南非泛滥平原晚第四纪相地层特征

IF 1.2 4区 地球科学 Q2 GEOLOGY
S. Grenfell, M. Grenfell
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引用次数: 2

摘要

南非河流冲积平原及其冲积沉积物反映了地质和地理驱动因素的多样性。我们使用最初为旱地湿地开发的遗传地貌分类系统来表征南非洪泛平原的地貌过程和沉积填充物的潜在序列。通过文献中的案例研究,我们考虑了冲积河和基岩-冲积混合河在宏观地貌背景下的差异,并评估了该背景对冲积平原持久性和作为古环境档案的潜力的影响。还评价了南非洪泛区的沉积相组合,包括侧向和斜向增生、河道、河道填充物、堤防垂直增生、洪泛区垂直增生和泥石流沉积。南非内陆的洪泛平原是典型的基岩-冲积混合平原,因为河床位于基岩之上或靠近基岩,沉积物厚度有限。相比之下,在构造盆地环境下,一些洪泛平原的沉积物厚度超过30 m。由此形成的河流是冲积的,因此能够调整其宽度、深度和坡度,以适应流量和泥沙供应的变化。同样,沿海洪泛平原河流是冲积的,这是由于末次盛冰期的下降和随后海平面上升时的沉积填充造成的。在考虑洪泛平原作为环境变化古档案的潜力时,有两点需要考虑。首先,由于复杂的过程形式反馈,洪泛平原地层学不是对单一变量的响应。相反,洪泛平原地层是自生和异生过程共同作用的结果。其次,大多数南非洪泛平原是沉积物循环带,因此,保存潜力通常很低。因此,虽然内部的洪泛平原环境可能有几百万年的历史,但其中的沉积物可能只有几千到几万年的历史。历史上研究主要集中在曲流河和基岩-冲积混合分支河冲积平原,而对其他冲积平原亚型的认识仍然有限。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Characterising the late Quaternary facies stratigraphy of floodplains in South Africa
South African river floodplains and their alluvial deposits reflect a diversity of geological and geographical drivers. We use a genetic geomorphic classification system originally developed for dryland wetlands to characterise geomorphic processes and potential successions of sedimentary fill for South African floodplains. Using case studies from the literature, we consider differences between alluvial rivers and mixed bedrock-alluvial rivers in the context of macro-scale geomorphic setting, and evaluate the impact of the setting on floodplain persistence and potential as a palaeo-environmental archive. Sedimentary facies associations represented in South African floodplains, including lateral and oblique accretion, channel, channel infill, levee vertical accretion, floodplain vertical accretion and debris flow deposits, are also evaluated. Floodplains of South Africa’s interior are typically mixed bedrock-alluvial as channel beds are set upon or close to bedrock and sediment thickness is limited. By contrast some floodplains in tectonic basin settings have sediment deposits exceeding 30 m in thickness. The resulting rivers are alluvial, and thus able to adjust their width, depth and slope to accommodate changes in discharge and sediment supply. Similarly, coastal floodplain rivers are alluvial due to downcutting during the last glacial maximum and subsequent sedimentary infilling as sea levels rose. When considering the potential of floodplains as palaeoarchives of environmental change, two considerations emerge. First, floodplain stratigraphy is not a response to a single variable due to complex process-form feedbacks. Rather, floodplain stratigraphy is an outcome of both autogenic and allogenic processes. Second, most South African floodplains are zones of sediment recycling, and as such, preservation potential is typically low. Thus, although floodplain settings of the interior may be a few million years old, the sediment within them may be only thousands to tens of thousands of years old. Our review indicates that research has historically focused on meandering river and mixed bedrock-alluvial anabranching river floodplains, while understanding of other floodplain sub-types remains limited.
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来源期刊
CiteScore
3.60
自引率
5.60%
发文量
18
审稿时长
>12 weeks
期刊介绍: The South African Journal of Geology publishes scientific papers, notes, stratigraphic descriptions and discussions in the broadly defined fields of geoscience that are related directly or indirectly to the geology of Africa. Contributions relevant to former supercontinental entities such as Gondwana and Rodinia are also welcome as are topical studies on any geoscience-related discipline. Review papers are welcome as long as they represent original, new syntheses. Special issues are also encouraged but terms for these must be negotiated with the Editors.
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