Diatomite evidence for a small palaeo mountain lake at 3400 m asl, Lesotho, southern Africa

IF 1.9 3区 地球科学 Q3 GEOGRAPHY, PHYSICAL Journal of Quaternary Science Pub Date : 2024-07-08 DOI:10.1002/jqs.3643
Jennifer M. Fitchett, Anson W. Mackay
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Abstract

The Eastern Lesotho Highlands experience an excess of rainfall sufficient to form the country's primary export, supplying the economic hub of southern Africa, Gauteng South Africa. However, there is currently only one natural lake in the country, Letšeng‐la Letsie, and evidence of palaeolakes in the region is therefore of particular interest. This study presents the analysis of a diatomite outcrop from a depression northwest of Mafadi Summit, at 3400 m asl. The presence of diatomite, dominated by the facultative planktonic species Staurosirella pinnata and Staurosira construens and abundant planktonic Aulacoseira ambigua, is indicative of the continuous presence of a shallow lake between ~4600 and 100 cal a bp. Comparative analysis of rainfall for the Mafadi and Letšeng‐la Letsie regions from CHIRPS gridded rainfall data demonstrates sufficient rainfall for a lake of comparable size, if not larger, as Mafadi receives considerably more rainfall than Letšeng‐la Letsie. Analysis of the SRTM 30‐m Digital Elevation Model and Topographic Position Index calculations demonstrate the feasibility of a shallow surface water feature at Mafadi. The conversion of this palaeolake into the contemporary wetland is hypothesized to be the result of post‐industrial warming, possibly augmented by migration of livestock into the Eastern Lesotho Highlands.
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非洲南部莱索托海拔 3400 米处一个小型古高山湖泊的硅藻土证据
莱索托东部高地降雨量过多,足以形成该国的主要出口产品,供应南部非洲的经济中心--南非豪登省。然而,该国目前只有一个天然湖泊--莱森湖(Letšeng-la Letsie),因此该地区古湖泊的证据特别引人关注。本研究分析了马法迪高峰西北部海拔 3400 米处的一个洼地中出露的硅藻土。硅藻土以面浮游物种 Staurosirella pinnata 和 Staurosira construens 以及丰富的浮游生物 Aulacoseira ambigua 为主,这表明在约 4600 至 100 卡年之间曾有一个浅湖持续存在。从 CHIRPS 网格雨量数据中对马法迪和 Letšeng-la Letsie 地区的降雨量进行的比较分析表明,由于马法迪的降雨量比 Letšeng-la Letsie 高出很多,因此即使不是更大的降雨量,也足以形成一个规模相当的湖泊。对 SRTM 30 米数字高程模型和地形位置指数计算的分析表明,在马法迪形成浅层地表水特征是可行的。据推测,这一古湖转变为当代湿地是工业化后气候变暖的结果,牲畜迁移到莱索托东部高地可能加剧了气候变暖。
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来源期刊
Journal of Quaternary Science
Journal of Quaternary Science 地学-地球科学综合
CiteScore
4.70
自引率
8.70%
发文量
82
审稿时长
6-12 weeks
期刊介绍: The Journal of Quaternary Science publishes original papers on any field of Quaternary research, and aims to promote a wider appreciation and deeper understanding of the earth''s history during the last 2.58 million years. Papers from a wide range of disciplines appear in JQS including, for example, Archaeology, Botany, Climatology, Geochemistry, Geochronology, Geology, Geomorphology, Geophysics, Glaciology, Limnology, Oceanography, Palaeoceanography, Palaeoclimatology, Palaeoecology, Palaeontology, Soil Science and Zoology. The journal particularly welcomes papers reporting the results of interdisciplinary or multidisciplinary research which are of wide international interest to Quaternary scientists. Short communications and correspondence relating to views and information contained in JQS may also be considered for publication.
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