The coastal hard rock with a thickness of over 5 m and a distribution area of nearly 200 ha in the Haishan Island, south China, has long drawn researchers＇ attention. However, there were controversies over its format...The coastal hard rock with a thickness of over 5 m and a distribution area of nearly 200 ha in the Haishan Island, south China, has long drawn researchers＇ attention. However, there were controversies over its formation and classification, and these controversies in turn lead to the dispute of sea level changes and coastal uplift-subsidence of this area. To investigate its diagenesis and evolution, petrographic analysis, elemental geochemistry, isotopic analysis, and radiocarbon dating were used in the present study. Radiocarbon dating indicates that the deposition of the Haishan Coquinite commenced in the mid Holocene and lasted to -600 a B.P. Petrographic analysis shows that the Haishan Coquinite is cemented by low-Mg calcite, indicating that the cementation occurred in a meteoric environment. The elemental geochemistry and isotopic values demonstrate that the coquinite suffered strong leaching, which was thought to be responsible for the meteoric cementation of the coquinite. According to these results, the diagenesis of the coquinite is revealed： deposition of the Haishan Coquinite commenced in the mid Holocene in a shoal environment, initial cementation occurred and cement may be high-Mg calcite or aragonite; latterly the coquinite exposed to meteoric environment as a result of lowering of relative sea level, and the cement altered to low-Mg, which took the morphologies of bladed calcite rim and equant spar. A four-stage evolution model is proposed： （1） deposition stage, （2） initial cementation, （3） exposure to and cementation in meteoric environment, and （4） erosion stage. The published reports indicate that the hard rock should be designated as coquinite. Based on these studies, mid-Holocene sea level in this area was discussed, and the Haishan Island was proposed to uplift with a rate of ～5 mm/a in the last -600 a.展开更多
The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorpholog...The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorphologic and lithological evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates strong lake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summer monsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levels in the mid-Holocene around 5000—7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the present Asian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south Inner Mongolian Plateau. The period was also probably colder, at least in the high Asian plateaus and mountains.展开更多
基于神农架青天洞石笋两个230Th年龄、582条纹层计数和183个氧同位素数据,重建了7～6 ka B.P.期间平均3年分辨率的1δ8O变化序列。持续约580年振幅达1.8‰的δ18O在平均值-9.66‰上下波动,指示了东亚季风降水强度的长期演化趋势和高频...基于神农架青天洞石笋两个230Th年龄、582条纹层计数和183个氧同位素数据,重建了7～6 ka B.P.期间平均3年分辨率的1δ8O变化序列。持续约580年振幅达1.8‰的δ18O在平均值-9.66‰上下波动,指示了东亚季风降水强度的长期演化趋势和高频振荡信息,大致划分为4个百年尺度旋回。青天洞与阿曼石笋δ18O记录的对比表明,东亚季风和印度季风在百年或更短时间尺度上同相位变化,可能反映了两地季风气候受统一的印度洋/太平洋大尺度水汽循环控制。功率谱分析揭示出163、81、16和11年的周期,大致与树轮Δ14C百年至数十年尺度太阳活动变化周期相同。展开更多
基金supported by the Chinese Academy of Sciences (Grant no.KZCX3-SW-234)the National Natural Science Foundation of China (Grant no.40476025)the Science and Technology Program of Guangdong Province (Grant no.2004B33201002).
文摘The coastal hard rock with a thickness of over 5 m and a distribution area of nearly 200 ha in the Haishan Island, south China, has long drawn researchers＇ attention. However, there were controversies over its formation and classification, and these controversies in turn lead to the dispute of sea level changes and coastal uplift-subsidence of this area. To investigate its diagenesis and evolution, petrographic analysis, elemental geochemistry, isotopic analysis, and radiocarbon dating were used in the present study. Radiocarbon dating indicates that the deposition of the Haishan Coquinite commenced in the mid Holocene and lasted to -600 a B.P. Petrographic analysis shows that the Haishan Coquinite is cemented by low-Mg calcite, indicating that the cementation occurred in a meteoric environment. The elemental geochemistry and isotopic values demonstrate that the coquinite suffered strong leaching, which was thought to be responsible for the meteoric cementation of the coquinite. According to these results, the diagenesis of the coquinite is revealed： deposition of the Haishan Coquinite commenced in the mid Holocene in a shoal environment, initial cementation occurred and cement may be high-Mg calcite or aragonite; latterly the coquinite exposed to meteoric environment as a result of lowering of relative sea level, and the cement altered to low-Mg, which took the morphologies of bladed calcite rim and equant spar. A four-stage evolution model is proposed： （1） deposition stage, （2） initial cementation, （3） exposure to and cementation in meteoric environment, and （4） erosion stage. The published reports indicate that the hard rock should be designated as coquinite. Based on these studies, mid-Holocene sea level in this area was discussed, and the Haishan Island was proposed to uplift with a rate of ～5 mm/a in the last -600 a.
基金supported by the National Natural Science Foundation of China(Grant No.40125001)the Hundred Talent Project of CAS and the International Collaboration Project(Grant No.2002CB714004).
文摘The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorphologic and lithological evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates strong lake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summer monsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levels in the mid-Holocene around 5000—7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the present Asian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south Inner Mongolian Plateau. The period was also probably colder, at least in the high Asian plateaus and mountains.
文摘基于神农架青天洞石笋两个230Th年龄、582条纹层计数和183个氧同位素数据,重建了7～6 ka B.P.期间平均3年分辨率的1δ8O变化序列。持续约580年振幅达1.8‰的δ18O在平均值-9.66‰上下波动,指示了东亚季风降水强度的长期演化趋势和高频振荡信息,大致划分为4个百年尺度旋回。青天洞与阿曼石笋δ18O记录的对比表明,东亚季风和印度季风在百年或更短时间尺度上同相位变化,可能反映了两地季风气候受统一的印度洋/太平洋大尺度水汽循环控制。功率谱分析揭示出163、81、16和11年的周期,大致与树轮Δ14C百年至数十年尺度太阳活动变化周期相同。
