2000 Vol. 18, No. 4
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Display Method:
2000, 18(4): 489-494.
Abstract:
Trace fossils are proving to be powerful tools for recognition and interpretation of event beds. Tempestites contain a mixed trace fossil assemblage that reflects fluctuations in energy levels. The two different ichnocoenoses reflect varying behavioral responses of the organisms colonizing two successive, individually distinct habitats. The resident or fair weather ichnocoenose can be considered representative of a stable benthic community, within which individual populations are at or near their carrying capacity. Periodic generation of the storm ichnocoenose, on the other hand, represents the flourishing of a community of opportunistic organisms in an unstable, high stress, physically controlled environment. The general succession, typical terrigenous tempestites represented by the tempestites in the Upper Cretaceous Cardium Fm. of Alberta, Canada, consists of (1)a fair weather resident trace fossil suite; (2) a sharp basal contact, with or without a basal lag; (3)parallel to subparallel laminations (reflecting hummocky or swaley cross stratification); (4)common escape structures; (5) the dwelling burrows of opportunistic organisms that colonize the unexploited storm unit; (6) gradational burrowed tops, representative of bioturbation resulting from subsequent burrowing by organisms from higher colonization levels; and (7) a fair weather resident trace fossil suite indicative of a return to quiescent conditions following abatement. Up to now, the ichnology in the carbonate tempestites has not been well studied and reported. The succession found in the Upper Cambrian Gushan Fm. from eastern North China Platform can be regarded as the typical carbonate tempestites. The succession includes the following parts (from bottom to top): (1) the trace fossils on the sole of the thin bedded limestone containing Phycodes, Thalassinoides, Palaeophycus and Planolites etc; (2) 1-2 cm thick muddy limestone or limestone with or without lamination; (3) the opportunistic trace fossils Diplocraterion, Arenicolites and Skolithos on the surface of the limestone; (4) the surface of the limestone covered by about 1 mm thick trilobite debris; (5)1-2 mm thick mudstone or shale.
Trace fossils are proving to be powerful tools for recognition and interpretation of event beds. Tempestites contain a mixed trace fossil assemblage that reflects fluctuations in energy levels. The two different ichnocoenoses reflect varying behavioral responses of the organisms colonizing two successive, individually distinct habitats. The resident or fair weather ichnocoenose can be considered representative of a stable benthic community, within which individual populations are at or near their carrying capacity. Periodic generation of the storm ichnocoenose, on the other hand, represents the flourishing of a community of opportunistic organisms in an unstable, high stress, physically controlled environment. The general succession, typical terrigenous tempestites represented by the tempestites in the Upper Cretaceous Cardium Fm. of Alberta, Canada, consists of (1)a fair weather resident trace fossil suite; (2) a sharp basal contact, with or without a basal lag; (3)parallel to subparallel laminations (reflecting hummocky or swaley cross stratification); (4)common escape structures; (5) the dwelling burrows of opportunistic organisms that colonize the unexploited storm unit; (6) gradational burrowed tops, representative of bioturbation resulting from subsequent burrowing by organisms from higher colonization levels; and (7) a fair weather resident trace fossil suite indicative of a return to quiescent conditions following abatement. Up to now, the ichnology in the carbonate tempestites has not been well studied and reported. The succession found in the Upper Cambrian Gushan Fm. from eastern North China Platform can be regarded as the typical carbonate tempestites. The succession includes the following parts (from bottom to top): (1) the trace fossils on the sole of the thin bedded limestone containing Phycodes, Thalassinoides, Palaeophycus and Planolites etc; (2) 1-2 cm thick muddy limestone or limestone with or without lamination; (3) the opportunistic trace fossils Diplocraterion, Arenicolites and Skolithos on the surface of the limestone; (4) the surface of the limestone covered by about 1 mm thick trilobite debris; (5)1-2 mm thick mudstone or shale.
2000, 18(4): 501-505.
Abstract:
Previous research interests are focused on the study of microfossils in the continental shelf and the Okinawa Trough of the East China Sea. In this paper, the sedimentary characteristics of different geological stage, paleoceanographic feature and sedimentary age are recognized through the analysis of microfossils and by means of δ18O curve and AMS14C dating. We use one of the 17 cores that the scientists from China,France and Korean obtained on the French vessel L＇ATALANTE in the continental shelf of the East China Sea in 1996. Grain sizes,minerals, CaCO3,microfossils,δ18o and AMS14C age are analysed and measured. The primary result is that 7 cool climatic stages are found according to the abundance change of cool water species and warm water species in microfossils. After that, the sedimentary stages are established in terms of mineralogical composition, carbonate content, granulometric composition, and AMS14C dating. They are 1)deposition of early Yumu glacial in the Late Pleistocene Epoch; 2)deposition of sub-interglacial epoch in Yumu; 3)deposition of Yumu glacial epoch in the Late Pleistocene; 4) deposition of post glacial in Holocene epoch. The result of AMS14C dating with the shells of planktonic foraminifera in the different sedimentary stage are as follows: 9 690 a B. P, 12 980 a B. P,26 350 a B. P,27 960 a B. P,37 410 a B. P,41 260 a BP.
Previous research interests are focused on the study of microfossils in the continental shelf and the Okinawa Trough of the East China Sea. In this paper, the sedimentary characteristics of different geological stage, paleoceanographic feature and sedimentary age are recognized through the analysis of microfossils and by means of δ18O curve and AMS14C dating. We use one of the 17 cores that the scientists from China,France and Korean obtained on the French vessel L＇ATALANTE in the continental shelf of the East China Sea in 1996. Grain sizes,minerals, CaCO3,microfossils,δ18o and AMS14C age are analysed and measured. The primary result is that 7 cool climatic stages are found according to the abundance change of cool water species and warm water species in microfossils. After that, the sedimentary stages are established in terms of mineralogical composition, carbonate content, granulometric composition, and AMS14C dating. They are 1)deposition of early Yumu glacial in the Late Pleistocene Epoch; 2)deposition of sub-interglacial epoch in Yumu; 3)deposition of Yumu glacial epoch in the Late Pleistocene; 4) deposition of post glacial in Holocene epoch. The result of AMS14C dating with the shells of planktonic foraminifera in the different sedimentary stage are as follows: 9 690 a B. P, 12 980 a B. P,26 350 a B. P,27 960 a B. P,37 410 a B. P,41 260 a BP.
2000, 18(4): 510-514,520.
Abstract:
The volcanic rocks of the Proterozoic Dahongyu Formation mainly distribute in Pinggu County of Beijing and Jixian county of Tianjin about 600 km 2 with 718 m and 490 m of the maximum thickness in the both areas. More than 40 paleo carters were survived in the areas.The types of volcanic rocks mainly are potassic basalts and trachyte. Sedimentary facies related to volcanic event in the Middle Proterozoic Dahongyu Formation in Beijing and its neighboring area mainly include two basic types: siliceous sand carbonate mixed facies and pyroclastic gravity flow deposit, in which the later can be divided into pyroclastic basic surge and volcanic breccia-carbonate mixed deposit. Siliceous sand carbonate mixed facies: the rock types of this facies include white and light blue siliceous bearing quazites, light blue sandy silicalites, blue grey tuff, siliceous dolomites, intraclast shaped silicalites and geltexture silicalites. Siliceous sand carbonate mixed facies widely distribute in the NE basin axis inclined to the NW side. Preliminary results of analysis, according to characteristics of rocks, geochemistry and sedimentation, show that enormous siliceous sediments of the Dahongyu Formation mainly originated from the submarine volcanic eruption in the temporary time. Pyroclastic basic surges: Basic surges directly cover on basalts and occur around the paleo craters. They are composed of coarse sand grade pyroclastic rocks with large scale dune like cross bedding and poly grade bedding, fine sand silt grade pyroclastic rocks and tuff shales. The pyroclastic basic surge was caused by sea water surging in small range, which was related to release of remnant steam bursting to seal of volcanic craters. Volcanic breccia carbonate mixed facies: Volcanic breccia carbonate generally is single bed placed in between dolomites. In the beds breccia components are composed of sedimentary rocks (40～60%) and of basalts and tractytes (30～40%). According to analysis of sedimentary breccia content more than volcanic breccia, this facies probably formed under the condition bursting and returnning breccia mixed with submarine surface carbonates and water in the basin, as submarine gravity flow deposited around the places of the volcanic craters.
The volcanic rocks of the Proterozoic Dahongyu Formation mainly distribute in Pinggu County of Beijing and Jixian county of Tianjin about 600 km 2 with 718 m and 490 m of the maximum thickness in the both areas. More than 40 paleo carters were survived in the areas.The types of volcanic rocks mainly are potassic basalts and trachyte. Sedimentary facies related to volcanic event in the Middle Proterozoic Dahongyu Formation in Beijing and its neighboring area mainly include two basic types: siliceous sand carbonate mixed facies and pyroclastic gravity flow deposit, in which the later can be divided into pyroclastic basic surge and volcanic breccia-carbonate mixed deposit. Siliceous sand carbonate mixed facies: the rock types of this facies include white and light blue siliceous bearing quazites, light blue sandy silicalites, blue grey tuff, siliceous dolomites, intraclast shaped silicalites and geltexture silicalites. Siliceous sand carbonate mixed facies widely distribute in the NE basin axis inclined to the NW side. Preliminary results of analysis, according to characteristics of rocks, geochemistry and sedimentation, show that enormous siliceous sediments of the Dahongyu Formation mainly originated from the submarine volcanic eruption in the temporary time. Pyroclastic basic surges: Basic surges directly cover on basalts and occur around the paleo craters. They are composed of coarse sand grade pyroclastic rocks with large scale dune like cross bedding and poly grade bedding, fine sand silt grade pyroclastic rocks and tuff shales. The pyroclastic basic surge was caused by sea water surging in small range, which was related to release of remnant steam bursting to seal of volcanic craters. Volcanic breccia carbonate mixed facies: Volcanic breccia carbonate generally is single bed placed in between dolomites. In the beds breccia components are composed of sedimentary rocks (40～60%) and of basalts and tractytes (30～40%). According to analysis of sedimentary breccia content more than volcanic breccia, this facies probably formed under the condition bursting and returnning breccia mixed with submarine surface carbonates and water in the basin, as submarine gravity flow deposited around the places of the volcanic craters.
2000, 18(4): 521-526.
Abstract:
Formed proceeding and evolution disciplinarian of fan delta are studied in detail using experimental sedimentary.It points that formed of fan delta dues to alternating function of spasmodic flooding and usually flowing.Debris flood and mud rock flow are mainly sedimentary at flooding period,tractional current is main as a rule.In course of continuing of sedimentary,formed of fan delta is increaseing out of sync in plane and rate of stretch is larger than rate of elongation in the course of declining of datum plane.Formed of fan delta is smooth tongue in the edge of delta.Removing and waver of braided river course leads to evolution disciplinarian of fan delta.Tectonic motive intension is similar positive correlativity with removing and waver of braided river course.Deep of lake,slope of accessing lake,formed of braided river course,flow change rate and grain size are importance agent that affecting evolution of fan delta.
Formed proceeding and evolution disciplinarian of fan delta are studied in detail using experimental sedimentary.It points that formed of fan delta dues to alternating function of spasmodic flooding and usually flowing.Debris flood and mud rock flow are mainly sedimentary at flooding period,tractional current is main as a rule.In course of continuing of sedimentary,formed of fan delta is increaseing out of sync in plane and rate of stretch is larger than rate of elongation in the course of declining of datum plane.Formed of fan delta is smooth tongue in the edge of delta.Removing and waver of braided river course leads to evolution disciplinarian of fan delta.Tectonic motive intension is similar positive correlativity with removing and waver of braided river course.Deep of lake,slope of accessing lake,formed of braided river course,flow change rate and grain size are importance agent that affecting evolution of fan delta.
