2019 Vol. 37, No. 1
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2019, 37(1): 1-16.
doi: 10.14027/j.issn.1000-0550.2018.185
Abstract:
The 20th International Sedimentological Congress was held in Quebec City (Canada) from August 13th to 17th in 2018. 931 scholars from 51 countries attended this conference. According to the arrangement of sessions in the conference, the current hot topics contain Anthropocene sedimentology, lacustrine sedimentology, deep-water sedimentary process, “source-to-sink” system, microbialites and the simulation of sedimentary process et al. The anthropic influence on modern geomorphological characteristics cannot be unneglected. The study of lacustrine sandbodies is not only meaningful for petroleum exploration and development but also has great implications for paleoclimate. Flow characteristics, sedimentary process and situ monitoring of deep-water sediment gravity flows have made great achievements in recent years. “Source-to-sink” perspectives are instructive to tectonic evolution of sedimentary basin, the nature of parent rocks from provenance area and the sedimentary dispersal characteristics. The recent advancement of microbialites mainly consists of mineralization and diagenesis of microorganisms and their implications for the reconstruction of paleoclimate. The weathering of sedimentary rocks as well as subsequent transportation and sedimentation in different depositional environments have become the main research focus of physical and numerical simulation. According to hot topics of recent meetings of sedimentology and the implementation of major geological plans, deep-time depositional record, process-product study, multidisciplinary investigation will be development directions of sedimentary research in the following years. Current sedimentary research in our country still concentrates on applied sedimentology, we not only pay much attention to modern experimental and testing technology, but also to fundamental field work and mechanism of sedimentary process. During the golden age of the fast development of sedimentology, youth sedimentologists should not miss this rare opportunity to grow into the tower of strength of domestic sedimentology, and reach the word-class level as soon as possible in the future.d
The 20th International Sedimentological Congress was held in Quebec City (Canada) from August 13th to 17th in 2018. 931 scholars from 51 countries attended this conference. According to the arrangement of sessions in the conference, the current hot topics contain Anthropocene sedimentology, lacustrine sedimentology, deep-water sedimentary process, “source-to-sink” system, microbialites and the simulation of sedimentary process et al. The anthropic influence on modern geomorphological characteristics cannot be unneglected. The study of lacustrine sandbodies is not only meaningful for petroleum exploration and development but also has great implications for paleoclimate. Flow characteristics, sedimentary process and situ monitoring of deep-water sediment gravity flows have made great achievements in recent years. “Source-to-sink” perspectives are instructive to tectonic evolution of sedimentary basin, the nature of parent rocks from provenance area and the sedimentary dispersal characteristics. The recent advancement of microbialites mainly consists of mineralization and diagenesis of microorganisms and their implications for the reconstruction of paleoclimate. The weathering of sedimentary rocks as well as subsequent transportation and sedimentation in different depositional environments have become the main research focus of physical and numerical simulation. According to hot topics of recent meetings of sedimentology and the implementation of major geological plans, deep-time depositional record, process-product study, multidisciplinary investigation will be development directions of sedimentary research in the following years. Current sedimentary research in our country still concentrates on applied sedimentology, we not only pay much attention to modern experimental and testing technology, but also to fundamental field work and mechanism of sedimentary process. During the golden age of the fast development of sedimentology, youth sedimentologists should not miss this rare opportunity to grow into the tower of strength of domestic sedimentology, and reach the word-class level as soon as possible in the future.d
2019, 37(1): 17-29.
doi: 10.14027/j.issn.1000-0550.2018.118
Abstract:
The Danxiashan of northern Guangdong province is representative of the World Natural Heritage site of "China Danxia". Previous studies were predominantly focused on description of landforms in the Danxiashan UNESCO Global Geopark. Little is known about depositional environments and paleoclimate during the formation of the Late Cretaceous redbeds, which are the bedrock of the Danxia landscapes. The Danxia Formation is further subdivided into three members. The first (Bazhai) and the second (Jinshiyan) members are outcropped at the measured Bazhai Section. The former is dominated by conglomerates with graded and parallel beddings and imbricated structures, whereas the latter is characterized by large-scale cross-bedded aeolian sandstones with paleosol interbeds. The third (Baizhaiding) member consists largely of conglomerate beds and was observed at other outcrops in the basin. Detailed stratigraphic column measurement, pebble counting, and petrographic and grain size analysis were performed to understand lithofacies changes in the Bazhai Section. The results show that seven lithofacies were recognized in the Danxia Formation: normal graded conglomerate, inverse graded conglomerate, parallel bedding conglomerate, structureless conglomerate, large-scale cross-bedded aeolian sandstone, medium- to thin-bedded sandstone, and paleosol. The pebbles of the Bazhai Member range from 0.5 cm to 9.5 cm in diameter and are mainly composed of quartzite, quartz sandstone, and brick-red sandstone. The grains of the sandstone samples from the Jinshiyan Member are 0.03-0.5 mm in diameter, well sorted, and dominantly consist of a saltation population, indicating aeolian environments. Therefore, lithofacies differences from the Bazhai to the Jinshiyan Members of the Danxia Formation are possibly indicative of a change from a stream-dominated alluvial fan system with higher deposition rate to an aeolian system, which in turn is considered as recording a paleoclimatic transformation from semi-humid to very arid conditions. The red aeolian sandstone-paleosol succession of the Jinshiyan Member might be linked with broad aridity in the middle latitudes of East Asia during the Campanian Stage. The Baizhaiding Member, the uppermost part of the Danxia Formation, is again characterized by conglomerate beds, which probably suggests a paleoclimate change towards semi-humid conditions. The abundant coarse clasts were transported to the basin by streams because of increased precipitation, reflecting new alluvial fans overlying on the aeolian sandstones and paleosols of the Jinshiyan Member.
The Danxiashan of northern Guangdong province is representative of the World Natural Heritage site of "China Danxia". Previous studies were predominantly focused on description of landforms in the Danxiashan UNESCO Global Geopark. Little is known about depositional environments and paleoclimate during the formation of the Late Cretaceous redbeds, which are the bedrock of the Danxia landscapes. The Danxia Formation is further subdivided into three members. The first (Bazhai) and the second (Jinshiyan) members are outcropped at the measured Bazhai Section. The former is dominated by conglomerates with graded and parallel beddings and imbricated structures, whereas the latter is characterized by large-scale cross-bedded aeolian sandstones with paleosol interbeds. The third (Baizhaiding) member consists largely of conglomerate beds and was observed at other outcrops in the basin. Detailed stratigraphic column measurement, pebble counting, and petrographic and grain size analysis were performed to understand lithofacies changes in the Bazhai Section. The results show that seven lithofacies were recognized in the Danxia Formation: normal graded conglomerate, inverse graded conglomerate, parallel bedding conglomerate, structureless conglomerate, large-scale cross-bedded aeolian sandstone, medium- to thin-bedded sandstone, and paleosol. The pebbles of the Bazhai Member range from 0.5 cm to 9.5 cm in diameter and are mainly composed of quartzite, quartz sandstone, and brick-red sandstone. The grains of the sandstone samples from the Jinshiyan Member are 0.03-0.5 mm in diameter, well sorted, and dominantly consist of a saltation population, indicating aeolian environments. Therefore, lithofacies differences from the Bazhai to the Jinshiyan Members of the Danxia Formation are possibly indicative of a change from a stream-dominated alluvial fan system with higher deposition rate to an aeolian system, which in turn is considered as recording a paleoclimatic transformation from semi-humid to very arid conditions. The red aeolian sandstone-paleosol succession of the Jinshiyan Member might be linked with broad aridity in the middle latitudes of East Asia during the Campanian Stage. The Baizhaiding Member, the uppermost part of the Danxia Formation, is again characterized by conglomerate beds, which probably suggests a paleoclimate change towards semi-humid conditions. The abundant coarse clasts were transported to the basin by streams because of increased precipitation, reflecting new alluvial fans overlying on the aeolian sandstones and paleosols of the Jinshiyan Member.
