2012 Vol. 30, No. 4
Display Method:
2012, 30(4): 603-618.
Abstract:
NeoProterozoic Sinian System of the Dalian District where is the only one outcrop area in North China, is recognized as a geonappe from South China Sinian System. The Sinian strata in the tourist scenic area of Golden Stone Beach area are composed of 7 formations (in ascending ward): the Yingchengzi(Z2y), the Shisanlitai(Z2s),the Majiatun(Z2m),the Cuijiatun(Z2c), the Zhoujiaweizi(Z2z), the Wangjiatan(Z2w),and the Xingmingchun(Z2x).REE minerals and noble metals bearing pelite is included in the Shisanlitai Formation which consists of rose colored stromatolite carbonate beds therefore the tourist scenic spot be named “Rose Garden” in the Goldstone Beach Scenic District. There are several greenish pelite beds where monazite and other REE minerals are found in the Shisanlitai Formation. Two beds among them are relative thicker than other, and more metal minerals are discovered.According to the change of ratio of FeO/Fe2O3 in strata, the main body rock of pink stromatolite limestone occurred in an oxidizing environment, however the greenish pelite in a reducing environment of a locally restrict area. Besides, a comparison of light rare earth elements (LREE) with North American Shale (NASC) shows that greenish pelite contains more LREEs but pink stromatolite limestone consists of less these elements than NASC. Further distinguished by three end-member diagram (La+Ce+Nd，Sm+Gd+Dy，and Yb+Y), the sediments deposited location of distance from marine beach shows that the greenish pelite beds should be near continent, but the pink stromatolite limestone be far away from continent.This paper issues a very rare slight metamorphosed NeoProterozoic pelite, which includes clastic and authigenicdiagenetic monazite, xenotime grains, as well as native gold, IrOs, Ir metal grains, zircon, rutile, apatite, ilmenite, hematite etc. heavy mineral associations, and some rock forming minerals. The pelite beds belong to NeoProterozoic Sinian System, the Shisanlitai Formation, which are composed of the interbedded reddish stromatolite limestone and greenish pelite intercalations. The sedimentary environmental textural facies indicators shows that there were a carbonate shore reef regions near the continent in the Shisanlitai Stage, which involves some likelagoon restrictive small basins under the reduction and oxidation alternation chemical condition and creates the favorable microenvironment for REE molecular exchanging to the authigenicdiagenetic monazite (“manshaped”, “birdshaped”) and xenotime (“catshaped”) in the syngenetic deposition and diagenetic stages. The noble metal grains are mainly clastic origin, but Au, Zn, Cu and Pb are related with oremade fluid. North China platform with the abundant REE elements and the noble metals is the original source of the NeoProterozoic REE minerals noble metals bearing pelite.
NeoProterozoic Sinian System of the Dalian District where is the only one outcrop area in North China, is recognized as a geonappe from South China Sinian System. The Sinian strata in the tourist scenic area of Golden Stone Beach area are composed of 7 formations (in ascending ward): the Yingchengzi(Z2y), the Shisanlitai(Z2s),the Majiatun(Z2m),the Cuijiatun(Z2c), the Zhoujiaweizi(Z2z), the Wangjiatan(Z2w),and the Xingmingchun(Z2x).REE minerals and noble metals bearing pelite is included in the Shisanlitai Formation which consists of rose colored stromatolite carbonate beds therefore the tourist scenic spot be named “Rose Garden” in the Goldstone Beach Scenic District. There are several greenish pelite beds where monazite and other REE minerals are found in the Shisanlitai Formation. Two beds among them are relative thicker than other, and more metal minerals are discovered.According to the change of ratio of FeO/Fe2O3 in strata, the main body rock of pink stromatolite limestone occurred in an oxidizing environment, however the greenish pelite in a reducing environment of a locally restrict area. Besides, a comparison of light rare earth elements (LREE) with North American Shale (NASC) shows that greenish pelite contains more LREEs but pink stromatolite limestone consists of less these elements than NASC. Further distinguished by three end-member diagram (La+Ce+Nd，Sm+Gd+Dy，and Yb+Y), the sediments deposited location of distance from marine beach shows that the greenish pelite beds should be near continent, but the pink stromatolite limestone be far away from continent.This paper issues a very rare slight metamorphosed NeoProterozoic pelite, which includes clastic and authigenicdiagenetic monazite, xenotime grains, as well as native gold, IrOs, Ir metal grains, zircon, rutile, apatite, ilmenite, hematite etc. heavy mineral associations, and some rock forming minerals. The pelite beds belong to NeoProterozoic Sinian System, the Shisanlitai Formation, which are composed of the interbedded reddish stromatolite limestone and greenish pelite intercalations. The sedimentary environmental textural facies indicators shows that there were a carbonate shore reef regions near the continent in the Shisanlitai Stage, which involves some likelagoon restrictive small basins under the reduction and oxidation alternation chemical condition and creates the favorable microenvironment for REE molecular exchanging to the authigenicdiagenetic monazite (“manshaped”, “birdshaped”) and xenotime (“catshaped”) in the syngenetic deposition and diagenetic stages. The noble metal grains are mainly clastic origin, but Au, Zn, Cu and Pb are related with oremade fluid. North China platform with the abundant REE elements and the noble metals is the original source of the NeoProterozoic REE minerals noble metals bearing pelite.
2012, 30(4): 619-628.
Abstract:
The Padana Formation represents the shallow marine stage of the Xigaze forearc basin in the south Tibet during the Late Cretaceous. This paper focused on the study of the sedimentary facies of the Padana Formation in the area of Sangsang in the southern Tibet. Five types of lithofacies were recognized in the Padana Formation, including conglomerates, sandstones, siltstones, shales and limestones. Abundant sedimentary structures were developed in sandstones and siltstones, including wedge cross bedding, planar cross bedding, grading beds, parallel lamination, mud interclasts, biotic burrows and bioturbations. Plenty of carbonate concretions and some biotic burrows occurred in shales. Based on the studies of lithofacies and sedimentary structures, we interpret that continental shelf and delta are the sedimentary facies of the Padana Formation. Furthermore, the delta facies include prodelta, delta front and delta plain subfacies. Delta front can be further divided into subaqueous distributary channel, mouth bar and interdistributary bay, while delta plain is composed of distributary channel and floodplain. The evolution of the sedimentary environments from continental shelf to delta upwards in the Padana Formation suggests shallowing of the Xigaze forearc basin which may reflect the filling history of the Xigaze forearc basin from underfilled to overfilled stages.
The Padana Formation represents the shallow marine stage of the Xigaze forearc basin in the south Tibet during the Late Cretaceous. This paper focused on the study of the sedimentary facies of the Padana Formation in the area of Sangsang in the southern Tibet. Five types of lithofacies were recognized in the Padana Formation, including conglomerates, sandstones, siltstones, shales and limestones. Abundant sedimentary structures were developed in sandstones and siltstones, including wedge cross bedding, planar cross bedding, grading beds, parallel lamination, mud interclasts, biotic burrows and bioturbations. Plenty of carbonate concretions and some biotic burrows occurred in shales. Based on the studies of lithofacies and sedimentary structures, we interpret that continental shelf and delta are the sedimentary facies of the Padana Formation. Furthermore, the delta facies include prodelta, delta front and delta plain subfacies. Delta front can be further divided into subaqueous distributary channel, mouth bar and interdistributary bay, while delta plain is composed of distributary channel and floodplain. The evolution of the sedimentary environments from continental shelf to delta upwards in the Padana Formation suggests shallowing of the Xigaze forearc basin which may reflect the filling history of the Xigaze forearc basin from underfilled to overfilled stages.
2012, 30(4): 629-638.
Abstract:
Accoding to the characteristics of the Bouguer gravity anomalies, the source and deposition areas were macroscopically distinguished in this paper. Based on the characteristics of heavy mineral, the location and extent of the source areas were described. In addition, the direction of the sources were determined on the basis of seismic reflection characteristics. Furthermore, the characteristics of provenancesedimentary system were finely pictured by the distribution of sandbody, and could be further verified through geochemical characteristics. Different ways exerted respective superiority, and various means revised each other, the provenancesedimentary system of the first member of the Paleogene Shahejie Formation in the Qikou sag of the Bohai bay basin was reconstructed by these ways. The results suggested that, there were five sources in the first member of Shahejie Formation in the Qikou sag, that were Gegu source, Xiaozhan source, Zengfutai source, Qianquan source and Beidagang buried hill source. The Gegu source was the largest source in the Qikou sag, the direction was overall the northwest to southeast, it provided sediments for Banqiao sag, and the sediments were further promoted into Qikou sag mainly in two directions but terminated at the downthrow wall of the Qizhong fault, the migration direction of the source location evolved from the southwest to the northeast in the first member of the Shahejie Formation, but the scale of the migration is small. The Xiaozhan source developed along Xiaozhan to Baishuitou area, the extent was small, the sediments were promoted into Banqiao sag in SSE and SE, the migration direction of the source location evolved from northeast to southwest. The scale of the Zengfutai source was limited which was influenced by the Dazhangtuo fault, the sediments filled into the Banqiao sag, and the source location migrated along northeast. The location of the Qianquan source was unstable, the migration direction of the source location evolved from west to northeast, the extent of migration was large scale, the sediments were promoted into Banqiao sag in two directions. The sediments of the Beidagang buried hill source were carried to the Qibei sag along the downthrow wall of the Gangxi and Gangdong fault and extended to the Zhangbei fault which showed from northwest to southeast, and being frequent bifurcation when impelled into Mapengkou and Gaochentou area. Combined with well cores, drilling, logging and paleobiology, it showed that Banqiao sag developed fan delta sedimentary system which was controlled by the Cangdong fault, that included fan delta plain, fan delta front and frontfan delta. The Qikou sag developed deeplake turbidite sedimentary system which was influenced by the strong activity of Changlu fault, it was involved from the sandbody of the fan delta sedimentary system which controlled by the Gegu source. The Qibei sag developed deeplake turbidite sedimentary system located in the background of the semi deeplake and deeplake controlled by the Gangxi and Gangdong fault. The distribution of sedimentary system was obviously influenced by the direction, shape and extent of the source area. The research proved that this comprehensive analysis of multimethods was effective for the reconstruction of provenancesedimentary system.
