1987 Vol. 5, No. 2
column
Display Method:
1987, 5(2): 1-15.
Abstract:
The sedimentary environment of Middle Triassic in Southwest and South Gui-zhou is controlled by the Kaiyuan-Pintang giant fault.The region on the west or northwest of this fault is a restricted carbonate platform or organic shoal facies on the margin of the platform, and the region on the east or southeast of the fault is a shelf-slope or trough basin facies, Banqi-Yata Region lies in the transitional zone between the platform area and trough basin area. In the section, the shelf facies (including the normal shelf deposit and tempestite ) , the slope facies ( including the normal carbonate slope deposit and contourite ) and the trough basin facies of the turbidite occur upwards correspondingly. The characteristics of the facies sequences indicate the transgressive sedimentary cycle of Middle Triassic. This paper deals with mainly the shelf-slope sedimentary characteristics of Middle Triassic in Banqi-Yata Region.The tempestite, contourite and turbidite are discussed in detail. There are three kinds of tempestite assemblages in the section, i.e. assmblage of shell-bed and calcisilitite, silty limestone, that of shell-bed and silty mudstone, and that of siltstone and mudstone. There exist typical structures, such as graded bedding, small hummocky crossbedding, wave-ripple cross-bedding, gutter cast.The characteristics of the tempestite, such as fine grain, thinner bed, very rare lag deposit and lack of amalgamtion indicate the tempestite belongs to the distal storm deposit on offshore shelf. The Banqi contourite is very different from the associated turbidite. Its beds are thin and grains well sorted but no graded bedding. Howere,the typical lenticular and wave-like cross-bedding develop. The turbidite in the study are mainly consists of the CDEF assemblage or DEF assemblage of the Bouma sequence, i.e.primarily fine grains. The channel-system deposit could not be found in the section and there is not a thinning or thickening upwards tendency either. The cycle curve in the corresponding diagram between bed numbers and bed thickness shows a sawtooth-like shape and the the characteristics of monotonous sequence. In the turbidite,"proxi-mal"and "distal" beds overlapped each other at random or thick-massive sandstones occur in "distal" beds.The above-mentioned characters indicate that the turbidite is not submarine-fan or typical basin-plain deposit but belongs to the trough longitudinal turbidite controlled by regional structures. Finally, the sedimentary pattern of Middle Triassic in the study region is presented. On the basis of the study on the Middle Triassic sedimentary facies, it is found that there's a close relationship between the sedimentary facies and the distribution of the middle-large scale Au deposits found out recently in the southwestern Guizhou, and that one kind of Au deposits lies in the shelf facies, another appears in the marginal subfacies of trough basin facies. In the light of the preliminary study, Au in the marginal subfacies mainly concentrates in the DE segments of Bouma sequence in the turbidite.
The sedimentary environment of Middle Triassic in Southwest and South Gui-zhou is controlled by the Kaiyuan-Pintang giant fault.The region on the west or northwest of this fault is a restricted carbonate platform or organic shoal facies on the margin of the platform, and the region on the east or southeast of the fault is a shelf-slope or trough basin facies, Banqi-Yata Region lies in the transitional zone between the platform area and trough basin area. In the section, the shelf facies (including the normal shelf deposit and tempestite ) , the slope facies ( including the normal carbonate slope deposit and contourite ) and the trough basin facies of the turbidite occur upwards correspondingly. The characteristics of the facies sequences indicate the transgressive sedimentary cycle of Middle Triassic. This paper deals with mainly the shelf-slope sedimentary characteristics of Middle Triassic in Banqi-Yata Region.The tempestite, contourite and turbidite are discussed in detail. There are three kinds of tempestite assemblages in the section, i.e. assmblage of shell-bed and calcisilitite, silty limestone, that of shell-bed and silty mudstone, and that of siltstone and mudstone. There exist typical structures, such as graded bedding, small hummocky crossbedding, wave-ripple cross-bedding, gutter cast.The characteristics of the tempestite, such as fine grain, thinner bed, very rare lag deposit and lack of amalgamtion indicate the tempestite belongs to the distal storm deposit on offshore shelf. The Banqi contourite is very different from the associated turbidite. Its beds are thin and grains well sorted but no graded bedding. Howere,the typical lenticular and wave-like cross-bedding develop. The turbidite in the study are mainly consists of the CDEF assemblage or DEF assemblage of the Bouma sequence, i.e.primarily fine grains. The channel-system deposit could not be found in the section and there is not a thinning or thickening upwards tendency either. The cycle curve in the corresponding diagram between bed numbers and bed thickness shows a sawtooth-like shape and the the characteristics of monotonous sequence. In the turbidite,"proxi-mal"and "distal" beds overlapped each other at random or thick-massive sandstones occur in "distal" beds.The above-mentioned characters indicate that the turbidite is not submarine-fan or typical basin-plain deposit but belongs to the trough longitudinal turbidite controlled by regional structures. Finally, the sedimentary pattern of Middle Triassic in the study region is presented. On the basis of the study on the Middle Triassic sedimentary facies, it is found that there's a close relationship between the sedimentary facies and the distribution of the middle-large scale Au deposits found out recently in the southwestern Guizhou, and that one kind of Au deposits lies in the shelf facies, another appears in the marginal subfacies of trough basin facies. In the light of the preliminary study, Au in the marginal subfacies mainly concentrates in the DE segments of Bouma sequence in the turbidite.
1987, 5(2): 29-38.
Abstract:
A kind of iron-bearing non-skeletal oncolites has been found in the Middle and Lower Ordovician grey biomicrite of Kuniutan and Datianba Formations at Shitai, Chao and He counties, Auhui. Beds containing this Kind of oncolites are intercalated between the brownish red or grey-green biomicrite, nodular biomicrite and argillaceous biomicrite. The oncolite content is: 1- 5% or more. The fact that the birdseye structure and desiccation cracks occur on some bed surface indicates that the beds are formed in a shallow subtidal or supratidal oxidizing environment. The sediments bearing the oncolite are distributed in a mud-bank-facies belt which is restricted to the southwestern margin of Ninzhen-Wannan carbonate platforms where are near Huaiyang ancient continent and Jiangnan ancient island which are considered as a source of iron for the oncolite, however, the sediments in the same facies belt but far away from the anceient continent and island develop little ironbearing oncolite. The iron-bearing non-skeletal oncolites are oval grains, 15-20mm in lenghth and the longest up to 32.8mm, consisting of a nucleus of bioclast and concentric laminated crust which is formed by the grown blue-green algae. Two types of oncolite can be recognized depending on the distinction of their microtexture. Type one is columoids consisting of columnar microstromatolites in a radiating arrangement around a nucleus. The second type is colu-strigatoids consisting of laminar-columnar micro stromatolites around a nucleus. Their crust can be distinguished into three parts; inner crust, middle crust ( major curst ) and outer