2002 Vol. 20, No. 2
column
Display Method:
2002, 20(2): 179-187.
Abstract:
Eleven sedimentary supersequences CQ 1～11 of marine Paleozoic and Mesozoic sediments are recognized in the Coqen basin, Lhasa Block. Detailed characteristics of sedimentation, age range, number, and T-R tecture are described in the paper, and correlations and discussions of supersequence between Tethys Himalaya and Lhasa Block are made. CQ 1 is temporally thought to be the Cambrian supersequence due to crystallinely metamorphic rocks. CQ 2 of the Ordovician supersequence is dominated by black shale and limestone, in which only regressive part is exposed and the transgressive sediment is not. CQ 3 within duration of ca. 39 Ma of the Silurian supersequence is characterized by a texture of depositional sequence sets from transgressive shalely and limy rocks to medium-thicked wackstone and packstone, within which abundant grapitutid and little thinned shelly brachiopod became shallower sea coral and conodent. The boundary between the CQ 2 and CQ 3 is placed at the Lower Ashgill of Upper Ordovician. As the Devonian supersequence in range of ca. 48 Ma, CQ4 can be broadly recognized in the Coqen basin, which is composed of transgrassive and regreassive sets. Thinned marlstone with the mixture of shale, siltstone, and sandstone and benthos associated with planktons comprises the former, and the later is of property of shallow sea dolomitized and crystalline limestone. This supersequence is separated the CQ 3 away by terrigenous sediment at the base of Devonian. CQ 5 is limited in Lower Carboniferous with an interval of ca. 33 Ma. It starts by the wormkalk at the bottom of Carboniferous and continues by bioclastic and intraclastic limestone, for which the transgrassive and regreassive depositional sets are vague to distinguish. CQ 6 ranges from upper Lower Carboniferous to lower Lower Permian with a total age of ca. 55 Ma. It is characterized by glaciomarine shale with lens of limestone and cool fauna fossils, and the boundary between CQ 6 and CQ 5 is located at the sharp contact of terrigenous rocks onto carbonate rocks. CQ 7 is the latest supersequence in Paleozoic, which has duration of age time ca. 30 Ma in most of Permian. The transgressive depositional sequence set is similar as the set in the CQ 6 and became the shallower carbonate sediments of regressive set. CQ 8 and CQ 7 are separated by disconformable and erosional surface at the base of the Triassic Quehala group. The age range of the supersequence is estimated 37 Ma. The transgressive set is not exposed, and the regression is consitituent of terrigenous turbidite of inner fan with little volcanic and carbonate rock. There is a nonconformity contact between the CQ 9 and CQ 8, above which the transgressive depositional sequence set is superposed by flysch middle and outer turbidite fan, and follows by changeable and complicated system sediment. It is ranges ca. 63 Ma and is separated over CQ 10 away by a regional unconformity. Supersequence CQ 10 is composed of kinds of limestone and clastic rocks in shallow sea environment deposited in Lower Cretaceous (50 Ma). The transgressive set is combined by hybrid sediments of shallow and volcanic rock, and the regressive by predominant carbonate rocks. The Upper Cretaceous supersequence CQ 11 is the only one superposed by much continental delta and shore facies. In general, the T-R sets are not readily differentiated either in filed or in room. Of them, three supersequencesCQ 1～3 are classified in Early Paleozoic; four CQ 4～7 and four CQ 8～11 are in Late Paleozoic and Mesozoic respectively. The sedimentation, age range, number, and T-R texture of the super sequences CQ 1～3 are similar, but different are in the CQ 4～7 and CQ 8～11 of Upper Paleozoic and Mesozoic. We suppose that the turnover of supersequence from Early to Late Paleozoic could be caused by the changes of tectonic and types of sedimentary basin, but not by second-order sea-level change, because there should be a same / similar sedimentary response to eustatic change for sedimentary basins
Eleven sedimentary supersequences CQ 1～11 of marine Paleozoic and Mesozoic sediments are recognized in the Coqen basin, Lhasa Block. Detailed characteristics of sedimentation, age range, number, and T-R tecture are described in the paper, and correlations and discussions of supersequence between Tethys Himalaya and Lhasa Block are made. CQ 1 is temporally thought to be the Cambrian supersequence due to crystallinely metamorphic rocks. CQ 2 of the Ordovician supersequence is dominated by black shale and limestone, in which only regressive part is exposed and the transgressive sediment is not. CQ 3 within duration of ca. 39 Ma of the Silurian supersequence is characterized by a texture of depositional sequence sets from transgressive shalely and limy rocks to medium-thicked wackstone and packstone, within which abundant grapitutid and little thinned shelly brachiopod became shallower sea coral and conodent. The boundary between the CQ 2 and CQ 3 is placed at the Lower Ashgill of Upper Ordovician. As the Devonian supersequence in range of ca. 48 Ma, CQ4 can be broadly recognized in the Coqen basin, which is composed of transgrassive and regreassive sets. Thinned marlstone with the mixture of shale, siltstone, and sandstone and benthos associated with planktons comprises the former, and the later is of property of shallow sea dolomitized and crystalline limestone. This supersequence is separated the CQ 3 away by terrigenous sediment at the base of Devonian. CQ 5 is limited in Lower Carboniferous with an interval of ca. 33 Ma. It starts by the wormkalk at the bottom of Carboniferous and continues by bioclastic and intraclastic limestone, for which the transgrassive and regreassive depositional sets are vague to distinguish. CQ 6 ranges from upper Lower Carboniferous to lower Lower Permian with a total age of ca. 55 Ma. It is characterized by glaciomarine shale with lens of limestone and cool fauna fossils, and the boundary between CQ 6 and CQ 5 is located at the sharp contact of terrigenous rocks onto carbonate rocks. CQ 7 is the latest supersequence in Paleozoic, which has duration of age time ca. 30 Ma in most of Permian. The transgressive depositional sequence set is similar as the set in the CQ 6 and became the shallower carbonate sediments of regressive set. CQ 8 and CQ 7 are separated by disconformable and erosional surface at the base of the Triassic Quehala group. The age range of the supersequence is estimated 37 Ma. The transgressive set is not exposed, and the regression is consitituent of terrigenous turbidite of inner fan with little volcanic and carbonate rock. There is a nonconformity contact between the CQ 9 and CQ 8, above which the transgressive depositional sequence set is superposed by flysch middle and outer turbidite fan, and follows by changeable and complicated system sediment. It is ranges ca. 63 Ma and is separated over CQ 10 away by a regional unconformity. Supersequence CQ 10 is composed of kinds of limestone and clastic rocks in shallow sea environment deposited in Lower Cretaceous (50 Ma). The transgressive set is combined by hybrid sediments of shallow and volcanic rock, and the regressive by predominant carbonate rocks. The Upper Cretaceous supersequence CQ 11 is the only one superposed by much continental delta and shore facies. In general, the T-R sets are not readily differentiated either in filed or in room. Of them, three supersequencesCQ 1～3 are classified in Early Paleozoic; four CQ 4～7 and four CQ 8～11 are in Late Paleozoic and Mesozoic respectively. The sedimentation, age range, number, and T-R texture of the super sequences CQ 1～3 are similar, but different are in the CQ 4～7 and CQ 8～11 of Upper Paleozoic and Mesozoic. We suppose that the turnover of supersequence from Early to Late Paleozoic could be caused by the changes of tectonic and types of sedimentary basin, but not by second-order sea-level change, because there should be a same / similar sedimentary response to eustatic change for sedimentary basins
2002, 20(2): 197-202.
Abstract:
Mainly three sets of coal layer assembles developed in Junggar Basin Jurassic strata, respectively lying in the lower section of Badaowan group,the down part of the upper section of Badaowan group and the bottom of Xishanyao group.In the division proposal of the Jurassic sequence stratigraphy of Junggar Basin,sb1,sb2,sb4 boundaries lay in the lower section of Badaowan group,the down part of the upper section of Badaowan group and close to the three coal layer assembles at the bottom of Xishanyao group. The accumulation of coal varies greatly due to the differences in required accommodation which supplies space for coal accumulation in different system tracts of different sequences as well as in different periods of the identical system tract,and the differences in coal layer developments which accommodate quick accumulation,with the differences in sedimentary environments.Thus there are time-penetrating phenomena in the Jurassic coal layers, and they may develop in each system tract of the sequence.Therefore,the Jurassic coal layers mainly developed in (1)the lowstand and highstand system tracts of sequence Ⅰ.(2)the lowstand system tract of sequence Ⅱ.(3)the highstand system tract of sequence Ⅲ.(4)the lowstand system tract of sequence Ⅳ locally.