Study of Sedimentary Facies and Environment of the Nieerku Formation, Suzihe Basin, Eastern Liaoning
2019, 37(1): 30-39.
doi: 10.14027/j.issn.1000-0550.2018.114
Abstract:
The Suzihe Basin is a Lower Cretaceous small fault basin in eastern Liaoning Province. The continental deposits in the basin offer unique conditions for the study of the evolution of the paleoenvironment and paleoclimate of terrestrial settings during the Cretaceous. The sediments of the late Lower Cretaceous Nieerku Formation in the Suzihe Basin contain various clastic and mud rocks, typical deposits and divers terrestrial fossils. An analysis of the sedimentary rock types, the sedimentary structure, fossils and sedimentation sequence, recognized fan delta facies and lake facies. The fan delta facies are divided into fan delta plain subfacies, fan delta front subfacies and pre-fan delta subfacies. The lake facies primarily contain shore to shallow-lake mudstones and sandstones. It was found that the Nieerku Formation formed on the steep slope of a faulted lacustrine basin in a fan delta/lake sedimentary system that underwent intermittent flooding. The Nieerku Formation evolved in a sedimentary environment from fan delta to lake, then to fan delta, indicating that the faulted lacustrine basin experienced two evolutionary stages: a deep depressional period and an early shrinkage period. The characteristics of the sedimentary rocks and facies, combined with paleontological data, specific sediments, clay minerals and geochemical data, confirm that the climate was generally hot and dry/humid in eastern Liaoning during the late Lower Cretaceous, which corresponds to a “greenhouse” climate, but the warm climate was not static. This supports the generally held view that the Cretaceous climate was turbulent.
The Suzihe Basin is a Lower Cretaceous small fault basin in eastern Liaoning Province. The continental deposits in the basin offer unique conditions for the study of the evolution of the paleoenvironment and paleoclimate of terrestrial settings during the Cretaceous. The sediments of the late Lower Cretaceous Nieerku Formation in the Suzihe Basin contain various clastic and mud rocks, typical deposits and divers terrestrial fossils. An analysis of the sedimentary rock types, the sedimentary structure, fossils and sedimentation sequence, recognized fan delta facies and lake facies. The fan delta facies are divided into fan delta plain subfacies, fan delta front subfacies and pre-fan delta subfacies. The lake facies primarily contain shore to shallow-lake mudstones and sandstones. It was found that the Nieerku Formation formed on the steep slope of a faulted lacustrine basin in a fan delta/lake sedimentary system that underwent intermittent flooding. The Nieerku Formation evolved in a sedimentary environment from fan delta to lake, then to fan delta, indicating that the faulted lacustrine basin experienced two evolutionary stages: a deep depressional period and an early shrinkage period. The characteristics of the sedimentary rocks and facies, combined with paleontological data, specific sediments, clay minerals and geochemical data, confirm that the climate was generally hot and dry/humid in eastern Liaoning during the late Lower Cretaceous, which corresponds to a “greenhouse” climate, but the warm climate was not static. This supports the generally held view that the Cretaceous climate was turbulent.
2019, 37(1): 40-50.
doi: 10.14027/j.issn.1000-0550.2018.110
Abstract:
The Xiaweidian outcrop in the Western Hills of Beijing is one of the typical outcrops of the Cambrian system in North China. It has always been a focus of study for geological scientists. This paper describes a detailed analysis of the sedimentary deposits of the Cambrian Zhangxia based on previous research, involving field observation and measurement combined with indoor wafer identification, XRD tests, and other technologies. Through research, the main face of the Zhangxia deposit was determined to be detrital bathyal shallow marine facies and platform facies. The subfacies and shale were limited in shallow seas; the main development of the platform was limited to platform, beach, and tidal flat subfacies, and the beach was divided into high-energy beach and intermittent high-energy beach. The Zhangxia Formation is an offshore, gently sloping carbonate platform, consisting of many M-level cycles which gradually become shallow as one moves upward. In general, the water from the bottom grows deeper, and the carbonate platform gradually becomes stable.
The Xiaweidian outcrop in the Western Hills of Beijing is one of the typical outcrops of the Cambrian system in North China. It has always been a focus of study for geological scientists. This paper describes a detailed analysis of the sedimentary deposits of the Cambrian Zhangxia based on previous research, involving field observation and measurement combined with indoor wafer identification, XRD tests, and other technologies. Through research, the main face of the Zhangxia deposit was determined to be detrital bathyal shallow marine facies and platform facies. The subfacies and shale were limited in shallow seas; the main development of the platform was limited to platform, beach, and tidal flat subfacies, and the beach was divided into high-energy beach and intermittent high-energy beach. The Zhangxia Formation is an offshore, gently sloping carbonate platform, consisting of many M-level cycles which gradually become shallow as one moves upward. In general, the water from the bottom grows deeper, and the carbonate platform gradually becomes stable.
2019, 37(1): 51-61.
doi: 10.14027/j.issn.1000-0550.2018.104
Abstract:
Material composition analysis, parameter calculation and statistics determined from log-probability curves were carried out on 149 samples collected from the Diexi ancient dammed lake upstream of the Minjiang River. Grain-size characteristics in different sedimentary environments were analyzed using related data, showing that upstream sediments in the lacustrine deposit are mainly composed of silty sand and sandy silt. However, midstream and downstream sediments are finer, consisting of clayey silt and silt. Because of disturbance by the river, upstream lacustrine sediments are coarser, with mean particle size between 4 to 6 φ, with negative skewness, wide, flat kurtosis and poor sorting. Midstream and downstream sediments are relatively fine (average particle size 6-8 φ), with positive skewness, medium kurtosis and better sorting. The sediments in the dammed lake are made up of three or four separate log-normal populations, depending on their location. Sediments in the upstream deposit consist of four log-normal populations; midstream and downstream sediments comprise three log-normal populations. The amount of surface creep population is largely provenance-controlled, with a larger percentage of this population upstream than midstream or downstream, indicating obviously different transport mode and sedimentary environments. Notable features of these sediments compared to other sedimentary environments are the poorly sorted saltation population and a truncation point toward finer sizes.