crust. Among them the middle crust is the thickest one. The formation of oncolites underwent several processes: the prepartion of nuclei; the growth of original crust rolling on the bottom) the suspention growth of major crust) the calcification of crust) the growth and abrasion of outer crust) and last the burial and consolidation of oncolites. Based on the thickness of the major crust and the number of algae lamina-minae per unit length, it can be determined that columoids grow faster and suspend longer than the colu-strigatoids. The constituents of the oncolite include calcite, limonite, hematite and cham-osite etc. and calcite is the major composition. The total amuont of ironstone in the oncolite comes to 5.92%. It is four times higher than that of country rocks. Most of iron materials concentrate in the algae laminae and the mucilage of algae with colloidal texture. The iron content ia the laminae has a cyclic change. Based on the distribution of iron it can be suggested that the blue-green algae absorb and precipitate iron materials while they are growing. This process is called concentration of iron in growing period.The iron can also be concentrated around the oncolite in cloud pattern during diagenetic process but it is not important while compared with the former. The oncolite not only contains iron but also contains other metal elements. For example, in the oncolite, Pb = 200ppm, Cu=100ppm, their contents are seven and three times as high as that of country rocks respectively. The evidence mentioned above shows that the growth of algae is of significance in concentrating iron and other metal elements, such as lead and copper, which may result in the formation of sedimentary iron deposits or other metal deposits,
A kind of iron-bearing non-skeletal oncolites has been found in the Middle and Lower Ordovician grey biomicrite of Kuniutan and Datianba Formations at Shitai, Chao and He counties, Auhui. Beds containing this Kind of oncolites are intercalated between the brownish red or grey-green biomicrite, nodular biomicrite and argillaceous biomicrite. The oncolite content is: 1- 5% or more. The fact that the birdseye structure and desiccation cracks occur on some bed surface indicates that the beds are formed in a shallow subtidal or supratidal oxidizing environment. The sediments bearing the oncolite are distributed in a mud-bank-facies belt which is restricted to the southwestern margin of Ninzhen-Wannan carbonate platforms where are near Huaiyang ancient continent and Jiangnan ancient island which are considered as a source of iron for the oncolite, however, the sediments in the same facies belt but far away from the anceient continent and island develop little ironbearing oncolite. The iron-bearing non-skeletal oncolites are oval grains, 15-20mm in lenghth and the longest up to 32.8mm, consisting of a nucleus of bioclast and concentric laminated crust which is formed by the grown blue-green algae. Two types of oncolite can be recognized depending on the distinction of their microtexture. Type one is columoids consisting of columnar microstromatolites in a radiating arrangement around a nucleus. The second type is colu-strigatoids consisting of laminar-columnar micro stromatolites around a nucleus. Their crust can be distinguished into three parts; inner crust, middle crust ( major curst ) and outer crust. Among them the middle crust is the thickest one. The formation of oncolites underwent several processes: the prepartion of nuclei; the growth of original crust rolling on the bottom) the suspention growth of major crust) the calcification of crust) the growth and abrasion of outer crust) and last the burial and consolidation of oncolites. Based on the thickness of the major crust and the number of algae lamina-minae per unit length, it can be determined that columoids grow faster and suspend longer than the colu-strigatoids. The constituents of the oncolite include calcite, limonite, hematite and cham-osite etc. and calcite is the major composition. The total amuont of ironstone in the oncolite comes to 5.92%. It is four times higher than that of country rocks. Most of iron materials concentrate in the algae laminae and the mucilage of algae with colloidal texture. The iron content ia the laminae has a cyclic change. Based on the distribution of iron it can be suggested that the blue-green algae absorb and precipitate iron materials while they are growing. This process is called concentration of iron in growing period.The iron can also be concentrated around the oncolite in cloud pattern during diagenetic process but it is not important while compared with the former. The oncolite not only contains iron but also contains other metal elements. For example, in the oncolite, Pb = 200ppm, Cu=100ppm, their contents are seven and three times as high as that of country rocks respectively. The evidence mentioned above shows that the growth of algae is of significance in concentrating iron and other metal elements, such as lead and copper, which may result in the formation of sedimentary iron deposits or other metal deposits,
1987, 5(2): 45-56.
Abstract:
This paper applies the mathematics model of the overthrust thermal effect described by Angevine, et al. ( 1983 ) to study the thermal history of the Permian source rocks in the Klamai-Ulh overthrust belt. Based on the thermal maturity indexes, such as the vitrinite reflectance of samples collected from different structure position, the paleotemperature is recovered and thermal maturity evolution of organic matters simulated. The thermal modeling demonstrates that the maturation of the source rock located at the lower part of overthrust stage increased owing to the affection of thermal conduct deriving from high geotemperature of the overthrust-sheet bottom, so the source rock of Permian reached the stage of oil-generation peak at the beginning of Jurassic. Howerer, the velocity of the source-rock maturation of the same age in the upper wall slowed up due to quickly cooling, and the maturity was almost not elevated in the post-overthrust stage. This mold of the overthrust thermal effect canbe applied to not only simple overthrust, but also multiple thrust. In this paper Zayier Overthrust Belt is studied as an example of multiple thrust. As its overthrust sheet is very thick and the overthrust thermal effect rather strong, the velocity ef thermal maturation becomes rather quick and source rocks come into overmaturation quickly.
This paper applies the mathematics model of the overthrust thermal effect described by Angevine, et al. ( 1983 ) to study the thermal history of the Permian source rocks in the Klamai-Ulh overthrust belt. Based on the thermal maturity indexes, such as the vitrinite reflectance of samples collected from different structure position, the paleotemperature is recovered and thermal maturity evolution of organic matters simulated. The thermal modeling demonstrates that the maturation of the source rock located at the lower part of overthrust stage increased owing to the affection of thermal conduct deriving from high geotemperature of the overthrust-sheet bottom, so the source rock of Permian reached the stage of oil-generation peak at the beginning of Jurassic. Howerer, the velocity of the source-rock maturation of the same age in the upper wall slowed up due to quickly cooling, and the maturity was almost not elevated in the post-overthrust stage. This mold of the overthrust thermal effect canbe applied to not only simple overthrust, but also multiple thrust. In this paper Zayier Overthrust Belt is studied as an example of multiple thrust. As its overthrust sheet is very thick and the overthrust thermal effect rather strong, the velocity ef thermal maturation becomes rather quick and source rocks come into overmaturation quickly.
1987, 5(2): 63-72.
