NEW CHRONOLOGY FOR THE EARLY MIOCENE MAMMALIAN FAUNAS OF KISINGIRI, WESTERN KENYA
NEW CHRONOLOGY FOR THE EARLY MIOCENE MAMMALIAN FAUNAS OF KISINGIRI, WESTERN KENYA
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DOI：
10.1144/gsjgs.145.3.0479
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发表时间：
1988-05-01
影响因子：
2.7
通讯作者：
HARRIS, JA
中科院分区：
文献类型：
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作者：
DRAKE, RE;VANCOUVERING, JA;HARRIS, JA
新的全熔融K-Ar年龄表明，肯尼亚西部鲁辛加岛、Mfwangano岛和Karungu早中新世Kisingiri层序下部的所有化石建造都是在不到50万年的ATC期间沉积的。17.8 Ma前。这与以前公布的碎屑-凝灰岩建造的K-Ar年龄形成了鲜明的对比，后者表明它们是在23-16 Ma之间长达700万年的时间内沉积的，与所有其他东非早中新世遗址的年龄范围重叠，包括Koru、Songhor、Napak、Bukwa、Lopot、Muruarot和Buluk。此外，新的Kisingiri结果揭示的分析问题让人们对黑云母年龄产生了怀疑，黑云母年龄为最重要的遗址提供了年代测定。因此，Kisingiri动物群与Koru、Sonhor和Napak动物群之间的强烈差异，长期以来被认为是由生态原因造成的，因为明显的年龄重叠，但实际上可能是由于时间上的差异。如果这种地质年代学的观点是正确的，那么现在就有可能确定东非中新世早期动物群的适应趋势和进化演替。
New total-fusion K-Ar ages indicate that all of the fossiliferous formations that make up the lower part of the Early Miocene Kisingiri sequence in western Kenya at Rusinga Island, Mfwangano Island, and Karungu were deposited during an interval of less than 0.5 million years atc. 17.8 Ma ago. This contrasts markedly with K-Ar ages previously published from these detrital-tuffaceous formations, which suggested that they were deposited over an interval of as much as 7 million years between 23 and 16 Ma, overlapping the age-ranges of all other East African Early Miocene sites including Koru, Songhor, Napak, Bukwa, Loperot, Muruarot and Buluk. In addition, the analytical problems revealed by the new Kisingiri results cast doubt on biotite ages which provide dating for the most important sites. Thus, the strong differences between the Kisingiri fauna and those of Koru, Sonhor and Napak, long held to be due to ecology because of the apparent overlap in ages, may actually be due to a difference in time. If this view of the geochronology is correct, it may now be possible to identify adaptive trends and evolutionary succession in the East African Early Miocene faunas.