1988 Vol. 6, No. 2
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Display Method:
1988, 6(2): 1-14.
Abstract:
Qinghai lake is the largest inlad lake in China. The precursors have researched largely for the lake region. However, so far the study on the stable isotope of the lake has not been reported. According to a lot of the water isotope data and the isotope compositions of the ostracod shells of QH-16A core in Qinghai lake, the paper deals with distributions of δD and δ18O of the water, puts forwards climatic fluctuation model since the postglacial, and expoundes the evolution of the water body environment in Qinghai lake since the postglacial. Sample preparation: δD and δI8O analysis of water was used metal zinc method and CO2-H2O equalibration, respectivtely; δ18O and δ13C analysis of ostracod shells was used phospheric acid decomposition. Under the confidence level of 20, the confidence limit of the former is 0.3‰ and 0.05‰ (V-SMOW), respectively; that of the latter is 0.09‰ and 0.06‰ (PDB), respectively. Qinghai lake water derived from rainwater. According to lots of analytic data, we obtained that the average δD value of the lake water is +10.8‰, the aveage δ18o value is +2.14‰ (v.s. V-SMOW). THe δD and δ18O distributions of various natural water in the lake region exist: precipitationground waterriverlake water. On the basis of the δD and δ180 distribution features of ground water, river and lake water, we evaluatied the inital water isotope compositions of the modern water body of Qinghai lake are -55% (δD) and -10‰, (δ18O), which have the feature of the mixture of remaining water and snow-melt, the δD vertical distribution of the lake water has the characteristic: δD is rich in the top, and poor in the bottom. We evaluated that the inflow of the underground ascending spring is quite enough in Qinghai lake. On the basis of δ18O, δ13C, Mg/Ca and Sr/Ca values of the ostracod shells in the modern lake sediments, Qinghai lake region undergoes five climatic fluctuation periods:cold-warm and dry-cool and wet-mild and dry-cold and dry. Their time span measured by 14C method respectively is:QH-I (10,200-12,300 a, B. P.), QH-Ⅱ (5,400-10,200 a. B. P.), QH-Ⅲ3,600-5,400 a, B. P.), QH-Ⅳ (2,400-3,600 a. B. P.) and QH-Ⅴ (since2,400 a, B. P.). The authors gave a climatic fluctation model since about12,300 a, B. P. and divded it into five climatic fluctuation periods and twenty-two climatic fluctuation stages. Qinghai lake probably underwent a dried-up stage during the summit of the late glacial (Wurm glacial stage). Under the warm climate in the postglacial, the lake started to recovery since the ice and snow on mountains melt and supplied the lake basin. Therefore, the isotopic compositons of the initial water in the recovering lake are much higher than the average isotopic composition of the rainwater in the region. Since about morethan 10000 years, the water body environment of Qinghai lake, controlled by the postglacial climatic fluctuation, was high salinity and shallow lake in the Early Holocene,. The lake water became deep gradually and the salinity also became low from 7,600 to 5,400 a, B. P. (in relation to Atlantic). The formation of the deep lake was in the Middle Holocene (ca. 4,500-2,400 a, B. P,). At about 3,600 a, B. P., the lake water reached the largest depth and the salinity was the lowest too. After this, the lake water got into a positively evolutive stage. In the Late Holocene (since ca. 2,400 a, B. P.), climatic environment was cold and dry. The lake water evoluted positively, the water level slowly falls, so far the water depth is ca. 20.4m. The salinity slowly increases until the present 14.146g/l.
Qinghai lake is the largest inlad lake in China. The precursors have researched largely for the lake region. However, so far the study on the stable isotope of the lake has not been reported. According to a lot of the water isotope data and the isotope compositions of the ostracod shells of QH-16A core in Qinghai lake, the paper deals with distributions of δD and δ18O of the water, puts forwards climatic fluctuation model since the postglacial, and expoundes the evolution of the water body environment in Qinghai lake since the postglacial. Sample preparation: δD and δI8O analysis of water was used metal zinc method and CO2-H2O equalibration, respectivtely; δ18O and δ13C analysis of ostracod shells was used phospheric acid decomposition. Under the confidence level of 20, the confidence limit of the former is 0.3‰ and 0.05‰ (V-SMOW), respectively; that of the latter is 0.09‰ and 0.06‰ (PDB), respectively. Qinghai lake water derived from rainwater. According to lots of analytic data, we obtained that the average δD value of the lake water is +10.8‰, the aveage δ18o value is +2.14‰ (v.s. V-SMOW). THe δD and δ18O distributions of various natural water in the lake region exist: precipitationground waterriverlake water. On the basis of the δD and δ180 distribution features of ground water, river and lake water, we evaluatied the inital water isotope compositions of the modern water body of Qinghai lake are -55% (δD) and -10‰, (δ18O), which have the feature of the mixture of remaining water and snow-melt, the δD vertical distribution of the lake water has the characteristic: δD is rich in the top, and poor in the bottom. We evaluated that the inflow of the underground ascending spring is quite enough in Qinghai lake. On the basis of δ18O, δ13C, Mg/Ca and Sr/Ca values of the ostracod shells in the modern lake sediments, Qinghai lake region undergoes five climatic fluctuation periods:cold-warm and dry-cool and wet-mild and dry-cold and dry. Their time span measured by 14C method respectively is:QH-I (10,200-12,300 a, B. P.), QH-Ⅱ (5,400-10,200 a. B. P.), QH-Ⅲ3,600-5,400 a, B. P.), QH-Ⅳ (2,400-3,600 a. B. P.) and QH-Ⅴ (since2,400 a, B. P.). The authors gave a climatic fluctation model since about12,300 a, B. P. and divded it into five climatic fluctuation periods and twenty-two climatic fluctuation stages. Qinghai lake probably underwent a dried-up stage during the summit of the late glacial (Wurm glacial stage). Under the warm climate in the postglacial, the lake started to recovery since the ice and snow on mountains melt and supplied the lake basin. Therefore, the isotopic compositons of the initial water in the recovering lake are much higher than the average isotopic composition of the rainwater in the region. Since about morethan 10000 years, the water body environment of Qinghai lake, controlled by the postglacial climatic fluctuation, was high salinity and shallow lake in the Early Holocene,. The lake water became deep gradually and the salinity also became low from 7,600 to 5,400 a, B. P. (in relation to Atlantic). The formation of the deep lake was in the Middle Holocene (ca. 4,500-2,400 a, B. P,). At about 3,600 a, B. P., the lake water reached the largest depth and the salinity was the lowest too. After this, the lake water got into a positively evolutive stage. In the Late Holocene (since ca. 2,400 a, B. P.), climatic environment was cold and dry. The lake water evoluted positively, the water level slowly falls, so far the water depth is ca. 20.4m. The salinity slowly increases until the present 14.146g/l.
1988, 6(2): 31-41.
