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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >New magnetostratigraphy for the OIduvai Subchron in the Koobi Fora Formation, northwest Kenya, with implications for early Homo
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New magnetostratigraphy for the OIduvai Subchron in the Koobi Fora Formation, northwest Kenya, with implications for early Homo

机译：肯尼亚西北Koobi Fora地层Oiduvai次子的新地层学研究

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A problematic magnetostratigraphy for the Koobi Fora Formation has contributed to debates on the evolutionary implications for early hominin fossils. To address this, 50 independent samples distributed over a nearly 63-m-thick interval were collected from the lower-middle KBS Member type section in fossil collection Area 102, northeast Turkana Basin. Characteristic directions obtained by thermal demagnetization define a coherent magnetostratigraphy that is supported by alternating-field studies on 28 sister specimens and the prior tephrochronological framework. Two long polarity intervals were recognized, each 30-40 m in thickness, and interpreted as the upper part of the normal polarity Olduvai Subchron and the overlying reverse polarity Matuyama Chron. The end Olduvai consists of a normal-reverse-normal polarity sequence occurring over a thickness of at least I m but perhaps up to 5 m, suggesting that this subchron has a short reverse interval in its uppermost part. Such a fine-scale structure also has been reported from several other sites, like the Pliocene-Pleistocene boundary and point stratotype section at Vrica, Italy, which serves as a basis for formally delimiting three temporally discrete polarity subintervals for the Olduvai Subchron. These paleomagnetic results that place the upper boundary of the Olduvai at similar to 48 m above the base of the KBS Member, coupled with published radioisotopic dates, firmly secure the age of partial cranium KNM-ER 3733 in the interval 1.78-1.48 Ma, with an interpolated age of similar to 1.7 Ma, giving this fossil the most unambiguous numerical-age constraints, as compared to the oldest Homo cranial remains from Europe and Asia. Nonetheless, assured placement of the top of the Olduvai Subchron in the KBS Member is not sufficient in the face of other uncertainties to influence conventional interpretations of the timing and direction for the global dispersal of early Homo erecturs.
机译：Koobi Fora地层的地层学存在问题，这引发了有关早期人化石化石的进化意义的辩论。为了解决这个问题，从图尔卡纳盆地东北部102号化石收集区的中下部KBS成员类型部分收集了50个独立的样本，分布在近63米的厚度内。通过热退磁获得的特征方向定义了相干地磁地层学，该相干地层学由对28个姊妹标本和以前的年代学框架的交替场研究支持。识别出两个长极性间隔，每个间隔的厚度为30-40 m，并解释为正常极性Olduvai Subchron和上覆的反极性Matuyama Chron的上部。 Olduvai端由一个正反转极性极性序列组成，该序列出现在至少1 m但可能高达5 m的厚度上，这表明该子年代在其最上部具有较短的反向间隔。这种精细的结构也从其他几个站点得到了报道，例如意大利Vrica的上新世-更新世边界和点平流层剖面，这是正式划定Olduvai子年代的三个时间离散极性子间隔的基础。这些古磁结果将Olduvai的上边界置于KBS成员底部上方约48 m处，再加上已公布的放射性同位素日期，牢固地确保了部分颅骨KNM-ER 3733的年龄在1.78-1.48 Ma之间，与欧洲和亚洲最古老的人类颅骨残骸相比，其内插年龄接近1.7 Ma，从而使该化石具有最明确的数字年龄限制。然而，面对其他不确定因素，确保将KBS成员中的Olduvai子历时的顶部放置到位不足以影响对早期直立人的全球传播时间和方向的传统解释。

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