2014 Vol. 32, No. 4
Display Method:
2014, 32(4): 611-622.
Abstract:
Subaqueous debris flow controlled by mass transport process is a sedimentation type in deep-water (deep-marine or deep-lacustrine) environment increasingly recognized in recent years. However, at present, there are no accepted criteria to identify the mass transport process of subaqueous sediments. Through the geological survey of several outcrop profiles in the center of the Ordos lacustrine basin, a kind of “argillaceous parcel” structure has been found for the first time in deep-water thick massive sandstone of Yanchang Formation, and its formation and evolution process have been analyzed. What we can conclude is that this sedimentary structure is mainly related to the specific formation mechanism and development process of “debris flow” in delta front. Its formation process shows that the sediments containing it were characterized by transportation of particles en masse (Bingham plastics) and supported by the strength of medium at all times. Accordingly, we are confident that the “argillaceous parcel” structure is the one of most significant evidence indicating the origin of deep-water thick massive sandstone of Yanchang Formation as debris flow. Consequently, the model of transport process from the start to transport and then to sedimentation of Yanchang Formation deep-water sandstone is established. Moreover, this paper attempts to point out that the “argillaceous parcel” structure is also a key identification marker for identifying the mass transport and its process in deep-marine sedimentation, and that our work is not only significant for the global deep-water (deep-marine and deep-lacustrine) oil & gas exploration but also positive for the “source to sink” research of sediments in the continental margins that is widely performed in the current geoscience field.
Subaqueous debris flow controlled by mass transport process is a sedimentation type in deep-water (deep-marine or deep-lacustrine) environment increasingly recognized in recent years. However, at present, there are no accepted criteria to identify the mass transport process of subaqueous sediments. Through the geological survey of several outcrop profiles in the center of the Ordos lacustrine basin, a kind of “argillaceous parcel” structure has been found for the first time in deep-water thick massive sandstone of Yanchang Formation, and its formation and evolution process have been analyzed. What we can conclude is that this sedimentary structure is mainly related to the specific formation mechanism and development process of “debris flow” in delta front. Its formation process shows that the sediments containing it were characterized by transportation of particles en masse (Bingham plastics) and supported by the strength of medium at all times. Accordingly, we are confident that the “argillaceous parcel” structure is the one of most significant evidence indicating the origin of deep-water thick massive sandstone of Yanchang Formation as debris flow. Consequently, the model of transport process from the start to transport and then to sedimentation of Yanchang Formation deep-water sandstone is established. Moreover, this paper attempts to point out that the “argillaceous parcel” structure is also a key identification marker for identifying the mass transport and its process in deep-marine sedimentation, and that our work is not only significant for the global deep-water (deep-marine and deep-lacustrine) oil & gas exploration but also positive for the “source to sink” research of sediments in the continental margins that is widely performed in the current geoscience field.
2014, 32(4): 634-642.
Abstract:
This paper mainly discussed the sedimentary characteristics, vertical sequence and geological significance of seismites of Palaeogene in Jinxian sag, Jizhong depression. In the Bohai Bay Basin, the Jinxian sag was a typical small fault basin of Cenozoic. And a lot of soft sediment deformation structures developed in the layers in the 4th Member of Shahejie Formation and the 1st Member of Kongdian Formation, including liquefied sand-mudstone veins, mud stocks, water-escape channels, load cast and flame structures, ball-and-pillow structures, vibrational liquefaction deformation structures, beads-shaped structures, micro synsedimentary faults and ground fissures. The study indicated that deformation structures above were typical characteristics of seismites. Based on the study, vertical sequence of seismites was established, including underlying unshocked layer, seismic fall layer, shattered layer, seismic corrugated layer, ball-and-pillow layer, liquefied homogeneous layer, and overlying unshocked layer. Seismites, evaporates and tuff which were all related to the activity of deep fracture, developed in the layers in the 4th Member of Shahejie Formation and the 1st Member of Kongdian Formation. The study indicated that activity of deep fracture induced multi-period earthquakes, and lead to further the formation of seismites. At the same time, as channel of magma upwelling and deep salt sources, the deep fracture provided material basis for the formation of evaporates and tuff. It indicated that the maximum tectonic intensity of Jinxian sag happened in that period, from sedimentary perspective. Seismic deposition can improve the permeability of reservoirs through the connection of original pores by micro fissures.
This paper mainly discussed the sedimentary characteristics, vertical sequence and geological significance of seismites of Palaeogene in Jinxian sag, Jizhong depression. In the Bohai Bay Basin, the Jinxian sag was a typical small fault basin of Cenozoic. And a lot of soft sediment deformation structures developed in the layers in the 4th Member of Shahejie Formation and the 1st Member of Kongdian Formation, including liquefied sand-mudstone veins, mud stocks, water-escape channels, load cast and flame structures, ball-and-pillow structures, vibrational liquefaction deformation structures, beads-shaped structures, micro synsedimentary faults and ground fissures. The study indicated that deformation structures above were typical characteristics of seismites. Based on the study, vertical sequence of seismites was established, including underlying unshocked layer, seismic fall layer, shattered layer, seismic corrugated layer, ball-and-pillow layer, liquefied homogeneous layer, and overlying unshocked layer. Seismites, evaporates and tuff which were all related to the activity of deep fracture, developed in the layers in the 4th Member of Shahejie Formation and the 1st Member of Kongdian Formation. The study indicated that activity of deep fracture induced multi-period earthquakes, and lead to further the formation of seismites. At the same time, as channel of magma upwelling and deep salt sources, the deep fracture provided material basis for the formation of evaporates and tuff. It indicated that the maximum tectonic intensity of Jinxian sag happened in that period, from sedimentary perspective. Seismic deposition can improve the permeability of reservoirs through the connection of original pores by micro fissures.
2014, 32(4): 654-662.
Abstract:
Comparing the seismic profiles, detrital material combinations and maturity, heavy mineral characteristics and sand ratio map from up and below the 18.5 Ma, which is the time line between the early and late stage of early Miocene, and stratigraphic boundary of the lower and upper Member of the Zhujiang Formation meaning while, in Dongsha massif, east of the Pearl River Mouth Basin, we can draw the conclusion that before 18.5 Ma, the Dongsha massif was still above the sea level and developed multiple flows radiated from the massif; as the sea-level rising , the massif lowed gradually, detrital materials from the Dongsha massif decreased while carbonate sources occupied, so reef appeared, and it peaked during 18.5 Ma to 16.5 Ma. After 16.5 Ma, the massif immersed as the prodelta of the Paleo-Zhujiang delta which sourced from northwest and prograded to the place, so the Dongsha massif lost the sources capability eventually.