Mainly three sets of coal layer assembles developed in Junggar Basin Jurassic strata, respectively lying in the lower section of Badaowan group,the down part of the upper section of Badaowan group and the bottom of Xishanyao group.In the division proposal of the Jurassic sequence stratigraphy of Junggar Basin,sb1,sb2,sb4 boundaries lay in the lower section of Badaowan group,the down part of the upper section of Badaowan group and close to the three coal layer assembles at the bottom of Xishanyao group. The accumulation of coal varies greatly due to the differences in required accommodation which supplies space for coal accumulation in different system tracts of different sequences as well as in different periods of the identical system tract,and the differences in coal layer developments which accommodate quick accumulation,with the differences in sedimentary environments.Thus there are time-penetrating phenomena in the Jurassic coal layers, and they may develop in each system tract of the sequence.Therefore,the Jurassic coal layers mainly developed in (1)the lowstand and highstand system tracts of sequence Ⅰ.(2)the lowstand system tract of sequence Ⅱ.(3)the highstand system tract of sequence Ⅲ.(4)the lowstand system tract of sequence Ⅳ locally.
2002, 20(2): 210-216.
Abstract:
Based on the analyses of structural sequences and base level, high-resolution stratigraphic framework is established and suggested a tectonic control on sequences formation in Dongying depression. The sequences developed in faulted lake-basin are composed of lomstand(LST),lake expansion(EST) and highstand system tracts(HST).They can be further grouped into three sequence styles, growth -fault style,structuracl-break style and ramp style, in the light of the features of lomstand system tracts and spatial configurations of depositional systems. The former is dominated by lowstand system tracts, the second is composed of complete three component system tracts(LST, EST and HST),which is similar to the pattern developed in marine passive continental margin, the last one is dominated by shallow-lake depositional packages. The structural break provides substantial accommodation space for the development of lowstand fan, which include lowstand deltas, turbiditic fans and fan-deltas. They are the major exploration targets for subtle hydrocarbon reservoir, which are of good commerical siginificances proven by drilling. This study shows a prosperous application of sequence stratigraphy into the esploration in continental basins.
Based on the analyses of structural sequences and base level, high-resolution stratigraphic framework is established and suggested a tectonic control on sequences formation in Dongying depression. The sequences developed in faulted lake-basin are composed of lomstand(LST),lake expansion(EST) and highstand system tracts(HST).They can be further grouped into three sequence styles, growth -fault style,structuracl-break style and ramp style, in the light of the features of lomstand system tracts and spatial configurations of depositional systems. The former is dominated by lowstand system tracts, the second is composed of complete three component system tracts(LST, EST and HST),which is similar to the pattern developed in marine passive continental margin, the last one is dominated by shallow-lake depositional packages. The structural break provides substantial accommodation space for the development of lowstand fan, which include lowstand deltas, turbiditic fans and fan-deltas. They are the major exploration targets for subtle hydrocarbon reservoir, which are of good commerical siginificances proven by drilling. This study shows a prosperous application of sequence stratigraphy into the esploration in continental basins.
2002, 20(2): 222-228.
Abstract:
The continental sequence deeply affected by natural geographic districts, geological forces and strata types, therefore occurred some kinds of types. There are three kinds of sequence types including alluvial sequence, lacustrine sequence and fluvial sequence that present in Jizhong basin during the syn extensional stage. The alluvial sequence is mainly composed of alluvial fan systems and grows up in the initial stages of the basin development. Here the relief contrast was strong, provenance supply was abundant and climate was arid, so the lacustrine area was narrow in proportion to the alluvial and fluvial area. The lacustrine sequence mainly made up of lacustrine sedimentary systems, and partially fluvial sediments and a little of alluvial interlayer. The stage was a period of rapid growth of the rift basin. The basin base subsidized fast and climate humid, lacustrine area larger, thereby gaining a period for hydrocarbon rock to form. The fluvial sequence began to form in last stage of the basin extend. The geographic contrast gradually was reduced. The deposit was far from the source region,and the area of the fluvial systems was deadly larger than the area of the lacustrine. The authors suggested that a polynomial relation exists between the lake level change and tectonic movement, provenance, climate factor and so on, the former only incarnates the synthetically changes of the latter. The sequence texture of the continental rift basin is under the control of the lake level change, like the sequence texture of the marine basin is controlled by sea level change. Therefore, the continental sequence may be trisection according to the lake level change. The sequences of the continental rift basin controlled by tectonic movement develop in succession, as the alluvial sequence located at the bottom, the lacustrine sequence at the middle and the fluvial sequence at the upper. This serial sequences is a response that sedimentary basin fill to the episodic tectonic movement. During the basin fill, there is clearly a difference among the sedimentary system tract growth of each sequence. In general, the lowstand system tract (LST) of the alluvial sequence is superior to the lacustrine and fluvial sequences. The LST of the lacustrine is absent and/or lack, but the transgressive system tract (TST) and/or highstand system tract (HST) deposited in the lake level rise are best of all development. The LST and/or HST deposited in the lake level fall of the fluvial sequence are the best in the each sequence. The tectonic movement is primary factor to control the continental sequence type, and the lake level change controls the texture of the sequences.
The continental sequence deeply affected by natural geographic districts, geological forces and strata types, therefore occurred some kinds of types. There are three kinds of sequence types including alluvial sequence, lacustrine sequence and fluvial sequence that present in Jizhong basin during the syn extensional stage. The alluvial sequence is mainly composed of alluvial fan systems and grows up in the initial stages of the basin development. Here the relief contrast was strong, provenance supply was abundant and climate was arid, so the lacustrine area was narrow in proportion to the alluvial and fluvial area. The lacustrine sequence mainly made up of lacustrine sedimentary systems, and partially fluvial sediments and a little of alluvial interlayer. The stage was a period of rapid growth of the rift basin. The basin base subsidized fast and climate humid, lacustrine area larger, thereby gaining a period for hydrocarbon rock to form. The fluvial sequence began to form in last stage of the basin extend. The geographic contrast gradually was reduced. The deposit was far from the source region,and the area of the fluvial systems was deadly larger than the area of the lacustrine. The authors suggested that a polynomial relation exists between the lake level change and tectonic movement, provenance, climate factor and so on, the former only incarnates the synthetically changes of the latter. The sequence texture of the continental rift basin is under the control of the lake level change, like the sequence texture of the marine basin is controlled by sea level change. Therefore, the continental sequence may be trisection according to the lake level change. The sequences of the continental rift basin controlled by tectonic movement develop in succession, as the alluvial sequence located at the bottom, the lacustrine sequence at the middle and the fluvial sequence at the upper. This serial sequences is a response that sedimentary basin fill to the episodic tectonic movement. During the basin fill, there is clearly a difference among the sedimentary system tract growth of each sequence. In general, the lowstand system tract (LST) of the alluvial sequence is superior to the lacustrine and fluvial sequences. The LST of the lacustrine is absent and/or lack, but the transgressive system tract (TST) and/or highstand system tract (HST) deposited in the lake level rise are best of all development. The LST and/or HST deposited in the lake level fall of the fluvial sequence are the best in the each sequence. The tectonic movement is primary factor to control the continental sequence type, and the lake level change controls the texture of the sequences.
2002, 20(2): 238-242.
Abstract:
Taking the Pingzhuang and Tiefa basins as an example, the authors proposed that the river-mouth-dam lake delta developed in the along-lake belt where the river, locating in one side of the basin boundary fault and in front of the fan, flew into the lake in the shrinkage phase of a versiera shape lake basin . It had similar sedimentary features to the delta controlled by the river of sea-bank. The Gilbert lake delta developed in the along-lake belt where the river, locating in one side of the sediment-erosion basin, flew into the lake. It had vertical-sequences strata composed of bottom-set bed, foreset bed and topset bed, with sand lobe shape. It had no relationship with fan in the origin space. Based on this, the authors discussed geologic setting of two kinds of lake deltas, and, moreover, investigated the origin of their developing conditions and progradational patterns.
Taking the Pingzhuang and Tiefa basins as an example, the authors proposed that the river-mouth-dam lake delta developed in the along-lake belt where the river, locating in one side of the basin boundary fault and in front of the fan, flew into the lake in the shrinkage phase of a versiera shape lake basin . It had similar sedimentary features to the delta controlled by the river of sea-bank. The Gilbert lake delta developed in the along-lake belt where the river, locating in one side of the sediment-erosion basin, flew into the lake. It had vertical-sequences strata composed of bottom-set bed, foreset bed and topset bed, with sand lobe shape. It had no relationship with fan in the origin space. Based on this, the authors discussed geologic setting of two kinds of lake deltas, and, moreover, investigated the origin of their developing conditions and progradational patterns.