Abstract:
In 1983-1984, The authors found the clastic turbidite of the deep water continental source and the pelagic deposits in the several-thousand-meter clastic rock of Cambrian-middle Ordovician in Xichangjing of Ejinaqi, Inner Mongolia. This area belongs to the Caledonian folded belt with the gabbro and ultrabasic rocks intruding into the Cambrian-Ordoviciaa System in the late period of the Caledonian cycle, and with magma activities of neutral or acid rocks, such as plagiogra-nite and quartz diorite of the Hercynian cycle. The Cambrian deposits in this area are mainly turbidite, 1504 metres in thickness and composed of siliceous rock, gravel-bearing graywacke, feldspar-quartz graywacke and a little of slate; the lower Ordovician deposits are also turbidite, 1320 metres in thickness and contain interbedding of feldspar-quartz graywacke and slate; whereas the middle Ordovician deposits of more than 1579 metres. The south side of this zone is an ancient continental folded basement of Precambrian; the north one is an area dispersed over by ophiolite suite and residual ancient ocean crust of the end of middle Ordovician-late Ordovician and disintegrated by a series of overthrust faults. Based on the field investigation of the authors, it is found that early Cambrian-early Ordovician in the study area is a principle developmental period of turbidity ourrent and the characteristics of turbidites in different era are as fol-lowst l.The lower Cambrian turbidite: It is 979 metres in thickness and its rhythmit-es are composed mainly of feldspar-quartz graywack and silty slate, in which the graywacke content is over 3/4. There are three groups of the Bouma sequence, from bottom to top they are: 1)ABD, ABCD, ABD, 2)ABCD, ABCD, AD, 3)AD, AD, AD. The Bouma sequence in the lower part of the turbidite is mainly Section A and lacks Section E, However, Section A in the middle part of the turbidite is thinner, generally speaking, the Bouma sequence in this part develops well and the oblique bedding of the Section C shows that the sediment is transported from south to north and the folded basement of Precambrian in the southern part is the material source area. The Bouma sequence of the upper turbidite develops only Sectoin A and C, indicating the turbidite is near the source area. 2.The lower Ordovician turbidite: It is 1300 metres in thickness including more than handred metres of deepwater sediments interbedded with the turbidite. Every section of the Bouma sequence is well developed with tongue-like and finger-like scouring floormolds. There are four groups of the Bouma sequence form bottom to top in this turbi-dite: 1)AD, AD, AD, 2 ) ACD, ACD, 3 ) AD, ABCD, 4 ) ABCD. In the Section C of the upper part of the turbidite apperars a sliding layer, indicating that there is a slope in the sedimentary environment, so that a gravity sliding motion under the water develops in the Section C and then a long tail-current period occurs and the thicker Section D is formed. The volcanic-sedimentary assemblages can be divided into five groups, they are. 1 ) the sedimentary assemblage of continental margin sea of the bottom of Lower Cambrian; 2 ) The semi-deepsea sedimentary assemblage of middle and upper Cambrian; 3 ) The deepsea sedimentary assemblage of the upper part of Lower Ordovi-cian; 4 ) The rift-margin volcanic assemblage of the lower part of middle Ordovi-cian; 5 ) The pelagic deposit assemblage of the upper part of middle Ordovician. Based on the characteristics of the turbidite and the comprehensive study on the volcanic-sedimentary assemblages,it is found that the sedimentary environment of Cambrian in the study area successively underwent continental margin sea, continental slope, continental rise and finally semi-deepsea. In early Ordovician, the eontinental slope environment appeared once again. The turbidites discussed in this paper are the results of the turbidite sedimentation on continental slope and continental rise. However, the sedimentary environment of middle Ordovician is the period from as active volcano of rift t
In 1983-1984, The authors found the clastic turbidite of the deep water continental source and the pelagic deposits in the several-thousand-meter clastic rock of Cambrian-middle Ordovician in Xichangjing of Ejinaqi, Inner Mongolia. This area belongs to the Caledonian folded belt with the gabbro and ultrabasic rocks intruding into the Cambrian-Ordoviciaa System in the late period of the Caledonian cycle, and with magma activities of neutral or acid rocks, such as plagiogra-nite and quartz diorite of the Hercynian cycle. The Cambrian deposits in this area are mainly turbidite, 1504 metres in thickness and composed of siliceous rock, gravel-bearing graywacke, feldspar-quartz graywacke and a little of slate; the lower Ordovician deposits are also turbidite, 1320 metres in thickness and contain interbedding of feldspar-quartz graywacke and slate; whereas the middle Ordovician deposits of more than 1579 metres. The south side of this zone is an ancient continental folded basement of Precambrian; the north one is an area dispersed over by ophiolite suite and residual ancient ocean crust of the end of middle Ordovician-late Ordovician and disintegrated by a series of overthrust faults. Based on the field investigation of the authors, it is found that early Cambrian-early Ordovician in the study area is a principle developmental period of turbidity ourrent and the characteristics of turbidites in different era are as fol-lowst l.The lower Cambrian turbidite: It is 979 metres in thickness and its rhythmit-es are composed mainly of feldspar-quartz graywack and silty slate, in which the graywacke content is over 3/4. There are three groups of the Bouma sequence, from bottom to top they are: 1)ABD, ABCD, ABD, 2)ABCD, ABCD, AD, 3)AD, AD, AD. The Bouma sequence in the lower part of the turbidite is mainly Section A and lacks Section E, However, Section A in the middle part of the turbidite is thinner, generally speaking, the Bouma sequence in this part develops well and the oblique bedding of the Section C shows that the sediment is transported from south to north and the folded basement of Precambrian in the southern part is the material source area. The Bouma sequence of the upper turbidite develops only Sectoin A and C, indicating the turbidite is near the source area. 2.The lower Ordovician turbidite: It is 1300 metres in thickness including more than handred metres of deepwater sediments interbedded with the turbidite. Every section of the Bouma sequence is well developed with tongue-like and finger-like scouring floormolds. There are four groups of the Bouma sequence form bottom to top in this turbi-dite: 1)AD, AD, AD, 2 ) ACD, ACD, 3 ) AD, ABCD, 4 ) ABCD. In the Section C of the upper part of the turbidite apperars a sliding layer, indicating that there is a slope in the sedimentary environment, so that a gravity sliding motion under the water develops in the Section C and then a long tail-current period occurs and the thicker Section D is formed. The volcanic-sedimentary assemblages can be divided into five groups, they are. 1 ) the sedimentary assemblage of continental margin sea of the bottom of Lower Cambrian; 2 ) The semi-deepsea sedimentary assemblage of middle and upper Cambrian; 3 ) The deepsea sedimentary assemblage of the upper part of Lower Ordovi-cian; 4 ) The rift-margin volcanic assemblage of the lower part of middle Ordovi-cian; 5 ) The pelagic deposit assemblage of the upper part of middle Ordovician. Based on the characteristics of the turbidite and the comprehensive study on the volcanic-sedimentary assemblages,it is found that the sedimentary environment of Cambrian in the study area successively underwent continental margin sea, continental slope, continental rise and finally semi-deepsea. In early Ordovician, the eontinental slope environment appeared once again. The turbidites discussed in this paper are the results of the turbidite sedimentation on continental slope and continental rise. However, the sedimentary environment of middle Ordovician is the period from as active volcano of rift t
1987, 5(2): 81-90.
Abstract:
In the studied area the outcroped strata are mainly three formations: the Middle Devonian Qiziqiao Formation ( D2q ) , the Upper Devonian Shetianqiao Formation ( D3S ) and Xikuangshan Formation ( D3x ) . According to its difference of lithologic character, each formation is subdivided into sevral members and sub-members. In the whole area there is few of terrigenous clastic rocks, carbonate rocks occupy mostly. The carbonate rocks consist of micrite ( including algal pellet micrite, laminated micrite, dolomitized micrite ) , arenitic micrite, sparry algal ooid limestone, sparry calcarenits, sparry bioclastic limestone etc..However the micri-tes constitute the main part, the other types of limestone are found in intercalations and these indicate that the rocks were generally formed in a environment of low energy. The texture origin components of limestonespellet, intraclast and terrigenous clastic quartz show the pulsatory variation and the organisms of algae are flourishing, these suggest that the rocks were formed in a tidal flat environment. Some limestones, especially in D2q, have been dolomitized and the origin of do lostone is explained in terms of seawater mixed with fresh water. This model also indirectly indicates that the rocks were formed in a tidal flat environment. Other evidences indicating their sedimentary environment are as follows: (l)wa-ter flow into two directions, such as beddings of fish bone, reactivation surface etc; ( 2 ) the mark of pulsative variation, such as lenticular bedding; ( 3 ) the indication of intermittant exposure, such as mud crack and birdeye structure. Based on above characteristics together with texture of sections and characteristics of sedimentary geochemistry, the sedimentary facies of this area can be classified into three facies zones; namely, coastal facies zone, restricted platform facies zone and open platform facies zone. The first zone is composed of terrigenous detritus beach facies. The second is subdivided into intertidal mud flat facies in turbid water, intertidal mud flat facies in clear water, intertidal mixed flat facies, tidal ditch facies and tidal beach facies. The third consists of the shallow water in subtidal zone. The study on the relationship of element assemblage gives a complementary evidence for analysis of sedimentary facies. In factor analysis of R type, three factors F1, F2 and F3 are taken. F1 apparently reveals the fact of turbid water deposit and clear water deposit alternately appeared in this area; F2 suggests a variation from shallow water to deep water and from low to high salt content in the tidal environment, F3 indicates the turbid water of carbonate flat suppress growing of organism. In factor analysis of Q type, the first three principal factors g1, g2 and g3 are also taken. All-bulk of the samples loading on the axis of fac-ttor g1 are larger, which shows the sedimentary area is to be a tidal environment ( because the samples of terrigenous detritus beach facies are not participated in the analysis ) . According to sedimentary facies, samples on the axis of factor g2 are evidently distributed. On one hand, it indicates that the geological significance of g2 is to place emphasis on the hydrodynamical variation resulting different facies types, on the another hand it indirectly suggests that the diagenetic environment is not a completely open system. The informations of primarily sedimentary environment are partly reserved, and thus characteristics of sedimentary geochemistry may be used as a complementary evidence of sedimentary facies. Sample loadings on the axis of factor g3 are more scattered, which reveals the characteristics of transitional facies from sea to continent. The vertical variation of sedimentary facies results from the lateral shift and overlap of laterally neighbouring facies. On the basis of this, a comprehensive sedimentary facies model of Dongbo-Pinghe area in the Middle and Late Devonian is established.
