In the transitional period between the Middle and the Late Triassic, the Indochina orogeny caused two tectonic events in South China：（1） the formation and uplift of the Qinling-Dabie orogenic belt along the norther...In the transitional period between the Middle and the Late Triassic, the Indochina orogeny caused two tectonic events in South China：（1） the formation and uplift of the Qinling-Dabie orogenic belt along the northern margin of the South China Plate, due to its collision with the North China Plate; and 2） the development of a 1300-km-wide intra-continental orogen in the southeastern part of the South China Plate, which led to a northwestward movement of the foreland thrust-fold zone. These tectonic events resulted in the ending of the Yangtze Platform, and were a stable paleogeographic factor from the Eidacaran to the end of the Middle Triassic. This platform was characterized by the widespread development of shallow-water carbonates. After the end of the Yangtze Platform, the upper Yangtze foreland basin（or Sichuan foreland basin） was formed during the Late Triassic and became a accumulation site of fluvial deposits that are composed of related strata of the Xujiahe Formation. In western Sichuan Province, the Xujiahe Formation overlies the Maantang Formation shallow-water carbonate rocks of the Xiaotangzi Formation siliciclastic rocks（from shelf shales to littoral facies）. The sequence-stratigraphic framework of the Upper Triassic in the upper Yangtze foreland basin indicates a particular alluvial architecture, characterized by sequences composed of（1） successions of low-energy fluvial deposits of high-accommodation phases, including coal seams, and（2） high-energy fluvial deposits of low-accommodation phases, including amalgamated river-channel sandstones. The spatial distribution of these fluvial deposits belonging to the Xujiahe Formation and its relative strata is characterized by gradual thinning-out, overlapping, and pinching-out toward both the east and south. This sedimentary record therefore expresses a particular sequence-stratigraphic succession of fluvial deposits within the filling succession of the foreland basin. The sequence-stratigraphic framework for the Upper Triassic in the Upper Yangtze region provides a record of the end of the Yangtze Platform and the formation of the upper Yangtze foreland basin.展开更多
The formation process of the Dianqiangui basin, a special basin, occurred after the Caledonian orogeny, in the south of Guizhou, the west of Guangxi and the southeast of Yunnan, experienced three periods: it began ...The formation process of the Dianqiangui basin, a special basin, occurred after the Caledonian orogeny, in the south of Guizhou, the west of Guangxi and the southeast of Yunnan, experienced three periods: it began in the Devonian, persisted in the Carboniferous, and became fiercer in the Permian. Controlled by syndepositional fault-zones, varieties of isolated carbonate platforms, large and small, were developed in the background of a deep-water basin, namely, an inter-platform ditch. And a special paleogeographical Late Paleozoic pattern marked by “platform-basin-hill-trough” was produced in both the Dianqiangui basin and its adjacent areas. Affected by regional tectonic activities and the global changes in the sea level, the platform carbonates and coal measures superimposed each other cyclically on the attached platform. The reef-building on the isolated platform and the margin of the attached platform corresponds to the development of the shale succession in the deep-water basin. All of these elementary characteristics reflect a regular and sophisticated filling succession of the Dianqiangui basin, a result of the dual controls of the regionally tectonic activities and the eustacy. Based on the two elementary features of the third-order sequences, i.e. the regularity of sedimentary-facies succession in space and the simultaneity of environmental changes in time, 25 third-order sequences could be discerned in the Upper Paleozoic strata in the Dianqiangui basin and its adjacent areas. On the basis of the two kinds of facies-changing surfaces and the two kinds of diachronisms in stratigraphic records, the regional Late Paleozoic sequence-stratigraphic framework in the Dianqiangui basin and its adjacent areas can be established. There are two types of facies-changing surfaces and two types of diachronisms in stratigraphic records: the static type, a result of the change in sedimentary facies in space, and the dynamic type, a result of the change in time. These two types of facies-changing surfaces led to the generation of the two types of diachronisms: the diachronism of facies-changing surfaces that was formed by the static facies-changing surfaces, and the diachronism of punctuated surfaces that was formed by the dynamic facies-changing surfaces. The two types of facies-changing surfaces and the two types of diachronisms in stratigraphic records are the key to the establishment of the sequence-stratigraphic framework. The sequence boundaries could be divided geologically into four types: tectonic unconformity, sedimentary unconformity, drowned unconformity and their correlative surfaces. All of these four types can be further grouped into exposed punctuated surfaces and deepened punctuated surfaces. The tectonic unconformity is similar to Type Ⅰ sequence boundary, and the sedimentary unconformity is similar to Type Ⅱ sequence boundary defined by Vail et al.. In terms of sequence stratigraphy, the tectonic unconformities of the Ziyun movement, the Qiangui epeirogeny and the Dongwu revolution as well as the drowned unconformity in the transitional period from the Permian to the Triassic can be systematically defined and their geological characteristics are briefly presented.展开更多
