COLLABORATIVE RESEARCH: Sedimentology and Environment of Deposition of the Hadar Formation, Ethiopia

合作研究：埃塞俄比亚哈达尔地层的沉积学和沉积环境

• 批准号: 9206516
• 负责人: Carl Vondra
• 金额: $ 8.28万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1992
• 资助国家: 美国
• 起止时间: 1992-07-15 至 1994-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9206516&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Sedimentology; Environment; Deposition

The premier East African hominid site of Hadar recently reopened for research after a 15 year lapse. Major geologic opportunities are offered by the Pliocene Hadar Formation because of its setting along the tectonic margin between the Ethiopian Plateau and the Afar Depression with an outstanding badlands exposure that extends well beyond the studied site of Hadar. We will build a facies model of deposition for the formation pegged to a very good stratigraphic/geochronologic framework. The previous sedimentological work stressed stratigraphic correlation and suggested only very generalized environments of deposition. Being just 50 km east of the presently 2.5 km high Plateau escarpment, these Pliocene deposits remarkably consist of 70% mud units and only 30% sands. Most of the muds are massive with incipient arid paleosols. Minor laminated mud sequences were deposited in a lake we hypothesize transgressed from the east (central Afar). While the massive mud sand sequence seems to represent deposits of a meandering river the sands are too laterally extensive and too gradational into cobble conglomerates (westward toward the escarpment) to be explained by presently available meandering stream models. By delineating and mapping detailed subfacies, especially in the sands and by cataloging lateral and vertical sequences and the first systematic paleocurrent data, we can assess sandflat versus various channelized flow options. For the muds we hope to delineate paleosols of varying maturity, and whether the lake was saline or fresh. Careful facies mapping along the several isochronal tuff surfaces will provide environmental mosaic time-slices across Hadar. This research should provide: (1) a significant segment of the history of the Afar tectonic boundary; (2) knowledge of the environments where the hominids lived and were preserved, and a strategy for exploring for them in the vast exposures east and west of Hadar, and; (3) a contribution toward a general facies model for thick rapid alluvial deposition where sheets sands exist in association with thick muds.

东非首屈一指的原始人类遗址哈达尔 (Hadar) 最近在时隔 15 年之后重新开放供研究。 上新世哈达尔地层提供了主要的地质机会，因为它位于埃塞俄比亚高原和阿法尔凹陷之间的构造边缘，具有突出的荒地暴露，远远超出了哈达尔研究地点。 我们将为地层建立一个沉积相模型，与一个非常好的地层/地质年代学框架挂钩。 以前的沉积学工作强调地层相关性，并且只提出了非常普遍的沉积环境。 这些上新世沉积物位于目前 2.5 公里高的高原悬崖以东仅 50 公里处，由 70% 的泥单元和仅 30% 的沙组成。 大多数泥浆都是大量的，含有早期干旱的古土壤。 少量层状泥浆序列沉积在一个湖泊中，我们假设该湖是从东部（阿法尔中部）侵入的。 虽然大量的泥砂层序似乎代表了蜿蜒河流的沉积物，但沙子横向范围太广，并且渐变成卵石砾岩（向西朝向悬崖），无法用目前可用的蜿蜒河流模型来解释。 通过描绘和绘制详细的亚相，特别是在砂中，并通过对横向和垂直序列进行编目以及第一个系统的古水流数据，我们可以评估沙坪与各种渠道化流动选项。 对于泥浆，我们希望能够描绘出不同成熟度的古土壤，以及该湖是咸水湖还是淡水湖。 沿着几个等时凝灰岩表面仔细绘制相图将提供整个哈达尔的环境马赛克时间切片。 这项研究应提供：（1）阿法尔构造边界历史的重要部分； (2) 对原始人类生活和保存环境的了解，以及在哈达尔东部和西部广阔地区探索原始人类的策略； （3）对厚层快速冲积沉积的一般相模型的贡献，其中席状砂与厚层泥浆共存。