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
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.