Comparing the seismic profiles, detrital material combinations and maturity, heavy mineral characteristics and sand ratio map from up and below the 18.5 Ma, which is the time line between the early and late stage of early Miocene, and stratigraphic boundary of the lower and upper Member of the Zhujiang Formation meaning while, in Dongsha massif, east of the Pearl River Mouth Basin, we can draw the conclusion that before 18.5 Ma, the Dongsha massif was still above the sea level and developed multiple flows radiated from the massif; as the sea-level rising , the massif lowed gradually, detrital materials from the Dongsha massif decreased while carbonate sources occupied, so reef appeared, and it peaked during 18.5 Ma to 16.5 Ma. After 16.5 Ma, the massif immersed as the prodelta of the Paleo-Zhujiang delta which sourced from northwest and prograded to the place, so the Dongsha massif lost the sources capability eventually.
2014, 32(4): 669-676.
Abstract:
Nam Co in high-altitude area is the ideal place to study the past climatic and environmental changes. In this paper, we tried to compare the measured lake sediment results of Nam Co with meteorological data in local stations and chose some proxies to reconstruct the climate and environment change record in the past 150 years in this area. The values of TOC, grain size, Sr/Ba and Rb/Sr had clear environment significance and reflected the climate change well. Geochemical multi-proxies of lake core NMC09 showed the final result as follows, the climate was characterized with warm and humid from 1 850~1 900 A.D.. During the period of 1 900~1 950 A.D., it was a cold-wet period, and had transformed to the warm and humid period gradually since 1920s. After the 1950s it had main trend of rising temperature although it had a little climate fluctuations, and the lake did not shrink obviously in spite of reduced precipitation. It suggested that rising temperature could lead to glacier melting accelerated to supply the run-off into Nam Co.
Nam Co in high-altitude area is the ideal place to study the past climatic and environmental changes. In this paper, we tried to compare the measured lake sediment results of Nam Co with meteorological data in local stations and chose some proxies to reconstruct the climate and environment change record in the past 150 years in this area. The values of TOC, grain size, Sr/Ba and Rb/Sr had clear environment significance and reflected the climate change well. Geochemical multi-proxies of lake core NMC09 showed the final result as follows, the climate was characterized with warm and humid from 1 850~1 900 A.D.. During the period of 1 900~1 950 A.D., it was a cold-wet period, and had transformed to the warm and humid period gradually since 1920s. After the 1950s it had main trend of rising temperature although it had a little climate fluctuations, and the lake did not shrink obviously in spite of reduced precipitation. It suggested that rising temperature could lead to glacier melting accelerated to supply the run-off into Nam Co.
2014, 32(4): 684-691.
Abstract:
In this study, rare earth elements (REEs) and grain size of Core LDC30 sediments taken from the southeastern Liaodong Bay have been analyzed to investigate the sediment elemental compositions, controlling factors and the provenance. The total content of rare earth elements of Core LDC30 is in average of 149.49 μg/g, slightly higher than the Yellow Sea and the East China Sea, but lower than the Bohai Sea, the South China Sea, and the average value of the global sediments. The REE patterns show significant enrichment in light REEs, with HREE relatively loss. The mean value of Eu is 0.71 which is in the scope of intermediate negative Eu abnormal, δCe is without anomalies. And the fractionation between light and heavy REEs is obvious. REEs concentrations of core sediments vary greatly in vertical profiles, LDC30 is divided into two sections by 51 cm. In the upper part (0~51 cm), REEs concentrations fluctuate more obvious than the underpart (51~99 cm),and the upper part REEs contents show an increasing trend with depth decreasing, while the underpart doesn't present a significant fluctuation in vertical. Besides that, the REE fractionation in the upperpart is more obvious than the underpart. δCe as a whole is relatively stable, but in the upper section shows a downward trend. δEu is being stable in vertical. The correlation between REE parameter and grain sizes is not obvious. But heavy minerals exert an important influence on REEs composition and distribution. The source of LDC30 sediments is relatively stable and shows strong terrigenous characteristics. Discrimination plots based on REE fractionation parameters suggest that the cored sediments originated mostly from the northern part rivers (Liaohe River, Xiaoling River, Shuangtaizi River) of the Liaodong Bay, and Luan river in the western part of Liaodong Bay has a certain contribution to the upper part of Core LDC30.
In this study, rare earth elements (REEs) and grain size of Core LDC30 sediments taken from the southeastern Liaodong Bay have been analyzed to investigate the sediment elemental compositions, controlling factors and the provenance. The total content of rare earth elements of Core LDC30 is in average of 149.49 μg/g, slightly higher than the Yellow Sea and the East China Sea, but lower than the Bohai Sea, the South China Sea, and the average value of the global sediments. The REE patterns show significant enrichment in light REEs, with HREE relatively loss. The mean value of Eu is 0.71 which is in the scope of intermediate negative Eu abnormal, δCe is without anomalies. And the fractionation between light and heavy REEs is obvious. REEs concentrations of core sediments vary greatly in vertical profiles, LDC30 is divided into two sections by 51 cm. In the upper part (0~51 cm), REEs concentrations fluctuate more obvious than the underpart (51~99 cm),and the upper part REEs contents show an increasing trend with depth decreasing, while the underpart doesn't present a significant fluctuation in vertical. Besides that, the REE fractionation in the upperpart is more obvious than the underpart. δCe as a whole is relatively stable, but in the upper section shows a downward trend. δEu is being stable in vertical. The correlation between REE parameter and grain sizes is not obvious. But heavy minerals exert an important influence on REEs composition and distribution. The source of LDC30 sediments is relatively stable and shows strong terrigenous characteristics. Discrimination plots based on REE fractionation parameters suggest that the cored sediments originated mostly from the northern part rivers (Liaohe River, Xiaoling River, Shuangtaizi River) of the Liaodong Bay, and Luan river in the western part of Liaodong Bay has a certain contribution to the upper part of Core LDC30.
2014, 32(4): 700-709.
