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Sequence stratigraphy and distribution of organic-rich Lower Cretaceous mixed clastic-carbonate strata in Matruh Basin, northwestern Egypt: Constrains on the Tethyan sea level changes, palaeoclimate, and tectonics
Marine and Petroleum Geology ( IF 4.2 ) Pub Date : 2021-04-29 , DOI: 10.1016/j.marpetgeo.2021.105105
Amr S. Deaf

Integrated palynological, lithological, and geophysical analyses of the Lower Cretaceous (upper Hauterivian-Aptian) in Matruh Basin enabled conducting a high-resolution sequence stratigraphic analysis. Fluctuations of the continental/marine palynomorphs ratio reflect changes in the Tethyan 3rd order sea levels and are mirrored by eminent vertical changes in the spontaneous potential and the lithofacies. These are used with abundance of the marine phytoplanktons and opaque/translucent phytoclasts ratio to identify three 3rd order (SQ1: 132.4–120.8 Ma, SQ2: 120.8–115.2 Ma, and SQ3: 115.2–113 Ma) and seven 4th order genetic sequences and to study the impact of the allogenic and autogenic processes on their deposition.

Deposition of the deltaic clastic systems tracts of the lower-middle Alam El Bueib (late Hauterivian-early Barremian) and Dahab (late Aptian) formations reflect the interaction between the regional humid climate and the Tethyan 3rd order sea levels, which superimposed the Tethyan 2nd order sea level. Interferences of minor regional tectonics were also important. The argillaceous deposits possess large amounts of terrestrial organic matter of low hydrogen index (HI: 185.8–211.5 mg HC/g TOC) indicating gas organic facies. These deposits show relatively high organic richness (1.81–2.50 TOC wt %) due to relatively low sediment dilution and water circulation (i.e. suboxic-anoxic conditions) and high primary productivity due to high riverine nutrient inputs.

Deposition of the inner-middle shelf clastic-carbonate systems tracts of the upper Alam El Bueib and Alamein formations (latest Barremian-middle Aptian) reflects the interaction between the climatically induced low terrigenous influx and carbonate sedimentation due to shift to relatively dry climate, changes in the Tethyan 3rd order sea levels, and the middle Aptian regional minor uplift. These systems tracts show relatively large amounts of terrestrial organic matter, a notable marine organic matter signature, and intermediate HI (283.1–239.0 mg HC/g TOC) indicating gas/oil organic facies. The shales and siltstones are relatively organic richer (1.88–2.28 TOC wt %) than the pure and the argillaceous dolostones (1.46–1.94 TOC wt %). This organic richness is related to combined low sedimentation rates, low water circulation (i.e. dysoxic-suboxic to suboxic-anoxic conditions), and relatively high primary productivity.

Overall, the Tethyan sea level changes, regional climate, and regional tectonics played a major role in the deposition of the organic-rich syn-rift Lower Cretaceous deposits in Matruh Basin.



中文翻译:

埃及西北部马特鲁盆地富含有机质的下白垩统混合碎屑碳酸盐岩层序地层和分布:特提斯海平面变化,古气候和构造的约束

对马特鲁盆地下白垩统(上奥特里夫-阿普特上层)的综合孢粉,岩性和地球物理分析能够进行高分辨率层序地层分析。大陆/海洋古物形态比率的波动反映了特提斯三阶海平面的变化,并反映了自发势能和岩相的显着垂直变化。这些与大量的海洋浮游植物和不透明/半透明的植物破骨细胞比率一起用于鉴定三个三阶(SQ1:132.4–120.8 Ma,SQ2:120.8–115.2 Ma和SQ3:115.2–113 Ma)以及七个四阶遗传序列研究同种异体和自体过程​​对其沉积的影响。

下中层的Alam El Bueib(晚期Hauterivian-Barremian)和Dahab(晚期Aptian)地层的三角洲碎屑系沉积反映了区域湿润气候与Tethyan三阶海平面之间的相互作用。订单海平面。较小的区域构造的干扰也很重要。泥质沉积物具有大量的低氢指数(HI:185.8–211.5 mg HC / g TOC)的陆地有机质,表明有气体有机相。这些沉积物显示出相对较高的有机物富集度(1.81-2.50 TOC wt%),这是由于相对较低的沉积物稀释度和水循环(即低氧-缺氧条件),以及由于河流养分输入较高而产生的较高的初级生产力。

Alam El Bueib上部地层和Alamein地层(最新的Barremian-Aptian中部)内中层碎屑碳酸盐体系的沉积反映了气候变化引起的低陆源性涌入与碳酸盐沉积之间的相互作用,这是由于向相对干燥的气候转变所致。在特提斯三阶海平面和中部阿皮提地区轻微隆升。这些系统区域显示出相对大量的陆地有机质,明显的海洋有机质特征以及指示气/油有机相的中等HI(283.1–239.0 mg HC / g TOC)。页岩和粉砂岩相对于纯净的和泥质白云岩(1.46-1.94 TOC wt%)而言,有机物含量相对较高(1.88–2.28 TOC wt%)。这种有机丰富性与低沉淀率,低水循环(例如

总的来说,特提斯海平面的变化,区域气候和区域构造在马特鲁盆地富含有机裂隙的下白垩统沉积物中起着重要作用。

更新日期:2021-05-13
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