Fossil evidence indicates that mangrove species have had their first appearance in the Late Cretaceous(70 65 Ma) and they have evolved around the Tethys seaway after the plate tectonics and the movement of the contine...Fossil evidence indicates that mangrove species have had their first appearance in the Late Cretaceous(70 65 Ma) and they have evolved around the Tethys seaway after the plate tectonics and the movement of the continents when Tethys Sea was fast closing as the massive continental fragments continued to shift and jostle across the globe. The oldest geological record of Acrostichum and Nypa palm offers good examples as these species prefer low-salinity requirements and have wide ecological tolerance. Such environmental and habitat preferences must have been the probable reason for their initial adaptation to mangrove habitat and a wider distribution. The open sea link must have also provided enough coastal areas for the establishment of mangrove ecosystem and subsequent spreading of the mangroves into newer areas by Early to Middle Eocene(ca 50–40 Ma). However, the mangroves started acquiring the present geographical positions towards OligoceneMiddle Miocene period. The fossil record and the modern analogues of Kandelia, Nypa and Pelliciera indicate that their biogeographical preferences have been shifted due to oceanic reorganization wherein the latter is now confined only to Atlantic East Pacific mangrove realm despite it was earlier widespread in the Tethys Sea. Although Rhizophora and Avicennia differ only at the species level and common occurrence of Acrostichum aureum, the present mangrove distribution shows the contrast in the biogeography of many genera due to geomorphic barriers and climatic changes. The Himalayan uplift and establishment of Asian summer monsoon system towards Late Neogene has also affected the coastal dynamics considerably which in turn modified the distribution of mangrove vegetation of the Indian subcontinent. The loss of sensitive habitats, disjunct distribution of a few species and local extinction of significant taxa has affected the overall biogeography of mangroves in South and SE Asia.展开更多
The Lhasa-Gangdise Terrane is taken as a representative mobile terrane during the Himalayan orogeny of the India- Eurasia continental collision, for which a corresponding kinematics-uplift model is set up. The paramet...The Lhasa-Gangdise Terrane is taken as a representative mobile terrane during the Himalayan orogeny of the India- Eurasia continental collision, for which a corresponding kinematics-uplift model is set up. The parameterization of the model is ultimately constrained by the uplift history outlined by synthesized paleogeoglaphic studies with consideration of the following factors: (1 ) kinematic features of india-Eurasia plate convergence; (2) 3-D mass conservation during terrane deformations incorporating shortening, thickening, extension, uplift and ero sion; and (3) instantaneous vertical movement of lithospheric material under the control of isostasy. The model study involves the following four groups of uplift-relevant parameters: ① plate converging velocity and its variations with time; ② extent of lateral mass transfer; ③ crustal structure: and ④) surface erosion mode. The results of calculation of 144 models of different Parameter combinations have indicated the non-uniqueness of solution. Nevertheless, it is also proved that for a fixed kinematic mode of plate convergence there exists a unique best-fitting model which may reproduce the observed uplift history, implying the uniqueness of dynamic environment of two converging plates. Therefore, the uplift of the Himalayan-Tibetan region is mainly controlled by plate dynamics-kinematics and is a complicated geological process of far-reaching implications.展开更多