Material composition analysis, parameter calculation and statistics determined from log-probability curves were carried out on 149 samples collected from the Diexi ancient dammed lake upstream of the Minjiang River. Grain-size characteristics in different sedimentary environments were analyzed using related data, showing that upstream sediments in the lacustrine deposit are mainly composed of silty sand and sandy silt. However, midstream and downstream sediments are finer, consisting of clayey silt and silt. Because of disturbance by the river, upstream lacustrine sediments are coarser, with mean particle size between 4 to 6 φ, with negative skewness, wide, flat kurtosis and poor sorting. Midstream and downstream sediments are relatively fine (average particle size 6-8 φ), with positive skewness, medium kurtosis and better sorting. The sediments in the dammed lake are made up of three or four separate log-normal populations, depending on their location. Sediments in the upstream deposit consist of four log-normal populations; midstream and downstream sediments comprise three log-normal populations. The amount of surface creep population is largely provenance-controlled, with a larger percentage of this population upstream than midstream or downstream, indicating obviously different transport mode and sedimentary environments. Notable features of these sediments compared to other sedimentary environments are the poorly sorted saltation population and a truncation point toward finer sizes.
2019, 37(1): 62-71.
doi: 10.14027/j.issn.1000-0550.2018.149
Abstract:
To trace the sedimentary source-to-sink systems of the Lvda 29-1 structure in the eastern Bohai Sea, six sandstone cuttings of the second Member of Shahejie Formation (Es2) were collected from LD29-1-1, LD29-1-1Sa and LD29-1-2 for detrital zircon U-Pb dating and cathodoluminescence (CL) image analysis. The results showed that the sandstones of LD29-1-1 contained 41.2% Cretaceous (K) zircons and featured a 108 Ma peak, and the columnar crystals were characterized by sharp edges. The LD29-1-1Sa and LD29-1-2 sandstones contained 74%-75% Mesoproterozoic (Pt2) zircons with peaks at ~1.5 Ga and ~1.8 Ga, and the broken crystals were well rounded. We concluded that the Es2 sandstones of LD29-1-1 were near-source deposited, and the provenance was the Mesozoic sedimentary rocks along the slope of the Changxingdao Uplift; the Es2 sandstones of LD29-1-1Sa and LD29-1-2 were distal from the source area and were dominated by the widespread Mesoproterozoic and Neoproterozoic sedimentary rocks exposed in Fuzhou on the western Liaodong Peninsula, with only a slight influence of Mesozoic sedimentary rocks from the slope of the Changxingdao Uplift.
To trace the sedimentary source-to-sink systems of the Lvda 29-1 structure in the eastern Bohai Sea, six sandstone cuttings of the second Member of Shahejie Formation (Es2) were collected from LD29-1-1, LD29-1-1Sa and LD29-1-2 for detrital zircon U-Pb dating and cathodoluminescence (CL) image analysis. The results showed that the sandstones of LD29-1-1 contained 41.2% Cretaceous (K) zircons and featured a 108 Ma peak, and the columnar crystals were characterized by sharp edges. The LD29-1-1Sa and LD29-1-2 sandstones contained 74%-75% Mesoproterozoic (Pt2) zircons with peaks at ~1.5 Ga and ~1.8 Ga, and the broken crystals were well rounded. We concluded that the Es2 sandstones of LD29-1-1 were near-source deposited, and the provenance was the Mesozoic sedimentary rocks along the slope of the Changxingdao Uplift; the Es2 sandstones of LD29-1-1Sa and LD29-1-2 were distal from the source area and were dominated by the widespread Mesoproterozoic and Neoproterozoic sedimentary rocks exposed in Fuzhou on the western Liaodong Peninsula, with only a slight influence of Mesozoic sedimentary rocks from the slope of the Changxingdao Uplift.
2019, 37(1): 72-85.
doi: 10.14027/j.issn.1000-0550.2018.098
Abstract:
A distinct landslide damming incident occurred during a prehistoric period in the upper Minjiang River at the southeastern margin of the Tibetan Plateau. This formed a very large dammed lake which breached and caused a large outburst flood at about 27 ka. Between the section of the ancient dam and its downstream areas (5 km), an abundance of diamicts have been observed for the first time. We determine that they are outburst deposits induced by breaching of the Diexi paleolandslide-dammed lake. The sedimentary structures of the outburst deposits include imbricates, cavitation, matrix and massive structures, gravel support-stacked, as well as rhythmitic interbedded structures, among others. From upstream to downstream, the thickness of the outburst deposits gradually thins, and the gravel shows a tendency to change from coarse to fine. Hyperconcentrated flood flows and normal stream or fluctuating flows are recorded, indicating contrasting regimes of sediment transport. Also, two kinds of sedimentary facies occur in the outburst deposits: boulder facies, and gravel and sand facies. From the way in which the sedimentary facies developed, at least one catastrophic outburst flood event can be assumed to have occurred in the Diexi paleodammed lake.
A distinct landslide damming incident occurred during a prehistoric period in the upper Minjiang River at the southeastern margin of the Tibetan Plateau. This formed a very large dammed lake which breached and caused a large outburst flood at about 27 ka. Between the section of the ancient dam and its downstream areas (5 km), an abundance of diamicts have been observed for the first time. We determine that they are outburst deposits induced by breaching of the Diexi paleolandslide-dammed lake. The sedimentary structures of the outburst deposits include imbricates, cavitation, matrix and massive structures, gravel support-stacked, as well as rhythmitic interbedded structures, among others. From upstream to downstream, the thickness of the outburst deposits gradually thins, and the gravel shows a tendency to change from coarse to fine. Hyperconcentrated flood flows and normal stream or fluctuating flows are recorded, indicating contrasting regimes of sediment transport. Also, two kinds of sedimentary facies occur in the outburst deposits: boulder facies, and gravel and sand facies. From the way in which the sedimentary facies developed, at least one catastrophic outburst flood event can be assumed to have occurred in the Diexi paleodammed lake.
2019, 37(1): 86-93.
doi: 10.14027/j.issn.1000-0550.2018.109
Abstract:
The distribution law of sand bodies in gravity flow sedimentary systems is very complex. By gravity flow fluid experiments, the cause of formation and the distribution law of different lithofacies have been determined. On this basis, through core observation, logging, and logging data analysis in Binnan oilfield sand, three subsections of gravity flow sand-body distribution rules were identified. The results show that: 1) Plastic fluid dilution and the particle support mechanism show complex changes in the process of movement, leading to a variety of fluid flows in which plastic fluid diluted to a certain extent will be converted into liquid; 2) The vertical evolution and lateral variation of the sequence of gravity flow deposits are the result of fluid property evolution, or in other words, the complex gravity flow sequence observed in geological records is the result of fluid property transformation; 3) The organic combination of gravity flow vertical sequence and a sedimentary model is the key to predicting sand distribution. Under the guidance of the model constructed in this research, the distribution of lithofacies was confirmed in in Binnan oilfield.
