Climate in Eastern Asia is composed of monsoon climate in the east,arid and semi-arid climate in the north and west,and the cold and dry climate of Qinghai-Tibetan Plateau in the southwest.The underlying causes for th...Climate in Eastern Asia is composed of monsoon climate in the east,arid and semi-arid climate in the north and west,and the cold and dry climate of Qinghai-Tibetan Plateau in the southwest.The underlying causes for the evolution of East Asian climate during late Cenozoic have long been investigated and debated,particularly with regards to the role played by the Qinghai-Tibetan Plateau uplift and the global cooling.In this paper,we reviewed major research developments in this area,and summarized the important results.Based on a synthesis of data,we propose that the Qinghai-Tibetan Plateau uplift alone cannot fully explain the formation of monsoon and arid climates in Eastern Asia during the past 22–25 Ma.Other factors such as the global ice volume and high-latitude temperature changes have also played a vital role.Moreover,atmospheric CO2changes may have modulated the monsoon and dry climate changes by affecting the location of the inter-tropical convergence zone(ITCZ),which controls the monsoon precipitation zone and the track of the East Asian winter monsoon during late Cenozoic.The integration of high-resolution geological record and numerical paleoclimate modeling could make new contributions to understanding the climate evolution and variation in eastern Asia in future studies.It could facilitate the investigation of the regional differences in East Asian environmental changes and the asynchronous nature between the uplift of Qinghai-Tibetan Plateau and their climatic effects.These would be the keys to understanding underlying driving forces for the evolution of the East Asian climate.展开更多
Tectonic evolution of the Tethys and the boundary between the Gondwanaland and the Eurasia during the Carboniferous and Permian remain hotly debated. Qiangtang region in the Qinghai-Tibet Plateau may be a key place to...Tectonic evolution of the Tethys and the boundary between the Gondwanaland and the Eurasia during the Carboniferous and Permian remain hotly debated. Qiangtang region in the Qinghai-Tibet Plateau may be a key place to study these problems. A paleomagnetic study was conducted on the Late Paleozoic rocks in the northern Qiangtang region （33.7°N, 86.7°W）, Tibet. Two sites （21 samples） in the Upper Carboniferous, eleven sites （101 samples） in the Permian, and two sites （16 samples） in the Lower Triassic were investigated. The rock magnetic data revealed hematite and magnetite as the main magnetic carders. In stepwise thermal demagnetization and/or combined alternating field （AC） demagnetization, two characteristic components in the majority of the samples were identified as （1） the Low-temperature Component （LTC）, characterized by northerly decli- nation and moderate to steep inclination, corresponding to a pole position overlay with the present North Pole. A minority of the samples present single component, and their directions are the same as （2） the High-temperature Component （HTC） of double components. The combined single-component and HTC data of the Permian can pass the R-test at 95% level and the F-test at 99% level, as well as the BC-test. The pole position from the Late Carboniferous is at 31.8°S, 45.7°E with dp=2.1, dm=3.9, that from the Early and Middle （Late） Permian is at 31.7°S, 46.8°E with @=9.2, dm=16.9 （34.4°N, 54.1°E with dp=6.9, dm=1 2.5） respectively, and that from the Early Triassic is at 16.9°S, 22.5°E with dp=4.9, dm=9.2. These pole positions are different from the other poles for the Qiangtang Block, which suggests the single-component and HTC directions are probably a primary magnetization and the northern Qiangtang Block was paleogeographically situated at low latitudes in the Northern Hemisphere in the Late Paleozoic.展开更多
The palaeolake evolution across the Tibetan Plateau and adjacent areas has been extensively studied, but the timing of late Pleistocene lake highstands remains controversial. Robust dating of lacustrine deposits is of...The palaeolake evolution across the Tibetan Plateau and adjacent areas has been extensively studied, but the timing of late Pleistocene lake highstands remains controversial. Robust dating of lacustrine deposits is of importance in resolving this issue. This paper presents 14 C or optically stimulated luminescence(OSL) age estimates from two sets of late Quaternary lacustrine sequences in the Qaidam Basin and Tengger Desert(northeastern Tibetan Plateau). The updated dating results show:(1) the radiocarbon dating technique apparently underestimated the age of the strata of >30 ka BP in Qaidam Basin;(2) although OSL and 14 C dating agreed with each other for Holocene age samples in the Tengger Desert area, there was a significant offset in dating results of sediments older than ~30 ka BP, largely resulting from radiocarbon dating underestimation;(3) both cases imply that most of the published radiocarbon ages(e.g., older than ~30 ka BP) should be treated with caution and perhaps its geological implication should be revaluated; and(4) the high lake events on the Tibetan Plateau and adjacent areas, traditionally assigned to MIS 3a based on 14 C dating, are likely older than ~80 ka based on OSL chronology.展开更多
Many well-preserved silicified megalodontids found from the Jiapila Formation of the Upper Triassic in western China show great variations in the amorphous teeth and the massive hinge plate,making the internal molds v...Many well-preserved silicified megalodontids found from the Jiapila Formation of the Upper Triassic in western China show great variations in the amorphous teeth and the massive hinge plate,making the internal molds vary greatly in size and shape.Thus,the internal molds of megalodontids do not always provide reliable taxonomic characters.As a result,about 3/4 of the 132 species and 6 of 9 genera of Triassic Megalodontidae erected on the basis of internal molds have to be revised.The revised definitions of genera Neomegalodon,Triadomegalodon,and Conchodon are given in this paper.展开更多
基金supported by the Global Change Research Program of Ministry of Science and Technology of China(Grant No.2010CB950200)National Natural Science Foundation of China(Grant No.40930103)
文摘Climate in Eastern Asia is composed of monsoon climate in the east,arid and semi-arid climate in the north and west,and the cold and dry climate of Qinghai-Tibetan Plateau in the southwest.The underlying causes for the evolution of East Asian climate during late Cenozoic have long been investigated and debated,particularly with regards to the role played by the Qinghai-Tibetan Plateau uplift and the global cooling.In this paper,we reviewed major research developments in this area,and summarized the important results.Based on a synthesis of data,we propose that the Qinghai-Tibetan Plateau uplift alone cannot fully explain the formation of monsoon and arid climates in Eastern Asia during the past 22–25 Ma.Other factors such as the global ice volume and high-latitude temperature changes have also played a vital role.Moreover,atmospheric CO2changes may have modulated the monsoon and dry climate changes by affecting the location of the inter-tropical convergence zone(ITCZ),which controls the monsoon precipitation zone and the track of the East Asian winter monsoon during late Cenozoic.The integration of high-resolution geological record and numerical paleoclimate modeling could make new contributions to understanding the climate evolution and variation in eastern Asia in future studies.It could facilitate the investigation of the regional differences in East Asian environmental changes and the asynchronous nature between the uplift of Qinghai-Tibetan Plateau and their climatic effects.These would be the keys to understanding underlying driving forces for the evolution of the East Asian climate.
