Discrimination, correlation, and provenance of Bed I tephrostratigraphic markers, Olduvai Gorge, Tanzania, based on multivariate analyses of phenocryst compositions
Discrimination, correlation, and provenance of Bed I tephrostratigraphic markers, Olduvai Gorge, Tanzania, based on multivariate analyses of phenocryst compositions
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DOI：
10.1016/j.sedgeo.2016.03.026
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发表时间：
2016-06-15
影响因子：
2.8
通讯作者：
Deino, Alan L.
中科院分区：
文献类型：
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作者：
Habermann, Joerg M.;McHenry, Lindsay J.;Deino, Alan L.
更新世动植物年表，包括坦桑尼亚奥杜瓦伊峡谷I层的古人类遗骸和相关的Oldowan工业，主要基于对夹层凝灰岩和熔岩的40Ar/39Ar测年，并结合盆地内详细的化石地层对比。尽管已经建立了奥杜瓦伊盆地东部的高分辨率年代地层格架，但西部次盆地的知名度较低，部分原因是I层内的主要侧向相变化和不连续的暴露。我们使用凝灰岩、火山碎屑砂岩、硅屑单元和熔岩中主要年轻矿物相(辉石、斜长石、斜长石)的化学成分的区分能力来解决这些对比困难。应用主成分分析和判别分析，对电子探针显微分析获得的这些成分进行了统计评价，建立了判别模型，成功地对大多数I层火山单元进行了分类。所有目标矿物的综合分析所产生的对比，提供了与已知地质背景一致的横向和垂直高分辨率的盆地范围I层化学地层学框架，扩展和完善了现有的地球化学数据库。通过对比第一断层近端的褐沸石与西部盆地下一层的中部和远端的层序，可以评估侧向相变和厚度趋势，从而确认恩戈罗戈罗火山是下一层的主要来源，而上一层的沉积物供应主要来自奥尔莫蒂火山。凝灰岩IA、I层熔岩和Mafic Tuff II和III单颗粒指纹的成分相似性，以及I层熔岩向北和西北方向的减薄，表明这些单元有共同的恩戈罗来源。在此应用的技术改进了以前的工作，通过用统计的严谨性来评估成分亲和力，而不是主要依赖于双变量曲线图的视觉比较。(C)2016爱思唯尔B.V.保留所有权利。
The chronology of Pleistocene flora and fauna, including hominin remains and associated Oldowan industries in Bed I, Olduvai Gorge, Tanzania, is primarily based on 40Ar/39Ar dating of intercalated tuffs and lavas, combined with detailed tephrostratigraphic correlations within the basin. Although a high-resolution chronostratigraphic framework has been established for the eastern part of the Olduvai Basin, the western subbasin is less well known due in part to major lateral facies changes within Bed I combined with discontinuous exposure. We address these correlation difficulties using the discriminative power of the chemical composition of the major juvenile mineral phases (augite, anorthoclase, plagioclase) from tuffs, volcaniclastic sandstones, siliciclastic units, and lavas. We statistically evaluate these compositions, obtained from electron probe micro-analysis, applying principal component analysis and discriminant analysis to develop discriminant models that successfully classify most Bed I volcanic units. The correlations, resulting from integrated analyses of all target minerals, provide a basin-wide Bed I chemostratigraphic framework at high lateral and vertical resolution, consistent with the known geological context, that expands and refines the geochemical databases currently available. Correlation of proximal ignimbrites at the First Fault with medial and distal Lower Bed I successions of the western basin enables assessment of lateral fades and thickness trends that confirm Ngorongoro Volcano as the primary source for Lower Bed I, whereas Upper Bed I sediment supply is mainly from Olmoti Volcano. Compositional similarity between Tuff IA, Bed I lava, and Mafic Tuffs II and III single-grain fingerprints, together with north- and northwestward thinning of Bed I lava, suggests a common Ngorongoro source for these units. The techniques applied herein improve upon previous work by evaluating compositional affinities with statistical rigor rather than primarily relying on visual comparison of bivariate plots. (C) 2016 Elsevier B.V. All rights reserved.