Abstract:
There are different types of tidal channel deposits in Taiyuan Formation (C32-3) and Shanxi Formation (P11) in western Henan Province. Taiyuan Formation consists mainly of alternated carbonate and clastic deposits and Shanxi Formation of coal-bearing clastic deposits. Most of the tidal channel deposits are elastics and a few are carbonates in Taiyuan Formation. The main characteristics of clastic tidal channel deposits are as follows: 1. Consist of quartz sandstones fining upwards. 2. With erosion surface and lag deposits at the bottom. 3. With large-scale tabular and trough cross bedding and a few herringbone and longitudinal cross bedding. 4. Tidal channel point bars formed by lateral aggredation. 5. Sand bodies spread widely owing to the migration of tidal channels and their thickness varied laterally. 6. Tidal channel sandstones associate with fine clastic deposits of shorezone laterally and overlain the bioclastic limestones bearing normal marine fossils assemblage. Carbonate tidal channel deposits consist of flat angular conglomerates of intraclast limestones, large-scale tabular and herringbone cross bedding may be found occassionally, and associated with thin bedded quartz sandstones of shore-zone in vertical and lateral sequence. Both clastic and carbonate tidal channel deposits are all developed on the shore zone of epeiric sea, therefore, they may called shore-zone tidal channel of epeiric sea. Depositional characteristics of the clastic tidal channels in the lower part of Shanxi Formation are similar to those of Taiyttan Formation. The differences are as follows. 1. Sandstones comprise more muddy matrix and plant fragments. 2. Coexist with tidal flat fine graindeposits in vertical and lateral which contain abundant siderite nodules. 3. Sandstones are more thick and distribute as narrow banded in plane view and lenses in cross section, gradually they were change into tidal flat deposits to lateral fanks. 4. The main coal bed was developed continuously over the tidal flat and tidal channel sand stone deposits. The thickness of the coal bed decreases sharply away from tidal and the quality becomes poor. This type of tidal channels is distributed on the back-barrier of mesotidal coast, therefore may be named tidal channels of back-barrier. The upper part of Shanxi Formation developed in the tidal channel deposits of the distal lower delta plain. The main characteristics are. 1. Composed of sublith-arenites, and comprises numerous carbonaceous and plant fragments, muscovites concentrated on the surfaces of the bedding, mudclasts. 2. With large-scale tabular and trough cross bedding, especially rare of double-mud-layers, single-mud-layers and tidal cyclic sequences formed by tidal currents. 3. Sandstones fining upwards, coexist with mouth bar coarsing upwards and lower delta plain deposits in lateral. These channels distributed in the distal of the distributary channels of lower delta plain, the fluvial and tidal currents used the same channel, and the distributary channel mouths were also tidal channels. Other tidal channels developed on tidal flats of interdistributary bays. In ancient deposits, it is difficult to distinguish them only by the depositional indicators, so may be called by a joint name - tidal channels of the distal lower delta plain. Tidal channels underlying the main coal bed all characterized by herringbone cross bedding and tidal point bars, indicating the existance of symmetric tidal currents. While tidal channel deposits overlying the main coal seam lack of herringbone cross bedding, but occur asymmetric tidal current depositional indicators such as tidal bundle, double-mud-layers and single-mud-layers. Paleocurrent pointed to the south (seaward), thus the channels were ebb tide dominated tidal channels. Different types of tidal channel deposits occur in regular order in the coal-bearing strata: from bottom to top, the shore zone tidal channels of epeiric sea occurred earlier, tidal channels associated of back-barrier subsequently, and tidal channels developed in distal of the lower d
There are different types of tidal channel deposits in Taiyuan Formation (C32-3) and Shanxi Formation (P11) in western Henan Province. Taiyuan Formation consists mainly of alternated carbonate and clastic deposits and Shanxi Formation of coal-bearing clastic deposits. Most of the tidal channel deposits are elastics and a few are carbonates in Taiyuan Formation. The main characteristics of clastic tidal channel deposits are as follows: 1. Consist of quartz sandstones fining upwards. 2. With erosion surface and lag deposits at the bottom. 3. With large-scale tabular and trough cross bedding and a few herringbone and longitudinal cross bedding. 4. Tidal channel point bars formed by lateral aggredation. 5. Sand bodies spread widely owing to the migration of tidal channels and their thickness varied laterally. 6. Tidal channel sandstones associate with fine clastic deposits of shorezone laterally and overlain the bioclastic limestones bearing normal marine fossils assemblage. Carbonate tidal channel deposits consist of flat angular conglomerates of intraclast limestones, large-scale tabular and herringbone cross bedding may be found occassionally, and associated with thin bedded quartz sandstones of shore-zone in vertical and lateral sequence. Both clastic and carbonate tidal channel deposits are all developed on the shore zone of epeiric sea, therefore, they may called shore-zone tidal channel of epeiric sea. Depositional characteristics of the clastic tidal channels in the lower part of Shanxi Formation are similar to those of Taiyttan Formation. The differences are as follows. 1. Sandstones comprise more muddy matrix and plant fragments. 2. Coexist with tidal flat fine graindeposits in vertical and lateral which contain abundant siderite nodules. 3. Sandstones are more thick and distribute as narrow banded in plane view and lenses in cross section, gradually they were change into tidal flat deposits to lateral fanks. 4. The main coal bed was developed continuously over the tidal flat and tidal channel sand stone deposits. The thickness of the coal bed decreases sharply away from tidal and the quality becomes poor. This type of tidal channels is distributed on the back-barrier of mesotidal coast, therefore may be named tidal channels of back-barrier. The upper part of Shanxi Formation developed in the tidal channel deposits of the distal lower delta plain. The main characteristics are. 1. Composed of sublith-arenites, and comprises numerous carbonaceous and plant fragments, muscovites concentrated on the surfaces of the bedding, mudclasts. 2. With large-scale tabular and trough cross bedding, especially rare of double-mud-layers, single-mud-layers and tidal cyclic sequences formed by tidal currents. 3. Sandstones fining upwards, coexist with mouth bar coarsing upwards and lower delta plain deposits in lateral. These channels distributed in the distal of the distributary channels of lower delta plain, the fluvial and tidal currents used the same channel, and the distributary channel mouths were also tidal channels. Other tidal channels developed on tidal flats of interdistributary bays. In ancient deposits, it is difficult to distinguish them only by the depositional indicators, so may be called by a joint name - tidal channels of the distal lower delta plain. Tidal channels underlying the main coal bed all characterized by herringbone cross bedding and tidal point bars, indicating the existance of symmetric tidal currents. While tidal channel deposits overlying the main coal seam lack of herringbone cross bedding, but occur asymmetric tidal current depositional indicators such as tidal bundle, double-mud-layers and single-mud-layers. Paleocurrent pointed to the south (seaward), thus the channels were ebb tide dominated tidal channels. Different types of tidal channel deposits occur in regular order in the coal-bearing strata: from bottom to top, the shore zone tidal channels of epeiric sea occurred earlier, tidal channels associated of back-barrier subsequently, and tidal channels developed in distal of the lower d
1988, 6(2): 50-60.