2002, 20(2): 249-254.
Abstract:
On the basis of the sedimentary characteristics and reservoir distribution law in Feixianguan Formation of Upper Permian-Lower Triassic,East Sichuan Basin, it can be determined that the characteristics and distribution of Changxin reefs and Feixiangguan oolitic banks are tighly relevent to the fluctuation of sea-level.The Changxin reefs developed during the rapid rising of sea-level on the ramp and inner ramp. When the growing speed of the reefs was lower than the rising one of sea-level,catch-up transgression reefs were formed,and when growing speed of the reefs was quicker than the rising one of sea-level,keep-up transgression reefs were formed.The Feixianguan oolitic banks were formed on the inner platform rim and some inner platform areas during the regression of sea-level, single platform rim banks were distributed widely and thickly,although the inner platform banks were of large number,they were thin and narrow in range.So,development formations of Changxin reefs rose towards transgression direction,and the Feixianguan oolitic banks migrated towards platform expandtion with regression. The Formation was deposited in a large scale of fluctuation of sea-level,the transgression begun in the early Wujiapin period, sea-level rose rapidly in the Changxin period ,and it reached summit in the early Feixianguan period,then lowered down in the following Feixianguan period until to the end of the time.
On the basis of the sedimentary characteristics and reservoir distribution law in Feixianguan Formation of Upper Permian-Lower Triassic,East Sichuan Basin, it can be determined that the characteristics and distribution of Changxin reefs and Feixiangguan oolitic banks are tighly relevent to the fluctuation of sea-level.The Changxin reefs developed during the rapid rising of sea-level on the ramp and inner ramp. When the growing speed of the reefs was lower than the rising one of sea-level,catch-up transgression reefs were formed,and when growing speed of the reefs was quicker than the rising one of sea-level,keep-up transgression reefs were formed.The Feixianguan oolitic banks were formed on the inner platform rim and some inner platform areas during the regression of sea-level, single platform rim banks were distributed widely and thickly,although the inner platform banks were of large number,they were thin and narrow in range.So,development formations of Changxin reefs rose towards transgression direction,and the Feixianguan oolitic banks migrated towards platform expandtion with regression. The Formation was deposited in a large scale of fluctuation of sea-level,the transgression begun in the early Wujiapin period, sea-level rose rapidly in the Changxin period ,and it reached summit in the early Feixianguan period,then lowered down in the following Feixianguan period until to the end of the time.
2002, 20(2): 261-266.
Abstract:
The Yellow River is of special hydrology, hydodynamics, sedimentary environment and deposits, resulting in forming a lot of unusual sedimentary phenomina: one of them is ice-induced slump or subsidence structure. Ice-induced slump and subsidence structure are considerably common in the lower course of the Yellow River. They mainly develop in the point bar and/or channel bar, sometimes also in levee. Their development influences and remakes the sedimentary views of the point bar and channel bar. Ice-induced slump structure is an unusual structure that is formed in such a state that the sediment is transformed from the being frozen to being melt, and its motion is featured by sliding, mainly with horizontal motion. Those ice-induced structures developing in the point bar and/or channel bar are like scales or wrinkles. Those ones like scales composed by several to more than ten,are dozens of centimeters in diameters with the thickness of mostly ten of centimeters,and their bottom boundaries are frozen ones; and those ones like wrinkles are very small in size and each wrinkle is below one centimeter in width, ten to thirty centimeters in length and two or three centimeters in thickness. Sometimes, a specical ice-induced slump may be seen in levee and it makes the edge of levee look like steps or gullies. Also, the ice-induced subsidence structure is a kind of special structures formed by ice layer's melting and its motion feature is subsiding, mainly moving vertically. Ice-melt-induced subsidence structures have the multangylar shapes and look hole-like. Their diameters are mostly several tens of centimeters to one or two meters and the largest may amount to more than ten meters and the depth is more than ten centemeters. They often develop in groups.
The Yellow River is of special hydrology, hydodynamics, sedimentary environment and deposits, resulting in forming a lot of unusual sedimentary phenomina: one of them is ice-induced slump or subsidence structure. Ice-induced slump and subsidence structure are considerably common in the lower course of the Yellow River. They mainly develop in the point bar and/or channel bar, sometimes also in levee. Their development influences and remakes the sedimentary views of the point bar and channel bar. Ice-induced slump structure is an unusual structure that is formed in such a state that the sediment is transformed from the being frozen to being melt, and its motion is featured by sliding, mainly with horizontal motion. Those ice-induced structures developing in the point bar and/or channel bar are like scales or wrinkles. Those ones like scales composed by several to more than ten,are dozens of centimeters in diameters with the thickness of mostly ten of centimeters,and their bottom boundaries are frozen ones; and those ones like wrinkles are very small in size and each wrinkle is below one centimeter in width, ten to thirty centimeters in length and two or three centimeters in thickness. Sometimes, a specical ice-induced slump may be seen in levee and it makes the edge of levee look like steps or gullies. Also, the ice-induced subsidence structure is a kind of special structures formed by ice layer's melting and its motion feature is subsiding, mainly moving vertically. Ice-melt-induced subsidence structures have the multangylar shapes and look hole-like. Their diameters are mostly several tens of centimeters to one or two meters and the largest may amount to more than ten meters and the depth is more than ten centemeters. They often develop in groups.
2002, 20(2): 275-281.
Abstract:
Late Ceinozoic forland basin deposits in Yecheng are composed of Miocene mudstone and sandstone (Wuqia Group), Early Pliocene sandstone with minor gritstone (Artux Formation) and Late Pliocene-Early Pleistocene conglomerate (Xiyu Formation). The Miocene strata are dominated by fine-grained clastic material, indicating a distal source and low gradient slope. Palaeocurrent measurements suggested northward direction, indicating that the Kunlun area was at low elevation. Deposition of Artux Formation marked the first appearance of gravel and lithic detritus, indicating the uplift of the Kunlun. Xiyu Formation is characterized by coarse debris flow deposits, marking the strong uplift of the northern part of Tibetan Plateau and unroofing of the Kunlun.
Late Ceinozoic forland basin deposits in Yecheng are composed of Miocene mudstone and sandstone (Wuqia Group), Early Pliocene sandstone with minor gritstone (Artux Formation) and Late Pliocene-Early Pleistocene conglomerate (Xiyu Formation). The Miocene strata are dominated by fine-grained clastic material, indicating a distal source and low gradient slope. Palaeocurrent measurements suggested northward direction, indicating that the Kunlun area was at low elevation. Deposition of Artux Formation marked the first appearance of gravel and lithic detritus, indicating the uplift of the Kunlun. Xiyu Formation is characterized by coarse debris flow deposits, marking the strong uplift of the northern part of Tibetan Plateau and unroofing of the Kunlun.
2002, 20(2): 288-292.
Abstract:
According to comprehensive analysis of Jurassic strata distribution, sedimentary characteristic and tectonic evolution, the Qaidam Basin experienced the development and super imposition of two types of basins during the Jurassic period, the middle Yanshan orogeny at the end of the Middle Jurassic was the transformation time of the basin types. During the Early Middle Jurassic, it was in an extensional tectonic environment and formed a series of minor-scale fault basin group, which was distributed in the south of Qilian Mountain and nearby the southern Altyn fault. During the Late Jurassic and cretaceous, it was in the compressional tectonic setting and formed the down-warped basin, which was controlled by the overthrust tectonic regime in the front of Qilian Mountain, the deposition scope was obviously widening.
According to comprehensive analysis of Jurassic strata distribution, sedimentary characteristic and tectonic evolution, the Qaidam Basin experienced the development and super imposition of two types of basins during the Jurassic period, the middle Yanshan orogeny at the end of the Middle Jurassic was the transformation time of the basin types. During the Early Middle Jurassic, it was in an extensional tectonic environment and formed a series of minor-scale fault basin group, which was distributed in the south of Qilian Mountain and nearby the southern Altyn fault. During the Late Jurassic and cretaceous, it was in the compressional tectonic setting and formed the down-warped basin, which was controlled by the overthrust tectonic regime in the front of Qilian Mountain, the deposition scope was obviously widening.