The distribution law of sand bodies in gravity flow sedimentary systems is very complex. By gravity flow fluid experiments, the cause of formation and the distribution law of different lithofacies have been determined. On this basis, through core observation, logging, and logging data analysis in Binnan oilfield sand, three subsections of gravity flow sand-body distribution rules were identified. The results show that: 1) Plastic fluid dilution and the particle support mechanism show complex changes in the process of movement, leading to a variety of fluid flows in which plastic fluid diluted to a certain extent will be converted into liquid; 2) The vertical evolution and lateral variation of the sequence of gravity flow deposits are the result of fluid property evolution, or in other words, the complex gravity flow sequence observed in geological records is the result of fluid property transformation; 3) The organic combination of gravity flow vertical sequence and a sedimentary model is the key to predicting sand distribution. Under the guidance of the model constructed in this research, the distribution of lithofacies was confirmed in in Binnan oilfield.
2019, 37(1): 94-103.
doi: 10.14027/j.issn.1000-0550.2018.140
Abstract:
On the basis of outcrop and thin section analyses, tempestites were identified in the fourth member of the Leikoupo Formation, Hanwang area, western Sichuan Basin. The major markers of storm sediments are scouring fill structures, storm-flow-generated gravelstones, chrysanthemum-like structures and hummocky cross-stratifications (HCS) etc. Three types of storm-deposited sequence were observed, in terms of their lithology, sedimentary position and depositional marks. Type I consists of storm gravelstone and graded members deposited at the lowest part of slopes near the storm wave base. Type II contains a storm gravelstone member, a graded member, a parallel lamination member and an HCS, which is deposited at the uppermost part of the slope near the fine-weather wave base. Type III comprises a graded member and a parallel lamination member, deposited at the platform margin. The depositional evolution of the tempestites shallows upward from the base of the slope to the upper part of the slope at the platform margin. The discovery of tempesites in the study area is highly significant in understanding paleolatitude and paleoplate evolution, paleoclimate change, stratigraphic isochronous contrast, and the sedimentary environment of the Sichuan Basin during the Middle Triassic, particularly the development of the Longmenshan island chain in the Songpan-Ganzi Sea.
On the basis of outcrop and thin section analyses, tempestites were identified in the fourth member of the Leikoupo Formation, Hanwang area, western Sichuan Basin. The major markers of storm sediments are scouring fill structures, storm-flow-generated gravelstones, chrysanthemum-like structures and hummocky cross-stratifications (HCS) etc. Three types of storm-deposited sequence were observed, in terms of their lithology, sedimentary position and depositional marks. Type I consists of storm gravelstone and graded members deposited at the lowest part of slopes near the storm wave base. Type II contains a storm gravelstone member, a graded member, a parallel lamination member and an HCS, which is deposited at the uppermost part of the slope near the fine-weather wave base. Type III comprises a graded member and a parallel lamination member, deposited at the platform margin. The depositional evolution of the tempestites shallows upward from the base of the slope to the upper part of the slope at the platform margin. The discovery of tempesites in the study area is highly significant in understanding paleolatitude and paleoplate evolution, paleoclimate change, stratigraphic isochronous contrast, and the sedimentary environment of the Sichuan Basin during the Middle Triassic, particularly the development of the Longmenshan island chain in the Songpan-Ganzi Sea.
2019, 37(1): 104-114.
doi: 10.14027/j.issn.1000-0550.2018.122
Abstract:
Lake basins on the northeastern Tibetan Plateau are regarded as important archives for the reconstruction of environmental and climate changes during the Upper Quaternary. Lake deposits serve as ideal indicators of various transport and depositional processes in changing hydro-climatic settings. Understanding such dynamic processes is of crucial interest when deciphering the process-response behavior of lakes from their sedimentary characteristics over time. The closed saline Kuhai Lake is an ideal location for unraveling sediment dynamics and related lake level changes during the last 14 ka B.P., as revealed by sediment core KH17 (around 7 m long) retrieved from the deepest part of the lake basin. Sediment grain size, loss on ignition (LOI) and X-ray fluorescence (XRF) were used to determine such depositional and transportation processes. Principal component analysis (PCA) shows that PC1, characterized by high positive loadings of K, Ti, Mn, Fe and Rb, is related to the detrital material transported by inflowing rivers. Ca and Sr in PC2 have high correlation coefficients indicating the varying intensity of local evaporation. Zr (high loadings on PC3) and Rb are related to coarse and fine sediment components respectively, which are mainly transported by wind and suspended load of inflows. The Zr/Rb ratio was used to judge the intensity of geochemical weathering. Fe/Mn and Sr/Ca indicate redox conditions and salinity, which are related to lake level changes. Based on the proxies, the environmental history over the past 14 ka was reconstructed as follows. During 13.6~13 ka B.P., the Kuhai Lake Basin was covered by a shallow water body, and strongly influenced by inflow variations. The Younger Dryas interval between 13 and 11.5 ka B.P. experienced cold, dry conditions and increased aeolian transport, which influenced the depositional environment. A 500-year warm and wet intermediate phase may have existed, according to the chronology. Temperatures increased to a large extent since the Early Holocene, which led to increased evaporation and the formation of carbonates following a slight lake level rise. The water depth peaked during the Middle Holocene, reaching the highest level experienced by the lake. After 5.3 ka BP, Kuhai Lake experienced a drier period, with high salinity and varying carbonate precipitation. Water supply has fluctuated greatly since the Late Holocene (2.7 ka B.P.).
Lake basins on the northeastern Tibetan Plateau are regarded as important archives for the reconstruction of environmental and climate changes during the Upper Quaternary. Lake deposits serve as ideal indicators of various transport and depositional processes in changing hydro-climatic settings. Understanding such dynamic processes is of crucial interest when deciphering the process-response behavior of lakes from their sedimentary characteristics over time. The closed saline Kuhai Lake is an ideal location for unraveling sediment dynamics and related lake level changes during the last 14 ka B.P., as revealed by sediment core KH17 (around 7 m long) retrieved from the deepest part of the lake basin. Sediment grain size, loss on ignition (LOI) and X-ray fluorescence (XRF) were used to determine such depositional and transportation processes. Principal component analysis (PCA) shows that PC1, characterized by high positive loadings of K, Ti, Mn, Fe and Rb, is related to the detrital material transported by inflowing rivers. Ca and Sr in PC2 have high correlation coefficients indicating the varying intensity of local evaporation. Zr (high loadings on PC3) and Rb are related to coarse and fine sediment components respectively, which are mainly transported by wind and suspended load of inflows. The Zr/Rb ratio was used to judge the intensity of geochemical weathering. Fe/Mn and Sr/Ca indicate redox conditions and salinity, which are related to lake level changes. Based on the proxies, the environmental history over the past 14 ka was reconstructed as follows. During 13.6~13 ka B.P., the Kuhai Lake Basin was covered by a shallow water body, and strongly influenced by inflow variations. The Younger Dryas interval between 13 and 11.5 ka B.P. experienced cold, dry conditions and increased aeolian transport, which influenced the depositional environment. A 500-year warm and wet intermediate phase may have existed, according to the chronology. Temperatures increased to a large extent since the Early Holocene, which led to increased evaporation and the formation of carbonates following a slight lake level rise. The water depth peaked during the Middle Holocene, reaching the highest level experienced by the lake. After 5.3 ka BP, Kuhai Lake experienced a drier period, with high salinity and varying carbonate precipitation. Water supply has fluctuated greatly since the Late Holocene (2.7 ka B.P.).
