1992 Vol. 10, No. 4
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Display Method:
1992, 10(4): 1-10.
Abstract:
The molecular volume of the liquid hydrocarbon equals to the sum of the topological volumes of the functional groups, conforming to the principle of additivity. The topological volume value of a functional group in all of the organic compound approximates to a constant respectively, i. e. V (CH2) =27.24Å. V (CH3) =55.11Å3, V (-ch = ch2) = 70.12Å3, V (-ch = ch-) =40.98Å3, V (-ch=ch) = 51.58Å. V (-C6H4-) =89.92Å3, V (-C6=H3) =61.51Å3. The topological volume of the liquid hydrocarbon can al so be obtained from the following eqation: V = K+13.89×C+6.67×H (Å3) K refers to the liquid coefficient, K= 15 for the cyclanes. C and H are number of carbon and hydrogen atoms respectively.
The molecular volume of the liquid hydrocarbon equals to the sum of the topological volumes of the functional groups, conforming to the principle of additivity. The topological volume value of a functional group in all of the organic compound approximates to a constant respectively, i. e. V (CH2) =27.24Å. V (CH3) =55.11Å3, V (-ch = ch2) = 70.12Å3, V (-ch = ch-) =40.98Å3, V (-ch=ch) = 51.58Å. V (-C6H4-) =89.92Å3, V (-C6=H3) =61.51Å3. The topological volume of the liquid hydrocarbon can al so be obtained from the following eqation: V = K+13.89×C+6.67×H (Å3) K refers to the liquid coefficient, K= 15 for the cyclanes. C and H are number of carbon and hydrogen atoms respectively.
1992, 10(4): 23-34.
Abstract:
Longtan Group in Early Upper Permian is mainly composited of clastic deposits bearing coals, wide spreaded in Lower Yangtze area, East China and extends in NE-SW direction. Its mian sedimentary body showed a clear delta sequence in some geological sections. The ancient current of Longtan Group sandstones flown in NW-SE directions without exception. The thickness of the group in the east part of Yangtze Plate is thicker than that in the west part and the thickest geological section up to 1000m which occures in the east part (e.g. in Binhai County, Northern Jiangsu); and it quickly thinned to several (ens meters westward. Correspondingly, the thickness of sandstones in Longtan Group thinned from east to west, and the tock associations regularly changed from mudstone- sandstone association in the east part, through sandstone-mudstone association in the middle, to carbonate-mudstone association in the west part. Plagioclase contents of the sandstones are richer in the east than in the west. Doubtlessly. Longtan Group is a clastic wedge that pinched out westward, i.e., a compressed molasse. One of the important characters of the sandstones is the abundance of tourmalines, its average content is about 510.2lg/ t, and a lot of detritus of metamorphic and magmatic rocks. Longtan Group sandstones can be identified as detrital graywack by their chemical compositions. The grain framework composition and the chemical composition of sandstiones indicate that the deposits of Longtan Group were accumulated under a tectonic setting com bining Atlantic type rift with a inactive convergence margin according to several author' s tectonic crimination models such as Dickinson et al.Bhatia, and so on. Evidently, an old orogenic belt must be presented in the eastern source area and extended near S-N directional strike. The present authors would like lo suggest that it is called Donghai Orogenic Belt. A series of thickness sections clearly show that, the intra-basin structure If Longtan Group is uneven, there are several NE-SW derictional synsedimentary uplifts and depressions in it, which are alternated with each other in the space and differentiated in sedimentary characteristics and thickness. The framework of uplifts alternating with depressions can he identified by the sedimentary characteristics of Late Devonian and Early Carbonifeous deposits in this area. Thus, the tectonic framewock had been sprouted since Late Devonian and developed into the most typtcal stage during Longtan Epock, which is considered to be the represent of the tectonic framework of whole Kale Palaeozoic in this area. The authors concluded that Longlan Group sedimentary basin is an impactogen that caused by crust txtension in the area and was created under the compression condition from Donghai Orogenic Bell.
Longtan Group in Early Upper Permian is mainly composited of clastic deposits bearing coals, wide spreaded in Lower Yangtze area, East China and extends in NE-SW direction. Its mian sedimentary body showed a clear delta sequence in some geological sections. The ancient current of Longtan Group sandstones flown in NW-SE directions without exception. The thickness of the group in the east part of Yangtze Plate is thicker than that in the west part and the thickest geological section up to 1000m which occures in the east part (e.g. in Binhai County, Northern Jiangsu); and it quickly thinned to several (ens meters westward. Correspondingly, the thickness of sandstones in Longtan Group thinned from east to west, and the tock associations regularly changed from mudstone- sandstone association in the east part, through sandstone-mudstone association in the middle, to carbonate-mudstone association in the west part. Plagioclase contents of the sandstones are richer in the east than in the west. Doubtlessly. Longtan Group is a clastic wedge that pinched out westward, i.e., a compressed molasse. One of the important characters of the sandstones is the abundance of tourmalines, its average content is about 510.2lg/ t, and a lot of detritus of metamorphic and magmatic rocks. Longtan Group sandstones can be identified as detrital graywack by their chemical compositions. The grain framework composition and the chemical composition of sandstiones indicate that the deposits of Longtan Group were accumulated under a tectonic setting com bining Atlantic type rift with a inactive convergence margin according to several author' s tectonic crimination models such as Dickinson et al.Bhatia, and so on. Evidently, an old orogenic belt must be presented in the eastern source area and extended near S-N directional strike. The present authors would like lo suggest that it is called Donghai Orogenic Belt. A series of thickness sections clearly show that, the intra-basin structure If Longtan Group is uneven, there are several NE-SW derictional synsedimentary uplifts and depressions in it, which are alternated with each other in the space and differentiated in sedimentary characteristics and thickness. The framework of uplifts alternating with depressions can he identified by the sedimentary characteristics of Late Devonian and Early Carbonifeous deposits in this area. Thus, the tectonic framewock had been sprouted since Late Devonian and developed into the most typtcal stage during Longtan Epock, which is considered to be the represent of the tectonic framework of whole Kale Palaeozoic in this area. The authors concluded that Longlan Group sedimentary basin is an impactogen that caused by crust txtension in the area and was created under the compression condition from Donghai Orogenic Bell.
1992, 10(4): 44-48.
Abstract:
1992, 10(4): 60-67.