2002, 20(2): 307-313.
Abstract:
ESR dating, grain size and magnetic susceptibility measurements indicated that there exists a great difference in properties between the Xiashu loess, a kind of aeolian sediments, and the loess in the north China.The evidence showed that there are more clay particles in the Xiashu loess. Kd, frequency-dependent susceptibility and other environmental indicators suggested 5 relatively warm and humid climatic periods in the mid-Pleistocene: 159～163ka,192ka,195～198ka,203～230ka and 311～350ka. The first warmer climatic period was corresponding to the slightly relative warmer climatic period shawed in the deep-sea oxygen isotope (V21-146 hole) stages 6 and the 2~ nd , 3~ rd and 4~ th warmer climatic periods were corresponding to the warmer climatic event reflected by S2 and to the marine oxygen isotope stage 7. There existed a good relation between the four buried palaeosol layers of Laohushan Xiashu loess section and the four warm, humid climatic periods of the Jurong section. Paleolithic excavation shows a certain amount of stone implements in the 6 and 7 layer, indicating human activities at that time. Magnetic susceptibility and grain-size records suggested a warm and humid environment at that time, which was suitable for the human activity. And, this was in good agreement with the research result from pithecanthrope cave of Tangshan in Nanjing. The stone implements of the Miaohoushan culture in North east China were similar in features to those from North China and Jurong Paleolithic site, probably suggesting that the channel of the Yangtze River used to lie in the south of Jurong, Ningzheng Region.
ESR dating, grain size and magnetic susceptibility measurements indicated that there exists a great difference in properties between the Xiashu loess, a kind of aeolian sediments, and the loess in the north China.The evidence showed that there are more clay particles in the Xiashu loess. Kd, frequency-dependent susceptibility and other environmental indicators suggested 5 relatively warm and humid climatic periods in the mid-Pleistocene: 159～163ka,192ka,195～198ka,203～230ka and 311～350ka. The first warmer climatic period was corresponding to the slightly relative warmer climatic period shawed in the deep-sea oxygen isotope (V21-146 hole) stages 6 and the 2~ nd , 3~ rd and 4~ th warmer climatic periods were corresponding to the warmer climatic event reflected by S2 and to the marine oxygen isotope stage 7. There existed a good relation between the four buried palaeosol layers of Laohushan Xiashu loess section and the four warm, humid climatic periods of the Jurong section. Paleolithic excavation shows a certain amount of stone implements in the 6 and 7 layer, indicating human activities at that time. Magnetic susceptibility and grain-size records suggested a warm and humid environment at that time, which was suitable for the human activity. And, this was in good agreement with the research result from pithecanthrope cave of Tangshan in Nanjing. The stone implements of the Miaohoushan culture in North east China were similar in features to those from North China and Jurong Paleolithic site, probably suggesting that the channel of the Yangtze River used to lie in the south of Jurong, Ningzheng Region.
2002, 20(2): 320-325.
Abstract:
Lower Palaeozoic strata in the Lunnan Low Uplift,of Tarim Basin, China, have recently been found to contain abundant migrated solid bitumen and petroleum-bearing fluid inclusions. In order to determine their origin and timing of the formation, bitumen/inclusion-rich core samples recovered from several wells in the area (mainly carbonate reservoir rocks and carrier units) were examined using a combination of organic petrographic and microthermometric techniques. Based on bitumen reflectance (BR o) measurements, solid bitumens were divided into three main groups, viz. (I) 1.20%～1.35%, (II) 0.80%～0.95% and (III) 0.05% . Hydrocarbon fluid inclusions were also grouped into three different assemblages based on their fluorescence colour and homogeneous temperatures ( T h): (I) yellow-green, T h = 80～90℃; (II) green, T h = 60～70℃ and (III) blue-green fluorescence, T h = 100～150℃. Spatial distributions of fluid inclusion Groups I, II and III within the structure closely match ed those for bitumen Groups I, II and III, respectively, and indicated that there were three separate episodes of large-scale oil migration and accumulation in the uplift. Using the BR o and inclusion Th data in combination with available burial and geothermal history in formation for the area, it was concluded that three corresponding phases of petroleum generation and migration took place during (I) Silurian to early Devonian, (II) Cretaceous to early Tertiary and (III) late Tertiary, from Cambrian-Ordovician source rocks. These findings provide useful insights into the complex origins of oil and gas pools in this region of Tarim Basin.
Lower Palaeozoic strata in the Lunnan Low Uplift,of Tarim Basin, China, have recently been found to contain abundant migrated solid bitumen and petroleum-bearing fluid inclusions. In order to determine their origin and timing of the formation, bitumen/inclusion-rich core samples recovered from several wells in the area (mainly carbonate reservoir rocks and carrier units) were examined using a combination of organic petrographic and microthermometric techniques. Based on bitumen reflectance (BR o) measurements, solid bitumens were divided into three main groups, viz. (I) 1.20%～1.35%, (II) 0.80%～0.95% and (III) 0.05% . Hydrocarbon fluid inclusions were also grouped into three different assemblages based on their fluorescence colour and homogeneous temperatures ( T h): (I) yellow-green, T h = 80～90℃; (II) green, T h = 60～70℃ and (III) blue-green fluorescence, T h = 100～150℃. Spatial distributions of fluid inclusion Groups I, II and III within the structure closely match ed those for bitumen Groups I, II and III, respectively, and indicated that there were three separate episodes of large-scale oil migration and accumulation in the uplift. Using the BR o and inclusion Th data in combination with available burial and geothermal history in formation for the area, it was concluded that three corresponding phases of petroleum generation and migration took place during (I) Silurian to early Devonian, (II) Cretaceous to early Tertiary and (III) late Tertiary, from Cambrian-Ordovician source rocks. These findings provide useful insights into the complex origins of oil and gas pools in this region of Tarim Basin.
2002, 20(2): 333-338.
Abstract:
Secondary petroleum migration is a complex geological phenomenon. This paper primarily discusses the changeable features of the process through the modelling experiment of secondary migration using the reservoir sandstone with ultra-low porosity and permeability. The experimental results indicate the average oiliness saturation in a horizontal migrating zone is 15%～25% under a hydrostatic condition, and the migrating efficiency is better. During migration, saturated , aromatic and non-hydrocarbons have a good relation with oiliness saturation. Driving power of secondary petroleum migration is a critical factor that controls migrating efficiency when the difference in conduits is very little. Oiliness saturation can be easily obtained in the conduits with good porosity and permeability.
Secondary petroleum migration is a complex geological phenomenon. This paper primarily discusses the changeable features of the process through the modelling experiment of secondary migration using the reservoir sandstone with ultra-low porosity and permeability. The experimental results indicate the average oiliness saturation in a horizontal migrating zone is 15%～25% under a hydrostatic condition, and the migrating efficiency is better. During migration, saturated , aromatic and non-hydrocarbons have a good relation with oiliness saturation. Driving power of secondary petroleum migration is a critical factor that controls migrating efficiency when the difference in conduits is very little. Oiliness saturation can be easily obtained in the conduits with good porosity and permeability.
2002, 20(2): 345-348.
Abstract:
The fluid inclusions in Sangonghe Formation of Jurassic in Yanqi basin Northwest China were investigated. The fluid inclusions in Sangonghe Formation , which mostly occurred in the dissolution or pressure solution pores of quartz grains, were usually small in their size and low in their abundance. Up to 80% of organic inclusions existed in the state of liquid hydrocarbon phase, only some 20% of them in gaseous and gaseous-liquid hydrocarbon phases. In addition to organic inclusions, there were some saline-aqueous solution inclusions. Combined with the evolution history of the diagenesis and organic matter maturation, the fluid inclusions were mainly formed in the stage of late diagenesis in late Jurassic. The homogenization temperatures of inclusions fell in the temperature interval of 101～130℃, with ranges of 101～110℃ and of 121～130℃ as two peaks. According to the temperature history of Sangonghe Formation, the temperature of 101～110℃ was consistent with the temperature of Sangonghe Formation in late Jurassic and the peak of 121～130℃ with the temperature in the end of Jurassic when the formation reached its deepest burial in geohistory. The composition of hydrocarbon inclusion also showed two peaks in gas chromatogram with one peak in C 18 or C 20 and the other in C 26 or C 27 , which indicated the two formation periods of the inclusion. The maturity indices of inclusion component showed that the inclusions were formed in low mature stage of source rock. In summary, the fluid inclusion of Sangonghe formation of Jurassic in Yanqi basin were mainly formed in two periods, with one in late Jurassic when the source rock of the basin was in low mature stage, and the other in the end of Jurassic when the formation reached its deepest burial and the source rock in mature stage.
