Marine red beds occur frequently in China through geological time.Despite their complex environments,the red beds are found in three depositional settings:1) oceanic,deep water,as in the Upper Cretaceous of southern T...Marine red beds occur frequently in China through geological time.Despite their complex environments,the red beds are found in three depositional settings:1) oceanic,deep water,as in the Upper Cretaceous of southern Tibet;2) outer shelf,deeper water,as in the Lower-Middle Ordovician of South China;and 3) inner shelf,shallow water,as in the Silurian and Triassic in South China.The Silurian marine red beds are recurrent in the lower Telychian,upper Telychian,and upper Ludlow.This paper is to document the marine nature of the lower Telychian red beds (LRBs) in the Upper Yangtze Region and to discuss the spatial and temporal distribution of the LRBs and their depositional environments.The LRBs are best developed on the north side of the Cathaysian Oldland,which can be interpreted as the source area.It is inferred that they were deposited during a marine regression,characterized by the lack of upwelling,low nutrition and organic productivity with a decrease of biodiversity and a high rate of sedimentation.The iron-rich sediments may have been transported by rivers on the oldland into the Upper Yangtze Sea,as rates of deposition were rapid enough to counteract normal reducing effect around sediment-water interface.The LRBs are different from the off-shore,deeper water red beds of lower Telychian in Avalonia and Baltica and further from the oceanic,deep water red beds of Upper Cretaceous in southern Tibet chiefly in palaeogeographic settings,biotic assemblages and marine environments.展开更多
Paleomagnetic and rock magnetic studies on samples of 18 sites from the Creta- ceous marine sedimentary rocks in the Tongyouluke section, Akto County, southwest Tarim, China show that the magnetic carriers of the Lowe...Paleomagnetic and rock magnetic studies on samples of 18 sites from the Creta- ceous marine sedimentary rocks in the Tongyouluke section, Akto County, southwest Tarim, China show that the magnetic carriers of the Lower Cretaceous are dominated by hematite with some magnetite, while the magnetic carriers of the Upper Cretaceous are characterized by a combination of magnetite and titanomagnetite as well as hematite and goethite. Stepwise thermal demagnetization is performed and vector analysis is used to isolate magnetic components, which illustrates a single magnetic component or double magnetic components. The high temperature stable components are dual polarities and pass polarity test, reversal test and consistency test. The overall mean direction of the Lower Cretaceous is D = 27.0°, I = 42.0°, α95=6.5° with pole position at φ = 190.3°, λ=63.1°, dp=4.9°, dm=8.0°. The overall mean direction of the Upper Cretaceous is D = 29.1°, I = 39.4°, α95=11.2° with pole position at φ =190.9°, λ=60.3°, dp= 8.0°, dm=13.4°. Compared with the inclination of the Early Cretaceous from red beds of north Tarim, the contemporary inclination of southwest Tarim is 10.0°±7.8° sharper, but it is still 8.1° ±8.9°, shallower than that of Early Cretaceous basalts in southwest Tarim. Although these pa- leomagnetic data show slightly larger confidence limit, the paleolatitude of the marine Cretaceous tends to lie between that of terrestrial red beds and volcanic rocks.展开更多
Silurian is a period with the shortest duration in Phanerozoic except for the Neogene and Quaternary. It represents an important and unique interval when the biotic diversity recovered quickly after the end-Ordovician...Silurian is a period with the shortest duration in Phanerozoic except for the Neogene and Quaternary. It represents an important and unique interval when the biotic diversity recovered quickly after the end-Ordovician mass extinction, different paleoplates or terranes conjoined, big oceans disappeared or narrowed, climate and sea level changed frequently, global biotic provincialism became weaker, some primitive plants started to occupy the land. Silurian is also the first system of which all the chronostratigraphic stratotypes(i.e. the GSSPs) including four series and seven stages were established by the International Subcommission on Silurian Stratigraphy(ISSS). Nonetheless, during the post-GSSP studies conducted by ISSS in the middle1980 s, some Silurian GSSPs were found to have some congenital defects such as no index fossils available that hinder the high resolution subdivision and correlation on a regional or global scale. In this paper, based on the latest development of Silurian study in China, the progress in biostratigraphy, chronostratigraphy, event stratigraphy(such as facies differentiation, heterochrony of black shales, marine red beds, carbonate rocks and reefs), chemostratigraphy, and tectonic stratigraphy(e.g., widespread of the late Silurian rocks in South China and its tectonic implication) are systematically summarized. Some existing problems and the areas to be focused in future work are also discussed. It is suitable for chronostratigraphic study to concentrate not only on the boundary but also doing multidisciplinary analysis on the biotic, chemical, magnetic, environmental, and chronologic aspects, in order to enhance the reliability and the potential for regional and global correlation of a certain GSSP.Some important achievements are expected in these areas in the Silurian study in China:(1) ecostratigraphy and basin analysis of the Llandovery, and the correlation of integrative stratigraphy with a high resolution;(2) establishment of the Wenlock to Pridoli chronostratigraphic framework;(3) the chemo-and magnetic stratigraphy and the age of some key intervals and horizons;(4)further investigation on paleogeography and plate tectonics; and(5) origin and early evolution of the terrestrial ecosystem. Some new breakthroughs might occur in the restudy on some of those problematic GSSPs of some particular series and stages.展开更多
基金supported by Chinese Academy of Sciences (Grant No. KZCX2-YW-Q05-01)National Basic Research Program of China (Grant No. 2012CB821901)China Geological Survey (Grant No. 1212011120116)
文摘Marine red beds occur frequently in China through geological time.Despite their complex environments,the red beds are found in three depositional settings:1) oceanic,deep water,as in the Upper Cretaceous of southern Tibet;2) outer shelf,deeper water,as in the Lower-Middle Ordovician of South China;and 3) inner shelf,shallow water,as in the Silurian and Triassic in South China.The Silurian marine red beds are recurrent in the lower Telychian,upper Telychian,and upper Ludlow.This paper is to document the marine nature of the lower Telychian red beds (LRBs) in the Upper Yangtze Region and to discuss the spatial and temporal distribution of the LRBs and their depositional environments.The LRBs are best developed on the north side of the Cathaysian Oldland,which can be interpreted as the source area.It is inferred that they were deposited during a marine regression,characterized by the lack of upwelling,low nutrition and organic productivity with a decrease of biodiversity and a high rate of sedimentation.The iron-rich sediments may have been transported by rivers on the oldland into the Upper Yangtze Sea,as rates of deposition were rapid enough to counteract normal reducing effect around sediment-water interface.The LRBs are different from the off-shore,deeper water red beds of lower Telychian in Avalonia and Baltica and further from the oceanic,deep water red beds of Upper Cretaceous in southern Tibet chiefly in palaeogeographic settings,biotic assemblages and marine environments.