In the studied area the outcroped strata are mainly three formations: the Middle Devonian Qiziqiao Formation ( D2q ) , the Upper Devonian Shetianqiao Formation ( D3S ) and Xikuangshan Formation ( D3x ) . According to its difference of lithologic character, each formation is subdivided into sevral members and sub-members. In the whole area there is few of terrigenous clastic rocks, carbonate rocks occupy mostly. The carbonate rocks consist of micrite ( including algal pellet micrite, laminated micrite, dolomitized micrite ) , arenitic micrite, sparry algal ooid limestone, sparry calcarenits, sparry bioclastic limestone etc..However the micri-tes constitute the main part, the other types of limestone are found in intercalations and these indicate that the rocks were generally formed in a environment of low energy. The texture origin components of limestonespellet, intraclast and terrigenous clastic quartz show the pulsatory variation and the organisms of algae are flourishing, these suggest that the rocks were formed in a tidal flat environment. Some limestones, especially in D2q, have been dolomitized and the origin of do lostone is explained in terms of seawater mixed with fresh water. This model also indirectly indicates that the rocks were formed in a tidal flat environment. Other evidences indicating their sedimentary environment are as follows: (l)wa-ter flow into two directions, such as beddings of fish bone, reactivation surface etc; ( 2 ) the mark of pulsative variation, such as lenticular bedding; ( 3 ) the indication of intermittant exposure, such as mud crack and birdeye structure. Based on above characteristics together with texture of sections and characteristics of sedimentary geochemistry, the sedimentary facies of this area can be classified into three facies zones; namely, coastal facies zone, restricted platform facies zone and open platform facies zone. The first zone is composed of terrigenous detritus beach facies. The second is subdivided into intertidal mud flat facies in turbid water, intertidal mud flat facies in clear water, intertidal mixed flat facies, tidal ditch facies and tidal beach facies. The third consists of the shallow water in subtidal zone. The study on the relationship of element assemblage gives a complementary evidence for analysis of sedimentary facies. In factor analysis of R type, three factors F1, F2 and F3 are taken. F1 apparently reveals the fact of turbid water deposit and clear water deposit alternately appeared in this area; F2 suggests a variation from shallow water to deep water and from low to high salt content in the tidal environment, F3 indicates the turbid water of carbonate flat suppress growing of organism. In factor analysis of Q type, the first three principal factors g1, g2 and g3 are also taken. All-bulk of the samples loading on the axis of fac-ttor g1 are larger, which shows the sedimentary area is to be a tidal environment ( because the samples of terrigenous detritus beach facies are not participated in the analysis ) . According to sedimentary facies, samples on the axis of factor g2 are evidently distributed. On one hand, it indicates that the geological significance of g2 is to place emphasis on the hydrodynamical variation resulting different facies types, on the another hand it indirectly suggests that the diagenetic environment is not a completely open system. The informations of primarily sedimentary environment are partly reserved, and thus characteristics of sedimentary geochemistry may be used as a complementary evidence of sedimentary facies. Sample loadings on the axis of factor g3 are more scattered, which reveals the characteristics of transitional facies from sea to continent. The vertical variation of sedimentary facies results from the lateral shift and overlap of laterally neighbouring facies. On the basis of this, a comprehensive sedimentary facies model of Dongbo-Pinghe area in the Middle and Late Devonian is established.
1987, 5(2): 113-124.
Abstract:
The Eogene Baigang formation is a major coal-bearing and oil-producing member in Baise Basin. Based on the study of the paleoenvironment and syndeposi-tional structure of this formation, a coal accumulation model, reflecting that both paleostructure and paleoenvironment control over the formation of coal-rich zone has been established in this paper. It is suggested that by means of the analysis of seismic facies the model be efficiently used to predict the coal-rich zone in coal exploration. Baise Basin is a semi-graben basin (about 16 x 90km ) with a depositional fault on its northern margin, and a series of X-E faults developing in the basement as well as subordinate depressions and swells have been identified in the basin. They obviously influence the sedimentation of the formation. The depositional facies of the Baigang formation can be divided into three zones: ( 1 ) Alluvial fan and fan delta deposits along the northern marginal fault, mainly consisting of coarse debris flow and water-lain deposits. The vertical sequences from the proximal fan delta are of a distinct association. The fan deltas have deltaic upward-coarsing sequences consisting of three beds (a topset, a for-set and a bottomset ) , and an obvious sedimentary polycyclity. The topset bed, which sometimes includes channel-fill deposits of coarse conglomerate, are actu- ally the subaerial part of the fans progressing towards lake. Individual depositional lobes, wedge-shape in cross sections are from 30 to 90 m thick and have an area of about 16 square kilometers. ( 2 ) Shallow-deep lake deposites in the central part of the basin, including thin sandstone with some graded bedding, organic-rich shale and dark mud-stone with ostracods and fish fossils. ( 3 ) Lakeshore and small-scale deltaic deposits in the south of the basin, containing small-scale shore deltaic sandstone, and sandy mudstone with plenty of mollusks. bioturbate structures and small-scale cross beddings. The small-scale shore deltaic deposits are relatively thinner and finer than the fan deltaic deposits along the northern margin This asymmetric configuration of the facies is controlled by the structure framework of the semi-graben. There are three seismic facies units divided by different reflection characteristics. Unit 1 distributed over the area of the ( 1 ) facies zone is characteristic of a wedge-shspe geometry, chaotic or divergence-foreset texture, high amplitude, middle continuity and low frequence. These characteristics indicate the high energy sedimentation of fans and fan deltas in the northern margin. Unit 2 in the central part of the basin is characterized by sheet shape, parallel texture, high continuity, middle amplitude, and high frequency. These characteristics indicate the relatively stable and low-energy sedimentation of the deep-shallow lake. Unit 3 in the south of the basin is distinguished by subparallel texture, weak or middle amplitude, low continuity and middle frequence. The distribution of depositional facies zones therefore, may be identified by the analysis of seismic facies. The coal accumulation of the Baigang formation is controlled by both the distribution of depositional facies zones and the paleostructure condition. The coal -rich zones are coincided with subordinate depressions and parallel to the facies zones ( 1 )and ( 3 ) of the basion and the coal-rich centers are separated by the little fan deltas, which are the most potentional oil reservoirs. The interdeltaic bays or areas, lacking the coarse detritus carried by rivers, are interpreted as the most favourable places to peat accumulation. As a result of the different subsidence along both sides of the basin, the coal-rich zone on the northern side of the marginal fault is markedly thicker than that on the other side. It may be seen that identifying the configuration of depositional facies and paleostructure condition is most important in the orediction of coal-rich zones, while the analysis of seismic facies units will be conductive to reconstructing the distribution of depositional faci
