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A sedimentological record of fluvial-aeolian interactions and climate variability in the hyperarid northern Namib Desert, Namibia 纳米比亚北部极度干旱的纳米布沙漠中河流-风成相互作用和气候变率的沉积学记录
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-09-01 DOI: 10.25131/SAJG.124.0008
R. Miller, C. Krapf, T. Hoey, J. Fitchett, A. Nguno, R. Muyambas, A. Ndeutepo, A. Medialdea, A. Whitehead, I. Stengel
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引用次数: 5
Lithostratigraphy of the Vuurdood Subsuite, an early mafic-ultramafic phase of the Palaeoproterozoic Vioolsdrif Intrusive Suite, Richtersveld Magmatic Arc, Northern Cape Province 北开普省Richtersveld岩浆弧古元古代紫岩侵入套早期基性-超基性期Vuurdood亚套岩石地层学
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-09-01 DOI: 10.25131/sajg.124.0049
D. Reid, H. Minnaar
Mafic-ultramafic plutonic intrusions form an early phase in the emplacement of the predominantly granitic Vioolsdrif Suite, which together with its extrusive carapace, the Orange River Group, form the Richtersveld Magmatic Arc, a Palaeoproterozoic crustal segment formed between 1910 and 1865 Ma. Their lithologic character and distinctive dark weathering features in the mountain desert landscape of the Richtersveld, neighbouring regions of the Northern Cape Province and southern Namibia, make them a separate mappable unit in what is a predominantly granitic terrain. The name of the subsuite is taken from a spectacular twin peak massif near Goodhouse (Vuurdoodberg), while the type locality is one of the best preserved central-type intrusive bodies at Swartkop, situated 2 km off the N7 highway about 20 km south of the border town of Vioolsdrif, where the rock types present include gabbro, metagabbro, quartz-metagabbro, peridotite and troctolite.
镁铁质-超镁铁质深部侵入形成于以花岗岩为主的紫岩套侵位的早期阶段,与它的挤出壳——橙河群一起,形成了Richtersveld岩浆弧,这是一个形成于1910年至1865年Ma之间的古元古代地壳段。它们的岩性特征和在Richtersveld、北开普省和纳米比亚南部邻近地区的山区沙漠景观中独特的深色风化特征,使它们成为一个独立的可绘制单元,主要是花岗岩地形。该亚套的名称取自Goodhouse (Vuurdoodberg)附近的一个壮观的双峰地块,而类型位置是Swartkop保存最完好的中央型侵入体之一,位于N7高速公路2公里外,位于边境城镇Vioolsdrif以南约20公里处,那里的岩石类型包括辉长岩、变长岩、石英-变长岩、橄榄岩和橄榄岩。
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引用次数: 0
Fossil wood from the Upper Cretaceous crater sediments of the Salpeterkop volcano, North West Province, South Africa 南非西北省萨尔彼得科普火山上白垩纪火山口沉积物中的木材化石
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-09-01 DOI: 10.25131/SAJG.124.0028
M. D. Wit, M. Bamford
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引用次数: 1
Cave and rock shelter sediments of southern Africa: a review of the chronostratigraphic and palaeoenvironmental record from Marine Isotope Stage 6 to 1 南部非洲洞穴和岩石避难所沉积物:海洋同位素第6至1阶段的年代地层和古环境记录综述
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-08-22 DOI: 10.25131/sajg.124.0052
D. Stratford, Kerstin Braun, P. Morrissey
Caves and rock shelters contribute important records to local, regional and sub-continental reconstructions of environment and climate change through the southern African Quaternary. Against a backdrop of pronounced climate change, the archaeological record of the Marine Isotope Stage 6 to 1 period in southern Africa documents a remarkable time in the behavioural and technological evolution of anatomically modern humans. Significant evidence of this evolution is represented in diverse components of the sedimentary record in caves and rock shelters in the region. We present a catalogue of published caves and rock shelters in southern Africa that preserve temporally-relevant clastic and chemical palaeoclimatic proxies in order to: (1) facilitate the integration of cave and rock shelter sedimentary data into broader, regional chronostratigraphically-correlated palaeoclimatic sequences; and (2) identify possible areas and proxies that require focused research in the future. To demonstrate the complexity of the Marine Isotope Stage 6 to 1 stratigraphic record and use of palaeoenvironmental proxies, we present three case studies representing interior and coastal contexts: Border Cave, Klasies River Mouth and Pinnacle Point. These examples aptly demonstrate the challenges of these contexts, but also the opportunities for palaeoenvironmental research in southern Africa when conducted through integrated, multidisciplinary approaches. Published records of palaeoenvironmental research from cave and rock shelter sequences in southern Africa are heavily biased to the South African coastal areas and the record is temporally and spatially fragmented. However, there are interesting patterns in the chronostratigraphic record and in the distribution of sites within the context of the geology and vegetation ecology of southern Africa that require further exploration. There are also promising techniques in stable isotope analysis that can be applied to abundant sedimentary components found in the region’s caves and rock shelters, and in its museums.
