Quantifying a tide-dominated, fluvial-wave influenced delta in Miocene facies of the Niger Delta Basin

IF 2 4区 地球科学 Q1 GEOLOGY
Sunny C. Ezeh, J. Bhattacharya
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Abstract

The modern Niger Delta has long been classified as a mixed tide-, wave- and fluvial-influenced delta. Still, no detailed studies have quantified the relative proportions of formative processes and facies. This work presents the first quantitative estimate of the relative influence of formative processes in Miocene deposits based on core data from the Greater Ughelli, Central and Coastal Swamp depositional belts of the Niger Delta Basin. Facies analysis of 288.2 m of core from 4 wells shows approximately 53% tidal facies, 33% fluvial facies and 14% wave-formed facies, indicating deposition in a prograding tide-dominated, fluvial- and wave-influenced delta. Cores from the Greater Ughelli and Central Swamp depobelts exhibit coarsening upwards, prograding deltaic facies successions overlain by fluvial mudstone. Tidal deposits in the Coastal Swamp depobelt show coarsening upwards prograding deltaic facies successions with well-developed tidal bundles indicating periodic deposition. The basal part of these facies successions also reveals repeated floods characterised by slump and load structures and dewatering features. Delta plain and delta front-prodeltaic facies associations are identified based on physical sedimentary and biological structures. The delta plain facies association consists of weakly bioturbated mudstone, fissile mudstone, and coarse-pebbly stratified sandstone facies with sparse trace fossils. The delta front-prodeltaic facies association contains muddy and sandy heteroliths, stratified, medium and coarse-grained, cross-bedded sandstone, and convoluted mudstone facies. The facies vary but characteristically contain trace fossil assemblages of the recently proposed Rosselia and Phycosiphon Ichnofacies, indicating delta front and prodeltaic settings, respectively. Variability in the facies is determined by the relative influence of hydrodynamic processes (tide, wave, and fluvial), variations in physicochemical stress, and the episodic character of deposition. In addition, based on the relative influence of each hydrodynamic processes, the facies differ through the successions, sometimes subtly.
量化尼日尔三角洲盆地中新世地层中以潮汐为主、受河道波影响的三角洲
现代尼日尔三角洲长期以来被归类为潮汐、波浪和河流混合影响的三角洲。然而,还没有详细的研究量化了形成过程和相的相对比例。本文基于尼日尔三角洲盆地大乌格里、中部和沿海沼泽沉积带的岩心数据,首次对中新世沉积形成过程的相对影响进行了定量估计。4口井288.2 m岩心的相分析显示,潮汐相约占53%,河流相约占33%,波浪相约占14%,表明沉积为一个以潮汐为主、河流和波浪影响的递进型三角洲。大乌格里和中央沼泽沉积带的岩心呈向上粗化、递进的三角洲相序列,上覆河流泥岩。滨海沼泽沉积带潮汐沉积表现为粗化向上推进的三角洲相序列,发育良好的潮汐束显示周期性沉积。这些相序列的基底部还显示出以滑塌、负荷构造和脱水特征为特征的反复洪水。根据物理沉积和生物构造,确定了三角洲平原和三角洲前缘-原三角洲相组合。三角洲平原相组合由弱生物扰动泥岩、易裂泥岩、粗砾层状砂岩相组成,化石稀少。三角洲前原三角洲相组合包括泥质和砂质杂岩、层状、中粒和粗粒、交错层状砂岩和卷曲泥岩相。该相变化多端,但具有新近提出的罗塞利亚相和藻虹河相的化石组合特征,分别表明三角洲前缘和前三角洲环境。相的可变性是由水动力过程(潮汐、波浪和河流)的相对影响、物理化学应力的变化和沉积的幕式特征决定的。此外,根据各水动力过程的相对影响,不同演替层序的相也有所不同,有时差别不大。
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来源期刊
CiteScore
3.80
自引率
5.00%
发文量
50
审稿时长
3 months
期刊介绍: The journal is broad and international in scope and welcomes contributions that further the fundamental understanding of sedimentary processes, the origin of sedimentary deposits, the workings of sedimentary systems, and the records of earth history contained within sedimentary rocks.
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