2016 Vol. 34, No. 4
Display Method:
2016, 34(4): 615-625.
doi: 10.14027/j.cnki.cjxb.2016.04.001
Abstract:
As the geochemical characteristics of surface sediments usually recorded the information of the sediments, such as the transport medium and sedimentation process, analyses of their mineral composition and provenance can provide valuable indications for paleoenvironmental reconstruction. This study provides factor analyses of 7 major dioxides and 15 micro elements in the surface sediments taken from the river-desert transition zones in the Keriya River, Mu Bulag River, and Xi Xar Moron River basins. It was found that the common factors derived from the factor analyses among the three river basins or their upper, middle, and lower reaches mainly included stable Fe and Mn minerals, less stable feldspars, calcite (dolomite) and other silicate minerals, and stable rare earth elements and heavy minerals. The factor analysis of the relationships between the rivers indicated that the surface sediments along the rivers from west to east showed progressively increasing abundance and movement of chemical elements and degrees of chemical weathering. The factor analyses at a river basin scale indicated that from the upper reaches to the lower reaches, samples exhibiting increasingly complex chemical compositions. The spatial distribution patterns of the chemical elements in the surface sediments from different river sections or different river banks showed correlations with their provenance, geomorphic pattern, water conditions, and other factors. From the riverbed to the river terrace, the surface sediments on the three geomorphic units, from riverbed-flood plain, low river terrace composed of sand dunes to the high terrace, exhibited heterogeneous, progressive variations in their chemical compositions. This may result from their varying distances from the river courses, provenances and dynamic factors. The preliminary results of the study are expected to provide references for research into the chemical composition characteristics of surface sediments in river-desert transition zones and their variation mechanisms in response to changes of aeolian-fluvial interactions.
As the geochemical characteristics of surface sediments usually recorded the information of the sediments, such as the transport medium and sedimentation process, analyses of their mineral composition and provenance can provide valuable indications for paleoenvironmental reconstruction. This study provides factor analyses of 7 major dioxides and 15 micro elements in the surface sediments taken from the river-desert transition zones in the Keriya River, Mu Bulag River, and Xi Xar Moron River basins. It was found that the common factors derived from the factor analyses among the three river basins or their upper, middle, and lower reaches mainly included stable Fe and Mn minerals, less stable feldspars, calcite (dolomite) and other silicate minerals, and stable rare earth elements and heavy minerals. The factor analysis of the relationships between the rivers indicated that the surface sediments along the rivers from west to east showed progressively increasing abundance and movement of chemical elements and degrees of chemical weathering. The factor analyses at a river basin scale indicated that from the upper reaches to the lower reaches, samples exhibiting increasingly complex chemical compositions. The spatial distribution patterns of the chemical elements in the surface sediments from different river sections or different river banks showed correlations with their provenance, geomorphic pattern, water conditions, and other factors. From the riverbed to the river terrace, the surface sediments on the three geomorphic units, from riverbed-flood plain, low river terrace composed of sand dunes to the high terrace, exhibited heterogeneous, progressive variations in their chemical compositions. This may result from their varying distances from the river courses, provenances and dynamic factors. The preliminary results of the study are expected to provide references for research into the chemical composition characteristics of surface sediments in river-desert transition zones and their variation mechanisms in response to changes of aeolian-fluvial interactions.
2016, 34(4): 626-633.
doi: 10.14027/j.cnki.cjxb.2016.04.002
Abstract:
The trace fossils in Guiyang area was a good proxy for ecosystem recovery after the end-Permian biotic crisis. A total of 8 ichnogenera and 9 ichnospecies were identified in the Anshun Formation(including four members,A1,A2,A3,A4), their vertical distribution and evolution indicate that:trace fossils were dominated by small, simple, horizontal burrows of Planolites montanus, Palaeophycus curvatus and Phycodes palmatus in A1; Trace fossils become more abundant and diverse, and bioturbation index increased in A2 and A3. In addition to the 3 ichnospecies ichnogenera noted in A1, 6 other ichnospecies were abundant in these two members:Beaconichnus darwinum, Chondrites recurvus, Thalassinoides paradoxicus, Thalassinoides horizontalis, Arenicolites isp., Rhizocorallium commune. Complex fauna with Rhizocorallium and Thalassinoides in A3 represented a significant improvement in the marine environment in the late Early Triassic. No trace fossils were found in A4. The sedimentary environment from A1 to A3 occur in platform margin shoal to platform slope to tidal to supratidal zone, respectively. During A1 to A3, the oxygen conditions of marine environment had ameliorated. This condition could provide an optimal zone for benthic colonization. The characteristics of the trace fossils from upper A1 to A3 indicated that the study area came into the habitable zone environment. A4 was deposited in the semi restricted platform, and in the region above the habitable zone that the biological activity is relatively weak. The study of trace fossils suggested marine benthic recovery system was relatively active in the carbonate platform margin.
The trace fossils in Guiyang area was a good proxy for ecosystem recovery after the end-Permian biotic crisis. A total of 8 ichnogenera and 9 ichnospecies were identified in the Anshun Formation(including four members,A1,A2,A3,A4), their vertical distribution and evolution indicate that:trace fossils were dominated by small, simple, horizontal burrows of Planolites montanus, Palaeophycus curvatus and Phycodes palmatus in A1; Trace fossils become more abundant and diverse, and bioturbation index increased in A2 and A3. In addition to the 3 ichnospecies ichnogenera noted in A1, 6 other ichnospecies were abundant in these two members:Beaconichnus darwinum, Chondrites recurvus, Thalassinoides paradoxicus, Thalassinoides horizontalis, Arenicolites isp., Rhizocorallium commune. Complex fauna with Rhizocorallium and Thalassinoides in A3 represented a significant improvement in the marine environment in the late Early Triassic. No trace fossils were found in A4. The sedimentary environment from A1 to A3 occur in platform margin shoal to platform slope to tidal to supratidal zone, respectively. During A1 to A3, the oxygen conditions of marine environment had ameliorated. This condition could provide an optimal zone for benthic colonization. The characteristics of the trace fossils from upper A1 to A3 indicated that the study area came into the habitable zone environment. A4 was deposited in the semi restricted platform, and in the region above the habitable zone that the biological activity is relatively weak. The study of trace fossils suggested marine benthic recovery system was relatively active in the carbonate platform margin.
2016, 34(4): 634-644.
doi: 10.14027/j.cnki.cjxb.2016.04.003
Abstract:
Based on 3-D seismic material and drill-hole data in Moxi-Gaoshiti area, the variation trend of the thickness from the bottom of Longwangmiao to the bottom of Permian was chosen to represent the tectonic palaeogeomorphology of the lower bottom of Longwangmiao Formation. Since the analysis found that the deposition of the overlying Gaotai Formation could fill and level up the Longwangmiao Formation at the end of Longwangmiao sedimentation, and there is a positive correlation between the thickness from the bottom of Longwangmiao to the bottom of Permian and the thickness of Gaotai Formation, the tectonic palaeogeomorphology of the lower bottom of Longwangmiao Formation could represent the Longwangmiao sedimentary palaeogeomorphology before the deposition of Gaotai Formation approximately. Meanwhile, the relatively low position at the southern margin of the palaeogeomorphology highland was the area where the grain beach of Longwangmiao Formation was most developed, it suggested that the palaeogeomorphology during the Longwangmiao sedimentation was similar to this palaeogeomorphology. After further analysis, we believe that palaeogeomorphology controlled the activity routines of the bedding flowing karst water which was supplied by the erosion window during the Caledonian-Hercynian period, and then determined the differences in development and quality change of the karst reservoirs:in the slope belt and the ravine area where the karst water converge, the karst reformation is the strongest, the reservoirs formed here are the best; in the isolated highlands, the reformation is relatively weak, and the reservoir quality is poor. The results show that this palaeogeomorphology was the result of inheritance developing of sedimentary palaeogeomorpholog during Longwangmiao depositon, and the newly drilled wells and development wells have proven its controlling action on sedimentation and reservoirs. This method and thought is helpful and referential for the same genre in similar geological background.