Abstract:
According to three principle factors controlling sedimentation of a basin (inundation of waters, changes of climate and structural movement), the continental basins in China can be classfied into two groups, each of them can be divided into three types respectively, and each of types can be differentiated into three species further. Normally and abnormally continental basins 1. Normally continental basins (type Mo) They developed in the interior of continent where were far from the coast and a higher elevation relatively. The transgression did not affcet the depositional process. The main factors that controlled the deposition were continental structure, climate, hydrology and organisms. The dark clays and carbonates deposited in these basins under humid and semi-dry climate have the ability of generating oil and gas in some extent. 2. Abnormally continental basins (type M1) They developed in the area where were offshore or lower elevation. The transgression affected the depositional process. Their properties of deposition, geochemistry and organisms have both characteristics of marine and continental facies. They were connected with sea or connected intermittently by channel. The clays and carbonates formed in transgression are favourable source rocks. The sand bodies formed in regression have fair reserviors. Basins developed under arid, moist and transition climate 1. Basins developed arid condition (type C1) Their characteristics are that they contain red clastic rocks, carbonates, sulphate rocks and chlorate minerals. The species of organisms is monotonous. A fair thickness of the source rock deposited in these basins while the supply of the sea water increased or the evaporating amount of the water decreased and basins sank continously. 2. Basins developed under moist condition (type C2) Their characteristics are that they have a large amount deposits derived from swamp envirnoment. Dark clays in the basins are good source rocks. Fluvial and delta sand bodies are considered to be reserviors. 3. Basins developed under transitional climate (type C3) The characteristics of deposition, geochemistry and organisms are between that of the arid basins and the moist basins. The deposits deposited in these basins are common source rocks. Faulted basins, depressional basins and faulted-depressional basins 1. Faulted basins (type S1) The process of generation and development of basins was mainly controlled by fault. Thicker source rocks would be deposited when basins was deficient of deposits, and a lithologic and structural oil poll would be formed when source rocks deposited well with fair reserviors in this area. 2. Depressional basins (type S2) Their generation and development were controlled mianly by depression. The lithology and lithofacies changed steadily. The source rock-reservior-cap rock relationship is fairly good. It contains big oil-gas accumulations usually. 3. Faulted-depression basins (type S3) The generation was controlled by mechanism of faulted-depression and depressional basin. The characteristic3 of deposits and oil gas are between type S1 and type S2. In conclusion, a classfication of basins according to three factors controlling the sedimentation of basins, is singificant for forecasting oil and gas prospect.
According to three principle factors controlling sedimentation of a basin (inundation of waters, changes of climate and structural movement), the continental basins in China can be classfied into two groups, each of them can be divided into three types respectively, and each of types can be differentiated into three species further. Normally and abnormally continental basins 1. Normally continental basins (type Mo) They developed in the interior of continent where were far from the coast and a higher elevation relatively. The transgression did not affcet the depositional process. The main factors that controlled the deposition were continental structure, climate, hydrology and organisms. The dark clays and carbonates deposited in these basins under humid and semi-dry climate have the ability of generating oil and gas in some extent. 2. Abnormally continental basins (type M1) They developed in the area where were offshore or lower elevation. The transgression affected the depositional process. Their properties of deposition, geochemistry and organisms have both characteristics of marine and continental facies. They were connected with sea or connected intermittently by channel. The clays and carbonates formed in transgression are favourable source rocks. The sand bodies formed in regression have fair reserviors. Basins developed under arid, moist and transition climate 1. Basins developed arid condition (type C1) Their characteristics are that they contain red clastic rocks, carbonates, sulphate rocks and chlorate minerals. The species of organisms is monotonous. A fair thickness of the source rock deposited in these basins while the supply of the sea water increased or the evaporating amount of the water decreased and basins sank continously. 2. Basins developed under moist condition (type C2) Their characteristics are that they have a large amount deposits derived from swamp envirnoment. Dark clays in the basins are good source rocks. Fluvial and delta sand bodies are considered to be reserviors. 3. Basins developed under transitional climate (type C3) The characteristics of deposition, geochemistry and organisms are between that of the arid basins and the moist basins. The deposits deposited in these basins are common source rocks. Faulted basins, depressional basins and faulted-depressional basins 1. Faulted basins (type S1) The process of generation and development of basins was mainly controlled by fault. Thicker source rocks would be deposited when basins was deficient of deposits, and a lithologic and structural oil poll would be formed when source rocks deposited well with fair reserviors in this area. 2. Depressional basins (type S2) Their generation and development were controlled mianly by depression. The lithology and lithofacies changed steadily. The source rock-reservior-cap rock relationship is fairly good. It contains big oil-gas accumulations usually. 3. Faulted-depression basins (type S3) The generation was controlled by mechanism of faulted-depression and depressional basin. The characteristic3 of deposits and oil gas are between type S1 and type S2. In conclusion, a classfication of basins according to three factors controlling the sedimentation of basins, is singificant for forecasting oil and gas prospect.
1988, 6(2): 68-76.
Abstract:
Late-Precambrian sedimentary carbonate rocks are well developed in Jixian County, Tianjin, especially those in the Wumishan Formation. They are about 3000m thick and are dominanted by sedimentary dolostone. In terms of the microscopical features and macroscopical occurrences, the transgressive sediments of the Wumishan Formation can be divided into three sedimentary facies zones. 1. Supratidal zone This is a uppertidal environment in open flat. Sediments are dolarenite and dolrudite which contain terrigenous grains. They are deposited in the environment of low grade momentum of sea water. 2. Intertidal zone The sedimentary area of this zone is from an extension of the supratidal zone flat mentioned above towards the sea. The sediments of this zone are mainly finegrained carbonates which contain silicolites and algites. Overall, this zone belongs to a tidal flat environment which is shelf-beachy facies of epicontinental sea. Sedimentation happens under a rather strong hydrodynamic environment. 3. Subtidal zone It has a sedimentary region of underwater flat being dominanted by relatively open high energy zone and a slope depression of relatively high energy zone on the flat. Overall, this zone belongs to an environment of lower tidal flat of shelf-beachy facies of epicontinental sea. The transgressive sedimentary model of the Wumishan Formation mentioned above can play similar role as Bouma's turbidite sequences in providing g'uidance and prognosis for further researches and offering bases for genetic explanation.
Late-Precambrian sedimentary carbonate rocks are well developed in Jixian County, Tianjin, especially those in the Wumishan Formation. They are about 3000m thick and are dominanted by sedimentary dolostone. In terms of the microscopical features and macroscopical occurrences, the transgressive sediments of the Wumishan Formation can be divided into three sedimentary facies zones. 1. Supratidal zone This is a uppertidal environment in open flat. Sediments are dolarenite and dolrudite which contain terrigenous grains. They are deposited in the environment of low grade momentum of sea water. 2. Intertidal zone The sedimentary area of this zone is from an extension of the supratidal zone flat mentioned above towards the sea. The sediments of this zone are mainly finegrained carbonates which contain silicolites and algites. Overall, this zone belongs to a tidal flat environment which is shelf-beachy facies of epicontinental sea. Sedimentation happens under a rather strong hydrodynamic environment. 3. Subtidal zone It has a sedimentary region of underwater flat being dominanted by relatively open high energy zone and a slope depression of relatively high energy zone on the flat. Overall, this zone belongs to an environment of lower tidal flat of shelf-beachy facies of epicontinental sea. The transgressive sedimentary model of the Wumishan Formation mentioned above can play similar role as Bouma's turbidite sequences in providing g'uidance and prognosis for further researches and offering bases for genetic explanation.
1988, 6(2): 78-96.
