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

东非最早的原始人遗址哈达尔最近 时隔15年后重新开放研究 主要地质 上新世哈达尔组提供了机会， 它的位置沿着埃塞俄比亚 高原和阿法尔洼地， 暴露范围远远超出了哈达尔研究地点。 我们 将为所锁定的地层建立沉积相模型 一个非常好的地层/地质年代学框架。 的 以往的沉积学工作强调地层对比 并且只表明了非常普遍的沉积环境。 在目前海拔2.5公里的高原以东50公里处 这些上新统沉积物明显由70%的泥组成 单位和只有30%的沙子。 大多数泥浆都很大， 初期干旱古土壤 较小的层状泥质层序为 沉积在一个我们假设是从东方侵入的湖中 （阿法尔中部）。 虽然大规模的泥砂序列似乎 代表着蜿蜒河流的沉积物， 横向延伸，过度渐变成卵石砾岩 （向西向悬崖）现在解释 曲流模型 通过详细的亚相描绘和绘图，特别是在 通过对横向和纵向层序进行编目， 第一个系统的古水流数据，我们可以评估砂坪与 各种渠道化的流动选择。 对于我们希望 描绘不同成熟度的古土壤，以及湖泊是否 盐水或新鲜的。 仔细绘制沿着几个 等时凝灰岩表面将提供环境镶嵌 哈达尔的时间片 本研究应提供：（1） 阿法尔构造边界历史的重要部分; (2)关于原始人生活环境的知识 保存下来，并为他们探索广阔的战略， 哈达尔东部和西部的暴露，以及;（3）对 厚层快速冲积沉积的一般相模型， 席状砂与厚泥浆一起存在。

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.