Department of Geosciences, University of Wisconsin-Milwaukee, 3209 N. Maryland Ave., Milwaukee, WI 53211, USA.
Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Brownlow Street, Liverpool, L69 3GP, United Kingdom; Stone Age Institute, 1392 W Dittemore Road, Gosport, IN, 47433, USA.
J Hum Evol. 2018 Jul;120:7-18. doi: 10.1016/j.jhevol.2017.12.006. Epub 2018 Apr 12.
Tuffaceous marker beds, derived from volcanic products from the Ngorongoro Volcanic Highlands, help define a stratigraphic framework for the world-renowned fossil and stone tool record exposed at Olduvai Gorge, Tanzania. However, previous efforts to constrain this tuff record, especially for Olduvai Bed II, have been limited because of erosion, contamination, reworking, and the alteration of volcanic glass under saline-alkaline conditions. This paper applies previously defined geochemical and mineralogical "fingerprints" for several major Bed II marker tuffs, based on glass (where available) and phenocrysts more resistant to alteration (feldspar, hornblende, augite, and titanomagnetite), to tuffs from stratigraphic sections in the Olduvai Junction Area, including previously and recently excavated Acheulean and Oldowan sites (HWK EE (Locality (Loc) 42), EF-HR (Loc 12a), FLK (Loc 45), and MNK (Loc 88)). The Middle Bed II Bird Print Tuff (BPT) is found to be more compositionally variable than previously reported but is still valuable as a stratigraphic marker over short distances. The confirmation of blocks of Tuff IID in conglomerate helps constrain Upper Bed II stratigraphy at sites where in-situ tuffs are absent. This paper also compiles the results of published geochronological research, providing stratigraphic context and updating previously reported dates using a consistent Ar/Ar reference standard age. The results of this work support the following paleoanthropologically relevant conclusions: 1) the early Acheulean site EF-HR (Loc 12a) is situated above the level of Hay's Tuff IIC, and thus sits in Upper rather than Middle Bed II, (2) the HWK EE (Loc 42) Oldowan site is constrained between Tuff IIA and Tuff IIB, just above the boundary between Lower and Middle Bed II, and 3) the Acheulean site at FLK W most likely lies within the Middle Augitic Sandstone, above Tuff IIB, similar to the placements by Leakey and Hay for the earliest Acheulean at Olduvai.
凝灰岩标志层来源于恩戈罗恩戈罗火山高原的火山产物，有助于建立坦桑尼亚奥杜威峡谷著名化石和石器记录的地层框架。然而，由于侵蚀、污染、再作用以及在咸碱性条件下火山玻璃的变化，以前对这些凝灰岩记录的限制，特别是对奥杜威 Bed II 的限制，一直受到限制。本文应用了以前定义的几个主要 Bed II 标志凝灰岩的地球化学和矿物学“指纹”，基于玻璃（如有）和更能抵抗变化的斑晶（长石、角闪石、辉石和钛磁铁矿），对奥杜威路口区地层剖面中的凝灰岩进行了研究，包括以前和最近挖掘的阿舍利和奥杜威遗址（HWK EE（地点（Loc）42）、EF-HR（Loc 12a）、FLK（Loc 45）和 MNK（Loc 88））。中间 Bed II 鸟印凝灰岩（BPT）比以前报道的成分变化更大，但在短距离内仍然是一种有价值的地层标志。在没有原地凝灰岩的地方，确认砾岩中的 Tuff IID 块有助于限制上 Bed II 的地层。本文还汇编了已发表的地球年代学研究结果，提供了地层背景，并使用一致的 Ar/Ar 参考标准年龄更新了以前报道的日期。这项工作的结果支持了以下与古人类学相关的结论：1）早期阿舍利遗址 EF-HR（Loc 12a）位于 Hay's Tuff IIC 之上，因此位于上 Bed II 而不是中 Bed II，2）HWK EE（Loc 42）奥杜威遗址位于 Tuff IIA 和 Tuff IIB 之间，正好在下 Bed II 和中 Bed II 的边界之上，3）FLK W 的阿舍利遗址很可能位于中辉绿砂岩之上，位于 Tuff IIB 之上，类似于莱基和海伊对奥杜威最早阿舍利遗址的位置。