2000, 18(4): 534-538.
Abstract:
Kuche Depression, situated in the northern part of Tarim Basin, was a foreland depression and there was a set of extremely thick, alluvial-lake classic deposits in it in Mesozoic Era. Five facies(meandering river facies, fandeltas facies, braided-river deltas facies, meandering-river deltas facies and lacutrine facies), fifteen subfacies and thirty-eight microfacies are recognised. Kuche Depression was a ”dustpan” shape depression with steep slope in the north side and gentle slope in the south side. Deposits are thicker in the north side than in the south and the depocenter did not coordinate with the center of subsidence. The lake in Kuche Depression went through a period from deep subsidence lacustrine (Triassic Period, fan-deltas and braided-river deltas sediments are dominant) to filling lacustrine (early and middle Jurassic, braided-river deltas is dominant) to broad and shallow lacustrine (late Jurassic and Cretaceous Period, coastal lake and shallow lake sediments are dominant). From Triassic Period to middle Jurassic, Kuche Depression was an isolated basin and area was small, not joining with Tarim Basin because there was a provenance in its south side. Beginning from late Jurassic, the southern provenance vanished and Kuche Depression joined with Tarim Basin as a part of it. Palaeoclimate change was very clear in Kuche Depression. It was an arid climate in early and middle Triassic, a damp climate from late Triassic to middle Jurassic because many seam are discovered, back to an arid climate from late Jurassic because all sediments have red color.
Kuche Depression, situated in the northern part of Tarim Basin, was a foreland depression and there was a set of extremely thick, alluvial-lake classic deposits in it in Mesozoic Era. Five facies(meandering river facies, fandeltas facies, braided-river deltas facies, meandering-river deltas facies and lacutrine facies), fifteen subfacies and thirty-eight microfacies are recognised. Kuche Depression was a ”dustpan” shape depression with steep slope in the north side and gentle slope in the south side. Deposits are thicker in the north side than in the south and the depocenter did not coordinate with the center of subsidence. The lake in Kuche Depression went through a period from deep subsidence lacustrine (Triassic Period, fan-deltas and braided-river deltas sediments are dominant) to filling lacustrine (early and middle Jurassic, braided-river deltas is dominant) to broad and shallow lacustrine (late Jurassic and Cretaceous Period, coastal lake and shallow lake sediments are dominant). From Triassic Period to middle Jurassic, Kuche Depression was an isolated basin and area was small, not joining with Tarim Basin because there was a provenance in its south side. Beginning from late Jurassic, the southern provenance vanished and Kuche Depression joined with Tarim Basin as a part of it. Palaeoclimate change was very clear in Kuche Depression. It was an arid climate in early and middle Triassic, a damp climate from late Triassic to middle Jurassic because many seam are discovered, back to an arid climate from late Jurassic because all sediments have red color.
2000, 18(4): 544-548.
Abstract:
The Hetian river gas field is a new and large gas field in Mazatage fault belt of Tarim basin. Ordovician carbonate rock is principal production formation. Lower Ordovician is characterized by developed dolomitization which can greatly improve reservoir property. There are two types of dolomite in Lower Ordovician. The bedded dolomite is in lower part. Their features is fine crystal, cathodolaminescence of violet red and blue violet, degree of order 0.57～0.68, low Sr and Na content, and negative carbon oxygen isotope value, implying that the bedded dolomite was formed in environment of early shallow buried fresh water and seawater mixing. On the contrary the upper part patch calcareous dolomite is medium crystal, degree of order 0.85～0.90, high Sr content, low Na content, and more negative value carbon oxygen isotope indicating that the patch dolomites was formed in environment of late deep buried compaction flow and fresh water mixing. The bedded dolomite was formed in an environment of restricted platform,where water was confined and salinity was high.There was porous water of high salinity with high Mg/Ca in intergranular pore of orginal sediment. It has much higher carbon oxygen isotope value and trace element contents than normal seawater. During burial, there was a lot of fresh water down from east northern Tabei old land along slope to this area. Fresh water and porous seawater with high salinity will be mixed in sediment, resulting in the dilution of pore water salinity, value of carbon oxygen isotope and trace element will decrease. But the Mg/Ca ratio will keep unchanged. So dolomitization will take place. Late Ordovician in Mazatage fault belt is open platform facies. Salinity of seawater is normal. Over lower Ordovician sediment is mainly mud limestone and mud intercalation limestone. When mud limestone was buried over 2 000 m, montmorillonite in clay mineral transferred to illite. A lot of ion of Sr, Fe, Ca, Mg and so on came into pore fluid. Because of gravity, pore fluid will flow downwards from Tabei old land along the Sajingzi fault. Two types of flow mixed in grain limestone of upper lower Ordovician. CaMg(CO 3) 2 was over saturation. Patch calcareous dolomite will be formed.Two types of dolomitization can be formed in mixed water, but the Mg ion sources are different. The later is aspecial genetic model.
The Hetian river gas field is a new and large gas field in Mazatage fault belt of Tarim basin. Ordovician carbonate rock is principal production formation. Lower Ordovician is characterized by developed dolomitization which can greatly improve reservoir property. There are two types of dolomite in Lower Ordovician. The bedded dolomite is in lower part. Their features is fine crystal, cathodolaminescence of violet red and blue violet, degree of order 0.57～0.68, low Sr and Na content, and negative carbon oxygen isotope value, implying that the bedded dolomite was formed in environment of early shallow buried fresh water and seawater mixing. On the contrary the upper part patch calcareous dolomite is medium crystal, degree of order 0.85～0.90, high Sr content, low Na content, and more negative value carbon oxygen isotope indicating that the patch dolomites was formed in environment of late deep buried compaction flow and fresh water mixing. The bedded dolomite was formed in an environment of restricted platform,where water was confined and salinity was high.There was porous water of high salinity with high Mg/Ca in intergranular pore of orginal sediment. It has much higher carbon oxygen isotope value and trace element contents than normal seawater. During burial, there was a lot of fresh water down from east northern Tabei old land along slope to this area. Fresh water and porous seawater with high salinity will be mixed in sediment, resulting in the dilution of pore water salinity, value of carbon oxygen isotope and trace element will decrease. But the Mg/Ca ratio will keep unchanged. So dolomitization will take place. Late Ordovician in Mazatage fault belt is open platform facies. Salinity of seawater is normal. Over lower Ordovician sediment is mainly mud limestone and mud intercalation limestone. When mud limestone was buried over 2 000 m, montmorillonite in clay mineral transferred to illite. A lot of ion of Sr, Fe, Ca, Mg and so on came into pore fluid. Because of gravity, pore fluid will flow downwards from Tabei old land along the Sajingzi fault. Two types of flow mixed in grain limestone of upper lower Ordovician. CaMg(CO 3) 2 was over saturation. Patch calcareous dolomite will be formed.Two types of dolomitization can be formed in mixed water, but the Mg ion sources are different. The later is aspecial genetic model.
2000, 18(4): 555-559.
Abstract:
After dolomites of Qiangtang Basin and Cuoqin Basin in Qingzang Plateau are observed and described in the field, vertical and horizontal distribution rules of dolomite in the study area are reduced. Applying structure index, cathode shining index and oxygen isotope index, genesis of dolomite are effectively judged by use of systematically indoor analysis and laboratory test method. Then it is concluded that dolomites of the study area are all produced by metasomatism or dolomitation, not originally. According to size and shape of crystals and inner structure of dolomites, dolomiting phase are divided into three phases: quasi-contemporaneous phase, diagenesis and catagenesis. Features of each phase are introduced. It is found that dolomites formed in diagenesis can be a good reservoir rock.Through selecting typical sections, two kinds of genetic models of dolomite in the study area are put forward, i.e. capillary concentration model and mixed water model.
After dolomites of Qiangtang Basin and Cuoqin Basin in Qingzang Plateau are observed and described in the field, vertical and horizontal distribution rules of dolomite in the study area are reduced. Applying structure index, cathode shining index and oxygen isotope index, genesis of dolomite are effectively judged by use of systematically indoor analysis and laboratory test method. Then it is concluded that dolomites of the study area are all produced by metasomatism or dolomitation, not originally. According to size and shape of crystals and inner structure of dolomites, dolomiting phase are divided into three phases: quasi-contemporaneous phase, diagenesis and catagenesis. Features of each phase are introduced. It is found that dolomites formed in diagenesis can be a good reservoir rock.Through selecting typical sections, two kinds of genetic models of dolomite in the study area are put forward, i.e. capillary concentration model and mixed water model.
2000, 18(4): 567-572.
Abstract:
There are plenty of petroleum geology implications in geochemical fields of oil field water systems. It is very important for studying the geochemical fields to guide exploration and development of petroleum. Oil field waters of Eogene System in Huanxilin Shuangtaizi area, the Western Depression, Liaohe basin, can be divided into six oil field water systems. The oil field water systems are:(1) the oil field water system of No.4 Section of Shahejie Formation, (2)the oil field water system of lower No.3 Section of Shahejie Formation, (3)the oil field water system of middle upper No.3 Section of Shahejie Formation, (4)the oil field water system of No.2 Section of Shahejie Formation, (5)the oil field water system of No.1 Section of Shahejie Formation, (6)the oil field water system of Dongying Formation. Though the types of all oil field water of the six systems in Huanxilin Shuangtaizi area, Western Depression, Liaohe basin are the low mineralized bicarbonate sodium, it is very different among mineralization intensity fields and reduction factor fields in the six oil field water systems. The differences are not only the different abnormal areas of the geochemical fields in the six oil field water systems, but the different locations of abnormal areas of the geochemical fields among the six oil field water systems also. The abnormal areas are represented their petroleum geology implications in the six oil field water systems respectively. Generally, the positive abnormal areas of mineralization intensity and the negative abnormal areas of reduction factor in oil field water system have the advantage of petroleum to be accumulated and reserved. The geochemical fields of oil field water systems of Eogene System in Huanxilin Shuangtaizi area, Western Depression, Liaohe basin don't show the consistent of the conditions of petroleum accumulation and reservation in the sections and formation of Eogene System in the study area.
There are plenty of petroleum geology implications in geochemical fields of oil field water systems. It is very important for studying the geochemical fields to guide exploration and development of petroleum. Oil field waters of Eogene System in Huanxilin Shuangtaizi area, the Western Depression, Liaohe basin, can be divided into six oil field water systems. The oil field water systems are:(1) the oil field water system of No.4 Section of Shahejie Formation, (2)the oil field water system of lower No.3 Section of Shahejie Formation, (3)the oil field water system of middle upper No.3 Section of Shahejie Formation, (4)the oil field water system of No.2 Section of Shahejie Formation, (5)the oil field water system of No.1 Section of Shahejie Formation, (6)the oil field water system of Dongying Formation. Though the types of all oil field water of the six systems in Huanxilin Shuangtaizi area, Western Depression, Liaohe basin are the low mineralized bicarbonate sodium, it is very different among mineralization intensity fields and reduction factor fields in the six oil field water systems. The differences are not only the different abnormal areas of the geochemical fields in the six oil field water systems, but the different locations of abnormal areas of the geochemical fields among the six oil field water systems also. The abnormal areas are represented their petroleum geology implications in the six oil field water systems respectively. Generally, the positive abnormal areas of mineralization intensity and the negative abnormal areas of reduction factor in oil field water system have the advantage of petroleum to be accumulated and reserved. The geochemical fields of oil field water systems of Eogene System in Huanxilin Shuangtaizi area, Western Depression, Liaohe basin don't show the consistent of the conditions of petroleum accumulation and reservation in the sections and formation of Eogene System in the study area.
