Depositional characteristics and evolution of Miocene deep-water channel systems in block A of Lower Congo-Congo Fan Basin, West Africa
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摘要: 深水水道体系沉积演化特征及其控制因素研究是揭示大陆边缘“源—汇”过程和取得深水油气勘探突破的关键。下刚果—刚果扇盆地中新统发育有大型深水水道沉积,基于A区块的地震、测井、岩心等资料,利用地震属性分析等手段,阐述了中新统层序地层格架内深水水道体系的沉积特征、演化规律并讨论了其控制因素。区内中新统可划分为4个三级层序(SQ1-SQ4),大体对应于下中新统、中中新统下段、中中新统上段及上中新统。深水水道体系岩性上以砂岩为主,沉积单元包括水道、天然堤—溢岸、末端朵体和块体搬运沉积等。SQ1以发育弱受限—不受限的加积型水道或末端朵体为主,SQ2主要发育弱受限的侵蚀型—加积型水道,SQ3以受限侵蚀型水道的发育为主导,SQ4多见孤立侵蚀型过路水道。构造隆升与剥蚀、冰期气候以及海平面变化等因素,为深水水道的发育提供了充足物源并可能导致了该地区古地貌的坡度变化,从而影响了重力流作用的强弱并控制了深水水道体系的发育和演化,盐构造活动对深水水道的发育具有重要的改向、限制、封堵、迁移或破坏作用。Abstract: Researches on the depositional characteristics, evolution and constraining factors of deep-water channel systems are the key factors to reveal the "source-sink" process at continental margin and make big breakthroughs in deep-water hydrocarbon exploration. Based on the integrated analyses of seismic, well logging and core data, a sequence stratigraphic framework was established for the Miocene in block A of the Lower Congo-Congo Fan Basin, and then the sedimentary characteristics, evolution and constraining factors of the Miocene deep-water channel systems were purposed. The Miocene in the study area was divided into four third-order sequences, including the Lower Miocene (SQ1), the lower part of Middle Miocene (SQ2), the upper part of Middle Miocene (SQ3), and the Upper Miocene (SQ4). The Miocene deep-water channel deposits are dominated by sandstones and include four types of sedimentary units (deep-water channel deposits, levee-overbank, lobes and mass transport deposits). In the SQ1, weakly restricted-unrestricted depositional channels and lobes were formed. In the SQ2, weakly restricted erosional-depositional channels were developed. In the SQ3, erosional channels were dominant. In the SQ4, erosional isolated channels were widely recognized. Tectonic uplift, denudation, glacial climate and sea level change provided abundant sediment supplies for the development of gravity flow deposits. They might lead to the slope change of paleo-geomorphology in the study area, which further affected the strength of gravity flow and controlled the development and evolution of deep-water channel systems. Moreover, salt structures played important roles in redirecting, restricting, blocking, migrating and destroying the deep-water channels.
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图 8 下刚果—刚果扇盆地A区块中新统各三级层序(SQ1-SQ4)深水道体系发育和演化特征的RMS地震属性解释
IC.过路侵蚀型孤立水道; RC.受限侵蚀型复合水道; WRC.弱受限侵蚀—加积型水道; SL.弱受限—不受限加积型水道/末端朵体; AC.废弃水道; S.岩体
Figure 8. Interpretation of root mean square (RMS) amplitude seismic slice at the base of SQ1-SQ4, showing the development and evolution characteristics of the Miocene deep-water channel systems in block A, Lower Congo-Congo Fan Basin
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