2019, 37(1): 115-123.
doi: 10.14027/j.issn.1000-0550.2018.100
Abstract:
The origin of the first hard clay layer in the Yangtze River Delta is a debated issue. To explore its origin, its grain size was examined by clustering analysis and discriminant analysis, and compared with the Xiashu loess in Nanjing and suspended particles in the Yangtze River. The grain size characteristic is uniform, with positive skewness, medium or sharp peak shape, bimodal distribution, S-shape cumulative frequency curve distribution, and with aeolian deposition characteristics. When the grain size analysis provides sedimentological evidence for a sedimentary environment, multivariate statistical analysis improves its accuracy. The first hard clay and Xiashu loess fall into the same classification; the suspended particles in the Yangtze River are in a separate class. The application of clustering analysis shows that the hard clay and Xiashu loess have the same aeolian genesis, as confirmed by discriminant analysis. Standard deviation curves of the hard clay, together with the present-day wind field, show that the grain size characteristics of the hard clay have two controlling factors: high-altitude westerly winds and the East Asian winter monsoon. All analyses indicate that the first hard clay layer in the Yangtze River Delta is an aeolian deposit transported by westerly winds and the northwestern monsoon.
The origin of the first hard clay layer in the Yangtze River Delta is a debated issue. To explore its origin, its grain size was examined by clustering analysis and discriminant analysis, and compared with the Xiashu loess in Nanjing and suspended particles in the Yangtze River. The grain size characteristic is uniform, with positive skewness, medium or sharp peak shape, bimodal distribution, S-shape cumulative frequency curve distribution, and with aeolian deposition characteristics. When the grain size analysis provides sedimentological evidence for a sedimentary environment, multivariate statistical analysis improves its accuracy. The first hard clay and Xiashu loess fall into the same classification; the suspended particles in the Yangtze River are in a separate class. The application of clustering analysis shows that the hard clay and Xiashu loess have the same aeolian genesis, as confirmed by discriminant analysis. Standard deviation curves of the hard clay, together with the present-day wind field, show that the grain size characteristics of the hard clay have two controlling factors: high-altitude westerly winds and the East Asian winter monsoon. All analyses indicate that the first hard clay layer in the Yangtze River Delta is an aeolian deposit transported by westerly winds and the northwestern monsoon.
2019, 37(1): 124-134.
doi: 10.14027/j.issn.1000-0550.2018.113
Abstract:
The sediment grain size distribution can be used to reveal sediment dynamic environments. Based on the grain size analysis of the surficial sediment collected from the Nanliujiang River subaqueous delta, Guangxi province, we identified the sediment sources and discussed associated sediment dynamic environments of the study area using end-member analysis and Folk classification. The analyzed results indicate that the surficial sediment can be divided into 9 types, including 5 types of sediment with gravel and 4 types of sediment with no gravel. The spatial distribution of the surficial sediment type is coincidental with environmental dynamic characteristics near the estuarine environment. According to end-member analysis, there are 5 distinguishable end-members (EM1-5), which represent 5 types of sediment dynamic environments. EM1 reflects the dynamic effects of wind waves and tidal currents on surficial sediments; EM2 indicates the dynamic process of surges on surficial sediments; EM3 reveals the effects of diluted Nanliujiang River water on surficial sediment transport processes; EM4 represents the relict sediment in the inner continental shelf; and EM5 is an end member disturbed by some noise, which may be induced by anthropogenic activities, such as coastal engineering construction. Based on our study results, if we try to use end-member analysis to study the sediment dynamic environment in an area with complex environments (e.g. small mountainous river estuary-shelf systems), we need to note two aspects: (1) we should take into consideration sediment sources and environmental dynamic characteristics in the study area; and (2) we can also combine other methods for mutual corroboration, such as parametric curve-fitting, and grain size trend analysis (GSTA).
The sediment grain size distribution can be used to reveal sediment dynamic environments. Based on the grain size analysis of the surficial sediment collected from the Nanliujiang River subaqueous delta, Guangxi province, we identified the sediment sources and discussed associated sediment dynamic environments of the study area using end-member analysis and Folk classification. The analyzed results indicate that the surficial sediment can be divided into 9 types, including 5 types of sediment with gravel and 4 types of sediment with no gravel. The spatial distribution of the surficial sediment type is coincidental with environmental dynamic characteristics near the estuarine environment. According to end-member analysis, there are 5 distinguishable end-members (EM1-5), which represent 5 types of sediment dynamic environments. EM1 reflects the dynamic effects of wind waves and tidal currents on surficial sediments; EM2 indicates the dynamic process of surges on surficial sediments; EM3 reveals the effects of diluted Nanliujiang River water on surficial sediment transport processes; EM4 represents the relict sediment in the inner continental shelf; and EM5 is an end member disturbed by some noise, which may be induced by anthropogenic activities, such as coastal engineering construction. Based on our study results, if we try to use end-member analysis to study the sediment dynamic environment in an area with complex environments (e.g. small mountainous river estuary-shelf systems), we need to note two aspects: (1) we should take into consideration sediment sources and environmental dynamic characteristics in the study area; and (2) we can also combine other methods for mutual corroboration, such as parametric curve-fitting, and grain size trend analysis (GSTA).
2019, 37(1): 135-142.
doi: 10.14027/j.issn.1000-0550.2018.094
Abstract:
A floodplain is a fluvial geomorphic unit formed by a flood that flows over the natural levee and below the river and is a unique sedimentary system formed by flood processes that contains a great deal of river hydrological information. However, because of the lateral sway of the river and the fast deposition rate of the floodplain, the sedimentary environment of the floodplain changes rapidly, which means that the floodplain sedimentary system has not been adequately studied for a long time. We examine the modern floodplain, on the right bank of the Xiu River in the triangle township of Yongxiu County, along the lower reaches of the river, as our case study. Testing the specific activity of 137Cs to establish the time scale, based on particle size and combined with the meteorological and hydrological observation data, we explore the instrument for the floodplain depositional system of flood event records and record features. Study shows that during the larger floods with the hydrodynamic instability, coarse grain size, poor sorting (or good), and wide particle size span; This section reveals 14 larger flood years have occurred since 1953 with a high detection rate. The average particle size (μm) and SS (sorting coefficient×particle size span) are the best indicators for flood events. These floods can be called abnormal floods, which are different with extreme flood inversions based on stagnant water deposition. Therefore, to a certain extent, this study will broaden the content and connotation of the ancient flood research.
