Measuring Ancient Rates of Weathered Petroleum Accumulation in the South China Sea

IODP第367号和第368号探险队正在南中国海某些地点向基底钻探沉积序列。这是为了研究构造裂谷过程中的地壳裂解机制。这样的裂谷作用形成了一个沉积盆地，随后又被沉积物填满。南中国海沉积充填物来源于中国南部及周边多个腹地，既有生产性含油气系统，也有非生产性含油气系统。这些含油气腹地内的地层受到侵蚀，含油气沉积物随后通过河流输送到南中国海，将导致地质时期沉积物中微量石油的聚集。测量剩余石油是复杂的，因为石油的大多数成分在地球表面降解，只留下最具化学抵抗力的成分。用GC-MS分析沉积物的有机含量可以检测出风化石油中存在的几种化合物类型，但随着风化程度的增加，可以检测到的数量减少。最终，只剩下最沥青和最重的石油成分。这些剩余石油很难分析，因此将采用一种新的基于表面增强拉曼散射的方法对南中国海区的样品进行分析。这种方法具有很高的灵敏度，能够检测出十亿分之几的残余石油。在这方面使用新开发的分析微量风化石油和残留石油的方法，将大大有助于它们的试验和发展。这一发展需要为常规环境基线监测以及更一般的石油和油类分析准备这些技术。在该项目期间，将使用便携式仪器在船上活动期间进行测量，然后与基于实验室的测量进行比较。这种离岸方法和实验室方法的比较是开发可在需要时应用的方法的关键。从地球科学和自然科学的角度来看，以这种方式在固定的位置研究地质时期的风化石油聚集有许多好处和优势。其中之一是在沉积物中获得先于人类的石油基线；例如，对人类开始开采石油之前沉积的沉积物进行测量。另一个好处是可以获得该遗址在其漫长的地质历史中经历的多种气候和沉积模式的数据。这有助于理解现代气候变化可能如何影响自然环境中石油的衰减。

IODP expeditions 367 and 368 are drilling sedimentary successions to basement at locations in the South China Sea. This is to investigate crustal-break up mechanisms during tectonic rifting. Rifting in this way creates a sedimentary basin which is subsequently filled by sediment. The sediment-fill within the South China Sea is derived from a number of hinterlands in Southern China and neighboring countries in which there are both productive and non-productive petroleum systems. The erosion of formations within these petroleum-bearing hinterlands, and the subsequent transport of the petroleum-bearing sediments to the South China Sea by river, will have lead to the accumulation of trace amounts of petroleum within sediments over geological time. Measuring residual petroleum is complicated because most of the components of petroleum degrade at the Earth's surface, leaving only the most chemically resistant components behind. Analysis of the organic content of sediment by GC-MS can detect a few of the compound-types present in weathered petroleum, but with increased weathering the amount that can be detected decreases. Eventually only the most asphaltic and heavy petroleum-components remain. This residual petroleum is difficult to analyse, and so for South China Sea samples will be analysed by a new surface enhanced Raman scattering-based method. This method is highly sensitive and capable of detecting sub parts per billion levels of residual petroleum. The use of newly developed methods for analysing trace amounts of weathered and residual petroleum in this context will greatly help in their trial and development. This development is needed to prepare these technologies for routine environmental base-line monitoring as well as more general petroleum and oil analysis. During this project measurements will be made during shipboard activities using a portable instrument, and then compared to laboratory-based measurements. This comparison of off-shore and laboratory methods is key for developing methods that can be applied at point of need. From a geoscience and natural science perspective, examining weathered petroleum accumulation over geological time in this way, at a fixed position, has a number of benefits and advantages. One of these is access to a pre-human baseline for petroleum within sediments; e.g. measurements are made on sediments deposited before human exploitation of petroleum began. Another benefit is access to data from the multiple climatic and depositional modes experienced by the site over the it's long geological history. This helps to understand how climate change in the modern era may affect the attenuation of petroleum in the natural environment.