Abstract:
Xicheng Pb-Zn Orefield is located in Huixian, Chengxian and Xihe counties, southeastern Gansu. The ore-bearing rock sequences consisting of marine clastic and carbonates rocks of middle Devonian. Two types of the strata-bound ore deposits have been divided based on the ore deposits feature: Changba and Bijiashan types. Especially Bijiashan type deposit, which's main host rocks are siliceous rocks. The siliceous rocks, distributing a little broader than ore bodies, are closely related to Pb- Zn mineralization and its thickness has a normal ratio with thickness of ore body. In section, the siliceous rocks, which are flatly contact with overlying phyllite and roughly contact with underlying carbonates, are bedded, bedded-like or lenticular and paralled or simultaneously folded with the adjoining rocks. The main types of the siliceous rocks are divided into brecciated siliceous rocks, dark-gyay or gray massive siliceous rocks, riband-band siliceous rocks and white vein quartzite. They have very obvious sedimentary charactes and coexist with hydrothermal sedimentary barite rocks except vein quartzite. Geochemical analysis show that the siliceous rocks possess characteristic geochemistry: (1) the content of silica and some significant ratios (SiO2 = 82.97% , Fe2O3 / FeO<1, K2O>Na2O, A12O3 = 28.41, SiO2/ (K2O+Na2O) =143.05, SiO2/ MgO=60.56, Fe+Mn/ Ti= 30.18) are quite similar to those in hydrothermal sedimentary siliceous rocks, but different from those in normal sedimentary siliceous rocks and volcanic siliceous roks; (2) the contents of trace elements such as Ag, As, Hg, Sb, Ge and Cd are higher than Clark value by 1-3 logarithmic scales, this feature is one of the indicators of hydrothermal sedimentary origin; (3) the results of REE analysis show that the REE models of siliceous rocks are HREE-rich type and negative cerium or europium anomalies, REE models of different types of siliceous rocks and Pb- Zn ore are quite similar. The total contents of REE in the siliceous rocks (Σ REE = 3.09-42.012ppm) is similar to those in Pb-Zn ore (Σ REE - 3.773-30.71ppm), and the character-istic parameters (Sm/Nd= 0.16-0.32, La/Yb= 6.62-22.14, δEu=0.42-1.15, δCe=0.49-0.98) are similar to those of hydrothermal exhalative sedimentary siliceous rocks from Fengtai and Dachang (China) orefields and so on, indicating both Pb-Zn ore and the siliceous rocks have the same material source, formation processes and environment. Through study of the characteristics of petrology and geochemistry of the siliceous rocks, the facts show that the siliceous rocks in Xicheng district are ocean floor hydrothermal exhalative sedimentary originated.
Xicheng Pb-Zn Orefield is located in Huixian, Chengxian and Xihe counties, southeastern Gansu. The ore-bearing rock sequences consisting of marine clastic and carbonates rocks of middle Devonian. Two types of the strata-bound ore deposits have been divided based on the ore deposits feature: Changba and Bijiashan types. Especially Bijiashan type deposit, which's main host rocks are siliceous rocks. The siliceous rocks, distributing a little broader than ore bodies, are closely related to Pb- Zn mineralization and its thickness has a normal ratio with thickness of ore body. In section, the siliceous rocks, which are flatly contact with overlying phyllite and roughly contact with underlying carbonates, are bedded, bedded-like or lenticular and paralled or simultaneously folded with the adjoining rocks. The main types of the siliceous rocks are divided into brecciated siliceous rocks, dark-gyay or gray massive siliceous rocks, riband-band siliceous rocks and white vein quartzite. They have very obvious sedimentary charactes and coexist with hydrothermal sedimentary barite rocks except vein quartzite. Geochemical analysis show that the siliceous rocks possess characteristic geochemistry: (1) the content of silica and some significant ratios (SiO2 = 82.97% , Fe2O3 / FeO<1, K2O>Na2O, A12O3 = 28.41, SiO2/ (K2O+Na2O) =143.05, SiO2/ MgO=60.56, Fe+Mn/ Ti= 30.18) are quite similar to those in hydrothermal sedimentary siliceous rocks, but different from those in normal sedimentary siliceous rocks and volcanic siliceous roks; (2) the contents of trace elements such as Ag, As, Hg, Sb, Ge and Cd are higher than Clark value by 1-3 logarithmic scales, this feature is one of the indicators of hydrothermal sedimentary origin; (3) the results of REE analysis show that the REE models of siliceous rocks are HREE-rich type and negative cerium or europium anomalies, REE models of different types of siliceous rocks and Pb- Zn ore are quite similar. The total contents of REE in the siliceous rocks (Σ REE = 3.09-42.012ppm) is similar to those in Pb-Zn ore (Σ REE - 3.773-30.71ppm), and the character-istic parameters (Sm/Nd= 0.16-0.32, La/Yb= 6.62-22.14, δEu=0.42-1.15, δCe=0.49-0.98) are similar to those of hydrothermal exhalative sedimentary siliceous rocks from Fengtai and Dachang (China) orefields and so on, indicating both Pb-Zn ore and the siliceous rocks have the same material source, formation processes and environment. Through study of the characteristics of petrology and geochemistry of the siliceous rocks, the facts show that the siliceous rocks in Xicheng district are ocean floor hydrothermal exhalative sedimentary originated.
1992, 10(4): 77-86.
Abstract:
The Qiulitage Group dolomite (Cambrian to Ordovician) is one of the main hydrocarbon producing horizons in Northern Tarim Basin. Detailed petrographic and geochemical studies indicate that the origin of various dolomites of the Qiulitage Group is different. Algal laminated dolomite, micritic dolomite and grains in grained dolomite are products of penecontemporaneous dolomitization. The evidence of penecontemporaneous dolomitization is that they maintain characteristics of primary fabrics (such as algal lamination and concentric lamination of oolite); oxygen isotope composition (δ18O-5.35 to -6.50‰ PDB) is near the primary oxygen isotope composition of cambrian to Ordovician marine carbonate (δ18O -4 to -6‰PDB) the content of Na (242.8 to 334.0 ppm) and Sr (197.5 to 206.0ppm) is high and the content of Fe (558 to 563ppm) and Mn (483 to 557ppm) is low. Medium to coarse crystalline dolomites and medium to coarse crystalline dolomite cements in grained dolomite are products of deep-burial diagenetic environment. The evidence of deep-burial origin for medium to coarse crystalline dolomites is that a) medium to coarse crystal of the dolomites; b) abundant xenotopic texture; c) remnans of depositional textures in medium to coarse crystalline dolomites; d) dolomite crystal cuts fructure; e) stylolite destroyed by dolomite crystal or remnants of stylolite in dolomite; f) similarity of trace element values for the medium to coarse dolomites to the dolomites distributed along stylolite; g) oxygen isotope composition (δ18O -8.50 to - 10.75‰ PDB) is light and carbon isotope composition (δ18O + 0. 25 to + 2. 27‰PDB) is relative constant; h) the content of Na (55-87ppm) and Sr (0-32ppm) is low and the content of Fe (1663 to 1792ppm) and Mn (1396 to 1632ppm) is high; i) high fluid inclusion homogenized temperature indicats that the crystalline temperature of medium to coarse dolomites is at least 75-80℃.