Accoding to the characteristics of the Bouguer gravity anomalies, the source and deposition areas were macroscopically distinguished in this paper. Based on the characteristics of heavy mineral, the location and extent of the source areas were described. In addition, the direction of the sources were determined on the basis of seismic reflection characteristics. Furthermore, the characteristics of provenancesedimentary system were finely pictured by the distribution of sandbody, and could be further verified through geochemical characteristics. Different ways exerted respective superiority, and various means revised each other, the provenancesedimentary system of the first member of the Paleogene Shahejie Formation in the Qikou sag of the Bohai bay basin was reconstructed by these ways. The results suggested that, there were five sources in the first member of Shahejie Formation in the Qikou sag, that were Gegu source, Xiaozhan source, Zengfutai source, Qianquan source and Beidagang buried hill source. The Gegu source was the largest source in the Qikou sag, the direction was overall the northwest to southeast, it provided sediments for Banqiao sag, and the sediments were further promoted into Qikou sag mainly in two directions but terminated at the downthrow wall of the Qizhong fault, the migration direction of the source location evolved from the southwest to the northeast in the first member of the Shahejie Formation, but the scale of the migration is small. The Xiaozhan source developed along Xiaozhan to Baishuitou area, the extent was small, the sediments were promoted into Banqiao sag in SSE and SE, the migration direction of the source location evolved from northeast to southwest. The scale of the Zengfutai source was limited which was influenced by the Dazhangtuo fault, the sediments filled into the Banqiao sag, and the source location migrated along northeast. The location of the Qianquan source was unstable, the migration direction of the source location evolved from west to northeast, the extent of migration was large scale, the sediments were promoted into Banqiao sag in two directions. The sediments of the Beidagang buried hill source were carried to the Qibei sag along the downthrow wall of the Gangxi and Gangdong fault and extended to the Zhangbei fault which showed from northwest to southeast, and being frequent bifurcation when impelled into Mapengkou and Gaochentou area. Combined with well cores, drilling, logging and paleobiology, it showed that Banqiao sag developed fan delta sedimentary system which was controlled by the Cangdong fault, that included fan delta plain, fan delta front and frontfan delta. The Qikou sag developed deeplake turbidite sedimentary system which was influenced by the strong activity of Changlu fault, it was involved from the sandbody of the fan delta sedimentary system which controlled by the Gegu source. The Qibei sag developed deeplake turbidite sedimentary system located in the background of the semi deeplake and deeplake controlled by the Gangxi and Gangdong fault. The distribution of sedimentary system was obviously influenced by the direction, shape and extent of the source area. The research proved that this comprehensive analysis of multimethods was effective for the reconstruction of provenancesedimentary system.
2012, 30(4): 639-645.
Abstract:
Landslides constitute important aspects of deepwater sediment fill; and the study of the landslide does much help unveiling the deposition process in deepwater settings. Using the high resolution multichannel seismic profiles, the frontally confined landslide is firstly discovered in Shenhu slope of the Northern South China Sea， of which distribution area is over 1 000 km2. The landslide undergoes a restricted downslope translation and does not overrun the undeformed downslope strata, so the seismic facies features are definitely different in the two sides of the ramp. With the internally chaotic reflection, the landslide is externally wedge shaped and the impressive fold and thrust develop in the toe domain of the landslide. Comparing with the frontally emergent landslide, the continuity of the frontally confined landslide sediment is better for the shorter downslope transport distance. Combined with the seismic reflection features of the slide and the comparison among the Shenhu landslide and the worldwide landslides, the type of the landslide is determined by the thickness of the slide and the slope angle, but the positive landformYitong shoal has no effect on the Shenhu landslide's evolution.
Landslides constitute important aspects of deepwater sediment fill; and the study of the landslide does much help unveiling the deposition process in deepwater settings. Using the high resolution multichannel seismic profiles, the frontally confined landslide is firstly discovered in Shenhu slope of the Northern South China Sea， of which distribution area is over 1 000 km2. The landslide undergoes a restricted downslope translation and does not overrun the undeformed downslope strata, so the seismic facies features are definitely different in the two sides of the ramp. With the internally chaotic reflection, the landslide is externally wedge shaped and the impressive fold and thrust develop in the toe domain of the landslide. Comparing with the frontally emergent landslide, the continuity of the frontally confined landslide sediment is better for the shorter downslope transport distance. Combined with the seismic reflection features of the slide and the comparison among the Shenhu landslide and the worldwide landslides, the type of the landslide is determined by the thickness of the slide and the slope angle, but the positive landformYitong shoal has no effect on the Shenhu landslide's evolution.
2012, 30(4): 646-653.
Abstract:
The Central Canyon in the Qiongdongnan basin shows a Sshaped NEtrending depositional system, which originates from the east margin of the Yinggehai basin, crosses the Central depression and extends into the Xisha trough. Based on the detailed interpretation of 2D and 3D seismic data and drillhole data, the Central Canyon can be divided into 4 segments. Each segment has not only different morphology in section, but also has distinct depositional architectures, genetic facies and sedimentsupplies. Analysis of morphology and infilling features indicates that the canyon shows the deeper downcutting and scours to the older strata eastwards. There are 4 types of V, U, W and composed shapes in vertical. Of them, Vtyped canyon shows the strongest downcutting, and the more significant scouring. Turbidite channel deposits are dominated in the western segment. Interbeds of turbidite channel and mass transport deposits occur in the eastern segment, but there are different ratios in different places. Turbidite channel deposits originate from the west side, however, mass transport deposits originate from the slope system in the northern side of the basin. Those deposits from different sedimentsupplies are composed of a multipleepisodic and multiple sedimentsupplied complex canyon system.
The Central Canyon in the Qiongdongnan basin shows a Sshaped NEtrending depositional system, which originates from the east margin of the Yinggehai basin, crosses the Central depression and extends into the Xisha trough. Based on the detailed interpretation of 2D and 3D seismic data and drillhole data, the Central Canyon can be divided into 4 segments. Each segment has not only different morphology in section, but also has distinct depositional architectures, genetic facies and sedimentsupplies. Analysis of morphology and infilling features indicates that the canyon shows the deeper downcutting and scours to the older strata eastwards. There are 4 types of V, U, W and composed shapes in vertical. Of them, Vtyped canyon shows the strongest downcutting, and the more significant scouring. Turbidite channel deposits are dominated in the western segment. Interbeds of turbidite channel and mass transport deposits occur in the eastern segment, but there are different ratios in different places. Turbidite channel deposits originate from the west side, however, mass transport deposits originate from the slope system in the northern side of the basin. Those deposits from different sedimentsupplies are composed of a multipleepisodic and multiple sedimentsupplied complex canyon system.
2012, 30(4): 654-660.
Abstract:
Based on the sedimentary and tectonic background of the north of Helan Mountains, the paper discussed the features of the provenance through comprehensive analysis of the conglomerate component and gravel features, paleocurrent direction, rare earth element, zircon dating and sedimentary trending. The conglomerate at the bottom of Upper Triassic mainly distributed in four different areas of Taerlin, Beisi, Shuimogou and Rujigou in Helan Mountain shows that the gravels were composed of quartzite, quartz sandstone, carbonate and granite. Paleocurrent data from various researchers reveal that the main current direction was northwest:wards which meant the river flowed from the northwest to the southeast in Triassic. And there was a successive paleocurrent direction throughout the Triassic. The result is also closely consistent to the paleocurrent in Shigouyi and Ciyaobao area in the west margin of Ordos Basin and they all indicate that there was a common provenance from the northwest. The rare earth element in sandstone can also give certain clues of the provenance. Nineteen samples were chosen to detect the quantity of rare elements from the Upper Triassic, PreCambrian and Cambrian to Middle Triassic. The paper also collects other rare element data of the gneiss and granulite of Helanshan Group in the northwest margin of Helan Mountain and of the granite formed during Hercynian to Indosinian period to the west of Helan Mountains. This pattern is almost the same as that in strata from Cambrian to MidTriassic and PreCambrian as well as the granite formed between Hercynian and Indosinian period, which supports that the provenance is from the corresponding rocks formed earlier than Late Triassic. The age peaks of the UPb dating of zircon show the provenance of Late Triassic is related to the metamorphic rock in Archean and Paleoproterozoic and also the magnetic rock during Hercynian and Indosinian period.Meanwhile, sedimentary environment analysis indicates that the gravels become smaller and sedimentary facies turns from alluvial fan, fluvial to lake from the west to the east of Helan Mountains. This proves that the Yinchuan Paleouplift did not appear in Late Triassic. Therefore the eastward provenance does not exist in Late Triassic of Helan Mountains.The paleocurrent data, heavy minerals and zircon UPb dating in Shigouyi area of the west of Ordos Basin suggest a similar provenance with Helan Mountains in direction and rock feature in Late Triassic. The fission track analysis shows that the uplift age of the whole Helan Mountains is later than Late Triassic. Two zircon fission track ages are 252Ma and 253Ma, older than the strata (MidJurassic and Late Triassic) from which they were chosen, which might propose that the provenance area had gone through the structure and thermal event and had been uplift in the late of Permian to supply major sedimentary source for Mesozoic.It is concluded that there is no east provenance and main northwest provenance in the north part of Helan Mountains. The provenance is predominant the metamorphic rocks (such as Helan Group and Alxa Group) and magmatic rocks from Alxa block and Xing'anling Mongolian Orogenic Belt in Archean and Paleoproterozoic. Several sedimentary and magmatic rocks rolled into the old orogenic belt partly provide the Late Triassic provenance. Meanwhile there are multiple provenances with various tectonic reformations and restoration of the model of the provenance evolution is significant to the evolution of the periphery orogenic belt and blocks.
Based on the sedimentary and tectonic background of the north of Helan Mountains, the paper discussed the features of the provenance through comprehensive analysis of the conglomerate component and gravel features, paleocurrent direction, rare earth element, zircon dating and sedimentary trending. The conglomerate at the bottom of Upper Triassic mainly distributed in four different areas of Taerlin, Beisi, Shuimogou and Rujigou in Helan Mountain shows that the gravels were composed of quartzite, quartz sandstone, carbonate and granite. Paleocurrent data from various researchers reveal that the main current direction was northwest:wards which meant the river flowed from the northwest to the southeast in Triassic. And there was a successive paleocurrent direction throughout the Triassic. The result is also closely consistent to the paleocurrent in Shigouyi and Ciyaobao area in the west margin of Ordos Basin and they all indicate that there was a common provenance from the northwest. The rare earth element in sandstone can also give certain clues of the provenance. Nineteen samples were chosen to detect the quantity of rare elements from the Upper Triassic, PreCambrian and Cambrian to Middle Triassic. The paper also collects other rare element data of the gneiss and granulite of Helanshan Group in the northwest margin of Helan Mountain and of the granite formed during Hercynian to Indosinian period to the west of Helan Mountains. This pattern is almost the same as that in strata from Cambrian to MidTriassic and PreCambrian as well as the granite formed between Hercynian and Indosinian period, which supports that the provenance is from the corresponding rocks formed earlier than Late Triassic. The age peaks of the UPb dating of zircon show the provenance of Late Triassic is related to the metamorphic rock in Archean and Paleoproterozoic and also the magnetic rock during Hercynian and Indosinian period.Meanwhile, sedimentary environment analysis indicates that the gravels become smaller and sedimentary facies turns from alluvial fan, fluvial to lake from the west to the east of Helan Mountains. This proves that the Yinchuan Paleouplift did not appear in Late Triassic. Therefore the eastward provenance does not exist in Late Triassic of Helan Mountains.The paleocurrent data, heavy minerals and zircon UPb dating in Shigouyi area of the west of Ordos Basin suggest a similar provenance with Helan Mountains in direction and rock feature in Late Triassic. The fission track analysis shows that the uplift age of the whole Helan Mountains is later than Late Triassic. Two zircon fission track ages are 252Ma and 253Ma, older than the strata (MidJurassic and Late Triassic) from which they were chosen, which might propose that the provenance area had gone through the structure and thermal event and had been uplift in the late of Permian to supply major sedimentary source for Mesozoic.It is concluded that there is no east provenance and main northwest provenance in the north part of Helan Mountains. The provenance is predominant the metamorphic rocks (such as Helan Group and Alxa Group) and magmatic rocks from Alxa block and Xing'anling Mongolian Orogenic Belt in Archean and Paleoproterozoic. Several sedimentary and magmatic rocks rolled into the old orogenic belt partly provide the Late Triassic provenance. Meanwhile there are multiple provenances with various tectonic reformations and restoration of the model of the provenance evolution is significant to the evolution of the periphery orogenic belt and blocks.