Abstract:
Morphology, sediment components and grain-size parameters revealed the depositional environment of coastal zone, especially the beach unit. Measurements had carried out in Longwan Beach and the First Beach of Xingcheng City, Huludao City, Liaoning Province from July 2010 to December 2011. That is to say, four researches had been taken in every summer and winter, which included the observations and analysis of both beach elevations and sedimentary grain size characteristics. It was shown that ①by using 1985 Yellow Sea Elevation -0.6m and -4.7 m as boundaries, the two beaches in the study area might be, respectively, divided into three geomorphic units named beach unit, underwater slope unit and continental shelf unit. ②The sedimentary settings of Longwan Beach were stable, while the beach unit and underwater slope unit in the First Beach of Xingcheng City were alluvial, which might be caused by the engineering of beach nourishment. ③The two beaches might be divided into four sedimentary zones through the transverse variations of sediment components and grain size parameters. The changing trends of median diameter didn’t show transverse decreasing trend, while the variation rules of other gain size parameters were complicated in different sedimentary areas, indicating that the hydrodynamic conditions of each sedimentary zone were different. ④Compared to the First Beach of Xingcheng City, the sediments sampled in the sedimentary area I on Longwan Beach were thicker and worse sorted. the underwater slope unit of Longwan Beach was formed in a weak dynamic condition while the continental shelf unit of the First Beach of Xingcheng City was dominated by strong tidal currents.
Morphology, sediment components and grain-size parameters revealed the depositional environment of coastal zone, especially the beach unit. Measurements had carried out in Longwan Beach and the First Beach of Xingcheng City, Huludao City, Liaoning Province from July 2010 to December 2011. That is to say, four researches had been taken in every summer and winter, which included the observations and analysis of both beach elevations and sedimentary grain size characteristics. It was shown that ①by using 1985 Yellow Sea Elevation -0.6m and -4.7 m as boundaries, the two beaches in the study area might be, respectively, divided into three geomorphic units named beach unit, underwater slope unit and continental shelf unit. ②The sedimentary settings of Longwan Beach were stable, while the beach unit and underwater slope unit in the First Beach of Xingcheng City were alluvial, which might be caused by the engineering of beach nourishment. ③The two beaches might be divided into four sedimentary zones through the transverse variations of sediment components and grain size parameters. The changing trends of median diameter didn’t show transverse decreasing trend, while the variation rules of other gain size parameters were complicated in different sedimentary areas, indicating that the hydrodynamic conditions of each sedimentary zone were different. ④Compared to the First Beach of Xingcheng City, the sediments sampled in the sedimentary area I on Longwan Beach were thicker and worse sorted. the underwater slope unit of Longwan Beach was formed in a weak dynamic condition while the continental shelf unit of the First Beach of Xingcheng City was dominated by strong tidal currents.
2014, 32(4): 724-733.
Abstract:
Late Indosinian is the key transition period in which the middle Yangtze area shifted to the new sedimentary pattern from marine sedimentary environment to continental sedimentation of rivers and lakes. On the basis of information from fundamental stratigraphic sections established in sub-basins in the middle Yangtze, the third-order sequence division and correlation, sedimentary facies analysis and lithofacies palaeogeography recovery were studied through high-resolution outcrop analysis on the guidance of basic theories of continental sequence stratigraphy and sedimentology. It shows that late Indosinian continental sedimentary system in the middle Yangtze is divided into 3 third-order sequences at most but generally 1～2 third-order sequences can be identified only as a result of strata undevelopment or erosion. There are 3, 2, 1 and 1 third-order sequences in the western margin of middle Yangtze, Jingdang Basin, Zigui Basin and Edong Basin, respectively. In contrast, the quantity of sequences in the west area is more than that in the east area. Sedimentary facies analysis indicates that all third-order sequences are characterized by continental clastic sediments which are rich in coal and palaeobotanic fragments, and also shows that the lithofacies paleogeography in the middle Yangtze area is totally made up of 2 types of sedimentary facies sets which are meandering river-delta-residue lake facies set and braided river-delta-residue lake set, and the former which mainly distributes in the west of middle Yangtze and Zigui Basin is dominant, while the latter develops in Edong Basin comparatively. It’s also concluded from study results that the middle Yangtze has a couple of subsidence and sedimentation centers in late Indosinian, and the ones in Jingdang Basin and the western margin of middle Yangtze are most important. The subsidence mechanism is the middle Yangtze crust northward subduction which results in flexural subsidence and intense extrusion deformation. The provenance is probably provided for sub-basins by Qingling-dabie collision and adjacent uplift created by deformation.
Late Indosinian is the key transition period in which the middle Yangtze area shifted to the new sedimentary pattern from marine sedimentary environment to continental sedimentation of rivers and lakes. On the basis of information from fundamental stratigraphic sections established in sub-basins in the middle Yangtze, the third-order sequence division and correlation, sedimentary facies analysis and lithofacies palaeogeography recovery were studied through high-resolution outcrop analysis on the guidance of basic theories of continental sequence stratigraphy and sedimentology. It shows that late Indosinian continental sedimentary system in the middle Yangtze is divided into 3 third-order sequences at most but generally 1～2 third-order sequences can be identified only as a result of strata undevelopment or erosion. There are 3, 2, 1 and 1 third-order sequences in the western margin of middle Yangtze, Jingdang Basin, Zigui Basin and Edong Basin, respectively. In contrast, the quantity of sequences in the west area is more than that in the east area. Sedimentary facies analysis indicates that all third-order sequences are characterized by continental clastic sediments which are rich in coal and palaeobotanic fragments, and also shows that the lithofacies paleogeography in the middle Yangtze area is totally made up of 2 types of sedimentary facies sets which are meandering river-delta-residue lake facies set and braided river-delta-residue lake set, and the former which mainly distributes in the west of middle Yangtze and Zigui Basin is dominant, while the latter develops in Edong Basin comparatively. It’s also concluded from study results that the middle Yangtze has a couple of subsidence and sedimentation centers in late Indosinian, and the ones in Jingdang Basin and the western margin of middle Yangtze are most important. The subsidence mechanism is the middle Yangtze crust northward subduction which results in flexural subsidence and intense extrusion deformation. The provenance is probably provided for sub-basins by Qingling-dabie collision and adjacent uplift created by deformation.
2014, 32(4): 744-753.
Abstract:
Five subfacies(A-E) which are all contained Inclined Heterolithic Stratification (IHS) and marine, brackish water traces have been found in Shahejie Formatiom Subdivission 3(Palaeogene) Dongpu depression, Henan, China. It is widely accepted that IHS invoke a tidal influence on a fluvial or estuarine system to provide the fluctuating regime required to produce the heterogeneous bedding which typically consists of repetitive sets of mud/sand couplets on a scale of centimeters to decimeter .Various mud/sand couplets with trace fossils of marine origin present in the wells located in Wenliu area of Dongpu depression clearly recorded a fluvial sourced sand containing syneresis and Diplocraterion traces in the upper estuary (subfacies A) muddy sediments with distortion of laminated material related to turbidity maximum and trace fossils of Palaeophycos, Planolites as well as Chondrites (SubfaciesB, C) and sand sourced from seaward consists of trace fossils of Terebellina, Rhizocorallium, Ophiomorpha, Terebellina in the lower estuary(subfacies D, E). They are interpreted as estuarine deposits based on sedimentologic and Ichnologic analysis. Examples both in home (Wenliu, Henan) and abroad (North America) show that sand sourced from seaward in the lower estuary are good target for hydrocarbon exploration.
