Detailed mineral magnetic measurements, integrated with grain-size distribution and X-ray diffraction （XRD） analyses, were made on the marine sediments of Core MD98-2172, retrieved from the Eastern Timor Sea. Values...Detailed mineral magnetic measurements, integrated with grain-size distribution and X-ray diffraction （XRD） analyses, were made on the marine sediments of Core MD98-2172, retrieved from the Eastern Timor Sea. Values of magnetic susceptibility in this core drop sharply down-core from -3.85 m deep below sediment/water interface and are very low at -5.35 m. However, both XRD and grain-size distribution results show no sudden change in terrigenous input during sedimentation. Mineral magnetic results indicate that the depth of -3.85 m may be an oxic/anoxic boundary. Therefore, the sediments below -3.85 m have been subjected to intense reductive diagenesis, whereas the sediments above -3.85 m are seldom affected. The magnetic properties of the sediments shallower than 3.85 m are dominated by pseudo-single domain （PSD） magnetite, with little down-core variation in its content and grain size. Below -3.85 m, the magnetic mineral assemblages that have survived in the sediments may record different stages of the reductive diagenesis： （1） the sediments from the 3.85-5.35 m interval are at the stage of iron oxide reduction; t＇SD magnetite is the major magnetic contributor, but it becomes less abundant and coarser down-core; （2） the sediments below -5.35 m are at the stage of sulphate reduction; ferrimagnetie minerals almost vanish and paramagnetic minerals contribute to down-core susceptibility variations, including pyrite as evidenced by high-temperature magnetic susceptibility measurements. However, the susceptibility variations below -5.35 m of Core MD98-2172 show obvious periodicity, despite the intense effect of reduetive diagenesis. Furthermore, the down-core susceptibility variations are coincident with fluctuations in the quantity of fine detrital particles （〈8 μm）, which may come mainly from the advection of the Indonesia Throughflow （ITF） and/or river input from Timor. Therefore, for Core MD98-2172, susceptibility variation below -5.35 m, which potentially correspond to fluctuations in the quantity of fine particles, may record the histories of the development of the ITF and precipitation on Timor.展开更多
Geothermal study shows that a higher geotemperature existed in the area in the middle Jurassic with volcanic eruption,subsequently cooling associated with block-faulting and rifting.There has been a thermal-cycle with...Geothermal study shows that a higher geotemperature existed in the area in the middle Jurassic with volcanic eruption,subsequently cooling associated with block-faulting and rifting.There has been a thermal-cycle with its higher geotemperature in the middle Jurassic since the late Paleozoic.The present geothermal gradient is from less than 3℃/100m to more than 5℃/100m, distributed in intersected short-belts.The terrestrial heat flow ranges from less than 40 mW.m-2 to more than 80mW.m-2, distributed in short-belts too. The distributing belts of the geothermal gradient and heat flow trend as the tectonic divisions in the area,and higher geothermal gradient or lower heat flow belt is corresponding to the positive tectonic division with lower Bouguer gravity anornaly.The tectonic development of the area is closely related to its geothermal evolution.展开更多