基金supported in pat by the National Natural Science Foumdation of hina(Gramt Nos.40274014)Tarim Oil Field Company,PetroChina Compay Limited(Contract No.4130109 008).
文摘Paleomagnetic and rock magnetic studies on samples of 18 sites from the Creta- ceous marine sedimentary rocks in the Tongyouluke section, Akto County, southwest Tarim, China show that the magnetic carriers of the Lower Cretaceous are dominated by hematite with some magnetite, while the magnetic carriers of the Upper Cretaceous are characterized by a combination of magnetite and titanomagnetite as well as hematite and goethite. Stepwise thermal demagnetization is performed and vector analysis is used to isolate magnetic components, which illustrates a single magnetic component or double magnetic components. The high temperature stable components are dual polarities and pass polarity test, reversal test and consistency test. The overall mean direction of the Lower Cretaceous is D = 27.0°, I = 42.0°, α95=6.5° with pole position at φ = 190.3°, λ=63.1°, dp=4.9°, dm=8.0°. The overall mean direction of the Upper Cretaceous is D = 29.1°, I = 39.4°, α95=11.2° with pole position at φ =190.9°, λ=60.3°, dp= 8.0°, dm=13.4°. Compared with the inclination of the Early Cretaceous from red beds of north Tarim, the contemporary inclination of southwest Tarim is 10.0°±7.8° sharper, but it is still 8.1° ±8.9°, shallower than that of Early Cretaceous basalts in southwest Tarim. Although these pa- leomagnetic data show slightly larger confidence limit, the paleolatitude of the marine Cretaceous tends to lie between that of terrestrial red beds and volcanic rocks.
基金supported by the Chinese Academy of Sciences (Grant Nos. XDPB05, XDB26000000)the National Natural Science Foundation of China (Grant Nos. 41530103, 41521061, 41290260)
文摘Silurian is a period with the shortest duration in Phanerozoic except for the Neogene and Quaternary. It represents an important and unique interval when the biotic diversity recovered quickly after the end-Ordovician mass extinction, different paleoplates or terranes conjoined, big oceans disappeared or narrowed, climate and sea level changed frequently, global biotic provincialism became weaker, some primitive plants started to occupy the land. Silurian is also the first system of which all the chronostratigraphic stratotypes(i.e. the GSSPs) including four series and seven stages were established by the International Subcommission on Silurian Stratigraphy(ISSS). Nonetheless, during the post-GSSP studies conducted by ISSS in the middle1980 s, some Silurian GSSPs were found to have some congenital defects such as no index fossils available that hinder the high resolution subdivision and correlation on a regional or global scale. In this paper, based on the latest development of Silurian study in China, the progress in biostratigraphy, chronostratigraphy, event stratigraphy(such as facies differentiation, heterochrony of black shales, marine red beds, carbonate rocks and reefs), chemostratigraphy, and tectonic stratigraphy(e.g., widespread of the late Silurian rocks in South China and its tectonic implication) are systematically summarized. Some existing problems and the areas to be focused in future work are also discussed. It is suitable for chronostratigraphic study to concentrate not only on the boundary but also doing multidisciplinary analysis on the biotic, chemical, magnetic, environmental, and chronologic aspects, in order to enhance the reliability and the potential for regional and global correlation of a certain GSSP.Some important achievements are expected in these areas in the Silurian study in China:(1) ecostratigraphy and basin analysis of the Llandovery, and the correlation of integrative stratigraphy with a high resolution;(2) establishment of the Wenlock to Pridoli chronostratigraphic framework;(3) the chemo-and magnetic stratigraphy and the age of some key intervals and horizons;(4)further investigation on paleogeography and plate tectonics; and(5) origin and early evolution of the terrestrial ecosystem. Some new breakthroughs might occur in the restudy on some of those problematic GSSPs of some particular series and stages.