Based on 3-D seismic material and drill-hole data in Moxi-Gaoshiti area, the variation trend of the thickness from the bottom of Longwangmiao to the bottom of Permian was chosen to represent the tectonic palaeogeomorphology of the lower bottom of Longwangmiao Formation. Since the analysis found that the deposition of the overlying Gaotai Formation could fill and level up the Longwangmiao Formation at the end of Longwangmiao sedimentation, and there is a positive correlation between the thickness from the bottom of Longwangmiao to the bottom of Permian and the thickness of Gaotai Formation, the tectonic palaeogeomorphology of the lower bottom of Longwangmiao Formation could represent the Longwangmiao sedimentary palaeogeomorphology before the deposition of Gaotai Formation approximately. Meanwhile, the relatively low position at the southern margin of the palaeogeomorphology highland was the area where the grain beach of Longwangmiao Formation was most developed, it suggested that the palaeogeomorphology during the Longwangmiao sedimentation was similar to this palaeogeomorphology. After further analysis, we believe that palaeogeomorphology controlled the activity routines of the bedding flowing karst water which was supplied by the erosion window during the Caledonian-Hercynian period, and then determined the differences in development and quality change of the karst reservoirs:in the slope belt and the ravine area where the karst water converge, the karst reformation is the strongest, the reservoirs formed here are the best; in the isolated highlands, the reformation is relatively weak, and the reservoir quality is poor. The results show that this palaeogeomorphology was the result of inheritance developing of sedimentary palaeogeomorpholog during Longwangmiao depositon, and the newly drilled wells and development wells have proven its controlling action on sedimentation and reservoirs. This method and thought is helpful and referential for the same genre in similar geological background.
2016, 34(4): 645-652.
doi: 10.14027/j.cnki.cjxb.2016.04.004
Abstract:
Alluvial fan could provide valuable information in recording local climate change, reflecting neotectonic movement and rebuilding paleogeographic environment. Compared with inland areas, coastal zone as the interface of three layers of atmosphere, ocean and land has distinct differences in depositional environment, resulting in unique material sources and dynamic condition. Thus, alluvial fan in coastal zone may have special geological landscape process and sedimentary structure characteristics. There is a great sandy hill which covered by grayish yellow eolian sand layer in the northern Junshan along the coast of Haitan island, Fujian Province. It seems to be a big aeolian dunes, but in fact alluvial fan shape. In this paper, we used the ground penetrating radar (GPR) to detect the internal sedimentary structure of the great sandy hill, and tried to find out its origin. Detection results show that in the middle-upper part of the great sandy hill, there developed sedimentary cycle composed of angular gravel or coarse to fine sand and groove depositional structure, which presents the depositional characteristics of traditional alluvial fan; in the middle-lower part of the great sandy hill, there developed curved depositional structure presented alternately in the layer. Based on the results, we also found that detecting depth of the alluvial fan record the wide range of three to five times of piedmont ancient flood sedimentary history. Combining the geological investigation in the great sandy hill, we assumed that the great sandy hill is the remnant of alluvial fan, which contains the characteristics of aeolian sediments along the coastal zone. The research is benefit for further understanding of the evolution of paleogeographic environment in the coastal zone of South China, and enriching the research of dynamic geomorphological processes on coastal zone and the sedimental structures of alluvial fan.
Alluvial fan could provide valuable information in recording local climate change, reflecting neotectonic movement and rebuilding paleogeographic environment. Compared with inland areas, coastal zone as the interface of three layers of atmosphere, ocean and land has distinct differences in depositional environment, resulting in unique material sources and dynamic condition. Thus, alluvial fan in coastal zone may have special geological landscape process and sedimentary structure characteristics. There is a great sandy hill which covered by grayish yellow eolian sand layer in the northern Junshan along the coast of Haitan island, Fujian Province. It seems to be a big aeolian dunes, but in fact alluvial fan shape. In this paper, we used the ground penetrating radar (GPR) to detect the internal sedimentary structure of the great sandy hill, and tried to find out its origin. Detection results show that in the middle-upper part of the great sandy hill, there developed sedimentary cycle composed of angular gravel or coarse to fine sand and groove depositional structure, which presents the depositional characteristics of traditional alluvial fan; in the middle-lower part of the great sandy hill, there developed curved depositional structure presented alternately in the layer. Based on the results, we also found that detecting depth of the alluvial fan record the wide range of three to five times of piedmont ancient flood sedimentary history. Combining the geological investigation in the great sandy hill, we assumed that the great sandy hill is the remnant of alluvial fan, which contains the characteristics of aeolian sediments along the coastal zone. The research is benefit for further understanding of the evolution of paleogeographic environment in the coastal zone of South China, and enriching the research of dynamic geomorphological processes on coastal zone and the sedimental structures of alluvial fan.
2016, 34(4): 653-661.
doi: 10.14027/j.cnki.cjxb.2016.04.005
Abstract:
The Lower Cambrian Uyirtus Formation is a set of complicated lithological source rocks, with widely distributed bedded siliceous rocks. Bedded siliceous rocks are always formed in special environment, thus, study of siliceous rocks will help to review ancient sedimentary environment of the time when Lower Cambrian Uyirtus Formation was depositing and predict the distribution of high quality source rocks. Through rock slice, SEM, probe detection combined with TOC analysis, noticing that the siliceous rocks formed in rift background which imply the enclosed high salinity alkaline water. The dynamic changes of the sedimentary water power made the silica rock have the layered structure and clastic structure. Terrigenous clastic, volcanic activity and organisms provide silicon for the water and hydrotherm suppling nutrient for the organisms that led to a flourishing development in algae and small shell species. The distribution of organisms controlled by the position of volcanic thermal water vent and the preservation condition in special water, so the Uyirtus Formation become good source rocks. The rifting is formed by the taphrogenesis within the platform that caused by tension stress in Early Cambrian period. This tectonic movement led to deposition of widely distributed source rocks, indicating that great exploration potential in Early Paleozoic-Neoproterozoic of Tarim basin.
The Lower Cambrian Uyirtus Formation is a set of complicated lithological source rocks, with widely distributed bedded siliceous rocks. Bedded siliceous rocks are always formed in special environment, thus, study of siliceous rocks will help to review ancient sedimentary environment of the time when Lower Cambrian Uyirtus Formation was depositing and predict the distribution of high quality source rocks. Through rock slice, SEM, probe detection combined with TOC analysis, noticing that the siliceous rocks formed in rift background which imply the enclosed high salinity alkaline water. The dynamic changes of the sedimentary water power made the silica rock have the layered structure and clastic structure. Terrigenous clastic, volcanic activity and organisms provide silicon for the water and hydrotherm suppling nutrient for the organisms that led to a flourishing development in algae and small shell species. The distribution of organisms controlled by the position of volcanic thermal water vent and the preservation condition in special water, so the Uyirtus Formation become good source rocks. The rifting is formed by the taphrogenesis within the platform that caused by tension stress in Early Cambrian period. This tectonic movement led to deposition of widely distributed source rocks, indicating that great exploration potential in Early Paleozoic-Neoproterozoic of Tarim basin.