The Timor Sea is a typical depression-type (diwa-type) sedimentary basin.Three tectolithostratigraphic layers (units) can be recognised in the area, frorn bottorn to top,i. e. the Precarnbrian sequence corresponding t...The Timor Sea is a typical depression-type (diwa-type) sedimentary basin.Three tectolithostratigraphic layers (units) can be recognised in the area, frorn bottorn to top,i. e. the Precarnbrian sequence corresponding to the geosyncline unit (Ⅰ), with a probable NNE-SSW structural line, the Paleozoic to Triassic sequence belonging to the platform unit (Ⅱ) with a NW-SE structural grain, and the Jurassic to Cenozoic sequence being depression unit with a main NE-SW structural trend. The tectonic divisions in the area can be classified into two systems including thirteen divisions. The NE trending divisions and those trending NW intersect each other and the new ones overprint the older ones, forming a chess-board structural configuration. The Bouguer gravity anomaly in the area corresponds to its structure framework. Negative and positive anornalies alternatively distribute in short belts. Geothermal study show that higher heat flow existed in the area in late Jurassic with volcanic eruption, subsequently cooling and block-faulting. The terrestrial heat flow field is distributed in short-belts too, trending as the tectonic divisions in the area. The tectonic evolution of the area may be divided into at least three stages, i. e. the Precambrian stage, the (rifting) stage frorn Cambrian to Triassic, and the block-faulting-rifting stage from Jurassic to Cenozoic.展开更多
本文通过对IODP 363航次于澳大利亚西北岸外陆架上钻取的U1483站岩芯进行沉积物粒度、镁同位素以及主量元素成分等分析,重建200 ka以来帝汶海西南部沉积物输入演化及其指示的源区风化和侵蚀历史,探讨海洋沉积物中细粒硅质碎屑组分镁同...本文通过对IODP 363航次于澳大利亚西北岸外陆架上钻取的U1483站岩芯进行沉积物粒度、镁同位素以及主量元素成分等分析,重建200 ka以来帝汶海西南部沉积物输入演化及其指示的源区风化和侵蚀历史,探讨海洋沉积物中细粒硅质碎屑组分镁同位素的古环境指示意义。U1483站陆源碎屑组分主要由黏土质粉砂组成,其δ^(26)Mg变化范围超过0.25‰。通过计算化学蚀变指数(chemical index of alteration,CIA)和两种物理侵蚀指标(包括陆源物质堆积速率和Ti/Ca比值),结果显示200 ka以来δ^(26)Mg指标与CIA具有非常一致的曲线形态。本文推测陆源碎屑组分的Mg同位素组成主要反映物源区大陆硅酸盐风化强度的变化,而受矿物学分选、岩性和早期成岩作用的影响较小。结合区域古气候记录,我们发现本研究中的风化和侵蚀记录与同一个站位已发表的澳洲夏季风降水和表层海水温度变化具有较好的耦合关系,而与赤道太平洋海平面变化的相关程度较低,反映了轨道时间尺度上沉积物所记录的物源区风化和侵蚀演化主要受控于澳洲古季风系统,表现为气候驱动型风化模式。本研究δ^(26)Mg指标的应用为我们理解区域大陆风化及其对气候演化的响应和反馈机制提供了全新的同位素视角。展开更多
基金Supported by the National Basic Research Program of China (No. 2006CB701400)the National Natural Science Foundation of China (Nos. 40621002,40974035,40272074)Projects of Ministry of Education of China ("111" Project B07011,IRT0546)
文摘Detailed mineral magnetic measurements, integrated with grain-size distribution and X-ray diffraction （XRD） analyses, were made on the marine sediments of Core MD98-2172, retrieved from the Eastern Timor Sea. Values of magnetic susceptibility in this core drop sharply down-core from -3.85 m deep below sediment/water interface and are very low at -5.35 m. However, both XRD and grain-size distribution results show no sudden change in terrigenous input during sedimentation. Mineral magnetic results indicate that the depth of -3.85 m may be an oxic/anoxic boundary. Therefore, the sediments below -3.85 m have been subjected to intense reductive diagenesis, whereas the sediments above -3.85 m are seldom affected. The magnetic properties of the sediments shallower than 3.85 m are dominated by pseudo-single domain （PSD） magnetite, with little down-core variation in its content and grain size. Below -3.85 m, the magnetic mineral assemblages that have survived in the sediments may record different stages of the reductive diagenesis： （1） the sediments from the 3.85-5.35 m interval are at the stage of iron oxide reduction; t＇SD magnetite is the major magnetic contributor, but it becomes less abundant and coarser down-core; （2） the sediments below -5.35 m are at the stage of sulphate reduction; ferrimagnetie minerals almost vanish and paramagnetic minerals contribute to down-core susceptibility variations, including pyrite as evidenced by high-temperature magnetic susceptibility measurements. However, the susceptibility variations below -5.35 m of Core MD98-2172 show obvious periodicity, despite the intense effect of reduetive diagenesis. Furthermore, the down-core susceptibility variations are coincident with fluctuations in the quantity of fine detrital particles （〈8 μm）, which may come mainly from the advection of the Indonesia Throughflow （ITF） and/or river input from Timor. Therefore, for Core MD98-2172, susceptibility variation below -5.35 m, which potentially correspond to fluctuations in the quantity of fine particles, may record the histories of the development of the ITF and precipitation on Timor.