The Eogene Baigang formation is a major coal-bearing and oil-producing member in Baise Basin. Based on the study of the paleoenvironment and syndeposi-tional structure of this formation, a coal accumulation model, reflecting that both paleostructure and paleoenvironment control over the formation of coal-rich zone has been established in this paper. It is suggested that by means of the analysis of seismic facies the model be efficiently used to predict the coal-rich zone in coal exploration. Baise Basin is a semi-graben basin (about 16 x 90km ) with a depositional fault on its northern margin, and a series of X-E faults developing in the basement as well as subordinate depressions and swells have been identified in the basin. They obviously influence the sedimentation of the formation. The depositional facies of the Baigang formation can be divided into three zones: ( 1 ) Alluvial fan and fan delta deposits along the northern marginal fault, mainly consisting of coarse debris flow and water-lain deposits. The vertical sequences from the proximal fan delta are of a distinct association. The fan deltas have deltaic upward-coarsing sequences consisting of three beds (a topset, a for-set and a bottomset ) , and an obvious sedimentary polycyclity. The topset bed, which sometimes includes channel-fill deposits of coarse conglomerate, are actu- ally the subaerial part of the fans progressing towards lake. Individual depositional lobes, wedge-shape in cross sections are from 30 to 90 m thick and have an area of about 16 square kilometers. ( 2 ) Shallow-deep lake deposites in the central part of the basin, including thin sandstone with some graded bedding, organic-rich shale and dark mud-stone with ostracods and fish fossils. ( 3 ) Lakeshore and small-scale deltaic deposits in the south of the basin, containing small-scale shore deltaic sandstone, and sandy mudstone with plenty of mollusks. bioturbate structures and small-scale cross beddings. The small-scale shore deltaic deposits are relatively thinner and finer than the fan deltaic deposits along the northern margin This asymmetric configuration of the facies is controlled by the structure framework of the semi-graben. There are three seismic facies units divided by different reflection characteristics. Unit 1 distributed over the area of the ( 1 ) facies zone is characteristic of a wedge-shspe geometry, chaotic or divergence-foreset texture, high amplitude, middle continuity and low frequence. These characteristics indicate the high energy sedimentation of fans and fan deltas in the northern margin. Unit 2 in the central part of the basin is characterized by sheet shape, parallel texture, high continuity, middle amplitude, and high frequency. These characteristics indicate the relatively stable and low-energy sedimentation of the deep-shallow lake. Unit 3 in the south of the basin is distinguished by subparallel texture, weak or middle amplitude, low continuity and middle frequence. The distribution of depositional facies zones therefore, may be identified by the analysis of seismic facies. The coal accumulation of the Baigang formation is controlled by both the distribution of depositional facies zones and the paleostructure condition. The coal -rich zones are coincided with subordinate depressions and parallel to the facies zones ( 1 )and ( 3 ) of the basion and the coal-rich centers are separated by the little fan deltas, which are the most potentional oil reservoirs. The interdeltaic bays or areas, lacking the coarse detritus carried by rivers, are interpreted as the most favourable places to peat accumulation. As a result of the different subsidence along both sides of the basin, the coal-rich zone on the northern side of the marginal fault is markedly thicker than that on the other side. It may be seen that identifying the configuration of depositional facies and paleostructure condition is most important in the orediction of coal-rich zones, while the analysis of seismic facies units will be conductive to reconstructing the distribution of depositional faci
1987, 5(2): 133-143.
Abstract:
The Nanliujiang Delta is located in the south of Hepu County, Guangxi. It is a small tide-dominated delta,whose area is about 150 km2. Types and characteristics of sedimentary sequences are summarized by analysing the data of drilling. Based on the comparison between the sequences of the post-glacial period and the modern Nanliujiang Delta, the sedimentary evolution of the delta in the post-glacial period has been interpreted. Three sedimentary stages are divided due to the relative variations between the sedimentary rate and the rate of sea-level rising. The first is a transgressive stage, i. e. the early post-glacial period ( before 7,000 B. P. ) when the sea-lev el rising rate is "greater than sedimentary rate and the risen sea-level leads to the rising of sedimentary base-level, which induces the retrogressive aggradation in the channel, forming the low sandy gravel layer; the second is a stable one, i. e. the middle post-glacial period ( around 7,000 B. P. ) when the sea-level rising rate is lowered and is approximate to the sedimentary rate and the strand sand bars in the marginal area of the modern delta are the products of the wave working upon the shore of the estuary in that period; the third is a regressive one, i.e. the late post-glacial period (after 7,000 B.P. ) when the relatively stable sea-level causes the sedimentary rate to exceed the sea-level rising rate and the delta is progradiag toward sea with the sedimeots brought by the river depositing in the moutharea. And also with the progradation of the delta, the deltaic sequence is produced and then is partly, somewhere with its underlying sandy gravel layer, cut by river. The result is the reworked post-glacial sequence. Relating sedimentary processes with their sediments, the authors have put forward a model for post-glacial sedimentation in the area. The post-glacial sequence is composed of the lower sandy gravel layer originated by retrogressive aggradation in the channel in transgression and the upper deltaic layer formed in regression. The sandy gravel layer is characterized by coarse sediments, poor sorting, poor roundness and the occurrence of some Foraminifera of euryhalinous species in its upper part, indicating an up-ward increase in mariness. The deltaic layer includes the lower neritic-prodelta mud, the middle delta-front sand and the upper delta-plain clay. The up-ward decrease in mariness of this layer is indicated by the fine-coarse-fine change in sediments and the decrease in marine fossils. This is the main sequence in the Nanliujiang Delta, accounting for two thirds of the delta area. Some of this type have been cut and reworked by river after its formation. As a result, parts of the upper layer or even to the bottom, are occupied by fluvial deposits. It can be deduced that with the progradation the Nanliujiang Delta will appear outside the Lianzhou Bay and expose itself to wave, so that in its front a wave-induced sand bar may be developed. The transformation from tide-dominated type to wave-dominated one may occur, similar to the case of the Hanjiang Delta, Guang-dong. Therefore, the third possible reason for the delta type transformation may be the progradation of delta itself.
The Nanliujiang Delta is located in the south of Hepu County, Guangxi. It is a small tide-dominated delta,whose area is about 150 km2. Types and characteristics of sedimentary sequences are summarized by analysing the data of drilling. Based on the comparison between the sequences of the post-glacial period and the modern Nanliujiang Delta, the sedimentary evolution of the delta in the post-glacial period has been interpreted. Three sedimentary stages are divided due to the relative variations between the sedimentary rate and the rate of sea-level rising. The first is a transgressive stage, i. e. the early post-glacial period ( before 7,000 B. P. ) when the sea-lev el rising rate is "greater than sedimentary rate and the risen sea-level leads to the rising of sedimentary base-level, which induces the retrogressive aggradation in the channel, forming the low sandy gravel layer; the second is a stable one, i. e. the middle post-glacial period ( around 7,000 B. P. ) when the sea-level rising rate is lowered and is approximate to the sedimentary rate and the strand sand bars in the marginal area of the modern delta are the products of the wave working upon the shore of the estuary in that period; the third is a regressive one, i.e. the late post-glacial period (after 7,000 B.P. ) when the relatively stable sea-level causes the sedimentary rate to exceed the sea-level rising rate and the delta is progradiag toward sea with the sedimeots brought by the river depositing in the moutharea. And also with the progradation of the delta, the deltaic sequence is produced and then is partly, somewhere with its underlying sandy gravel layer, cut by river. The result is the reworked post-glacial sequence. Relating sedimentary processes with their sediments, the authors have put forward a model for post-glacial sedimentation in the area. The post-glacial sequence is composed of the lower sandy gravel layer originated by retrogressive aggradation in the channel in transgression and the upper deltaic layer formed in regression. The sandy gravel layer is characterized by coarse sediments, poor sorting, poor roundness and the occurrence of some Foraminifera of euryhalinous species in its upper part, indicating an up-ward increase in mariness. The deltaic layer includes the lower neritic-prodelta mud, the middle delta-front sand and the upper delta-plain clay. The up-ward decrease in mariness of this layer is indicated by the fine-coarse-fine change in sediments and the decrease in marine fossils. This is the main sequence in the Nanliujiang Delta, accounting for two thirds of the delta area. Some of this type have been cut and reworked by river after its formation. As a result, parts of the upper layer or even to the bottom, are occupied by fluvial deposits. It can be deduced that with the progradation the Nanliujiang Delta will appear outside the Lianzhou Bay and expose itself to wave, so that in its front a wave-induced sand bar may be developed. The transformation from tide-dominated type to wave-dominated one may occur, similar to the case of the Hanjiang Delta, Guang-dong. Therefore, the third possible reason for the delta type transformation may be the progradation of delta itself.
