Carbon and oxygen isotope and dating analyses of foraminiferan in sediment cores collected from three different areas of the northern slope of the South China Sea were conducted, in order to examine the records of the...Carbon and oxygen isotope and dating analyses of foraminiferan in sediment cores collected from three different areas of the northern slope of the South China Sea were conducted, in order to examine the records of the gas hydrate decomposition events since the late Quaternary under the conditions of methane seepage. The results show that: 1) the δ13C values of the benthic foraminiferan Uvigerina spp. (size range of 0.25-0.35 ram) are from -0.212% to -0.021% and the δ180 values of the planktonic foraminiferan Globigerinoides ruber (size range of 0.25-0.35 ram) are from -0.311% to -0.060%; 2) three cores (ZD2, ZD3 and ZS5) from the bottom of a hole are aged for 11 814, 26 616 and 64 090 a corresponding to the early oxygen isotope stage (MIS) Ⅰ, Ⅲ and Ⅳ final period, respectively; 3) a negative-skewed layer of carbon isotope corresponds to that of MIS II (cold period), whose degree of negative bias is -0.2%0; and 4) the δ13C compositions of foraminiferans are similar to those of the Blake Ridge and the Gulf of Mexico sediments of the late Quaternary. According to the analysis, the reasons for these results are that the studied area is a typical area of methane seep environment in the area during MIS II due to the global sea-level fall and sea pressure decrease. Gas hydrate is decomposed and released, and a large number of light carbon isotopes of methane are released into the ocean, dissolved to inorganic carbon (DIC) pool and recorded in the foraminiferan shells. A pyrite layer developed in the negative bias layers of the foraminiferans confirms that the δ13C of foraminiferans is more affected by methane and less by the reduction of marine productivity and early diagenesis. The use of foraminiferan δ13C could accurately determine late Quaternary hydrate release events and provide evidence for both reconstructing the geological history of methane release events and exploring natural gas hydrate.展开更多
The Longling-Ruili fault is an important active fault in Southwestern China, striking generally northeast. The fault controls the development of the sedimentary series and magmatic action on its two sides, as well as ...The Longling-Ruili fault is an important active fault in Southwestern China, striking generally northeast. The fault controls the development of the sedimentary series and magmatic action on its two sides, as well as the development of the Longling basin, Mangshi basin and the Zhefang basin along it. Due to limited Quaternary sediments and harsh natural conditions, the study of late Quaternary fault activity on the northern segment of the Longling-Ruili fault is lacking and the time of the newest faulting and the Quaternary slip rate are not clear at present. Based on the interpretation of remote images, quantitative geomorphologic deformation measurements and dating of young terrace deposits and alluvial fans, this paper obtains some new results as follows. The northern segment of the Longling-Ruili fault is a Holocene dextral strike-slip fault with some component of a normal slip. The terrace T1 composing mainly of alluvial deposits formed during 4ka B. P. was offset by the northern segment of the Longling-Ruili fault and its left-lateral and its vertical displacements are 8m - 12m and 2m, respectively. The late Pleistocene alluvial fan was displaced with a left-lateral and vertical displacement of 70m and lgm, respectively. The strike-slip rate of the Longling-Ruili fault is 2.2mm/a 2.5mm/a and the vertical slip rate is 0.6mm/a since the late Pleistocene epoch. The strike-slip rate of the Longling-Ruili fault is 1.8mm/a - 3.0mm/a and vertical slip rate is 0.5mm/a during the Holocene epoch. The proportion of horizontal to vertical displacement is about 4: 1, which means that the vertical slip rate on the northern segment of the Longling-Ruili fault is about 25 % of the horizontal slip rate. The left-lateral slip rate in the late Holocene is consistent with the GPS measurement. The strike slip rate is of great consistency in different time scales since the late Pleistocene epoch, indicating that the activity of the Longling-Ruili fault is of great stability.展开更多
Based on detailed investigations and prospecting,this paper describes the geometrical characteristics and tectonic activities of Wanquan fault in northwest of Beijing. This fault strikes mainly northeast or northeast ...Based on detailed investigations and prospecting,this paper describes the geometrical characteristics and tectonic activities of Wanquan fault in northwest of Beijing. This fault strikes mainly northeast or northeast to north,dipping southeast,and extends over a length of 15km. It is a major geological and geomorphological margin,controlling the neotectonic movement in this region. On the southeast side of Wanquan fault are the Late Quaternary unconsolidated deposits,forming a basin or deposition; but on the other side is Mesozoic volcano debris,forming lower-mountains and hills. Wanquan fault is a mid- to-high-angle normal fault dipping southeast. This fault was more active in the Quaternary. Since the middle-late part of the alate Pleistocene,the average rate with vertical slip of a single fault is over 0. 03 ~ 0. 3mm /a,but the fault has multiple slipping surfaces,and a total rate with vertical slip will be estimated.展开更多