The fluid inclusions in Sangonghe Formation of Jurassic in Yanqi basin Northwest China were investigated. The fluid inclusions in Sangonghe Formation , which mostly occurred in the dissolution or pressure solution pores of quartz grains, were usually small in their size and low in their abundance. Up to 80% of organic inclusions existed in the state of liquid hydrocarbon phase, only some 20% of them in gaseous and gaseous-liquid hydrocarbon phases. In addition to organic inclusions, there were some saline-aqueous solution inclusions. Combined with the evolution history of the diagenesis and organic matter maturation, the fluid inclusions were mainly formed in the stage of late diagenesis in late Jurassic. The homogenization temperatures of inclusions fell in the temperature interval of 101～130℃, with ranges of 101～110℃ and of 121～130℃ as two peaks. According to the temperature history of Sangonghe Formation, the temperature of 101～110℃ was consistent with the temperature of Sangonghe Formation in late Jurassic and the peak of 121～130℃ with the temperature in the end of Jurassic when the formation reached its deepest burial in geohistory. The composition of hydrocarbon inclusion also showed two peaks in gas chromatogram with one peak in C 18 or C 20 and the other in C 26 or C 27 , which indicated the two formation periods of the inclusion. The maturity indices of inclusion component showed that the inclusions were formed in low mature stage of source rock. In summary, the fluid inclusion of Sangonghe formation of Jurassic in Yanqi basin were mainly formed in two periods, with one in late Jurassic when the source rock of the basin was in low mature stage, and the other in the end of Jurassic when the formation reached its deepest burial and the source rock in mature stage.
2002, 20(2): 354-358.
Abstract:
PC99 is a Microsoft Windows 95/98/2000-based, Visual Basic freeware program. It utilizes a simple interface that facilitates the graphical presentation, statistical analysis, and comparison of paleocurrent data files. The graphical presentation formats supported by PC99 are rose and circular diagrams. Circular diagrams allow up to 10 individual and/or composite paleocurrent data files to be simulfaneously displayed and compared. Rose diagrams may be generated with a choice of radial scale, and petal width, thus aiding interpretation of paleocurrent patterns. Paleocurrent data of the Cenozoic Hoh Xil Basin, northern Tibet, are presented and their spatiotemporal distribution characteristics are examined by using PC99. We found PC99 a highly efficient tool for the graphical display and interpretation of paleocurrent data.
PC99 is a Microsoft Windows 95/98/2000-based, Visual Basic freeware program. It utilizes a simple interface that facilitates the graphical presentation, statistical analysis, and comparison of paleocurrent data files. The graphical presentation formats supported by PC99 are rose and circular diagrams. Circular diagrams allow up to 10 individual and/or composite paleocurrent data files to be simulfaneously displayed and compared. Rose diagrams may be generated with a choice of radial scale, and petal width, thus aiding interpretation of paleocurrent patterns. Paleocurrent data of the Cenozoic Hoh Xil Basin, northern Tibet, are presented and their spatiotemporal distribution characteristics are examined by using PC99. We found PC99 a highly efficient tool for the graphical display and interpretation of paleocurrent data.
2002, 20(2): 188-196.
Abstract:
A series of steady carbonate and clastic rocks of coastal-shallow sea facies were deposited in the Nadigangri area,Qiangtang Basin,during the middle Jurassic. The middle Jurassic can be divided into five 3rd-graded sequences through sequence interpretation . On the basis of C, O and Sr isotopic compositions of four of those, δ13 C、δ180、N(87Sr/86Sr) values are all of distinct difference and regularity among different sequences, sequence boundaries and systems stracts. It is suggested that the going up and down of sea level occurred many times and the climate and tectonics change during the middle Jurassic, which controlled the formation and evolution of the middle Jurassic sequences. As a result, C, O and Sr isotopes can provide some quantitative geological and geochemical evidence for analyzing the middle Jurassic sequence.
A series of steady carbonate and clastic rocks of coastal-shallow sea facies were deposited in the Nadigangri area,Qiangtang Basin,during the middle Jurassic. The middle Jurassic can be divided into five 3rd-graded sequences through sequence interpretation . On the basis of C, O and Sr isotopic compositions of four of those, δ13 C、δ180、N(87Sr/86Sr) values are all of distinct difference and regularity among different sequences, sequence boundaries and systems stracts. It is suggested that the going up and down of sea level occurred many times and the climate and tectonics change during the middle Jurassic, which controlled the formation and evolution of the middle Jurassic sequences. As a result, C, O and Sr isotopes can provide some quantitative geological and geochemical evidence for analyzing the middle Jurassic sequence.
2002, 20(2): 203-209.
Abstract:
According to the identification mark of the short-term base-level cylce interface and under the guidance of the theory and technology of the high-resolution sequence stratigraphy, the authors divide the short-term base-level cycle of Nadu Formation in Baise Basin into three basic structure types which are up-deepening non-symmetry, up-shallowing non-symmetry and symmetry from up-deepening to up-shallowing. Furtherly in the light of the high or low accommodation, and the thickness of the uprising periods and subsiding periods of the short-term base-level cycle, seven subtypes of structure are distinguished and they are up-deepening non-symmetry of low accommodation (Type A1) or high accommodation(Type A2)up-shallowening non-symmetry of low accommodation (TypeB1) or high accommodation (Type B2)complete～nearly complete symmetry (Type C1)in complete symmetry with the majority of uprising semi-cycle(Type C2) or subsiding semi-cycle(Type C3).In this paper the sedimentary environment,stacking patterns,lithlolgic association and sedimentary dynamic processes of each basic type and subtype of structure is discussed in detail. And the development position of the advantage reservoir sand body in each structure type are pointed out. On the basis of these studies, the change rule and distribution pattern of the short-term base-level cycle sequence are summarized. From the terrigenous to lacustrine environment, the short-term base level cycle sequence types have the change rule that is in succession from Type A1 to Type A2, then to Type C2, to Type C1 Type C3 Type B1 and at last to Type B2.In the structure types of short-term base-level cycle sequence, the advantage reservoir sand body mainly develops in Type A1, secondly in Type A2Type B1 and Type C1. In this paper, the authors also briefly discuss the application of the short-term base-level cycle sequence in oil and gas exploration and development stage.
According to the identification mark of the short-term base-level cylce interface and under the guidance of the theory and technology of the high-resolution sequence stratigraphy, the authors divide the short-term base-level cycle of Nadu Formation in Baise Basin into three basic structure types which are up-deepening non-symmetry, up-shallowing non-symmetry and symmetry from up-deepening to up-shallowing. Furtherly in the light of the high or low accommodation, and the thickness of the uprising periods and subsiding periods of the short-term base-level cycle, seven subtypes of structure are distinguished and they are up-deepening non-symmetry of low accommodation (Type A1) or high accommodation(Type A2)up-shallowening non-symmetry of low accommodation (TypeB1) or high accommodation (Type B2)complete～nearly complete symmetry (Type C1)in complete symmetry with the majority of uprising semi-cycle(Type C2) or subsiding semi-cycle(Type C3).In this paper the sedimentary environment,stacking patterns,lithlolgic association and sedimentary dynamic processes of each basic type and subtype of structure is discussed in detail. And the development position of the advantage reservoir sand body in each structure type are pointed out. On the basis of these studies, the change rule and distribution pattern of the short-term base-level cycle sequence are summarized. From the terrigenous to lacustrine environment, the short-term base level cycle sequence types have the change rule that is in succession from Type A1 to Type A2, then to Type C2, to Type C1 Type C3 Type B1 and at last to Type B2.In the structure types of short-term base-level cycle sequence, the advantage reservoir sand body mainly develops in Type A1, secondly in Type A2Type B1 and Type C1. In this paper, the authors also briefly discuss the application of the short-term base-level cycle sequence in oil and gas exploration and development stage.
2002, 20(2): 217-221.
Abstract:
Sequence stratigraphic research in lake basin has got good application, which takes a significant role in stratigraphic correlation and sedimentary system distributing prediction in lake basin. Topographic ramp often come into being in the edge of depression lake basin in the process of basin basement deformation under extrusion stress, the key factors controlling sequence development such as subsiding rate of basement and initial topographic slope have apparent difference on the two sides of ramp, which in turn has controlled the sequence development model and the space allocating relation of sedimentary system to great extent. By constructing mathematics model of basement subsiding rate, changing rate of lake water surface, sediments filling rate, sediments filling rule, and facies defining rule, computer simulation were put forward to recur the sequence developing and facies changing procedures in lake basin with topographic ramp. Comparison between actual data with simulating shows that the simulation result is available.
