Sedimentary and petrophysical characteristics of various turbidites at IODP Sites U1499 and U1500 in the northern South China Sea
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摘要:
深海浊流沉积是重要的油气和天然气水合物勘探目标，对古海洋、古环境、古构造乃至古气候等方面的研究具有重要的科学意义。前人对于浊积岩的研究多从沉积学角度进行，从岩石物理角度开展的相关研究很少。本文将岩芯宏观沉积学分析、薄片（或涂片）分析与岩石物性分析相结合，研究南海海盆北部IODP 367航次U1499、U1500站位浊流沉积的沉积特征和岩石物理响应。共识别出了3类浊积岩：钙质、陆源碎屑和陆源碎屑—钙质混积浊积岩，以陆源碎屑和混积浊积岩最发育。不同类型的浊积岩表现出不同的岩石物性特征：钙质浊积岩表现为低磁化率、高颜色反射率亮度、密度变化较大和低自然伽马；陆源碎屑浊积岩表现为低磁化率、中—低亮度、中—高密度、中—低自然伽马；混积浊积岩的磁化率、亮度和自然伽马变化大，密度中—高。南海海盆浊积岩的丰度在发育时间上以晚中新世和中—晚更新世最高，然后依次为早更新世、上新世和早—中中新世。晚中新世和中—晚更新世全球海平面总体处于低位时期，有利于浊积岩的发育。自晚中新世以来，南海海盆钙质浊积岩的丰度总体呈逐渐减少趋势，可能与南海海盆水深逐渐加大、碳酸盐沉积逐渐萎缩等因素有关。
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关键词:
- 浊流沉积 /
- 岩石物性 /
- IODP 367航次 /
- 海盆 /
- 南海
Abstract:The deep-sea turbidite is an important target for petroleum and gas hydrate exploration, and is of significance to paleoceanographic, paleoenvironmental, paleotectonic and paleoclimatic researches. Turbidites have been investigated mostly in a sedimentological and less in a petrophysical perspective. In this paper, cores and thin sections (and /or smear slides) are used to study the sedimentary characteristics and petrophysical responses of the turbidites at the IODP Sites of U1499 and U1500 in the northern part of the South China Sea (SCS). Three types of turbidites are identified, i.e. the calcareous, terrigenous, and terrigenous-calcareous mixed turbidites. The later two types dominate. Each type of turbidites has its own petrophysical characteristics. The calcareous turbidites are characterized by low magnetic susceptibility, high brightness in color reflectance spectrometry, variable density, and low natural gamma radiation; the terrigenous turbidites characterized by low magnetic susceptibility, low to medium brightness, medium to high density, and medium to low natural gamma radiation; and the mixed turbidites characterized by variable magnetic susceptibility, brightness and natural gamma radiation and medium to high density. The turbidites mainly occur in the late Miocene and the middle-late Pleistocene sequences, followed by the early Pleistocene, the Pliocene, and the early-middle Miocene. The euatatic lowstand periods in the late Miocene and middle-late Pleistocene could be favorable for the deposition of the turbidites in the SCS. The gradual decrease in the abundance of calcarous turbidites since late Miocene could be associated with the gradual deepening of the oceanic basin and the shrinking of carbonate depositional area in the SCS.
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Key words:
- turbidites /
- petrophysical properties /
- IODP Expedition 367 /
- oceanic basin /
- South China Sea
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