Located in Xilin Gol League of Inner Mongolia Autonomous Region,the Xilinhot-Abaga volcanic cluster is in the centre of the Daxing’anling-Datong volcanic eruption belt.More than 300 Quaternary basaltic volcanoes of d...Located in Xilin Gol League of Inner Mongolia Autonomous Region,the Xilinhot-Abaga volcanic cluster is in the centre of the Daxing’anling-Datong volcanic eruption belt.More than 300 Quaternary basaltic volcanoes of different types are developed in the volcanic eruption belt.Maars are found for the first time in the study area,with those in Haotewula in the southeast of Abagaqi,and Chelewula and Esigewula in the northwest of Abagaqi to be the most representative.They all are large in scale,with cone diameters generally 3~4km,with the largest up to 6.5km.The maars show intact structure,a similar two-ringed mountain landscape and obviously phased eruption which contained a vigorous phreatomagmatic explosion at the earlier stage,and weak magmatic explosion at the later stage,and basaltic lava effusion in the last stage.The eruption sequence reflects the interaction between magma and water,the change of intrusive speed and outflow rate of magma.The Middle Pleistocene deposits of sand and gravel in the valley are covered by basal surge deposits.The TL age of sandstone-shale 'xenolith'which was found in the spatter deposits close to the crater is( 0.112 ± 0.0096) Ma,indicating that the eruption time of the Maars was the early Late Pleistocene.展开更多
The varicoloured Fenghuoshan Group occurs widely in the Qiangtang-Hoh Xil region of the northern Qinghai-Xizang Plateau. Few fossils have been found to date in this sedimentary succession because lithological conditio...The varicoloured Fenghuoshan Group occurs widely in the Qiangtang-Hoh Xil region of the northern Qinghai-Xizang Plateau. Few fossils have been found to date in this sedimentary succession because lithological conditions are not conducive to their preservation. As a result, there has been a long-term disagreement among geologists about its age. Despite a few lists of fossil names in individual publi- cations, no detailed research on the palaeontology, including palynology, has been reported previously. In this study, we recovered many pollen grains and spores from two samples that were collected on the northern slope of Fenghuo Moun- tain. They indicate an age no younger than Maastrichtian for the upper part of the Fenghuoshan Group. It is considered likely that the entire Fenghuoshan Group represents deposi- tion between the late Early Cretaceous （possibly Albian） and the Maastrichtian. The palynoflora consists mainly of angio- sperm pollen, gymnosperm pollen and fern and bryophyte spores being subordinate. Pollen grains referable to the Ephedrales and the Taxaceae-Cupressaceae groups dominate the assemblage, implying a warm, arid climate and subtropical forest-shrub vegetation at the time of deposition.展开更多
基金sponsored by the Special Fund of Public Research,China Earthquake Administration(200782713)Special Fund of the Geological Heritage Protection,Department of Land and Resources,Inner Mongolia Autonomous Region,China(20101030)
文摘Located in Xilin Gol League of Inner Mongolia Autonomous Region,the Xilinhot-Abaga volcanic cluster is in the centre of the Daxing’anling-Datong volcanic eruption belt.More than 300 Quaternary basaltic volcanoes of different types are developed in the volcanic eruption belt.Maars are found for the first time in the study area,with those in Haotewula in the southeast of Abagaqi,and Chelewula and Esigewula in the northwest of Abagaqi to be the most representative.They all are large in scale,with cone diameters generally 3~4km,with the largest up to 6.5km.The maars show intact structure,a similar two-ringed mountain landscape and obviously phased eruption which contained a vigorous phreatomagmatic explosion at the earlier stage,and weak magmatic explosion at the later stage,and basaltic lava effusion in the last stage.The eruption sequence reflects the interaction between magma and water,the change of intrusive speed and outflow rate of magma.The Middle Pleistocene deposits of sand and gravel in the valley are covered by basal surge deposits.The TL age of sandstone-shale 'xenolith'which was found in the spatter deposits close to the crater is( 0.112 ± 0.0096) Ma,indicating that the eruption time of the Maars was the early Late Pleistocene.
基金supported by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences(XDB03010103)the National Basic Research Program of China(2012CB822004)the National Natural Science Foundation of China(41172011)
文摘The varicoloured Fenghuoshan Group occurs widely in the Qiangtang-Hoh Xil region of the northern Qinghai-Xizang Plateau. Few fossils have been found to date in this sedimentary succession because lithological conditions are not conducive to their preservation. As a result, there has been a long-term disagreement among geologists about its age. Despite a few lists of fossil names in individual publi- cations, no detailed research on the palaeontology, including palynology, has been reported previously. In this study, we recovered many pollen grains and spores from two samples that were collected on the northern slope of Fenghuo Moun- tain. They indicate an age no younger than Maastrichtian for the upper part of the Fenghuoshan Group. It is considered likely that the entire Fenghuoshan Group represents deposi- tion between the late Early Cretaceous （possibly Albian） and the Maastrichtian. The palynoflora consists mainly of angio- sperm pollen, gymnosperm pollen and fern and bryophyte spores being subordinate. Pollen grains referable to the Ephedrales and the Taxaceae-Cupressaceae groups dominate the assemblage, implying a warm, arid climate and subtropical forest-shrub vegetation at the time of deposition.