2012, 30(4): 661-671.
Abstract:
The field outcrops, especially the arraying direction of gravel and various bedding structures revealed by the outcrops, seismic data, core and heavy mineral data have been fully used to analyze the four key parameters that indicate the paleoprovenance direction, which include paleocurrent directions, structural features of seismic reflection, stability coefficient, differentiation characteristics of heavy mineral assemblage and the sedimentary characteristics of Jixi basin. Comprehensive studies show that the four parameters match well. There were mainly two provenances located in the west and southeast of the basin, respectively, in Chengzihe Formation. The west provenance was the main one, which provided sediments from the northwest, west and southwest to Jixi basin, and gradually headed east while divided into two branches at Hengshan uplift, entered the south and north part of the basin, respectively. After analyzing depositional system of heavy minerals and comparing the types of circumbasin parent rock, west provenance was thought to be primarily from the orogenic belt of XiaoxinganZhangguangcai Range. Progradation configuration in the seismic profiles pointed out that upon the southeast of the basin there existed another subordinate provenance with less influence, which was considered to be the secondary provenance. During the period of Muling Formation, the paleocurrent characteristics revealed that the main traits formed in Chengzihe Formation were mostly inherited, i.e. the basin still had two separate provenances, but the provenances relatively retreated, showing transgression from Chengzihe to Muling Formation, meanwhile, the range of the lake basin became larger. The southwest provenance had a bigger impact area compared with Chengzihe Formation. The features of heavy mineral assemblage reflected that the types of mother rock from the west part of the basin were consistent with orogenic belt of XiaoxinganZhangguangcai Range, which indicated that the west provenance mainly came from the aforementioned orogenic belt, while the mother rock types from southeast site were consistent with Yanji fold belt, illustrating that southeast provenance mainly came from it, gradually augmented its influence on development of Jixi basin from Chengzihe Formation to Muling Formation.
The field outcrops, especially the arraying direction of gravel and various bedding structures revealed by the outcrops, seismic data, core and heavy mineral data have been fully used to analyze the four key parameters that indicate the paleoprovenance direction, which include paleocurrent directions, structural features of seismic reflection, stability coefficient, differentiation characteristics of heavy mineral assemblage and the sedimentary characteristics of Jixi basin. Comprehensive studies show that the four parameters match well. There were mainly two provenances located in the west and southeast of the basin, respectively, in Chengzihe Formation. The west provenance was the main one, which provided sediments from the northwest, west and southwest to Jixi basin, and gradually headed east while divided into two branches at Hengshan uplift, entered the south and north part of the basin, respectively. After analyzing depositional system of heavy minerals and comparing the types of circumbasin parent rock, west provenance was thought to be primarily from the orogenic belt of XiaoxinganZhangguangcai Range. Progradation configuration in the seismic profiles pointed out that upon the southeast of the basin there existed another subordinate provenance with less influence, which was considered to be the secondary provenance. During the period of Muling Formation, the paleocurrent characteristics revealed that the main traits formed in Chengzihe Formation were mostly inherited, i.e. the basin still had two separate provenances, but the provenances relatively retreated, showing transgression from Chengzihe to Muling Formation, meanwhile, the range of the lake basin became larger. The southwest provenance had a bigger impact area compared with Chengzihe Formation. The features of heavy mineral assemblage reflected that the types of mother rock from the west part of the basin were consistent with orogenic belt of XiaoxinganZhangguangcai Range, which indicated that the west provenance mainly came from the aforementioned orogenic belt, while the mother rock types from southeast site were consistent with Yanji fold belt, illustrating that southeast provenance mainly came from it, gradually augmented its influence on development of Jixi basin from Chengzihe Formation to Muling Formation.
2012, 30(4): 672-678.
Abstract:
The Rare Earth Element study of sediments in the Baiyun deepwater area of the northern South China Sea shows three chondritenormalized REE distribution characteristics in different parts of the deepwater area from Oligocene to Miocene, indicating that different provenances may dominate the deepwater area. From the Oligocene to the Miocene, the sediments of the northern Baiyun deepwater area came from the paleoPearl River, featuring relative LREE (light rare earth element) enrichment, even content of HREE (heavy rare earth element) and negative Euanomalies, just like the chondritenormalized REE pattern of PAAS (postArchean average Australian shale). This REE characteristic suggested a parent rock type of sedimentary rocks or acid rocks or both. The sediments of the southern part of Baiyun deepwater area showed reduced divergence between LREE and HREE with obvious positive Euanomalies, suggesting a supply of basic materials. Well B6 located on a volcanic island in the central part of the Baiyun deepwater area. The Oligocene sediments of Well B6 contained a large amount of intermediate to basic volcanic materials, featuring positive Euanomalies. But the chrondritenormalized REE distribution pattern of the sediments of Well B6 became similar to the REE distribution pattern of the sediments in the north in early Miocene. The sediments of the eastern part of the deepwater area featured no Euanomalies or positive Euanomalies, indicating that this area was influenced by the volcanic activities on the Dongsha Rise. Negative Euanomalies didn't occur around this area until 18.5 Ma. The sediments from the northern deepwater area to the location area of W3 was dominated by the paleoPearl River from the Oligocene to Miocene. The southern part of the deepwater area was influenced by the basic volcanic materials continuously, and the volcanic activities still happened in the midMiocene, much less frequently though. The sediments in the eastern deepwater area mainly came from the Dongsha Rise from the Oligocene to the early Miocene (32~18.5 Ma) and contained plenty of intermediate to basic volcanic materials, with no Euanomaly or positive Euanomalies. The volcanic activities on the Dongsha Rise stopped after 18.5 Ma. Biocarbonatite and carbonatite terrains began to occur while the supply of terrigenous debris to the eastern part of Baiyun deepwater area was cut off. Ever since the midMiocene (16.510.5Ma), as the tectonic activities in the northern South China Sea weakened, the provenance was simplified and the deepwater area was totally controlled by the Pearl River and its delta. The Baiyun movement at the end of the Oligocene and the beginning of the Neogene, greatly influenced the sediment composition in the Baiyun deepwater area. Abrupt composition changes of the sediments occurred at this boundary, indicating that the paleoPearl River experienced headwater erosion and drainage expansion, causing the changes of parent rock types. The REE content of the sediments of the Pearl River dominating area also showed abrupt changes. Moreover, this suggested that from the late Oligocene to the early Miocene, volcanic activities increased in the eastern, western, and southern parts of the deepwater area in the northern South China Sea. The fierce tectonic activities there lead to an obviously increased content of intermediate and basic volcanic materials in the sediments. Well W3, W4 and W9 located in the southern deepwater area and were near each other, however, the composition of their sediments had great differences. The source of Well W3 stayed stable from the late Oligocene to the Miocene, and this area was dominated by the paleoPearl River delta. During the period of the Baiyun movement at 23.8Ma, Well W3 accepted an instant influence of basic volcanic activities. The basic source of Well W4 and Well W9 played an important role from the Oligocene to the early Miocene, indicating a great influence of the basic volcanic rocks on the South Rise, which did not start weakening until the midMiocene.
The Rare Earth Element study of sediments in the Baiyun deepwater area of the northern South China Sea shows three chondritenormalized REE distribution characteristics in different parts of the deepwater area from Oligocene to Miocene, indicating that different provenances may dominate the deepwater area. From the Oligocene to the Miocene, the sediments of the northern Baiyun deepwater area came from the paleoPearl River, featuring relative LREE (light rare earth element) enrichment, even content of HREE (heavy rare earth element) and negative Euanomalies, just like the chondritenormalized REE pattern of PAAS (postArchean average Australian shale). This REE characteristic suggested a parent rock type of sedimentary rocks or acid rocks or both. The sediments of the southern part of Baiyun deepwater area showed reduced divergence between LREE and HREE with obvious positive Euanomalies, suggesting a supply of basic materials. Well B6 located on a volcanic island in the central part of the Baiyun deepwater area. The Oligocene sediments of Well B6 contained a large amount of intermediate to basic volcanic materials, featuring positive Euanomalies. But the chrondritenormalized REE distribution pattern of the sediments of Well B6 became similar to the REE distribution pattern of the sediments in the north in early Miocene. The sediments of the eastern part of the deepwater area featured no Euanomalies or positive Euanomalies, indicating that this area was influenced by the volcanic activities on the Dongsha Rise. Negative Euanomalies didn't occur around this area until 18.5 Ma. The sediments from the northern deepwater area to the location area of W3 was dominated by the paleoPearl River from the Oligocene to Miocene. The southern part of the deepwater area was influenced by the basic volcanic materials continuously, and the volcanic activities still happened in the midMiocene, much less frequently though. The sediments in the eastern deepwater area mainly came from the Dongsha Rise from the Oligocene to the early Miocene (32~18.5 Ma) and contained plenty of intermediate to basic volcanic materials, with no Euanomaly or positive Euanomalies. The volcanic activities on the Dongsha Rise stopped after 18.5 Ma. Biocarbonatite and carbonatite terrains began to occur while the supply of terrigenous debris to the eastern part of Baiyun deepwater area was cut off. Ever since the midMiocene (16.510.5Ma), as the tectonic activities in the northern South China Sea weakened, the provenance was simplified and the deepwater area was totally controlled by the Pearl River and its delta. The Baiyun movement at the end of the Oligocene and the beginning of the Neogene, greatly influenced the sediment composition in the Baiyun deepwater area. Abrupt composition changes of the sediments occurred at this boundary, indicating that the paleoPearl River experienced headwater erosion and drainage expansion, causing the changes of parent rock types. The REE content of the sediments of the Pearl River dominating area also showed abrupt changes. Moreover, this suggested that from the late Oligocene to the early Miocene, volcanic activities increased in the eastern, western, and southern parts of the deepwater area in the northern South China Sea. The fierce tectonic activities there lead to an obviously increased content of intermediate and basic volcanic materials in the sediments. Well W3, W4 and W9 located in the southern deepwater area and were near each other, however, the composition of their sediments had great differences. The source of Well W3 stayed stable from the late Oligocene to the Miocene, and this area was dominated by the paleoPearl River delta. During the period of the Baiyun movement at 23.8Ma, Well W3 accepted an instant influence of basic volcanic activities. The basic source of Well W4 and Well W9 played an important role from the Oligocene to the early Miocene, indicating a great influence of the basic volcanic rocks on the South Rise, which did not start weakening until the midMiocene.
2012, 30(4): 679-688.