Abstract:
The aim of the present investigation is to demonstrate the mineralogy and geochemistry of the tidal flat microenvironment in a restricted area and to reveal their variation caused by sedimentation processes. The sedimentary samples taken from different places of the backside tidal flats between the Wagerooge barrier island and the mainland south coast, West Germany are used for grain size analysis and measurement of heavy metals: Fe, Mn, Cu, Pb, Zn and organic carbon. These samples are representative of the average characteristics of sedimentary column of 20cm depth under tidal surface. The grain size distribution on the tidal flats shows a general mainland-parellel zonation. The north salt marsh near the barrier island contains a plenty of sands blown from barrier island sand dune. Clay mineral composition and the content of heavy metals: Fe, Cu, Mn, Pb, Zn in 2μm fine fraction are almost equal in different places of the tidal flats. It indicates that there is no local input of them and tidal flat sediments have suffered the sufficient mixing induced by repeated erosion and resedimentation under the effect of tidal currents. In addition, in all samples illite as a dominent clay mineral is followed by smectite, kaolinite and chlorite, which corresponds to clay mineral association found in the North Sea. In the north and south salt marshes, there is the highest organic carbon content, which may be probably related to the in site formation. Near the tidal inlet organic carbon content increases relatively because most of organic carbon come from the North Sea with tidal currents through the inlet.
The aim of the present investigation is to demonstrate the mineralogy and geochemistry of the tidal flat microenvironment in a restricted area and to reveal their variation caused by sedimentation processes. The sedimentary samples taken from different places of the backside tidal flats between the Wagerooge barrier island and the mainland south coast, West Germany are used for grain size analysis and measurement of heavy metals: Fe, Mn, Cu, Pb, Zn and organic carbon. These samples are representative of the average characteristics of sedimentary column of 20cm depth under tidal surface. The grain size distribution on the tidal flats shows a general mainland-parellel zonation. The north salt marsh near the barrier island contains a plenty of sands blown from barrier island sand dune. Clay mineral composition and the content of heavy metals: Fe, Cu, Mn, Pb, Zn in 2μm fine fraction are almost equal in different places of the tidal flats. It indicates that there is no local input of them and tidal flat sediments have suffered the sufficient mixing induced by repeated erosion and resedimentation under the effect of tidal currents. In addition, in all samples illite as a dominent clay mineral is followed by smectite, kaolinite and chlorite, which corresponds to clay mineral association found in the North Sea. In the north and south salt marshes, there is the highest organic carbon content, which may be probably related to the in site formation. Near the tidal inlet organic carbon content increases relatively because most of organic carbon come from the North Sea with tidal currents through the inlet.
1988, 6(2): 106-117.
Abstract:
Hanxia Section is situated in the piedmont of the northern slope of the Qilianshan (Nanshan) Mountains, with a distance of some 28km, due west fo Yumen, Gansu Province. The section stretches approximately in a direction of north-sourth. The Mesozoic strata of the section appears as overturned monoclinal strata dipping steeply towards SSW. Dips of the strata are from 60 to 85 degrees. All the strata of the Mesozoic age exposed in the section were previously termed as Xinminbu Formation as a whole. Purely based on the independent data reflected by the plaeomagnetic measurements obtained from 38 samples, 181 specimens, collected from Hanxia Section, a new point about the stratigraphic division of the so-called Xinminbu Formation which was originaly defined as Lower Cretaceous Series is proposed in the present paper. Stratigraphers have paid special attentions to Xinminbu Formation for a long time because of its typicalness and representativeness in continental Mesozoic strata in Northwestern China. However, biostratigraphers have not reached unanimous views on the problem that which geological period of Xinminbu Formation should belong to, up to now. They, therefore, hold different opinions on stratigraphic division of Xinminbu Formation exposed in Hanxia Section. Some of them regard that Xinminbu Formation entirely belongs to the Lower Cretaceous Series, whereas others believe that the lower of it should belong to the Upper Jurassic and the upper of it still represents Lower Cretaceous. Moreover, few hold that Sinminbu Formation belongs to the Upper Jurassic as a whole. Still others deem that we should give it a general name of Jura-Cretaceous. Three characteristic magnetic curves and a magnetic polarity zonation of Hanxia Section have been drawn out on the basis of the data of paleomagnetic measurements of oriented samples gathered from the section (Fig. 1). By means of comparing the magnetic polarity zonation with the world's Mesozoic paleomagnetic polarity stratigraphy and the paleomagnetic polarity scale of oceanic sediments, both 7 normal and 7 reversed polarity subzones have been identified from the results of so-called Xinminbu Formation of this section. Consequently, the writer believes that the Xinminbu Formation of Hanxia Section includes two stratigraphic units belong to different geological times. Taking Serra Geral reversed polarity subzone as a boundary, the Xinminbu Formation of the section can be divided into two parts which in fact belong to two different geological periods respectively. The lower, to a thickness of 459.8m, should be regarded as sediment of Late Jurassic age. The upper is still of Lower Cretaceous Series, being 635.5m thick. The two are of successive sediments. No sedimentary hiatus exists between them. Concretely speaking, the strata beneath the third reversed subzone, corresponding to Serra Geral reversed subzone, should be taken as the Upper Jurassic Series. These Jurassic strata include both all of the normal polarity members belong to Graham normal polarity zone, a thickness of about 344 m, and those belong to the mixed polarity zone, which embrace both 2 normal and 2 reversed subzones, about 116m thick. Therefore, Layer of No.8, the thick-bedded conglomerate with a dark grey colour, is the uppermost layer of Jurassic Series; whereas Layer of No.9, the grey-black paper shale and the grey-green conglomerate, is the lowermost layer of Cretaceous. It is here that the boundary between Jurassic and Cretaceous exposed within Hanxia Section. As for the ages of the basaltic dikes existing in the section, the writer thinks paleomagnetically that the eruption of them should precede the Miocene and postdate the Early Cretaceous. In addition, the eruption consists of two magmatic activities of different times. Besides these, the writer gives out the comparison of the magnetostratigraphic division with the preexisting biostratigraphic division (Fig.2.) The writer does not think it is a good idea for geologists to continuce using such a petrological stratigraphic term, Xinminbu Formatio
