered as high quality hydrocarbon-source rock in past, but recent exploration shows this oil-bearing formation is a possible shale reservoir and rich in oil and gas resources. However, the research of its characteristics of lithology and reservoir is still limited, and the traditional research methods of petrological characteristics of sandstone are disappointment for the shale which are composed of fine grains. Consequently, it is extraordinarily important to confirm the lithology and reservoir characteristics of Chang 7 oil-bearing formation by quantitatively calculate the content of clay minerals in the rocks of it. In the quantitative analysis of XRD, the diffraction peak intensity of each mineral is related to the content of the mineral, but it is not a simple proportional relationship, so we need rectify the result by the K factor. Because the special structure and the different crystallization degree of clay minerals are the main factors which influence the K factor, instead of using the results of the former researches, we need calculate the K factors of the clay minerals in Chang7 oil-bearing formation. Therefore, based on the internal standard method of XRD analysis, we carried out the clay mineral separation step to deal with the samples for increasing the proportion of clay minerals, and used quartz as the internal standard material. Depending on the change of quartz content, the diffraction intensity of minerals in two XRD analysis of with and without the internal standard material, we can calculate the K factors. Then, using the internal standard method, the content of each mineral in the rock can be calculated by the K factors. In order to verify the K factor, we choose monomineralic balancing method based on XRF and thermogravimetric analysis to get quantitative and semi-quantitative result, respectively. The analysis result has good consistency with mineral content that calculated based on the K value. The consistency shows the K factor is reliable. In practice, the mineral content calculated by K factor analysis method is useful in judging lithology and comparing mineral content and variation relationship of different kind rocks.
The shale in Chang 7 oil-bearing formation of the upper Triassic Yanchang Formation, Ordos Basin, have always been considered as high quality hydrocarbon-source rock in past, but recent exploration shows this oil-bearing formation is a possible shale reservoir and rich in oil and gas resources. However, the research of its characteristics of lithology and reservoir is still limited, and the traditional research methods of petrological characteristics of sandstone are disappointment for the shale which are composed of fine grains. Consequently, it is extraordinarily important to confirm the lithology and reservoir characteristics of Chang 7 oil-bearing formation by quantitatively calculate the content of clay minerals in the rocks of it. In the quantitative analysis of XRD, the diffraction peak intensity of each mineral is related to the content of the mineral, but it is not a simple proportional relationship, so we need rectify the result by the K factor. Because the special structure and the different crystallization degree of clay minerals are the main factors which influence the K factor, instead of using the results of the former researches, we need calculate the K factors of the clay minerals in Chang7 oil-bearing formation. Therefore, based on the internal standard method of XRD analysis, we carried out the clay mineral separation step to deal with the samples for increasing the proportion of clay minerals, and used quartz as the internal standard material. Depending on the change of quartz content, the diffraction intensity of minerals in two XRD analysis of with and without the internal standard material, we can calculate the K factors. Then, using the internal standard method, the content of each mineral in the rock can be calculated by the K factors. In order to verify the K factor, we choose monomineralic balancing method based on XRF and thermogravimetric analysis to get quantitative and semi-quantitative result, respectively. The analysis result has good consistency with mineral content that calculated based on the K value. The consistency shows the K factor is reliable. In practice, the mineral content calculated by K factor analysis method is useful in judging lithology and comparing mineral content and variation relationship of different kind rocks.
2017, 35(4): 789-796.
doi: 10.14027/j.cnki.cjxb.2017.04.013
Abstract:
Based on core data description, logging data analyses, thin section analyses, SEM observations, X-ray diffraction (XRD) analysis, C/O isotopic analyses and trace element analyses, sedimentary facies and depositional environments of Permian carbonate rocks taken from Pha Nok Khao Formation of Khroat basin were systemacially examined. This study shows that the Permian depositional sequence belongs to carbonate ramp deposits with no barrier. The study area locates in the fore-slope area of carbonate platform, which can be divided into shallow water fore-slope sub-facies and relatively deeper water fore-slope sub-facies. The former indicates a weak hydrodynamic condition, weak oxidation-weak reduction environment, with depositional water depth below or around sea wave base within a slope environment. The latter indicates a relatively deeper water depth than the former. Its environment is characterized by weak oxidation-moderate oxidation environment, with its depositional water depth below sea wave base. The Permian carbonate stata in the study area is a typically low-energy depositonal sequence with a relatively deeper water depth and weak hydrodynamic condition, and the vertical evolution of sedimentary environment is stable. High-energy sedimentary facies does not develop in the study area, indicating that the basic conditions for favorable reservoir development possibly do not exist and the development of potential carbonate reservoirs in Pha Nok Khao Formation will be controlled by alteration of tectonic movements or diagenesis.
