Berkeley Geochronology Center, Berkeley, CA 94709, USA.
J Hum Evol. 2012 Aug;63(2):251-73. doi: 10.1016/j.jhevol.2012.05.004. Epub 2012 Jul 17.
(40)Ar/(39)Ar dating of tuffs and lavas of the late Pleistocene volcanic and sedimentary sequence of Olduvai Gorge, north-central Tanzania, provides the basis for a revision of Bed I chronostratigraphy. Bed I extends from immediately above the Naabi Ignimbrite at 2.038 ± 0.005 Ma to Tuff IF at 1.803 ± 0.002 Ma. Tuff IB, a prominent widespread marker tuff in the basin and a key to understanding hominin evolutionary chronologies and paleoclimate histories, has an age of 1.848 ± 0.003 Ma. The largest lake expansion event in the closed Olduvai lake basin during Bed I times encompassed the episode of eruption and emplacement of this tuff. This lake event is nearly coincident with the maximum precessional insolation peak of the entire Bed I/Lower Bed II interval, calculated from an astronomical model of the boreal summer orbital insolation time-series. The succeeding precessional peak also apparently coincides with the next youngest expansion of paleo-Lake Olduvai. The extreme wet/dry climate shifts seen in the upper part of Bed I occur during an Earth-orbital eccentricity maximum, similar to episodic lake expansions documented elsewhere in the East African Rift during the Neogene.
（40）Ar/（39）Ar 年代测定表明，坦桑尼亚中北部奥杜威峡谷晚更新世火山和沉积序列中的凝灰岩和熔岩，为重新修订 Bed I 年代地层学提供了依据。Bed I 从紧邻 Naabi 火山灰流之上的 2.038±0.005Ma 延伸至 1.803±0.002Ma 的 Tuff IF。Tuff IB 是盆地中一个显著的广泛分布的标志凝灰岩，是理解人类进化年代学和古气候历史的关键，其年龄为 1.848±0.003Ma。在 Bed I 时期，Olduvai 封闭湖盆中最大的湖泊扩张事件涵盖了该凝灰岩喷发和就位的事件。这一湖泊事件几乎与整个 Bed I/Lower Bed II 间隔的最大岁差太阳辐射峰值同时发生，这是根据北极夏季轨道太阳辐射时间序列的天文模型计算得出的。下一个岁差峰值显然也与下一个古 Olduvai 湖的最大扩张相吻合。在 Bed I 的上部，人们观察到了极端的干湿气候转变，这种转变发生在地球轨道偏心率最大值期间，类似于东非大裂谷在新近纪其他地方记录的间歇性湖泊扩张。
