The Late Palaeozoic Ice Age unconformity in southern Namibia viewed as a patchwork mosaic
The Late Palaeozoic Ice Age unconformity in southern Namibia viewed as a patchwork mosaic
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纳米比亚南部的晚古生代冰河时代不整合面被视为拼凑而成的马赛克
DOI：
10.1002/dep2.163
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Mundil, Roland
中科院分区：
文献类型：
--
作者：
Le Heron, Daniel P.;Kettler, Christoph;Griffis, Neil P.;Dietrich, Pierre;Montañez, Isabel P.;Osleger, David A.;Hofmann, Axel;Douillet, Guilhem;Mundil, Roland
早在150年前，人们就已经知道晚古生代冰期期间非洲南部的冰块扩张，包括高地地区的分布控制着冰川作用的形态。在纳米比亚，越来越多的注意力集中在北部考科兰地区的长而深的古河谷网络，但在南部地形平坦的平原，在阿拉诺斯和卡拉斯堡盆地，尝试的工作相对较少。阿拉诺斯地区的沙漠地形不连续地暴露了Dwyka群的杂岩，约300 km，沿橙子河沿着向南延伸到纳米比亚-南非边境的Karasburg地区。虽然在地层水平上进行了检查，但Dwyka冰川岩石与下伏岩性之间的接触性质尚未得到系统的研究。本文介绍了2019年南半球冬季实地考察的结果，其中描述了一个高度变化的基底接触，记录了冈瓦纳这一部分冰块的生长，流动和扩张过程。在盆地边缘，冰川下产生的不整合面在硬化基岩上显示出经典的冰川条纹状路面。相比之下，在更多的盆地内区域的基底冰下不整合的特点是软沉积物条纹表面和变形。在阿拉诺斯盆地，软沉积物剪切带起源于冰下环境。这种类型的冰下不整合面发育在分化良好、松散的硅质碎屑物质之上。当冰在分选较差的物质上前进或蚕食先前存在的杂岩时，形成了被认为是单一碎屑厚的巨石主导间隔的“巨石路面”。重要的是，这些巨石路面富含碎屑，这些碎屑是由覆盖的冰在现场形成的。通过整合条纹方向，褶皱聚散度和古水流信息的测量，前冰流路径可以在很宽的区域内重建。
The expansion of ice masses across southern Africa during the Late Palaeozoic Ice Age has been known for 150 years, including the distribution of upland areas in controlling the configuration of glaciation. In Namibia, increasing attention has focussed on long and deep palaeovalley networks in the Kaokoland region in the north, but comparatively little work has been attempted in the topographically subdued plains of the south, in the Aranos and Karasburg basins. The desert terrain of the Aranos area exposes diamictites of the Dwyka Group discontinuously over about 300 km, extending further south to the Karasburg area at the Namibian‐South African border along the Orange River. Whilst examined at a stratigraphic level, the nature of the contact between the Dwyka glacial rocks and underlying lithologies has not been systematically investigated. This paper presents the results from fieldwork in austral winter 2019, in which a highly varying basal contact is described that records the processes of growth, flow and expansion of ice masses across this part of Gondwana. At the basin margins, subglacially produced unconformities exhibit classic glacially striated pavements on indurated bedrock. In comparison, the basal subglacial unconformity in the more basinward regions is characterised by soft‐sediment striated surfaces and deformation. In the Aranos Basin, soft‐sediment shear zones originated in the subglacial environment. This type of subglacial unconformity developed over well‐differentiated, unconsolidated, siliciclastic materials. Where ice advanced over more poorly sorted material or cannibalised pre‐existing diamictites, ‘boulder‐pavements’ recognised as single clast‐thick boulder‐dominated intervals formed. Importantly, these boulder‐pavements are enriched in clasts, which were facetted and striated in‐situ by overriding ice. By integrating measurements of striation orientations, fold vergence and palaeocurrent information, former ice flow pathways can potentially be reconstructed over a wide area.
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影响因子：
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作者：
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通讯作者：
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影响因子：
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DOI：
10.1016/0031-0182(83)90108-6
发表时间：
1983
期刊：
Palaeogeography, Palaeoclimatology, Palaeoecology
影响因子：
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作者：
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DOI：
10.1016/j.palaeo.2018.04.013
发表时间：
2019-10
期刊：
Palaeogeography, Palaeoclimatology, Palaeoecology
影响因子：
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作者：
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影响因子：
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