2016, 34(4): 662-669.
doi: 10.14027/j.cnki.cjxb.2016.04.006
Abstract:
Present sediments investigation have identified 9 microgeomorphic units on the surface of No.4 Jiaobei Sand, Modaomen estury, Zhujiang river, which represent 9 micofacies of this sand. These microgeomorphic units and microfacies include:(1) subwater zone, (2)lower tidal swash-backwash zone, (3)higher tidal swash-backwash zone, (4)storm swash-backwash zone, (5)bar top washover zone, (6)backshore washover zone, (7)middle washover fan, (8)marginal washover fan and (9) inter-distributary wetland. Sediments are mainly fine to silty sand with middle to poorly sorting, minerals are mainly quartz and clay. The fluvial dominated Modaomen main channel developed in the east of the Jiaobei 4 sand while a tidal channel developed along from Baitenghai to Denglongsha and Sanzao island in the west. The southeastward wave played a dominate role in the south of Jiaobei 4 sand and an inter distributary wetland was situated betweenNo.3 and No.4 Jiaobei sand area. Similar processes have been for forming No.4 and other Jiaobei sands. Bottom current within the main channel transported the mouth bar sediments laterally to form a shoal in the right side of the channel, then the shoal was reconstructed into cup-like No.1 Jiaobei sand by tidal and wave. The wave eroded the shore face of the No.1 Jiaobei sand and deposited the sediment at the wave-shaded area, which make the sand accrete landward and then form the No.2, No.3 and No.4 Jiaobei sand in front of it one after another. No.1, No.2 and No.3 Jiaobei sand are now connected to form Jiaobei island above the sea. The No.4 Jiaobei sand may connect with No.3 Jiaobei sand, and then a new No.5 Jaiobei sand will appear in the future. As a result, the western bank of the Modaomen main channel will be changed into a sand ridge plain with tidal flat and recurved ridges.
Present sediments investigation have identified 9 microgeomorphic units on the surface of No.4 Jiaobei Sand, Modaomen estury, Zhujiang river, which represent 9 micofacies of this sand. These microgeomorphic units and microfacies include:(1) subwater zone, (2)lower tidal swash-backwash zone, (3)higher tidal swash-backwash zone, (4)storm swash-backwash zone, (5)bar top washover zone, (6)backshore washover zone, (7)middle washover fan, (8)marginal washover fan and (9) inter-distributary wetland. Sediments are mainly fine to silty sand with middle to poorly sorting, minerals are mainly quartz and clay. The fluvial dominated Modaomen main channel developed in the east of the Jiaobei 4 sand while a tidal channel developed along from Baitenghai to Denglongsha and Sanzao island in the west. The southeastward wave played a dominate role in the south of Jiaobei 4 sand and an inter distributary wetland was situated betweenNo.3 and No.4 Jiaobei sand area. Similar processes have been for forming No.4 and other Jiaobei sands. Bottom current within the main channel transported the mouth bar sediments laterally to form a shoal in the right side of the channel, then the shoal was reconstructed into cup-like No.1 Jiaobei sand by tidal and wave. The wave eroded the shore face of the No.1 Jiaobei sand and deposited the sediment at the wave-shaded area, which make the sand accrete landward and then form the No.2, No.3 and No.4 Jiaobei sand in front of it one after another. No.1, No.2 and No.3 Jiaobei sand are now connected to form Jiaobei island above the sea. The No.4 Jiaobei sand may connect with No.3 Jiaobei sand, and then a new No.5 Jaiobei sand will appear in the future. As a result, the western bank of the Modaomen main channel will be changed into a sand ridge plain with tidal flat and recurved ridges.
2016, 34(4): 670-678.
doi: 10.14027/j.cnki.cjxb.2016.04.007
Abstract:
There had been a coastal plain in a continental shelf of the Yellow Sea during the late Pleistocene, on which filled abundant terrestrial-sourced sediments under transportation and deposition of ancient Yangtze River and Yellow River. The South Yellow Sea Radial Sand Ridges, the Yangtze River Deltas and the abandoned Yellow River Deltas were developed on the sediment system. However the evolution patterns and mechanisms are hardly understood if only based on discrete evidence from geological cores. To recognize key issues on the glaciation sea levels and costal sedimentation changes, on the basis of hydrology, sedimentology, and geomorphologic elevations, this study attemptes to construct a numeric model to simulate the changes in the processes and patterns. The model is constructed in two modules:one submodel is built for the glacial-driven sea level and post-tectonic and sediment compaction-impacted relative sea level. The other submodel is for coastal sedimentation under varied sea levels and with river mud-transportation. Three coastal types in the South Yellow Sea radial sand ridges, the Yangtze River deltas and the abandoned Yellow River deltas were prescribed, and the Holocene boundaries of coastal lines that were reconstructed by geological evidence were also prescribed. The model was run by glaciation and climate forces of the late Pleistocene, and simulated the patterns and processes of sea levels, coastal lines and coastal-estuaries sediment flux since 140 ka B.P., 40 ka B.P. and 10 ka B.P. respectively. The results showed that seal levels were the lowest in 19 ka B.P. when it was during the last maximum glaciation, which inland lakes were formed between continental coasts and the Ryukyu Islands. During the late glaciation ca.14 ka B.P., the sea level started to rise and the inland lakes were formed in sea areas of the Yellow Sea. Between the early Holocene and the mid-Holocene, the sea transgression was occurred to the low plains of Jiangsu, and the coastal lines arrived the west to Fangong Dam, ca 6ka B.P.. Furthermore effects of the climatic glacial, tectonic subsiding and sediment compaction were analyzed and results showed that the changes were responded to long-term climate variations, sea-land surface interaction, and terrestrial sediment transportations. The simulations are consistent with geological sequence and strata depths, which the simulation of the relative sea-levels are between -30.2~-23.7 m a.s.l. The simulation errors in varying localities are between ±(2.5~4.5) m, suggesting that the error bar is relative small and the modeling results can be accepted. The study is of significance to understand the characteristics of sedimentation and patterns under multiple complex land-sea interactions and to illustrate the climate and glacial mechanisms for changes in Jiangsu coasts and sediments since the late Pleistocene.
There had been a coastal plain in a continental shelf of the Yellow Sea during the late Pleistocene, on which filled abundant terrestrial-sourced sediments under transportation and deposition of ancient Yangtze River and Yellow River. The South Yellow Sea Radial Sand Ridges, the Yangtze River Deltas and the abandoned Yellow River Deltas were developed on the sediment system. However the evolution patterns and mechanisms are hardly understood if only based on discrete evidence from geological cores. To recognize key issues on the glaciation sea levels and costal sedimentation changes, on the basis of hydrology, sedimentology, and geomorphologic elevations, this study attemptes to construct a numeric model to simulate the changes in the processes and patterns. The model is constructed in two modules:one submodel is built for the glacial-driven sea level and post-tectonic and sediment compaction-impacted relative sea level. The other submodel is for coastal sedimentation under varied sea levels and with river mud-transportation. Three coastal types in the South Yellow Sea radial sand ridges, the Yangtze River deltas and the abandoned Yellow River deltas were prescribed, and the Holocene boundaries of coastal lines that were reconstructed by geological evidence were also prescribed. The model was run by glaciation and climate forces of the late Pleistocene, and simulated the patterns and processes of sea levels, coastal lines and coastal-estuaries sediment flux since 140 ka B.P., 40 ka B.P. and 10 ka B.P. respectively. The results showed that seal levels were the lowest in 19 ka B.P. when it was during the last maximum glaciation, which inland lakes were formed between continental coasts and the Ryukyu Islands. During the late glaciation ca.14 ka B.P., the sea level started to rise and the inland lakes were formed in sea areas of the Yellow Sea. Between the early Holocene and the mid-Holocene, the sea transgression was occurred to the low plains of Jiangsu, and the coastal lines arrived the west to Fangong Dam, ca 6ka B.P.. Furthermore effects of the climatic glacial, tectonic subsiding and sediment compaction were analyzed and results showed that the changes were responded to long-term climate variations, sea-land surface interaction, and terrestrial sediment transportations. The simulations are consistent with geological sequence and strata depths, which the simulation of the relative sea-levels are between -30.2~-23.7 m a.s.l. The simulation errors in varying localities are between ±(2.5~4.5) m, suggesting that the error bar is relative small and the modeling results can be accepted. The study is of significance to understand the characteristics of sedimentation and patterns under multiple complex land-sea interactions and to illustrate the climate and glacial mechanisms for changes in Jiangsu coasts and sediments since the late Pleistocene.