2000, 18(4): 580-584.
Abstract:
Tarim basin is a large,complex and multicycle basin, and has a complex geologic evolution history.Nevertheless,little is known about the geology of the Southeast Tarim basin.With the development of oil, people pay more attention to Mesozoic stratum exposed on basin margin.There develop Jurassic terrestrial coal measure strata and Cretaceous red beds.The present paper aims at analysing Jurassic system by use of sequence stratigraphy to study Mesozoic stratum distribution,contrast,sedimentary character,and to build up pattern of sequence stratigraphy.Using unconformity as main mark of different sequences,it shows Jurassic makes up a second order sequence,which represents a structural subsidence uplift process.Inside Jurassic,lacustrine invasion onlap and basinmargin exposure truncation can differentiate the third order sequence,which represents a relative water invasion water regression process. Sequence I subface is a regional erosion unconformity.It because of appearance on piedmont thrust belt on field outcrop is fault contact and bottom development incomplete.The sequence consists of alluvial fan facies or braided river facies with positive cycle.Its storage condition is good.Sequence 2 subface is lacustrine invasion onlap surface land alluvial fan facies is replaced by delta facies.Delta plain consist of braided river sequence with positive cycle.Delta front and lacustrine facies consist of prograding sequence with counter cycle.The sequence have good storage condition.Its upper part is a coal measure strata and it has fairly good oil source rock.Sequence 3 subface is lacustrine invasion onlap surface.The sequence consists of delta facies with counter cycle and rhythmic unit of lacustrine facies.At this moment lacustrine invasion is the largest.It takes shape of condensed section of deep lake facies.That is good oil source bed and overlying formation.Sequence 4 subface is basin margin truncation surface.That consists of river facies with positive cycle.At this moment,the lake is with small scope,climate change arid and hot.Sequence 5 subface is basin margin truncation surface.Its top surface is regional unconformity,which consists of alluvial fan facies with positive cycle in arid climate.It can become good reservoir that develops secondary dissolved porosity. Jurassic in southeast Tarim basin distributes extensively with a great thickness.It has good hydrocarbon, potential,and is also major hydrocarbon bearing sequence.In Sequence 3,condensed section of deep lake and semi deep lake is the most favorable oil source rock.Moreover,it is a regional overlying formation.Sequence 1 and 2 one of the most profitable exploration horizons since sequcence 5 and lower Cretaccous Kezileqiapu Formation is reservoir,and lacustrine shale and gypsum layer in Kezileqiapu Formation is its caprock.
Tarim basin is a large,complex and multicycle basin, and has a complex geologic evolution history.Nevertheless,little is known about the geology of the Southeast Tarim basin.With the development of oil, people pay more attention to Mesozoic stratum exposed on basin margin.There develop Jurassic terrestrial coal measure strata and Cretaceous red beds.The present paper aims at analysing Jurassic system by use of sequence stratigraphy to study Mesozoic stratum distribution,contrast,sedimentary character,and to build up pattern of sequence stratigraphy.Using unconformity as main mark of different sequences,it shows Jurassic makes up a second order sequence,which represents a structural subsidence uplift process.Inside Jurassic,lacustrine invasion onlap and basinmargin exposure truncation can differentiate the third order sequence,which represents a relative water invasion water regression process. Sequence I subface is a regional erosion unconformity.It because of appearance on piedmont thrust belt on field outcrop is fault contact and bottom development incomplete.The sequence consists of alluvial fan facies or braided river facies with positive cycle.Its storage condition is good.Sequence 2 subface is lacustrine invasion onlap surface land alluvial fan facies is replaced by delta facies.Delta plain consist of braided river sequence with positive cycle.Delta front and lacustrine facies consist of prograding sequence with counter cycle.The sequence have good storage condition.Its upper part is a coal measure strata and it has fairly good oil source rock.Sequence 3 subface is lacustrine invasion onlap surface.The sequence consists of delta facies with counter cycle and rhythmic unit of lacustrine facies.At this moment lacustrine invasion is the largest.It takes shape of condensed section of deep lake facies.That is good oil source bed and overlying formation.Sequence 4 subface is basin margin truncation surface.That consists of river facies with positive cycle.At this moment,the lake is with small scope,climate change arid and hot.Sequence 5 subface is basin margin truncation surface.Its top surface is regional unconformity,which consists of alluvial fan facies with positive cycle in arid climate.It can become good reservoir that develops secondary dissolved porosity. Jurassic in southeast Tarim basin distributes extensively with a great thickness.It has good hydrocarbon, potential,and is also major hydrocarbon bearing sequence.In Sequence 3,condensed section of deep lake and semi deep lake is the most favorable oil source rock.Moreover,it is a regional overlying formation.Sequence 1 and 2 one of the most profitable exploration horizons since sequcence 5 and lower Cretaccous Kezileqiapu Formation is reservoir,and lacustrine shale and gypsum layer in Kezileqiapu Formation is its caprock.
2000, 18(4): 590-594.
Abstract:
Desmocollinite is one of the major macerals of Late Permian Longtan Formation coals in Shuicheng, Guizhou Province, Southwest China. The characteristics of hydrocarbon generation of desmocollinite are important to evaluate and explore oil and gas resources derive from coals. In this paper, Rock eval, Py GC and experimental simulation in an open system were used to study hydrocarbon generation potential, hydrocarbon composition, hydrocarbon generation model and thermoevolutional characteristics of desmocollinite. The results indicate that desmocollinite has high hydrocarbon generation potential, with (S 1+S 2) of 191.6mg/g, which is higher than that of fusinite (S 1+S 2 is 26.2mg/g,), and lower than of barkinite (S 1+S 2 is 297mg/g); light hydrocarbon (C 6-C 14 )and wet gas (C 2-C 5)are the main hydrocarbon composition; the "oil window" of desmocollinite is within 375～475 ℃, the main temperature range of hydrocarbon generation is at 400～450 ℃ with a peak range of 410～430 ℃, and the temperature of maximum hydrocarbon generating rates is at 420 ℃. These studies show that desmocollinite from barkinite rich coal is one of oil generated macerals, which is attributed to abundant submicro liptinites in desmocollinite,and desmocollinite also can generate a large amount of hydrocarbon in higher mature degree, these hydrocarbon generating model of desmocollinite is favorable for exploring oil and gas resources in South China.
Desmocollinite is one of the major macerals of Late Permian Longtan Formation coals in Shuicheng, Guizhou Province, Southwest China. The characteristics of hydrocarbon generation of desmocollinite are important to evaluate and explore oil and gas resources derive from coals. In this paper, Rock eval, Py GC and experimental simulation in an open system were used to study hydrocarbon generation potential, hydrocarbon composition, hydrocarbon generation model and thermoevolutional characteristics of desmocollinite. The results indicate that desmocollinite has high hydrocarbon generation potential, with (S 1+S 2) of 191.6mg/g, which is higher than that of fusinite (S 1+S 2 is 26.2mg/g,), and lower than of barkinite (S 1+S 2 is 297mg/g); light hydrocarbon (C 6-C 14 )and wet gas (C 2-C 5)are the main hydrocarbon composition; the "oil window" of desmocollinite is within 375～475 ℃, the main temperature range of hydrocarbon generation is at 400～450 ℃ with a peak range of 410～430 ℃, and the temperature of maximum hydrocarbon generating rates is at 420 ℃. These studies show that desmocollinite from barkinite rich coal is one of oil generated macerals, which is attributed to abundant submicro liptinites in desmocollinite,and desmocollinite also can generate a large amount of hydrocarbon in higher mature degree, these hydrocarbon generating model of desmocollinite is favorable for exploring oil and gas resources in South China.
2000, 18(4): 600-605.
Abstract:
The existing state of organic matter in carbonate rocks not only has dissemination state, but also has inclusion state. The acid liquid soluble organic matter I is also divided while extracting the inclusion organic matter. The analysis of the quantity, IR spectrocopy, GC and GC－MS among the bitumen A, Bitumen C and acid liquid soluble organic matter show that their characteristics are not the same. The results play an important role for evaluating the hydrocarbon producion potential and discussing the hydrocarbon generating mechanism and process of carbonate rocks
The existing state of organic matter in carbonate rocks not only has dissemination state, but also has inclusion state. The acid liquid soluble organic matter I is also divided while extracting the inclusion organic matter. The analysis of the quantity, IR spectrocopy, GC and GC－MS among the bitumen A, Bitumen C and acid liquid soluble organic matter show that their characteristics are not the same. The results play an important role for evaluating the hydrocarbon producion potential and discussing the hydrocarbon generating mechanism and process of carbonate rocks
2000, 18(4): 611-614.
Abstract:
As an unconventional natural gas, the characteristics of carbon isotope in coal bed methane (CBM) is similar to conventional gas. This paper summarizes the character of China coal bed methane carbon isotope according to field desorption,thermo-modeling and carbon isotope testing. Taking Qinshui CBM field as a example, it points out the potential area and profitable target zone for CBM exploration and development from carbon isotope fractionation effect and desorption,diffusion and movement effect of CBM,combined with hydrology and structural condition. Geologic target area in China has complex tectonic and high maturation, lots of CBM was lost during evolution stage. The variation of carbon isotope value can directly reflect the CBM accumulation degree. Due to desorption, diffusion and movement effect of CBM, the thermo-modeling value of carbon isotope was much higher than carbon isotope value. Meanwhile,the carbon isotope,which also reflects the preservation condition of CBM trap, is important to evaluate the origin of CBM reservoir and exploration potential. Four different types are divided in terms of carbon isotope value distribution. According to this theory, Qinshui CBM basin in Jincheng area, Shanxi province was found. Rope coring technique was used and carbon isotope testing of field desorption gas was firstly conducted in Qinshui CBM basin. The desorption gas sample for carbon isotope analysis was collected at 4,24 and 96 hours by water displacement. Because of 12C having less electrical property than 13C, CBM molecule with 12C was prior to molecule with 13C in desorption procedure and lead to carbon isotope fractionation, the early adsorption gas had lighter carbon isotope than late adsorption gas. Qinshui CBM field is a large gas field and can be divided into 3 zones in terms of carbon isotope distribution feature. Carbon isotope in coal seam 15 is lighter than coal seam 3 because of being interfered by carbonate water. The best location lies in primary-secondary zone with carbon isotope at - 30‰～ - 40‰.
As an unconventional natural gas, the characteristics of carbon isotope in coal bed methane (CBM) is similar to conventional gas. This paper summarizes the character of China coal bed methane carbon isotope according to field desorption,thermo-modeling and carbon isotope testing. Taking Qinshui CBM field as a example, it points out the potential area and profitable target zone for CBM exploration and development from carbon isotope fractionation effect and desorption,diffusion and movement effect of CBM,combined with hydrology and structural condition. Geologic target area in China has complex tectonic and high maturation, lots of CBM was lost during evolution stage. The variation of carbon isotope value can directly reflect the CBM accumulation degree. Due to desorption, diffusion and movement effect of CBM, the thermo-modeling value of carbon isotope was much higher than carbon isotope value. Meanwhile,the carbon isotope,which also reflects the preservation condition of CBM trap, is important to evaluate the origin of CBM reservoir and exploration potential. Four different types are divided in terms of carbon isotope value distribution. According to this theory, Qinshui CBM basin in Jincheng area, Shanxi province was found. Rope coring technique was used and carbon isotope testing of field desorption gas was firstly conducted in Qinshui CBM basin. The desorption gas sample for carbon isotope analysis was collected at 4,24 and 96 hours by water displacement. Because of 12C having less electrical property than 13C, CBM molecule with 12C was prior to molecule with 13C in desorption procedure and lead to carbon isotope fractionation, the early adsorption gas had lighter carbon isotope than late adsorption gas. Qinshui CBM field is a large gas field and can be divided into 3 zones in terms of carbon isotope distribution feature. Carbon isotope in coal seam 15 is lighter than coal seam 3 because of being interfered by carbonate water. The best location lies in primary-secondary zone with carbon isotope at - 30‰～ - 40‰.
