A late Holocene palaeoenvironmental 'snapshot' of the Angamma Delta, Lake Megachad at the end of the African Humid Period
A late Holocene palaeoenvironmental 'snapshot' of the Angamma Delta, Lake Megachad at the end of the African Humid Period
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DOI：
10.1016/j.quascirev.2018.04.025
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发表时间：
2018-12-15
影响因子：
4
通讯作者：
Sloane, Hilary J.
中科院分区：
文献类型：
--
作者：
Bristow, Charlie S.;Holmes, Jonathan A.;Sloane, Hilary J.
在非洲湿润期（AHP），湖泊和湿地面积大幅增加。梅加查德湖是几个巨大湖泊之一，在全新世中期回归之前，在 AHP 期间经历了剧烈的波动。然而，AHP 终止的时间和性质一直存在争议。我们提供了古湖北端安格马三角洲沉积物中梅加查德湖水位波动的证据。三角洲斜坡沉积物在 AHP 高度大约 7000 cal BP 沉积。上覆生物碎屑沉积物的海拔为 285-290 m，温度为 4300 至 4800 cal BP，位于古湖高位 (339 m) 以下，但接近加扎勒河基台的海拔，该基台将湖泊的两个子盆地分开。介形类三角洲 O-18 值表明北部次流域的水域蒸发至与现代乍得湖相似的水平。古生态学证据表明，该湖是常年存在的，蒸发富集归因于基台出现时湖水的循环受到限制。生物碎屑沉积物的年龄和海拔，加上已发表的湖泊水位重建，表明了复杂的湖泊水位历史，在层次分析法结束时出现了一次重大回归，随后是短暂的湖泊水位上升，然后进一步回归。这一关于湖水位变化的新证据为其他地质记录和一些建模实验提供了支持，这些实验表明层次分析法结束时水文气候的快速波动。 (C) 2018 年由爱思唯尔有限公司出版。
During the African Humid Period (AHP) there was a large increase in the area of lakes and wetlands. Lake Megachad, one of several huge lakes, underwent dramatic fluctuations during the AHP prior to regression in the mid Holocene. However, the timing and nature of AHP termination has been disputed. We present evidence from sediments of the Angamma Delta, from the northern end of the palaeolake, for Lake Megachad lake-level fluctuations at the end of the AHP. Delta slope deposits were deposited around 7000 cal BP at the height of the AHP. Overlying bioclastic sediments, from 4300 to 4800 cal BP at an elevation of 285-290 m, lie below the palaeolake highstand (339 m) but close to the elevation of the Bahr el Ghazal sill, which divided the lake's two sub-basins. Ostracod delta O-18 values indicate that the waters of the northern sub-basin were evaporated to levels similar to modern Lake Chad. Palaeoecological evidence suggests that the lake was perennial and evaporative enrichment is attributed to restricted circulation of lake waters as the sill emerged. The age and elevation of the bioclastic sediment, coupled with published lake level reconstructions, suggest a complex lake-level history with a major regression at the end of the AHP, followed by a short lived, lake level rise and then a further regression. This new evidence for changes in lake level provides support for other geological records and some modelling experiments that suggest rapid fluctuations in hydroclimate at the end of the AHP. (C) 2018 Published by Elsevier Ltd.