Paleoenvironments of the earliest stone toolmakers, Gona, Ethiopia
Paleoenvironments of the earliest stone toolmakers, Gona, Ethiopia
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DOI：
10.1130/b25358.1
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发表时间：
2004-11
影响因子：
4.9
通讯作者：
J. Quade;N. Levin;Sileshi Semaw;D. Stout;P. Renne;Michael J. Rogers;S. Simpson
中科院分区：
文献类型：
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作者：
J. Quade;N. Levin;Sileshi Semaw;D. Stout;P. Renne;Michael J. Rogers;S. Simpson
沿着阿瓦什河（埃塞俄比亚）北部的Hadar和Busidima组的河流-湖泊沉积物记录了近300万年（3.4至<0.6 Ma）的人类进化，包括最早的2.5-2.6 Ma的石器制作记录。本文汇集了来自两个地层的早期古人类的沉积学和同位素证据，但特别强调了早期工具制造者的环境。前2.92 Ma记录（Hadar组）的特征是低梯度的河流、古滩和湖泊沉积，其未被分割的地形与现代阿瓦什河中部靠近Gewane的河段最相似。Gona地区经历了阿瓦什河（Awash River）的多次深度切割和沉积，从2.92 -约2.7 Ma开始，一直持续到<0.6 Ma （Busidima组）。每层沉积演替的厚度为10 ~ 20 m，从底部的砾岩到顶部的盖层古土壤依次向上扩展。在这一时期，以这些向上倾斜的序列为代表的祖先阿瓦什主要是蜿蜒的，向东北流动，就像今天一样。在Busidima组中，也广泛地暴露出了向轴向冲刷体系分支的较小河道。与轴系砾岩相比，支流河道输送的火山碎屑更细、更不成熟，夹杂着大量从邻近的坏地改造而来的碳酸盐结核。在最古老的考古遗址中发现的石器（Oldowan; 2.6-2.0 Ma）只与轴向冲刷系统有关，在层状粉砂或覆盖古土壤的向上序列中。这些工具是用河道上的圆形鹅卵石制成的，但这些工具的制造和使用总是远离河道的沙洲，在附近的沙洲和以淤泥为主的泛滥平原上。记录中较高的考古遗址（阿舍利，<1.7 Ma）出现在类似的轴向河流环境中，以及远离人工制品原料来源的支流河道。哈达尔组和布西底马组成熟古土壤多为灰褐色至深褐色的垂向土，具有丰富的粘土质滑面、伪背斜和垂向裂缝、碳酸盐结核等特征。这样的钙性倒伏在今天的地区很常见，这表明过去3.4万年的古气候是半干旱的，季节性很强。从versols中成土碳酸盐的碳同位素结果可以重建c3植物（树木和灌木）与c4植物（草）在时间上的比例。δ 13
Fluvio-lacustrine sediments of the Hadar and Busidima Formations along the northern Awash River (Ethiopia) archive almost three million years (3.4 to <0.6 Ma) of human evolution, including the earliest documented record of stone toolmaking at 2.5–2.6 Ma. This paper brings together sedimentologic and isotopic evidence for the paleoenvironmental context of early hominids from both formations, but with particular emphasis on the setting for the early toolmakers. The pre–2.92 Ma record (Hadar Formation) is characterized by low-gradient fl uvial, paludal, and lacustrine deposition in an undissected topography most analogous to reaches of the modern middle Awash River near Gewane. The Gona area experienced repeated deep dissection and aggradation by the Awash River, starting between 2.92 and ca. 2.7 Ma and continuing through the top of the record at <0.6 Ma (Busidima Formation). Each aggradational succession is 10–20 m in thickness and fi nes upward from wellrounded conglomerates at the base to capping paleosols at the top. During this period the ancestral Awash represented by these fi ning upward sequences was dominantly meandering and fl owed northeast, as it does today. Smaller channels tributary to the axial Awash system are also extensively exposed in the Busidima Formation. Compared to the axial-system conglomerates, the tributary channels transported fi ner, less mature volcanic clasts mixed with abundant carbonate nodules reworked from adjacent badlands. Stone artifacts (Oldowan; 2.6–2.0 Ma) at the oldest archaeological sites are only associated with the axial Awash system, in the bedded silts or capping paleosols of the fi ning upward sequences. The implements were made from rounded cobbles from the channels, but manufacture and use of the tools was always away from the channel bars, on the nearby sandy banks and silt-dominated fl oodplains. Archaeological sites higher in the record (Acheulian; <1.7 Ma) occur in similar axial river contexts, as well as along tributary channels further removed from artifact raw material sources. Mature paleosols in the Hadar and Busidima Formations are mostly pale to darkbrown Vertisols typifi ed by abundant clay slickensides, pseudo-anticlinal and vertical fracturing, and carbonate nodules. Such calcic Vertisols are common in the region today, demonstrating that the paleoclimate over the past 3.4 m.y. has been semi-arid and strongly seasonal. Carbon isotopic results from pedogenic carbonates in the Vertisols allow reconstruction of the proportion of C 3 plants (trees and shrubs) to C 4 plants (grasses) through time. The δ 13