Abstract:
The Moyang section located in the southern margin of the Great Bank of Guizhou developed typical deposits of shallowmarine environments in the Late Permian, including Changhsingian reefs, disconformity surfaces near the mass extinction horizon，and one probably kind of palaeokarst sediments. Calcareous algalsponge boundstone characterized by Archaeolithoporella, Tubiphytes and winded sponges, and early marine cements constitute the frameworks in the upper of the Changxing Formation. Disconformity surfaces (with the contacts between the lower and upper facies stylolitized or eroded) make a distinction between the latest Permian oolitic limestone and the Changhsingian skeletal packstonegrainstone containing the dominated fusulinids, sphinctozoan sponges, Tubiphytes and other types of calcareous algae. In some outcrops, one special kind of breccias found in the upper part of the Changxing Formation, which overlain or incised by giantooidbearing oolite directly in the topmost, comprises numerous clasts of bioclastic limestone, lime mudstone and silicate, with diverse and angular shapes. In addition, the presence of collapse structures and white cement layers consisting of coarse sparry calcite indicate the possible karstification. Based upon these features, we suggest the fall in relative sealevel of Moyang caused the subaerial exposure of the top of the Changhsingian complex in the latest Permian. Under meteoric vadose diagenesis, karstic processes formed collapse breccia, fissures, solution vugs and speleothem carbonate in the ridgy topography (with persisting growth of the bioreef). In contrast, erosional surfaces developing in nonridgy topography probably formed by the process of weathering, and reworking in ensuing rise of sealevel. Not like other sections growing microbialites after the event horizon, the Moyang section developed oolitic limestones bearing oncoids and giant ooids at that moment. This phenomenon implies an unusual phenomenon developing oolite facies overlying top of the Changhsingian bioclastic grainstone directly, and hence, has the significance of helping us understand the origin of the mass extinction and temporal oceanic conditions.
The Moyang section located in the southern margin of the Great Bank of Guizhou developed typical deposits of shallowmarine environments in the Late Permian, including Changhsingian reefs, disconformity surfaces near the mass extinction horizon，and one probably kind of palaeokarst sediments. Calcareous algalsponge boundstone characterized by Archaeolithoporella, Tubiphytes and winded sponges, and early marine cements constitute the frameworks in the upper of the Changxing Formation. Disconformity surfaces (with the contacts between the lower and upper facies stylolitized or eroded) make a distinction between the latest Permian oolitic limestone and the Changhsingian skeletal packstonegrainstone containing the dominated fusulinids, sphinctozoan sponges, Tubiphytes and other types of calcareous algae. In some outcrops, one special kind of breccias found in the upper part of the Changxing Formation, which overlain or incised by giantooidbearing oolite directly in the topmost, comprises numerous clasts of bioclastic limestone, lime mudstone and silicate, with diverse and angular shapes. In addition, the presence of collapse structures and white cement layers consisting of coarse sparry calcite indicate the possible karstification. Based upon these features, we suggest the fall in relative sealevel of Moyang caused the subaerial exposure of the top of the Changhsingian complex in the latest Permian. Under meteoric vadose diagenesis, karstic processes formed collapse breccia, fissures, solution vugs and speleothem carbonate in the ridgy topography (with persisting growth of the bioreef). In contrast, erosional surfaces developing in nonridgy topography probably formed by the process of weathering, and reworking in ensuing rise of sealevel. Not like other sections growing microbialites after the event horizon, the Moyang section developed oolitic limestones bearing oncoids and giant ooids at that moment. This phenomenon implies an unusual phenomenon developing oolite facies overlying top of the Changhsingian bioclastic grainstone directly, and hence, has the significance of helping us understand the origin of the mass extinction and temporal oceanic conditions.
2012, 30(4): 689-695.
Abstract:
The Yixian stage standard section crops along MashenmiaoDaobadiSanbailong Jingangshan area strikingly from the west to the east in Yixian basin, they are upwardly Mashenmiao layer, Laogonggou layer, Yenangou layer, Zhuanchengzi layer, Dakangpu layer, Zhujiagou layer and Jingangshan layer. As the upper part of Yixian formation, Jingangshan layer is a set of lacustrine deposit in Zaocishan area. Based on sedimentary petrology and stratigraphic studies, these sedimentary strata could be divided into lake margin clastic turbidity facies, shallow water flat facies and semideep lake facies (in ascending order).The turbidity facies consists of three coarsefine grading sedimentary rhythms. The coarse petrologic units are mottled, greygreen feldspar and lithic tuffaceous glutenite and greywhite gravel bearing tuff; the fine units are made of greywhite gravel bearing tuff, greygreen compact tuff, purified bentonite and slightly bentonitic siltstone. The coarse turbidity facies is product of the head of turbidity current, distribution normal grading usually develops in this petrology unit. As the result of the body and tail parts of turbidity current, the finer turbidity facies present themselves with horizontal bedding. In the middle part of Jingangshan layer, the shallow water flat facies is composed of five bentonitic siltstone (purified bentonite and /or shale ) marl rhythms. In lake flat facies, the thickness ratios of carbonate deposit and underlying volcanic clastic deposit range from 0.11 to 0.47, it indicates that lacustrine margin experiences five stages of equal interval lake flat sedimentation.The upper part of Jingangshan layer is the association of pale papersheeted shale and silty shale. The coarser petrologic unites of lake margin clastic facies in lower part of Jingangshan layer indicate that they are proximal deposite, the finer unites show the polycylic volcanism during the forming process of lake margin clastic facies. The five bentonitic siltstone marl sedimentary rhythms of middle part lake flat facies may indicate the lake water level survived at least five shoaling changes. Under the regional arid climate, the marl deposit was formed in the lake flat facies. And the deeper area of central lake basin may receive a great volume of suspensive finegrained materials to form the hydrostatic deposits of semideep lake facies.
The Yixian stage standard section crops along MashenmiaoDaobadiSanbailong Jingangshan area strikingly from the west to the east in Yixian basin, they are upwardly Mashenmiao layer, Laogonggou layer, Yenangou layer, Zhuanchengzi layer, Dakangpu layer, Zhujiagou layer and Jingangshan layer. As the upper part of Yixian formation, Jingangshan layer is a set of lacustrine deposit in Zaocishan area. Based on sedimentary petrology and stratigraphic studies, these sedimentary strata could be divided into lake margin clastic turbidity facies, shallow water flat facies and semideep lake facies (in ascending order).The turbidity facies consists of three coarsefine grading sedimentary rhythms. The coarse petrologic units are mottled, greygreen feldspar and lithic tuffaceous glutenite and greywhite gravel bearing tuff; the fine units are made of greywhite gravel bearing tuff, greygreen compact tuff, purified bentonite and slightly bentonitic siltstone. The coarse turbidity facies is product of the head of turbidity current, distribution normal grading usually develops in this petrology unit. As the result of the body and tail parts of turbidity current, the finer turbidity facies present themselves with horizontal bedding. In the middle part of Jingangshan layer, the shallow water flat facies is composed of five bentonitic siltstone (purified bentonite and /or shale ) marl rhythms. In lake flat facies, the thickness ratios of carbonate deposit and underlying volcanic clastic deposit range from 0.11 to 0.47, it indicates that lacustrine margin experiences five stages of equal interval lake flat sedimentation.The upper part of Jingangshan layer is the association of pale papersheeted shale and silty shale. The coarser petrologic unites of lake margin clastic facies in lower part of Jingangshan layer indicate that they are proximal deposite, the finer unites show the polycylic volcanism during the forming process of lake margin clastic facies. The five bentonitic siltstone marl sedimentary rhythms of middle part lake flat facies may indicate the lake water level survived at least five shoaling changes. Under the regional arid climate, the marl deposit was formed in the lake flat facies. And the deeper area of central lake basin may receive a great volume of suspensive finegrained materials to form the hydrostatic deposits of semideep lake facies.
2012, 30(4): 696-705.
Abstract:
LishuiJiaojiang Sag is the representative offshore superimposed riftsubsidence basin of China. Integrated study of well core, seismic, drilling, and logging shows that there are five sedimentary systems of the Paleocene in LishuiJiaojiang Sag: fan delta system, delta system, lake system, system and gravity flow system. The distribution patterns of the depositional systems in space are analyzed as that there was lacustrine environment in the Yueguifeng Formation, and then, strong rifting proceeded, the basin underwent a largescale transgression, sedimentary environment changed into marine environment, delta system developed in the west gentle slope which was provided by the Minzhe uplift, fan delta system developed in the east steep hill which was controlled by synsedimentary faults. Lingfeng buried hill was out of water surface in the Yueguifeng ang Lingfeng Formation, there deposited several fan delta systems and nearshore subaqueous fan systems in its both sides. Based on the research, two favorable areas are proposed as fan delta (nearshore subaqueous fan) and littoralshallow sea (lake) sand body on both sides of the Lingfeng buried hill, delta front and slumping gravity flow sand body matching fault block favorable structure in the south of the western slope of West Subsag of Lishui Sag.
LishuiJiaojiang Sag is the representative offshore superimposed riftsubsidence basin of China. Integrated study of well core, seismic, drilling, and logging shows that there are five sedimentary systems of the Paleocene in LishuiJiaojiang Sag: fan delta system, delta system, lake system, system and gravity flow system. The distribution patterns of the depositional systems in space are analyzed as that there was lacustrine environment in the Yueguifeng Formation, and then, strong rifting proceeded, the basin underwent a largescale transgression, sedimentary environment changed into marine environment, delta system developed in the west gentle slope which was provided by the Minzhe uplift, fan delta system developed in the east steep hill which was controlled by synsedimentary faults. Lingfeng buried hill was out of water surface in the Yueguifeng ang Lingfeng Formation, there deposited several fan delta systems and nearshore subaqueous fan systems in its both sides. Based on the research, two favorable areas are proposed as fan delta (nearshore subaqueous fan) and littoralshallow sea (lake) sand body on both sides of the Lingfeng buried hill, delta front and slumping gravity flow sand body matching fault block favorable structure in the south of the western slope of West Subsag of Lishui Sag.
2012, 30(4): 706-715.
Abstract:
It is the most important area of exploration in the southern Fuxin uplift of Songliao Basin in recent years, and its major oil producing zone is Fuyu oil layer in the 4th Member, Quantou Formation. Currently, it is still large differences on depositional system and sedimentary facies and depositional characteristics in understanding of Fuyu oil layer, and understanding of the differences restricted the pace of exploration and development of oil and gas. Therefore, it is urgently needed to study on depositional characteristics and model. It can be the next steps for this area to provide the basis for exploration and development of oil and gas.Based on 18 well cores , 1595 heavy mineral data and logging data of nearly 800 well, depositional characteristics and models of Fuyu oil layer in the southern Fuxin uplift was analyzed. It is realized that the southern Fuxin uplift is a intersections area of the two sources, the southwest Baokang and the southeast ChangchunHaide in the period of Fuyu oil layer. Ⅰarea and Ⅲ area are controlled by the southwest Baokang Sources. Ⅱarea and Ⅳ area are mainly controlled by the two sources, the southwest Baokang and the southeast ChangchunHaide. Branched highenergy shallow lacustrine fluvialdominated delta of Fuyu oil layer in the southern Fuxin uplift are mainly controlled by the two sources, the southwest Baokang and the southeast ChangchunHaide. As SSW distribution submerged distributary channel sandbodies as sand body framework of this delta system is abundant, closely and narrow. It is continual than original understanding and it extends to the far underwater, until disappearing into thin sheet sands. And many fluvialdominated bandings are formed. Based on understanding of sedimentary background and depositional characteristics and sedimentary facies types of Fuyu oil layer in the southern Fuxin uplift, depositional model of "double source" shallow lacustrine fluvialdominated delta is established: (1) Continental restrictive distributary channel is the center of the delta distributary plain subfacies. and fluvialdominated banding is formed, which is planar sedimentary microfacies sequences of distributary channel→levees→crevasse splay, overbank sand→interdistributary estuary. (2) Underwater distributary channels are main in the delta front. and fluvialdominated banding is formed, which is planar sedimentary microfacies sequences of underwater distributary channel→sheet sand→inner margin of sheet sand→outer margin of sheet sand→underwater interdistributary. (3) It is no significant demarcation between delta front and predelta. tidedominated sheet sand was formed in the shallow lacustrine fluvialdominated delta outer front, which is mainly controlled by wave in lakes. Multiple sheet sands show parallel venation of vertical sources. Single sheet sand is banding and ringlike planar distributing model of sheet sand→inner margin of sheet sand→outer margin of sheet sand→underwater interdistributary from central to around.