基金supported by the China Geology Survey Bureau Program (Grant No. 1212010610102)the National Natural Science Foundation of China (Grant No. 41074045)the Special Key Subject Funds of Colleges and Universities in Shaanxi Province (Grant No. 081802)
文摘Tectonic evolution of the Tethys and the boundary between the Gondwanaland and the Eurasia during the Carboniferous and Permian remain hotly debated. Qiangtang region in the Qinghai-Tibet Plateau may be a key place to study these problems. A paleomagnetic study was conducted on the Late Paleozoic rocks in the northern Qiangtang region （33.7°N, 86.7°W）, Tibet. Two sites （21 samples） in the Upper Carboniferous, eleven sites （101 samples） in the Permian, and two sites （16 samples） in the Lower Triassic were investigated. The rock magnetic data revealed hematite and magnetite as the main magnetic carders. In stepwise thermal demagnetization and/or combined alternating field （AC） demagnetization, two characteristic components in the majority of the samples were identified as （1） the Low-temperature Component （LTC）, characterized by northerly decli- nation and moderate to steep inclination, corresponding to a pole position overlay with the present North Pole. A minority of the samples present single component, and their directions are the same as （2） the High-temperature Component （HTC） of double components. The combined single-component and HTC data of the Permian can pass the R-test at 95% level and the F-test at 99% level, as well as the BC-test. The pole position from the Late Carboniferous is at 31.8°S, 45.7°E with dp=2.1, dm=3.9, that from the Early and Middle （Late） Permian is at 31.7°S, 46.8°E with @=9.2, dm=16.9 （34.4°N, 54.1°E with dp=6.9, dm=1 2.5） respectively, and that from the Early Triassic is at 16.9°S, 22.5°E with dp=4.9, dm=9.2. These pole positions are different from the other poles for the Qiangtang Block, which suggests the single-component and HTC directions are probably a primary magnetization and the northern Qiangtang Block was paleogeographically situated at low latitudes in the Northern Hemisphere in the Late Paleozoic.
基金supported by the National Natural Science Foundation of China(Grant Nos.41271002,41430530)the State Key Laboratory of Loess and Quaternary Geology(Grant No.SKLLQG1101)+2 种基金the NIGLAS 1-3-5 Project(Grant No.NIGLAS2012135004)the State Key Laboratory of Lake Science and Environment(Grant No.2012SKL002)the China Postdoctoral Science Foundation(Grant Nos.2012M520061,2013T60567)
文摘The palaeolake evolution across the Tibetan Plateau and adjacent areas has been extensively studied, but the timing of late Pleistocene lake highstands remains controversial. Robust dating of lacustrine deposits is of importance in resolving this issue. This paper presents 14 C or optically stimulated luminescence(OSL) age estimates from two sets of late Quaternary lacustrine sequences in the Qaidam Basin and Tengger Desert(northeastern Tibetan Plateau). The updated dating results show:(1) the radiocarbon dating technique apparently underestimated the age of the strata of >30 ka BP in Qaidam Basin;(2) although OSL and 14 C dating agreed with each other for Holocene age samples in the Tengger Desert area, there was a significant offset in dating results of sediments older than ~30 ka BP, largely resulting from radiocarbon dating underestimation;(3) both cases imply that most of the published radiocarbon ages(e.g., older than ~30 ka BP) should be treated with caution and perhaps its geological implication should be revaluated; and(4) the high lake events on the Tibetan Plateau and adjacent areas, traditionally assigned to MIS 3a based on 14 C dating, are likely older than ~80 ka based on OSL chronology.
基金supported by National Natural Science Foundation of China (Gant No. 41172025)China Geological Survey Project (Grant No. 1212011120116)
文摘Many well-preserved silicified megalodontids found from the Jiapila Formation of the Upper Triassic in western China show great variations in the amorphous teeth and the massive hinge plate,making the internal molds vary greatly in size and shape.Thus,the internal molds of megalodontids do not always provide reliable taxonomic characters.As a result,about 3/4 of the 132 species and 6 of 9 genera of Triassic Megalodontidae erected on the basis of internal molds have to be revised.The revised definitions of genera Neomegalodon,Triadomegalodon,and Conchodon are given in this paper.