The Qiulitage Group dolomite (Cambrian to Ordovician) is one of the main hydrocarbon producing horizons in Northern Tarim Basin. Detailed petrographic and geochemical studies indicate that the origin of various dolomites of the Qiulitage Group is different. Algal laminated dolomite, micritic dolomite and grains in grained dolomite are products of penecontemporaneous dolomitization. The evidence of penecontemporaneous dolomitization is that they maintain characteristics of primary fabrics (such as algal lamination and concentric lamination of oolite); oxygen isotope composition (δ18O-5.35 to -6.50‰ PDB) is near the primary oxygen isotope composition of cambrian to Ordovician marine carbonate (δ18O -4 to -6‰PDB) the content of Na (242.8 to 334.0 ppm) and Sr (197.5 to 206.0ppm) is high and the content of Fe (558 to 563ppm) and Mn (483 to 557ppm) is low. Medium to coarse crystalline dolomites and medium to coarse crystalline dolomite cements in grained dolomite are products of deep-burial diagenetic environment. The evidence of deep-burial origin for medium to coarse crystalline dolomites is that a) medium to coarse crystal of the dolomites; b) abundant xenotopic texture; c) remnans of depositional textures in medium to coarse crystalline dolomites; d) dolomite crystal cuts fructure; e) stylolite destroyed by dolomite crystal or remnants of stylolite in dolomite; f) similarity of trace element values for the medium to coarse dolomites to the dolomites distributed along stylolite; g) oxygen isotope composition (δ18O -8.50 to - 10.75‰ PDB) is light and carbon isotope composition (δ18O + 0. 25 to + 2. 27‰PDB) is relative constant; h) the content of Na (55-87ppm) and Sr (0-32ppm) is low and the content of Fe (1663 to 1792ppm) and Mn (1396 to 1632ppm) is high; i) high fluid inclusion homogenized temperature indicats that the crystalline temperature of medium to coarse dolomites is at least 75-80℃.
1992, 10(4): 94-100.
Abstract:
On the basis of fuzzy pattern recognition, a practical method of recognition of marine carbonatite fades is presented in this paper. The standard pattern can be constructed in the situation of cluster analysis and known samples. The cluster centre is obtained by the F-PFS method or the characteristic vector. Besides of the using of cluster analysis, the recognition of unknown sample mainly uses the calculation of similarity degree and the recogition is according to the nearest neighbour criterion. Then, a new similarity degree of complement distance with the different weights is presented in the paper. That is S(Xi, Yj)=sA-1 Σ Wk(1-Dijk)p (2) k - I Where the weight Wk is determained by the technique which is presented by the authors and is according to the rate of right judgement of the single factor. Four facies can be identified by using fuzzy cluster analysis, other samples can be recognized by using the fuzzy recognition method. The percent of right judgment is 81.8%. Six standard patterns were built based on the known facies samples of Shouzi Section. Both the samples of Jingshan Section and the rest samples of Shouzi Section were recognized with this model, the percent of right judgment is 79.2%. The results of fuzzy recognition show that fuzzy cluster analysis and similarity degree are a kind of new effective method for the classification of carbonatite facies. Furthermore, cluster centres based on the fuzzy cluster or known facies samples could become the basis of later fuzzy recognition marine carbonatite facies.
On the basis of fuzzy pattern recognition, a practical method of recognition of marine carbonatite fades is presented in this paper. The standard pattern can be constructed in the situation of cluster analysis and known samples. The cluster centre is obtained by the F-PFS method or the characteristic vector. Besides of the using of cluster analysis, the recognition of unknown sample mainly uses the calculation of similarity degree and the recogition is according to the nearest neighbour criterion. Then, a new similarity degree of complement distance with the different weights is presented in the paper. That is S(Xi, Yj)=sA-1 Σ Wk(1-Dijk)p (2) k - I Where the weight Wk is determained by the technique which is presented by the authors and is according to the rate of right judgement of the single factor. Four facies can be identified by using fuzzy cluster analysis, other samples can be recognized by using the fuzzy recognition method. The percent of right judgment is 81.8%. Six standard patterns were built based on the known facies samples of Shouzi Section. Both the samples of Jingshan Section and the rest samples of Shouzi Section were recognized with this model, the percent of right judgment is 79.2%. The results of fuzzy recognition show that fuzzy cluster analysis and similarity degree are a kind of new effective method for the classification of carbonatite facies. Furthermore, cluster centres based on the fuzzy cluster or known facies samples could become the basis of later fuzzy recognition marine carbonatite facies.
1992, 10(4): 111-118.
Abstract:
Estuarme depositional environments have been seldom recognized from antient deposits. The deposits of Changxing Age, Late Permian in Gemudi were deposited in estuarine-tidal depositional environments. 325 core holes and several outcrops, in an area of 325 square kilometre, were studied in this paper. The ancient estuarine depositional environments are reconstructed through the following aspects. Is It is explained by microscopic study that the clastic material is transported from western Kongdian Rise. The water body at Gemudi are desalinated by river discharges, which are confirmed by lower contents of boron in mudstones and the brackish-water fauna that is characterized by small body and thinner shall, such as chonetessp. lingulasp. and some fragments of marine fauna. 2) Tidal sedimentation dominate the main depositional prosesses. The paticuiar combination of sedimentary structures which often occur in modern tidal environments, such as the flaser bedding, lenticular bedding, the double mudbeds and the chevron cross-bedding. 3) According to the regional setting, Gemudi is sited in the mouth of an ancient river that empted into the sea from the west. The evidences of land runoff can be found in deposits, such as the large trunks. 4) The vertical tidal flat deposits, bay fine-grained clastic and carbonate deposits, are similar to the modern estuarine sequences. 5) From the depositional dip direction, the sandstone contents decrease at first, then rise again, and the marine deposits especially the limestone increase. 6) It is found from the isopach maps of sandstones that the tidal channel are developed in the western and the tidal ridges and bay deposits are dominated in the eastern part. That the tidal energy is stronger than the fluvial energy is the major cause of estuary developing, in Gemudi. The relative strength between basin reworking and fluvial discharge is prerequisite for estuary or delta environment developing where an river empted into sea. Three subfacies can be recognized in Geniudi estuary, they are marginal tidal flat (including tidal channels and tidal flats), bay and tidal ridge. In a word, ancient esluarine deposits can be recognized by the analysis of paleosaiinity, evidences of tidal sedimentation, land runoff and regional settings.
Estuarme depositional environments have been seldom recognized from antient deposits. The deposits of Changxing Age, Late Permian in Gemudi were deposited in estuarine-tidal depositional environments. 325 core holes and several outcrops, in an area of 325 square kilometre, were studied in this paper. The ancient estuarine depositional environments are reconstructed through the following aspects. Is It is explained by microscopic study that the clastic material is transported from western Kongdian Rise. The water body at Gemudi are desalinated by river discharges, which are confirmed by lower contents of boron in mudstones and the brackish-water fauna that is characterized by small body and thinner shall, such as chonetessp. lingulasp. and some fragments of marine fauna. 2) Tidal sedimentation dominate the main depositional prosesses. The paticuiar combination of sedimentary structures which often occur in modern tidal environments, such as the flaser bedding, lenticular bedding, the double mudbeds and the chevron cross-bedding. 3) According to the regional setting, Gemudi is sited in the mouth of an ancient river that empted into the sea from the west. The evidences of land runoff can be found in deposits, such as the large trunks. 4) The vertical tidal flat deposits, bay fine-grained clastic and carbonate deposits, are similar to the modern estuarine sequences. 5) From the depositional dip direction, the sandstone contents decrease at first, then rise again, and the marine deposits especially the limestone increase. 6) It is found from the isopach maps of sandstones that the tidal channel are developed in the western and the tidal ridges and bay deposits are dominated in the eastern part. That the tidal energy is stronger than the fluvial energy is the major cause of estuary developing, in Gemudi. The relative strength between basin reworking and fluvial discharge is prerequisite for estuary or delta environment developing where an river empted into sea. Three subfacies can be recognized in Geniudi estuary, they are marginal tidal flat (including tidal channels and tidal flats), bay and tidal ridge. In a word, ancient esluarine deposits can be recognized by the analysis of paleosaiinity, evidences of tidal sedimentation, land runoff and regional settings.