The western boundary of the Eastern Himalayan Syntaxis (EHS) is a deformation belt up to 30km wide (Fig.1). Trending ca. N35°E, it separates the Gangdise magmatic belt in the west from the gneiss of EHS in the ea...The western boundary of the Eastern Himalayan Syntaxis (EHS) is a deformation belt up to 30km wide (Fig.1). Trending ca. N35°E, it separates the Gangdise magmatic belt in the west from the gneiss of EHS in the east. Its rock association, mica\|schist, quartzite, marble, and amphibolite, can be traced to the south to Gangdise belt and they were probably metamorphosed from the sediments along Yarlung Zangbo. This belt consists of several intensive deformation zones, the largest one of which is along the belt’s western margin from Dongjug to Mainling and we called this ca. 10km wide shear zone as the Dongjug\|Mainling shear zone (DMSZ).DMSZ experienced earlier ductile shear and later ductile\|brittle normal faulting. The earlier deformation produced mylonitic rocks. Their foliation trends N30°～40°E and dips northwest with the angle ranging from 55°to 80°, steepening northeastward. The penetrative kinematic lineation in the rocks has a varying attitude along the trend of DMSZ. It dips southwest with an angle of ca.35° in the southwest near Mainling, whereas dips northeast in the northeast. Moreover, the northeast dipping lineation steepens northeastwards, e.g., its angle ranges form 30° to 45° in the segment from Serkyim La to Dongjug but becomes 60～70° in the northeast most in another zone near Parlung. Kinematic indicators show that the motion of DMSZ had a left\|lateral slipping component, but the vertical motion components were different in the southwest from the northeast. From Serkyim La to the northeast, DMSZ had a kinematics of NW plate (Gangdise belt) thrusting over the SE plate (EHS) and its thrusting component increased toward northeast. However, the DMSZ has a vertical motion with the SE plate (EHS) as the uplifting plate.展开更多
This paper discusses the tectonic divisions of the Himalayan collision belt anddeals with the tectonic evolution of the collision belt in the context of crustal accretion in thefront of the collision belt, deep diapir...This paper discusses the tectonic divisions of the Himalayan collision belt anddeals with the tectonic evolution of the collision belt in the context of crustal accretion in thefront of the collision belt, deep diapirism and thermal-uplift extension and deep material flow-ing of the lithosphere-backflowing. Finally it proposes a model of the tectonic evolution-progressive intracontinental deformation model-of the Himalayan belt.展开更多
The Late Quaternary thick sedimentary fills of the Ganga basin predominantly consist of unconsolidated fluvial sandy deposits which are often intercalated with mud. These deposits at various places record the evidence...The Late Quaternary thick sedimentary fills of the Ganga basin predominantly consist of unconsolidated fluvial sandy deposits which are often intercalated with mud. These deposits at various places record the evidence of earthquakes, which occurred in the recent geological past. The evidence is contained and manifested in the form of Soft Sediment Deformation Structures (SSDSs). Saturated sediments/muds/soils are liquefied by earthquake tremors which either generate SSDS or produce structural discordance in the pre-existing sedimentary structures. The present study reports the occurrence of SSDS, e.g. load and associated flame structures, clastic dikes and sill structures, slump structures and sedimentary breccias, etc. from the Ganga River and adjacent oxbow lake sediment deposits. An attempt has been made to establish the origin of soft sediment structures of this region in accordance with its neotectonic history and in turn, identification of seismic structural proxies to delineate paleoseismic events in this region with futuristic implications. The preservation of soft sediment deformation structures in large numbers with multiple geomorphology and scale, in the river and adjoining lake sediments, is indicative of frequent earthquakes of high magnitude consequent to tectonic activism in the Himalayan region.展开更多