文摘Geothermal study shows that a higher geotemperature existed in the area in the middle Jurassic with volcanic eruption,subsequently cooling associated with block-faulting and rifting.There has been a thermal-cycle with its higher geotemperature in the middle Jurassic since the late Paleozoic.The present geothermal gradient is from less than 3℃/100m to more than 5℃/100m, distributed in intersected short-belts.The terrestrial heat flow ranges from less than 40 mW.m-2 to more than 80mW.m-2, distributed in short-belts too. The distributing belts of the geothermal gradient and heat flow trend as the tectonic divisions in the area,and higher geothermal gradient or lower heat flow belt is corresponding to the positive tectonic division with lower Bouguer gravity anornaly.The tectonic development of the area is closely related to its geothermal evolution.
文摘The Timor Sea is a typical depression-type (diwa-type) sedimentary basin.Three tectolithostratigraphic layers (units) can be recognised in the area, frorn bottorn to top,i. e. the Precarnbrian sequence corresponding to the geosyncline unit (Ⅰ), with a probable NNE-SSW structural line, the Paleozoic to Triassic sequence belonging to the platform unit (Ⅱ) with a NW-SE structural grain, and the Jurassic to Cenozoic sequence being depression unit with a main NE-SW structural trend. The tectonic divisions in the area can be classified into two systems including thirteen divisions. The NE trending divisions and those trending NW intersect each other and the new ones overprint the older ones, forming a chess-board structural configuration. The Bouguer gravity anomaly in the area corresponds to its structure framework. Negative and positive anornalies alternatively distribute in short belts. Geothermal study show that higher heat flow existed in the area in late Jurassic with volcanic eruption, subsequently cooling and block-faulting. The terrestrial heat flow field is distributed in short-belts too, trending as the tectonic divisions in the area. The tectonic evolution of the area may be divided into at least three stages, i. e. the Precambrian stage, the (rifting) stage frorn Cambrian to Triassic, and the block-faulting-rifting stage from Jurassic to Cenozoic.
文摘本文通过对IODP 363航次于澳大利亚西北岸外陆架上钻取的U1483站岩芯进行沉积物粒度、镁同位素以及主量元素成分等分析,重建200 ka以来帝汶海西南部沉积物输入演化及其指示的源区风化和侵蚀历史,探讨海洋沉积物中细粒硅质碎屑组分镁同位素的古环境指示意义。U1483站陆源碎屑组分主要由黏土质粉砂组成,其δ^(26)Mg变化范围超过0.25‰。通过计算化学蚀变指数(chemical index of alteration,CIA)和两种物理侵蚀指标(包括陆源物质堆积速率和Ti/Ca比值),结果显示200 ka以来δ^(26)Mg指标与CIA具有非常一致的曲线形态。本文推测陆源碎屑组分的Mg同位素组成主要反映物源区大陆硅酸盐风化强度的变化,而受矿物学分选、岩性和早期成岩作用的影响较小。结合区域古气候记录,我们发现本研究中的风化和侵蚀记录与同一个站位已发表的澳洲夏季风降水和表层海水温度变化具有较好的耦合关系,而与赤道太平洋海平面变化的相关程度较低,反映了轨道时间尺度上沉积物所记录的物源区风化和侵蚀演化主要受控于澳洲古季风系统,表现为气候驱动型风化模式。本研究δ^(26)Mg指标的应用为我们理解区域大陆风化及其对气候演化的响应和反馈机制提供了全新的同位素视角。