1992, 10(4): 129-136.
Abstract:
The composition and distribution of main clay minerals from the sediments in the western Taiwan Strait have been determined by x-ray diffraction, infrared absorbtive spectroscopy and chemical methods and their origins are studied. The conclusions are drawn as follows: (1) Hydromica is the most abundant clay mineral of the sediments from the studied area, followed by. kaolinite (for the Fujian alongshore waters) or chlorite, (2) The content of hydromicatends to increase seaward, while kaolinite tends to decrease correspondingly. Kaolinite distribution obviously subjects to the terrestrial effects. Chlorite and montmorillonite distributions show porphyritic pattern in the studied area. (3) Most of the hydromica minerals in the studied area are of muscovite type. The kaolinite is a terrigenous secondary mineral. In addition to terrestrial orgin, the chlorite is mainly alteration producl of basic volcanic substance and of other clay mimerals. Montmorillonite in this area is mainly authigenic mineral. (4) The lobate contours of kaolimite content shows that the dispersive directions of the clay minerals are both southward with turning eastward in the Fujian alongshore waters and northeastward in the region to the east of Dongshan Island, which shows that the dispersive directions of the clay minerals have been influenced by Minzhe alongshore currents and the South China Sea warm current. (5) The vertical changes of clay mineral content provide evidences of paleoclimate and ancient sedimentary environment. In Core 737, the sediments of O-160cm are the product of warm climate in Atlantic stage of postglacial with low montmorillonite and high hydromica contents, and the sediments of 160-652cm are of cold climate in Boreal and Preboreal stages with high montmorillonite and low hrdromica contents, while low montmorillonite contents at 435- 440, 515-520 and 642-652cm show minor sedimentary cycles with warmer climate.
The composition and distribution of main clay minerals from the sediments in the western Taiwan Strait have been determined by x-ray diffraction, infrared absorbtive spectroscopy and chemical methods and their origins are studied. The conclusions are drawn as follows: (1) Hydromica is the most abundant clay mineral of the sediments from the studied area, followed by. kaolinite (for the Fujian alongshore waters) or chlorite, (2) The content of hydromicatends to increase seaward, while kaolinite tends to decrease correspondingly. Kaolinite distribution obviously subjects to the terrestrial effects. Chlorite and montmorillonite distributions show porphyritic pattern in the studied area. (3) Most of the hydromica minerals in the studied area are of muscovite type. The kaolinite is a terrigenous secondary mineral. In addition to terrestrial orgin, the chlorite is mainly alteration producl of basic volcanic substance and of other clay mimerals. Montmorillonite in this area is mainly authigenic mineral. (4) The lobate contours of kaolimite content shows that the dispersive directions of the clay minerals are both southward with turning eastward in the Fujian alongshore waters and northeastward in the region to the east of Dongshan Island, which shows that the dispersive directions of the clay minerals have been influenced by Minzhe alongshore currents and the South China Sea warm current. (5) The vertical changes of clay mineral content provide evidences of paleoclimate and ancient sedimentary environment. In Core 737, the sediments of O-160cm are the product of warm climate in Atlantic stage of postglacial with low montmorillonite and high hydromica contents, and the sediments of 160-652cm are of cold climate in Boreal and Preboreal stages with high montmorillonite and low hrdromica contents, while low montmorillonite contents at 435- 440, 515-520 and 642-652cm show minor sedimentary cycles with warmer climate.
1992, 10(4): 146-153.
Abstract:
Channel island is a kind of fluvial topographical unit that is different to channel bar and side bar in river channels. Most of them developed in anastomsed rivers. Five of the seven channel islands in Jingjiang reach of Yangtze river have been investigated. The largest one has an area of 6.17km~2 and the smallest one has an area of 0.66km. Lengthes range from 6.9km~2 to 2.70km and width from 1.98km to 0.34km. Sediments are fining downstream island by island and for every of them from the fore to the tail. There groups of lithofacies distribute at different parts of a channel island. Gravel facies including Gm, Gt, Gp are dominated at the fore of channel island; Sandy facies including St, Sr, Sp, Sn, Si are mainly developed at the middle of channel island; Fines including Fi, Fm are found at the tail of channel island Two facies-assemblage G-S-F and S-F are found vertically. The word" Upper Channel Island Sequence" has been proposed by the author to describe the stratification situated at the top of channel island. Within the upper channel island sequences, fines are 70. 17% in thickness and 62.5% in unit-numbers, sands are only 27.3% in thickness and 33.3% in unit-numbers. Merely gravel unit has been discovered in the channel island. Frequences of sedimentary structures are distributed as: ripple laminations 23.3%, horizontal laminations 35%, parallel bedding 6.5 massive bedding 8.4%, rootlite and burrows are 9.3% and 7.4% respectly. A few of tabular beddings are discovered on these sequences. Four types of three dimension (3D) architecture elements including 1) NDA. 2) DAC 3) LABB and 4) UA are concluded to constitute the 3D architecture of an channel island sandbody.
Channel island is a kind of fluvial topographical unit that is different to channel bar and side bar in river channels. Most of them developed in anastomsed rivers. Five of the seven channel islands in Jingjiang reach of Yangtze river have been investigated. The largest one has an area of 6.17km~2 and the smallest one has an area of 0.66km. Lengthes range from 6.9km~2 to 2.70km and width from 1.98km to 0.34km. Sediments are fining downstream island by island and for every of them from the fore to the tail. There groups of lithofacies distribute at different parts of a channel island. Gravel facies including Gm, Gt, Gp are dominated at the fore of channel island; Sandy facies including St, Sr, Sp, Sn, Si are mainly developed at the middle of channel island; Fines including Fi, Fm are found at the tail of channel island Two facies-assemblage G-S-F and S-F are found vertically. The word" Upper Channel Island Sequence" has been proposed by the author to describe the stratification situated at the top of channel island. Within the upper channel island sequences, fines are 70. 17% in thickness and 62.5% in unit-numbers, sands are only 27.3% in thickness and 33.3% in unit-numbers. Merely gravel unit has been discovered in the channel island. Frequences of sedimentary structures are distributed as: ripple laminations 23.3%, horizontal laminations 35%, parallel bedding 6.5 massive bedding 8.4%, rootlite and burrows are 9.3% and 7.4% respectly. A few of tabular beddings are discovered on these sequences. Four types of three dimension (3D) architecture elements including 1) NDA. 2) DAC 3) LABB and 4) UA are concluded to constitute the 3D architecture of an channel island sandbody.
1992, 10(4): 11-22.
