Based on the new material of seven Ordovician-Silurian boundary sections investigated recently, together with previously published data, we analyze the temporal and spatial distributions of the Lungmachi black shales,...Based on the new material of seven Ordovician-Silurian boundary sections investigated recently, together with previously published data, we analyze the temporal and spatial distributions of the Lungmachi black shales, a key petroleum source bed widely distributed in South China. The Lungmachi black shales range in age from the Normalograptus persculptus Biozone of the uppermost Ordovician to the Spirograptus guerichi Biozone of the lower Telychian, and ten graptolite biozones can be recognized within this unit. The basal and upper contacts of the Lungmachi black shales are diachronous. The basal contact ranges from the N. persculptus to the C. cyphus biozones, a span of five graptolite biozones over two stages. The upper contact ranges from the D. pectinatus-M. argenteus Biozone to the Spirograptus guerichi Biozone, which spans four graptolite biozones over two stages. The Yichang Uplift resulted in the formation of the Hunan-Hubei Submarine High in the border area of Hubei, Hunan, and Chongqing. This is supported by a break in sedimentation in this area spanning all or part of the Hirnantian, and in many areas extending into the underlying Katian and overlying Rhuddanian. Comparison of the distribution of the Katian to Rhuddanian strata in this area indicates a growth and subsequent reduction in area of the Hunan-Hubei Submarine High particularly in the Hirnantian to early Rhuddanian. This may partly represent the influence of the process of formation and melting of ice sheet in Ordovician South Pole and consequent sea level change.展开更多
The Lungmachi Formation is widely distributed in Guizhou, Chongqing and the adjacent area. It is important for the study of Silurian biostratigraphy and shale-gas investigation. Based on those biostratigraphically wel...The Lungmachi Formation is widely distributed in Guizhou, Chongqing and the adjacent area. It is important for the study of Silurian biostratigraphy and shale-gas investigation. Based on those biostratigraphically well-studied sections from Guiyang to Huayingshan, we reveal the stage-progressive distribution pattern of the Lungmachi black shales. The distribution of the Lungmachi black shales in the studying area can be subdivided into four geographic belts from the south to the north,reflecting the joint effect of regional and global environmental changes. The graptolite depth zonation model was adopted herein to infer the water depth of major graptolite assemblages from the black shales. The changes in the water depth indicate two major stages. The first stage is named the transgressive distribution stage which ranged from the Persculptograptus persculptus Biozone(LM1, upper Hirnantian) to the Coronograptus cyphus Biozone(LM5, upper Rhuddanian), an interval mostly controlled by global sea-level rise. The second stage, ranging from the Demirastrites triangulatus Biozone(LM6, lower Aeronian) to the Spirograptus guerichi Biozone(LM9, lower Telychian), is named the regressive shrinking stage, during which the black shales were gradually replaced by mixed-facies or carbonate sediments from the south to the north, representing the effects of the persistent uplifting of the Central Guizhou Oldland.展开更多
基金supported by Chinese Academy of Sciences (Grant No. KZCX2-EW-111)National Natural Science Foundation of China (Grant Nos. 40839910 and 40772002)Natural Sciences and Engineering Research Council of Canada (MJM)
文摘Based on the new material of seven Ordovician-Silurian boundary sections investigated recently, together with previously published data, we analyze the temporal and spatial distributions of the Lungmachi black shales, a key petroleum source bed widely distributed in South China. The Lungmachi black shales range in age from the Normalograptus persculptus Biozone of the uppermost Ordovician to the Spirograptus guerichi Biozone of the lower Telychian, and ten graptolite biozones can be recognized within this unit. The basal and upper contacts of the Lungmachi black shales are diachronous. The basal contact ranges from the N. persculptus to the C. cyphus biozones, a span of five graptolite biozones over two stages. The upper contact ranges from the D. pectinatus-M. argenteus Biozone to the Spirograptus guerichi Biozone, which spans four graptolite biozones over two stages. The Yichang Uplift resulted in the formation of the Hunan-Hubei Submarine High in the border area of Hubei, Hunan, and Chongqing. This is supported by a break in sedimentation in this area spanning all or part of the Hirnantian, and in many areas extending into the underlying Katian and overlying Rhuddanian. Comparison of the distribution of the Katian to Rhuddanian strata in this area indicates a growth and subsequent reduction in area of the Hunan-Hubei Submarine High particularly in the Hirnantian to early Rhuddanian. This may partly represent the influence of the process of formation and melting of ice sheet in Ordovician South Pole and consequent sea level change.
基金supported by Chinese Academy of Sciences (Grant No. XDB10010100)National Natural Science Foundation of China (Grant Nos. U1562213 and 41272042)
文摘The Lungmachi Formation is widely distributed in Guizhou, Chongqing and the adjacent area. It is important for the study of Silurian biostratigraphy and shale-gas investigation. Based on those biostratigraphically well-studied sections from Guiyang to Huayingshan, we reveal the stage-progressive distribution pattern of the Lungmachi black shales. The distribution of the Lungmachi black shales in the studying area can be subdivided into four geographic belts from the south to the north,reflecting the joint effect of regional and global environmental changes. The graptolite depth zonation model was adopted herein to infer the water depth of major graptolite assemblages from the black shales. The changes in the water depth indicate two major stages. The first stage is named the transgressive distribution stage which ranged from the Persculptograptus persculptus Biozone(LM1, upper Hirnantian) to the Coronograptus cyphus Biozone(LM5, upper Rhuddanian), an interval mostly controlled by global sea-level rise. The second stage, ranging from the Demirastrites triangulatus Biozone(LM6, lower Aeronian) to the Spirograptus guerichi Biozone(LM9, lower Telychian), is named the regressive shrinking stage, during which the black shales were gradually replaced by mixed-facies or carbonate sediments from the south to the north, representing the effects of the persistent uplifting of the Central Guizhou Oldland.