Hanxia Section is situated in the piedmont of the northern slope of the Qilianshan (Nanshan) Mountains, with a distance of some 28km, due west fo Yumen, Gansu Province. The section stretches approximately in a direction of north-sourth. The Mesozoic strata of the section appears as overturned monoclinal strata dipping steeply towards SSW. Dips of the strata are from 60 to 85 degrees. All the strata of the Mesozoic age exposed in the section were previously termed as Xinminbu Formation as a whole. Purely based on the independent data reflected by the plaeomagnetic measurements obtained from 38 samples, 181 specimens, collected from Hanxia Section, a new point about the stratigraphic division of the so-called Xinminbu Formation which was originaly defined as Lower Cretaceous Series is proposed in the present paper. Stratigraphers have paid special attentions to Xinminbu Formation for a long time because of its typicalness and representativeness in continental Mesozoic strata in Northwestern China. However, biostratigraphers have not reached unanimous views on the problem that which geological period of Xinminbu Formation should belong to, up to now. They, therefore, hold different opinions on stratigraphic division of Xinminbu Formation exposed in Hanxia Section. Some of them regard that Xinminbu Formation entirely belongs to the Lower Cretaceous Series, whereas others believe that the lower of it should belong to the Upper Jurassic and the upper of it still represents Lower Cretaceous. Moreover, few hold that Sinminbu Formation belongs to the Upper Jurassic as a whole. Still others deem that we should give it a general name of Jura-Cretaceous. Three characteristic magnetic curves and a magnetic polarity zonation of Hanxia Section have been drawn out on the basis of the data of paleomagnetic measurements of oriented samples gathered from the section (Fig. 1). By means of comparing the magnetic polarity zonation with the world's Mesozoic paleomagnetic polarity stratigraphy and the paleomagnetic polarity scale of oceanic sediments, both 7 normal and 7 reversed polarity subzones have been identified from the results of so-called Xinminbu Formation of this section. Consequently, the writer believes that the Xinminbu Formation of Hanxia Section includes two stratigraphic units belong to different geological times. Taking Serra Geral reversed polarity subzone as a boundary, the Xinminbu Formation of the section can be divided into two parts which in fact belong to two different geological periods respectively. The lower, to a thickness of 459.8m, should be regarded as sediment of Late Jurassic age. The upper is still of Lower Cretaceous Series, being 635.5m thick. The two are of successive sediments. No sedimentary hiatus exists between them. Concretely speaking, the strata beneath the third reversed subzone, corresponding to Serra Geral reversed subzone, should be taken as the Upper Jurassic Series. These Jurassic strata include both all of the normal polarity members belong to Graham normal polarity zone, a thickness of about 344 m, and those belong to the mixed polarity zone, which embrace both 2 normal and 2 reversed subzones, about 116m thick. Therefore, Layer of No.8, the thick-bedded conglomerate with a dark grey colour, is the uppermost layer of Jurassic Series; whereas Layer of No.9, the grey-black paper shale and the grey-green conglomerate, is the lowermost layer of Cretaceous. It is here that the boundary between Jurassic and Cretaceous exposed within Hanxia Section. As for the ages of the basaltic dikes existing in the section, the writer thinks paleomagnetically that the eruption of them should precede the Miocene and postdate the Early Cretaceous. In addition, the eruption consists of two magmatic activities of different times. Besides these, the writer gives out the comparison of the magnetostratigraphic division with the preexisting biostratigraphic division (Fig.2.) The writer does not think it is a good idea for geologists to continuce using such a petrological stratigraphic term, Xinminbu Formatio
1988, 6(2): 123-131.
Abstract:
Late Permian lacustrine deposits consists predominantly of interbedded grayish-brown sandstones and conglomerates and red to gray mudstones in the Eerduosi Basin. This series mentioned above is 500-600 m thick and five main facies associations are recognized: subaqueous fan, alluvail plain on lake bank, lacustrine delta, marginal lacustrine, and offshore lacustrine facies association. Of these the characteristics and distributions are derived from this study: Subaqueous fan deposits are of three subfacies types differ from each other in fabric, commonly formed at southwest margin of the studied area. The inner-fan deposits are characterized by developing of channel. Only a few structure of tractive current are in the mid-fan and outer-fan, Common character is that, sorting and stratification are generally not well developed. Alluvail plain deposits consist of interbedded grayish-brown sandstones, pebbly sandstones and red mudstones, commonly formed at north of studied area. The sandstones and pebbly sandstones are characterized by moderate to poor sorting, developing of platy cross-bedding and trough cross-bedding, fining-upward in the bedding set thickness and grain size. Fossils are not abundant in this facies but calc-nodules are abundant. Lacustrine delta deposits, formed at north and east, have developing character of Gilbert-type, contain abundant trough cross-bedding and gently inclined cross-bedding laminations analogous to foresets in the Gilbert deltas. Marginal-lacustrine deposits are divided into four subfacies: (1) lake bay subfacies that be dominanted by red to green mudstones, containing algae and faunal fragment; (2) shoreline subfacies which be dominanted by poorly sorted pebbly sandstones or well sorted sandstones, containing horizontal and cross-bedding, muddy ripping and vertebrates fragment; (3) nearshore lacustrine subfacies that be dominanted by red to grey mudstones, containing plants, ostracodes, bivalve, conchostracas and trace fossils; and (4) nearshore bar association subfacias which composed of elongate lenticular sandstones bodies having convex-downward bases or flat bases and convex-upward tops, and may containing crossbeds that dip to one or more sides of the lens. Offshore lacustrine deposits formed at south of the studied area. They consist mainly of gray to brown-gray horizontal or lumpy bedding mudstones, and contain conchostraca and bivalve.
Late Permian lacustrine deposits consists predominantly of interbedded grayish-brown sandstones and conglomerates and red to gray mudstones in the Eerduosi Basin. This series mentioned above is 500-600 m thick and five main facies associations are recognized: subaqueous fan, alluvail plain on lake bank, lacustrine delta, marginal lacustrine, and offshore lacustrine facies association. Of these the characteristics and distributions are derived from this study: Subaqueous fan deposits are of three subfacies types differ from each other in fabric, commonly formed at southwest margin of the studied area. The inner-fan deposits are characterized by developing of channel. Only a few structure of tractive current are in the mid-fan and outer-fan, Common character is that, sorting and stratification are generally not well developed. Alluvail plain deposits consist of interbedded grayish-brown sandstones, pebbly sandstones and red mudstones, commonly formed at north of studied area. The sandstones and pebbly sandstones are characterized by moderate to poor sorting, developing of platy cross-bedding and trough cross-bedding, fining-upward in the bedding set thickness and grain size. Fossils are not abundant in this facies but calc-nodules are abundant. Lacustrine delta deposits, formed at north and east, have developing character of Gilbert-type, contain abundant trough cross-bedding and gently inclined cross-bedding laminations analogous to foresets in the Gilbert deltas. Marginal-lacustrine deposits are divided into four subfacies: (1) lake bay subfacies that be dominanted by red to green mudstones, containing algae and faunal fragment; (2) shoreline subfacies which be dominanted by poorly sorted pebbly sandstones or well sorted sandstones, containing horizontal and cross-bedding, muddy ripping and vertebrates fragment; (3) nearshore lacustrine subfacies that be dominanted by red to grey mudstones, containing plants, ostracodes, bivalve, conchostracas and trace fossils; and (4) nearshore bar association subfacias which composed of elongate lenticular sandstones bodies having convex-downward bases or flat bases and convex-upward tops, and may containing crossbeds that dip to one or more sides of the lens. Offshore lacustrine deposits formed at south of the studied area. They consist mainly of gray to brown-gray horizontal or lumpy bedding mudstones, and contain conchostraca and bivalve.
1988, 6(2): 15-30.