Based on core data description, logging data analyses, thin section analyses, SEM observations, X-ray diffraction (XRD) analysis, C/O isotopic analyses and trace element analyses, sedimentary facies and depositional environments of Permian carbonate rocks taken from Pha Nok Khao Formation of Khroat basin were systemacially examined. This study shows that the Permian depositional sequence belongs to carbonate ramp deposits with no barrier. The study area locates in the fore-slope area of carbonate platform, which can be divided into shallow water fore-slope sub-facies and relatively deeper water fore-slope sub-facies. The former indicates a weak hydrodynamic condition, weak oxidation-weak reduction environment, with depositional water depth below or around sea wave base within a slope environment. The latter indicates a relatively deeper water depth than the former. Its environment is characterized by weak oxidation-moderate oxidation environment, with its depositional water depth below sea wave base. The Permian carbonate stata in the study area is a typically low-energy depositonal sequence with a relatively deeper water depth and weak hydrodynamic condition, and the vertical evolution of sedimentary environment is stable. High-energy sedimentary facies does not develop in the study area, indicating that the basic conditions for favorable reservoir development possibly do not exist and the development of potential carbonate reservoirs in Pha Nok Khao Formation will be controlled by alteration of tectonic movements or diagenesis.
2017, 35(4): 797-811.
doi: 10.14027/j.cnki.cjxb.2017.04.014
Abstract:
Samples of core and formation water in Dengying Formation of central Sichuan Basin were studied for petrology and geochemistry in order to understand the evolution of carbonate sediment diagenesis and pore fluids. There are several shallow marine carbonate platforms in Precambian Dengying Formation on the Yang zi mass. It is known that dolomite constitutes an important part of Dengying Formation, which is a major gas reservoir in Sichuan basin. The carbonate sediments in deposition and diagenesis of Dengying stratum were widely influenced by pore space water and diagenetic alteration. Seawater cementation, early meteoric diagenesis(dissolution and precipitation), epigenetic karstification, structurally controlled hydrothermal dolomitization and MVT(Missipi Valley-Type mineralization),dissolution in production of C and H, pyrobitumen filling in oil pyrolysis occur in the Dengying stratum, in which Karstification and hydrothermal dolomitization play an important role in development of reservoir. The pore space fluids of Dengying strata were widely modified by dolomitization and karstification. Analysed present formation water data suggest this diagenesis exsert an influence on the formation fluids of evaporative seawater. Diagenesis has an influence on reservoir of Dengying Formation, in which karstification and hydrothermal dolomitization play an important role in increase of porosity and permeability.
Analyzed formation water data indicated the evaporated sea water in the Ca-Br and Mg-Br relation. Mg concentrations have been reduced on average compared with evaporated sea water. Ca concentrations have been increased on average compared with evaporated sea water. Some workers believe that this is dolomitization of limestone.
Samples of core and formation water in Dengying Formation of central Sichuan Basin were studied for petrology and geochemistry in order to understand the evolution of carbonate sediment diagenesis and pore fluids. There are several shallow marine carbonate platforms in Precambian Dengying Formation on the Yang zi mass. It is known that dolomite constitutes an important part of Dengying Formation, which is a major gas reservoir in Sichuan basin. The carbonate sediments in deposition and diagenesis of Dengying stratum were widely influenced by pore space water and diagenetic alteration. Seawater cementation, early meteoric diagenesis(dissolution and precipitation), epigenetic karstification, structurally controlled hydrothermal dolomitization and MVT(Missipi Valley-Type mineralization),dissolution in production of C and H, pyrobitumen filling in oil pyrolysis occur in the Dengying stratum, in which Karstification and hydrothermal dolomitization play an important role in development of reservoir. The pore space fluids of Dengying strata were widely modified by dolomitization and karstification. Analysed present formation water data suggest this diagenesis exsert an influence on the formation fluids of evaporative seawater. Diagenesis has an influence on reservoir of Dengying Formation, in which karstification and hydrothermal dolomitization play an important role in increase of porosity and permeability.
Analyzed formation water data indicated the evaporated sea water in the Ca-Br and Mg-Br relation. Mg concentrations have been reduced on average compared with evaporated sea water. Ca concentrations have been increased on average compared with evaporated sea water. Some workers believe that this is dolomitization of limestone.