1987, 5(2): 16-28.
Abstract:
This paper mainly deals with the intense change of hydrodynamics and corresponding sediment accumulation in the modern coast of Zhoushan during Typhoons 8114 and 8310, and discusses the sedimentary characteristics of storm-sand and gravel beaches. These may provide evidences for finding and interpreting similar ancient sedimentary deposits. 1. Common characteristics of the two typhoons ( 1 ) The routes of the two typhoon centers were similar, both approached to the coast of Zhoushan in the direction of NW 315, then at the points of 30.4N 123.5E and 29.8N 124E (near the Zhoushan coast) changed the direction of NE and moved north- eastward. ( 2 ) The wind velocity in the typhoon centers was up to 45-55m/s, the resulting maximum wave height was up to 7.5-17m, the maximum tidal ranged from 4.5 to 5.4m in the nearshore area. This is why the two typhoons exerted the largest effect on the stuied area. 2. Characteristics of storm deposits on sandy coast ( 1 ) The coast underwent an intense erosion and deposition during the typhoon invasion. The measurements before and after the typhoons have shown that the lower part of aeolian dunes and the middle and upper parts of backshore were dominated by accumulation with an increase of elevation about 10-20cm, while the foreshore and the lower part of backshore by erosion. The berms built before the typhoons were eroded 30-50cm, and foreshore reduced 10-20cm. ( 2 ) Sediments formed under fine weather conditions were extensively reworked or even destroyed by typhoon-induced storm waves,and partially or wholly replaced by storm deposits. The characteristics of storm deposits are as follows: (i) sediments become coaser. The mean grain size changes from 2.20-1.50φ before the onset of the typhoons to 1.97-1.00φ during the typhoons: (ii) sediment sorting becomes poorer.The values of standard deviation increase from 0,37-0.40 before the typhoons to 0.45-0.60 during the typhoons; (iii) The sedimentary structure assemblage characterized by hammocky crossbeddings is upwards composed of scour- filled beddings, parallel beddings, hamtnocky and swash cross-beddings and climbing beddings; (iv) the storm deposits in this area are different from the shallow-sea storm deposits whose mean grain size is coaser.in sedimentary sequences appears amalgation without graded beddings and the association with turbidite, remains of organism are mainly nearshore benthonic fauna with strong bioturbation structure. 3. Characteristics of storm deposits on the gravel coast Our observasion has shown that most of gravel beaches in this area are the results of typhoon-induced storm waves. Under fine weather conditions, the top of the ridge has an elevation of 2-4m, and only the middle and lower parts of its sea side are modified and reworked by waves, tides and currents; under storm weather conditions, water may reach or even swash over the top of the ridge, and brings lots of pebbles to the top of the ridge.The characteristics of storm gravel beaches are as follows: (1) Gravel beaches are dominatea by large disc-shaped and flat pebbles, which are mainly distributed at the top of the ridge. Therefore, they can act as an indicator of beaches, espacially beaches formed by storm waves; (2) The shaping and sorting have a marked zonation, from the top of the ridge to sea appaer large disc zone, imbricate zone, infield frame zone, spherical rod and outer frame zone. However, this kind of zonation is evident only in the environments that sorting and reworking are relatively active, with highstorm energy. It should be pointed out that gravel beaches are generally the results of the high energy hydrodynamics, and normal gravel beaches, if exist, only the results of reworking of storm gravel beaches. 4. The study purpose of modern storm deposits is to find out more ancient storm ones. With marks and vertical sequences of storm deposits, we have found similar sequences of storm deposits, respectively in the Silurian and Triassic strata in the Chaohu area of Anhui Province.For example,the Fcnto group of Middle Silu
This paper mainly deals with the intense change of hydrodynamics and corresponding sediment accumulation in the modern coast of Zhoushan during Typhoons 8114 and 8310, and discusses the sedimentary characteristics of storm-sand and gravel beaches. These may provide evidences for finding and interpreting similar ancient sedimentary deposits. 1. Common characteristics of the two typhoons ( 1 ) The routes of the two typhoon centers were similar, both approached to the coast of Zhoushan in the direction of NW 315, then at the points of 30.4N 123.5E and 29.8N 124E (near the Zhoushan coast) changed the direction of NE and moved north- eastward. ( 2 ) The wind velocity in the typhoon centers was up to 45-55m/s, the resulting maximum wave height was up to 7.5-17m, the maximum tidal ranged from 4.5 to 5.4m in the nearshore area. This is why the two typhoons exerted the largest effect on the stuied area. 2. Characteristics of storm deposits on sandy coast ( 1 ) The coast underwent an intense erosion and deposition during the typhoon invasion. The measurements before and after the typhoons have shown that the lower part of aeolian dunes and the middle and upper parts of backshore were dominated by accumulation with an increase of elevation about 10-20cm, while the foreshore and the lower part of backshore by erosion. The berms built before the typhoons were eroded 30-50cm, and foreshore reduced 10-20cm. ( 2 ) Sediments formed under fine weather conditions were extensively reworked or even destroyed by typhoon-induced storm waves,and partially or wholly replaced by storm deposits. The characteristics of storm deposits are as follows: (i) sediments become coaser. The mean grain size changes from 2.20-1.50φ before the onset of the typhoons to 1.97-1.00φ during the typhoons: (ii) sediment sorting becomes poorer.The values of standard deviation increase from 0,37-0.40 before the typhoons to 0.45-0.60 during the typhoons; (iii) The sedimentary structure assemblage characterized by hammocky crossbeddings is upwards composed of scour- filled beddings, parallel beddings, hamtnocky and swash cross-beddings and climbing beddings; (iv) the storm deposits in this area are different from the shallow-sea storm deposits whose mean grain size is coaser.in sedimentary sequences appears amalgation without graded beddings and the association with turbidite, remains of organism are mainly nearshore benthonic fauna with strong bioturbation structure. 3. Characteristics of storm deposits on the gravel coast Our observasion has shown that most of gravel beaches in this area are the results of typhoon-induced storm waves. Under fine weather conditions, the top of the ridge has an elevation of 2-4m, and only the middle and lower parts of its sea side are modified and reworked by waves, tides and currents; under storm weather conditions, water may reach or even swash over the top of the ridge, and brings lots of pebbles to the top of the ridge.The characteristics of storm gravel beaches are as follows: (1) Gravel beaches are dominatea by large disc-shaped and flat pebbles, which are mainly distributed at the top of the ridge. Therefore, they can act as an indicator of beaches, espacially beaches formed by storm waves; (2) The shaping and sorting have a marked zonation, from the top of the ridge to sea appaer large disc zone, imbricate zone, infield frame zone, spherical rod and outer frame zone. However, this kind of zonation is evident only in the environments that sorting and reworking are relatively active, with highstorm energy. It should be pointed out that gravel beaches are generally the results of the high energy hydrodynamics, and normal gravel beaches, if exist, only the results of reworking of storm gravel beaches. 4. The study purpose of modern storm deposits is to find out more ancient storm ones. With marks and vertical sequences of storm deposits, we have found similar sequences of storm deposits, respectively in the Silurian and Triassic strata in the Chaohu area of Anhui Province.For example,the Fcnto group of Middle Silu
1987, 5(2): 39-44.
