Geochronology of the pre-KBS Tuff sequence, Omo Group, Turkana Basin
Geochronology of the pre-KBS Tuff sequence, Omo Group, Turkana Basin
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图尔卡纳盆地奥莫群前 KBS 凝灰岩层序的地质年代学
DOI：
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发表时间：
2008
影响因子：
2.7
通讯作者：
F. Brown
中科院分区：
文献类型：
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作者：
I. Mcdougall;F. Brown
位于肯尼亚北方和埃塞俄比亚南部的Omo-Turkana盆地大约在4.3Ma前的上新世早期发育在北方肯尼亚裂谷中。近800米的沉积物，包括在奥莫组，在盆地中露头。序列中大量的流纹岩凝灰岩不仅促进了奥莫群地层之间的可靠对比，而且为精确的40 Ar/39 Ar年龄测量提供了材料。本文报道了从奥莫群下部凝灰岩中的浮石碎屑到KBS凝灰岩水平的碱长石晶体的年龄，以前的年龄为1.87 ± 0.02 Ma。从17个地层水平，包括2.4 Ma的时间间隔，从该组的基础KBS凝灰岩的结果提供了一个数值的时间框架的地质历史的上新世序列的下部。新的年龄，其精度为1%的顺序，都是一致的地层顺序，提供信心，他们准确地记录火山爆发的年龄，与沉积的凝灰岩和浮石发生后不久。
The Omo–Turkana Basin of northern Kenya and southern Ethiopia developed in the northern Kenya Rift about 4.3 Ma ago in the Early Pliocene. Nearly 800 m of sediments, included within the Omo Group, crop out in the basin. Numerous rhyolitic tuffs in the sequence not only have facilitated secure correlations between the formations of the Omo Group but also have provided material for precise 40Ar/39Ar age measurements. Here we report ages on alkali feldspar crystals from pumice clasts within tuffs in the lower part of the Omo Group up to the level of the KBS Tuff, which has previously been dated at 1.87 ± 0.02 Ma. The results from 17 stratigraphic levels encompassing the 2.4 Ma time interval from the base of the group to the KBS Tuff provide a numerical time framework for the geological history of the lower part of the Pliocene sequence. The new ages, which have a precision of the order of 1%, are all consistent with the stratigraphic order, providing confidence that they accurately record the ages of the volcanic eruptions, with deposition of the tuffs and pumices occurring shortly thereafter.