Five subfacies(A-E) which are all contained Inclined Heterolithic Stratification (IHS) and marine, brackish water traces have been found in Shahejie Formatiom Subdivission 3(Palaeogene) Dongpu depression, Henan, China. It is widely accepted that IHS invoke a tidal influence on a fluvial or estuarine system to provide the fluctuating regime required to produce the heterogeneous bedding which typically consists of repetitive sets of mud/sand couplets on a scale of centimeters to decimeter .Various mud/sand couplets with trace fossils of marine origin present in the wells located in Wenliu area of Dongpu depression clearly recorded a fluvial sourced sand containing syneresis and Diplocraterion traces in the upper estuary (subfacies A) muddy sediments with distortion of laminated material related to turbidity maximum and trace fossils of Palaeophycos, Planolites as well as Chondrites (SubfaciesB, C) and sand sourced from seaward consists of trace fossils of Terebellina, Rhizocorallium, Ophiomorpha, Terebellina in the lower estuary(subfacies D, E). They are interpreted as estuarine deposits based on sedimentologic and Ichnologic analysis. Examples both in home (Wenliu, Henan) and abroad (North America) show that sand sourced from seaward in the lower estuary are good target for hydrocarbon exploration.
2014, 32(4): 766-775.
Abstract:
The Kalpin area develops multilayer source rocks of Cambrian, Ordovician, Carboniferous and Permian. The oil seepages are distributed widely with multiple layers. The Kalpin area underwent a large-scale hydrocarbon accumulation and destructive process. The preservation conditions are the key factors for petroleum exploration activity. As a high-quality caprock, the Cambrian salt-gypsum rock constitutes a good combination with the source rock of Yuertusi Formation, and the carbonate reservoir of inter-salt and subsalt. The light oil seepages of outcrop in Qingsong Ordovician stone pit indicate the possible presence of residual carbonate reservoirs, and Cincinnatian reservoir of the Central plateau uplift in the USA is a good example for the shallow reservoir. The oil seeps are mostly outcropped in the Carboniferous and Permian, and oil and gas reservoir may be preserved with good reservoir performance of Carboniferous and Permian biolithite in the burial area. The field investigation is difficult to further deepen the understanding and exploration in Kalpin thrust belt, and well drilling is necessary after the evaluation and selection of geological targets. Under the current economic and technological conditions, three geological targets are more realistic: Salamubulake anticline is needed to understand the Cambrian salt-gypsum rock, source rock of Yuertusi Formaiton, and oil possibilities in the carbonate reservoir of inter-salt and subsalt; the residual reservoir distribution in the Qingsong Ordovician stone pit; the reef limestone of Carboniferous and Permian in the Halajun Basin in the southwest of Piqiang village.
The Kalpin area develops multilayer source rocks of Cambrian, Ordovician, Carboniferous and Permian. The oil seepages are distributed widely with multiple layers. The Kalpin area underwent a large-scale hydrocarbon accumulation and destructive process. The preservation conditions are the key factors for petroleum exploration activity. As a high-quality caprock, the Cambrian salt-gypsum rock constitutes a good combination with the source rock of Yuertusi Formation, and the carbonate reservoir of inter-salt and subsalt. The light oil seepages of outcrop in Qingsong Ordovician stone pit indicate the possible presence of residual carbonate reservoirs, and Cincinnatian reservoir of the Central plateau uplift in the USA is a good example for the shallow reservoir. The oil seeps are mostly outcropped in the Carboniferous and Permian, and oil and gas reservoir may be preserved with good reservoir performance of Carboniferous and Permian biolithite in the burial area. The field investigation is difficult to further deepen the understanding and exploration in Kalpin thrust belt, and well drilling is necessary after the evaluation and selection of geological targets. Under the current economic and technological conditions, three geological targets are more realistic: Salamubulake anticline is needed to understand the Cambrian salt-gypsum rock, source rock of Yuertusi Formaiton, and oil possibilities in the carbonate reservoir of inter-salt and subsalt; the residual reservoir distribution in the Qingsong Ordovician stone pit; the reef limestone of Carboniferous and Permian in the Halajun Basin in the southwest of Piqiang village.
2014, 32(4): 784-789.
Abstract:
In order to understand the organic geochemistry feature of the source rocks, GC-MS analyses on saturated hydrocarbons in the Upper Permian Lucaogou & Pingdiquan Formation source rocks from the Junggar and Santanghu Basins in Eastern Xinjiang were performed. Complete short-chain steranes with C19-21~C26 R were detected in mass chromatograms at m/z217. The detection of these compound series indicates that a flourish of sponges, algae (e.g., red algae and Gloeocapsomorpha prisca) and other lower aquatic organisms existed in saline waters under arid conditions. These original organic materials experienced severe bacterial biodegradation during the early deposition stage; the original organic matter and the products of microbial degradation were preserved together and became precursors of hydrocarbon generation.
In order to understand the organic geochemistry feature of the source rocks, GC-MS analyses on saturated hydrocarbons in the Upper Permian Lucaogou & Pingdiquan Formation source rocks from the Junggar and Santanghu Basins in Eastern Xinjiang were performed. Complete short-chain steranes with C19-21~C26 R were detected in mass chromatograms at m/z217. The detection of these compound series indicates that a flourish of sponges, algae (e.g., red algae and Gloeocapsomorpha prisca) and other lower aquatic organisms existed in saline waters under arid conditions. These original organic materials experienced severe bacterial biodegradation during the early deposition stage; the original organic matter and the products of microbial degradation were preserved together and became precursors of hydrocarbon generation.
2014, 32(4): 623-633.
Abstract:
Heqing-Songgui area is located in Heqing County of Dali prefecture in YunNan province, it is situated in southeast of Tibetan Plateau and the middle of Hengduan mountains, between Maan mountain and Jinsha river, it belongs to Heqing-Songgui basin where the west bank of Jinsha river. This paper is as ore-bearing rock series on Zhongwo Formation of upper triassic in Heqing-Songgui area, and for the characteristics and classification of sedimentary facies and evolution has carried on the systematic research. According to the detailed observation of the rock types' characteristics, restricted gulf facies-lagoon facies have been developed in the study area. Top of subtidal zone, intertidal zone, supralittoral zone, upralittoral-swamp are developed. Based on depth analysis about profile structure and rock geochemistry, by NW-SE/SSW-NNE/EW three sedimentary facies profiles comparative studying, restored facies and palaeogeography their appearance and evolution. Al-bearing rock series which in the bottom of Zhongwo Formation is strictly controlled by unconformity surface topography and karst landform which is on the upper top of Beiya Formation limestone, it can provide theoretical basis for Bauxite exploration.