Abstract:
Sequence stratigraphy erected by Northern American geologists has established a relatively perfect concept system and research methodology, based on the investigation of continental margin basins. It has a great influence upon the development of sedimentary basin analysis, biostratigraphy and other fields of geology. Economically important Mesozoic oil and coal-bearing basins and Late Palaeozoic coal-bearing ba sins in China, however, are mostly continental basins or paralic basins characterized by epeiric sea environments, it is impossible to mechanically use the model from continental margin study in the sequence stratigraphic analysis of thses basins. Several key points' that should be stressed are as follows: 1) Unconformities identified in the basins mentioned above are mainly related to tectonic movements, most of them are minor-dip unconformable contacts. Such surfaces have been recognized in Sichuan and Ordos basins mainly by palaeogeological mapping beneath the surfaces. 2) Although it may be impossible to figure out the influence of sea level changes in continental basins, polyphasic major lake level change episodes are usually basin-wide identifiable in large lacustrine basins such as Songliao, Ofdos and Jungar. 3) Even if in paralic basin the low sea level events can not generate unconformities because of very gentle palaeoslop in the basin. 4) The integrated study of seismic stratigraphy and outcrop or core examination should be emphazied in reconstruction of sequence stratigraphic framework. On the basis of integrated analysis, the mapping of depositional section network is neccessary and effective for correlation. 5) High resolution event stratigraphy, particularly the event markers such as volcanic ash beds, coal seams related to the abundance of regional clastic systems, and palaeoweathering residue or surfaces, have been verifies to be very useful in the reconstruction of chronostratigraphic framework. It is evident that the concept system of sequence stratigraphy should be reconsidered in a broad sense so that to widely use in the study of different types of sedimentary basin. Based on our investigation of Mesozoic
Sequence stratigraphy erected by Northern American geologists has established a relatively perfect concept system and research methodology, based on the investigation of continental margin basins. It has a great influence upon the development of sedimentary basin analysis, biostratigraphy and other fields of geology. Economically important Mesozoic oil and coal-bearing basins and Late Palaeozoic coal-bearing ba sins in China, however, are mostly continental basins or paralic basins characterized by epeiric sea environments, it is impossible to mechanically use the model from continental margin study in the sequence stratigraphic analysis of thses basins. Several key points' that should be stressed are as follows: 1) Unconformities identified in the basins mentioned above are mainly related to tectonic movements, most of them are minor-dip unconformable contacts. Such surfaces have been recognized in Sichuan and Ordos basins mainly by palaeogeological mapping beneath the surfaces. 2) Although it may be impossible to figure out the influence of sea level changes in continental basins, polyphasic major lake level change episodes are usually basin-wide identifiable in large lacustrine basins such as Songliao, Ofdos and Jungar. 3) Even if in paralic basin the low sea level events can not generate unconformities because of very gentle palaeoslop in the basin. 4) The integrated study of seismic stratigraphy and outcrop or core examination should be emphazied in reconstruction of sequence stratigraphic framework. On the basis of integrated analysis, the mapping of depositional section network is neccessary and effective for correlation. 5) High resolution event stratigraphy, particularly the event markers such as volcanic ash beds, coal seams related to the abundance of regional clastic systems, and palaeoweathering residue or surfaces, have been verifies to be very useful in the reconstruction of chronostratigraphic framework. It is evident that the concept system of sequence stratigraphy should be reconsidered in a broad sense so that to widely use in the study of different types of sedimentary basin. Based on our investigation of Mesozoic
1992, 10(4): 35-43.
Abstract:
Songtao mangenes deposits, developed in the fine clastic sediments of Datangpo formation of Sinian, Guizhuo Province, belinging to carbonate deposits, have the following hydrothernal sedimentary geological and geochemical characteristices. 1. The mangenes deposits, yieldded in the high terrestrial heat extended margin basin area, poss "eye-like" structure both in lithofacies and in mangenes contents of single body of mangenes deposits. 2.The ore structures are mainly regularly distributed laminated-banded and meassive. It is usually massive in the center and then turned into banded-laminated to the edges. The thickness of bands and laminated are gradually finer and the number in creace to the sides. The bulk ores have the intraclast texture. 3. The ores are principally composited by Mn-carbonate, authigenic quartz and argillic minerals. Mn-carbonate and authigenic quartz are common in hydrothermal deposits. In addition, hydrothermal constitutions such as syngenetic barite, gypsum and pyrite ect. are found frequently. 4. The sample of the mangenes ores fell in the hydrothermal fiels of the diagrams of Fe- Mn-(Cu+Ni+Co× 10 and logU-logTh. The REE compositions in mangenes ores have the mixed features of hydrothermal and hydrogenic the estimated ratio of hydrothermal to hydrogenic compositon is about 70% to 30%. The REE distribution modet of the over lying argillites of the mangenes diposits is simlar to those of Nouth Amrica Shale, but it incline to the left in the underlying argillites, because of the effection of the hydrotherma solution. 5.δ13C values of carbonates in the ores are -4.2-10.7%, close to that of soluted carbon in the hot spring water seafloor. δ34S values of pyrits are +42.9-+57.3%, distribute as pagoda modle resulted from hydrothermal solution of sulphur from the crustal rocks. The initial ratio of 87Sr / 86Sr in the host rocks is 0.72391 ± 0.00132, similar to those of old salic rocks. The value of ores is 0.70595 ±0.00015, different from that of host rocks, between the 0.7909 of marine water and 0.7031 of seafloor hot spring water. 6. According to R°f pitchin the mangenes ores, the ores was formed under 170- 195℃ , similar to the inclusion temparature (173- 240℃ ) of the authibenic, quartz in the adjacent mangenes mine. Moreover, the temprature of the bottom of orebed is higher than that of the top, consistent with the hydrothermal characteristics.
Songtao mangenes deposits, developed in the fine clastic sediments of Datangpo formation of Sinian, Guizhuo Province, belinging to carbonate deposits, have the following hydrothernal sedimentary geological and geochemical characteristices. 1. The mangenes deposits, yieldded in the high terrestrial heat extended margin basin area, poss "eye-like" structure both in lithofacies and in mangenes contents of single body of mangenes deposits. 2.The ore structures are mainly regularly distributed laminated-banded and meassive. It is usually massive in the center and then turned into banded-laminated to the edges. The thickness of bands and laminated are gradually finer and the number in creace to the sides. The bulk ores have the intraclast texture. 3. The ores are principally composited by Mn-carbonate, authigenic quartz and argillic minerals. Mn-carbonate and authigenic quartz are common in hydrothermal deposits. In addition, hydrothermal constitutions such as syngenetic barite, gypsum and pyrite ect. are found frequently. 4. The sample of the mangenes ores fell in the hydrothermal fiels of the diagrams of Fe- Mn-(Cu+Ni+Co× 10 and logU-logTh. The REE compositions in mangenes ores have the mixed features of hydrothermal and hydrogenic the estimated ratio of hydrothermal to hydrogenic compositon is about 70% to 30%. The REE distribution modet of the over lying argillites of the mangenes diposits is simlar to those of Nouth Amrica Shale, but it incline to the left in the underlying argillites, because of the effection of the hydrotherma solution. 5.δ13C values of carbonates in the ores are -4.2-10.7%, close to that of soluted carbon in the hot spring water seafloor. δ34S values of pyrits are +42.9-+57.3%, distribute as pagoda modle resulted from hydrothermal solution of sulphur from the crustal rocks. The initial ratio of 87Sr / 86Sr in the host rocks is 0.72391 ± 0.00132, similar to those of old salic rocks. The value of ores is 0.70595 ±0.00015, different from that of host rocks, between the 0.7909 of marine water and 0.7031 of seafloor hot spring water. 6. According to R°f pitchin the mangenes ores, the ores was formed under 170- 195℃ , similar to the inclusion temparature (173- 240℃ ) of the authibenic, quartz in the adjacent mangenes mine. Moreover, the temprature of the bottom of orebed is higher than that of the top, consistent with the hydrothermal characteristics.