It is the most important area of exploration in the southern Fuxin uplift of Songliao Basin in recent years, and its major oil producing zone is Fuyu oil layer in the 4th Member, Quantou Formation. Currently, it is still large differences on depositional system and sedimentary facies and depositional characteristics in understanding of Fuyu oil layer, and understanding of the differences restricted the pace of exploration and development of oil and gas. Therefore, it is urgently needed to study on depositional characteristics and model. It can be the next steps for this area to provide the basis for exploration and development of oil and gas.Based on 18 well cores , 1595 heavy mineral data and logging data of nearly 800 well, depositional characteristics and models of Fuyu oil layer in the southern Fuxin uplift was analyzed. It is realized that the southern Fuxin uplift is a intersections area of the two sources, the southwest Baokang and the southeast ChangchunHaide in the period of Fuyu oil layer. Ⅰarea and Ⅲ area are controlled by the southwest Baokang Sources. Ⅱarea and Ⅳ area are mainly controlled by the two sources, the southwest Baokang and the southeast ChangchunHaide. Branched highenergy shallow lacustrine fluvialdominated delta of Fuyu oil layer in the southern Fuxin uplift are mainly controlled by the two sources, the southwest Baokang and the southeast ChangchunHaide. As SSW distribution submerged distributary channel sandbodies as sand body framework of this delta system is abundant, closely and narrow. It is continual than original understanding and it extends to the far underwater, until disappearing into thin sheet sands. And many fluvialdominated bandings are formed. Based on understanding of sedimentary background and depositional characteristics and sedimentary facies types of Fuyu oil layer in the southern Fuxin uplift, depositional model of "double source" shallow lacustrine fluvialdominated delta is established: (1) Continental restrictive distributary channel is the center of the delta distributary plain subfacies. and fluvialdominated banding is formed, which is planar sedimentary microfacies sequences of distributary channel→levees→crevasse splay, overbank sand→interdistributary estuary. (2) Underwater distributary channels are main in the delta front. and fluvialdominated banding is formed, which is planar sedimentary microfacies sequences of underwater distributary channel→sheet sand→inner margin of sheet sand→outer margin of sheet sand→underwater interdistributary. (3) It is no significant demarcation between delta front and predelta. tidedominated sheet sand was formed in the shallow lacustrine fluvialdominated delta outer front, which is mainly controlled by wave in lakes. Multiple sheet sands show parallel venation of vertical sources. Single sheet sand is banding and ringlike planar distributing model of sheet sand→inner margin of sheet sand→outer margin of sheet sand→underwater interdistributary from central to around.
2012, 30(4): 716-723.
Abstract:
Laser method analysis and sieving method analysis,as two of the most common methods used in granularity analysis of sedimentary geology,data conversion and rectification among them is a constantly encountered and inevitable question when doing data comparison and connection. This paper designed two experiments for this.The first experiment contrasted analysis results of the two analysis method of narrow granularity range samples, made statistics on the larger amplitude of sieving to laser method,and puts forward a correction method.The second experiment analysed samples of different psephicity,studied correlativity of psephicity and the diffenrence degree between the two analysis methods,regard the rectify method proposed by the first experiment is suitable for granularity analysis and rectify of natural sediments in general conditions. The article illustrated the rectify result of the proposed calibration method and discussed the problems exsiting in the method of laser granularity. When the laser granularity method used in natural sediment granularity analysis, resultly obvious graduation,normalize,petronas merger phenomenon,distorted real granularity distribution are commonnly seen. The paper argued that the specific conditions of actual samples are far more complex than the set conditions of Mie theory,sample parameters with condition not brining into the calculation process,so granularity solution of laser method is not accurate.Better data rectification method need the software and hardware improvements of laser particle analyzer.There are still some questions need to be discussed of the laser method used in granularity analysis of natural sediments.
Laser method analysis and sieving method analysis,as two of the most common methods used in granularity analysis of sedimentary geology,data conversion and rectification among them is a constantly encountered and inevitable question when doing data comparison and connection. This paper designed two experiments for this.The first experiment contrasted analysis results of the two analysis method of narrow granularity range samples, made statistics on the larger amplitude of sieving to laser method,and puts forward a correction method.The second experiment analysed samples of different psephicity,studied correlativity of psephicity and the diffenrence degree between the two analysis methods,regard the rectify method proposed by the first experiment is suitable for granularity analysis and rectify of natural sediments in general conditions. The article illustrated the rectify result of the proposed calibration method and discussed the problems exsiting in the method of laser granularity. When the laser granularity method used in natural sediment granularity analysis, resultly obvious graduation,normalize,petronas merger phenomenon,distorted real granularity distribution are commonnly seen. The paper argued that the specific conditions of actual samples are far more complex than the set conditions of Mie theory,sample parameters with condition not brining into the calculation process,so granularity solution of laser method is not accurate.Better data rectification method need the software and hardware improvements of laser particle analyzer.There are still some questions need to be discussed of the laser method used in granularity analysis of natural sediments.
2012, 30(4): 724-730.
Abstract:
Taking a typical coastal Aeolian transverse ridge at Changli Gold Coast in Hebei province as an example, which is one of the most typical coastal aeolian distribution regions in China and famous for the tall and typical coastal transverse ridges, the distribution characteristics of 21 kinds of geochemical element in the modern aeolian sands on the surface of coastal aeolian dune(coastal Aeolian transverse ridge)are analysed. The research results show, in 21 geochemical elements which are contained in the modern aeolian sands on the surface of coastal aeolian transverse ridge, the differentiations of three geochemical elements at different sites over the surface of coastal dune are obvious, which are Co and Zr as well as Mg. The differentiations at different sites over coastal dune surface of Cr, Pb, Ti, Nb, As, Mn, Zn and Ba, are moderate,but the differentiations of some geochemical elements are slight, such as Y, Ca Fe, Na, Al, Sr, P, K, Rb and Si. The change features of geochemical elements in the modern aeolian sands at different sites, such as windward slope base, windward slope, dune crest, leeward slope and leeward slope base, on the surface of coastal aeolian transverse ridge are different, which could be concluded into different change models. The features and models of differentiation of geochemical elements at different sites over the surface of coastal aeolian transverse ridge are mainly controlled by the depositional environment, chemical characteristics of geochemical elements as well as grainsize of aeolian sands and so on. For examples, the geochemical elements such as Y, Ca Fe, Na, Al, Sr, P, K, Rb and Si, their differentiation features are mailly affected by depositional environment, but the differentiation of some microelements, such as Cr and Co, is mailly controlled by grain size of sands and the wind force. Based on the conclusions above, because there are clear differentiations of some geochemical elements such as some microelements at different sites over the surface of coastal aeolian transverse ridge, it should be very modest to use the change of microelements in different stratum profiles to deduce the change of coastal environment or climate by use of traditional environment analysis ways as usual.
Taking a typical coastal Aeolian transverse ridge at Changli Gold Coast in Hebei province as an example, which is one of the most typical coastal aeolian distribution regions in China and famous for the tall and typical coastal transverse ridges, the distribution characteristics of 21 kinds of geochemical element in the modern aeolian sands on the surface of coastal aeolian dune(coastal Aeolian transverse ridge)are analysed. The research results show, in 21 geochemical elements which are contained in the modern aeolian sands on the surface of coastal aeolian transverse ridge, the differentiations of three geochemical elements at different sites over the surface of coastal dune are obvious, which are Co and Zr as well as Mg. The differentiations at different sites over coastal dune surface of Cr, Pb, Ti, Nb, As, Mn, Zn and Ba, are moderate,but the differentiations of some geochemical elements are slight, such as Y, Ca Fe, Na, Al, Sr, P, K, Rb and Si. The change features of geochemical elements in the modern aeolian sands at different sites, such as windward slope base, windward slope, dune crest, leeward slope and leeward slope base, on the surface of coastal aeolian transverse ridge are different, which could be concluded into different change models. The features and models of differentiation of geochemical elements at different sites over the surface of coastal aeolian transverse ridge are mainly controlled by the depositional environment, chemical characteristics of geochemical elements as well as grainsize of aeolian sands and so on. For examples, the geochemical elements such as Y, Ca Fe, Na, Al, Sr, P, K, Rb and Si, their differentiation features are mailly affected by depositional environment, but the differentiation of some microelements, such as Cr and Co, is mailly controlled by grain size of sands and the wind force. Based on the conclusions above, because there are clear differentiations of some geochemical elements such as some microelements at different sites over the surface of coastal aeolian transverse ridge, it should be very modest to use the change of microelements in different stratum profiles to deduce the change of coastal environment or climate by use of traditional environment analysis ways as usual.
2012, 30(4): 731-738.