2000, 18(4): 619-623.
Abstract:
Jiudong basin is formed by the stacking of two stage different nature and different generation basin.It was rift basin from Early Middle jurassic to Early Creaceous and squeezed sag basin since Cenozoic.The present geothermal gradient and heat flow of Jiudong basin is very low,of which the present geothermal gradient is 3.00 ℃/100m and the heat flow value is 51 mW/m 2.In later Mesozoic,the palaeothermal gradient of Yinger depression,which reached 3.50～4.20 ℃/100m,is higher than present thermal gradient.Thermal gradient of Jiudong basin has decreased since Cenozoic,Yinger depression has subsided on a large scale.The maturity of thermal evolution of source rocks in Yinger depression is controlled by present temperature.Research on the relations between geothermal history and oil gas generation in Yinger depression indicate that Chijinbu Formation source rock of Lower Creaceous have two stage of oil generation,i.e. Late Creaceous and since Tertiary.Xiagou Formation and Zhonggou Formation source rocks of Lower Creaceous only have one main stage of oil generation,main stage of oil generation is since Pliocene.It has good prospect for exploring oil in Yinger depression.
Jiudong basin is formed by the stacking of two stage different nature and different generation basin.It was rift basin from Early Middle jurassic to Early Creaceous and squeezed sag basin since Cenozoic.The present geothermal gradient and heat flow of Jiudong basin is very low,of which the present geothermal gradient is 3.00 ℃/100m and the heat flow value is 51 mW/m 2.In later Mesozoic,the palaeothermal gradient of Yinger depression,which reached 3.50～4.20 ℃/100m,is higher than present thermal gradient.Thermal gradient of Jiudong basin has decreased since Cenozoic,Yinger depression has subsided on a large scale.The maturity of thermal evolution of source rocks in Yinger depression is controlled by present temperature.Research on the relations between geothermal history and oil gas generation in Yinger depression indicate that Chijinbu Formation source rock of Lower Creaceous have two stage of oil generation,i.e. Late Creaceous and since Tertiary.Xiagou Formation and Zhonggou Formation source rocks of Lower Creaceous only have one main stage of oil generation,main stage of oil generation is since Pliocene.It has good prospect for exploring oil in Yinger depression.
2000, 18(4): 639-645.
Abstract:
Riverine water samples were collected from the lower reach hydrometric station of Xijiang River, namely Makou, in four hydrological seasons. The samples were analyzed of their organic carbon. The analysis results demonstrated that the distribution of organic carbon, including particulate organic carbon (POC) and dissolved organic carbon (DOC), is fairly suitable in the sampling section in every season. The contents of organic carbon and total suspended substance (TSS) in riverine water body varied seasonally with the discharge in a positive pattern. With the content of total suspended substances increasing, the quality partition of organic carbon in TSS decreased in a logarithm tendency. The weathering flux of organic carbon in Xijiang River drainage area is about 10.18×10 6gC/km 2·yr., which is two to three times in quantiy of the average value in the global external drainage area. The POC is the main constitute of the riverine organic carbon, which weathering flux is about 8.30×10 6gC/km 2·yr. The weathering flux of dissolved organic carbon is about 1.88×10 6gC/km 2·yr. The mechanical erosion is very intense in this drainage area, which is considered to be related to the typical monsoon climate and to the comparatively great undulation of the landforms in this drainage basin. The long history and fairly intense utility of the land for agriculture use are all responsible for the serious soil erosion in this area.
Riverine water samples were collected from the lower reach hydrometric station of Xijiang River, namely Makou, in four hydrological seasons. The samples were analyzed of their organic carbon. The analysis results demonstrated that the distribution of organic carbon, including particulate organic carbon (POC) and dissolved organic carbon (DOC), is fairly suitable in the sampling section in every season. The contents of organic carbon and total suspended substance (TSS) in riverine water body varied seasonally with the discharge in a positive pattern. With the content of total suspended substances increasing, the quality partition of organic carbon in TSS decreased in a logarithm tendency. The weathering flux of organic carbon in Xijiang River drainage area is about 10.18×10 6gC/km 2·yr., which is two to three times in quantiy of the average value in the global external drainage area. The POC is the main constitute of the riverine organic carbon, which weathering flux is about 8.30×10 6gC/km 2·yr. The weathering flux of dissolved organic carbon is about 1.88×10 6gC/km 2·yr. The mechanical erosion is very intense in this drainage area, which is considered to be related to the typical monsoon climate and to the comparatively great undulation of the landforms in this drainage basin. The long history and fairly intense utility of the land for agriculture use are all responsible for the serious soil erosion in this area.
2000, 18(4): 495-500.
Abstract:
A huge amount of trace fossils have been found for the first time in the middle part of the Lower Permian Biyoulety Group in the northwest margin of Tarim plate,and they are Glockeria Ksiazkiewicz1968,Helminthoida sp.,Megagrapton sp.,Paleodictyon sp.,Paleodictyon(Glenodictyum)Croaticum Ulchman1995,Planolites sp.,Protopaleodictyon sp.,Scalaritubamissouriensis Weller1899,Spirophycus sp. et al.According to the analysis of the behavior types of organisms and the features of ethological environment,these trace fossils mainly contain the deep-sea Fodinichnia,Pascichnia and Agrichnia,lack of Domichnia,Cubichnia and Repichnia et al that were usually found in shallow water.This trace fossil assemblage reflects the characteristics of behavior types of organisms in deep-sea environment and is interpreted to represent a typical deep-sea Nereites ichnofacies. Based on the research of Unggur section(Wuqia County),the lower part of the Biyoulety Group is composed of mudy limestone,silty mudstone,siltstone and limestone of neritic shelf facies;while its middle part is made up turbidite deposits with silicilith intercalated in the deep-sea fan that contained the abundant trace fossils of Nereites ichnofacies;the upper part of the Biyoulety Group is dominantly composed of siliceous limestone,limestone,sandy limestone,silty mudstone and calcareous sandstone of neritic shelf-littoral facies.Through the related water-depth analysis of shape types,behavior habits and characteristics of trace fossils in this area,we can conclude that these trace fossil associations found in this area are different in each part of turbiditic fan that formed different sedimentary environments from distal area(outer fan) to proximal area(inner fan) of turbidity fan. 1) The trace fossil association produced by both organism feeding and semi-dwelling mainly occurs in inner fan.Such as Glockeria(Fodinichnia),it was formed by the radial feeding in the vertical burrows that the organism dwelled and feeded and generated at the shallower depths(200-1 300m),and the water energy was higher condition in this environment and disadvantageous for the organism living on the depositional surface. Pascichnia and Agrichnia were not found here,while a lot of "spanning facies" type members- Planolites co-occurred. 2) The Pascichnia of horizontal curve,snake and spiral shapes and Fodinichnia with the backfill structure appear in the middle fan.Such as Scalarituba and Spirophycus,lack of "spanning facies" type members here. 3) The association of trace fossils in the outer fan is characterized by the large appearance of network shape Agrichnia and regular snake-shaped Pascichnia,the radial Fodinichnia are not found in this environment.The Pascichnia in this association also appearred as regular habits and characteristics of gnawing for food.The trace fossils of deep-water types are of absolutely predominant role in quantity,for example: Helminthoida,Paleodictyon and Megagrapton and so on.The water depths at which this association of trace fossils formed below sea-level concentrated from 600m(800m) to 2 000m,and they are of higher abundance and degree and horizontally preserved on the surface of rock strata. In addition, the Biyoulety Group distributed over Bayankurut area(northwest of Unggur,Wuqia County) is a typical thick turbidite composed of greyish green thin slate,black sandy limestone and mudstone.The turbidite is of typical Bouma sequence that mainly developed D and E beddings and also the flute cast that indicates the ancient current direction about 300°±.A lot of deep-water trace fossils,such as Protopaleodictyon sp. and so on,were found in this strata and of the distribution characteristics of large scale snake shape,and also were the important ichnofossils of Nereites ichnofacies.Linking the sedimentary feature and environment analysis of the host rocks of trace fossils,we can infer this area also reached the deep-sea ri
A huge amount of trace fossils have been found for the first time in the middle part of the Lower Permian Biyoulety Group in the northwest margin of Tarim plate,and they are Glockeria Ksiazkiewicz1968,Helminthoida sp.,Megagrapton sp.,Paleodictyon sp.,Paleodictyon(Glenodictyum)Croaticum Ulchman1995,Planolites sp.,Protopaleodictyon sp.,Scalaritubamissouriensis Weller1899,Spirophycus sp. et al.According to the analysis of the behavior types of organisms and the features of ethological environment,these trace fossils mainly contain the deep-sea Fodinichnia,Pascichnia and Agrichnia,lack of Domichnia,Cubichnia and Repichnia et al that were usually found in shallow water.This trace fossil assemblage reflects the characteristics of behavior types of organisms in deep-sea environment and is interpreted to represent a typical deep-sea Nereites ichnofacies. Based on the research of Unggur section(Wuqia County),the lower part of the Biyoulety Group is composed of mudy limestone,silty mudstone,siltstone and limestone of neritic shelf facies;while its middle part is made up turbidite deposits with silicilith intercalated in the deep-sea fan that contained the abundant trace fossils of Nereites ichnofacies;the upper part of the Biyoulety Group is dominantly composed of siliceous limestone,limestone,sandy limestone,silty mudstone and calcareous sandstone of neritic shelf-littoral facies.Through the related water-depth analysis of shape types,behavior habits and characteristics of trace fossils in this area,we can conclude that these trace fossil associations found in this area are different in each part of turbiditic fan that formed different sedimentary environments from distal area(outer fan) to proximal area(inner fan) of turbidity fan. 1) The trace fossil association produced by both organism feeding and semi-dwelling mainly occurs in inner fan.Such as Glockeria(Fodinichnia),it was formed by the radial feeding in the vertical burrows that the organism dwelled and feeded and generated at the shallower depths(200-1 300m),and the water energy was higher condition in this environment and disadvantageous for the organism living on the depositional surface. Pascichnia and Agrichnia were not found here,while a lot of "spanning facies" type members- Planolites co-occurred. 2) The Pascichnia of horizontal curve,snake and spiral shapes and Fodinichnia with the backfill structure appear in the middle fan.Such as Scalarituba and Spirophycus,lack of "spanning facies" type members here. 3) The association of trace fossils in the outer fan is characterized by the large appearance of network shape Agrichnia and regular snake-shaped Pascichnia,the radial Fodinichnia are not found in this environment.The Pascichnia in this association also appearred as regular habits and characteristics of gnawing for food.The trace fossils of deep-water types are of absolutely predominant role in quantity,for example: Helminthoida,Paleodictyon and Megagrapton and so on.The water depths at which this association of trace fossils formed below sea-level concentrated from 600m(800m) to 2 000m,and they are of higher abundance and degree and horizontally preserved on the surface of rock strata. In addition, the Biyoulety Group distributed over Bayankurut area(northwest of Unggur,Wuqia County) is a typical thick turbidite composed of greyish green thin slate,black sandy limestone and mudstone.The turbidite is of typical Bouma sequence that mainly developed D and E beddings and also the flute cast that indicates the ancient current direction about 300°±.A lot of deep-water trace fossils,such as Protopaleodictyon sp. and so on,were found in this strata and of the distribution characteristics of large scale snake shape,and also were the important ichnofossils of Nereites ichnofacies.Linking the sedimentary feature and environment analysis of the host rocks of trace fossils,we can infer this area also reached the deep-sea ri
2000, 18(4): 506-509.