Grain-size Distribution Patterns of the Surface Sediments and Their Influential Factors in Lake Lugu
2016, 34(4): 679-687.
doi: 10.14027/j.cnki.cjxb.2016.04.008
Abstract:
Lugu Lake is one of the typical plateau-type lakes in the transitional zone between Tibet Plateau and Yunnan-Guizhou Plateau. With relatively weak human impacts, lake Lugu is one of the most suitable lakes for palaoenvironmental study. Based on the grain-size analysis results on 70 surface (modern) sediment samples in south main lake, combined with the investigation/observation results on the surrounding natural conditions, we have analyzed the spatial distribution features of the different particle compositions and their influential factors controlling the spatial distribution of grain sizes in the Lake. The results show that the grain-size of the samples can be classified into three types, including clayey silt, sand silt and sand. Meanwhile, the grain size components in the studied area have some obvious spatial distribution patterns, for example, the grain size in the east side of the study area controlled by the rivers (Shankua River and Sanjiacun River) show a obvious tongue-shape mainly composed of clay, and with eastward and northwestward distributions, respectively. Whole in the south part of the study area, the particle distribution pattern is influenced by lake current. In the northwest, the grain-size is dominated by sand because of suspension effect. The lake current carries a lot of sediments from the north and southwest of the study area to the south of the lake and deposit there. Generally speaking, the differences between the grain size distribution patterns are mainly attributed to the lake dynamic processes and the different respond of the sediments to the climate changes. The study on lake surface sediments not only promotes the understanding of the lake dynamics and the status of material input, but also important to select suitable sites to take cores for the paleoclimate-paleoenvironmental reconstruction.
Lugu Lake is one of the typical plateau-type lakes in the transitional zone between Tibet Plateau and Yunnan-Guizhou Plateau. With relatively weak human impacts, lake Lugu is one of the most suitable lakes for palaoenvironmental study. Based on the grain-size analysis results on 70 surface (modern) sediment samples in south main lake, combined with the investigation/observation results on the surrounding natural conditions, we have analyzed the spatial distribution features of the different particle compositions and their influential factors controlling the spatial distribution of grain sizes in the Lake. The results show that the grain-size of the samples can be classified into three types, including clayey silt, sand silt and sand. Meanwhile, the grain size components in the studied area have some obvious spatial distribution patterns, for example, the grain size in the east side of the study area controlled by the rivers (Shankua River and Sanjiacun River) show a obvious tongue-shape mainly composed of clay, and with eastward and northwestward distributions, respectively. Whole in the south part of the study area, the particle distribution pattern is influenced by lake current. In the northwest, the grain-size is dominated by sand because of suspension effect. The lake current carries a lot of sediments from the north and southwest of the study area to the south of the lake and deposit there. Generally speaking, the differences between the grain size distribution patterns are mainly attributed to the lake dynamic processes and the different respond of the sediments to the climate changes. The study on lake surface sediments not only promotes the understanding of the lake dynamics and the status of material input, but also important to select suitable sites to take cores for the paleoclimate-paleoenvironmental reconstruction.
2016, 34(4): 688-693.
doi: 10.14027/j.cnki.cjxb.2016.04.009
Abstract:
Ordos Basin in the Late Triassic stage developed large-scale depression lake basin.The rise and fall of Lake water affected the area of the sedimentation, depth and depositional system distribution in the lake basin, thereby affecting the whole basin characteristics of the development of the source rock combination, reservoir and sealling rock in the Late Triassic formation. Through identification of outcrop, drilling rock cores palaeontological fossils, combined with paleontological assemblages of Ordos Basin in the Late Triassic lacustrine paleo-ecological environment were recovered. It is concluded that the Late-Triassic Ordos Basin was a shallow lake in which the depth of the water was less than 60 m, the salinity of the water was freshwater-brackish and the weather was warm and humid. From the shore to the lake centre it can be divided into four paleontology phase:river-marsh biofacies-assemblage zone in which the water depth was predicted within 1~2 m, shore-delta biofacies-assemblage zone in which the water depth was predicted within 3~15 m, shallow lake biofacies-assemblage zone in which the water depth was predicted within 15~35 m and semi-deep lake biofacies-assemblage zone in which the water depth was predicted between 35~60 m. These conclusions have important theoretical significance to understanding the characteristic of the Ordos lake basin in late Triassic Yanchang Stage. These facies division, for the restoration of the Ordos Basin during the Late Triassic lithofacies palaeogeography laid the foundation for the extension of the sedimentary basin boundaries, depositional systems and sedimentary facies division.
Ordos Basin in the Late Triassic stage developed large-scale depression lake basin.The rise and fall of Lake water affected the area of the sedimentation, depth and depositional system distribution in the lake basin, thereby affecting the whole basin characteristics of the development of the source rock combination, reservoir and sealling rock in the Late Triassic formation. Through identification of outcrop, drilling rock cores palaeontological fossils, combined with paleontological assemblages of Ordos Basin in the Late Triassic lacustrine paleo-ecological environment were recovered. It is concluded that the Late-Triassic Ordos Basin was a shallow lake in which the depth of the water was less than 60 m, the salinity of the water was freshwater-brackish and the weather was warm and humid. From the shore to the lake centre it can be divided into four paleontology phase:river-marsh biofacies-assemblage zone in which the water depth was predicted within 1~2 m, shore-delta biofacies-assemblage zone in which the water depth was predicted within 3~15 m, shallow lake biofacies-assemblage zone in which the water depth was predicted within 15~35 m and semi-deep lake biofacies-assemblage zone in which the water depth was predicted between 35~60 m. These conclusions have important theoretical significance to understanding the characteristic of the Ordos lake basin in late Triassic Yanchang Stage. These facies division, for the restoration of the Ordos Basin during the Late Triassic lithofacies palaeogeography laid the foundation for the extension of the sedimentary basin boundaries, depositional systems and sedimentary facies division.