1992, 10(4): 49-59.
Abstract:
In the present paper, the distribution of carbon isotopes of sedimentary organic matter are studied in the aspects of soluable portion (i.e., abstracts) and insoluble component (i.e., kerogen) as well as in the groups of EOM (i. e. , saturated hydrocarbon, aromatic hydrocarbon, non- hydrocarbon and asphaltene), results show that the distribation of δ~(13)C value are as follows: it is higher in kerogen than in abstracts, and for the abstracts, it decreases in the proper order of asphaltene, non-hydrocarbon, aromatic hydrocarbon and saturated hydrocarbon. The study revealed that different sedimentary environment that fed by different biologic group may resulted in the abnormal distribution of carbon isotopic composition, for instance, it may be havier in non-hydrocarbon than in asphaltene, and aromatic hydrocarbon havier than non-hydrocarbon, the authors defined these phenominon as partially reversed carbon isotopic distribution of sedimentary organic matter; and if the carbon isotop is havier in soluble sedimentary organic matter than in kerogen, it would be called as totally reversed distribution. Normal carbon istopic composition are usually found in higher plant input limnetic facies and interfluval lacustrine, Partially reversed distribution is usually found in the facies that input mainly by higher plant but suffered intensivly bacterial action and input also by lipid of lower biomass. Totally reversed carbon isotopic distribution is often found in marine sedimentaty rocks that with a very high evolution degree of organic matter.
In the present paper, the distribution of carbon isotopes of sedimentary organic matter are studied in the aspects of soluable portion (i.e., abstracts) and insoluble component (i.e., kerogen) as well as in the groups of EOM (i. e. , saturated hydrocarbon, aromatic hydrocarbon, non- hydrocarbon and asphaltene), results show that the distribation of δ~(13)C value are as follows: it is higher in kerogen than in abstracts, and for the abstracts, it decreases in the proper order of asphaltene, non-hydrocarbon, aromatic hydrocarbon and saturated hydrocarbon. The study revealed that different sedimentary environment that fed by different biologic group may resulted in the abnormal distribution of carbon isotopic composition, for instance, it may be havier in non-hydrocarbon than in asphaltene, and aromatic hydrocarbon havier than non-hydrocarbon, the authors defined these phenominon as partially reversed carbon isotopic distribution of sedimentary organic matter; and if the carbon isotop is havier in soluble sedimentary organic matter than in kerogen, it would be called as totally reversed distribution. Normal carbon istopic composition are usually found in higher plant input limnetic facies and interfluval lacustrine, Partially reversed distribution is usually found in the facies that input mainly by higher plant but suffered intensivly bacterial action and input also by lipid of lower biomass. Totally reversed carbon isotopic distribution is often found in marine sedimentaty rocks that with a very high evolution degree of organic matter.
1992, 10(4): 68-76.
Abstract:
This paper presents the change and the distribution of accumulative-pores during diagenesis in the Third Oil Group of Lower Xingouzui Formation in Tuoshi area, Qianjiang depression. The following are the principal viewpoints. 1. The accumulative-pores in sandstones of Third Oil Group of Lower Xingouzui formation in Tuoshi can be divided into two stages. The first stage is the occurrence of intergranular pores formed by dissolution of carbonate cements, occurred before or during the precipitation of ferrodolomite and after the precipita- tion of ferrocalcite in early- mature stage of mesodiagenesis, the porosity roughly corresponds to the porosity of sandstones that deposited before the midstage of Jinsha Formation. The second stage is the forming of intragranular pore formed by dissolution of grains, occurred after or during precipitation of anhydrite in late- mature stage of mesodiagenesis, and before overmature stage of mesodiagenesis, the porosity roughly corresponds to the whole porosity of sandstones that deposited before the third Member of Qianjiang Formation. 2. Different stage of accumulative-pores controlled the different stages of oil accumulation. The pores that formed in the first and the second stage had partly been filled by low-mature and high-mature oil respectively. However, the low-mature oil was lost and oxidized that caused by tectonic movement, so the pores formed in the first stage became unefficient pores. 3. The diagenetic evolution of sandstones controlled the change of accumulative-pors in Third oil group of Lower Xingouzui formation in Tuoshi. The precipitation of carbonate and its evolution of diagenesis as well as the dissolution of grains are the main factors that caused the two stages of accumulative-pores forming. 4. The development of accumulative-pores in sandstones are related to the sandstones' component, depositional texture, sedimentary facies and the mineralization of formation water. The sandstones that formed in storm channel are the favourite sites of acculative-pores developing, but not are the sandstones in storm interchannel and the area around well Tuo-8. 5. The resultant accumulative-pores are different in scale, quantity and effectivity of preservation because of their different diagenetic environment. The spaces that favourable for the development of accumulative-pores may also the same for hydrocarbon accumulation.
This paper presents the change and the distribution of accumulative-pores during diagenesis in the Third Oil Group of Lower Xingouzui Formation in Tuoshi area, Qianjiang depression. The following are the principal viewpoints. 1. The accumulative-pores in sandstones of Third Oil Group of Lower Xingouzui formation in Tuoshi can be divided into two stages. The first stage is the occurrence of intergranular pores formed by dissolution of carbonate cements, occurred before or during the precipitation of ferrodolomite and after the precipita- tion of ferrocalcite in early- mature stage of mesodiagenesis, the porosity roughly corresponds to the porosity of sandstones that deposited before the midstage of Jinsha Formation. The second stage is the forming of intragranular pore formed by dissolution of grains, occurred after or during precipitation of anhydrite in late- mature stage of mesodiagenesis, and before overmature stage of mesodiagenesis, the porosity roughly corresponds to the whole porosity of sandstones that deposited before the third Member of Qianjiang Formation. 2. Different stage of accumulative-pores controlled the different stages of oil accumulation. The pores that formed in the first and the second stage had partly been filled by low-mature and high-mature oil respectively. However, the low-mature oil was lost and oxidized that caused by tectonic movement, so the pores formed in the first stage became unefficient pores. 3. The diagenetic evolution of sandstones controlled the change of accumulative-pors in Third oil group of Lower Xingouzui formation in Tuoshi. The precipitation of carbonate and its evolution of diagenesis as well as the dissolution of grains are the main factors that caused the two stages of accumulative-pores forming. 4. The development of accumulative-pores in sandstones are related to the sandstones' component, depositional texture, sedimentary facies and the mineralization of formation water. The sandstones that formed in storm channel are the favourite sites of acculative-pores developing, but not are the sandstones in storm interchannel and the area around well Tuo-8. 5. The resultant accumulative-pores are different in scale, quantity and effectivity of preservation because of their different diagenetic environment. The spaces that favourable for the development of accumulative-pores may also the same for hydrocarbon accumulation.
1992, 10(4): 87-93.