Abstract:
The Nanling of South China is one of the most important areas of nonferrous metal mineral resources. Based on incomplete statistical figures, strata-bound lead-zinc, pyrite, tungsten,tin, mercury, antimony and barite ore deposits have been found in Devonian of this area. There are ten's medium to large scale deposits ezplorated and numbers of small deposits spread far and wide. According to genetic types, these deposits can be classified into diagenetic, diagenetic-epigenetic, volcanic exhalation-sedimentary, superimposed and mixed hydrothrmal ore deposits. Four metallogentic models have been established: 1. submarine vadose circulating volcanic exhalation-deposition; 2. basinal diagenetic compactive fluids; 3. basinal thermal brine; 4. mixed hydrothermal metallogenic model. Although these strata-bound deposits are different in types and genesis, many similarities in their ore-controlling factors and distributon may be found. The main controlling factors are stratigraphy (formation), lithofacies and tectonic setting. Thereby, it is considered that any geologic factor controlling the ore formation could not be treated in isolation. The formation of any large scale ore deposit should be considered as the result of the coaction of various geological factors in certain geological settings, and those factors affect and interact commonly each other. The stratigraphic horizon, lithofacies and tectonic setting are thought as main factors for controlling the diagenetic-epigenetic strata-bound ore deposits, and three factors are concordant spatially. When the formation of ttrata-bound ore deposits are related to magmatism, the regional large fault, lithofacies zone, magmatic activity and metallogenesis often show the consistency. That is, the fault controlled early the lithofacies (or volcanic activity), and subsequently controlled the emplacement of magmatic rocks and the migration, circulation and final enrichment of the metallogenetic solutions.
The Nanling of South China is one of the most important areas of nonferrous metal mineral resources. Based on incomplete statistical figures, strata-bound lead-zinc, pyrite, tungsten,tin, mercury, antimony and barite ore deposits have been found in Devonian of this area. There are ten's medium to large scale deposits ezplorated and numbers of small deposits spread far and wide. According to genetic types, these deposits can be classified into diagenetic, diagenetic-epigenetic, volcanic exhalation-sedimentary, superimposed and mixed hydrothrmal ore deposits. Four metallogentic models have been established: 1. submarine vadose circulating volcanic exhalation-deposition; 2. basinal diagenetic compactive fluids; 3. basinal thermal brine; 4. mixed hydrothermal metallogenic model. Although these strata-bound deposits are different in types and genesis, many similarities in their ore-controlling factors and distributon may be found. The main controlling factors are stratigraphy (formation), lithofacies and tectonic setting. Thereby, it is considered that any geologic factor controlling the ore formation could not be treated in isolation. The formation of any large scale ore deposit should be considered as the result of the coaction of various geological factors in certain geological settings, and those factors affect and interact commonly each other. The stratigraphic horizon, lithofacies and tectonic setting are thought as main factors for controlling the diagenetic-epigenetic strata-bound ore deposits, and three factors are concordant spatially. When the formation of ttrata-bound ore deposits are related to magmatism, the regional large fault, lithofacies zone, magmatic activity and metallogenesis often show the consistency. That is, the fault controlled early the lithofacies (or volcanic activity), and subsequently controlled the emplacement of magmatic rocks and the migration, circulation and final enrichment of the metallogenetic solutions.
1988, 6(2): 42-49.
Abstract:
This paper deals with the barrier coastal environments of the continental sea are the main paleogeographic conditions ia the Upper Palaeozoic coal-bearing formations in the south of China and in the Middle, Upper Carboniferous coal-bearing formations in the north of China. The tidal deposits are one of the important deposits of those parts in coal-bearing formations and the storm deposits can be usually found. Some main coal seams are formed in the peat flats where the tidal currents are the main hydrodynamic conditions. The concept of "peat flat" is set forth by the author. It is a important type of the coal-forming environments in the Upper Palaeozoic coal-bearing formations in the south of China and in the Middle, Upper Carboniferous coal-bearing formations in the north of China. The difinition of the peat flat is as follows: mangrove forests or other tidal plants having a similar bioecology in ancient time can be grown in the intertidal flats and some supertidal flats of the tropical and subtropical zones and the peat deposits can be formed from which over a large area. Such environments of coal formed directly in the tidal flats are called peat flats. The concept of peat flats is not same as that of peat swamps. Peat flats belong to marine facies and peat deposits are formed in the tidal current action where the water level changes frequently and the tidal currents have double directions. The water medium belongs to brackish water or sea water and coalfoming plants are the tidal plants with which some marine organisms can be lived. The features of coal seams formed on peat flats are as follows: The coal seams distributed wide and stablely and contrasted easily. The thickness of coal seams changes more and their divergence is notable. The sulphur content is higher. These features are of great use as important signs for the work in the geologic survey and exploration of the coal field.
This paper deals with the barrier coastal environments of the continental sea are the main paleogeographic conditions ia the Upper Palaeozoic coal-bearing formations in the south of China and in the Middle, Upper Carboniferous coal-bearing formations in the north of China. The tidal deposits are one of the important deposits of those parts in coal-bearing formations and the storm deposits can be usually found. Some main coal seams are formed in the peat flats where the tidal currents are the main hydrodynamic conditions. The concept of "peat flat" is set forth by the author. It is a important type of the coal-forming environments in the Upper Palaeozoic coal-bearing formations in the south of China and in the Middle, Upper Carboniferous coal-bearing formations in the north of China. The difinition of the peat flat is as follows: mangrove forests or other tidal plants having a similar bioecology in ancient time can be grown in the intertidal flats and some supertidal flats of the tropical and subtropical zones and the peat deposits can be formed from which over a large area. Such environments of coal formed directly in the tidal flats are called peat flats. The concept of peat flats is not same as that of peat swamps. Peat flats belong to marine facies and peat deposits are formed in the tidal current action where the water level changes frequently and the tidal currents have double directions. The water medium belongs to brackish water or sea water and coalfoming plants are the tidal plants with which some marine organisms can be lived. The features of coal seams formed on peat flats are as follows: The coal seams distributed wide and stablely and contrasted easily. The thickness of coal seams changes more and their divergence is notable. The sulphur content is higher. These features are of great use as important signs for the work in the geologic survey and exploration of the coal field.
1988, 6(2): 61-67.
Abstract:
Yutang organic reefs in the third member of the Early Cambrian Qingxudong Formation from Huayuan, western Hunan are distinct kinds of epiphyton barrier reefs in the world. They stretch along north-northeast discontinuously and are located on the south-eastern edge of Chuan-Dian-Qian (Sichuan-Yunnan-Guizhou) Carbonate Platform. They belong to a barrier reef zone about 100km long, which is composed of a series of elongated reef bodies. On their east side is Xiang-Qian (Hunan-Guizhou) Open Sea Basin. The geological background of reef formation was controlled by the upthro-wn block of Tongren-Dayong giant fault. Individual reef bodies are 2-6km long, 0.2-0.8km wide, and their high/wide are l:5-1:20, which appear like domes with steep east side and gentle west side. The space between two reef bodies where exists tidal channel or oolitic shoal is 1.5-2km. The main reef-building organisms are: Epiphyton plumosum, E. racemosum, E.pusillum, E.nubilum; Nicholsonia sp.; Gircanella sp.; and other blue-green algae. The attaching organisms are a few trilobites, ostracodas and echinoderms. According to the features of reef rock assemblages, Yutang organic reef can be divided into three subfacies: 1) reef core-main part of reef body, on the slope break line at the carbonate platform margin. In this area, there is organic ecologic zonation from front to back, i. e. Nicholsonia sp. Epiphyton sp. Girvanella sp.. The formef two kinds of algae have framework like straight or winding clumpy branches, which the bladed calcites often fill in the space between the tangled branches. These algae are 2-40mm high, and have the ability of resistant. They always formed framestones and made up reef crest in the front margin of reef core. The later shows level-sleep and tangled draping structure and occurred in the back of reef core, which slightly inclines towards open sea. It often captured a lot of mud and formed bindstones in reef flat of the back margin of reef core. The profile of the reef core consists of reef base, reef crest, reef flat, and reef shoal, and includes three superimposed reef-building sedimentary cycles, totally 120-160m thick; 2) reef front which includes steep upper slope with angle of 430, and gentle lower slope with angle decreasing to 10. The upper slope is composed of talus breccia sediments from reef core, which is 100-300m wide, 60-100m thick,forming an upper slope apron in the reef front. On the lower slope, develop proximal and distal carbonate turbidite about 40-60m thick; 3) reef back-lagoon and tidal flat which gently inclined towards the carbonate platform and were protected by the barrier reef. They consist of alternate algal pellet limestone and algal calcarenite or stromatolitic limestone, of 80-100m thick. They were connected by each tidal channel between two reef bodies with open sea. On the column of the third member of Qingxudong Formation, the three reef-building sedimentary cycles of Yutang organic reef as above mentioned, can be corresponed to three depressing processes of sedimentary basin caused by syndeposi-tional faulting. Each cycle took place in the temporary stable period after the depression of the basin. Experienced shallowing of sea water, the depth of water varied from 30m to Om in the reef-building period,energy of sedimentary environment increases, and then becomes continuous turbulent.