Abstract:
Based on the analysis of the surface textures of Quartz grains from surface soil, last interglacial paleosol (S1), upper silt layer (L9), upper and middle red clay (RC1 and RC2) samples by Scanning Electronic Microscope, this paper show us that there exist much more silica precipitation and clearly solution evidences on the surface of the primary quartz in Lingtai surface soil, last interglacial paleosol and upper red clay samples, which reveal that eolian deposit has been modified to some degree by pedogenesis procedure after deposition because of suitable climate conditions. However, the quartz surface in the upper silt layer and middle red clay layer is very clean, and shows clearly subangular to subrounded shape and collision pits which are typical eolian evidence. All the quartz pretreated by hydrogen peroxide and hydrochloric acid are characterized by clearly subangular to subrounded shape and abundant collision pits or pocks, which prove that the red clay has the similar sedimentary origin as the overlapped loesspaleosol sequences; but the solution and precipitation evidences on the primary quartz surface may indicate the climate condition during the late Tertiary is different from the Quaternary periods' warmer-wetter and colder-dryer climatic condition.
Based on the analysis of the surface textures of Quartz grains from surface soil, last interglacial paleosol (S1), upper silt layer (L9), upper and middle red clay (RC1 and RC2) samples by Scanning Electronic Microscope, this paper show us that there exist much more silica precipitation and clearly solution evidences on the surface of the primary quartz in Lingtai surface soil, last interglacial paleosol and upper red clay samples, which reveal that eolian deposit has been modified to some degree by pedogenesis procedure after deposition because of suitable climate conditions. However, the quartz surface in the upper silt layer and middle red clay layer is very clean, and shows clearly subangular to subrounded shape and collision pits which are typical eolian evidence. All the quartz pretreated by hydrogen peroxide and hydrochloric acid are characterized by clearly subangular to subrounded shape and abundant collision pits or pocks, which prove that the red clay has the similar sedimentary origin as the overlapped loesspaleosol sequences; but the solution and precipitation evidences on the primary quartz surface may indicate the climate condition during the late Tertiary is different from the Quaternary periods' warmer-wetter and colder-dryer climatic condition.
2000, 18(4): 515-520.
Abstract:
By the aid of X ray diffractometer, transmit electron microscopes (TEM) and scQan electron microscopes (SEM), authors have revealed the altered features of landing ash from Daqingshan Inner Mongolia Late Paleozoic era (C 2—P 1 ), and discussed the effect of depositional setting on ash alteration. In peat moor, the landing ash is directly altered into kaolinite in situ,forming cryptocrystalline kaolinite mudstone. The mudstone is almost monomineralic and keeps the shapes of crystallinoclastic and shard. Under TEM, the kaolinites in the form of unitary and aggregate are mostly glassy.Their arris are not tidy, with different shapes small particle size and strong aggregation. Under SEM, worm kaolinites and pisolite kaolinites are usually paragenetic. Both made up porphyritic texture in the range of micron. In non peat moor, the landing ash is firstly altered into gel, then into clay minerals in allochthon, becoming clay mudstone. The mudstone is polymineralic, with mineral components composed of illite, montmorillonite and interstratified illite montmorillonite and so on. Under TEM, the kaolinites are coagulative and clastic; under SEM, the sedimentary characters are often seen, such as microbedding and microbedding plane made up of oriented clay minerals. After the ash transferred by air deposits, its alteration and products in peat moor are different from non peat moor because the conditions of physics and chemistry vary with environment. The paper shows much to insight on deeply understanding of volcanic event strata and studing genesis of kaolinton in coal series.
By the aid of X ray diffractometer, transmit electron microscopes (TEM) and scQan electron microscopes (SEM), authors have revealed the altered features of landing ash from Daqingshan Inner Mongolia Late Paleozoic era (C 2—P 1 ), and discussed the effect of depositional setting on ash alteration. In peat moor, the landing ash is directly altered into kaolinite in situ,forming cryptocrystalline kaolinite mudstone. The mudstone is almost monomineralic and keeps the shapes of crystallinoclastic and shard. Under TEM, the kaolinites in the form of unitary and aggregate are mostly glassy.Their arris are not tidy, with different shapes small particle size and strong aggregation. Under SEM, worm kaolinites and pisolite kaolinites are usually paragenetic. Both made up porphyritic texture in the range of micron. In non peat moor, the landing ash is firstly altered into gel, then into clay minerals in allochthon, becoming clay mudstone. The mudstone is polymineralic, with mineral components composed of illite, montmorillonite and interstratified illite montmorillonite and so on. Under TEM, the kaolinites are coagulative and clastic; under SEM, the sedimentary characters are often seen, such as microbedding and microbedding plane made up of oriented clay minerals. After the ash transferred by air deposits, its alteration and products in peat moor are different from non peat moor because the conditions of physics and chemistry vary with environment. The paper shows much to insight on deeply understanding of volcanic event strata and studing genesis of kaolinton in coal series.
2000, 18(4): 527-533.
Abstract:
In recent years, the flow of the Yellow River has often been interrupted, which has resulted in exposure of channel bars and point bars, and even extensive exposure of the riverbed. Consequently, a large number of rill marks have developed. They are diverse in morphology. According to the hydrodynamic types of their formation, they can be grouped into 6 categories, i. e. the wave-eroded, backwash, seepage, rain-eroded, water-drainage and runoff rill marks. Morphologically, they can be divided into more than ten types: the linear, tooth-shaped, comb-shaped, fence-like, ear-like, braided, branched, leaf-like, flower-like, root-like, dendritic, net-like, radial etc. Their cross sections include the broad-u type (the width/depth ratio is over 2, and may reach 10－20), U-type (width/depth ratio from 1 to 2), V-type, Ω-type and (-type. Their occurrences may be attributed to the variations in composition, grain-size, color, fabric and morphology. They have 5 scales: the micro-scale (length and width within 1 cm), small-scale (length and width within 10 cm), medium-scale (length and width ranging from 10－100cm), large-scale (length and width 1－5 m) and giant- scale (length or width over 5 m).
In recent years, the flow of the Yellow River has often been interrupted, which has resulted in exposure of channel bars and point bars, and even extensive exposure of the riverbed. Consequently, a large number of rill marks have developed. They are diverse in morphology. According to the hydrodynamic types of their formation, they can be grouped into 6 categories, i. e. the wave-eroded, backwash, seepage, rain-eroded, water-drainage and runoff rill marks. Morphologically, they can be divided into more than ten types: the linear, tooth-shaped, comb-shaped, fence-like, ear-like, braided, branched, leaf-like, flower-like, root-like, dendritic, net-like, radial etc. Their cross sections include the broad-u type (the width/depth ratio is over 2, and may reach 10－20), U-type (width/depth ratio from 1 to 2), V-type, Ω-type and (-type. Their occurrences may be attributed to the variations in composition, grain-size, color, fabric and morphology. They have 5 scales: the micro-scale (length and width within 1 cm), small-scale (length and width within 10 cm), medium-scale (length and width ranging from 10－100cm), large-scale (length and width 1－5 m) and giant- scale (length or width over 5 m).
2000, 18(4): 539-543,566.
Abstract:
The Jurassic strata are widely distributed in the northwestern China.The Early to early Middle Jurassic strata are major coal bearing strata in the northwestern China that consist of sedimentary products of warm humid climte,which are easily traced and correlated regionally.The late Middle to Late Jurassic strata are mainly composed of red beds,interbedded conglomerate and light gray sandstones deposited in the alluvial and fluvial environments,showing paleoclimate changed from humid to dry features.In recent years,hydrocarbon exploration and researches in the Jurassic of NW China found the following facts:many present basin margin areas often lack basin marginal coarse grain sediments of the Jurassic,while present tectonic uplift belts separating sedimentary basins are not present in some periods of the Jurassic or even whole Jurassic.Thus,it is necessary to reconstruct original sedimentary province of the Jurassic basins in NW China. Reconstruction of sedimentary province of the Jurassic in NW China is based on marginal sedimentary facies analysis,stratigraphic contact relationship analysis,paleocurrent system analysis,and tectonic/structural framework analysis.Marginal sedimentary facies analysis focuses on identifying alluvial fan and fluvial depositional systems that define sedimentary extent of basins.Stratigraphic contact relationship analysis is study on relationship between the residual Jurassic strata and underlying or overlaying strata because the relationship reflects depositional setting of the Jurassic strata and transform extent after the Jurassic deposition.Paleocurrent system analysis can help recognize relationship among remade basins at present.Identification of source area,shape and boundary of basins can be carried out on the basis of paleocurrent distribution.Tectonic/structural framework directly or indirectly affects deposition,sometimes are main factor to control sdimentary province and distribution of depositional systems.The Jurassic deposits of NW China are obviously controlled by tectonic/structural framework.For example,there are three subsiding zones in the Qaidam Qilian sedimentary province during the Middle to Late Jurassic deposition,which show similar sedimentary features.Thus,study results of data rich subsiding zones can help predict distribution of depositional systems of little data subsiding zones. Reconstruction of sedimentary province of the Jurassic in NW China is based on the four methods stated above combined with distribution of residual Jurassic outcrops and depositional systems.The results show that the original sedimentary province of the Early to Middle Jurassic is much larger than the residual sedimentary province of the Early Middle Jurassic at present,for example,the Junggar,Turpan hami and other basins are one large sedimentary province;whereas the original sedimentary province of the Middle to Late Jurassic is no big change compared with the residual sedimentary province of the Middle to Late Jurassic.
The Jurassic strata are widely distributed in the northwestern China.The Early to early Middle Jurassic strata are major coal bearing strata in the northwestern China that consist of sedimentary products of warm humid climte,which are easily traced and correlated regionally.The late Middle to Late Jurassic strata are mainly composed of red beds,interbedded conglomerate and light gray sandstones deposited in the alluvial and fluvial environments,showing paleoclimate changed from humid to dry features.In recent years,hydrocarbon exploration and researches in the Jurassic of NW China found the following facts:many present basin margin areas often lack basin marginal coarse grain sediments of the Jurassic,while present tectonic uplift belts separating sedimentary basins are not present in some periods of the Jurassic or even whole Jurassic.Thus,it is necessary to reconstruct original sedimentary province of the Jurassic basins in NW China. Reconstruction of sedimentary province of the Jurassic in NW China is based on marginal sedimentary facies analysis,stratigraphic contact relationship analysis,paleocurrent system analysis,and tectonic/structural framework analysis.Marginal sedimentary facies analysis focuses on identifying alluvial fan and fluvial depositional systems that define sedimentary extent of basins.Stratigraphic contact relationship analysis is study on relationship between the residual Jurassic strata and underlying or overlaying strata because the relationship reflects depositional setting of the Jurassic strata and transform extent after the Jurassic deposition.Paleocurrent system analysis can help recognize relationship among remade basins at present.Identification of source area,shape and boundary of basins can be carried out on the basis of paleocurrent distribution.Tectonic/structural framework directly or indirectly affects deposition,sometimes are main factor to control sdimentary province and distribution of depositional systems.The Jurassic deposits of NW China are obviously controlled by tectonic/structural framework.For example,there are three subsiding zones in the Qaidam Qilian sedimentary province during the Middle to Late Jurassic deposition,which show similar sedimentary features.Thus,study results of data rich subsiding zones can help predict distribution of depositional systems of little data subsiding zones. Reconstruction of sedimentary province of the Jurassic in NW China is based on the four methods stated above combined with distribution of residual Jurassic outcrops and depositional systems.The results show that the original sedimentary province of the Early to Middle Jurassic is much larger than the residual sedimentary province of the Early Middle Jurassic at present,for example,the Junggar,Turpan hami and other basins are one large sedimentary province;whereas the original sedimentary province of the Middle to Late Jurassic is no big change compared with the residual sedimentary province of the Middle to Late Jurassic.