Sequence stratigraphic research in lake basin has got good application, which takes a significant role in stratigraphic correlation and sedimentary system distributing prediction in lake basin. Topographic ramp often come into being in the edge of depression lake basin in the process of basin basement deformation under extrusion stress, the key factors controlling sequence development such as subsiding rate of basement and initial topographic slope have apparent difference on the two sides of ramp, which in turn has controlled the sequence development model and the space allocating relation of sedimentary system to great extent. By constructing mathematics model of basement subsiding rate, changing rate of lake water surface, sediments filling rate, sediments filling rule, and facies defining rule, computer simulation were put forward to recur the sequence developing and facies changing procedures in lake basin with topographic ramp. Comparison between actual data with simulating shows that the simulation result is available.
2002, 20(2): 229-237.
Abstract:
For the first time, the paper systematically rebuilds the Mesozoic lithofacies and palaeogeography in the Chalangla area of Qiangtang Basin in Northern Tibet by using methods of stratigraphically dominant facies/subfacies and integrated analyses. This is on the basis of the measured sections and route geologic survey profiles as well as sedimentary facies analyses. Marine-continental transition facies were dominant in Late Triassic, forming regression sedimentary cycles and consequently developing delta facies, coastal facies, and littoral-neritic facies belt from NE towards SW. In the Middle Jurassic epoch developed neritic facies deposits, consequently delta-platform-neritic continental shelf facies occurred from NE towards SW and displayed in NWW～SEE direction. Twice marine transgression peaks occurred at J2 q Period and J2 b Period,and constituted two sedimentary cycles from marine ingression to regression. In the Late Jurassic epoch developed sea-continental transitional facies,which were delta, tidal flat, platform facies belts and displayed in NW～SE direction.In the Cretaceous period discrepancy in lithofacies and palaeogeography was present from the early to late. In the early stage developed platform edge shallow facies to restricted platform facies on the background of remnant sea, which formed the third marine transgression peak. After rapid overall swelling, in the late stage occurred alluvial fan-braided river facies sedimentary cycles made of red polyterrigenous molasse deposits with multi-source supplying. The Mesozoic provenance was mainly the central uplift belt in the north, and secondly the highland in the east and uplift region in the west. In the process of sedimentary evolution, sedimentary source areas were different in different geologic ages, and the terrain in general,was characteristic of being higher in north and east but lower in south and west.
For the first time, the paper systematically rebuilds the Mesozoic lithofacies and palaeogeography in the Chalangla area of Qiangtang Basin in Northern Tibet by using methods of stratigraphically dominant facies/subfacies and integrated analyses. This is on the basis of the measured sections and route geologic survey profiles as well as sedimentary facies analyses. Marine-continental transition facies were dominant in Late Triassic, forming regression sedimentary cycles and consequently developing delta facies, coastal facies, and littoral-neritic facies belt from NE towards SW. In the Middle Jurassic epoch developed neritic facies deposits, consequently delta-platform-neritic continental shelf facies occurred from NE towards SW and displayed in NWW～SEE direction. Twice marine transgression peaks occurred at J2 q Period and J2 b Period,and constituted two sedimentary cycles from marine ingression to regression. In the Late Jurassic epoch developed sea-continental transitional facies,which were delta, tidal flat, platform facies belts and displayed in NW～SE direction.In the Cretaceous period discrepancy in lithofacies and palaeogeography was present from the early to late. In the early stage developed platform edge shallow facies to restricted platform facies on the background of remnant sea, which formed the third marine transgression peak. After rapid overall swelling, in the late stage occurred alluvial fan-braided river facies sedimentary cycles made of red polyterrigenous molasse deposits with multi-source supplying. The Mesozoic provenance was mainly the central uplift belt in the north, and secondly the highland in the east and uplift region in the west. In the process of sedimentary evolution, sedimentary source areas were different in different geologic ages, and the terrain in general,was characteristic of being higher in north and east but lower in south and west.
2002, 20(2): 243-248.
Abstract:
As one of the special bioherms, mud mounds (micrite mounds) developed during the Paleozoic. According to recent researches, many experts in the world have believed that many mud mounds be built by different microbes in the Paleozoic, the lime mud sediments and the mud mounds built by cynobacteria have also been found in modern lakes. But the body fossils of microbes such as bacteria have not been seen in the Paleozoic mud mounds, and the function of the microbial biosedimentation buildup, and how the bacteria made carbonate deposition are not clear. During Early Paleozoic, there were many mud mounds developed in the north Sichuan. According to the SEM studies, the authors found three kinds of microbial body fossils from the Silurian mud mounds and the microbial biosedimentation:1.Smooth ball-like body fossil with egg shape,5μm × 3μm in size; 2. Rough ellipsoid fossil, 60μm×50μm in size; 3. Foamed network-like fossil formed by foamed network biofilm material covered the micrite. The biomarks analyses also proved that the microbial materials are in mud mounds. The microbial body fossils of mud mounds shower different functiosn of biosedimentation buildupmentation. The studies confirmed the microbes were very important in the mud mound formation in Paleozoic.
As one of the special bioherms, mud mounds (micrite mounds) developed during the Paleozoic. According to recent researches, many experts in the world have believed that many mud mounds be built by different microbes in the Paleozoic, the lime mud sediments and the mud mounds built by cynobacteria have also been found in modern lakes. But the body fossils of microbes such as bacteria have not been seen in the Paleozoic mud mounds, and the function of the microbial biosedimentation buildup, and how the bacteria made carbonate deposition are not clear. During Early Paleozoic, there were many mud mounds developed in the north Sichuan. According to the SEM studies, the authors found three kinds of microbial body fossils from the Silurian mud mounds and the microbial biosedimentation:1.Smooth ball-like body fossil with egg shape,5μm × 3μm in size; 2. Rough ellipsoid fossil, 60μm×50μm in size; 3. Foamed network-like fossil formed by foamed network biofilm material covered the micrite. The biomarks analyses also proved that the microbial materials are in mud mounds. The microbial body fossils of mud mounds shower different functiosn of biosedimentation buildupmentation. The studies confirmed the microbes were very important in the mud mound formation in Paleozoic.
2002, 20(2): 255-260.
Abstract:
Since the 1970~s, sedimentology has entered into a quantitative study era. The Europe an sedimentologist creatively did a lot of quantitative study on ancient ripple marks in the marine sediments in Alps and lacustrine sediments in Shedland of England in the 1980s. A series of mathematical formulae have been established. A number of physical parameters of sedimentary environments of Changchengian quartz sandstones A, B, and C in the Xuanhua area, northwest Hebei are estimated based on the mathematical formula in this study. The calculation results show the velocities of water particles of sedimentary environments from sandstones A via B to C becom smaller, then bigger; the motion periods for water particles become shorter, then longer; the water depths of environments become shallower, then deeper; the wave heights of waters become lower, then higher; the energy of waters becomes smaller, then larger. These estimations are in fair harmony with the observations in the field. The grain size analyses demonstrate the jumping population of sandstones dominated in sedimentary environments and the suspension population at 20～40% of the total grains. No tractive population is present in the analyzed samples. So,the grains are transport in the form of jumping and suspension. in shallower water bodies.
Since the 1970~s, sedimentology has entered into a quantitative study era. The Europe an sedimentologist creatively did a lot of quantitative study on ancient ripple marks in the marine sediments in Alps and lacustrine sediments in Shedland of England in the 1980s. A series of mathematical formulae have been established. A number of physical parameters of sedimentary environments of Changchengian quartz sandstones A, B, and C in the Xuanhua area, northwest Hebei are estimated based on the mathematical formula in this study. The calculation results show the velocities of water particles of sedimentary environments from sandstones A via B to C becom smaller, then bigger; the motion periods for water particles become shorter, then longer; the water depths of environments become shallower, then deeper; the wave heights of waters become lower, then higher; the energy of waters becomes smaller, then larger. These estimations are in fair harmony with the observations in the field. The grain size analyses demonstrate the jumping population of sandstones dominated in sedimentary environments and the suspension population at 20～40% of the total grains. No tractive population is present in the analyzed samples. So,the grains are transport in the form of jumping and suspension. in shallower water bodies.
2002, 20(2): 267-273.