Much geological research has illustrated the transition of paleoenvironmental patterns during the Cenozoic from a planetary-wind-dominant type to a monsoon-dominant type, indicating the initiation of the East Asian mo...Much geological research has illustrated the transition of paleoenvironmental patterns during the Cenozoic from a planetary-wind-dominant type to a monsoon-dominant type, indicating the initiation of the East Asian monsoon and inland-type aridity. However, there is a dispute about the causes and mechanisms of the transition, especially about the impact of the Himalayan/Tibetan Plateau uplift and the Paratethys Sea retreat, Thirty numerical sensitivity experiments under different land-sea distributions and Himalayan/Tibetan Plateau topography conditions are performed here to simulate the evolution of climate belts with emphasis on changes in the rain band, and these are compared with the changes in the paleoenvironmental patterns during the Cenozoic recovered by geological records. The consistency between simulations and the geological evidence indicates that both the Tibetan Plateau uplift and the Paratethys Sea retreat play important roles in the formation of the monsoon-dominant environmental pattern. Furthermore, the simulations show the monsoon-dominant environmental pattern comes into being when the Himalayan/Tibetan Plateau reaches 1000-2000 m high and the Paratethys Sea retreats to the Turan Plate.展开更多
文摘Fossil evidence indicates that mangrove species have had their first appearance in the Late Cretaceous(70 65 Ma) and they have evolved around the Tethys seaway after the plate tectonics and the movement of the continents when Tethys Sea was fast closing as the massive continental fragments continued to shift and jostle across the globe. The oldest geological record of Acrostichum and Nypa palm offers good examples as these species prefer low-salinity requirements and have wide ecological tolerance. Such environmental and habitat preferences must have been the probable reason for their initial adaptation to mangrove habitat and a wider distribution. The open sea link must have also provided enough coastal areas for the establishment of mangrove ecosystem and subsequent spreading of the mangroves into newer areas by Early to Middle Eocene(ca 50–40 Ma). However, the mangroves started acquiring the present geographical positions towards OligoceneMiddle Miocene period. The fossil record and the modern analogues of Kandelia, Nypa and Pelliciera indicate that their biogeographical preferences have been shifted due to oceanic reorganization wherein the latter is now confined only to Atlantic East Pacific mangrove realm despite it was earlier widespread in the Tethys Sea. Although Rhizophora and Avicennia differ only at the species level and common occurrence of Acrostichum aureum, the present mangrove distribution shows the contrast in the biogeography of many genera due to geomorphic barriers and climatic changes. The Himalayan uplift and establishment of Asian summer monsoon system towards Late Neogene has also affected the coastal dynamics considerably which in turn modified the distribution of mangrove vegetation of the Indian subcontinent. The loss of sensitive habitats, disjunct distribution of a few species and local extinction of significant taxa has affected the overall biogeography of mangroves in South and SE Asia.
文摘The Lhasa-Gangdise Terrane is taken as a representative mobile terrane during the Himalayan orogeny of the India- Eurasia continental collision, for which a corresponding kinematics-uplift model is set up. The parameterization of the model is ultimately constrained by the uplift history outlined by synthesized paleogeoglaphic studies with consideration of the following factors: (1 ) kinematic features of india-Eurasia plate convergence; (2) 3-D mass conservation during terrane deformations incorporating shortening, thickening, extension, uplift and ero sion; and (3) instantaneous vertical movement of lithospheric material under the control of isostasy. The model study involves the following four groups of uplift-relevant parameters: ① plate converging velocity and its variations with time; ② extent of lateral mass transfer; ③ crustal structure: and ④) surface erosion mode. The results of calculation of 144 models of different Parameter combinations have indicated the non-uniqueness of solution. Nevertheless, it is also proved that for a fixed kinematic mode of plate convergence there exists a unique best-fitting model which may reproduce the observed uplift history, implying the uniqueness of dynamic environment of two converging plates. Therefore, the uplift of the Himalayan-Tibetan region is mainly controlled by plate dynamics-kinematics and is a complicated geological process of far-reaching implications.