Abstract:
Climate change in the north margin of the East Monsoon area is sensitive to the intensity of summer monsoon, so this zone is a key region of the past climate research, where changes of the water levels of the closed lakes and areas of lakes are the important indicators of climate change. Lake sediments are valuable archives of past climates providing a detailed regionally climatic record of variations. Previous results for Holocene climate change show some discrepancies. Some researchers reported that there was a cold and dry climate state with low lake level stands during the Early Holocene(11.0~8.0 kaBP), and the climate in the Mid Holocene(8.0~5.0 kaBP), however, was warm and wet (Holocene Optimum) with high lake level stands. But, in recent years, new developed records indicate a mid Holocene drought existed in the East Asian monsoon marginal area. This paper presents a new record from Huangqihai Lake to address the pattern of Holocene climate change. Huangqihai Lake (40°41′41°43′N, 112°49′113°40′E), a closedbasin lake in Inner Mongolia of China, lies at the northern limit of the East Asian summer monsoon and in the central part of Asian Winter Monsoon. Thus, its lacustrine sediment sensitively recorded the changes of the monsoon system. The catchment basin consists of metamorphic pyrogenic rock, Tertiary basalt and Quaternary clastic sediments. Multilevel sand ridges and lacustrine sediment were exposed in the present lake shore plain, which are ideal materials of recording lake evolution. Section H6 (N40°50′11″, E113°23′8″) at the front margin of the first lake terrace of Huangqihai Lake was exposed due to the stream downcut of the Bataigou River.The sedimentary stratigraphy were composed of lacustrine and fluvial deposits. Based on OSL chronology, the grain size data and the elements analysis ,we concluded that Huangqihai Lake maintained a high lake level state during early and middle Holocene(ca.11.4±1.1～6.7±0.7kaBP). This high lake level period can be divided into three phases as follows. At the first phase(11.4±1.1～9.3±0.9 kaBP) , proportions of clay and silt show a gradually increase dominated by the silt fraction, contrary to the sand fraction, and high contents of chemistry elements; which indicate that the lake experienced the high lake level and wet climate was in favor of chemical weathering activity at that time. At the second phase(9.3±0.9～7.7±0.7kaBP) , the proportions of silt and clay began to decrease and the sand fraction was increasing. The lake salinity had been rising and the contents of chemistry elements had been falling. these showed that the lake level began to decline, and the climate became drying, and the chemical weathering appeared weakenning for a dry climate state. At the third phase(7.7±0.7kaBP～6.7±0.7kaBP) , corresponding to the end period of Maximum lake level, the dramatically fluctuation of proxies shown the characteristics of largely oscillation. Meanwhile, preliminary studies about element ratio of Mn/Li suggested that this ratio could be regarded as a proxy of chemical weathering in catchment.
Climate change in the north margin of the East Monsoon area is sensitive to the intensity of summer monsoon, so this zone is a key region of the past climate research, where changes of the water levels of the closed lakes and areas of lakes are the important indicators of climate change. Lake sediments are valuable archives of past climates providing a detailed regionally climatic record of variations. Previous results for Holocene climate change show some discrepancies. Some researchers reported that there was a cold and dry climate state with low lake level stands during the Early Holocene(11.0~8.0 kaBP), and the climate in the Mid Holocene(8.0~5.0 kaBP), however, was warm and wet (Holocene Optimum) with high lake level stands. But, in recent years, new developed records indicate a mid Holocene drought existed in the East Asian monsoon marginal area. This paper presents a new record from Huangqihai Lake to address the pattern of Holocene climate change. Huangqihai Lake (40°41′41°43′N, 112°49′113°40′E), a closedbasin lake in Inner Mongolia of China, lies at the northern limit of the East Asian summer monsoon and in the central part of Asian Winter Monsoon. Thus, its lacustrine sediment sensitively recorded the changes of the monsoon system. The catchment basin consists of metamorphic pyrogenic rock, Tertiary basalt and Quaternary clastic sediments. Multilevel sand ridges and lacustrine sediment were exposed in the present lake shore plain, which are ideal materials of recording lake evolution. Section H6 (N40°50′11″, E113°23′8″) at the front margin of the first lake terrace of Huangqihai Lake was exposed due to the stream downcut of the Bataigou River.The sedimentary stratigraphy were composed of lacustrine and fluvial deposits. Based on OSL chronology, the grain size data and the elements analysis ,we concluded that Huangqihai Lake maintained a high lake level state during early and middle Holocene(ca.11.4±1.1～6.7±0.7kaBP). This high lake level period can be divided into three phases as follows. At the first phase(11.4±1.1～9.3±0.9 kaBP) , proportions of clay and silt show a gradually increase dominated by the silt fraction, contrary to the sand fraction, and high contents of chemistry elements; which indicate that the lake experienced the high lake level and wet climate was in favor of chemical weathering activity at that time. At the second phase(9.3±0.9～7.7±0.7kaBP) , the proportions of silt and clay began to decrease and the sand fraction was increasing. The lake salinity had been rising and the contents of chemistry elements had been falling. these showed that the lake level began to decline, and the climate became drying, and the chemical weathering appeared weakenning for a dry climate state. At the third phase(7.7±0.7kaBP～6.7±0.7kaBP) , corresponding to the end period of Maximum lake level, the dramatically fluctuation of proxies shown the characteristics of largely oscillation. Meanwhile, preliminary studies about element ratio of Mn/Li suggested that this ratio could be regarded as a proxy of chemical weathering in catchment.
2012, 30(4): 739-746.
Abstract:
The main reason for bad potential evaluation of Liaoxi depression is that hydrocarbon generation of Es3 and Es4 cannot be recognized, which is the principal issue of hydrocarbon exploration in Liaoxi depression. Based on source control theory and sedimentary faces study, analyzed geochemistry characteristics, through basin modeling and oil source research, we evaluated Shahejie Fm. source rock comprehensively. Based on a great quantity of seismic and well material, we identified fan delta faces coastal shallowlake faces middledeep lake faces of Shahejie Fm. in Liaoxi depression, especially middle deep lake face of Es4. Source supply is sufficient in lower segment of Es3 and the size of middledeep lake is very small, its area of southern sag is largest, smaller in middle sag and least in northern sag. Source supply becomes smaller in middle segment of Es3 and the size of middledeep lake is very big that mainly locates in middle sag. The area of southern sag is larger and smaller in northern sag. Mud. stone of middledeep lake face is the precondition of forming source rock. Through 33 oil samples and 48 rock samples analysis of Liaoxi depression, we concluded that content of sapropelic and exinite of organic material is commonly higher and rich of planktonic algae in Shahejie Fm. source rock. Its kerogen type is ⅠⅡ. Basin modeling concluded that hydrocarbon generating threshold is 2 500 m, Es3 source rock below this depth and Es1 source rock is upper this depth. After oilsource correlation research, we considered that oil geochemistry characteristics are similar with source rock geochemistry of Es3 and Es4 in Liaoxi depression. Hence, Es3 and Es4 source rock is the most important oil source in Liaoxi depression. With organic faces and sedimentary faces researching, organic material of Es source rock is entirely rich. But there are some differences of these sags in Liaoxi depression. Geochemical indexes of northern sag of Liaoxi depression are higher, subordinate of middle sag, lower of southern sag. From distributions of middledeep lake face, the author identified small scale of middledeep lake face of Es3 is developed in northern sag of Liaoxi depression, large scale of middledeep lake face of Es3 and Es4 are developed in middle sag of Liaoxi depression, and large scale of middledeep lake face of Es3 is developed in southern sag of Liaoxi depression. Middle sag of Liaoxi depression has a large potentiality of hydrocarbon generation, smaller in southern sag and least in northern sag based on comprehensive analysis.
The main reason for bad potential evaluation of Liaoxi depression is that hydrocarbon generation of Es3 and Es4 cannot be recognized, which is the principal issue of hydrocarbon exploration in Liaoxi depression. Based on source control theory and sedimentary faces study, analyzed geochemistry characteristics, through basin modeling and oil source research, we evaluated Shahejie Fm. source rock comprehensively. Based on a great quantity of seismic and well material, we identified fan delta faces coastal shallowlake faces middledeep lake faces of Shahejie Fm. in Liaoxi depression, especially middle deep lake face of Es4. Source supply is sufficient in lower segment of Es3 and the size of middledeep lake is very small, its area of southern sag is largest, smaller in middle sag and least in northern sag. Source supply becomes smaller in middle segment of Es3 and the size of middledeep lake is very big that mainly locates in middle sag. The area of southern sag is larger and smaller in northern sag. Mud. stone of middledeep lake face is the precondition of forming source rock. Through 33 oil samples and 48 rock samples analysis of Liaoxi depression, we concluded that content of sapropelic and exinite of organic material is commonly higher and rich of planktonic algae in Shahejie Fm. source rock. Its kerogen type is ⅠⅡ. Basin modeling concluded that hydrocarbon generating threshold is 2 500 m, Es3 source rock below this depth and Es1 source rock is upper this depth. After oilsource correlation research, we considered that oil geochemistry characteristics are similar with source rock geochemistry of Es3 and Es4 in Liaoxi depression. Hence, Es3 and Es4 source rock is the most important oil source in Liaoxi depression. With organic faces and sedimentary faces researching, organic material of Es source rock is entirely rich. But there are some differences of these sags in Liaoxi depression. Geochemical indexes of northern sag of Liaoxi depression are higher, subordinate of middle sag, lower of southern sag. From distributions of middledeep lake face, the author identified small scale of middledeep lake face of Es3 is developed in northern sag of Liaoxi depression, large scale of middledeep lake face of Es3 and Es4 are developed in middle sag of Liaoxi depression, and large scale of middledeep lake face of Es3 is developed in southern sag of Liaoxi depression. Middle sag of Liaoxi depression has a large potentiality of hydrocarbon generation, smaller in southern sag and least in northern sag based on comprehensive analysis.
2012, 30(4): 747-754.
Abstract:
As poolforming energy parameters, geotemperature and pressure influence the whole process from oilgas generating, migrating and accumulating to dissipating. The controlling mechanisms of geotemperature on oilgas generated and geopressure on migrating have been investigated, while influences of geotemperature on oilgas migrating and accumulating have not been considered sufficiently. In order to uncover geotemperature influence on migrating and accumulating of oil and gas, physical, chemical and physical chemical mechanisms during oilgas migrating and accumulating have been investigated systemically. After these investigating and analyzing, a conclusion that each reservoiring processes of oil and gas are influenced by geotemperature has been gained. There are two types of influencing mechanisms of geotemperature on oilgas migrating. Proving dynamic and driving oil and gas directly is the first mechanism. Inhomogeneous distribution of geotemperature could provide heatstress which drives oil and gas migrating directly. According to the heat stress theory, if temperature differences exist among different parties of a same body, heat stress would appear immediately. As giant geological bodies, stratums not for a moment have homogeneous temperature. Those eternal temperature differences imply timeless heat stress which has been and will be driving oil and gas migrating from higher temperature area to lower temperature area. The inference that temperature could drive oil and gas has been testified by Qiu Nansheng's experiment, in which the phenomenon of oil migrating from the higher temperature end of tube to the lower end was observed. In oilgas migrating process, geoheat could not only provide power for oilgas migrating, but also control migrating efficiency by changing some physical parameters, such as sorption, diffusivity and solubility. According to present relative achievements about accumulation of oil and gas, geotemperature not only partly influences accumulating location of oil and gas, but also mainly controls oil and gas's accumulating phases. Where oil and gas will accumulate in is determined by many factors, such as source rock, reservoir, capping, migrating process, preserved process, etc. However, these factors are more or less influenced by geotemperature. Based on phase of reservoired oil and gas, reservoirs could be classified into heavy oil reservoir, normal oil reservoir，condense oil reservoir，oilgas reservoir and gas reservoir. Phase of reservoired oil and gas is determined by their primordial phase and subsequent change. Geotemperature is one of the two primary factors that determine primordial phase of oil and gas (another factor is the organic materials type of source rock). According to present data gain from experiments and experiences, reflection of vitrinite(Ro %), the directly decisive parameter of primordial phase of oil and gas, is a function of geotemperature. In Zhanhua sag, when geotemperature is under 100℃ (Ro<0.5%), the source rock in Es3x generates biogas only. From 100℃ to 175℃(Ro is from 0.5% to 1.35%), routine oil is the main produce. When geotemperature increase to 175℃(Ro>1.35%), produce of the source rock is condensable oil containing with wet gas. When geotemperature is above 200℃(Ro>2.0%), produce of the source rock will be dry gas only. In summary, in accumulating, distributing situation and accumulating phase of oil and gas are influenced by geotemperature (associating with pressure). Two facts are noteworthy, the first one is that geotemperature is not only, but one of many factors which control reservoiring processes of oil and gas. According to the authors, geotemperature has inherent relationships with geopressure and tectonic stress, and the three factors always control oil and gas migrating and accumulating cooperatively. Another one is that the oil and gas reservoirs we are looking for all reservoired during geological time. It is the paleogeotemperature that influenced oil and gas's migrating and accumulating process. So paleogeotemperature should be estimated before analyzing influences of geotemperature on oilgas migrating and accumulating.