A floodplain is a fluvial geomorphic unit formed by a flood that flows over the natural levee and below the river and is a unique sedimentary system formed by flood processes that contains a great deal of river hydrological information. However, because of the lateral sway of the river and the fast deposition rate of the floodplain, the sedimentary environment of the floodplain changes rapidly, which means that the floodplain sedimentary system has not been adequately studied for a long time. We examine the modern floodplain, on the right bank of the Xiu River in the triangle township of Yongxiu County, along the lower reaches of the river, as our case study. Testing the specific activity of 137Cs to establish the time scale, based on particle size and combined with the meteorological and hydrological observation data, we explore the instrument for the floodplain depositional system of flood event records and record features. Study shows that during the larger floods with the hydrodynamic instability, coarse grain size, poor sorting (or good), and wide particle size span; This section reveals 14 larger flood years have occurred since 1953 with a high detection rate. The average particle size (μm) and SS (sorting coefficient×particle size span) are the best indicators for flood events. These floods can be called abnormal floods, which are different with extreme flood inversions based on stagnant water deposition. Therefore, to a certain extent, this study will broaden the content and connotation of the ancient flood research.
2019, 37(1): 143-154.
doi: 10.14027/j.issn.1000-0550.2018.126
Abstract:
In and around Dongting Lake, which is the second largest freshwater lake in China, provides an important window for studying Chinese Holocene paleoclimate evolution and global change. Research of the Holocene paleoclimate in the area is seriously deficient without quantitative studies. Detailed ecological investigation of recent ostracods is an essential precondition and foundation for quantitative reconstruction of paleoclimate using fauna data. Recent ostracods from Dongting Lake are described first, including six genera and 10 species, Schellencandona cf. belgica, Ilyocypris bradyi, I. salebrosa, Fabaeformiscandona fabaeformis, Cypria kraepelini, Typhlocypris cf. rostrata, Cypridopsis vidua and C. sp. (comprising three species). These species were reported initially in Hunan Province. Descriptions of S. cf. belgica and T. cf. rostrata are rare in China, especially the latter. S. cf. belgica, I. bradyi and F. fabaeformis are the predominant species, with wide distribution and high abundance, while I. salebrosa has relatively low abundance and is of limited distribution. C. kraepelini and T. cf. rostrata are relatively highly abundant, and C. vidua and C. sp. are of low abundance. There are no obvious differences in the habitat parameters of these species; their general habitat data is: water temperature 20.33 ℃, pH 7.34-8.60, dissolved oxygen content 5.23-9.01 mg/L, electrical conductivity 197-391 μS/cm, and water depth 1.0-8.4 m (tending towards 1-4 m). F. fabaeformis and C. kraepelini are found at a somewhat greater depth than previously thought, possibly because the water in Dongting Lake is relatively mobile. It is possible that I. salebrosa favors warm, shallow water. This study supports quantitative reconstruction of the Holocene paleoclimate in the area using ostracods, and enriches the habitat data of recent ostracods in China.
In and around Dongting Lake, which is the second largest freshwater lake in China, provides an important window for studying Chinese Holocene paleoclimate evolution and global change. Research of the Holocene paleoclimate in the area is seriously deficient without quantitative studies. Detailed ecological investigation of recent ostracods is an essential precondition and foundation for quantitative reconstruction of paleoclimate using fauna data. Recent ostracods from Dongting Lake are described first, including six genera and 10 species, Schellencandona cf. belgica, Ilyocypris bradyi, I. salebrosa, Fabaeformiscandona fabaeformis, Cypria kraepelini, Typhlocypris cf. rostrata, Cypridopsis vidua and C. sp. (comprising three species). These species were reported initially in Hunan Province. Descriptions of S. cf. belgica and T. cf. rostrata are rare in China, especially the latter. S. cf. belgica, I. bradyi and F. fabaeformis are the predominant species, with wide distribution and high abundance, while I. salebrosa has relatively low abundance and is of limited distribution. C. kraepelini and T. cf. rostrata are relatively highly abundant, and C. vidua and C. sp. are of low abundance. There are no obvious differences in the habitat parameters of these species; their general habitat data is: water temperature 20.33 ℃, pH 7.34-8.60, dissolved oxygen content 5.23-9.01 mg/L, electrical conductivity 197-391 μS/cm, and water depth 1.0-8.4 m (tending towards 1-4 m). F. fabaeformis and C. kraepelini are found at a somewhat greater depth than previously thought, possibly because the water in Dongting Lake is relatively mobile. It is possible that I. salebrosa favors warm, shallow water. This study supports quantitative reconstruction of the Holocene paleoclimate in the area using ostracods, and enriches the habitat data of recent ostracods in China.
2019, 37(1): 155-162.
doi: 10.14027/j.issn.1000-0550.2018.106
Abstract:
Based on numerous high-resolution seismic profiles, sediment waves are identified in the eastern waters of Taiwan Island, and their distribution, morphological characteristics, internal structure, and potential origin are illustrated. The sediment waves are located at the junction of the Taitung canyon with other canyons on the slope. The wavelength of a single waveform is 0.8-7.2 km, and the wave height is about 18-75 m, which is a northeast-southwest (NE—SW) distribution. Sediment waves located inside the bend section of Taitung canyon have characteristics of upward migration, their bottoms develop MTD, and the interior can be subdivided into lower transition units and upper wavy units. The sediment wave on the outside of the bend is characterized by vertical accretion, and there is no mass flow deposit at the bottom. According to the sediment wave geometry, the flow thicknesses across the entire wave field are calculated as 196-356 m, and the current velocity falls in the range of 15-21 cm/s. The morphological characteristics, internal structure, and distribution of sediment waves and our numerical calculations show that these sediment waves are turbidity currents. The development of the sediment wave field in east Taiwan is the same as that of the sediment wave field in southwestern Taiwan. It is the sedimentary response of the Taiwan orogeny. Turbidity sediments overflow in the bend section of Taitung canyon or in places of less topographical constraint, thus forming a sediment wave field.
Based on numerous high-resolution seismic profiles, sediment waves are identified in the eastern waters of Taiwan Island, and their distribution, morphological characteristics, internal structure, and potential origin are illustrated. The sediment waves are located at the junction of the Taitung canyon with other canyons on the slope. The wavelength of a single waveform is 0.8-7.2 km, and the wave height is about 18-75 m, which is a northeast-southwest (NE—SW) distribution. Sediment waves located inside the bend section of Taitung canyon have characteristics of upward migration, their bottoms develop MTD, and the interior can be subdivided into lower transition units and upper wavy units. The sediment wave on the outside of the bend is characterized by vertical accretion, and there is no mass flow deposit at the bottom. According to the sediment wave geometry, the flow thicknesses across the entire wave field are calculated as 196-356 m, and the current velocity falls in the range of 15-21 cm/s. The morphological characteristics, internal structure, and distribution of sediment waves and our numerical calculations show that these sediment waves are turbidity currents. The development of the sediment wave field in east Taiwan is the same as that of the sediment wave field in southwestern Taiwan. It is the sedimentary response of the Taiwan orogeny. Turbidity sediments overflow in the bend section of Taitung canyon or in places of less topographical constraint, thus forming a sediment wave field.