Heqing-Songgui area is located in Heqing County of Dali prefecture in YunNan province, it is situated in southeast of Tibetan Plateau and the middle of Hengduan mountains, between Maan mountain and Jinsha river, it belongs to Heqing-Songgui basin where the west bank of Jinsha river. This paper is as ore-bearing rock series on Zhongwo Formation of upper triassic in Heqing-Songgui area, and for the characteristics and classification of sedimentary facies and evolution has carried on the systematic research. According to the detailed observation of the rock types' characteristics, restricted gulf facies-lagoon facies have been developed in the study area. Top of subtidal zone, intertidal zone, supralittoral zone, upralittoral-swamp are developed. Based on depth analysis about profile structure and rock geochemistry, by NW-SE/SSW-NNE/EW three sedimentary facies profiles comparative studying, restored facies and palaeogeography their appearance and evolution. Al-bearing rock series which in the bottom of Zhongwo Formation is strictly controlled by unconformity surface topography and karst landform which is on the upper top of Beiya Formation limestone, it can provide theoretical basis for Bauxite exploration.
2014, 32(4): 643-653.
Abstract:
Research result of provenance tracing and geological events setting for clastic sandstone deposit in the first member of Shanxi Formation and the eighth member of Shihezi Formation of the Upper Paleozoic in Wushenqi area, Ordos Basin, using LA-ICP-MS in situ U-Pb dating and U, Th element content, combined with adjacent areas age and lithology data analysis of the detrital zircons from the sandstones reveals that the age of source rock in the first member of Shanxi Formation and the eighth member of Shihezi Formation from Archean, Proterozoic, Proterozoic, Late Paleozoic, respectively, with relationship about the formation, proliferation and cratonization of the North China block, and is the product of a multi-stage evolution of the North China Craton geological events. By comparative study of isotopic chronology with the potential parent rocks, it can be concluded that the provenance of the clastic sandstone deposit in Wushenqi area mainly came from the environment of within the North China Craton and the northern edge of the Ordos Basin, and the basement metamorphic rocks and the metamorphic rocks, which it exposed in the environment of eastern North China Platform in the Early Archean and the new Archean, the gneissic granite and TTG genesis or granulites bodes from the northern edge of the Ordos Basin and the West of the Ural Mountains-Jining area in the Late Archean and the Late Paleoproterozoic, In addition, magmatic rocks bodes of Yinshan block formed in continental crust is one of the important areas of provenance in Wushenqi area between 390~310Ma. The new results is of very important significance for deeply corresponding to the time between the age of detrital zircon in the Upper Paleozoic from Wushenqi area and the North China Craton geological events, but it is the first time to provide important information from the source rock on the geological events of the North China craton,which it may exist in Wushenqi area.
Research result of provenance tracing and geological events setting for clastic sandstone deposit in the first member of Shanxi Formation and the eighth member of Shihezi Formation of the Upper Paleozoic in Wushenqi area, Ordos Basin, using LA-ICP-MS in situ U-Pb dating and U, Th element content, combined with adjacent areas age and lithology data analysis of the detrital zircons from the sandstones reveals that the age of source rock in the first member of Shanxi Formation and the eighth member of Shihezi Formation from Archean, Proterozoic, Proterozoic, Late Paleozoic, respectively, with relationship about the formation, proliferation and cratonization of the North China block, and is the product of a multi-stage evolution of the North China Craton geological events. By comparative study of isotopic chronology with the potential parent rocks, it can be concluded that the provenance of the clastic sandstone deposit in Wushenqi area mainly came from the environment of within the North China Craton and the northern edge of the Ordos Basin, and the basement metamorphic rocks and the metamorphic rocks, which it exposed in the environment of eastern North China Platform in the Early Archean and the new Archean, the gneissic granite and TTG genesis or granulites bodes from the northern edge of the Ordos Basin and the West of the Ural Mountains-Jining area in the Late Archean and the Late Paleoproterozoic, In addition, magmatic rocks bodes of Yinshan block formed in continental crust is one of the important areas of provenance in Wushenqi area between 390~310Ma. The new results is of very important significance for deeply corresponding to the time between the age of detrital zircon in the Upper Paleozoic from Wushenqi area and the North China Craton geological events, but it is the first time to provide important information from the source rock on the geological events of the North China craton,which it may exist in Wushenqi area.
2014, 32(4): 663-668.
Abstract:
We put great importance to research of leaching behavior of elements in soil science and aeolian sedimentary geochemistry. However, the present study is limited to the level of qualitative description, at the same time, there are many mistakes in the methods and parameters. This paper mainly analyzes the microcosmic process of chemical leaching. we hold the view that it is Logarithmic between the atmospheric precipitation and the poured out elements in liquid. Futhermore, the exact function relation is given. The experimental result of the soil soaking, centrifuging and ion chromatography using the soil surrounding Lanzhou city, also proved the function relation is established. Additionally, we obtained the methods how do a quantitative representation of elements leaching properties by using leaching coefficient η or λ. It may have a important significance on the research of the assessment of soil fertility maintenance capability and aeolian deposition-geochemistry
We put great importance to research of leaching behavior of elements in soil science and aeolian sedimentary geochemistry. However, the present study is limited to the level of qualitative description, at the same time, there are many mistakes in the methods and parameters. This paper mainly analyzes the microcosmic process of chemical leaching. we hold the view that it is Logarithmic between the atmospheric precipitation and the poured out elements in liquid. Futhermore, the exact function relation is given. The experimental result of the soil soaking, centrifuging and ion chromatography using the soil surrounding Lanzhou city, also proved the function relation is established. Additionally, we obtained the methods how do a quantitative representation of elements leaching properties by using leaching coefficient η or λ. It may have a important significance on the research of the assessment of soil fertility maintenance capability and aeolian deposition-geochemistry
2014, 32(4): 677-683.