洞穴和岩石避难所为非洲南部第四纪环境和气候变化的地方、区域和亚大陆重建提供了重要记录。在明显气候变化的背景下,南部非洲海洋同位素第6至1阶段的考古记录记录记录了现代解剖学人类行为和技术进化的一个非凡时期。这种进化的重要证据体现在该地区洞穴和岩石避难所的沉积记录的不同组成部分中。我们提供了一份已出版的南部非洲洞穴和岩石避难所目录,这些洞穴和岩石庇护所保存了时间相关的碎屑和化学古气候指标,以便:(1)促进将洞穴和岩石庇护沉积数据整合到更广泛的区域时间层相关古气候序列中;以及(2)确定未来需要重点研究的可能领域和替代方案。为了证明海洋同位素第6至1阶段地层记录的复杂性和古环境指标的使用,我们提出了三个代表内陆和沿海环境的案例研究:Border Cave、Klasies河口和Pinnacle Point。这些例子恰当地展示了这些背景下的挑战,但也展示了通过综合、多学科方法进行南部非洲古环境研究的机会。已发表的关于南部非洲洞穴和岩石避难所序列的古环境研究记录严重偏向于南非沿海地区,而且该记录在时间和空间上都是分散的。然而,在南部非洲的地质和植被生态背景下,年代地层记录和遗址分布有一些有趣的模式,需要进一步勘探。稳定同位素分析也有很有前途的技术,可以应用于该地区洞穴、岩石避难所和博物馆中发现的丰富沉积成分。
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引用次数: 5
The chronostratigraphy of the Anthropocene in southern Africa: Current status and potential 非洲南部人类世的年代地层学:现状与潜力
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-08-22 DOI: 10.25131/sajg.124.0053
N. Rose, S. Turner, L. Unger, C. Curtis
The process for the formal ratification of the proposed Anthropocene Epoch involves the identification of a globally isochronous stratigraphic signal to mark its starting point. The search for a Global Boundary Stratotype Section and Point (GSSP), a unique reference sequence that would be used to fix the start of the epoch, is in progress but none of the candidate sections are located in Africa. We assessed the currently available stratigraphic evidence for the possible markers of the Anthropocene in southern Africa and found that, although most markers have been identified in the region, the robustly dated, high resolution records required for the GSSP are very sparse. We then assessed the extent and stratigraphic resolution of a range of potential natural archives and conclude that a small number of permanent lakes, as well as marine sediments, corals and peats from selected locations in southern Africa could provide the temporal resolution required. With sufficient chronological control and multi-proxy analyses, one of these archives could provide a useful auxiliary stratotype thereby helping to confirm the global reach, and extending the utility, of the selected Anthropocene GSSP.
正式批准拟议的“人类世”的过程包括确定一个全球等时地层信号,以标记其起点。寻找全球边界层型剖面和点(GSSP)的工作正在进行中,这是一个独特的参考序列,将用于确定epoch的开始,但没有一个候选剖面位于非洲。我们评估了目前可获得的非洲南部人类世可能标志的地层证据,发现尽管该地区已确定了大多数标志,但GSSP所需的可靠日期、高分辨率记录非常稀少。然后,我们评估了一系列潜在的自然档案的范围和地层分辨率,并得出结论,非洲南部选定地点的少量永久湖泊,以及海洋沉积物,珊瑚和泥炭可以提供所需的时间分辨率。有了足够的时间控制和多代理分析,这些档案中的一个可以提供一个有用的辅助层型,从而有助于确认全球范围,并扩大选定的人类世GSSP的效用。
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引用次数: 2
Misinterpretation of zircon ages in layered intrusions 层状侵入体中锆石的误读
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-08-14 DOI: 10.25131/sajg.125.0001
R. Latypov, S. Chistyakova
A recent re-interpretation of the Bushveld Complex and other layered intrusions as stacks of randomly emplaced, amalgamated sills is mostly fuelled by finding of zircon ages that are not getting progressively younger from the base upwards, as expected from a classical model for the formation of layered intrusions. Rather, they display several reversals from older to younger ages and vice-versa with moving up-section through the layered intrusions. Here, we show that the reported zircon ages are at odds with the relative ages of rocks as defined by cross-cutting relations in potholes of the Bushveld Complex. This indicates that interpretation of the zircon isotopic data as the emplacement age of the studied rocks/units is incorrect, making a new emplacement model for layered intrusions baseless. This conclusion is further buttressed by the phase equilibria analysis showing that regular cumulate sequences of layered intrusions are not reconcilable with a model of randomly emplaced sills. In this model, the late sills are free to intrude at any stratigraphic position of the pre-existing rocks, producing magmatic bodies with chaotic crystallization sequences and mineral compositional trends that are never observed in layered intrusions. There are thus no valid justifications for the re-evaluation of the current petrological model of the Bushveld Complex and other layered intrusions as large, long-lived and largely molten magma chambers. A fundamental implication of this analysis is that the current high-precision U-Pb TIMS ages from layered intrusions are inherently unreliable on the scale of several million years and cannot therefore be used for rigorous estimations of the timing of crystallization, duration of magmatism, and cooling of these intrusions.
