The annual laminae gray level variations in the stalagmite TS9501 of Shihua Cave, Beijing are studied in detail. The environmental factors influencing the laminae gray level are also analyzed. The following conditions...The annual laminae gray level variations in the stalagmite TS9501 of Shihua Cave, Beijing are studied in detail. The environmental factors influencing the laminae gray level are also analyzed. The following conditions may be necessary to the study on the lamina gray level. A) The seasonal differences of climate in the studied area are strong. B) The cave has a rapid and simple hydrological connection with the surface, such that the gray level variation is great; therefore, climatic changes can be more clearly recorded in a stalagmite. C) No water from other sources due to lateral flow adds to the seepage over the cave. D) There are more organic impurities than inorganic ones, whose content changes distinctly with time in the sample. By comparison with the modern instrumental climate records, it was found that the gray level of laminae is mainly related to the air temperature, especially the summer mean temperature. Therefore, the gray level can be used as a proxy of the air temperature. The variation of the lamina gray level also represents the oscillation of Indian summer monsoon as identified in the modern climate records. The variability of the temperature in Beijing area over the last 1 ka is reconstructed. The results show that there are several cold periods corresponding to historical records. An important phenomenon is noticed that the climatic pattern before about 1400AD is different from that after about 1400AD. In Beijing area, before about 1400AD, low amplitude and high frequency temperature oscillations dominated the signal. The climate pattern is warm-dry and cold-wet. After about 1400AD, both the temperature and rainfall varied synchronously, temperature oscillated strongly and the Little Ice Age occurred. The climate pattern is cold-dry and warm-wet. This transition of the climate pattern is also observed in other worldwide paleoclimatic records, demonstrating that there was a global climate event at about 1400AD.展开更多
The Altyn Tagh Fault and the Altyn Mountain define respectively the tectonic and geographical northern edges of the Tibetan Plateau, and figure prominently in the growth and rising mechanism of the plateau. The rhombu...The Altyn Tagh Fault and the Altyn Mountain define respectively the tectonic and geographical northern edges of the Tibetan Plateau, and figure prominently in the growth and rising mechanism of the plateau. The rhombus-shaped Altyn Mountain has long been thought to have an intimate relation with the Altyn Tagh Fault; however, its formation mechanism remains unclear and debatable. In this paper, we focus on the EW-trending uplifts in the Altyn Mountain, and investigated three Cenozoic sedimentary sections in the vicinity of the EW-trending uplifts located along the southern side of the central segment of the Altyn Tagh Fault. Magnetostratigraphy and pollen analysis were used to constrain ages of the sediments. Clast composition of conglomerate and paleocurrents obtained from clast imbrications were applied to determine the provenance. We also established a geological section parallel to the Altyn Tagh Fault on sedimentary facies across the northwestern Qaidam Basin. The results indicate that these en-echelon EW-trending uplifts formed as early as ca. 36 Ma and were preferred to be under the control of basal shear of the Altyn Tagh Fault in the middle-lower crust, symbolizing the early uplift of the Altyn Mountain during the Cenozoic. Left-slip along the Altyn Tagh Fault occurring during the Miocene and afterwards displaced and altered these uplifts, shaping the Altyn Mountain to its present fabric.展开更多
An angular unconformity has been identified between the upper and the lower Youshashan Formation based on the study of the regional geology, drillhole, and geophysical data of the Altyn Tagh Mountain foreland, western...An angular unconformity has been identified between the upper and the lower Youshashan Formation based on the study of the regional geology, drillhole, and geophysical data of the Altyn Tagh Mountain foreland, western Qaidam Basin. The distribution of the unconformity, the contacts between the upper and the lower Youshashan Formation, and its relation to the characteristics of the paleo-structure belts suggest a close relationship between the unconformities in the southern flank of the Altyn Tagh Mountain in the west of the Qaidam Basin and the activity of the Altyn Tagh Fault. It was the same time when the Atlyn Tagh Fault Zone was transformed from regional uplifting to rapid-strike-slipping movement during the Miocene, resulting in the cessation of the regional uplift and subsequent massive regional transgression during the deposition of the upper Youshashan Formation, which unconformably overlies (onlaps) the underlying strata of different ages.展开更多