2017, 35(4): 812-823.
doi: 10.14027/j.cnki.cjxb.2017.04.015
Abstract:
Based on the core observation, thin-section identification, physical property test and other technical methods, with porosity, reservoir space characteristics, diagenesis characteristics, reservoir pore throat size distribution characteristics and lubricity characteristics for comprehensive classification basis, the sand-conglomerate reservoir in the near-shore subaqueous fan of the fourth member of Shahejie Formation (Es4) in Yanjia area Dongying depression have been divided into three categories and seven small classes. Ⅰ-1 type reservoir is characterized by medium-weak compaction and weak cementation, with primary pores relative development; Ⅰ-2 type reservoir is characterized by medium compaction and strong dissolution, feldspar and debris dissolution pores and intragranular pores are relatively growing; Ⅰ-3 type reservoir is characterized by medium cementation and strong dissolution, with dissolved pores of carbonate and feldspar relative development; Ⅱ-1 type is characterized by medium-strong compaction and medium dissolution, feldspar and lithic dissolved pores are relatively developing; Ⅱ-2 type is characterized by medium-strong cementation and medium dissolution, with carbonate and feldspar dissolved pores relative development; pores do not develop in Ⅲ type reservoir, Ⅲ-1 type reservoir is characterized by strong compaction and Ⅲ-2 type reservoir is characterized by strong cementation. FromⅠ-1 type reservoir to Ⅲ-2 type reservoir, porosity reduces, pore throat structure becomes worse, the fluorescence intensity becomes low, and oil and gas shows in core become weaker. Combined testing and production test data, reservoir combinations in different sedimentary subfacies have been evaluated. The results show that reservoir combination type in different sedimentary facies and its productivity have big differences. Reservoir combination in the middle fan is relatively superior and single-layer thickness of reservoir combination is various, corresponding to the medium-high daily liquid production per unit thickness. Reservoir combination in root fan comes the second and have a larger single-layer, corresponding to the relative lower daily liquid production per unit thickness. Reservoir combination in fan edge is the worst and single-layer thickness of reservoir combination is very thin, corresponding to the lower daily liquid production per unit thickness.
Based on the core observation, thin-section identification, physical property test and other technical methods, with porosity, reservoir space characteristics, diagenesis characteristics, reservoir pore throat size distribution characteristics and lubricity characteristics for comprehensive classification basis, the sand-conglomerate reservoir in the near-shore subaqueous fan of the fourth member of Shahejie Formation (Es4) in Yanjia area Dongying depression have been divided into three categories and seven small classes. Ⅰ-1 type reservoir is characterized by medium-weak compaction and weak cementation, with primary pores relative development; Ⅰ-2 type reservoir is characterized by medium compaction and strong dissolution, feldspar and debris dissolution pores and intragranular pores are relatively growing; Ⅰ-3 type reservoir is characterized by medium cementation and strong dissolution, with dissolved pores of carbonate and feldspar relative development; Ⅱ-1 type is characterized by medium-strong compaction and medium dissolution, feldspar and lithic dissolved pores are relatively developing; Ⅱ-2 type is characterized by medium-strong cementation and medium dissolution, with carbonate and feldspar dissolved pores relative development; pores do not develop in Ⅲ type reservoir, Ⅲ-1 type reservoir is characterized by strong compaction and Ⅲ-2 type reservoir is characterized by strong cementation. FromⅠ-1 type reservoir to Ⅲ-2 type reservoir, porosity reduces, pore throat structure becomes worse, the fluorescence intensity becomes low, and oil and gas shows in core become weaker. Combined testing and production test data, reservoir combinations in different sedimentary subfacies have been evaluated. The results show that reservoir combination type in different sedimentary facies and its productivity have big differences. Reservoir combination in the middle fan is relatively superior and single-layer thickness of reservoir combination is various, corresponding to the medium-high daily liquid production per unit thickness. Reservoir combination in root fan comes the second and have a larger single-layer, corresponding to the relative lower daily liquid production per unit thickness. Reservoir combination in fan edge is the worst and single-layer thickness of reservoir combination is very thin, corresponding to the lower daily liquid production per unit thickness.