最近对布什维尔德杂岩和其他层状侵入岩的重新解释是一堆随机放置的、混合的岩质,这主要是由于发现锆石并没有像层状侵入岩形成的经典模型所期望的那样,从底部往上逐渐变年轻。相反,它们显示了从年老到年轻的几次反转,反之亦然,通过分层侵入向上移动。在这里,我们发现报道的锆石年龄与Bushveld杂岩坑槽中通过横切关系确定的岩石相对年龄不一致。这表明,将锆石同位素资料解释为所研究岩石/单元的侵位年龄是不正确的,使得层状侵入体的新侵位模型没有根据。相平衡分析进一步支持了这一结论,表明层状侵入体的规则累积序列与随机放置的模型不相容。在这个模型中,晚期岩床可以自由侵入已有岩石的任何地层位置,产生具有混乱结晶序列和矿物组成趋势的岩浆体,这在层状侵入岩中是从未观察到的。因此,没有有效的理由重新评估布什维尔德复合体和其他层状侵入体的当前岩石学模型,认为它们是大型的、长期存在的、大部分是熔融的岩浆房。这一分析的一个基本含义是,目前来自层状侵入体的高精度U-Pb TIMS年龄在数百万年的尺度上本质上是不可靠的,因此不能用于严格估计这些侵入体的结晶时间、岩浆活动持续时间和冷却时间。
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引用次数: 7
Micromammals and the Late Quaternary of southern Africa 非洲南部第四纪晚期的微地震
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-07-31 DOI: 10.25131/sajg.124.0035
D. Avery
Improvements in excavation methods, dating, analytical techniques and statistical applications have all led to a substantial increase in recoverable environmental evidence from micromammals. Because these animals are so small the information they provide is on a smaller geographical scale than that afforded by most other lines of evidence. However, with increasing amounts of data and greater interpretational precision in all spheres, the chances are improving of being able to mesh information from different scales. Blombos, Pinnacle Point and Klasies River on the southern coast of South Africa have clearly demonstrated that micromammalian data can contribute to multidisciplinary interpretations of past conditions, in this case during MIS 5 and 6. Little attention has been paid to the generally small samples from Iron Age sites but the presence of the House rat Rattus rattus may provide important information about human movements and may also contribute to our understanding of the Anthropocene once this has been formally defined. Micromammals have not yet been used as chronostratigraphic indicators in southern Africa but it may be possible to develop biochronologies using them and to incorporate this material into African Land Mammal Ages.