2016, 34(4): 694-706.
doi: 10.14027/j.cnki.cjxb.2016.04.010
Abstract:
Huachi area is located in the southwest of Shanbei slope of Ordos Basin in China, with a flat strata and simple structure. Yanchang Formation of the Upper Triassic is terrigenous clastic rock series of fluvial facies and lacustrine facies, formed in the process of continuous depression and stable settlement in Ordos Basin, and vertically divided into 10 oil layers. During the deposition of Chang 7 member, the basin was in the maximum lake flooding period, developing sandy debris flow and turbidite fans in the center and on the slope. Having experienced long diagenetic evolution, Chang 7 member formed current reservoir characteristics. Diagenetic facies is the material reflection of diagenetic environment, and the combination of diagenesis and diagenetic minerals, and it is also the production of diagenesis and evolution stages in specific sedimentary, physical and chemical environment. Diagenetic facies includes the characteristics of rock particles, cement, fabric and cracks-holes, which highly generalizes diagenesis, diagenetic minerals, diagenetic environment, diagenetic events, and diagenetic evolutionary sequence during the period between the formation of sediment and the occurrence of metamorphism. The research on cores of diagenetic facies are diagenesis and diagenetic minerals. What's more, diagenetic facies plays an important role in the formation of effective reservoir, therefore to study diagenetic facies of tight sandstone oil reservoir has a broad application prospects. In this paper, diagenesis and diagenetic minerals of Chang 7 tight sandstone oil reservoir in Huachi area of Ordos Basin are studied by using core observation, thin section examination, scanning election microscope data, cathode luminescence and physical property analysis. According to the types and intensity of diagenesis and the combination feature of diagenetic minerals, diagenetic facies in the study area is qualitatively divided into four types, including instable components dissolution facies, clay minerals filling facies, and carbonate cementation facies and tight compaction facies. Then based on the analysis of conventional logging curves, such as gamma log, density log, acoustic transit time log, compensated neutron log and resistivity log, which are sensitive to diagenetic facies, crossplots are made to further quantitatively classify the four diagenetic facies and establish logging cognition model of diagenetic facies. Take Well Cheng 96 in Huachi area, for example, the quantitative recognition and classification of diagenetic facies coincide well with thin section of sampling point, formation testing and physical property analysis in single well on the longitude, which verifies the reliability of the model. The study of quantitative logging characterization method of diagenetic facies can provide theoretical guidance and technical support for comprehensive assessment of tight sandstone oil and for prediction of favorable zones in oil-gas reservoir development.
Huachi area is located in the southwest of Shanbei slope of Ordos Basin in China, with a flat strata and simple structure. Yanchang Formation of the Upper Triassic is terrigenous clastic rock series of fluvial facies and lacustrine facies, formed in the process of continuous depression and stable settlement in Ordos Basin, and vertically divided into 10 oil layers. During the deposition of Chang 7 member, the basin was in the maximum lake flooding period, developing sandy debris flow and turbidite fans in the center and on the slope. Having experienced long diagenetic evolution, Chang 7 member formed current reservoir characteristics. Diagenetic facies is the material reflection of diagenetic environment, and the combination of diagenesis and diagenetic minerals, and it is also the production of diagenesis and evolution stages in specific sedimentary, physical and chemical environment. Diagenetic facies includes the characteristics of rock particles, cement, fabric and cracks-holes, which highly generalizes diagenesis, diagenetic minerals, diagenetic environment, diagenetic events, and diagenetic evolutionary sequence during the period between the formation of sediment and the occurrence of metamorphism. The research on cores of diagenetic facies are diagenesis and diagenetic minerals. What's more, diagenetic facies plays an important role in the formation of effective reservoir, therefore to study diagenetic facies of tight sandstone oil reservoir has a broad application prospects. In this paper, diagenesis and diagenetic minerals of Chang 7 tight sandstone oil reservoir in Huachi area of Ordos Basin are studied by using core observation, thin section examination, scanning election microscope data, cathode luminescence and physical property analysis. According to the types and intensity of diagenesis and the combination feature of diagenetic minerals, diagenetic facies in the study area is qualitatively divided into four types, including instable components dissolution facies, clay minerals filling facies, and carbonate cementation facies and tight compaction facies. Then based on the analysis of conventional logging curves, such as gamma log, density log, acoustic transit time log, compensated neutron log and resistivity log, which are sensitive to diagenetic facies, crossplots are made to further quantitatively classify the four diagenetic facies and establish logging cognition model of diagenetic facies. Take Well Cheng 96 in Huachi area, for example, the quantitative recognition and classification of diagenetic facies coincide well with thin section of sampling point, formation testing and physical property analysis in single well on the longitude, which verifies the reliability of the model. The study of quantitative logging characterization method of diagenetic facies can provide theoretical guidance and technical support for comprehensive assessment of tight sandstone oil and for prediction of favorable zones in oil-gas reservoir development.
2016, 34(4): 707-715.
doi: 10.14027/j.cnki.cjxb.2016.04.011
Abstract:
High-frequency sequences are commonly developed in carbonate strata, and eogenetic karst related to fourth- to fifth- order sequence boundaries are of great importance to the improvement of carbonate reservoir quality. However, how to identify high-frequency sequences objectively is a generally acknowledged issue which has been long been explored. In this study, we analyze the high-frequency sequences of the Lianglitage Formation in the Tazhong area of Tarim Basin, by using the natural gamma ray logging data and utilizing moving average flitering and wavelet transformation methods. Th/U ratio log, after moving average filtering process, can clearly and objectively reflect the depositional cycles, with its increase indicating the deepening of depositional environment and the concentration of clay, and its decrease indicating the shallowing of depositional environment and purer limestone deposits. The Lianglitage Formation in this well can be divided into three third-order sequences, eight fourth-order sequences, and 32 fifth-order sequences, the sea-level change reflected by various rank sequences are well coincided with the three one-dimensional discrete curves derived from wavelet transform analysis. Correlation between wells indicates the third- and fourth-order sequences of the lower part of the Lianglitage Formation vary between different areas in the Tazhong Uplift, and the differences attribute to the distinct paleogeomorphology of the Tazhong Uplift before Late Ordovician. The fourth- and fifth-order sequences are believed to reflect the eccentricity long periods and short periods, respectively, in Milankovitch cycles. The reservoir units in the well are all related to the fourth- and fifth-sequence boundaries. The results of this study are of great significance of analyzing high-frequency sequences in carbonate strata based on well-logging data, as well as forecasting favorable reservoirs in a high-resolution sequence framework in this area.
High-frequency sequences are commonly developed in carbonate strata, and eogenetic karst related to fourth- to fifth- order sequence boundaries are of great importance to the improvement of carbonate reservoir quality. However, how to identify high-frequency sequences objectively is a generally acknowledged issue which has been long been explored. In this study, we analyze the high-frequency sequences of the Lianglitage Formation in the Tazhong area of Tarim Basin, by using the natural gamma ray logging data and utilizing moving average flitering and wavelet transformation methods. Th/U ratio log, after moving average filtering process, can clearly and objectively reflect the depositional cycles, with its increase indicating the deepening of depositional environment and the concentration of clay, and its decrease indicating the shallowing of depositional environment and purer limestone deposits. The Lianglitage Formation in this well can be divided into three third-order sequences, eight fourth-order sequences, and 32 fifth-order sequences, the sea-level change reflected by various rank sequences are well coincided with the three one-dimensional discrete curves derived from wavelet transform analysis. Correlation between wells indicates the third- and fourth-order sequences of the lower part of the Lianglitage Formation vary between different areas in the Tazhong Uplift, and the differences attribute to the distinct paleogeomorphology of the Tazhong Uplift before Late Ordovician. The fourth- and fifth-order sequences are believed to reflect the eccentricity long periods and short periods, respectively, in Milankovitch cycles. The reservoir units in the well are all related to the fourth- and fifth-sequence boundaries. The results of this study are of great significance of analyzing high-frequency sequences in carbonate strata based on well-logging data, as well as forecasting favorable reservoirs in a high-resolution sequence framework in this area.