2019, 37(1): 163-176.
doi: 10.14027/j.issn.1000-0550.2018.156
Abstract:
The study was based on detailed observations of the outcrop profiles in Rujigou and Yanjiazhuang, and drill cores from Huan52, Huan78 and Yan40 wells in the study area, and combined with previous research results. Analysis of the lithology and rock associations is discussed, as well as the sedimentary facies and their characteristics and the evolutionary process of the Yanchang Formation in the study area. The research suggests that 12 lithological types and seven rock association types are recognized in the Yanchang Formation at the western margin of the Ordos Basin. Within the study area, fan delta-lake, a braided river delta and an alluvial fan sedimentary system were the main developments in the Yanchang period. Cribriform deposition, water distributary channels, interdistributary channels, underwater distributary channels, mouth bar and distal bar were also substantially developed, together with other sedimentary microfacies and subfacies types. In the northern part of the study area in Rujigou, fan delta facies were mainly developed in the early Yanchang Formation, with lacustrine facies transitioning into fan delta facies in the middle stage. Deep-lake facies developed in the late stage. In the central area of the Yanchang Formation, in Huanxian-Yanwu, early braided river facies developed, and delta front subfacies and lacustrine facies were formed in the middle stage, with transition to delta facies subjected to uplift-denudation. In southern Yan Jia Zhuang, in the early Yanchang Formation the main developments were alluvial fan facies, then fan delta front facies in the middle stage, and uplifting and denudation in the late stage.
The study was based on detailed observations of the outcrop profiles in Rujigou and Yanjiazhuang, and drill cores from Huan52, Huan78 and Yan40 wells in the study area, and combined with previous research results. Analysis of the lithology and rock associations is discussed, as well as the sedimentary facies and their characteristics and the evolutionary process of the Yanchang Formation in the study area. The research suggests that 12 lithological types and seven rock association types are recognized in the Yanchang Formation at the western margin of the Ordos Basin. Within the study area, fan delta-lake, a braided river delta and an alluvial fan sedimentary system were the main developments in the Yanchang period. Cribriform deposition, water distributary channels, interdistributary channels, underwater distributary channels, mouth bar and distal bar were also substantially developed, together with other sedimentary microfacies and subfacies types. In the northern part of the study area in Rujigou, fan delta facies were mainly developed in the early Yanchang Formation, with lacustrine facies transitioning into fan delta facies in the middle stage. Deep-lake facies developed in the late stage. In the central area of the Yanchang Formation, in Huanxian-Yanwu, early braided river facies developed, and delta front subfacies and lacustrine facies were formed in the middle stage, with transition to delta facies subjected to uplift-denudation. In southern Yan Jia Zhuang, in the early Yanchang Formation the main developments were alluvial fan facies, then fan delta front facies in the middle stage, and uplifting and denudation in the late stage.
2019, 37(1): 177-188.
doi: 10.14027/j.issn.1000-0550.2018.119
Abstract:
The Jinhu Sag contains the main oil-bearing blocks in the northern Jiangsu Basin, and mixed sediments of terrigenous fragments and lacustrine carbonates are widely developed in the Second Member of the Funing Formation in the Jinhu Sag. This paper describes a systematic study of the mixed sedimentation of the Second Member of the Funing Formation in Jinhu Sag, with cores, mud logging, well logging, and other study area data acquisition methods. This work discovered that, in the sedimentary period of the Second Member of the Funing Formation in Jinhu Sag, the mixed sedimentary rock with the best micro performance was mixosedimentite formed by mixed deposits of terrigenous fragments and carbonate components, and the best macro performance was obtained from a layered system of terrigenous rock-carbonate rock, terrigenous rock-mixosedimentite, carbonate rock-mixosedimentite, and mixosedimentite. The types of mixed deposits include mainly blended mixed deposits, complex mixed deposits, and some saltatory mixed deposits. This paper carefully analyzes the mixed deposits in the study area, including their geological settings, petrological characteristics, and depositional environments, establishes a mixed sedimentation model, and discusses the controlling factors of the mixed deposits. The main controlling factors are the transgressive effects of the Second Member of the Funing Formation. Tectonic action, climatic conditions, lake surface changes, and provenance also have important effects on the mixed deposits in the study area.
The Jinhu Sag contains the main oil-bearing blocks in the northern Jiangsu Basin, and mixed sediments of terrigenous fragments and lacustrine carbonates are widely developed in the Second Member of the Funing Formation in the Jinhu Sag. This paper describes a systematic study of the mixed sedimentation of the Second Member of the Funing Formation in Jinhu Sag, with cores, mud logging, well logging, and other study area data acquisition methods. This work discovered that, in the sedimentary period of the Second Member of the Funing Formation in Jinhu Sag, the mixed sedimentary rock with the best micro performance was mixosedimentite formed by mixed deposits of terrigenous fragments and carbonate components, and the best macro performance was obtained from a layered system of terrigenous rock-carbonate rock, terrigenous rock-mixosedimentite, carbonate rock-mixosedimentite, and mixosedimentite. The types of mixed deposits include mainly blended mixed deposits, complex mixed deposits, and some saltatory mixed deposits. This paper carefully analyzes the mixed deposits in the study area, including their geological settings, petrological characteristics, and depositional environments, establishes a mixed sedimentation model, and discusses the controlling factors of the mixed deposits. The main controlling factors are the transgressive effects of the Second Member of the Funing Formation. Tectonic action, climatic conditions, lake surface changes, and provenance also have important effects on the mixed deposits in the study area.
2019, 37(1): 189-199.
doi: 10.14027/j.issn.1000-0550.2018.146
Abstract:
The appearance of paleogeography is the result of the joint action of tectonic evolution and sedimentary filling. In this study, which was based on previous research and exploration results, systematic observations and analyses of the field outcrops in Hannan-Northeastern Sichuan Basin were conducted. The results reveal that there are four types of paleogeographic units in Dengying Formation in the Late Sinian: ancient Hannan paleo-uplift， restricted platforms open platforms and slopes. The terrain in the northeastern part of the Hannan-Northeastern Sichuan Basin is lowest in the south and highest in the north; the depositional elements are distributed in the north-south and northeasterly directions. The paleogeographic appearance in the study area was of “one uplift, two depressions”. It is suggested that the study area was in an extensional setting, which is reflected by the characteristics of co-sedimentary faults identified from outcrops and drillings. In addition, the location of the rift/depression identified in the geophysical data is consistent with the location of the ancient land on the paleogeographic map. This confirms the existence of the Mianzhu-Lezhi-Longchang-Changning pull/rift and Wanyuan-Dazhou rift in Sichuan Basin, and also indicates an extensional setting in the study area during the Dengying period. The paleogeographic background was transformed from one of stable deposition to active extension, and experienced stable deposition, prelude and main extension. Thus, this study further indicates the coupling relationship between sedimentary evolution and tectonic setting.