基金funded by the Natural Sciences Foundation of China (grant No.41030318)
文摘In the transitional period between the Middle and the Late Triassic, the Indochina orogeny caused two tectonic events in South China：（1） the formation and uplift of the Qinling-Dabie orogenic belt along the northern margin of the South China Plate, due to its collision with the North China Plate; and 2） the development of a 1300-km-wide intra-continental orogen in the southeastern part of the South China Plate, which led to a northwestward movement of the foreland thrust-fold zone. These tectonic events resulted in the ending of the Yangtze Platform, and were a stable paleogeographic factor from the Eidacaran to the end of the Middle Triassic. This platform was characterized by the widespread development of shallow-water carbonates. After the end of the Yangtze Platform, the upper Yangtze foreland basin（or Sichuan foreland basin） was formed during the Late Triassic and became a accumulation site of fluvial deposits that are composed of related strata of the Xujiahe Formation. In western Sichuan Province, the Xujiahe Formation overlies the Maantang Formation shallow-water carbonate rocks of the Xiaotangzi Formation siliciclastic rocks（from shelf shales to littoral facies）. The sequence-stratigraphic framework of the Upper Triassic in the upper Yangtze foreland basin indicates a particular alluvial architecture, characterized by sequences composed of（1） successions of low-energy fluvial deposits of high-accommodation phases, including coal seams, and（2） high-energy fluvial deposits of low-accommodation phases, including amalgamated river-channel sandstones. The spatial distribution of these fluvial deposits belonging to the Xujiahe Formation and its relative strata is characterized by gradual thinning-out, overlapping, and pinching-out toward both the east and south. This sedimentary record therefore expresses a particular sequence-stratigraphic succession of fluvial deposits within the filling succession of the foreland basin. The sequence-stratigraphic framework for the Upper Triassic in the Upper Yangtze region provides a record of the end of the Yangtze Platform and the formation of the upper Yangtze foreland basin.
文摘The formation process of the Dianqiangui basin, a special basin, occurred after the Caledonian orogeny, in the south of Guizhou, the west of Guangxi and the southeast of Yunnan, experienced three periods: it began in the Devonian, persisted in the Carboniferous, and became fiercer in the Permian. Controlled by syndepositional fault-zones, varieties of isolated carbonate platforms, large and small, were developed in the background of a deep-water basin, namely, an inter-platform ditch. And a special paleogeographical Late Paleozoic pattern marked by “platform-basin-hill-trough” was produced in both the Dianqiangui basin and its adjacent areas. Affected by regional tectonic activities and the global changes in the sea level, the platform carbonates and coal measures superimposed each other cyclically on the attached platform. The reef-building on the isolated platform and the margin of the attached platform corresponds to the development of the shale succession in the deep-water basin. All of these elementary characteristics reflect a regular and sophisticated filling succession of the Dianqiangui basin, a result of the dual controls of the regionally tectonic activities and the eustacy. Based on the two elementary features of the third-order sequences, i.e. the regularity of sedimentary-facies succession in space and the simultaneity of environmental changes in time, 25 third-order sequences could be discerned in the Upper Paleozoic strata in the Dianqiangui basin and its adjacent areas. On the basis of the two kinds of facies-changing surfaces and the two kinds of diachronisms in stratigraphic records, the regional Late Paleozoic sequence-stratigraphic framework in the Dianqiangui basin and its adjacent areas can be established. There are two types of facies-changing surfaces and two types of diachronisms in stratigraphic records: the static type, a result of the change in sedimentary facies in space, and the dynamic type, a result of the change in time. These two types of facies-changing surfaces led to the generation of the two types of diachronisms: the diachronism of facies-changing surfaces that was formed by the static facies-changing surfaces, and the diachronism of punctuated surfaces that was formed by the dynamic facies-changing surfaces. The two types of facies-changing surfaces and the two types of diachronisms in stratigraphic records are the key to the establishment of the sequence-stratigraphic framework. The sequence boundaries could be divided geologically into four types: tectonic unconformity, sedimentary unconformity, drowned unconformity and their correlative surfaces. All of these four types can be further grouped into exposed punctuated surfaces and deepened punctuated surfaces. The tectonic unconformity is similar to Type Ⅰ sequence boundary, and the sedimentary unconformity is similar to Type Ⅱ sequence boundary defined by Vail et al.. In terms of sequence stratigraphy, the tectonic unconformities of the Ziyun movement, the Qiangui epeirogeny and the Dongwu revolution as well as the drowned unconformity in the transitional period from the Permian to the Triassic can be systematically defined and their geological characteristics are briefly presented.