Abstract:
Based on the observation of the recent tidal flat sedimentary structures of Chongming Island and Jianggang Port, three types of tidal cycle sequences have been established. The first type of sequences is called successive sequence of tidal cycle (or α-sequence ) , which contains 28 mud beds. The middle of the sequence is composed of a group of densely-concentrated mud beds formed during neap tide, and the springs between them are gradually widened upwards or downwards in the sequence. The second type of sequences is called regularly-spaced grouping sequence of tidal ( or β-sequence ) . It is charaterized by several groups of densely-concentrated mud bed deposited during neap tide, together with small-ripple beddings instead of mud beds deposited during spring tide. The third type of sequences is called climbing sequence of tidal cycle (on γ-sequence ) . This type of sequences consists of climbing fine sand lenticles deposited by tidal flow. The scales of lenticles change vertically from large to small, and then from small to large in response to the alternating process of spring tide -neap tide -spring tide. Between spring and neap tide occur mud beds deposited during the period of slack tide. These three types of tidal sequences make up several interrelated associations. They present either as monotonous α-sequences, or as vertically and transversaly alternative association of α and β-sequences, Whereas the γ-sequence is always associated with stronger tidal flows. There are some good ancient examples indicating that above-mentioned structures are of certain practical significance. Plenty of a and p-sequences and imperfect γ-sequences have been found in the Palaeozoic coal-bearing successions in North China and Southwest China. They can be used as certain criteria to identify ancient tidal sediments.
Based on the observation of the recent tidal flat sedimentary structures of Chongming Island and Jianggang Port, three types of tidal cycle sequences have been established. The first type of sequences is called successive sequence of tidal cycle (or α-sequence ) , which contains 28 mud beds. The middle of the sequence is composed of a group of densely-concentrated mud beds formed during neap tide, and the springs between them are gradually widened upwards or downwards in the sequence. The second type of sequences is called regularly-spaced grouping sequence of tidal ( or β-sequence ) . It is charaterized by several groups of densely-concentrated mud bed deposited during neap tide, together with small-ripple beddings instead of mud beds deposited during spring tide. The third type of sequences is called climbing sequence of tidal cycle (on γ-sequence ) . This type of sequences consists of climbing fine sand lenticles deposited by tidal flow. The scales of lenticles change vertically from large to small, and then from small to large in response to the alternating process of spring tide -neap tide -spring tide. Between spring and neap tide occur mud beds deposited during the period of slack tide. These three types of tidal sequences make up several interrelated associations. They present either as monotonous α-sequences, or as vertically and transversaly alternative association of α and β-sequences, Whereas the γ-sequence is always associated with stronger tidal flows. There are some good ancient examples indicating that above-mentioned structures are of certain practical significance. Plenty of a and p-sequences and imperfect γ-sequences have been found in the Palaeozoic coal-bearing successions in North China and Southwest China. They can be used as certain criteria to identify ancient tidal sediments.
1987, 5(2): 57-62.
Abstract:
Sulfate-reducing bacteria as a biogeochemical factor possess considerable functions for petroleum formation, secondary sulfide ore formation and gypsum ore destruction, soil alkalization and salification, and even for iron-steel corrosion. The bacteria also effect the kinds and growth of organiams in aquatic environments. Sulfate-reducing bacteria, therefore, are very important in economic fields. For many years, scientists have investigated their ecology, physiology and biochemistry etc. and accumulated considerable amount of data. This paper deals initially with sulfate-reducing bacteria from Dachaidan Salt Lake and Huining Saline Lake in China.
Sulfate-reducing bacteria as a biogeochemical factor possess considerable functions for petroleum formation, secondary sulfide ore formation and gypsum ore destruction, soil alkalization and salification, and even for iron-steel corrosion. The bacteria also effect the kinds and growth of organiams in aquatic environments. Sulfate-reducing bacteria, therefore, are very important in economic fields. For many years, scientists have investigated their ecology, physiology and biochemistry etc. and accumulated considerable amount of data. This paper deals initially with sulfate-reducing bacteria from Dachaidan Salt Lake and Huining Saline Lake in China.
1987, 5(2): 71-80.
Abstract:
The Yuqian group (or Changwu group) in the west part of Zhejiang province is a set of flysch formation with thickness about 2,000m, in which many kinds of trace fossils are found. In this paper, we only discuss the new species ( Spirode-smos kaihuaensis ) found in kaihua County ( Fig. l ). Spirodesmos kaihuaensis, distributed along the bedding surface, is elliptical, multi-annular, with 3-5 rings. The major axis( A) of the ellipse is up to 35cm, the minor axis ( B ) is up to 18.5cm, and ratio ( A/B ) is about 2. All of the major axis of the elliptical traces are parallel to each other in the NE direction. The authors consider that the traces were produced by some animals which have no hard shells. The animals ploughed sediments in a round way, depending on their innate thigmotaxis and strophotaxis and developing the ringlike traces when they were looking for food. The major axes of the elliptical trace are parallel to the direction of water flow as a result of the pushing force of water flow on the organism, the animals prefered to move in the direction parallel to the water flow rather than perpendicular to it so as to reduce the pushing force of water flow. The trace fossils coexist with many kinds of sedimentary structures, such as symmetric wave marks, interference wave marks, foreset beddings, lenticular beddings etc. , showing a shallow water environment. From all kinds of data, authors concluded that Spirodesmos Kaihuaensis was formed in a subtidal zone of a gulf, which was situated in the north side of the southwest part of the Early palaeozoic sedimentary basin in the west part of Zhe-jiang province. This area was near to an old land which supplied an abundence of organic matter to the basin. In the area there existed a bottom current with lower kinetic energy, flowing in a uniform direction. The water bottom was influenced by wave accasionally. Such an environment benefited trace fossils.
The Yuqian group (or Changwu group) in the west part of Zhejiang province is a set of flysch formation with thickness about 2,000m, in which many kinds of trace fossils are found. In this paper, we only discuss the new species ( Spirode-smos kaihuaensis ) found in kaihua County ( Fig. l ). Spirodesmos kaihuaensis, distributed along the bedding surface, is elliptical, multi-annular, with 3-5 rings. The major axis( A) of the ellipse is up to 35cm, the minor axis ( B ) is up to 18.5cm, and ratio ( A/B ) is about 2. All of the major axis of the elliptical traces are parallel to each other in the NE direction. The authors consider that the traces were produced by some animals which have no hard shells. The animals ploughed sediments in a round way, depending on their innate thigmotaxis and strophotaxis and developing the ringlike traces when they were looking for food. The major axes of the elliptical trace are parallel to the direction of water flow as a result of the pushing force of water flow on the organism, the animals prefered to move in the direction parallel to the water flow rather than perpendicular to it so as to reduce the pushing force of water flow. The trace fossils coexist with many kinds of sedimentary structures, such as symmetric wave marks, interference wave marks, foreset beddings, lenticular beddings etc. , showing a shallow water environment. From all kinds of data, authors concluded that Spirodesmos Kaihuaensis was formed in a subtidal zone of a gulf, which was situated in the north side of the southwest part of the Early palaeozoic sedimentary basin in the west part of Zhe-jiang province. This area was near to an old land which supplied an abundence of organic matter to the basin. In the area there existed a bottom current with lower kinetic energy, flowing in a uniform direction. The water bottom was influenced by wave accasionally. Such an environment benefited trace fossils.
1987, 5(2): 91-102.