Abstract:
The Tan-Lu fault zone in northern Anhui occurs between the Zhangbaling uplift belt in the east and the Hefei basin in the waet.Isotopic dating of strike-slip mylonites, ultramylonite as well as associated igneous rocks in uplift belt indicated that the strike-slip displacement of the fault zone took place in early Cretaceous. A series of structural and sedimentary studies demonstrated that the early Cretaceous strike-slip movement on the Tan-Lu fault zone caused the Zhangbaling uplift belt with a NNE strike to the east of the Hefei basin, which therefore became source region of the basin. Correspondingly NNE Daiqiao-Heidong depression with deposition of the Zhuxiang formation appeared in the east of the Hefei basin. The depression was considered as a strike-slip flexure basin. It was developed in a strike-slip depression to the west of the Zhangbaling strike-slip uplift belt.
The Tan-Lu fault zone in northern Anhui occurs between the Zhangbaling uplift belt in the east and the Hefei basin in the waet.Isotopic dating of strike-slip mylonites, ultramylonite as well as associated igneous rocks in uplift belt indicated that the strike-slip displacement of the fault zone took place in early Cretaceous. A series of structural and sedimentary studies demonstrated that the early Cretaceous strike-slip movement on the Tan-Lu fault zone caused the Zhangbaling uplift belt with a NNE strike to the east of the Hefei basin, which therefore became source region of the basin. Correspondingly NNE Daiqiao-Heidong depression with deposition of the Zhuxiang formation appeared in the east of the Hefei basin. The depression was considered as a strike-slip flexure basin. It was developed in a strike-slip depression to the west of the Zhangbaling strike-slip uplift belt.
2002, 20(2): 282-287.
Abstract:
The late Cenozoic uplift of the Tibetan Plateau played a great role in the geomorphic and depositional evolution of its adjacent areas. This effect has brought about the Liupan Mountain at the northeastern tectonic margin of the Tibetan Plateau developed with quite different geomorphology in its two sides, resulting in large differences in wind-blown depositional environment between the eastern and western parts of the Chinese Loess Plateau. A well-preserved pediment, covered by 235 m thick loess, was recently found at the western side of the Liupan Mountain, which stands above the highest terrace of the Yellow River in the northeastern Longzhong Basin. The paleomagnetism of the loess section shows that the pediment developed at ～1.8 Ma BP, so did that of the pediments in Lanzhou-Linxia region in the southwestern Longzhong Basin. This implies that the Longzhong Basin to the west of the Liupan Mountain had been subject to long term denudation before ～1.8 Ma BP, and wight have finally developed a joined pediment or so-called Gansu Peneplain covering the whole Longzhong Basin. The large incision of the pediment and start of deposition of loess on the pediment at ～1.8 Ma BP suggest that the Tibetan Plateau and the Liupan Mountain rose strongly at that time, causing not only the end of the pediment but also the subsequent appearance of the Yellow River in the Basin.
The late Cenozoic uplift of the Tibetan Plateau played a great role in the geomorphic and depositional evolution of its adjacent areas. This effect has brought about the Liupan Mountain at the northeastern tectonic margin of the Tibetan Plateau developed with quite different geomorphology in its two sides, resulting in large differences in wind-blown depositional environment between the eastern and western parts of the Chinese Loess Plateau. A well-preserved pediment, covered by 235 m thick loess, was recently found at the western side of the Liupan Mountain, which stands above the highest terrace of the Yellow River in the northeastern Longzhong Basin. The paleomagnetism of the loess section shows that the pediment developed at ～1.8 Ma BP, so did that of the pediments in Lanzhou-Linxia region in the southwestern Longzhong Basin. This implies that the Longzhong Basin to the west of the Liupan Mountain had been subject to long term denudation before ～1.8 Ma BP, and wight have finally developed a joined pediment or so-called Gansu Peneplain covering the whole Longzhong Basin. The large incision of the pediment and start of deposition of loess on the pediment at ～1.8 Ma BP suggest that the Tibetan Plateau and the Liupan Mountain rose strongly at that time, causing not only the end of the pediment but also the subsequent appearance of the Yellow River in the Basin.
2002, 20(2): 293-302.
Abstract:
Mircrofabrics from core sediments were observed in polarizing microscope and scanning microscope and used in interpreting the origin of three types of clay as well as the changes of sedimentary environments in four sites-the Honghu Lake,the Donghu Lake,the Wanghu Lake and the Dajiuhu Lake along the middle reach of the Yangtze River.Micro-beddings,orientation of particles and large sizes of micro-voids and particles with contacting patterns of face to face or edge to edge occurred in the light-colored clay formed since 0.4～0.5ka BP in the lakes.Their origin was ascirbed to clastic sediments from rivers surrounding the lakes.It was suggested that the lakes were connected with rivers and large amount of sedimens came from rivers into the lakes during that period.The typical microfabrics in the blue clay formed in 1～2.5ka BP were gelatinous texture,agglutinational texture,small sizes of particles and voids,low sphericity and diatoms of freshwater Class Centrium .Their origin was ascribed to the result of the interaction between organic colloids and clay colloids.It was suggested that the lakes in the Jianghan plain were of open and stable fresh water lake environments rich in planktons and with small amount of clay carried by rivers during this period.The main microfabrics in the black clay formed during 0.4～1ka Bp were gelatinous texture,large circular voids and plant fiber.The voids had a bimodal distribution.The sediment was formed mainly due to the accumulation of large amount of aquatic vascular bundle plants.It was suggested that the lakes were shallow and rich in aquatic vascular bundle plants,and some of them were swamping.The framework of fish bone in the sediments indicated that there was large number of fish in the Dajiuhu area during the Holocene warm period of 2.9～4ka BP,but the thermophilous fish did not migrate upwards apparently.
Mircrofabrics from core sediments were observed in polarizing microscope and scanning microscope and used in interpreting the origin of three types of clay as well as the changes of sedimentary environments in four sites-the Honghu Lake,the Donghu Lake,the Wanghu Lake and the Dajiuhu Lake along the middle reach of the Yangtze River.Micro-beddings,orientation of particles and large sizes of micro-voids and particles with contacting patterns of face to face or edge to edge occurred in the light-colored clay formed since 0.4～0.5ka BP in the lakes.Their origin was ascirbed to clastic sediments from rivers surrounding the lakes.It was suggested that the lakes were connected with rivers and large amount of sedimens came from rivers into the lakes during that period.The typical microfabrics in the blue clay formed in 1～2.5ka BP were gelatinous texture,agglutinational texture,small sizes of particles and voids,low sphericity and diatoms of freshwater Class Centrium .Their origin was ascribed to the result of the interaction between organic colloids and clay colloids.It was suggested that the lakes in the Jianghan plain were of open and stable fresh water lake environments rich in planktons and with small amount of clay carried by rivers during this period.The main microfabrics in the black clay formed during 0.4～1ka Bp were gelatinous texture,large circular voids and plant fiber.The voids had a bimodal distribution.The sediment was formed mainly due to the accumulation of large amount of aquatic vascular bundle plants.It was suggested that the lakes were shallow and rich in aquatic vascular bundle plants,and some of them were swamping.The framework of fish bone in the sediments indicated that there was large number of fish in the Dajiuhu area during the Holocene warm period of 2.9～4ka BP,but the thermophilous fish did not migrate upwards apparently.
2002, 20(2): 314-319.
Abstract:
The Kuche petroleum system is a forland type one riched in oil and particularly natural gas generated from the Triassic and Jurassic source rocks including coal source. Many natural gas and condensate fields as well as some oil fields have been discovered, of which the natural gas and condensate are thought to have been generated mainly from coal source of Jurassic and the normal oil from the Triassic mudstone source. Study of these fields' accumulation timing and filling history is significant to exploration in Kuche and therefore the major concern of this paper. Based on synthetic analyses of trap timing, reservoir geochemistry (gas maturity correlation), hydrocarbon fluid inclusions, dew-point pressure and oil/gas-water contact evolution, 3 periods of the formation and filling history of oil and natural gas reservoirs in the Kuche petroleum system are discerned, i.e. early-middle Kangcun period (17～10 Ma), late Kangcun to early-middle Kuche period (10～3 Ma) and late Kuche to Xiyu period (3～1 Ma). The late Kuche to Xiyu period is the major one for formation of natural gas fields of high maturity to over-maturity in Kuche forland thrust belts, in which the discovered gas fields of Kela 2, Kela 3, Dabei 1, Yinan 2 and Tuzi 1 were formed. The late Kangcun to early-middle Kuche period is a critical moment for accumulation of oil and condensate of low to intermediate maturity. And the early-middle Kuche period is a minor one for formation of low-maturity oil and gas reservoirs sourced from coal-type organic matter. Oil and gas fields of early-middle Kangcun and late Kangcun to early-middle Kuche periods were distributed mainly in the Luntai uplift, whereas gas fields of late Kuche to Xiyu period totally in the Kuche forland thrust belts. The early formed oil and condensate accumulations in the forland thrust belts, if there is, have possibly been adjusted and even destroyed by the later strong orogeny and/or the intrusion of natural gas of high maturity and over maturity. The remanined oil accumulations in the thrust belts were mostly secondary reformed during the late Kuche to Xiyu period.