Abstract:
This paper analyzes the element contents in different topsoil and with the methods of statistics inquired into the element contents and its spatial characteristics in Hetao plain. The results show that the element contents (Al and Fe) of Hetao have significant differences with active elements (Na and Sr), but the heavy metal elements(Cu，Mn，Pb，Zn) display abnormally and variable coefficient is larger, which shows heavily influenced by human activities and acts as the indicator of human industrial activities. Spatial distribution of the elements in topsoil shows that the stable elements(Ca，Mg) in the topsoil have a strong spatial autocorrelation, which reflects that the soil parent material have a great effect on element contents; theoretical model of the element P is linear, this result has something to do with using excess P fertilization in much farmland; heavy metal elements in the topsoil have a medium spatial autocorrelation, which subjects to the small scale factors such as industrial and agricultural production. In Hetao plain, the spatial characteristics of heavy metal element contents show that the northern and southern area are relatively high, and northern area exceeds the southern area, the change from the western to eastern area is not obvious, this phenomenon is closely related to human activities such as local industrial mining, urbanization development, industrial and agricultural production and so on.
This paper analyzes the element contents in different topsoil and with the methods of statistics inquired into the element contents and its spatial characteristics in Hetao plain. The results show that the element contents (Al and Fe) of Hetao have significant differences with active elements (Na and Sr), but the heavy metal elements(Cu，Mn，Pb，Zn) display abnormally and variable coefficient is larger, which shows heavily influenced by human activities and acts as the indicator of human industrial activities. Spatial distribution of the elements in topsoil shows that the stable elements(Ca，Mg) in the topsoil have a strong spatial autocorrelation, which reflects that the soil parent material have a great effect on element contents; theoretical model of the element P is linear, this result has something to do with using excess P fertilization in much farmland; heavy metal elements in the topsoil have a medium spatial autocorrelation, which subjects to the small scale factors such as industrial and agricultural production. In Hetao plain, the spatial characteristics of heavy metal element contents show that the northern and southern area are relatively high, and northern area exceeds the southern area, the change from the western to eastern area is not obvious, this phenomenon is closely related to human activities such as local industrial mining, urbanization development, industrial and agricultural production and so on.
2014, 32(4): 692-699.
Abstract:
The response of Changjiang delta to river sediment declination has attracted more and more attention in recent years. The present paper analyses radiometric 210Pb and 137Cs and grain size of the core on the north of the subaqueous delta and extracts sensitive grain size population, which help explore the response of the delta to channel regime evolution and river sediment declination. The radioactive nuclear results show mean sedimentation rate of 3.28 cm/yr for the whole core by 210Pb. This rate is much higher than 1.78~1.90 cm/yr by 137Cs for the upper core section (<104 cm), mainly because of different deposit environments in the two sections. Combined with the results of 210Pb, 137Cs and spherical carbon particle in the previous study, sedimentation rate of the upper core section is about 1.85 cm/yr. Grain size results show that from finer sediments with the same feature as surface sediments of mud region in the Changjiang estuary control the lower core section before 1954, which implies the northern boundary of mud region beyond this core at that time. The sediments become coarsening upward the core after 1954, which feature are close to shelf sediments. The above environmental change might be closely related to the block of north branch in the estuary after 1954, when it was away from influence of Changjiang freshwater and sediments became coarser due to reformation and join of continental material by marine dynamics. However, in terms of sediment composition, we did not find an obvious response to significant sediment supply decline of the Changjiang after 1980’s. Therefore, besides sediment supply declination, coarsening due to estuarine channel regime evolution might be a contributor to western retreat of clay-sand boundary off the Changjiang estuary in the recent studies.
The response of Changjiang delta to river sediment declination has attracted more and more attention in recent years. The present paper analyses radiometric 210Pb and 137Cs and grain size of the core on the north of the subaqueous delta and extracts sensitive grain size population, which help explore the response of the delta to channel regime evolution and river sediment declination. The radioactive nuclear results show mean sedimentation rate of 3.28 cm/yr for the whole core by 210Pb. This rate is much higher than 1.78~1.90 cm/yr by 137Cs for the upper core section (<104 cm), mainly because of different deposit environments in the two sections. Combined with the results of 210Pb, 137Cs and spherical carbon particle in the previous study, sedimentation rate of the upper core section is about 1.85 cm/yr. Grain size results show that from finer sediments with the same feature as surface sediments of mud region in the Changjiang estuary control the lower core section before 1954, which implies the northern boundary of mud region beyond this core at that time. The sediments become coarsening upward the core after 1954, which feature are close to shelf sediments. The above environmental change might be closely related to the block of north branch in the estuary after 1954, when it was away from influence of Changjiang freshwater and sediments became coarser due to reformation and join of continental material by marine dynamics. However, in terms of sediment composition, we did not find an obvious response to significant sediment supply decline of the Changjiang after 1980’s. Therefore, besides sediment supply declination, coarsening due to estuarine channel regime evolution might be a contributor to western retreat of clay-sand boundary off the Changjiang estuary in the recent studies.
2014, 32(4): 710-723.
Abstract:
In China, gentle-slope deltas have formed lots of large oilfields. As to the depositional model of gentle-slope deltas, numerous studies have been made, but most of them were on ancient strata. As different researchers may give out different interpretation about stratigraphic correlation and sedimentary environments, the depositional models summaried are various, and their reliability is low. Therefore, in this paper a modern gentle-slope delta-Gangjiang Delta in Poyang Lake-was studied systematically, through methods such as field observation and measurement, troughs, shallow boreholes, radar, grainsize analysis, etc. And the depositional model of gentle-slope delta was established. Following important conclusions were drawn through this study：① Two new types of sandbodies were found on the delta plain, i.e. branching-point bar and combining-point bar, the former occurs at the branching point of a distributary channel, and the latter occurs at the combining point of two distributary channels. This implies that branching points and combining points are also favorable place for oil and gas accumulation. ② Within channel sandbodies, three types of mud drapes are found, i.e. sheet drape, isolated drape and residual drape, and their origin was interpreted. ③ Statistics of quantitative parameters of distributary channels were made, and it was found that in downstream direction the channels become narrower as branching increases, and the width decrease about 1/2 after each branching; channel branching frequency increases; channel sinuosity decreases; channel sediment becomes finer and thinner, and sandbody interconnection degree decreases. ④ In delta front, there are no underwater distributary channels, and only mouth bars and sand sheet are developed. ⑤ Due to gentle slope, small fluctuation of lake level may cause lagre scale shifting of coastline, and may result in frequent alternation of subaerial and underwater deposits. In seismic reflection profile, gentle-slope delta deposits will not show imbricated reflection, and only show parallel or subparallel reflection.