Abstract:
In early Oligocene, the depositional environment of Qaidam Basin had its own features. The basin was in a semiarid climatic zone and surrounded by mountains. On the northwest it was bounded by the Aerjing mountain with a steeper slope; on the northweast by the Qilian mountain with a gentle slope; on the south by The Kunlun mountain, where the basin slope was between the two above. within the basin, Sub-basinal fault and trough with different depth developed on the base- ment of gentle-slope depression Basically, the basin was a closed drainage basin, in which the lacustrine waterbody had a relatively high salinity and the lake boundary changed greatly, the expanding and shrinking of the water body was obvious. During the period of the lowest water level; The lake covered an area in accordance with that of the deep part of the subbasinal fault, while during the period of lake water expanding, water could submerge not only the other part of the subbasinal fault but also the gentle slope region, especially in the gentle-slope depression water body would cover a much larger area with slightly rising of water level.So in the area between maximal and minimal extents of the lake water, an expanding lake basin, lacking waterbody at intervals, was finally formed. Studying the strata formed in such environments ( mainly the lower part of Lower Gan Caigou Formation of Oligocene but its upper part involved occasionally in the marginal area ) , we find that the sedimentation of this kind of lake basins has the following characteristics: In steep slope area, the gradient is high, the peak period of water input and expansion is in accordance with that of sediment input, the progradation of both shorewards lacustrine deposits and lakewards terrigenous sediments is vertically great, sediments is thickening more quickly than those in other areas at the same time, so alternate-progradation is very active. Diluvial-lacustrine depositional system is well developed. Clastic rock bodies can be divided into two kinds of assemblages: diluvial fan-lacustrine beach and diluvial fan-sudaquatic diluvial fan. The latter may be easily mistaken for the Gilbert delta, the distinction is that the topset of subaquatic fan is lacustrine deposits and the alternate-progradation structures are well developed. In sub-steep slops, affeced by overfast velocity and aggradation of flow as well as intermittently expanding and shrinking of the lake area, hidden-bedding sandstones and conglomerates which are mainly deposited in the expanding lake area are well-developed. The framework of sedimentary system mainly consists of conglomerate and sandstone bodies of diluvial fans, mainstream channel of river and unconventional deltaic facies. According to the change of lake water body, unconventional delta can be devided into three types, i. e. drying up, expanding and interactive. In the extensive gentle slope area, meander stream channels develop very well in the fluvial deltaic system. Since streams are far away from their sources, well-sorted thick sandstone bodies can be formed. Among the above mentioned sandstone and conglomeratic bodies, those of steep slopes and sub-steep slopes are near the source area of oil and gas generation so they are the preferable targets for oil and gas exploration. Sandstone bodies of unconventional delta are easily sealed and often filled with pore fluids with abnormal high pressure, which is favourable for preserving primary pores and forming secondary pores. Even burried in great depth, they still have enough spaces for preserving oil and gas, So they are more important for petroleum exploration.
In early Oligocene, the depositional environment of Qaidam Basin had its own features. The basin was in a semiarid climatic zone and surrounded by mountains. On the northwest it was bounded by the Aerjing mountain with a steeper slope; on the northweast by the Qilian mountain with a gentle slope; on the south by The Kunlun mountain, where the basin slope was between the two above. within the basin, Sub-basinal fault and trough with different depth developed on the base- ment of gentle-slope depression Basically, the basin was a closed drainage basin, in which the lacustrine waterbody had a relatively high salinity and the lake boundary changed greatly, the expanding and shrinking of the water body was obvious. During the period of the lowest water level; The lake covered an area in accordance with that of the deep part of the subbasinal fault, while during the period of lake water expanding, water could submerge not only the other part of the subbasinal fault but also the gentle slope region, especially in the gentle-slope depression water body would cover a much larger area with slightly rising of water level.So in the area between maximal and minimal extents of the lake water, an expanding lake basin, lacking waterbody at intervals, was finally formed. Studying the strata formed in such environments ( mainly the lower part of Lower Gan Caigou Formation of Oligocene but its upper part involved occasionally in the marginal area ) , we find that the sedimentation of this kind of lake basins has the following characteristics: In steep slope area, the gradient is high, the peak period of water input and expansion is in accordance with that of sediment input, the progradation of both shorewards lacustrine deposits and lakewards terrigenous sediments is vertically great, sediments is thickening more quickly than those in other areas at the same time, so alternate-progradation is very active. Diluvial-lacustrine depositional system is well developed. Clastic rock bodies can be divided into two kinds of assemblages: diluvial fan-lacustrine beach and diluvial fan-sudaquatic diluvial fan. The latter may be easily mistaken for the Gilbert delta, the distinction is that the topset of subaquatic fan is lacustrine deposits and the alternate-progradation structures are well developed. In sub-steep slops, affeced by overfast velocity and aggradation of flow as well as intermittently expanding and shrinking of the lake area, hidden-bedding sandstones and conglomerates which are mainly deposited in the expanding lake area are well-developed. The framework of sedimentary system mainly consists of conglomerate and sandstone bodies of diluvial fans, mainstream channel of river and unconventional deltaic facies. According to the change of lake water body, unconventional delta can be devided into three types, i. e. drying up, expanding and interactive. In the extensive gentle slope area, meander stream channels develop very well in the fluvial deltaic system. Since streams are far away from their sources, well-sorted thick sandstone bodies can be formed. Among the above mentioned sandstone and conglomeratic bodies, those of steep slopes and sub-steep slopes are near the source area of oil and gas generation so they are the preferable targets for oil and gas exploration. Sandstone bodies of unconventional delta are easily sealed and often filled with pore fluids with abnormal high pressure, which is favourable for preserving primary pores and forming secondary pores. Even burried in great depth, they still have enough spaces for preserving oil and gas, So they are more important for petroleum exploration.
1987, 5(2): 125-132.
Abstract:
There are abundant terpeooid compounds in terrestrial immature source rocks of our country. A sample taken from Tertiary immature source rocks is analysed by GC-MS. It is identified that more than 20 terpenoid compounds in the sample, which are rarely observed in low-mature or mature source rocks. The identified compounds are as follows: The peak A is a C19 tricyclic terpane related to abietic acid and is thought to represent an evidence for the contribution of higher plant materials, the peak B, D, E are C24 saturared tetracyclic terpanes, and their m. w. are 330. The peak G belongs to C30 triterpene. The peak H is a mixed one which includes C29 and C30 triterpenes and C30 triterpane. The peak I belongs to a terpenoid compound also and is not clear in its structure. The peak K1 is a neohop-13 ( 18 )-ene. The peak K2 is identified as a terpenoid compound with unknown stucture. The peak Ks is also a mixed one which includes C29 17α(H) norhopane, C30 triterpene and Cso triterpane. The peak L is mixed one too and consists of C29 17β ( H ) normortane and neohop-12-ene. The other peaks such as N. 0, P, R are the triterpanes which are common components in low mature or mature source rocks and crude oils.
There are abundant terpeooid compounds in terrestrial immature source rocks of our country. A sample taken from Tertiary immature source rocks is analysed by GC-MS. It is identified that more than 20 terpenoid compounds in the sample, which are rarely observed in low-mature or mature source rocks. The identified compounds are as follows: The peak A is a C19 tricyclic terpane related to abietic acid and is thought to represent an evidence for the contribution of higher plant materials, the peak B, D, E are C24 saturared tetracyclic terpanes, and their m. w. are 330. The peak G belongs to C30 triterpene. The peak H is a mixed one which includes C29 and C30 triterpenes and C30 triterpane. The peak I belongs to a terpenoid compound also and is not clear in its structure. The peak K1 is a neohop-13 ( 18 )-ene. The peak K2 is identified as a terpenoid compound with unknown stucture. The peak Ks is also a mixed one which includes C29 17α(H) norhopane, C30 triterpene and Cso triterpane. The peak L is mixed one too and consists of C29 17β ( H ) normortane and neohop-12-ene. The other peaks such as N. 0, P, R are the triterpanes which are common components in low mature or mature source rocks and crude oils.