Yutang organic reefs in the third member of the Early Cambrian Qingxudong Formation from Huayuan, western Hunan are distinct kinds of epiphyton barrier reefs in the world. They stretch along north-northeast discontinuously and are located on the south-eastern edge of Chuan-Dian-Qian (Sichuan-Yunnan-Guizhou) Carbonate Platform. They belong to a barrier reef zone about 100km long, which is composed of a series of elongated reef bodies. On their east side is Xiang-Qian (Hunan-Guizhou) Open Sea Basin. The geological background of reef formation was controlled by the upthro-wn block of Tongren-Dayong giant fault. Individual reef bodies are 2-6km long, 0.2-0.8km wide, and their high/wide are l:5-1:20, which appear like domes with steep east side and gentle west side. The space between two reef bodies where exists tidal channel or oolitic shoal is 1.5-2km. The main reef-building organisms are: Epiphyton plumosum, E. racemosum, E.pusillum, E.nubilum; Nicholsonia sp.; Gircanella sp.; and other blue-green algae. The attaching organisms are a few trilobites, ostracodas and echinoderms. According to the features of reef rock assemblages, Yutang organic reef can be divided into three subfacies: 1) reef core-main part of reef body, on the slope break line at the carbonate platform margin. In this area, there is organic ecologic zonation from front to back, i. e. Nicholsonia sp. Epiphyton sp. Girvanella sp.. The formef two kinds of algae have framework like straight or winding clumpy branches, which the bladed calcites often fill in the space between the tangled branches. These algae are 2-40mm high, and have the ability of resistant. They always formed framestones and made up reef crest in the front margin of reef core. The later shows level-sleep and tangled draping structure and occurred in the back of reef core, which slightly inclines towards open sea. It often captured a lot of mud and formed bindstones in reef flat of the back margin of reef core. The profile of the reef core consists of reef base, reef crest, reef flat, and reef shoal, and includes three superimposed reef-building sedimentary cycles, totally 120-160m thick; 2) reef front which includes steep upper slope with angle of 430, and gentle lower slope with angle decreasing to 10. The upper slope is composed of talus breccia sediments from reef core, which is 100-300m wide, 60-100m thick,forming an upper slope apron in the reef front. On the lower slope, develop proximal and distal carbonate turbidite about 40-60m thick; 3) reef back-lagoon and tidal flat which gently inclined towards the carbonate platform and were protected by the barrier reef. They consist of alternate algal pellet limestone and algal calcarenite or stromatolitic limestone, of 80-100m thick. They were connected by each tidal channel between two reef bodies with open sea. On the column of the third member of Qingxudong Formation, the three reef-building sedimentary cycles of Yutang organic reef as above mentioned, can be corresponed to three depressing processes of sedimentary basin caused by syndeposi-tional faulting. Each cycle took place in the temporary stable period after the depression of the basin. Experienced shallowing of sea water, the depth of water varied from 30m to Om in the reef-building period,energy of sedimentary environment increases, and then becomes continuous turbulent.
1988, 6(2): 77-86.
Abstract:
In South China, the nodular limestone which is a special carbonate type.was distributel in Devonian System. The petrological research, δ13C and δ18O, X-ray diffraction, CaCO3 and organic carbon contents are done and the origin of the nodular limestone is detailedly studied. In Dachang area of Guangxi Province, the nodules of the nodular limestone which is more pure show the lens, nodule and pod. The nodule without or with a few quartz fragments is mainly composed of calcite (CaCO390%). The matrix of the nodular limestone, however, is more complex, which contains some clay minerals, a few quartz fragments and black organic materials as well as a few autogenetic quartz grains.The δ13C values of the nodules and matrixes are more than -2‰, however, the δ13C values of the nodules of same samples is higher than the values of the matrix, in which the average difference between them is about 1‰, and differences are about coincident. CaCO3 content of the nodules is higher than that of the matrixes and the difference is more obvious. In Fankou, the nodular limestone contains more bioclasts, than in Dachang. the nodule and the matrix contain more quartz fragments. The matrix contains more quartz fragments than the nodule, but does not contains autogenetic quartz grains. The nodules being composed of block of the bioclastic limestone do not show internal structure, but show flame and flow structures, disturbance, slip and roll-up beddings. The composition has no more difference between the matrix and the nodule which are mainly composed of calcite, quartz clast and clay minerals, as well as a few dolomite and pyrite. TheδI3C values of the matrix and the nodule are lower than -2‰, and the difference of the δ13C values between the matrix and the nodule is no marked in same sample. Somtimes the value of matrix is higher, somtimes the value of the nodule is higher than that of the matrix. These characters and developmental history of Devonian System in South China indicate that, Dachang area lay on the depression with deep water and far distance from shore, and with or without a few addition of terrigenous materials. The nodule was formed without submarine flow. The submarine flow formed in certain period soluted carbonate which deposited in precedent stage and remained more insoluble clay minerals, so that the matrix was formed, the isotopic exchange between submarine flow and the carbonate decreases the δ13C value of the matrix. During the sedimentation of the nodular limestone in the Middle and Upper Devonian System in Fankou, this area belongs to a lagoon environment with shallow water and offshore. Bioclastic limestone and micrite beds formed by alternational sedimentation formed the nodular limestone under the pressure, in which the soft micrite sediments removed upward and formed the flame and flow structures. Semisolided mass of the bioclastic limestone formed the nodule under the pressure. The δ13C values between the nodule and the matrix do not show any distinctively difference, because they belong to the same sedimentary environment.