As poolforming energy parameters, geotemperature and pressure influence the whole process from oilgas generating, migrating and accumulating to dissipating. The controlling mechanisms of geotemperature on oilgas generated and geopressure on migrating have been investigated, while influences of geotemperature on oilgas migrating and accumulating have not been considered sufficiently. In order to uncover geotemperature influence on migrating and accumulating of oil and gas, physical, chemical and physical chemical mechanisms during oilgas migrating and accumulating have been investigated systemically. After these investigating and analyzing, a conclusion that each reservoiring processes of oil and gas are influenced by geotemperature has been gained. There are two types of influencing mechanisms of geotemperature on oilgas migrating. Proving dynamic and driving oil and gas directly is the first mechanism. Inhomogeneous distribution of geotemperature could provide heatstress which drives oil and gas migrating directly. According to the heat stress theory, if temperature differences exist among different parties of a same body, heat stress would appear immediately. As giant geological bodies, stratums not for a moment have homogeneous temperature. Those eternal temperature differences imply timeless heat stress which has been and will be driving oil and gas migrating from higher temperature area to lower temperature area. The inference that temperature could drive oil and gas has been testified by Qiu Nansheng's experiment, in which the phenomenon of oil migrating from the higher temperature end of tube to the lower end was observed. In oilgas migrating process, geoheat could not only provide power for oilgas migrating, but also control migrating efficiency by changing some physical parameters, such as sorption, diffusivity and solubility. According to present relative achievements about accumulation of oil and gas, geotemperature not only partly influences accumulating location of oil and gas, but also mainly controls oil and gas's accumulating phases. Where oil and gas will accumulate in is determined by many factors, such as source rock, reservoir, capping, migrating process, preserved process, etc. However, these factors are more or less influenced by geotemperature. Based on phase of reservoired oil and gas, reservoirs could be classified into heavy oil reservoir, normal oil reservoir，condense oil reservoir，oilgas reservoir and gas reservoir. Phase of reservoired oil and gas is determined by their primordial phase and subsequent change. Geotemperature is one of the two primary factors that determine primordial phase of oil and gas (another factor is the organic materials type of source rock). According to present data gain from experiments and experiences, reflection of vitrinite(Ro %), the directly decisive parameter of primordial phase of oil and gas, is a function of geotemperature. In Zhanhua sag, when geotemperature is under 100℃ (Ro<0.5%), the source rock in Es3x generates biogas only. From 100℃ to 175℃(Ro is from 0.5% to 1.35%), routine oil is the main produce. When geotemperature increase to 175℃(Ro>1.35%), produce of the source rock is condensable oil containing with wet gas. When geotemperature is above 200℃(Ro>2.0%), produce of the source rock will be dry gas only. In summary, in accumulating, distributing situation and accumulating phase of oil and gas are influenced by geotemperature (associating with pressure). Two facts are noteworthy, the first one is that geotemperature is not only, but one of many factors which control reservoiring processes of oil and gas. According to the authors, geotemperature has inherent relationships with geopressure and tectonic stress, and the three factors always control oil and gas migrating and accumulating cooperatively. Another one is that the oil and gas reservoirs we are looking for all reservoired during geological time. It is the paleogeotemperature that influenced oil and gas's migrating and accumulating process. So paleogeotemperature should be estimated before analyzing influences of geotemperature on oilgas migrating and accumulating.
2012, 30(4): 755-760.
Abstract:
Biomarker nalkanes have been demonstrated as a useful tool in paleolimnological reconstruction since different types of plants have distinctive carbon chain lengths of nalkanes. Peat deposits from Ruoergai Plateau are excellent archives for Holocene paleoenvironmental records. For example, Hong et al.(2003) successfully reconstructed paleoclimatic changes over the last 12 ka based on δ13C series of both Carex mulieensis (Carex m.) remains cellulose and peat cellulose from Hongyuan peat sequence. Zheng et al. (2007a) and Yamamoto et al. (2010) investigated the lipid compositions and nalkane δ13C values of another Hongyuan peat profile over the 13 ka, respectively. However, Holocene paleoenvironmental information has been not obtained from lacustrine sediments there. Therefore, there is a need for additional records of environmental change to improve the accuracy of organic geochemical tools in paleoecological reconstruction. In this work, we carry out preliminary research on the saturated hydrocarbons of a 346cmlong limnological profile from Northern Ruoergai Plateau by gas chromatography and mass spectrometry (GCMS), together with 14C dating, lithology and total organic carbon content (TOC) to evaluate the paleoenvironmental information of molecular fossil compositions and their parameters to organic sources, microbial activity and paleoclimate changes. The nalkanes (C16~C35) dominated by the middlelong chain homologues and high OEP1 and OEP2 values indicate that the organic matter of the sedimentary section are mainly derived from higher plants, especially herbaceous plants. Lithology, TOC and pristane/phytane (Pr/Ph) ratios indicate the basin sedimentary evolution process from strong reducing deep lake conditions in the early Holocene (ca. 11.3~7.3 cal ka BP, 346~203cm) to weak reducing swamp environments during the midHolocene (ca. 7.3~4.5 cal ka BP, >203cm). In the sedimentary period, variations in the proportions of algal, landplant, and aquatic macrophyte inputs of organic matter delivered to the sedimentary profile is well recorded through four nalkanes proxies including middlechain and longchain odd over even carbon number predominance (OEP1 and OEP2, respectively), C25/C31 and ∑C21-/∑C22+ nalkane ratios. In particularly, there is likely important input of Sphagnum to the organic matter in the 120cm depth upwards resulting in the exceptional distribution of these above proxies. In the same sedimentary period, there also is relatively strong microbial degradation resulting to alter the nalkane compositions. Furthermore, the records of the section confirm that Ruoergai Plateau have apparent climatic instability during the period from 9.8 to 8.6 cal ka BP. Of course, there is a clear need to do more work not only on the profile but also on modern vegetation lipid compositions from Ruoergai Plateau in the future exploitation of molecular proxies as tools for the generation of palaeoenvironmental information from the wealth of limnological profiles available.
Biomarker nalkanes have been demonstrated as a useful tool in paleolimnological reconstruction since different types of plants have distinctive carbon chain lengths of nalkanes. Peat deposits from Ruoergai Plateau are excellent archives for Holocene paleoenvironmental records. For example, Hong et al.(2003) successfully reconstructed paleoclimatic changes over the last 12 ka based on δ13C series of both Carex mulieensis (Carex m.) remains cellulose and peat cellulose from Hongyuan peat sequence. Zheng et al. (2007a) and Yamamoto et al. (2010) investigated the lipid compositions and nalkane δ13C values of another Hongyuan peat profile over the 13 ka, respectively. However, Holocene paleoenvironmental information has been not obtained from lacustrine sediments there. Therefore, there is a need for additional records of environmental change to improve the accuracy of organic geochemical tools in paleoecological reconstruction. In this work, we carry out preliminary research on the saturated hydrocarbons of a 346cmlong limnological profile from Northern Ruoergai Plateau by gas chromatography and mass spectrometry (GCMS), together with 14C dating, lithology and total organic carbon content (TOC) to evaluate the paleoenvironmental information of molecular fossil compositions and their parameters to organic sources, microbial activity and paleoclimate changes. The nalkanes (C16~C35) dominated by the middlelong chain homologues and high OEP1 and OEP2 values indicate that the organic matter of the sedimentary section are mainly derived from higher plants, especially herbaceous plants. Lithology, TOC and pristane/phytane (Pr/Ph) ratios indicate the basin sedimentary evolution process from strong reducing deep lake conditions in the early Holocene (ca. 11.3~7.3 cal ka BP, 346~203cm) to weak reducing swamp environments during the midHolocene (ca. 7.3~4.5 cal ka BP, >203cm). In the sedimentary period, variations in the proportions of algal, landplant, and aquatic macrophyte inputs of organic matter delivered to the sedimentary profile is well recorded through four nalkanes proxies including middlechain and longchain odd over even carbon number predominance (OEP1 and OEP2, respectively), C25/C31 and ∑C21-/∑C22+ nalkane ratios. In particularly, there is likely important input of Sphagnum to the organic matter in the 120cm depth upwards resulting in the exceptional distribution of these above proxies. In the same sedimentary period, there also is relatively strong microbial degradation resulting to alter the nalkane compositions. Furthermore, the records of the section confirm that Ruoergai Plateau have apparent climatic instability during the period from 9.8 to 8.6 cal ka BP. Of course, there is a clear need to do more work not only on the profile but also on modern vegetation lipid compositions from Ruoergai Plateau in the future exploitation of molecular proxies as tools for the generation of palaeoenvironmental information from the wealth of limnological profiles available.
2012, 30(4): 761-769.
Abstract:
The Lower Cambrian source rock samples from three typical profiles in the southern Guizhou Depression were analyzed for TOC values, δ13C values, Tmax temperatures, potential generation, and biomarkers using RockEval, GC, GCMS to elucidate the geochemical characteristics and its origin. The results show that the Lower Cambrian black shales in the southern Guizhou Depression are regional marine excellent source rocks with depth of 50150m, and have the TOC values of 0.13%15.40%, average 3.31%(n=169); the kerogens of the source rocks have the δ13C values of 35.79‰-29.88‰, average 32.85‰(n=35), and the kerogen macerals are mainly sapropelinites; the values of the marine vitrinite reflectance of the kerogens are 1.95%3.96%, and the values of the equivalent vitrinite reflectance are 2.02%3.47%; the distribution shapes of the nalkanes are mainly single peak, and the maximum peak carbon are mainly C22, the C30 hopane and C27ααα20R regular sterane are abundant, the regular steranes are mainly C27>C29>C28, the Pr/Ph values are 0.270.62, the source rocks have relative high abundance of gammacerane and dibenzothiophene, the OEP values are 0.821.11,C31 homohopane 22S/(22S+22R) have values of 0.560.63,average 0.59; the source rocks are generally characterized by enrichment in light REE, Ba, Mo, V and U element, relative strong negative anomaly of Ce element , relative strong positive anomaly of Eu element and relative high ratio of U/Th. In summary, the Lower Cambrian marine source rocks in the southern Guizhou Depression have a wide distribution with a thickness of from tens of meters to hundreds of meters, the source rocks have high TOC values, are excellent for organic matter type, and have a postmaturity. It is the product which is jointly controlled by high paleoproductivity and anoxic environment. It can provide abundant organic matter for hydrocarbon generation in the southern Guizhou Depression.