Abstract:
Lower Carboniferous in central Hunan, South China includes Shaodong. Menggongao Liujialang, Shidengzi, Ceshui and Zimenqiao formations. Shaodong Formation and Ceshui Formation mainly consist of clastic rocks and formed in the offshore muddy shelf and shoreline barrier-lagoon envi-ronments respectively. The other four formations mainly consist of carbonate rocks intercatated with the calcareous mudstone and shale, in which Menggongao and Shidengzi formations mainly formed in the offshore shallow carbonate shelf, Liujiatang formation mainly formed in the deep shelf and shelf basic and Zimenqiao formation formed in the peritidal and offshore shallow carbonate shelf environments. Mudstone (including mudstone, silty mudstone, calcareous mudstone and calcareous shale) is one of the major rock types in each formation. X-ray diffraction and SEM analyses show that the clay minerals of Lower Carboniferous mudstones in central Hunan are kaolinites, illites. I / S mixed layer minerals and chlorites, in which kaolinite and illite are the two important minerals. Clay minerals are distributed regularly in the Lower Carboniferous section. The highest and lowest contents of kaolinite occur in Ceshui and Lijiatang formations respectively, and illite shows the reverse trend. I/ S mixed laver mineral is up to the highest content in Menggongao- Shidengzi and Zimenqiao formations. Chlorite is less common and with higher contents in Shaodong formation. Refering to the major lithofacies of each formation, the environmental distribution model can be outlined. From clastic barrier-lagoon to offshore muddy shelf, offshore shallow carbonate shelf, deep shelf and shelf basin, that is from the clastic shoreline to the shelf basin, kaolinites decreases suddenly and the highest content is in the clastic shorline, illites increases gradually and up to the highest content in the shelf basin, I / S mixed layer minerals and chlorite increase firstly and then decrease and their highest contents are in offshore shallow carbonate shelf and offshore muddy shelf respectively. The environmental distributions of clay minerals are mainly controlled by water acidity and salinity of the depositional environment. On the landward, the acid and fresh-brackish water favous the deposition of kaolinite such as in Ceshui formation, and on the basinward, the alkaline and marine water favors the deposition of illite such as in Liujiatang formation. This conclusion also supports the idea that the assemblages of clay mineral can act as the indicator of the paleosalinity. Ceshui formation is the major coal measure of Lower Carboniferous. The vertical distributions of clay minerals show that, from the bottom to the top, the major type of clay minerals changes from illite, kaolinite to illite, which suggests that the depositional environment of Ceshui formation experienced weak alkaline marine water, acid fresh-brackish water to alkaline marine water.
Lower Carboniferous in central Hunan, South China includes Shaodong. Menggongao Liujialang, Shidengzi, Ceshui and Zimenqiao formations. Shaodong Formation and Ceshui Formation mainly consist of clastic rocks and formed in the offshore muddy shelf and shoreline barrier-lagoon envi-ronments respectively. The other four formations mainly consist of carbonate rocks intercatated with the calcareous mudstone and shale, in which Menggongao and Shidengzi formations mainly formed in the offshore shallow carbonate shelf, Liujiatang formation mainly formed in the deep shelf and shelf basic and Zimenqiao formation formed in the peritidal and offshore shallow carbonate shelf environments. Mudstone (including mudstone, silty mudstone, calcareous mudstone and calcareous shale) is one of the major rock types in each formation. X-ray diffraction and SEM analyses show that the clay minerals of Lower Carboniferous mudstones in central Hunan are kaolinites, illites. I / S mixed layer minerals and chlorites, in which kaolinite and illite are the two important minerals. Clay minerals are distributed regularly in the Lower Carboniferous section. The highest and lowest contents of kaolinite occur in Ceshui and Lijiatang formations respectively, and illite shows the reverse trend. I/ S mixed laver mineral is up to the highest content in Menggongao- Shidengzi and Zimenqiao formations. Chlorite is less common and with higher contents in Shaodong formation. Refering to the major lithofacies of each formation, the environmental distribution model can be outlined. From clastic barrier-lagoon to offshore muddy shelf, offshore shallow carbonate shelf, deep shelf and shelf basin, that is from the clastic shoreline to the shelf basin, kaolinites decreases suddenly and the highest content is in the clastic shorline, illites increases gradually and up to the highest content in the shelf basin, I / S mixed layer minerals and chlorite increase firstly and then decrease and their highest contents are in offshore shallow carbonate shelf and offshore muddy shelf respectively. The environmental distributions of clay minerals are mainly controlled by water acidity and salinity of the depositional environment. On the landward, the acid and fresh-brackish water favous the deposition of kaolinite such as in Ceshui formation, and on the basinward, the alkaline and marine water favors the deposition of illite such as in Liujiatang formation. This conclusion also supports the idea that the assemblages of clay mineral can act as the indicator of the paleosalinity. Ceshui formation is the major coal measure of Lower Carboniferous. The vertical distributions of clay minerals show that, from the bottom to the top, the major type of clay minerals changes from illite, kaolinite to illite, which suggests that the depositional environment of Ceshui formation experienced weak alkaline marine water, acid fresh-brackish water to alkaline marine water.
1992, 10(4): 101-110.
Abstract:
Liaocheng coal field situates in the northwestern margin of western Shandong uplift, is an unit of Carboniferous-Permian coal-bearing basin of Northern China. Taiyuan Formation, one of the main coal-bearing stratum, composed of sandstone, siltstone, mudstone, limestone and coal seams, can be divided into five complete sedimentary cycles, and 6 coal seams were found in the formation, they are the fifth to the tenth coal seams, among them, the ninth and the tenth are main workable ones. Conventional geophisical logging have been made of all the boreholes, the logs obtained mainly are apparant resistivity, spontaneous potential, natural gamma-ray logging and so on. For the research of sedimentary environment, apparent resistivity and natural gamma-ray log were used as principles. Based on the study of sedimentology and well logging, the authors discussed the sedimentary characicrs and geophisic feature, then divide the log into five facies (expresed as A, B, C, D and E), and concluded that the sedimentary environment of Taiyuan Formation was tranzitional, including barrier island, lagon, tidal flat, subtidal zone and peat swamp etc. The nineth and tenth coal seams were the products of swamping lagoon. A ccording to the study of sedimentary envirenment, the authors discussed the accumulative characteristics of the nineth and tenth coal seams and quatitatiely pridicted their thickness, and then a gray mathematical model GM (1, 1) was established to quantitatively pridict thickness of the two coal seams. The results of qualitative and quantitative pridict are bascally coincident.
Liaocheng coal field situates in the northwestern margin of western Shandong uplift, is an unit of Carboniferous-Permian coal-bearing basin of Northern China. Taiyuan Formation, one of the main coal-bearing stratum, composed of sandstone, siltstone, mudstone, limestone and coal seams, can be divided into five complete sedimentary cycles, and 6 coal seams were found in the formation, they are the fifth to the tenth coal seams, among them, the ninth and the tenth are main workable ones. Conventional geophisical logging have been made of all the boreholes, the logs obtained mainly are apparant resistivity, spontaneous potential, natural gamma-ray logging and so on. For the research of sedimentary environment, apparent resistivity and natural gamma-ray log were used as principles. Based on the study of sedimentology and well logging, the authors discussed the sedimentary characicrs and geophisic feature, then divide the log into five facies (expresed as A, B, C, D and E), and concluded that the sedimentary environment of Taiyuan Formation was tranzitional, including barrier island, lagon, tidal flat, subtidal zone and peat swamp etc. The nineth and tenth coal seams were the products of swamping lagoon. A ccording to the study of sedimentary envirenment, the authors discussed the accumulative characteristics of the nineth and tenth coal seams and quatitatiely pridicted their thickness, and then a gray mathematical model GM (1, 1) was established to quantitatively pridict thickness of the two coal seams. The results of qualitative and quantitative pridict are bascally coincident.