2017, 35(4): 824-833.
doi: 10.14027/j.cnki.cjxb.2017.04.016
Abstract:
Based on the analysis of source rock, reservoir, crude oil origin and spatial configuration relationship between source rock and reservoir, it was proposed of the stratiform and self-generating and self-preserving tight oil accumulation model of the Lucaogou Formation in the Jimusaer sag of the Junggar Basin. In salt water lake facies sedimentary rocks of the Lucaogou Formation, individual lithology had different content of original organic matter which trended to generate oil, in them, as main source rock, shale has the highest organic matter abundance and hydrocarbon potential, oil-prone parent matter type and the mature stage for oil generation. The sandstone and carbonate reservoirs which were distributed in source rock layer had reservoir background of low porosity and low permeability, and their oilness has a close relationship with physical property difference. The Lucaogou Formation had basic tight oil accumulation condition because of alternating layers between shale and reservoir, and reservoir involved in shale. The crudes oil in the Upper and the Lower member of the Lucaogou Formation, which having obvious density and geochemistry differences, came from the source rocks adjent to them, respectively. Comprhansive researches show the Lucaogou Formation has stratabound tight oil accumulation model with close migration distance and self-generating and self-reservoir in Jimusaer sag of Junggar Basin.
Based on the analysis of source rock, reservoir, crude oil origin and spatial configuration relationship between source rock and reservoir, it was proposed of the stratiform and self-generating and self-preserving tight oil accumulation model of the Lucaogou Formation in the Jimusaer sag of the Junggar Basin. In salt water lake facies sedimentary rocks of the Lucaogou Formation, individual lithology had different content of original organic matter which trended to generate oil, in them, as main source rock, shale has the highest organic matter abundance and hydrocarbon potential, oil-prone parent matter type and the mature stage for oil generation. The sandstone and carbonate reservoirs which were distributed in source rock layer had reservoir background of low porosity and low permeability, and their oilness has a close relationship with physical property difference. The Lucaogou Formation had basic tight oil accumulation condition because of alternating layers between shale and reservoir, and reservoir involved in shale. The crudes oil in the Upper and the Lower member of the Lucaogou Formation, which having obvious density and geochemistry differences, came from the source rocks adjent to them, respectively. Comprhansive researches show the Lucaogou Formation has stratabound tight oil accumulation model with close migration distance and self-generating and self-reservoir in Jimusaer sag of Junggar Basin.
2017, 35(4): 834-842.
doi: 10.14027/j.cnki.cjxb.2017.04.017
Abstract:
The tetracyclic polyprenoid compounds are the powerful tools for recognition of the fresh/brackish water algal input into lacustrine depositional setting of hydrocarbon source rocks.The tetracyclic polyprenoid compounds (TPP) are observed in the samples derived from the Paleogene source rocks and crude oils in Qikou Sag in offshore Bohai Bay Basin in East China rifted lacustrine basins. Two isomers of the tetracyclic polyprenoids are detected based on the retention time of gas chromatography (GC), mass spectrum characteristics and compared with other literatures. Tetracyclic polyprenoid compounds are present in relatively high concentrations in oils and associated source rocks deposited under increased saline conditions and may be useful in the recognizing changes in water salinity. The tetracyclic polyprenoids are new geochemical markers of the oil-source rock correlations in Qikou sag in offshore Bohai Bay Basin in East China rifted lacustrine basins and sorting effectively out the crude oil from the hydrocarbon resource rocks of the 3rd Member(Es3) and 1st Member(Es1) of the Eocene Shahejie Formation. The tetracyclic polyprenoids are significantly useful to assessing the algal input, depositional environment and the correlations between the oils and source rocks.
The tetracyclic polyprenoid compounds are the powerful tools for recognition of the fresh/brackish water algal input into lacustrine depositional setting of hydrocarbon source rocks.The tetracyclic polyprenoid compounds (TPP) are observed in the samples derived from the Paleogene source rocks and crude oils in Qikou Sag in offshore Bohai Bay Basin in East China rifted lacustrine basins. Two isomers of the tetracyclic polyprenoids are detected based on the retention time of gas chromatography (GC), mass spectrum characteristics and compared with other literatures. Tetracyclic polyprenoid compounds are present in relatively high concentrations in oils and associated source rocks deposited under increased saline conditions and may be useful in the recognizing changes in water salinity. The tetracyclic polyprenoids are new geochemical markers of the oil-source rock correlations in Qikou sag in offshore Bohai Bay Basin in East China rifted lacustrine basins and sorting effectively out the crude oil from the hydrocarbon resource rocks of the 3rd Member(Es3) and 1st Member(Es1) of the Eocene Shahejie Formation. The tetracyclic polyprenoids are significantly useful to assessing the algal input, depositional environment and the correlations between the oils and source rocks.