In China, gentle-slope deltas have formed lots of large oilfields. As to the depositional model of gentle-slope deltas, numerous studies have been made, but most of them were on ancient strata. As different researchers may give out different interpretation about stratigraphic correlation and sedimentary environments, the depositional models summaried are various, and their reliability is low. Therefore, in this paper a modern gentle-slope delta-Gangjiang Delta in Poyang Lake-was studied systematically, through methods such as field observation and measurement, troughs, shallow boreholes, radar, grainsize analysis, etc. And the depositional model of gentle-slope delta was established. Following important conclusions were drawn through this study：① Two new types of sandbodies were found on the delta plain, i.e. branching-point bar and combining-point bar, the former occurs at the branching point of a distributary channel, and the latter occurs at the combining point of two distributary channels. This implies that branching points and combining points are also favorable place for oil and gas accumulation. ② Within channel sandbodies, three types of mud drapes are found, i.e. sheet drape, isolated drape and residual drape, and their origin was interpreted. ③ Statistics of quantitative parameters of distributary channels were made, and it was found that in downstream direction the channels become narrower as branching increases, and the width decrease about 1/2 after each branching; channel branching frequency increases; channel sinuosity decreases; channel sediment becomes finer and thinner, and sandbody interconnection degree decreases. ④ In delta front, there are no underwater distributary channels, and only mouth bars and sand sheet are developed. ⑤ Due to gentle slope, small fluctuation of lake level may cause lagre scale shifting of coastline, and may result in frequent alternation of subaerial and underwater deposits. In seismic reflection profile, gentle-slope delta deposits will not show imbricated reflection, and only show parallel or subparallel reflection.
2014, 32(4): 734-743.
Abstract:
Based on rock core documentation, well logging analysis and the rock fragment data, we carried out the sedimentology research on the Triassic Baikouquan Group in Wu 36 area of Junggar Basin. This study revealed that the Baikouquan Group developped in alluvial fan system. The glutenite is characterized by unusually high natural gamma and the mudstone is characterized by low inside the alluvial fan. This feature is mainly controlled by the high radioactive substance in the original rock, for example the tuff. The spatial variation in high natural gamma anomaly was influenced by sediment grain size, transport distance and facies distribution. According to the spatial variation characteristics of Gamma anomaly, we established a clay content formula and put forward a new method on the division of sedimentary facies. Our study area mainly develops mid-fan braided stream line microfacies, mid-fan braided stream sand island microfacies, mid-fan sheetflood microfacies and cross flow microfacies in marginal subfacies. We also carefully portrayed the distribution and vertical evolution of these sedimentary microfacies of different stages. The results show that the 3rd member in Baikouquan Group developed four fan bodies. There is a sedimentary evolutionary sequence in the vertical profile controlled by fast dereliction and slow retrograding. The 2nd member in Baikouquan Group developed three fan bodies and presented a retrograding evolutionary sequence in the vertical. The 1st member in Baikouquan Group performed the alluvial fan marginal sedimentary. Compared with the actual production, this study better explained the production status of the regional producing well and verified the feasibility and practicality of using natural gamma characteristics of high natural gamma glutinite to make research on sedimentary microfacies.
Based on rock core documentation, well logging analysis and the rock fragment data, we carried out the sedimentology research on the Triassic Baikouquan Group in Wu 36 area of Junggar Basin. This study revealed that the Baikouquan Group developped in alluvial fan system. The glutenite is characterized by unusually high natural gamma and the mudstone is characterized by low inside the alluvial fan. This feature is mainly controlled by the high radioactive substance in the original rock, for example the tuff. The spatial variation in high natural gamma anomaly was influenced by sediment grain size, transport distance and facies distribution. According to the spatial variation characteristics of Gamma anomaly, we established a clay content formula and put forward a new method on the division of sedimentary facies. Our study area mainly develops mid-fan braided stream line microfacies, mid-fan braided stream sand island microfacies, mid-fan sheetflood microfacies and cross flow microfacies in marginal subfacies. We also carefully portrayed the distribution and vertical evolution of these sedimentary microfacies of different stages. The results show that the 3rd member in Baikouquan Group developed four fan bodies. There is a sedimentary evolutionary sequence in the vertical profile controlled by fast dereliction and slow retrograding. The 2nd member in Baikouquan Group developed three fan bodies and presented a retrograding evolutionary sequence in the vertical. The 1st member in Baikouquan Group performed the alluvial fan marginal sedimentary. Compared with the actual production, this study better explained the production status of the regional producing well and verified the feasibility and practicality of using natural gamma characteristics of high natural gamma glutinite to make research on sedimentary microfacies.
2014, 32(4): 754-765.
Abstract:
In order to in-depth show the specialty and the main controlling factors of the Carboniferous weathering crust reservoirs in Ke-Bai fault zone of Junggar Basin and to seek high-quality reservoirs, cores, conventional thin section, casting thin section, fluorescence thin sections, and FMI were analyzed, finally the basic features and forming mechanism of volcanic pores and fractures were discussed. Results show that the types and characteristics of the pores and fractures in volcanic reservoir are diversified, which is composed mainly of secondary pores and fractures, characterized by low porosity and extremely low permeability. Because of higher brittleness, more structural fractures are found in lava rocks, and primary pores are mainly distributed on the top of lava rocks. Secondary pores and fractures are likely to form near faults and weathering crust, and the effective reservoirs exist within 300m downward from the unconformity. According to the combination way, the reservoir space can be divided into four categories: fracture-pore, fracture-intergranular pore, fracture-phenocryst dissolved pore, and fracture-matrix dissolved pore. The late weathering leaching, tectonic fracturing and dissolution effect are benificial for reservoir performance improvement of weathering crust, but hydrothermal alteration and cementation-filling effect are destructive. Oil accumulation was mainly controlled by fault and unconformity, and step-type fault block oil reservoirs mainly controlled by fracture and large stratigraphic oil reservoirs mainly controlled by unconformity form in the region.
In order to in-depth show the specialty and the main controlling factors of the Carboniferous weathering crust reservoirs in Ke-Bai fault zone of Junggar Basin and to seek high-quality reservoirs, cores, conventional thin section, casting thin section, fluorescence thin sections, and FMI were analyzed, finally the basic features and forming mechanism of volcanic pores and fractures were discussed. Results show that the types and characteristics of the pores and fractures in volcanic reservoir are diversified, which is composed mainly of secondary pores and fractures, characterized by low porosity and extremely low permeability. Because of higher brittleness, more structural fractures are found in lava rocks, and primary pores are mainly distributed on the top of lava rocks. Secondary pores and fractures are likely to form near faults and weathering crust, and the effective reservoirs exist within 300m downward from the unconformity. According to the combination way, the reservoir space can be divided into four categories: fracture-pore, fracture-intergranular pore, fracture-phenocryst dissolved pore, and fracture-matrix dissolved pore. The late weathering leaching, tectonic fracturing and dissolution effect are benificial for reservoir performance improvement of weathering crust, but hydrothermal alteration and cementation-filling effect are destructive. Oil accumulation was mainly controlled by fault and unconformity, and step-type fault block oil reservoirs mainly controlled by fracture and large stratigraphic oil reservoirs mainly controlled by unconformity form in the region.