2016, 34(4): 716-724.
doi: 10.14027/j.cnki.cjxb.2016.04.012
Abstract:
Lithology recognition is an important work in log evaluation of tight glutenite. Glutenite is characterized by diverse lithology and complex component. These factors always result in difficulty in lithology recognition and logging interpretation of porosity. In this article, take tight glutenite in the lower part of the 4th member of Shahejie formation in steep-slope zone in north Dongying Sag as an example, based on petrologic characteristics, glutenite was classified according to different rock types and framework minerals. Rock thin sections were used to demarcate lithology in log curve, and log response for different lithology were extracted, then the author established lithology recognition method for tight sandstone based on principal component analysis, and finally established porosity evaluation method based on log curve for different lithology. Practice indicates that application of this method can increase accuracy both in lithology recognition and porosity prediction by a wide margin.
Lithology recognition is an important work in log evaluation of tight glutenite. Glutenite is characterized by diverse lithology and complex component. These factors always result in difficulty in lithology recognition and logging interpretation of porosity. In this article, take tight glutenite in the lower part of the 4th member of Shahejie formation in steep-slope zone in north Dongying Sag as an example, based on petrologic characteristics, glutenite was classified according to different rock types and framework minerals. Rock thin sections were used to demarcate lithology in log curve, and log response for different lithology were extracted, then the author established lithology recognition method for tight sandstone based on principal component analysis, and finally established porosity evaluation method based on log curve for different lithology. Practice indicates that application of this method can increase accuracy both in lithology recognition and porosity prediction by a wide margin.
2016, 34(4): 725-734.
doi: 10.14027/j.cnki.cjxb.2016.04.013
Abstract:
Based on cores data, geological logging data and logging data in mature exploration area, sedimentary characteristics and models of Dalinghe oil layer in Shu2 area of the West Sag has been analyzed. It shows that the gravity flow channels are widely developed in the sublacustrine fan of Dalinghe oil layer. The plane distribution, sandbody extended direction and distribution pattern of sublacustrine fan is controlled by gravity flow channels and ancient landform. The gravity flow channels and its controls on sedimentary body are banding distribution along the source direction. The main channel is gradually extended to relatively larger scale braided channel. The sides of the braided channel are the edges of the braided channel, which are banding distribution or tongue distribution. The braided channel is gradually becoming multi branched and small braided channel endings to the direction of the lake. Microfacies sequence of sublacustrine fan is the main channel→the embankment of main channel→deep lacustrine mudstone or the braided channel→the edges of the braided channel→endings microfacies→deep lacustrine mudstone. Each banded sedimentary body controlled by the braided channel is separated by deep lacustrine mudstone. And it is banding distribution or tongue distribution extending to the center of the basin far away.
Based on cores data, geological logging data and logging data in mature exploration area, sedimentary characteristics and models of Dalinghe oil layer in Shu2 area of the West Sag has been analyzed. It shows that the gravity flow channels are widely developed in the sublacustrine fan of Dalinghe oil layer. The plane distribution, sandbody extended direction and distribution pattern of sublacustrine fan is controlled by gravity flow channels and ancient landform. The gravity flow channels and its controls on sedimentary body are banding distribution along the source direction. The main channel is gradually extended to relatively larger scale braided channel. The sides of the braided channel are the edges of the braided channel, which are banding distribution or tongue distribution. The braided channel is gradually becoming multi branched and small braided channel endings to the direction of the lake. Microfacies sequence of sublacustrine fan is the main channel→the embankment of main channel→deep lacustrine mudstone or the braided channel→the edges of the braided channel→endings microfacies→deep lacustrine mudstone. Each banded sedimentary body controlled by the braided channel is separated by deep lacustrine mudstone. And it is banding distribution or tongue distribution extending to the center of the basin far away.
2016, 34(4): 735-746.
doi: 10.14027/j.cnki.cjxb.2016.04.014
Abstract:
Based on casting thin sections, scanning electron microscope, clay mineral X-ray diffraction, cathodeluminescence, fluid inclusion and laser-raman spectrum, the paper reveals the process of evolution of burial diagenesis of tight reservoir of the Upper Paleozoic in Daniudi Gas Field from aspects including burial history, temperature, pressure, diagenetic feature of reservoir, diagenesis fluid and porosity evolution of reservior. The research shows the process of burial diagenesis can be divided to four stages. They are rapid burial stage (a) in which the effect of decreasing of primary porosity was remarkable(compaction rates ranged from 30% to 97.5%), complexly diagenetic stage(b) in which there were two phases of gas charging (B.P. 200 Ma and B.P 180 Ma); definition stage for reservoir characteristic (c) when there was one phase of gas charging (B.P. 140 Ma) and reservoir tended towards stability and tight and stage of being weak-reworked for reservoir (d) when amplitude of tectonic uplift was about one kilometer and tension fissure weakly developed. Porosity of most reservoir decreased to 10%, and became tight. With several times of gas charging, the reservoir appeared to present the diagenetic and accumulational model of being tight when gas charging. Hydrpcarbon-changing happened before reservoir's being tight. Microfractures may be the key factor for improving reservoir's permeability.
Based on casting thin sections, scanning electron microscope, clay mineral X-ray diffraction, cathodeluminescence, fluid inclusion and laser-raman spectrum, the paper reveals the process of evolution of burial diagenesis of tight reservoir of the Upper Paleozoic in Daniudi Gas Field from aspects including burial history, temperature, pressure, diagenetic feature of reservoir, diagenesis fluid and porosity evolution of reservior. The research shows the process of burial diagenesis can be divided to four stages. They are rapid burial stage (a) in which the effect of decreasing of primary porosity was remarkable(compaction rates ranged from 30% to 97.5%), complexly diagenetic stage(b) in which there were two phases of gas charging (B.P. 200 Ma and B.P 180 Ma); definition stage for reservoir characteristic (c) when there was one phase of gas charging (B.P. 140 Ma) and reservoir tended towards stability and tight and stage of being weak-reworked for reservoir (d) when amplitude of tectonic uplift was about one kilometer and tension fissure weakly developed. Porosity of most reservoir decreased to 10%, and became tight. With several times of gas charging, the reservoir appeared to present the diagenetic and accumulational model of being tight when gas charging. Hydrpcarbon-changing happened before reservoir's being tight. Microfractures may be the key factor for improving reservoir's permeability.
2016, 34(4): 747-757.
doi: 10.14027/j.cnki.cjxb.2016.04.015
Abstract:
Dolostone is a significant reservoir type of pre-salt Carboniferous carbonate rocks in Pre-Caspian Basin. Based on the analysis of core, thin section, petrophysical properties, geochemical data and other related data, reservoir classification and performance of dolostones in KT-Ⅰ Formation were analysed, and their controlling factors and development models were also investigated. The results show that types of dolostones have a significant influence on their petrophysical properties. Among all the types, reservoir property and oil richness of residual bioclast dolostone mainly with moldic pore and dissolution enlarged pores is the best, that of silt to fine crystalline dolostone mainly with intercrystal pore and its dissolution pore is medium, as well as mud to silt crystalline dolostone mainly with moldic pore and intercrystal pore, but mud crystalline dolostone mainly with intercrystal micropore is poor on reservoir property. Bioclast shoal with more primary porosity formed in the relatively high hydrodynamic environment is favorable for dolomite reservoir formation of high quality. Penecontemporaneous dissolution of fresh water and early dolomitization mainly via seepage-reflux dolomitization (dolomite order degree falls in between 0.32 and 0.67, δ13C ranges from -0.22‰ to 5.94‰ and δ18O ranges from -1.09‰ to 2.45‰) before massive compaction have a dominant effct on early porosity formation and preservation for dolomite reservoir in the Late Carboniferous. At the burial diagenesis stage the formation of fractures with different causes and dissolution of acidic fluids are the vital factors for further porosity increasement of dolomite reservoir since the Early Permian.