2000, 18(4): 549-554.
Abstract:
In South China, especially in Southwest China, Sinian dolostone is widely distributed and with great thickness,which is of favorable potential of oil/gas accumulation. But the formation is very old in geologic age and complicated in diagenesis, which results in the uneven distribution and apparent inhomogeneity of the reservoirs. In the area, the Sinian dolostone reservoirs are dominantly concentrated at the top and middle parts of the Dengying Formation, and pore spaces are completely dominated by pores, vugs and fractures with secondary origination.Study indicates that the formation and evolution of the porosity are controlled by diagenesis.The destructive diagenesis,which is unfavorable for the formation and evolution of porosity,are mainly compression, cementation of primary porosity and filling of chemical prceipitation in secondary porosity, and the constructive diagenesis,which stimulates the formation and resolution of porosity,include recrystallization, dissolution in hypergenesis and in burial diagenesis. Compression is the main factor of closing all the primary porosity in fine dolostone; the primary intergranular porosity in grain dolostone and algae bound dolostone and algae framework porosity were eliminated after cementation of three phase dolosparite with the shapes of fiber, silt fine crystal and coarse crystal, and only a little residual primary porosity was preserved.The chemical fillings in the secondary pores, vugs and fractures are the cause of the porosity being not able to be preserved. There are mainly three phases of chemical fillings.The first phase is characterized by fiber like dolomite with the shapes of grape lace, the second one takes shape of fine to course dolomite, and the third one megacrystal dolomite. They may reduce the secondary porosity by 20%～80%, or up to 100% locally. The cements and chemical fillings precipitated in different diagenesis environments differ from each other not only in shapes of the crystals occurrence and succession of formation,also in geochemical features. Recrystallization occurred in burial diagenesis is apparent in the dolostone with no or little insoluble residues.The recrystallization results in the dolomite crystals in original rocks growing bigger and more automorphic, and the outcome is that total porosity in original rocks is not increased,but the effective porosity and permeability are increased, which is favorable for the passing of soluble formation water during buried diagenesis.Moreover,a good basis is laid for burial dissolution and formation and evolution of porosity are stimulated. Dissolution is the main factor of forming the secondary porosity, the hypergenesis dissolution at the end of Sinian was related to Tong Wan Movement. The dissolution developed not only lots of inter breccia pores, vugs and residual grape lace like vugs, but made the porosity concentrate in the range of 5 to 75 meters under weathering boundary. There are two phases of dissolution in burial episode, the first one happened in mature stage, and the second one in over mature stage of organic matters,dissolution is tightly bound to the process of maturing and evoluting of organic matters within the formations. To sum up, the porosity in Sinian dolostone reservoirs in Southwest Sichuan is the end product of natural process of sedimentation, diagenesis and tectonics in as long as 0.6 billion years. Diagenesis turned the dolostone deposits dominated by primary porosity into the dolostone reservoirs completely dominated by secondary porosity.
In South China, especially in Southwest China, Sinian dolostone is widely distributed and with great thickness,which is of favorable potential of oil/gas accumulation. But the formation is very old in geologic age and complicated in diagenesis, which results in the uneven distribution and apparent inhomogeneity of the reservoirs. In the area, the Sinian dolostone reservoirs are dominantly concentrated at the top and middle parts of the Dengying Formation, and pore spaces are completely dominated by pores, vugs and fractures with secondary origination.Study indicates that the formation and evolution of the porosity are controlled by diagenesis.The destructive diagenesis,which is unfavorable for the formation and evolution of porosity,are mainly compression, cementation of primary porosity and filling of chemical prceipitation in secondary porosity, and the constructive diagenesis,which stimulates the formation and resolution of porosity,include recrystallization, dissolution in hypergenesis and in burial diagenesis. Compression is the main factor of closing all the primary porosity in fine dolostone; the primary intergranular porosity in grain dolostone and algae bound dolostone and algae framework porosity were eliminated after cementation of three phase dolosparite with the shapes of fiber, silt fine crystal and coarse crystal, and only a little residual primary porosity was preserved.The chemical fillings in the secondary pores, vugs and fractures are the cause of the porosity being not able to be preserved. There are mainly three phases of chemical fillings.The first phase is characterized by fiber like dolomite with the shapes of grape lace, the second one takes shape of fine to course dolomite, and the third one megacrystal dolomite. They may reduce the secondary porosity by 20%～80%, or up to 100% locally. The cements and chemical fillings precipitated in different diagenesis environments differ from each other not only in shapes of the crystals occurrence and succession of formation,also in geochemical features. Recrystallization occurred in burial diagenesis is apparent in the dolostone with no or little insoluble residues.The recrystallization results in the dolomite crystals in original rocks growing bigger and more automorphic, and the outcome is that total porosity in original rocks is not increased,but the effective porosity and permeability are increased, which is favorable for the passing of soluble formation water during buried diagenesis.Moreover,a good basis is laid for burial dissolution and formation and evolution of porosity are stimulated. Dissolution is the main factor of forming the secondary porosity, the hypergenesis dissolution at the end of Sinian was related to Tong Wan Movement. The dissolution developed not only lots of inter breccia pores, vugs and residual grape lace like vugs, but made the porosity concentrate in the range of 5 to 75 meters under weathering boundary. There are two phases of dissolution in burial episode, the first one happened in mature stage, and the second one in over mature stage of organic matters,dissolution is tightly bound to the process of maturing and evoluting of organic matters within the formations. To sum up, the porosity in Sinian dolostone reservoirs in Southwest Sichuan is the end product of natural process of sedimentation, diagenesis and tectonics in as long as 0.6 billion years. Diagenesis turned the dolostone deposits dominated by primary porosity into the dolostone reservoirs completely dominated by secondary porosity.
2000, 18(4): 560-566.
Abstract:
Fluid rock interactions in sedimentary basin plays an important role in changing characteristics of reservoir rocks and properties of pore fluid,and then affects accumulation and distribution of oil and gas in reservoir.This paper has analyzed formation temperature,pressure condition and the geochemical feature of pore fluid in Eogene,Dongying Depression,Bohai Gulf Basin.The systems of fluid dynamics have been divided.The fluid dynamics characteristics and its distribution feature in defferent system of fluid dynamics are discussed.Base on the analytical result of composition and structural feature of mineral in mudstone which sampling from 4 section of Shahejie Formation in typical well of Niuzhuang Sag,Dongying Depression.The environment medium condition (including salinity,pH value and Eh value)in rock diagenetic process and geochemical characteristics of the pore fluid in rock are supposed.According to the combination feature of the major mineral in mud rock stratum and sandstone layer and its distribution law on stratigraphic profile of typical oil field,fluid rock interaction process would also been divided three stages,which is similar to fluid pressure and chemical characteristics.This paper summarizes the basic characteristics of fluid rock interaction of different stage in Eogene reservoir,Dongying Depression.The physicochemical factors affecting rock fluid interaction have been discussed,which include formation temperature,pore fluid nature and underground fluid dynamics feature and unusual formation pressure tape and so on.Based on the discussion above,a general geological/geochemical model of fluid rock interaction is established.This research shows the distribution feature,the evolution law of diagenetic mineral,the environment and fashion of fluid rock interaction are all different in different fluid dynamics system,which is to say that the geological/geochemical model of fluid rock interaction are different in different fluid dynamics system.
Fluid rock interactions in sedimentary basin plays an important role in changing characteristics of reservoir rocks and properties of pore fluid,and then affects accumulation and distribution of oil and gas in reservoir.This paper has analyzed formation temperature,pressure condition and the geochemical feature of pore fluid in Eogene,Dongying Depression,Bohai Gulf Basin.The systems of fluid dynamics have been divided.The fluid dynamics characteristics and its distribution feature in defferent system of fluid dynamics are discussed.Base on the analytical result of composition and structural feature of mineral in mudstone which sampling from 4 section of Shahejie Formation in typical well of Niuzhuang Sag,Dongying Depression.The environment medium condition (including salinity,pH value and Eh value)in rock diagenetic process and geochemical characteristics of the pore fluid in rock are supposed.According to the combination feature of the major mineral in mud rock stratum and sandstone layer and its distribution law on stratigraphic profile of typical oil field,fluid rock interaction process would also been divided three stages,which is similar to fluid pressure and chemical characteristics.This paper summarizes the basic characteristics of fluid rock interaction of different stage in Eogene reservoir,Dongying Depression.The physicochemical factors affecting rock fluid interaction have been discussed,which include formation temperature,pore fluid nature and underground fluid dynamics feature and unusual formation pressure tape and so on.Based on the discussion above,a general geological/geochemical model of fluid rock interaction is established.This research shows the distribution feature,the evolution law of diagenetic mineral,the environment and fashion of fluid rock interaction are all different in different fluid dynamics system,which is to say that the geological/geochemical model of fluid rock interaction are different in different fluid dynamics system.
2000, 18(4): 573-579,610.
Abstract:
The Chuxiong Basin in centeral Yunnan is a Mesozoic oil-bearing peripheral foreland basin, which was developed mainly during the Late Triassic, and passed gradually into an intracontinental downwarped basin during Jurassic period. The integration of geological and geophysical data shows that the basin is separated by the YupaojiangShaqiao fault into two parts. According to the classic models, the Triassic sediments in the western thrust zone are generally interpreted as the foredeep sediments, while the eastern part is believed to be a foreland bulge and an intracontinental depression. However, the authors in the present paper argued, on the basis of structure and texture, distribution,stacking pattern and provenance in combination with the geochemical and geophysical data, that the Triassic sediments in the western thrust zone should be assigned to the wedge-top sediments. whereas the foreland area in the eastern part recorded progressive deposition in the foreland basin system. The earlier foredeep sediments might have been consumed under the nappe zone in the west rather than cropped out on the surface. (1)Viewed from the horizontal distribution of sedimentary facies, although the strata in the western thrust zone have undergone multiple phases of tectonic deformation, the earlier Triassic sediments are still well preserved. On the other hand, relatively weak tectonic deformation of the strata in the foreland area in the east once ocurred, and the early strata were apparently consumed under the thrust zone in the west. (2)The stacking patterns of the sediments indicate that the Middle and Lower Triassic strata in the basin should be ascribed to the typical passive continental marginal sediments, which are overlain unconformably by the Carnian or Norian(Upper Triassic)strata with a depositional break during the Ladinian-Carnian, implying that the Chuxiong foreland basin might originate during the early Carnian. Before this period, the whole basin was once in the passive continental marginal area, where stable carbonate deposits prevailed. (3)The Upper Triassic strata may be divided into four second-order sequences altogether four for the wedge-top sediments in the west,three for the eastern part,and one or two for the margins of the basin. The isochronous surfaces in individual sequences can be regionally correlated. (4)The evidences from structure and texture,composition, palaeocurrent direction and geochemical signature have revealed that the Upper Triassic sediments from the wedge-top sediments in the western nappe zone are characterized by low compositional and textural maturity, and progressively thinned sediment thickness toward the western orogenic zone as the source area. The presentday foreland area in the east only accepted the post-Norian deposits with high compositional and textural maturity. The principal source of detritus lay to the Xikang-Yunnan oldland in the east. During the late Late Triassic, the thust zone overthrusted upon the thick rigid lithospheric crust,giving rise to weak warping and slow subsidence of the basin. For this reason, no typical foredeep sediments are observed.