1992, 10(4): 119-128.
Abstract:
Two different scale dipositional micro-and small sequences are distinguished to de essential componentsof the sequences of low-energy coast. Micro-sequences, with the thickness of mm scale, are mainly formedby tidevs, and can be distinguished as mud laminae and sand laminae. Small sequences are composed ofmicro--sequences and are generally several to 20cm thick. According to the relative ratio of mud and sandlaminaes inside, the small sequences can also be classified as fine (muddy) small-sequences and coarse(sandy) ones which are belived to be formed under fair weather and storm weather respectively, and can alsobe regarded as normal and event sequences respectively. Grain size and sand contents in both normal andevent layers increase from low tidal level both seaward (downward) to subtidal zone and upward (landward)to upper intertidal flat. Near the lower water level the sand contents in the normal layers can be higher thenthat of the event layers in the upper tidal flat, and the sands are also coarser. The differences in sand contentsand the. grain size between adjacent normal and event deposites are obvious. The seaward charges from thelower tidal flat to the wave base are similar to the landward changes that occured from the lower tidal flat tothe uwner tidal flat Comparision among the presen，subrecent and aneclent sectiuns in many areas demonstrated that the ba-sic sequences of the low-wergy coast of China is a sequence shat fines from lower tidal flat both upward tothe upper tidal deposits and downward to the wave base deposits. In the tidal flat where the tidal channels aredeveloped the tidal sequence fines only upward with a ubvions erosional surface at the bottom and withunderlying mud deposits, which is similar to the classic sequence described by Klein(1977).In the areaswhere river mouth sand bars and tidal sand ridges ace developed, thc; sequence also fines only upwards butwith underlying sand deposits. Adjacent coastal rocky hills or man-made dams can make the slope of the up-per tidlal Rat or supertidal steepen, which subsequently cause the sedunents coarser at the top of the low-en-ergy coast sequence. Shell layers can someUmes be found in the coarsened upper tidal deposits. Such sequencehad been detected in the Yangtae Delta and the Paleozoic tidal deposits in western Zhejiang Province.
Two different scale dipositional micro-and small sequences are distinguished to de essential componentsof the sequences of low-energy coast. Micro-sequences, with the thickness of mm scale, are mainly formedby tidevs, and can be distinguished as mud laminae and sand laminae. Small sequences are composed ofmicro--sequences and are generally several to 20cm thick. According to the relative ratio of mud and sandlaminaes inside, the small sequences can also be classified as fine (muddy) small-sequences and coarse(sandy) ones which are belived to be formed under fair weather and storm weather respectively, and can alsobe regarded as normal and event sequences respectively. Grain size and sand contents in both normal andevent layers increase from low tidal level both seaward (downward) to subtidal zone and upward (landward)to upper intertidal flat. Near the lower water level the sand contents in the normal layers can be higher thenthat of the event layers in the upper tidal flat, and the sands are also coarser. The differences in sand contentsand the. grain size between adjacent normal and event deposites are obvious. The seaward charges from thelower tidal flat to the wave base are similar to the landward changes that occured from the lower tidal flat tothe uwner tidal flat Comparision among the presen，subrecent and aneclent sectiuns in many areas demonstrated that the ba-sic sequences of the low-wergy coast of China is a sequence shat fines from lower tidal flat both upward tothe upper tidal deposits and downward to the wave base deposits. In the tidal flat where the tidal channels aredeveloped the tidal sequence fines only upward with a ubvions erosional surface at the bottom and withunderlying mud deposits, which is similar to the classic sequence described by Klein(1977).In the areaswhere river mouth sand bars and tidal sand ridges ace developed, thc; sequence also fines only upwards butwith underlying sand deposits. Adjacent coastal rocky hills or man-made dams can make the slope of the up-per tidlal Rat or supertidal steepen, which subsequently cause the sedunents coarser at the top of the low-en-ergy coast sequence. Shell layers can someUmes be found in the coarsened upper tidal deposits. Such sequencehad been detected in the Yangtae Delta and the Paleozoic tidal deposits in western Zhejiang Province.
1992, 10(4): 137-145.
Abstract:
The Loyalty Basin, northeast of new Caledonia, is about 100km wide and 2350m deep in the transect between Thio (New Caledonia) and the island of Lifou. It is bounded to the southwest by New Caledonia and its surrounding barrier reef and to the northeast by the barrier reef of the Loyalty Ridge. Lifou Island, a raised atoll, is an emerged part of the Loyalty Ridge. The sediments cored in the Loyalty Basin during the BIOCAL mission is 1985 are bioturbated and composed of an alternation of turbidites and hemipelagites. The hemipelagites are brownyellowish muddy oozes to calcareous muds; the turbidites are composed of sandy and silty oozes capped transitionally with muddy oozes. The hemipelagite and the Te division of the Bouma sequence have different characteristics but are not located in the core. However, they can be distinguished by carbonate composition and grain size. All the sediments originate from five sources: (1) New Caledonia (quartz, clay and heavy minerals), (2) the barrier reef (fragments of algae, madreporarian corals, foraminifera and mud of the periplatform, (3) plankton (foraminifera, coccoliths and pteropoda), (4) the bathyal community and (5) pyroclastic fragments. Turbidites, distributed in cores between Thio and Lifou, constitute a low-profile submarine fan fed by the main canyons of the slope opposite the Thio Pass. The fan developed from a rim of slumps and mud flows located near the base of the slope. The fan extends 50km toward the northeast as far as the tectonic Levi Ridge. The hemipelagites are predominant beyond this ridge.
The Loyalty Basin, northeast of new Caledonia, is about 100km wide and 2350m deep in the transect between Thio (New Caledonia) and the island of Lifou. It is bounded to the southwest by New Caledonia and its surrounding barrier reef and to the northeast by the barrier reef of the Loyalty Ridge. Lifou Island, a raised atoll, is an emerged part of the Loyalty Ridge. The sediments cored in the Loyalty Basin during the BIOCAL mission is 1985 are bioturbated and composed of an alternation of turbidites and hemipelagites. The hemipelagites are brownyellowish muddy oozes to calcareous muds; the turbidites are composed of sandy and silty oozes capped transitionally with muddy oozes. The hemipelagite and the Te division of the Bouma sequence have different characteristics but are not located in the core. However, they can be distinguished by carbonate composition and grain size. All the sediments originate from five sources: (1) New Caledonia (quartz, clay and heavy minerals), (2) the barrier reef (fragments of algae, madreporarian corals, foraminifera and mud of the periplatform, (3) plankton (foraminifera, coccoliths and pteropoda), (4) the bathyal community and (5) pyroclastic fragments. Turbidites, distributed in cores between Thio and Lifou, constitute a low-profile submarine fan fed by the main canyons of the slope opposite the Thio Pass. The fan developed from a rim of slumps and mud flows located near the base of the slope. The fan extends 50km toward the northeast as far as the tectonic Levi Ridge. The hemipelagites are predominant beyond this ridge.