The appearance of paleogeography is the result of the joint action of tectonic evolution and sedimentary filling. In this study, which was based on previous research and exploration results, systematic observations and analyses of the field outcrops in Hannan-Northeastern Sichuan Basin were conducted. The results reveal that there are four types of paleogeographic units in Dengying Formation in the Late Sinian: ancient Hannan paleo-uplift， restricted platforms open platforms and slopes. The terrain in the northeastern part of the Hannan-Northeastern Sichuan Basin is lowest in the south and highest in the north; the depositional elements are distributed in the north-south and northeasterly directions. The paleogeographic appearance in the study area was of “one uplift, two depressions”. It is suggested that the study area was in an extensional setting, which is reflected by the characteristics of co-sedimentary faults identified from outcrops and drillings. In addition, the location of the rift/depression identified in the geophysical data is consistent with the location of the ancient land on the paleogeographic map. This confirms the existence of the Mianzhu-Lezhi-Longchang-Changning pull/rift and Wanyuan-Dazhou rift in Sichuan Basin, and also indicates an extensional setting in the study area during the Dengying period. The paleogeographic background was transformed from one of stable deposition to active extension, and experienced stable deposition, prelude and main extension. Thus, this study further indicates the coupling relationship between sedimentary evolution and tectonic setting.
2019, 37(1): 200-211.
doi: 10.14027/j.issn.1000-0550.2018.086
Abstract:
The development of the high-quality reservoir in medium-deep sections often decides hydrocarbon enrichment. The depth of medium-deep sections in the Bohai sea is approximately greater than 3 000 m with poor reservoir physical properties. We found a mixed reservoir, including terrigenous detrital and Carbonate oolitics and bioclasts, with excellent physical properties in the 1st and 2nd member of the Shahejie Formation (E3s1+2) in the QHD29-2E structure, and the research of the controlling factors, which have significant implications for similar areas. The features of lithology and reservoir space were revealed by observations of core, rock thin section, scanning electronic microscope (SEM), examining the physical properties, and X ray diffraction (XRD). The isotope fluid inclusion method and reservoir forming mechanism were further addressed. We determined that the rocks in E3s1+2 are composed mainly of terrigenous detrital bearing-carbonate mixed rocks, terrigenous detrital-carbonate mixed rock, and carbonate bearing- terrigenous detrital mixed rock with high porosity and low-very low permeability; for the reservoir space, primary porosity, including intergranular and body cavity pores, as well as secondary pores like moldic pores, were generally found. According to research, snail-rich mixed shoal formed due to strong lake wave action in a saline lacustrine basin. Additionally, dolomitization in the earlier stage and the latter secondary erosion are dominant factors affecting the formation of the excellent reservoirs in the QHD29-2E structure.
The development of the high-quality reservoir in medium-deep sections often decides hydrocarbon enrichment. The depth of medium-deep sections in the Bohai sea is approximately greater than 3 000 m with poor reservoir physical properties. We found a mixed reservoir, including terrigenous detrital and Carbonate oolitics and bioclasts, with excellent physical properties in the 1st and 2nd member of the Shahejie Formation (E3s1+2) in the QHD29-2E structure, and the research of the controlling factors, which have significant implications for similar areas. The features of lithology and reservoir space were revealed by observations of core, rock thin section, scanning electronic microscope (SEM), examining the physical properties, and X ray diffraction (XRD). The isotope fluid inclusion method and reservoir forming mechanism were further addressed. We determined that the rocks in E3s1+2 are composed mainly of terrigenous detrital bearing-carbonate mixed rocks, terrigenous detrital-carbonate mixed rock, and carbonate bearing- terrigenous detrital mixed rock with high porosity and low-very low permeability; for the reservoir space, primary porosity, including intergranular and body cavity pores, as well as secondary pores like moldic pores, were generally found. According to research, snail-rich mixed shoal formed due to strong lake wave action in a saline lacustrine basin. Additionally, dolomitization in the earlier stage and the latter secondary erosion are dominant factors affecting the formation of the excellent reservoirs in the QHD29-2E structure.
2019, 37(1): 212-223.
doi: 10.14027/j.issn.1000-0550.2018.105
Abstract:
The Xiquan area is tectonically at the west ramp of the Beisantai salient and is suitable for oil and gas accumulation. Although a few Carboniferous reservoirs were found in past decades, because of the complex controlling factors and confused distribution in both longitudinal and horizontal directions of reservoirs in this area, the proved rate is low, and further exploration is difficult. This paper clarifies the petrologic and reservoir characteristics of Carboniferous reservoirs. The results include that Carboniferous reservoirs in the Xiquan area consist mainly of lava and pyroclastic rock; that reservoir physical properties in the South are better than in the North; and that favorable reservoirs have mainly developed in eruptive volcanic breccia and effusive facies of andesite and dacite. On this basis, the main controlling factors of reservoir distribution have been clarified: 1) reservoirs mainly concentrate near the weathering crust in the vertical profile, 2) the lateral variation of lithology controls the plane distribution of the reservoirs, and 3) reservoir distribution is closely related to the development of unconformities. In addition reservoir distribution laws have been summarized: oil and gas mainly concentrate near unconformities and stretch from Northeast to the Southwest like stripes; the vertical distribution of oil layers is related to the depth of eluvial zones of unconformity and is different between South and North; and heterogeneity influences contiguous distribution in the reservoir plane.
The Xiquan area is tectonically at the west ramp of the Beisantai salient and is suitable for oil and gas accumulation. Although a few Carboniferous reservoirs were found in past decades, because of the complex controlling factors and confused distribution in both longitudinal and horizontal directions of reservoirs in this area, the proved rate is low, and further exploration is difficult. This paper clarifies the petrologic and reservoir characteristics of Carboniferous reservoirs. The results include that Carboniferous reservoirs in the Xiquan area consist mainly of lava and pyroclastic rock; that reservoir physical properties in the South are better than in the North; and that favorable reservoirs have mainly developed in eruptive volcanic breccia and effusive facies of andesite and dacite. On this basis, the main controlling factors of reservoir distribution have been clarified: 1) reservoirs mainly concentrate near the weathering crust in the vertical profile, 2) the lateral variation of lithology controls the plane distribution of the reservoirs, and 3) reservoir distribution is closely related to the development of unconformities. In addition reservoir distribution laws have been summarized: oil and gas mainly concentrate near unconformities and stretch from Northeast to the Southwest like stripes; the vertical distribution of oil layers is related to the depth of eluvial zones of unconformity and is different between South and North; and heterogeneity influences contiguous distribution in the reservoir plane.
