卵石形态计量学分析在验证输移过程和解释古环境中的应用——以尼日利亚尼日尔三角洲盆地Ogwashi组(渐新世)为例

IF 0.9 Q3 GEOLOGY
O. B. Ogbe, J. Osokpor, Chukwunomso V. Emelue, A. Ocheli
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引用次数: 0

摘要

摘要本文通过对卵石的形态计量分析,讨论了对渐新世Ogwashi组(尼日利亚尼日尔三角洲盆地)的古环境解释,这是一种基本上依赖于对卵石大小和形状的定量评估的研究方法,卵石在一系列沉积环境中的迁移过程中会发生变化。独立函数的二元图和三元图的关系是从尼日利亚阿萨巴附近伊布萨采石场新暴露的砂岩剖面中确定的。卵石的粒径从细(11.00 mm)到极粗(41.33 mm)不等,平均粒径为21.05 mm(粗卵石)。平坦度指数与最大投影球度指数的二元图显示,37%的卵石落在海滩(海洋)环境中,33%落在河流环境中;剩下的30%是不确定的。最大投影球度指数与扁长指数二元图表明,47%的卵石落在海洋环境中,22%落在河流环境中,其余31%不确定。球度-形状三元图显示,卵石主要包括比例几乎相等的带刃、板状、极带刃和极板状,以及较小的细长和极细长的石头,这表明卵石的来源多种多样。球度形式二元图表明,卵石主要为圆盘形和叶片形,少量为球形和杆状。在二元图和三元图的不同区段中,卵石的比例几乎相等,卵石粒度和形状的广泛分布表明,Ogwashi组由再沉积沉积物组成,这些沉积物可能是在海洋和河流环境的混合环境中运输和沉积的,可能存在过渡环境。换句话说,卵石可以被解释为边缘海洋环境中受海洋影响的河流沉积物。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Morphometric analysis of pebbles in verification of transport processes and interpretation of palaeoenvironment: A case study from the Ogwashi Formation (Oligocene), Niger Delta Basin, Nigeria
Abstract The present paper discusses a palaeoenvironmental interpretation of the Oligocene Ogwashi Formation (Niger Delta Basin, Nigeria) through morphometric analysis of pebbles, a research method essentially depending on the quantitative evaluation of pebble size and shape which change during transport processes in a range of depositional environments. The relationship of bivariate and ternary-diagram plots of independent functions was determined from freshly exposed sandstone sections in quarries at Ibusa, near Asaba, Nigeria. The grain size of pebbles ranges from fine (11.00 mm) to very coarse (41.33 mm), with a mean size of 21.05 mm (coarse pebbles). A bivariate plot of the flatness index vs maximum projection sphericity index shows 37% of the pebbles to fall within a beach (marine) environment, and 33% within a fluvial environment; the remaining 30% are uncertain. The maximum projection sphericity index vs oblate-prolate index bivariate plot indicates that 47% of pebbles fall within a marine environment and 22% within a fluvial environment, while the remaining 31% are uncertain. The sphericity-form ternary diagram plot shows that the pebbles primarily comprise bladed, platy, very bladed and very platy of near-equal proportions with minor elongate and very elongate stones, which suggests that the pebbles are diverse in origin. The sphericity-form bivariate plot indicates that the pebbles are largely of disc and blade shapes with a minor number of spherical and rod shapes. The near-equal proportion of pebbles in different segments of the bivariate and ternary diagram plots, and the wide distribution of the pebble grain sizes and shapes suggest the Ogwashi Formation is composed of redeposited sediments that likely were transported and deposited in a mix of marine and fluvial settings with possible transitional environments. In other words, the pebbles can be interpreted as marine-influenced fluvial sediments in marginal-marine settings.
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来源期刊
Geologos
Geologos GEOLOGY-
CiteScore
1.70
自引率
0.00%
发文量
7
审稿时长
12 weeks
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