The Chuxiong Basin in centeral Yunnan is a Mesozoic oil-bearing peripheral foreland basin, which was developed mainly during the Late Triassic, and passed gradually into an intracontinental downwarped basin during Jurassic period. The integration of geological and geophysical data shows that the basin is separated by the YupaojiangShaqiao fault into two parts. According to the classic models, the Triassic sediments in the western thrust zone are generally interpreted as the foredeep sediments, while the eastern part is believed to be a foreland bulge and an intracontinental depression. However, the authors in the present paper argued, on the basis of structure and texture, distribution,stacking pattern and provenance in combination with the geochemical and geophysical data, that the Triassic sediments in the western thrust zone should be assigned to the wedge-top sediments. whereas the foreland area in the eastern part recorded progressive deposition in the foreland basin system. The earlier foredeep sediments might have been consumed under the nappe zone in the west rather than cropped out on the surface. (1)Viewed from the horizontal distribution of sedimentary facies, although the strata in the western thrust zone have undergone multiple phases of tectonic deformation, the earlier Triassic sediments are still well preserved. On the other hand, relatively weak tectonic deformation of the strata in the foreland area in the east once ocurred, and the early strata were apparently consumed under the thrust zone in the west. (2)The stacking patterns of the sediments indicate that the Middle and Lower Triassic strata in the basin should be ascribed to the typical passive continental marginal sediments, which are overlain unconformably by the Carnian or Norian(Upper Triassic)strata with a depositional break during the Ladinian-Carnian, implying that the Chuxiong foreland basin might originate during the early Carnian. Before this period, the whole basin was once in the passive continental marginal area, where stable carbonate deposits prevailed. (3)The Upper Triassic strata may be divided into four second-order sequences altogether four for the wedge-top sediments in the west,three for the eastern part,and one or two for the margins of the basin. The isochronous surfaces in individual sequences can be regionally correlated. (4)The evidences from structure and texture,composition, palaeocurrent direction and geochemical signature have revealed that the Upper Triassic sediments from the wedge-top sediments in the western nappe zone are characterized by low compositional and textural maturity, and progressively thinned sediment thickness toward the western orogenic zone as the source area. The presentday foreland area in the east only accepted the post-Norian deposits with high compositional and textural maturity. The principal source of detritus lay to the Xikang-Yunnan oldland in the east. During the late Late Triassic, the thust zone overthrusted upon the thick rigid lithospheric crust,giving rise to weak warping and slow subsidence of the basin. For this reason, no typical foredeep sediments are observed.
2000, 18(4): 585-589.
Abstract:
The generation and development of sedimentary organic facies are controlled by many factors, such as palaeoclimate, palaeostructure and palaeogeography etc. It is known that these factors have changed periodically in the geological history, and this change must have led to periodical changes of sedimentary organic facies. This can be indicated by distribution of the sedimentary organic facies in the time stratigraphic framework or sequence stratigraphic framework.Due to the lateral variation in the palaeoenviroments, many types of sedimentary organic facies can develop all over the basin during a single period. The lateral zonation of organic facies can be reflected in their vertical superimposition,which to some extend follows the Walther's law. The sedimentary systems tracts in the sequence stratigraphic framework have been proved to be effective methods to analyze regularities and to predict nature of the organic petrology, organic geochemistry and non organic geochemistry of the potential source rocks. Based on the above knowledge, the organic petrological, geochemical and palynological mathods have been used to analyze the distribution of the sedimentary organic facies in the continental facies stratigraphic framework of the middle Jurassic coal bearing series in Taibei sag of the Turpan Hami basin and the southern Junggar edge.Turpan Hami and Junggar basins are typical basins of which hydrocarbon generated from coal measure in China and the continental facies sequence stratigraphic framework in this area have been studied by many scholars and experts.In the muddestone, the organic quantity and potential hydrocarbon generating ability are indicated by fluorescent organic constituent index, TOC, S 1+S 2.The distance from provenance is revealed by SiO 2+AI 2O 3 content. The deep change of sedimentary media is indicated by Ca/Mg. The salinity and reducibility of media is reflected by Sr/Ba.Climate change is indicated by P,Sr/Cu, and the both change of the different sedimentary system tract and cycling of the different types sedimentary organic facies can be reflected by all of these change in vertical profile.The results show that, in general, all types of organic sedmentary facies show vertically symmetrical distribution centered at the transgresssives systems trace(TST). The best hydrocarbon source rocks are preserved in the middle part of the TST, and the potential for hydrocarbon generation becomes poor upwards and downwards from this position.
The generation and development of sedimentary organic facies are controlled by many factors, such as palaeoclimate, palaeostructure and palaeogeography etc. It is known that these factors have changed periodically in the geological history, and this change must have led to periodical changes of sedimentary organic facies. This can be indicated by distribution of the sedimentary organic facies in the time stratigraphic framework or sequence stratigraphic framework.Due to the lateral variation in the palaeoenviroments, many types of sedimentary organic facies can develop all over the basin during a single period. The lateral zonation of organic facies can be reflected in their vertical superimposition,which to some extend follows the Walther's law. The sedimentary systems tracts in the sequence stratigraphic framework have been proved to be effective methods to analyze regularities and to predict nature of the organic petrology, organic geochemistry and non organic geochemistry of the potential source rocks. Based on the above knowledge, the organic petrological, geochemical and palynological mathods have been used to analyze the distribution of the sedimentary organic facies in the continental facies stratigraphic framework of the middle Jurassic coal bearing series in Taibei sag of the Turpan Hami basin and the southern Junggar edge.Turpan Hami and Junggar basins are typical basins of which hydrocarbon generated from coal measure in China and the continental facies sequence stratigraphic framework in this area have been studied by many scholars and experts.In the muddestone, the organic quantity and potential hydrocarbon generating ability are indicated by fluorescent organic constituent index, TOC, S 1+S 2.The distance from provenance is revealed by SiO 2+AI 2O 3 content. The deep change of sedimentary media is indicated by Ca/Mg. The salinity and reducibility of media is reflected by Sr/Ba.Climate change is indicated by P,Sr/Cu, and the both change of the different sedimentary system tract and cycling of the different types sedimentary organic facies can be reflected by all of these change in vertical profile.The results show that, in general, all types of organic sedmentary facies show vertically symmetrical distribution centered at the transgresssives systems trace(TST). The best hydrocarbon source rocks are preserved in the middle part of the TST, and the potential for hydrocarbon generation becomes poor upwards and downwards from this position.
2000, 18(4): 595-599.
Abstract:
More than ten year's advanced research work has been done by numbers of outstanding geologists, so that theresearch of coal-derived hydrocarbon for Turpan-Hami Basin has developped a lot. However, gemetic potential for Jurassic coal-system mudstone and coal is not enough to explain the formatic scale of oil-gas accumulation of Turpan-Hami Basin. The cannel-boghead, discovered firstly in Triassic in Keyayi depression in western Turpan-Hami basin, is the best source rock with the characteristics of good type, high quality and great genetic-potential. The discovery of cannel-boghead has not only main significance in evaluating hydrocarbon-generated prospect of preJurassic in this area but has enlightenment in analyzing diversify of coal-derived hydrocarbon types. The results of the synthetical research demonstrate that the cannel-boghead, probably, either is one of the generating hydrocarbon materials of pre-Jurassic oil accumulation in Tainan depression, or makes contribution to oil-gas accumulation of Jurassic. Fairly abundant cannel-boghead distributed in deep lake with semiarid, bracksh, and strong reduction in Keyayi depression and Taibei depression in Middle Trassic, in Qiudong area of Taibei depression in Early Jurassic as well as in northern Taibei sag in late Early Permian. These cannel-boghead and lacustrine mudstones all provided hydrocarbon-generated matters to oil-gas accumulation of Turpan - Hami Basin. The hydrocarbon-generated condition of Turpan-Hami Basin is very similar with that of Jungger Basin. Besiders, the mantle matters probably comtribute greatly on forming oil-gas accumulation of Turpan-Hami Basin.
More than ten year's advanced research work has been done by numbers of outstanding geologists, so that theresearch of coal-derived hydrocarbon for Turpan-Hami Basin has developped a lot. However, gemetic potential for Jurassic coal-system mudstone and coal is not enough to explain the formatic scale of oil-gas accumulation of Turpan-Hami Basin. The cannel-boghead, discovered firstly in Triassic in Keyayi depression in western Turpan-Hami basin, is the best source rock with the characteristics of good type, high quality and great genetic-potential. The discovery of cannel-boghead has not only main significance in evaluating hydrocarbon-generated prospect of preJurassic in this area but has enlightenment in analyzing diversify of coal-derived hydrocarbon types. The results of the synthetical research demonstrate that the cannel-boghead, probably, either is one of the generating hydrocarbon materials of pre-Jurassic oil accumulation in Tainan depression, or makes contribution to oil-gas accumulation of Jurassic. Fairly abundant cannel-boghead distributed in deep lake with semiarid, bracksh, and strong reduction in Keyayi depression and Taibei depression in Middle Trassic, in Qiudong area of Taibei depression in Early Jurassic as well as in northern Taibei sag in late Early Permian. These cannel-boghead and lacustrine mudstones all provided hydrocarbon-generated matters to oil-gas accumulation of Turpan - Hami Basin. The hydrocarbon-generated condition of Turpan-Hami Basin is very similar with that of Jungger Basin. Besiders, the mantle matters probably comtribute greatly on forming oil-gas accumulation of Turpan-Hami Basin.
2000, 18(4): 606-610.
Abstract:
Tarim Basin, located in the northwest China, is one of the largest basins in the world, which has not been well explored. In recent years the large scale of petroleum exploration in the basin has led to the discovery of a series of oil and gas fields, with an approximate 1∶1 ratio of oil to gas resource. This means that the natural gas resource is very important for the hydrocarbon resource in the Tarim basin. In this basin most of the discovered gases are condensate associated gas and oil associated gas. It is show by chemical components analysis that the content of hydrocarbon of the natural gases from this basin is mostly higher than 65%. The content of CO2 is mostly less than 5%. The content of N2 is mostly less than 10% and the N2 in some gases reaches 25% to 35%. The C 1/C 2+ ratios of gases from Tabei area show a generally decreasing trend from east to west.The content of N 2 in gases shows generally Qincreasing trend from east to west.The carbon isotopic composition of methane becomes gradually lighter from east to west. All these may be responsible to the low palaeozoic source rock,of which maturity is generally becoming lower from east to west.
Tarim Basin, located in the northwest China, is one of the largest basins in the world, which has not been well explored. In recent years the large scale of petroleum exploration in the basin has led to the discovery of a series of oil and gas fields, with an approximate 1∶1 ratio of oil to gas resource. This means that the natural gas resource is very important for the hydrocarbon resource in the Tarim basin. In this basin most of the discovered gases are condensate associated gas and oil associated gas. It is show by chemical components analysis that the content of hydrocarbon of the natural gases from this basin is mostly higher than 65%. The content of CO2 is mostly less than 5%. The content of N2 is mostly less than 10% and the N2 in some gases reaches 25% to 35%. The C 1/C 2+ ratios of gases from Tabei area show a generally decreasing trend from east to west.The content of N 2 in gases shows generally Qincreasing trend from east to west.The carbon isotopic composition of methane becomes gradually lighter from east to west. All these may be responsible to the low palaeozoic source rock,of which maturity is generally becoming lower from east to west.