文摘The western boundary of the Eastern Himalayan Syntaxis (EHS) is a deformation belt up to 30km wide (Fig.1). Trending ca. N35°E, it separates the Gangdise magmatic belt in the west from the gneiss of EHS in the east. Its rock association, mica\|schist, quartzite, marble, and amphibolite, can be traced to the south to Gangdise belt and they were probably metamorphosed from the sediments along Yarlung Zangbo. This belt consists of several intensive deformation zones, the largest one of which is along the belt’s western margin from Dongjug to Mainling and we called this ca. 10km wide shear zone as the Dongjug\|Mainling shear zone (DMSZ).DMSZ experienced earlier ductile shear and later ductile\|brittle normal faulting. The earlier deformation produced mylonitic rocks. Their foliation trends N30°～40°E and dips northwest with the angle ranging from 55°to 80°, steepening northeastward. The penetrative kinematic lineation in the rocks has a varying attitude along the trend of DMSZ. It dips southwest with an angle of ca.35° in the southwest near Mainling, whereas dips northeast in the northeast. Moreover, the northeast dipping lineation steepens northeastwards, e.g., its angle ranges form 30° to 45° in the segment from Serkyim La to Dongjug but becomes 60～70° in the northeast most in another zone near Parlung. Kinematic indicators show that the motion of DMSZ had a left\|lateral slipping component, but the vertical motion components were different in the southwest from the northeast. From Serkyim La to the northeast, DMSZ had a kinematics of NW plate (Gangdise belt) thrusting over the SE plate (EHS) and its thrusting component increased toward northeast. However, the DMSZ has a vertical motion with the SE plate (EHS) as the uplifting plate.
基金This study was a part of the Project Research on Deformation Dynamics on the North Margin of the Qinghai-Tibet Plateau(No,86-06-207)- a key Project of deep geology of the Ministry of Geology and Mineral Resources in the Eighth Five-Year Plan period(1991
文摘This paper discusses the tectonic divisions of the Himalayan collision belt anddeals with the tectonic evolution of the collision belt in the context of crustal accretion in thefront of the collision belt, deep diapirism and thermal-uplift extension and deep material flow-ing of the lithosphere-backflowing. Finally it proposes a model of the tectonic evolution-progressive intracontinental deformation model-of the Himalayan belt.
文摘The Late Quaternary thick sedimentary fills of the Ganga basin predominantly consist of unconsolidated fluvial sandy deposits which are often intercalated with mud. These deposits at various places record the evidence of earthquakes, which occurred in the recent geological past. The evidence is contained and manifested in the form of Soft Sediment Deformation Structures (SSDSs). Saturated sediments/muds/soils are liquefied by earthquake tremors which either generate SSDS or produce structural discordance in the pre-existing sedimentary structures. The present study reports the occurrence of SSDS, e.g. load and associated flame structures, clastic dikes and sill structures, slump structures and sedimentary breccias, etc. from the Ganga River and adjacent oxbow lake sediment deposits. An attempt has been made to establish the origin of soft sediment structures of this region in accordance with its neotectonic history and in turn, identification of seismic structural proxies to delineate paleoseismic events in this region with futuristic implications. The preservation of soft sediment deformation structures in large numbers with multiple geomorphology and scale, in the river and adjoining lake sediments, is indicative of frequent earthquakes of high magnitude consequent to tectonic activism in the Himalayan region.
基金This study was supported by the National Natural Science Foundation of China(Grant Nos.40125014 and 40231001)the Key Program of the Chinese Academy of Sciences KZCX3-SW-139.
文摘Much geological research has illustrated the transition of paleoenvironmental patterns during the Cenozoic from a planetary-wind-dominant type to a monsoon-dominant type, indicating the initiation of the East Asian monsoon and inland-type aridity. However, there is a dispute about the causes and mechanisms of the transition, especially about the impact of the Himalayan/Tibetan Plateau uplift and the Paratethys Sea retreat, Thirty numerical sensitivity experiments under different land-sea distributions and Himalayan/Tibetan Plateau topography conditions are performed here to simulate the evolution of climate belts with emphasis on changes in the rain band, and these are compared with the changes in the paleoenvironmental patterns during the Cenozoic recovered by geological records. The consistency between simulations and the geological evidence indicates that both the Tibetan Plateau uplift and the Paratethys Sea retreat play important roles in the formation of the monsoon-dominant environmental pattern. Furthermore, the simulations show the monsoon-dominant environmental pattern comes into being when the Himalayan/Tibetan Plateau reaches 1000-2000 m high and the Paratethys Sea retreats to the Turan Plate.