In South China, the nodular limestone which is a special carbonate type.was distributel in Devonian System. The petrological research, δ13C and δ18O, X-ray diffraction, CaCO3 and organic carbon contents are done and the origin of the nodular limestone is detailedly studied. In Dachang area of Guangxi Province, the nodules of the nodular limestone which is more pure show the lens, nodule and pod. The nodule without or with a few quartz fragments is mainly composed of calcite (CaCO390%). The matrix of the nodular limestone, however, is more complex, which contains some clay minerals, a few quartz fragments and black organic materials as well as a few autogenetic quartz grains.The δ13C values of the nodules and matrixes are more than -2‰, however, the δ13C values of the nodules of same samples is higher than the values of the matrix, in which the average difference between them is about 1‰, and differences are about coincident. CaCO3 content of the nodules is higher than that of the matrixes and the difference is more obvious. In Fankou, the nodular limestone contains more bioclasts, than in Dachang. the nodule and the matrix contain more quartz fragments. The matrix contains more quartz fragments than the nodule, but does not contains autogenetic quartz grains. The nodules being composed of block of the bioclastic limestone do not show internal structure, but show flame and flow structures, disturbance, slip and roll-up beddings. The composition has no more difference between the matrix and the nodule which are mainly composed of calcite, quartz clast and clay minerals, as well as a few dolomite and pyrite. TheδI3C values of the matrix and the nodule are lower than -2‰, and the difference of the δ13C values between the matrix and the nodule is no marked in same sample. Somtimes the value of matrix is higher, somtimes the value of the nodule is higher than that of the matrix. These characters and developmental history of Devonian System in South China indicate that, Dachang area lay on the depression with deep water and far distance from shore, and with or without a few addition of terrigenous materials. The nodule was formed without submarine flow. The submarine flow formed in certain period soluted carbonate which deposited in precedent stage and remained more insoluble clay minerals, so that the matrix was formed, the isotopic exchange between submarine flow and the carbonate decreases the δ13C value of the matrix. During the sedimentation of the nodular limestone in the Middle and Upper Devonian System in Fankou, this area belongs to a lagoon environment with shallow water and offshore. Bioclastic limestone and micrite beds formed by alternational sedimentation formed the nodular limestone under the pressure, in which the soft micrite sediments removed upward and formed the flame and flow structures. Semisolided mass of the bioclastic limestone formed the nodule under the pressure. The δ13C values between the nodule and the matrix do not show any distinctively difference, because they belong to the same sedimentary environment.
1988, 6(2): 97-105.
Abstract:
During the field work for Sediment Dynamic System (SDS) four box-core samples were taken in a tidal channel of Skgit Bay, Puget Sands Washington U. S. A. By using the X-radiography equipment and the conventional analysis in laboratory, some results have been got from sedimentary structures as follows; 1. The tidal active layer (or reactivity layer) is defined, its thickness of 1.5-2.5 cm, and its influential factors are examined critically. 2. According to the features of the sedimentary structures, the layers of flood current and ebb current can be differentiated, the layers of bedload and suspended load discriminated, too. 3. There is a dominant current found along the bottom of the channel, and it is defined as the flood current 4. Based on the granulometric data of the sediment, the speed of the tidal current ups to more than 40 cm/sec. The judgments above are confirmed by spot data measured by SDS. 5. Using the X-radiographied films, the information of the channel sedimentation is got, for example net deposition rate is 0.5-1.0 cm, erosion rate is 1.0-1.5 cm in a tidal cycle. 6. A simple sedimentation model of a tidal channel in estuarine environment is set up finally
During the field work for Sediment Dynamic System (SDS) four box-core samples were taken in a tidal channel of Skgit Bay, Puget Sands Washington U. S. A. By using the X-radiography equipment and the conventional analysis in laboratory, some results have been got from sedimentary structures as follows; 1. The tidal active layer (or reactivity layer) is defined, its thickness of 1.5-2.5 cm, and its influential factors are examined critically. 2. According to the features of the sedimentary structures, the layers of flood current and ebb current can be differentiated, the layers of bedload and suspended load discriminated, too. 3. There is a dominant current found along the bottom of the channel, and it is defined as the flood current 4. Based on the granulometric data of the sediment, the speed of the tidal current ups to more than 40 cm/sec. The judgments above are confirmed by spot data measured by SDS. 5. Using the X-radiographied films, the information of the channel sedimentation is got, for example net deposition rate is 0.5-1.0 cm, erosion rate is 1.0-1.5 cm in a tidal cycle. 6. A simple sedimentation model of a tidal channel in estuarine environment is set up finally
1988, 6(2): 118-122.
Abstract:
Ancient storms affected both sediments and organisms and left some special marks on the fossils, which are useful to us to identify the ancient storm deposits. The main marks are listed as follows: 1. The heavy skeleton blocks of the organisms, which lived in the deeper water environments, were transported and mixed with the shallower water biocoenosis. These phenomena usually occurred near the facies change zone. 2. The big masses of the organisms, living in native places, were overthrown and kept in an unstable position. 3. The infauna shells were digged out and mixed with the epifauna shells. All shells preserved in very poor chosen condition. 4. The large frameworks of the organisms, which built wave-resistive structures, were broken and their fragments with sharp edges kept nearby the structures. 5. The layers of encrusting organisms were torn and some upward gaps were formed on it. 6. Numerous broken branches and complete skeletons of the same dendritic organisms accumulated together in their native places. The broken branches were preserved in unworn and unchosen condition. 7. The upset productids with two complete concavo-convex shells were preserved together with the same kind of shells, keeping in their growing positions. 8. Many single corals bent into some marked angles. An angle indicated one of the storms happend during the growing processes of these corals. 9. More or less complete calyxes and long stems of crinoids were preserved with the skeletons of other organisms, which were broken by waves. 10. Numerous small shells accumulated on the top of the layer consisting of larger fossils and showed the positive graded bedding. These small shells only belong to few species. As listed above, the fossil marks of ancient storm deposits are various and sometimes very similar to some phenomena caused by other agencies, such as ordinary waves, tides, bottom currents, turbidity currents and so on. This paper also discusses the differences between them. But, it is still necessary to consult the sedimentological evidences, when these fossil marks are used,
Ancient storms affected both sediments and organisms and left some special marks on the fossils, which are useful to us to identify the ancient storm deposits. The main marks are listed as follows: 1. The heavy skeleton blocks of the organisms, which lived in the deeper water environments, were transported and mixed with the shallower water biocoenosis. These phenomena usually occurred near the facies change zone. 2. The big masses of the organisms, living in native places, were overthrown and kept in an unstable position. 3. The infauna shells were digged out and mixed with the epifauna shells. All shells preserved in very poor chosen condition. 4. The large frameworks of the organisms, which built wave-resistive structures, were broken and their fragments with sharp edges kept nearby the structures. 5. The layers of encrusting organisms were torn and some upward gaps were formed on it. 6. Numerous broken branches and complete skeletons of the same dendritic organisms accumulated together in their native places. The broken branches were preserved in unworn and unchosen condition. 7. The upset productids with two complete concavo-convex shells were preserved together with the same kind of shells, keeping in their growing positions. 8. Many single corals bent into some marked angles. An angle indicated one of the storms happend during the growing processes of these corals. 9. More or less complete calyxes and long stems of crinoids were preserved with the skeletons of other organisms, which were broken by waves. 10. Numerous small shells accumulated on the top of the layer consisting of larger fossils and showed the positive graded bedding. These small shells only belong to few species. As listed above, the fossil marks of ancient storm deposits are various and sometimes very similar to some phenomena caused by other agencies, such as ordinary waves, tides, bottom currents, turbidity currents and so on. This paper also discusses the differences between them. But, it is still necessary to consult the sedimentological evidences, when these fossil marks are used,