Dolostone is a significant reservoir type of pre-salt Carboniferous carbonate rocks in Pre-Caspian Basin. Based on the analysis of core, thin section, petrophysical properties, geochemical data and other related data, reservoir classification and performance of dolostones in KT-Ⅰ Formation were analysed, and their controlling factors and development models were also investigated. The results show that types of dolostones have a significant influence on their petrophysical properties. Among all the types, reservoir property and oil richness of residual bioclast dolostone mainly with moldic pore and dissolution enlarged pores is the best, that of silt to fine crystalline dolostone mainly with intercrystal pore and its dissolution pore is medium, as well as mud to silt crystalline dolostone mainly with moldic pore and intercrystal pore, but mud crystalline dolostone mainly with intercrystal micropore is poor on reservoir property. Bioclast shoal with more primary porosity formed in the relatively high hydrodynamic environment is favorable for dolomite reservoir formation of high quality. Penecontemporaneous dissolution of fresh water and early dolomitization mainly via seepage-reflux dolomitization (dolomite order degree falls in between 0.32 and 0.67, δ13C ranges from -0.22‰ to 5.94‰ and δ18O ranges from -1.09‰ to 2.45‰) before massive compaction have a dominant effct on early porosity formation and preservation for dolomite reservoir in the Late Carboniferous. At the burial diagenesis stage the formation of fractures with different causes and dissolution of acidic fluids are the vital factors for further porosity increasement of dolomite reservoir since the Early Permian.
2016, 34(4): 758-774.
doi: 10.14027/j.cnki.cjxb.2016.04.016
Abstract:
The prediction of the sweet spots of sand-rich tight sandstone reservoir has been both important and difficult in the field. This paper, taking the 2nd member of Xujiahe Formation in Hechuan, Central Sichuan Basin as an example, explores this issue by employing high resolution sequence stratigraphy controlled by successive palaeogeomorphology. Based on the recovery of the karst ancient landform of Leikoupo Formation before the 2nd Member of Xujiahe Formation deposition, it is suggested that the sedimentary filling was controlled by successive karst ancient landform, and the formation filling pattern where the sand bodies in the 2nd Member of Xujiahe Formation overlapped highland on the periphery gradually. With the guidance of this pattern and high-resolution sequence stratigraphy, by identifying sequence boundary and flooding surface types in varying degrees and integrating seismic, logging and core data, the 2nd Member of Xujiahe Formation is divided into 1 long-term base-level cycle which includes 6 mid-term base-level cycles, namely MSC1 to MSC 6. Overall, MSC1-MSC3 are characterized by the development of retrogradational braided river delta that overlaps southeastwards and is identified as rising semi-cycle; it switches to descending semi-cycle in the maximum flooding surface in MSC4; MSC4-MSC6 are characterized by the development of progradational braided river delta, with the particle size gradually becoming coarser upwards. Taking MSC3, the most informative cycle, as an example, the correlation between ancient land form, sequence thickness, sand body thickness, sand body physical property and sweet spot distribution is established and the sweet spot distribution areas of favorable reservoirs are predicted. The insights and methods indicated in the paper are of reference value for the study of sand-rich tight sandstone reservoirs, and particularly the study of areas with thinly scattered well network, informative seismic data but limited resolution. Some findings can be directly applied to regional oil & gas exploration and development.
The prediction of the sweet spots of sand-rich tight sandstone reservoir has been both important and difficult in the field. This paper, taking the 2nd member of Xujiahe Formation in Hechuan, Central Sichuan Basin as an example, explores this issue by employing high resolution sequence stratigraphy controlled by successive palaeogeomorphology. Based on the recovery of the karst ancient landform of Leikoupo Formation before the 2nd Member of Xujiahe Formation deposition, it is suggested that the sedimentary filling was controlled by successive karst ancient landform, and the formation filling pattern where the sand bodies in the 2nd Member of Xujiahe Formation overlapped highland on the periphery gradually. With the guidance of this pattern and high-resolution sequence stratigraphy, by identifying sequence boundary and flooding surface types in varying degrees and integrating seismic, logging and core data, the 2nd Member of Xujiahe Formation is divided into 1 long-term base-level cycle which includes 6 mid-term base-level cycles, namely MSC1 to MSC 6. Overall, MSC1-MSC3 are characterized by the development of retrogradational braided river delta that overlaps southeastwards and is identified as rising semi-cycle; it switches to descending semi-cycle in the maximum flooding surface in MSC4; MSC4-MSC6 are characterized by the development of progradational braided river delta, with the particle size gradually becoming coarser upwards. Taking MSC3, the most informative cycle, as an example, the correlation between ancient land form, sequence thickness, sand body thickness, sand body physical property and sweet spot distribution is established and the sweet spot distribution areas of favorable reservoirs are predicted. The insights and methods indicated in the paper are of reference value for the study of sand-rich tight sandstone reservoirs, and particularly the study of areas with thinly scattered well network, informative seismic data but limited resolution. Some findings can be directly applied to regional oil & gas exploration and development.
2016, 34(4): 775-784.
doi: 10.14027/j.cnki.cjxb.2016.04.017
Abstract:
Shanxi Formation and Xiashihezi Formation of Upper Paleozoic in Ordos Basin are the main exploration target zone. Coal seams of Benxi Formation and Taiyuan Formation are the main source rocks. The study of Upper Paleozoic sedimentary facies and evolution characteristics has some guidance significance for the oil and gas exploration. Based on the field measurement of Palougou outcrop profile in Baode area, by analyzing lithology and rock-association as well as the sedimentary facies, sedimentary sequences of different sedimentary systems have been built, and the sedimentary evolution of Upper Paleozoic in this area has been studied. The results show that the formations of Upper Paleozoic (Benxi Formation, Taiyuan Formation, lower Shihezi Formation, upper Shihezi Formation and Shiqianfeng Formation)develop from bottom to top in Baode area and 4 types of sedimentary facies (barrier beach, carbonate platform, meandering river and braided river) are identified as well as 8 typical sedimentary sequences. Controlled by the regional tectonic evolution, a large-scale seawater invasion takes place at the age of Benxi Formation and Taiyuan Formation, then seawater withdrawn from the basin gradually from Shanxi Formation to Shiqianfeng Formation. This area of late Paleozoic era experienced depositional process in the order of barrier beach, carbonate platform, and fluvial facies.
Shanxi Formation and Xiashihezi Formation of Upper Paleozoic in Ordos Basin are the main exploration target zone. Coal seams of Benxi Formation and Taiyuan Formation are the main source rocks. The study of Upper Paleozoic sedimentary facies and evolution characteristics has some guidance significance for the oil and gas exploration. Based on the field measurement of Palougou outcrop profile in Baode area, by analyzing lithology and rock-association as well as the sedimentary facies, sedimentary sequences of different sedimentary systems have been built, and the sedimentary evolution of Upper Paleozoic in this area has been studied. The results show that the formations of Upper Paleozoic (Benxi Formation, Taiyuan Formation, lower Shihezi Formation, upper Shihezi Formation and Shiqianfeng Formation)develop from bottom to top in Baode area and 4 types of sedimentary facies (barrier beach, carbonate platform, meandering river and braided river) are identified as well as 8 typical sedimentary sequences. Controlled by the regional tectonic evolution, a large-scale seawater invasion takes place at the age of Benxi Formation and Taiyuan Formation, then seawater withdrawn from the basin gradually from Shanxi Formation to Shiqianfeng Formation. This area of late Paleozoic era experienced depositional process in the order of barrier beach, carbonate platform, and fluvial facies.