基金Project(40976035) supported by the National Natural Science Foundation of ChinaProject(2009CB219501) supported by the National Basic Research Program of ChinaProject(908-ZC-I-07) supported by the Special Program of Comprehensive Survey and Assessment Offshore China Sea
文摘Carbon and oxygen isotope and dating analyses of foraminiferan in sediment cores collected from three different areas of the northern slope of the South China Sea were conducted, in order to examine the records of the gas hydrate decomposition events since the late Quaternary under the conditions of methane seepage. The results show that: 1) the δ13C values of the benthic foraminiferan Uvigerina spp. (size range of 0.25-0.35 ram) are from -0.212% to -0.021% and the δ180 values of the planktonic foraminiferan Globigerinoides ruber (size range of 0.25-0.35 ram) are from -0.311% to -0.060%; 2) three cores (ZD2, ZD3 and ZS5) from the bottom of a hole are aged for 11 814, 26 616 and 64 090 a corresponding to the early oxygen isotope stage (MIS) Ⅰ, Ⅲ and Ⅳ final period, respectively; 3) a negative-skewed layer of carbon isotope corresponds to that of MIS II (cold period), whose degree of negative bias is -0.2%0; and 4) the δ13C compositions of foraminiferans are similar to those of the Blake Ridge and the Gulf of Mexico sediments of the late Quaternary. According to the analysis, the reasons for these results are that the studied area is a typical area of methane seep environment in the area during MIS II due to the global sea-level fall and sea pressure decrease. Gas hydrate is decomposed and released, and a large number of light carbon isotopes of methane are released into the ocean, dissolved to inorganic carbon (DIC) pool and recorded in the foraminiferan shells. A pyrite layer developed in the negative bias layers of the foraminiferans confirms that the δ13C of foraminiferans is more affected by methane and less by the reduction of marine productivity and early diagenesis. The use of foraminiferan δ13C could accurately determine late Quaternary hydrate release events and provide evidence for both reconstructing the geological history of methane release events and exploring natural gas hydrate.
基金sponsored by the Science and Technology Development Program of the Ministry of Railways(2008G027B),the People's Republic of Chinathe National Key Technology R&D Program(2006BAC13B)103),China
文摘The Longling-Ruili fault is an important active fault in Southwestern China, striking generally northeast. The fault controls the development of the sedimentary series and magmatic action on its two sides, as well as the development of the Longling basin, Mangshi basin and the Zhefang basin along it. Due to limited Quaternary sediments and harsh natural conditions, the study of late Quaternary fault activity on the northern segment of the Longling-Ruili fault is lacking and the time of the newest faulting and the Quaternary slip rate are not clear at present. Based on the interpretation of remote images, quantitative geomorphologic deformation measurements and dating of young terrace deposits and alluvial fans, this paper obtains some new results as follows. The northern segment of the Longling-Ruili fault is a Holocene dextral strike-slip fault with some component of a normal slip. The terrace T1 composing mainly of alluvial deposits formed during 4ka B. P. was offset by the northern segment of the Longling-Ruili fault and its left-lateral and its vertical displacements are 8m - 12m and 2m, respectively. The late Pleistocene alluvial fan was displaced with a left-lateral and vertical displacement of 70m and lgm, respectively. The strike-slip rate of the Longling-Ruili fault is 2.2mm/a 2.5mm/a and the vertical slip rate is 0.6mm/a since the late Pleistocene epoch. The strike-slip rate of the Longling-Ruili fault is 1.8mm/a - 3.0mm/a and vertical slip rate is 0.5mm/a during the Holocene epoch. The proportion of horizontal to vertical displacement is about 4: 1, which means that the vertical slip rate on the northern segment of the Longling-Ruili fault is about 25 % of the horizontal slip rate. The left-lateral slip rate in the late Holocene is consistent with the GPS measurement. The strike slip rate is of great consistency in different time scales since the late Pleistocene epoch, indicating that the activity of the Longling-Ruili fault is of great stability.
基金Urban Active Faults Detection and Seismic Hazard Assessment Project of the Hebei Province ( funded by the Development and Reform Bureau of the Hebei Province [2007]No.1684)A Special Scientific Research Project in Earthquake Industry ( 200908001)
文摘Based on detailed investigations and prospecting,this paper describes the geometrical characteristics and tectonic activities of Wanquan fault in northwest of Beijing. This fault strikes mainly northeast or northeast to north,dipping southeast,and extends over a length of 15km. It is a major geological and geomorphological margin,controlling the neotectonic movement in this region. On the southeast side of Wanquan fault are the Late Quaternary unconsolidated deposits,forming a basin or deposition; but on the other side is Mesozoic volcano debris,forming lower-mountains and hills. Wanquan fault is a mid- to-high-angle normal fault dipping southeast. This fault was more active in the Quaternary. Since the middle-late part of the alate Pleistocene,the average rate with vertical slip of a single fault is over 0. 03 ~ 0. 3mm /a,but the fault has multiple slipping surfaces,and a total rate with vertical slip will be estimated.