2014, 32(4): 776-783.
Abstract:
The lithological class reservoir of depression syncline area is a new field of oil and gas exploration. This paper took Song-Liao Basin Shengxi-Xujiaweizi syncline Putaohua reservoir as the research object, and in the base of tectonic units segmentation in syncline area, analyzed the reservoir type and oil-water distribution law of different tectonic parts: Syncline outer edge ramp area mainly develops oil-water interface relatively unified structure-lithological reservoir; Syncline transition steep slope zone develops oil upside of the water or oil-water interblended fault-lithological reservoir; Syncline center deep depression area develops oil-water interblended lithological reservoir; Oil is controlled by the antiformal structure of fault dense zone which present “banded” distributions on plane, it is controlled by the sedimentary evolution sequence and propertied differences in the vertical direction and distributions with “select layer”. Then, it is concluded four main factors of the syncline area accumulation by studied syncline area accumulation mainly factor and model:① the effective hydrocarbon source rocks matching palaeostructure control oil distribution on plane;② oil source faults compose of advantage translocation channels;③ physical property differences cause the high pore and permeability of distributary channel sand bodies becomes oil accumulation premium reservoirs;④ fault dense zone antiformal structure becomes the main part of oil enrichment. Finally, syncline area has established four kinds of accumulation models: ① the control reservoir model of syncline center deep depression area fault dense zone antiformal structure; ② the control reservoir model of syncline center deep depression area dense zone distributary channel oil selective filling; ③ the control reservoir model of syncline transition steep slope zone reverse fault barrier; ④ the control reservoir model of syncline outer ramp area positive structure trap.
The lithological class reservoir of depression syncline area is a new field of oil and gas exploration. This paper took Song-Liao Basin Shengxi-Xujiaweizi syncline Putaohua reservoir as the research object, and in the base of tectonic units segmentation in syncline area, analyzed the reservoir type and oil-water distribution law of different tectonic parts: Syncline outer edge ramp area mainly develops oil-water interface relatively unified structure-lithological reservoir; Syncline transition steep slope zone develops oil upside of the water or oil-water interblended fault-lithological reservoir; Syncline center deep depression area develops oil-water interblended lithological reservoir; Oil is controlled by the antiformal structure of fault dense zone which present “banded” distributions on plane, it is controlled by the sedimentary evolution sequence and propertied differences in the vertical direction and distributions with “select layer”. Then, it is concluded four main factors of the syncline area accumulation by studied syncline area accumulation mainly factor and model:① the effective hydrocarbon source rocks matching palaeostructure control oil distribution on plane;② oil source faults compose of advantage translocation channels;③ physical property differences cause the high pore and permeability of distributary channel sand bodies becomes oil accumulation premium reservoirs;④ fault dense zone antiformal structure becomes the main part of oil enrichment. Finally, syncline area has established four kinds of accumulation models: ① the control reservoir model of syncline center deep depression area fault dense zone antiformal structure; ② the control reservoir model of syncline center deep depression area dense zone distributary channel oil selective filling; ③ the control reservoir model of syncline transition steep slope zone reverse fault barrier; ④ the control reservoir model of syncline outer ramp area positive structure trap.
2014, 32(4): 790-796.
Abstract:
Geochemical characteristics of saturated hydrocarbons have been discussed on the basis of GC/MS analysis for the 10 typical coal-bearing source rock samples in northeast Ordos Basin. Three series of rearranged hopanes, 17α (H)-diahopanes, 18α (H)-neohopanes and unidentified earlyeluting rearranged hopanes, were detected. The analytical results showed that the hopane series compounds have two different distribution patterns. One is conventional pattern, which has high abundance of regular hopanes, low abundance of 17α (H)-diahopanes and 18α (H)-neohopanes, represented by source rock samples from Yu 20 and Shuang 1 well. The other one is unconventional model, characterized by abnormally rich in 17α (H)-diahopanes and a C30-early-eluting rearranged hopane, represented by source rock samples from Su 27 well. The source rocks from Su 27 well high relative abundance of 17α (H)-diahopanes and also high absolute concentration. The main controlling factors of extremely abundant 17α (H)-diahopanes are discussed from the composition of organic materials, maceral, the abundance of organic matters and its occurrence, maturity, depositional and diagenetic environment. The result shows that the origin and accumulation of high abundance of 17α (H)-diahopanes in source rocks has a close relationship with higher plants source materials. Weak oxidation to oxidation fan marginal peat bog facies is a favorable sedimentary facies for forming a significant proportion of 17α (H)-diahopanes. However, the influences of maceral, maturity, the abundance of organic matters and its occurrence are not sure.
Geochemical characteristics of saturated hydrocarbons have been discussed on the basis of GC/MS analysis for the 10 typical coal-bearing source rock samples in northeast Ordos Basin. Three series of rearranged hopanes, 17α (H)-diahopanes, 18α (H)-neohopanes and unidentified earlyeluting rearranged hopanes, were detected. The analytical results showed that the hopane series compounds have two different distribution patterns. One is conventional pattern, which has high abundance of regular hopanes, low abundance of 17α (H)-diahopanes and 18α (H)-neohopanes, represented by source rock samples from Yu 20 and Shuang 1 well. The other one is unconventional model, characterized by abnormally rich in 17α (H)-diahopanes and a C30-early-eluting rearranged hopane, represented by source rock samples from Su 27 well. The source rocks from Su 27 well high relative abundance of 17α (H)-diahopanes and also high absolute concentration. The main controlling factors of extremely abundant 17α (H)-diahopanes are discussed from the composition of organic materials, maceral, the abundance of organic matters and its occurrence, maturity, depositional and diagenetic environment. The result shows that the origin and accumulation of high abundance of 17α (H)-diahopanes in source rocks has a close relationship with higher plants source materials. Weak oxidation to oxidation fan marginal peat bog facies is a favorable sedimentary facies for forming a significant proportion of 17α (H)-diahopanes. However, the influences of maceral, maturity, the abundance of organic matters and its occurrence are not sure.