The Kuche petroleum system is a forland type one riched in oil and particularly natural gas generated from the Triassic and Jurassic source rocks including coal source. Many natural gas and condensate fields as well as some oil fields have been discovered, of which the natural gas and condensate are thought to have been generated mainly from coal source of Jurassic and the normal oil from the Triassic mudstone source. Study of these fields' accumulation timing and filling history is significant to exploration in Kuche and therefore the major concern of this paper. Based on synthetic analyses of trap timing, reservoir geochemistry (gas maturity correlation), hydrocarbon fluid inclusions, dew-point pressure and oil/gas-water contact evolution, 3 periods of the formation and filling history of oil and natural gas reservoirs in the Kuche petroleum system are discerned, i.e. early-middle Kangcun period (17～10 Ma), late Kangcun to early-middle Kuche period (10～3 Ma) and late Kuche to Xiyu period (3～1 Ma). The late Kuche to Xiyu period is the major one for formation of natural gas fields of high maturity to over-maturity in Kuche forland thrust belts, in which the discovered gas fields of Kela 2, Kela 3, Dabei 1, Yinan 2 and Tuzi 1 were formed. The late Kangcun to early-middle Kuche period is a critical moment for accumulation of oil and condensate of low to intermediate maturity. And the early-middle Kuche period is a minor one for formation of low-maturity oil and gas reservoirs sourced from coal-type organic matter. Oil and gas fields of early-middle Kangcun and late Kangcun to early-middle Kuche periods were distributed mainly in the Luntai uplift, whereas gas fields of late Kuche to Xiyu period totally in the Kuche forland thrust belts. The early formed oil and condensate accumulations in the forland thrust belts, if there is, have possibly been adjusted and even destroyed by the later strong orogeny and/or the intrusion of natural gas of high maturity and over maturity. The remanined oil accumulations in the thrust belts were mostly secondary reformed during the late Kuche to Xiyu period.
2002, 20(2): 326-332.
Abstract:
In the Quaternary formation and Upper-Tertiary formation of Yinggehai Basin, except for abnormal pressure and compaction, there are mainly four factors affecting acoustic time, which are lithology variation, cementation, gas in the formation and crack. They usually co-exist and are difficult to distinguish. According to the ideology of seismic processing, i.e., pre-stack noise attenuation/signal enhancement, we superpose multi-wells' acoustic time data of the same local region. In result, the information of reflecting pore characters enhances. It is an effective method to avoid other factors to disturb acoustic velocity. Furthermore, applying this method in processing velocity spectra, the predicted result of the formation pressure conforms to the measured pressure during drilling.
In the Quaternary formation and Upper-Tertiary formation of Yinggehai Basin, except for abnormal pressure and compaction, there are mainly four factors affecting acoustic time, which are lithology variation, cementation, gas in the formation and crack. They usually co-exist and are difficult to distinguish. According to the ideology of seismic processing, i.e., pre-stack noise attenuation/signal enhancement, we superpose multi-wells' acoustic time data of the same local region. In result, the information of reflecting pore characters enhances. It is an effective method to avoid other factors to disturb acoustic velocity. Furthermore, applying this method in processing velocity spectra, the predicted result of the formation pressure conforms to the measured pressure during drilling.
2002, 20(2): 339-344.
Abstract:
The hydrodynamics has been an important content in basin analysis and petroleum exploration. Before the characteristics of fluid migration and accumulation being studied, evolution history of paleo-hydrodynamics must be restored first of all, because of being as specific history events set in geologically history periods. The outline of paleo-hydrodynamics evolution could be obtained by means of integrating methods of compaction curves analysis, basin numerical modelling and fluid enclosure determining. It is discovered that the development and evolution of paleo-hydrodynamics are of cycles, on the background of cycling evolution of basins, by way of restoring and investigating paleo-hydrodynamics in NW China petroliferous basins. The hydrodynamic cycle is charactertic ot evolution of overpressure along with times composed of two or more circulations from increasing to decreasing, and plane distribution of fluid potentials being of several stages in different geologic periods. So the characteristics of fluid migration, accumulation and pool forming lying on hydrodynamic environments are formed, such as multi-phase of main expulsion, stages of hydrocarbon secondary migration and accumulation, divergence of reservoir distribution between geologic periods and present .
The hydrodynamics has been an important content in basin analysis and petroleum exploration. Before the characteristics of fluid migration and accumulation being studied, evolution history of paleo-hydrodynamics must be restored first of all, because of being as specific history events set in geologically history periods. The outline of paleo-hydrodynamics evolution could be obtained by means of integrating methods of compaction curves analysis, basin numerical modelling and fluid enclosure determining. It is discovered that the development and evolution of paleo-hydrodynamics are of cycles, on the background of cycling evolution of basins, by way of restoring and investigating paleo-hydrodynamics in NW China petroliferous basins. The hydrodynamic cycle is charactertic ot evolution of overpressure along with times composed of two or more circulations from increasing to decreasing, and plane distribution of fluid potentials being of several stages in different geologic periods. So the characteristics of fluid migration, accumulation and pool forming lying on hydrodynamic environments are formed, such as multi-phase of main expulsion, stages of hydrocarbon secondary migration and accumulation, divergence of reservoir distribution between geologic periods and present .
2002, 20(2): 349-353.
Abstract:
Changxing Reef of Upper Permian and Feixianguan oolitic beach of Lower Triassic are the focus point of exploration work in Sichuan Basin during the ninth-five-year-plan. Through the study on organic geochemistry of source rocks of Upper Permian and Lower Triassic, reservoir bitumen and natural gases of Changxin Fm. reef and Feixianguan Fm. oolitic beach gas reservoirs, the shoreside coal measures mudstone and the sea trough carbonate of Upper Permian Series have been defined as the main source rocks,which are high maturate and controlled by the different sedimentary facies, and the reservoir bitumen and natural gases of Changxing Fm. reef and Feixianguan Fm. oolitic beach gas reservoirs are originated from the source rock of Upper Permian Series, the natural gas is a dry gas being thermally degraded from oil, the solid bitumen is a residue of oil retained in reservoir rocks, and the migration of natural gases is mainly vertical. The volume of H 2S is high in some exploratory wells of Feixianguan Fm. oolitic beach gas reservoirs, such as Gaofengchang, Longmen, Tieshanpo, Dukouhe, Luojiazhai structure, etc. H 2S is associated with the distribution of anhydrite in Feixianguan Fm. oolitic beach reservoir and related with the thermochemical sulfate reduction (TSR).And all above are closely related with the sedimentary facies.
Changxing Reef of Upper Permian and Feixianguan oolitic beach of Lower Triassic are the focus point of exploration work in Sichuan Basin during the ninth-five-year-plan. Through the study on organic geochemistry of source rocks of Upper Permian and Lower Triassic, reservoir bitumen and natural gases of Changxin Fm. reef and Feixianguan Fm. oolitic beach gas reservoirs, the shoreside coal measures mudstone and the sea trough carbonate of Upper Permian Series have been defined as the main source rocks,which are high maturate and controlled by the different sedimentary facies, and the reservoir bitumen and natural gases of Changxing Fm. reef and Feixianguan Fm. oolitic beach gas reservoirs are originated from the source rock of Upper Permian Series, the natural gas is a dry gas being thermally degraded from oil, the solid bitumen is a residue of oil retained in reservoir rocks, and the migration of natural gases is mainly vertical. The volume of H 2S is high in some exploratory wells of Feixianguan Fm. oolitic beach gas reservoirs, such as Gaofengchang, Longmen, Tieshanpo, Dukouhe, Luojiazhai structure, etc. H 2S is associated with the distribution of anhydrite in Feixianguan Fm. oolitic beach reservoir and related with the thermochemical sulfate reduction (TSR).And all above are closely related with the sedimentary facies.