2017, 35(4): 843-852.
doi: 10.14027/j.cnki.cjxb.2017.04.018
Abstract:
Alkylbenzene series compounds widely distributed in the lithosphere, but its parent material source and the indicating significance is still in controversy. This paper focused on the samples of saturated hydrocarbon fractions which were from the Late Triassic Xujiahe Formation in central Sichuan Basin and the Late Triassic Yanchang Formation in Ordos Basin. A series of long-chain alkylbenzene and its isomers (branched alkylbenzene) were tested by GC-MS analysis. The results indicated those samples had I-II1 type organic matters and formed in a sub-oxidizing environment with strong clay catalysis and bacterial degradation, the sedimentary environment of samples are the similar. However, that the relative content of long-chain alkylbenzene and its isomers distribution patterns are different, on the basis of predecessors' research combined with hydrocarbon source rocks in the study area and thermal evolution background, suggested that lipid such as fatty and alcohol, or simple aromatic compounds with lipid reaction is a possible source of alkylbenzene, in addition, the thermal effect leads to long-chain alkylbenzene transform to its isomers. The study shows that long-chain alkylbenzene and its isomers indicate the effective degree of thermal evolution of organic matter and the source of parent material parameters.
Alkylbenzene series compounds widely distributed in the lithosphere, but its parent material source and the indicating significance is still in controversy. This paper focused on the samples of saturated hydrocarbon fractions which were from the Late Triassic Xujiahe Formation in central Sichuan Basin and the Late Triassic Yanchang Formation in Ordos Basin. A series of long-chain alkylbenzene and its isomers (branched alkylbenzene) were tested by GC-MS analysis. The results indicated those samples had I-II1 type organic matters and formed in a sub-oxidizing environment with strong clay catalysis and bacterial degradation, the sedimentary environment of samples are the similar. However, that the relative content of long-chain alkylbenzene and its isomers distribution patterns are different, on the basis of predecessors' research combined with hydrocarbon source rocks in the study area and thermal evolution background, suggested that lipid such as fatty and alcohol, or simple aromatic compounds with lipid reaction is a possible source of alkylbenzene, in addition, the thermal effect leads to long-chain alkylbenzene transform to its isomers. The study shows that long-chain alkylbenzene and its isomers indicate the effective degree of thermal evolution of organic matter and the source of parent material parameters.
2017, 35(4): 853-862.
doi: 10.14027/j.cnki.cjxb.2017.04.019
Abstract:
Taking source rock core samples collected from 6 wells of Majiagou Formation of Ordovician in Ordos Basin as the target, branched alkanes in the saturated hydrocarbons were investigated by GC/MS. The results show that there is relatively high abundance of medium-chain branched alkanes of which carbon number range from 15 to 21, including 2-methyl (iso-alkanes), 3-methyl (anteiso-alkanes), high-methyl branched alkanes, dual-methyl branched alkanes and acyclic isoprenoid alkanes, in which the carbon number of iso-alkanes and anteiso-alkanes has a wide distribution, including short, medium and long-chain. According to sedimentary characteristics and other organic geochemical indexs in the study area, methyl-branched-chain alkanes with medium-chain length of Majiagou Formation of Ordovician in Ordos Basin are considered deriving from some special bacteria and algae, and the cyanobacteria is the most likely direct input parent material. Meanwhile, some heterotrophic bacteria's transformation to the original sediments is one of the important reasons that the accumulation of medium-chain branched alkanes. The long-chains iso-alkanes and anteiso-alkanes may have much to do with thermal catalytic rearrangement.
Taking source rock core samples collected from 6 wells of Majiagou Formation of Ordovician in Ordos Basin as the target, branched alkanes in the saturated hydrocarbons were investigated by GC/MS. The results show that there is relatively high abundance of medium-chain branched alkanes of which carbon number range from 15 to 21, including 2-methyl (iso-alkanes), 3-methyl (anteiso-alkanes), high-methyl branched alkanes, dual-methyl branched alkanes and acyclic isoprenoid alkanes, in which the carbon number of iso-alkanes and anteiso-alkanes has a wide distribution, including short, medium and long-chain. According to sedimentary characteristics and other organic geochemical indexs in the study area, methyl-branched-chain alkanes with medium-chain length of Majiagou Formation of Ordovician in Ordos Basin are considered deriving from some special bacteria and algae, and the cyanobacteria is the most likely direct input parent material. Meanwhile, some heterotrophic bacteria's transformation to the original sediments is one of the important reasons that the accumulation of medium-chain branched alkanes. The long-chains iso-alkanes and anteiso-alkanes may have much to do with thermal catalytic rearrangement.