The Lower Cambrian source rock samples from three typical profiles in the southern Guizhou Depression were analyzed for TOC values, δ13C values, Tmax temperatures, potential generation, and biomarkers using RockEval, GC, GCMS to elucidate the geochemical characteristics and its origin. The results show that the Lower Cambrian black shales in the southern Guizhou Depression are regional marine excellent source rocks with depth of 50150m, and have the TOC values of 0.13%15.40%, average 3.31%(n=169); the kerogens of the source rocks have the δ13C values of 35.79‰-29.88‰, average 32.85‰(n=35), and the kerogen macerals are mainly sapropelinites; the values of the marine vitrinite reflectance of the kerogens are 1.95%3.96%, and the values of the equivalent vitrinite reflectance are 2.02%3.47%; the distribution shapes of the nalkanes are mainly single peak, and the maximum peak carbon are mainly C22, the C30 hopane and C27ααα20R regular sterane are abundant, the regular steranes are mainly C27>C29>C28, the Pr/Ph values are 0.270.62, the source rocks have relative high abundance of gammacerane and dibenzothiophene, the OEP values are 0.821.11,C31 homohopane 22S/(22S+22R) have values of 0.560.63,average 0.59; the source rocks are generally characterized by enrichment in light REE, Ba, Mo, V and U element, relative strong negative anomaly of Ce element , relative strong positive anomaly of Eu element and relative high ratio of U/Th. In summary, the Lower Cambrian marine source rocks in the southern Guizhou Depression have a wide distribution with a thickness of from tens of meters to hundreds of meters, the source rocks have high TOC values, are excellent for organic matter type, and have a postmaturity. It is the product which is jointly controlled by high paleoproductivity and anoxic environment. It can provide abundant organic matter for hydrocarbon generation in the southern Guizhou Depression.
2012, 30(4): 770-778.
Abstract:
Because of the samilar paleoclimate and palosedimentary environment, regular biomarkers and isotope distinction of the source rocks and generated petroleum in the subsag belong to the same sag is tiny, which bring difficulties to oilsource correlation. By extracting molecular fossils information using GCMS technology, according to the relative content of 4methyl steranes and distribution characteristics of 4methyl steranes isomers, oilsource correlation work are performed ,which provides a new method for oilsource correlation in similar area. Es4s and Es3x two sets of source rocks are developed in the study area, they are characterized by high organic matter abundance, mature to over mature thermal evolution degrees. Organic matter of Es4s are formed in brackishsaline water with reductive environment, organic matter of Es3x are formed in freshsaline water with reductive environment , organic matter input of both source rocks are dominated by lower aquatic organisms and terrigenous higher plants, while terrigenous higher plants are more abundant near provenance. Relative content of 4methyl steranes of Es3x source rocks is higher than that of Es4s source rocks, indicating the better organic matter input of Es3x source rocks.The value of 4methyl steranes/C29 steranes of Es3x source rocks in the middle, west and deep subsag is 4.51,2.79 and 1.27, respectively, which is caused by the different proportion of dinophyceae in total organic matter. The distribution characteristics of C20, C21, C23 tricyclic terpanes and ααα20RC27,C28,C29regular steranes of oils with alike maturity in different region is quite similar, 4methyl steranes/C29steranes value of crude oils in the middle, west and east region is 2.89, 2.39, 2.06, respectively, which make a big difference, while the carbon isotope characteristics of crude oils are opposite, distribution characteristics of 4methyl steranes isomers of each region is also different. Oilsource correlation demonstrate that Es4s and Es3x crude oils of northern steep slope zone mainly originate from Es3x source rocks in nearby sag, crude oils of the western zone are provided by Es3x source rocks of the western sag, crude oils of the middle zone are provided by Es3x source rocks of the middle sag, crude oils of the eastern zone are provided by Es3x source rocks of deep sag in the eastern zone, and no contribution from source rocks of the Gubei Sag.
Because of the samilar paleoclimate and palosedimentary environment, regular biomarkers and isotope distinction of the source rocks and generated petroleum in the subsag belong to the same sag is tiny, which bring difficulties to oilsource correlation. By extracting molecular fossils information using GCMS technology, according to the relative content of 4methyl steranes and distribution characteristics of 4methyl steranes isomers, oilsource correlation work are performed ,which provides a new method for oilsource correlation in similar area. Es4s and Es3x two sets of source rocks are developed in the study area, they are characterized by high organic matter abundance, mature to over mature thermal evolution degrees. Organic matter of Es4s are formed in brackishsaline water with reductive environment, organic matter of Es3x are formed in freshsaline water with reductive environment , organic matter input of both source rocks are dominated by lower aquatic organisms and terrigenous higher plants, while terrigenous higher plants are more abundant near provenance. Relative content of 4methyl steranes of Es3x source rocks is higher than that of Es4s source rocks, indicating the better organic matter input of Es3x source rocks.The value of 4methyl steranes/C29 steranes of Es3x source rocks in the middle, west and deep subsag is 4.51,2.79 and 1.27, respectively, which is caused by the different proportion of dinophyceae in total organic matter. The distribution characteristics of C20, C21, C23 tricyclic terpanes and ααα20RC27,C28,C29regular steranes of oils with alike maturity in different region is quite similar, 4methyl steranes/C29steranes value of crude oils in the middle, west and east region is 2.89, 2.39, 2.06, respectively, which make a big difference, while the carbon isotope characteristics of crude oils are opposite, distribution characteristics of 4methyl steranes isomers of each region is also different. Oilsource correlation demonstrate that Es4s and Es3x crude oils of northern steep slope zone mainly originate from Es3x source rocks in nearby sag, crude oils of the western zone are provided by Es3x source rocks of the western sag, crude oils of the middle zone are provided by Es3x source rocks of the middle sag, crude oils of the eastern zone are provided by Es3x source rocks of deep sag in the eastern zone, and no contribution from source rocks of the Gubei Sag.
2012, 30(4): 779-786.
Abstract:
As the dynamics of oilgas exploration is bigger, many large gas fields has been found in the basin in recently. Biaomiao area is in the eastern of Dongpu depression, which is the exploration degree high oilgas area in Dongpu depression, there are mainly gas in the Baimiao area,some industrial oilgas wells has been found now, the producing gas condition is very superior,it has discovered Es3下,Es31,Es32,Es334 four sets of main oilgas formation. The gas area is smaller in the upper and part bigger in the lower part. The gas in Baimiao are at the top of gas reservoirs with oil hoop. Oil and gas distribution is gas in the upper and oil in the lower part. For oil and gas relation is complicated in Baimiao area,the research on the regulation of oil and gas is very poor and no systematic analysis up to now. It influences the step of gas exploration. The analysis on the formation time of oilgas reservoirs is hot problem, the determination of it helps to recognize the formation regulation of oilgas reservoirs. In recent, there are important progresses in the aspect of the chronology of formation time of hydrocarbon reservoirs.There are many methods, such as illite dating method, homogenization temperatures of fluid inclusion, the formation history of traps, hydrocarbon generated and hydrocarbon expulsed process,and so on.The different method is of different sense. On the basis of illite dating method and homogenization temperatures of fluid inclusion，it is found that the formation time of hydrocarbon reserviors exist mainly two stages in Baimiao area of Dongpu depression. One is about 31.4～20.4 Ma, which is corresponding to sedimentary period of Dongying FormationEarly period of Guantao Formation.The other is from 2 Ma to now, corresponding to Quaternary to now. In the first stage, a great majority of the formation age of natural gas reserviors distribute in the denudation period from 27 Ma to 17 Ma,which is the main formation time. The decreasing of pressure in the denuded period help to formation of oil and gas reserviors. In the second stage,from 2 Ma to now, the Baimiao area is in the deficient compensation state since sedimentary period of Guantao formation, the area having not second process of generating gas. on the one hand, Qianliyuan depression and Gegangji depression continue producing gases, which migrate to the Baimiao area; on the other hand, the gas reserviors formed in the first stage is adjusted again. Gas in this stage comes mainly from the second time gas of Qianliyuan depression and Gegangji depression. The faults are important to control the formation time of oilgas reservoirs, the formation time in different area is very different. The Biaomiao area is divided into two forming oilgas reservoirs by Duzhai fault. The formation time of oilgas reservoirs is earlier in West area and later in East area. In vertical order,the formation time of oilgas reservoirs is earlier in old position and later in new position. In general, the characteristics of the formation time of the natural gas reserviors in Baimiao area is earlier in the west area and later in the east area, earlier in the north area and later in the south area. The results are important for the deep exploration in Dongpu depression.
As the dynamics of oilgas exploration is bigger, many large gas fields has been found in the basin in recently. Biaomiao area is in the eastern of Dongpu depression, which is the exploration degree high oilgas area in Dongpu depression, there are mainly gas in the Baimiao area,some industrial oilgas wells has been found now, the producing gas condition is very superior,it has discovered Es3下,Es31,Es32,Es334 four sets of main oilgas formation. The gas area is smaller in the upper and part bigger in the lower part. The gas in Baimiao are at the top of gas reservoirs with oil hoop. Oil and gas distribution is gas in the upper and oil in the lower part. For oil and gas relation is complicated in Baimiao area,the research on the regulation of oil and gas is very poor and no systematic analysis up to now. It influences the step of gas exploration. The analysis on the formation time of oilgas reservoirs is hot problem, the determination of it helps to recognize the formation regulation of oilgas reservoirs. In recent, there are important progresses in the aspect of the chronology of formation time of hydrocarbon reservoirs.There are many methods, such as illite dating method, homogenization temperatures of fluid inclusion, the formation history of traps, hydrocarbon generated and hydrocarbon expulsed process,and so on.The different method is of different sense. On the basis of illite dating method and homogenization temperatures of fluid inclusion，it is found that the formation time of hydrocarbon reserviors exist mainly two stages in Baimiao area of Dongpu depression. One is about 31.4～20.4 Ma, which is corresponding to sedimentary period of Dongying FormationEarly period of Guantao Formation.The other is from 2 Ma to now, corresponding to Quaternary to now. In the first stage, a great majority of the formation age of natural gas reserviors distribute in the denudation period from 27 Ma to 17 Ma,which is the main formation time. The decreasing of pressure in the denuded period help to formation of oil and gas reserviors. In the second stage,from 2 Ma to now, the Baimiao area is in the deficient compensation state since sedimentary period of Guantao formation, the area having not second process of generating gas. on the one hand, Qianliyuan depression and Gegangji depression continue producing gases, which migrate to the Baimiao area; on the other hand, the gas reserviors formed in the first stage is adjusted again. Gas in this stage comes mainly from the second time gas of Qianliyuan depression and Gegangji depression. The faults are important to control the formation time of oilgas reservoirs, the formation time in different area is very different. The Biaomiao area is divided into two forming oilgas reservoirs by Duzhai fault. The formation time of oilgas reservoirs is earlier in West area and later in East area. In vertical order,the formation time of oilgas reservoirs is earlier in old position and later in new position. In general, the characteristics of the formation time of the natural gas reserviors in Baimiao area is earlier in the west area and later in the east area, earlier in the north area and later in the south area. The results are important for the deep exploration in Dongpu depression.
