Late Cretaceous volcanism and fluid circulation in the South Atlantic: Insights from continental carbonates in the onshore Namibe Basin (Angola)
Late Cretaceous volcanism and fluid circulation in the South Atlantic: Insights from continental carbonates in the onshore Namibe Basin (Angola)
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DOI：
10.1016/j.marpetgeo.2021.105351
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发表时间：
2021-09
影响因子：
4.2
通讯作者：
E. Fiordalisi;M. Marchegiano;C. John;N. Oxtoby;N. Rochelle-Bates;G. do Couto Pereira;V. Machado;R. Dixon;I. Sharp;S. Schröder
中科院分区：
文献类型：
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作者：
E. Fiordalisi;M. Marchegiano;C. John;N. Oxtoby;N. Rochelle-Bates;G. do Couto Pereira;V. Machado;R. Dixon;I. Sharp;S. Schröder
纳米贝盆地发育于早白垩世，是非洲和南美洲之间的南大西洋裂谷系统的一部分。岩浆活动发生在同裂带(瓦兰吉尼亚-豪特里亚)和裂谷后(科尼亚西-早坎帕尼亚)阶段，后者触发了流体循环事件，对储集层质量和油气远景产生了重大影响。马里基塔成员(Mb.)在晚白垩世岩浆脉冲期间形成，并记录了相关的流体循环。因此，对这些碳酸盐岩的研究提供了对古流体来源和循环路径的洞察，最终有助于约束成岩阶段，它们对储集层质量的影响，以及油气的再动员。通过整合野外、岩相和地球化学数据，研究碳酸盐岩。碳酸盐岩在地层上受上白垩统岩浆岩的约束，并构成一系列与断层有关的泉丘系统，横向进入湖泊沉积。主要成岩作用包括普遍的白云石化、硅化作用和多期压裂作用。白云石化过程中的流体温度在∼32℃至56℃之间，而硅化作用发生在∼70℃至260℃之间。流体可能遵循断层控制的对流循环路径。流体成分由负碳同位素、富氧和锶同位素以及稀土元素数据显示的渗入/变质的大气和海水组成。流体改造是通过与地下岩石单元的相互作用进行的，如基底、火山/硅质碎屑含水层和蒸发岩。然而，硅化过程中较高的温度也可能表明岩浆流体的晚期贡献。孔隙度内的沥青可能反映了岩浆流体驱动的区域性油气动员过程。
The Namibe Basin developed in the Early Cretaceous as part of the South Atlantic rift system between Africa and South America. Magmatic activity occurred during the syn-rift (Valanginian-Hauterivian) and post-rift (Coniacian-Early Campanian) phases, with the latter triggering fluid circulation events that had significant impacts on reservoir quality and hydrocarbon prospectivity. The continental carbonates of the Mariquita Member (Mb.) developed during the Late Cretaceous magmatic pulse and record the associated fluid circulation. Thus, study of these carbonates provides insights into paleo-fluid sources and circulation pathways, which can ultimately help to constrain diagenetic phases, their effects on reservoir quality, and hydrocarbon re-mobilisation.This study analyses the tectonostratigraphic setting, facies and diagenesis of the Mariquita Mb. carbonates by integrating field, petrographic and geochemical data. The carbonates are stratigraphically bound by Upper Cretaceous magmatic rocks, and constitute a series of fault-associated spring mound systems that pass laterally into lacustrine sediments. The main diagenetic events include pervasive dolomitisation, silicification and multi-stage fracturing. Fluid temperatures during dolomitisation were between ∼32 and 56 °C, while silicification occurred between ∼70 and > 260 °C. Fluids likely followed fault-controlled convective circulation pathways. The fluid compositions comprised infiltrated/modified meteoric and marine waters, as suggested by negative carbon isotopes, enriched oxygen and strontium isotopes, and REE data. Fluid modification occurred via interaction with subsurface rock units, such as basement, volcanic/siliciclastic aquifers and evaporites. However, higher temperatures during silicification could suggest late contributions from magmatic fluids too. Bitumen within porosity possibly reflects regional hydrocarbon mobilisation processes driven by magmatic fluids.