花东海盆浊流沉积的磁性特征及其环境意义

对取自台湾以东花东海盆GX168孔的浊流沉积物进行系统的岩石磁学研究,揭示其沉积学和岩石磁学特征,分析其物源和形成机制.研究结果显示,剖面上共识别出12层浊流沉积物,其分布存在规律,下部350~700cm共发育11层浊流沉积物,而0~350cm仅出现1层浊流沉积物.浊流沉积物粒径明显较背景沉积物粗,石英、长石含量更高,底部与下伏背景沉积呈突变接触,顶部与上覆背景沉积呈渐变接触,内部发育典型的正粒序韵律结构.浊流沉积物和背景沉积物具有相似的磁学特征,两者均以磁铁矿为主要载磁矿物类型,且磁铁矿颗粒均以准单畴和多畴颗粒为主.同时,两者也存在一定差异,浊流沉积物中磁铁矿较背景沉积物更为富集,磁化率和饱和等温剩磁更强,磁铁矿粒径更粗,这与浊流沉积物原始沉积区更靠近物源区有关.花东海盆浊流沉积形成的诱发机制可能是末次冰期以来频发的海平面波动造成陆坡之上沉积物重力失稳,导致陆坡沉积物向海盆搬运.

Magnetic properties of turbidites in the Huatung Basin and their environmental implications

Turbidity currents are part of a continuum of sediment-gravity flows, and are traditionally defined as those sediment-gravity flows in which sediment is suspended by fluid turbulence. Turbidity currents are principal mode of transportation of clastic grains to the deep ocean. The occurrence of turbidity current plays an important role in the formations of canyon, submarine fan and deep-sea oil. Previous study shows lots of turbidite records were identified in the West Philippine Sea and adjacent regions. However, few works focus on the magnetic properties of the turbidites in this area. In this paper, systematic rock-magnetism measurements, including magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization, saturation isothermal remanent magnetization, thermomagnetism and hysteresis loops were performed on the marine sediments of core GX168 from the Huatung Basin to uncover the sedimentological characteristics and magnetic features of turbidite sequences and the differences with the background sedimentation, also, further explore the provenance and formation mechanism.#br#There are overall 12 turbidite layers in the core GX168. There was significant regularity in the distribution of turbidite on profile:11 turbidite layers distributed in the interval from 350 cm to 700 cm in depth, but only one turbidite layer was found from the interval of 0~350 cm in depth. The results show turbidite characterized by sand and silty sand in lithology contain more coarse sediment grains than background sedimentation with dominant lithology of clay. The content of quartz and feldspar in turbidite is higher than that of background sedimentation, which is the reason of lighter colors of turbidite than that of background sedimentation. The contact between bottom boundary of turbidite succession and underlying sediments is generally sharp and instant; while the contact between the top boundary of turbidite and overlying sediments is transitional transition. The turbidite is characterized by typical graded bedding sequence.#br#Turbidite and background sedimentation share similar magnetic properties including:magnetites are the dominant magnetic carries for both of them, and the grain sizes of magnetite particles are both pseudo-single-domain (PSD) and multi-domain (MD). However, there are some differences between them:the turbidite enrich more magnetic minerals than background sedimentation obviously; the magnetic susceptibility and saturation isothermal remanent magnetization of turbidite is stronger in comparison to that of background sedimentation, and the grain size of magnetite in turbidite is coarser than that of background sedimentation. The similar magnetic properties between the turbidite and background sedimentation suggest the same provenance. However, the differences of concentration and grain size between them were resulted by primary depositional setting of turbidite closer to the provenance than background sedimentation. The occurrence of these turbidity currents sedimentation in the Huatung basin is implied to be potentially related to the gravity-induced slumping of sediments on slope (e.g. slope failure) that caused by sea-level fluctuation frequently during the Last Glaciation, and the sediments on the slope were transported to the deep basin.