2016, 34(4): 785-793.
doi: 10.14027/j.cnki.cjxb.2016.04.018
Abstract:
Based upon the data on seismic, well logging, core and geochemistry in Indus fan deepwater area and shallow shelf, we predict the development characteristics of Paleocene and Eocene source rocks of the Indus fan deepwater area, and discuss the depositional models of source rocks. The results show that Paleocene and Eocene source rocks has the most favorable conditions for development of high-quality hydrocarbon source rocks as it mainly developed transgressive system tracts and thinner thickness highstand system tract in Upper Eocene, deposited in a deepwater outershelf environment. Paleocene and Eocene source rocks are characterized by extensive distribution, large thickness with the maximum thickness of 900 m. The organic material forms of source rocks are type Ⅱ-Ⅲ, which are mixed organic matter. By the comprehensive analysis of various geological features, the distribution and model of source rocks has been reconstructed in the Indus Fan deepwater area. During the sedimentary period of the Paleocene and Eocene, the paleogeographic characteristics show narrow variation, which located in the low latitude belt near the equator, indicating warm and moist climate. As a good organic preservation condition was provided, the abundance of organic matter of Paleocene and Eocene source rocks is mainly controlled by the paleo-productivity and the organic matter flux to the sag. The research results will offer convenient service for oil and gas exploration in Indus Fan deepwater area.
Based upon the data on seismic, well logging, core and geochemistry in Indus fan deepwater area and shallow shelf, we predict the development characteristics of Paleocene and Eocene source rocks of the Indus fan deepwater area, and discuss the depositional models of source rocks. The results show that Paleocene and Eocene source rocks has the most favorable conditions for development of high-quality hydrocarbon source rocks as it mainly developed transgressive system tracts and thinner thickness highstand system tract in Upper Eocene, deposited in a deepwater outershelf environment. Paleocene and Eocene source rocks are characterized by extensive distribution, large thickness with the maximum thickness of 900 m. The organic material forms of source rocks are type Ⅱ-Ⅲ, which are mixed organic matter. By the comprehensive analysis of various geological features, the distribution and model of source rocks has been reconstructed in the Indus Fan deepwater area. During the sedimentary period of the Paleocene and Eocene, the paleogeographic characteristics show narrow variation, which located in the low latitude belt near the equator, indicating warm and moist climate. As a good organic preservation condition was provided, the abundance of organic matter of Paleocene and Eocene source rocks is mainly controlled by the paleo-productivity and the organic matter flux to the sag. The research results will offer convenient service for oil and gas exploration in Indus Fan deepwater area.
2016, 34(4): 794-802.
doi: 10.14027/j.cnki.cjxb.2016.04.019
Abstract:
Jurassic source rocks and oil sands from Well LV has been analyzed by usual organic geochemical methods and stable carbon isotopic detection in the North Yellow basin, in order to study the geochemical characteristics of the source rocks and the crude oils and oil-to-source correlation. The results show that the maturity of Jurassic source rock is higher, its kerogen type is maily Ⅲ. Middle Jurassic source rocks are higher in organic carbon and lower in hydrocarbon yields, chloroform bitumen "A" and HC, which means they are relatively poor source rocks. The kerogen carbon isotope of the middle Jurassic source rocks is heavy. There is a remarkable difference of carbon isotopic values of middle Jurassic source rocks(-24.4‰~-23.5‰) and crude oils(about -29‰). Therefore, there is no relationship among them. However, TOC content of the upper Jurassic source rocks is lower than that of the middle Jurassic source rocks, but hydrocarbon yields, chloroform bitumen "A" and HC of the upper Jurassic source rocks are higher. The character of chloroform bitumen "A" carbon isotope, distribution pattern of carbon isohopic distributions of individual n-alkanes and biomarkers of upper Jurassic source rocks are similar to crude oils. Comprehensive analysis could draw a conclusion that there is closely relationship between crude oil and the upper Jurassic hydrocarbon source rock, which has good kerogen type and mature parent materials from both higher plants and lower aquatic organisms.
Jurassic source rocks and oil sands from Well LV has been analyzed by usual organic geochemical methods and stable carbon isotopic detection in the North Yellow basin, in order to study the geochemical characteristics of the source rocks and the crude oils and oil-to-source correlation. The results show that the maturity of Jurassic source rock is higher, its kerogen type is maily Ⅲ. Middle Jurassic source rocks are higher in organic carbon and lower in hydrocarbon yields, chloroform bitumen "A" and HC, which means they are relatively poor source rocks. The kerogen carbon isotope of the middle Jurassic source rocks is heavy. There is a remarkable difference of carbon isotopic values of middle Jurassic source rocks(-24.4‰~-23.5‰) and crude oils(about -29‰). Therefore, there is no relationship among them. However, TOC content of the upper Jurassic source rocks is lower than that of the middle Jurassic source rocks, but hydrocarbon yields, chloroform bitumen "A" and HC of the upper Jurassic source rocks are higher. The character of chloroform bitumen "A" carbon isotope, distribution pattern of carbon isohopic distributions of individual n-alkanes and biomarkers of upper Jurassic source rocks are similar to crude oils. Comprehensive analysis could draw a conclusion that there is closely relationship between crude oil and the upper Jurassic hydrocarbon source rock, which has good kerogen type and mature parent materials from both higher plants and lower aquatic organisms.
2016, 34(4): 803-810.
doi: 10.14027/j.cnki.cjxb.2016.04.020
Abstract:
Based on geochemical analyses of Yuertusi Formation at Dongergou section of Tarim basin, trace elements and rare earth elements are used to probe paleoenvironmental conditions.Using δEu, Fe/Ti and (Fe+Mn)/Ti ratios for the interpretation of hydrothermal activity, Al/Ti ratios as paleoproductivity proxies and V/Cr, V/(V+Ni) and Ni/Co ratios as paleoredox proxies, the relationship of hydrothermal activity, paleoproductivity, paleoredox and total organic carbon was discussed. The data shows that Yuertusi Formation was deposited under dominantly euxinic conditions with a low paleoproductivity and that the lower part of the section experienced a strong hydrothermal activities. Although the hydrothermal activities improve the paleoproductivity of the lower part, the total organic carbon is low and ranges from 0.01% to 3.58% with an average of 0.64%. The middle-upper part of the section have a weak hydrothermal activities, but the total organic is high and ranges from 0.06% to 12.19% with an average of 8.95%. There are plenty of algal in the thin section of cherts related with hydrothermal activities. The study suggests that strong hydrothermal activities provided a lot of silica-rich fluid, which diluted the organic matter in the sediments and destroyed the formation of high-quality source rocks.
Based on geochemical analyses of Yuertusi Formation at Dongergou section of Tarim basin, trace elements and rare earth elements are used to probe paleoenvironmental conditions.Using δEu, Fe/Ti and (Fe+Mn)/Ti ratios for the interpretation of hydrothermal activity, Al/Ti ratios as paleoproductivity proxies and V/Cr, V/(V+Ni) and Ni/Co ratios as paleoredox proxies, the relationship of hydrothermal activity, paleoproductivity, paleoredox and total organic carbon was discussed. The data shows that Yuertusi Formation was deposited under dominantly euxinic conditions with a low paleoproductivity and that the lower part of the section experienced a strong hydrothermal activities. Although the hydrothermal activities improve the paleoproductivity of the lower part, the total organic carbon is low and ranges from 0.01% to 3.58% with an average of 0.64%. The middle-upper part of the section have a weak hydrothermal activities, but the total organic is high and ranges from 0.06% to 12.19% with an average of 8.95%. There are plenty of algal in the thin section of cherts related with hydrothermal activities. The study suggests that strong hydrothermal activities provided a lot of silica-rich fluid, which diluted the organic matter in the sediments and destroyed the formation of high-quality source rocks.