2000, 18(4): 615-618,623.
Abstract:
Molecular nitrogen (N2 )content of marine saporpelic ytpe gases derived from Lower Paleozoic source rock is high, ranging from 1.61～36.2 percent of molecular nitrogen. N 2 content of wet gases ranges from 10.1% to 36.2%, while dry gases less than 10%, it is to say that N 2 content of wet gases is higher than that of dry gases.Why is there large difference of N 2 content between wet gases and dry gases derived from the same type source rock? What relationship it has with gas migration and accumulation ? Based on the composition and isotope geochemical characteristics of associated gases and non hydrocarbon gases,as well as rare gas in nature gas,N 2 genesis and origin are ascertained in this paper. The study shows that natural gases of middle high N 2 content belong to organic genesis,which is originated from lower Paleozoic marine carbonate source rock. It is indicates that N 2 content difference between wet and dry gas has close relationship to source rock, maturity and natural gas accumulation history.For the same type source rock, N 2 content in gas is controlled by source rock maturity and entrapment conditions.Because of the difference of nitrogen existence form in organic matter of carbonate and mudstone or shale source rock,nitrogen is mainly combined in kerogen by chemical bond for carbonate source rock,but for mudstone or shale source rock,besides chemical bond,nitrogen is bonded in clay mineral by ion substitution form during organic matter maturation.Thermal simulation shows that nitrogen release mechanism is different for the different source rock.N 2 release capacity reachs peak at the generation peak for carbonate source rock, N 2 content of gases decreasing at the high super maturity stage.While for mudstone or shale source rock, N 2 release capacity reachs peak at the high super stage.Therefore,N 2 content of natural gas entrapped at different maturity stage of source different, N 2 content variation in natural gases can be used to reveal natural gas accumulation history, and also to evaluate trap effectiveness. Lower N 2 content of dry gas in Tabei area demonstrates that oil and gas containing higher N 2 content at the generation peak have been lost,and that natural gas captured in the present traps is mainly originated from high super maturity source rock,The above conclusion is supported by heavy methane carbon isotope and large dryness of the gas,and also supported by geologic conditions of Tabei area. Higher N 2 content and lighter methane carbon isotope of wet gas in Tazhong area shows that gas maturity is lower than that of dry gas in most part of Tabei area,natural gas with high N 2 content formed by source rock at the generation peak is captured by trap.
Molecular nitrogen (N2 )content of marine saporpelic ytpe gases derived from Lower Paleozoic source rock is high, ranging from 1.61～36.2 percent of molecular nitrogen. N 2 content of wet gases ranges from 10.1% to 36.2%, while dry gases less than 10%, it is to say that N 2 content of wet gases is higher than that of dry gases.Why is there large difference of N 2 content between wet gases and dry gases derived from the same type source rock? What relationship it has with gas migration and accumulation ? Based on the composition and isotope geochemical characteristics of associated gases and non hydrocarbon gases,as well as rare gas in nature gas,N 2 genesis and origin are ascertained in this paper. The study shows that natural gases of middle high N 2 content belong to organic genesis,which is originated from lower Paleozoic marine carbonate source rock. It is indicates that N 2 content difference between wet and dry gas has close relationship to source rock, maturity and natural gas accumulation history.For the same type source rock, N 2 content in gas is controlled by source rock maturity and entrapment conditions.Because of the difference of nitrogen existence form in organic matter of carbonate and mudstone or shale source rock,nitrogen is mainly combined in kerogen by chemical bond for carbonate source rock,but for mudstone or shale source rock,besides chemical bond,nitrogen is bonded in clay mineral by ion substitution form during organic matter maturation.Thermal simulation shows that nitrogen release mechanism is different for the different source rock.N 2 release capacity reachs peak at the generation peak for carbonate source rock, N 2 content of gases decreasing at the high super maturity stage.While for mudstone or shale source rock, N 2 release capacity reachs peak at the high super stage.Therefore,N 2 content of natural gas entrapped at different maturity stage of source different, N 2 content variation in natural gases can be used to reveal natural gas accumulation history, and also to evaluate trap effectiveness. Lower N 2 content of dry gas in Tabei area demonstrates that oil and gas containing higher N 2 content at the generation peak have been lost,and that natural gas captured in the present traps is mainly originated from high super maturity source rock,The above conclusion is supported by heavy methane carbon isotope and large dryness of the gas,and also supported by geologic conditions of Tabei area. Higher N 2 content and lighter methane carbon isotope of wet gas in Tazhong area shows that gas maturity is lower than that of dry gas in most part of Tabei area,natural gas with high N 2 content formed by source rock at the generation peak is captured by trap.
2000, 18(4): 629-633.
Abstract:
Although 90 percent area of the ocean with depth from 300 to 3 000 meters is suitable to occurrence of gas hydrate in view of temperature and pressure condition,gas hydrate dose not occur everywhere in ocean. The occurrence of gas hydrate is tightly related to geological setting.From tectonic point of view,gas hydrate in the ocean occurs along continenatl margin:one kind is at active passive margin prism,the other is at the continental slope or slope foot.The fromation of gas hydrate is also tightly related to sediment type,sedimentation rate and organic source,as well as heat flow,i.e.more content of organic matter quickly buried in sediments is material condition for the formation of gas hydrate;more coarse sediments,consequently more porosity and more content of porous aquifer supply plentiful space for the cementation of gas hydrate.Gas in hydrate is subjected to biogenesis and thermal degradation of organic matter,so that more content of biomass and higher heat flow are favorable for the formation of gas hydrate. Two kinds of marks are commonly used for distingushing gas hydrate. In seabed sediments,one is geophysical mark,i.e.blank reflection and simulated seafloor reflector (BSR) which is caused by the different acoustic wave velocity between hydrate zone and underneath sediments and parallel to seafloor and oblique to bedding.In contrast to seafloor reflection,simulated seafloor reflector has reversed polarity.The other is geochemical mark,i.e.positive CH 4,H 2S and CO 2 gas geochemical anomalous,as well as negative saltness or chlorinity anomalous should be present due to the decomposition of gas hydrate in the log profile. The western lower slope of Mid Okinawa Trough possesses good geological setting and conditions for the formation of gas hydrate.First of all,the water depth is more than 1 000 meters, which is suitable to the formation of gas hydrate from the temperature perssure point of view.Secondly,sedimentss almost silty mud and muddy silt which may supply plentiful cemented space for gas hydrate.Thirdly,the content of organic matter in sediment is much higher than adjacent area,the sedimentation rate is also higher(10～40 cm·ka),causing the abundant organic matter buried quickly,so that the gas source is stored for the formation of gas hydeate.The last is that the values of heat flow change from 70 to 437 mw/m 2,much higher than the other area,supplying plentiful heat for thermal degradation of organic matter.A channel seismic reflection profile(A—A′)at the lower slope margin,with depth from 1 500 to 1 800 meters,shows that a simulated seafloor reflector occurs at depth of 2 250 meters beneath sea floor and gradually disappears up slope,which is parallel to seafloor and oblique to bedding,and also has negative polarity (reversed polarity) in contrast to seafloor reflection.Therefore,we initially deduce that the gas hydrate may occur at the western lower slope of Mid Okinawa Trough.
Although 90 percent area of the ocean with depth from 300 to 3 000 meters is suitable to occurrence of gas hydrate in view of temperature and pressure condition,gas hydrate dose not occur everywhere in ocean. The occurrence of gas hydrate is tightly related to geological setting.From tectonic point of view,gas hydrate in the ocean occurs along continenatl margin:one kind is at active passive margin prism,the other is at the continental slope or slope foot.The fromation of gas hydrate is also tightly related to sediment type,sedimentation rate and organic source,as well as heat flow,i.e.more content of organic matter quickly buried in sediments is material condition for the formation of gas hydrate;more coarse sediments,consequently more porosity and more content of porous aquifer supply plentiful space for the cementation of gas hydrate.Gas in hydrate is subjected to biogenesis and thermal degradation of organic matter,so that more content of biomass and higher heat flow are favorable for the formation of gas hydrate. Two kinds of marks are commonly used for distingushing gas hydrate. In seabed sediments,one is geophysical mark,i.e.blank reflection and simulated seafloor reflector (BSR) which is caused by the different acoustic wave velocity between hydrate zone and underneath sediments and parallel to seafloor and oblique to bedding.In contrast to seafloor reflection,simulated seafloor reflector has reversed polarity.The other is geochemical mark,i.e.positive CH 4,H 2S and CO 2 gas geochemical anomalous,as well as negative saltness or chlorinity anomalous should be present due to the decomposition of gas hydrate in the log profile. The western lower slope of Mid Okinawa Trough possesses good geological setting and conditions for the formation of gas hydrate.First of all,the water depth is more than 1 000 meters, which is suitable to the formation of gas hydrate from the temperature perssure point of view.Secondly,sedimentss almost silty mud and muddy silt which may supply plentiful cemented space for gas hydrate.Thirdly,the content of organic matter in sediment is much higher than adjacent area,the sedimentation rate is also higher(10～40 cm·ka),causing the abundant organic matter buried quickly,so that the gas source is stored for the formation of gas hydeate.The last is that the values of heat flow change from 70 to 437 mw/m 2,much higher than the other area,supplying plentiful heat for thermal degradation of organic matter.A channel seismic reflection profile(A—A′)at the lower slope margin,with depth from 1 500 to 1 800 meters,shows that a simulated seafloor reflector occurs at depth of 2 250 meters beneath sea floor and gradually disappears up slope,which is parallel to seafloor and oblique to bedding,and also has negative polarity (reversed polarity) in contrast to seafloor reflection.Therefore,we initially deduce that the gas hydrate may occur at the western lower slope of Mid Okinawa Trough.
2000, 18(4): 646-650.
Abstract:
Carbon isotopic compositions of organic matters in the sediments during late Glacial Maximum and Late Glacial Period have been analyzed in arid semiarid areas of northwestern China. It shows that the sediment have recorded in detail the process of climatic oscillation that changed from dry and cool to warm and wet in thousand or hundred years scale during this period in the transition of monsoon edge belts. High resolution record of organic carbon isotopic compositions is the same as that of GRIP oxygen isotopic composition. It also indicates that there is a relative climatic changes between the globe and arid China. The climate was warm and wet in the transition period of late Glacial Maximum to Late Glacial, and terrestrial plants grew briskly. And the monsoon had taken an important action in the climatic oscillation in Shiyang river basin. The proxy of δ 13 C is the effective indicator of reconstructing the palaeoclimatic variation in the arid China because of its sensitivity to the climatic changes.
Carbon isotopic compositions of organic matters in the sediments during late Glacial Maximum and Late Glacial Period have been analyzed in arid semiarid areas of northwestern China. It shows that the sediment have recorded in detail the process of climatic oscillation that changed from dry and cool to warm and wet in thousand or hundred years scale during this period in the transition of monsoon edge belts. High resolution record of organic carbon isotopic compositions is the same as that of GRIP oxygen isotopic composition. It also indicates that there is a relative climatic changes between the globe and arid China. The climate was warm and wet in the transition period of late Glacial Maximum to Late Glacial, and terrestrial plants grew briskly. And the monsoon had taken an important action in the climatic oscillation in Shiyang river basin. The proxy of δ 13 C is the effective indicator of reconstructing the palaeoclimatic variation in the arid China because of its sensitivity to the climatic changes.