文摘The annual laminae gray level variations in the stalagmite TS9501 of Shihua Cave, Beijing are studied in detail. The environmental factors influencing the laminae gray level are also analyzed. The following conditions may be necessary to the study on the lamina gray level. A) The seasonal differences of climate in the studied area are strong. B) The cave has a rapid and simple hydrological connection with the surface, such that the gray level variation is great; therefore, climatic changes can be more clearly recorded in a stalagmite. C) No water from other sources due to lateral flow adds to the seepage over the cave. D) There are more organic impurities than inorganic ones, whose content changes distinctly with time in the sample. By comparison with the modern instrumental climate records, it was found that the gray level of laminae is mainly related to the air temperature, especially the summer mean temperature. Therefore, the gray level can be used as a proxy of the air temperature. The variation of the lamina gray level also represents the oscillation of Indian summer monsoon as identified in the modern climate records. The variability of the temperature in Beijing area over the last 1 ka is reconstructed. The results show that there are several cold periods corresponding to historical records. An important phenomenon is noticed that the climatic pattern before about 1400AD is different from that after about 1400AD. In Beijing area, before about 1400AD, low amplitude and high frequency temperature oscillations dominated the signal. The climate pattern is warm-dry and cold-wet. After about 1400AD, both the temperature and rainfall varied synchronously, temperature oscillated strongly and the Little Ice Age occurred. The climate pattern is cold-dry and warm-wet. This transition of the climate pattern is also observed in other worldwide paleoclimatic records, demonstrating that there was a global climate event at about 1400AD.
基金supported by Chinese National Key Scientific and Technological Projects (Grant Nos. 2011ZX05009-001 and2011ZX05003-002)
文摘The Altyn Tagh Fault and the Altyn Mountain define respectively the tectonic and geographical northern edges of the Tibetan Plateau, and figure prominently in the growth and rising mechanism of the plateau. The rhombus-shaped Altyn Mountain has long been thought to have an intimate relation with the Altyn Tagh Fault; however, its formation mechanism remains unclear and debatable. In this paper, we focus on the EW-trending uplifts in the Altyn Mountain, and investigated three Cenozoic sedimentary sections in the vicinity of the EW-trending uplifts located along the southern side of the central segment of the Altyn Tagh Fault. Magnetostratigraphy and pollen analysis were used to constrain ages of the sediments. Clast composition of conglomerate and paleocurrents obtained from clast imbrications were applied to determine the provenance. We also established a geological section parallel to the Altyn Tagh Fault on sedimentary facies across the northwestern Qaidam Basin. The results indicate that these en-echelon EW-trending uplifts formed as early as ca. 36 Ma and were preferred to be under the control of basal shear of the Altyn Tagh Fault in the middle-lower crust, symbolizing the early uplift of the Altyn Mountain during the Cenozoic. Left-slip along the Altyn Tagh Fault occurring during the Miocene and afterwards displaced and altered these uplifts, shaping the Altyn Mountain to its present fabric.
基金supported by National "Tenth Five" Science and Technology Foundation Project (Grant No.2004BA616A-04-01)Qinghai Oilfield Company,China National Petroleum Corporation Foundation Project (Grant No.02-107401-7)
文摘An angular unconformity has been identified between the upper and the lower Youshashan Formation based on the study of the regional geology, drillhole, and geophysical data of the Altyn Tagh Mountain foreland, western Qaidam Basin. The distribution of the unconformity, the contacts between the upper and the lower Youshashan Formation, and its relation to the characteristics of the paleo-structure belts suggest a close relationship between the unconformities in the southern flank of the Altyn Tagh Mountain in the west of the Qaidam Basin and the activity of the Altyn Tagh Fault. It was the same time when the Atlyn Tagh Fault Zone was transformed from regional uplifting to rapid-strike-slipping movement during the Miocene, resulting in the cessation of the regional uplift and subsequent massive regional transgression during the deposition of the upper Youshashan Formation, which unconformably overlies (onlaps) the underlying strata of different ages.