挖掘方法、年代测定、分析技术和统计应用的改进都导致了从微观显微镜中可回收的环境证据的大幅增加。因为这些动物太小了,它们提供的信息在地理范围上比大多数其他证据提供的信息要小。然而,随着数据量的增加和所有领域的解释精度的提高,能够对不同尺度的信息进行网格化的可能性正在提高。南非南部海岸的Blombos、Pinnacle Point和Klasies河清楚地表明,微观管理数据有助于对过去条件的多学科解释,在MIS 5和6期间。人们很少关注来自铁器时代遗址的通常较小的样本,但家鼠鼠的存在可能会提供有关人类活动的重要信息,一旦人类世被正式定义,也可能有助于我们对人类世的理解。在南部非洲,微哺乳动物尚未被用作年代地层指标,但使用它们开发生物基因组学并将这种材料纳入非洲陆地哺乳动物时代是可能的。
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引用次数: 2
Elemental proxy evidence for late Quaternary palaeoenvironmental change in southern African sedimentary records: interpretation and applications 南部非洲沉积记录中晚第四纪古环境变化的元素代理证据:解释和应用
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-07-31 DOI: 10.25131/sajg.124.0046
M. Humphries
Sediments are the most important source of Late Quaternary palaeoclimate information in southern Africa, but have been little studied from a geochemical perspective. However, recent advances in analytical techniques that allow rapid and near-continuous elemental records to be obtained from sedimentary sequences has resulted in the increasing use of elemental indicators for reconstructing climate. This paper explores the diverse information that can be acquired from the inorganic component of sediments and reviews some of the progress that has been made over the last two decades in interpreting the climatic history of southern Africa using elemental records. Despite the general scarcity of elemental records, excellent examples from the region exist, which provide some of the longest and most highly resolved sequences of environmental change currently available. Records from Tswaing crater and marine deposits on the southern KwaZulu-Natal coastline have provided rare glimpses into hydroclimate variability over the last 200 000 years, suggesting that summer rainfall in the region responded predominantly to insolation forcing on glacial-interglacial timescales. Over shorter timescales, lakes and wetlands found in the Wilderness embayment on the southern Cape coast and along the Maputaland coast in north-eastern South Africa have yielded highly-resolved elemental records of Holocene environmental change, providing insight into the changing interactions between tropical (e.g., El Niño-Southern Oscillation) and temperate (e.g., mid-latitude westerlies) climate systems affecting rainfall variability in the region. The examples discussed demonstrate the multiple environmental processes that can be inferred from elemental proxies and the unique insight this can provide in advancing our understanding of past climate change on different timescales. The interpretation of geochemical data can be complicated by the complex nature of sedimentary environments, various proxy assumptions and analytical challenges, and the reliability of sediment-based climate reconstructions is substantially enhanced through multi-proxy approaches.
沉积物是非洲南部晚第四纪古气候信息的最重要来源,但很少从地球化学角度进行研究。然而,分析技术的最新进展使得能够从沉积序列中获得快速且近乎连续的元素记录,这导致越来越多地使用元素指标来重建气候。本文探讨了从沉积物的无机成分中可以获得的各种信息,并回顾了过去二十年来在利用元素记录解释南部非洲气候史方面取得的一些进展。尽管基本记录普遍缺乏,但该地区仍有优秀的例子,提供了目前可用的一些最长、分辨率最高的环境变化序列。Tswaing火山口和夸祖鲁-纳塔尔州南部海岸线上的海洋沉积物的记录为过去20万年来的水文气候变化提供了罕见的一瞥,表明该地区的夏季降雨主要是对冰川间冰川时间尺度上的日照强迫的反应。在较短的时间内,在南非东北部开普省南部海岸和马普特兰海岸的荒野海湾中发现的湖泊和湿地产生了全新世环境变化的高度解析的基本记录,深入了解影响该地区降雨量变化的热带(如厄尔尼诺-南方涛动)和温带(如中纬度西风带)气候系统之间不断变化的相互作用。所讨论的例子展示了可以从元素代理推断出的多种环境过程,以及这可以为推进我们对不同时间尺度上过去气候变化的理解提供的独特见解。沉积环境的复杂性、各种代理假设和分析挑战可能会使地球化学数据的解释变得复杂,并且通过多代理方法大大提高了基于沉积物的气候重建的可靠性。
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引用次数: 2
Stratigraphy of late Quaternary mountain slope landforms and deposits in southern Africa and their significance for the dynamics of mountain sediment systems 非洲南部晚第四纪山地斜坡地貌和沉积物的地层学及其对山地沉积物系统动力学的意义
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-07-28 DOI: 10.25131/sajg.124.0037
J. Knight, S. Grab
Mountains are areas of high potential sediment yield due to their steep slopes and generally cool, wet climates. Mountain sediments are moved by gravity-driven and often cryogenically-influenced processes, and captured within valleys or footslopes in the form of screes, alluvial/colluvial fans and terraces, or on hillslopes in the form of solifluction sheets, debris lobes/ridges and openwork block deposits. This study critically examines the geomorphic, sedimentary, stratigraphic and dating evidence from cryogenically-influenced late Quaternary slope deposits found along the highest sectors of the Great Escarpment in the Eastern Cape Province (South Africa) and Maloti–Drakensberg range (Lesotho, and KwaZulu-Natal Province, South Africa). This evidence is set in the context of mountain weathering and erosion/transportation processes during the late Quaternary, and the dynamics of such sedimentary systems. Despite many general reports and observations, there is little detailed and quantitative evidence for late Quaternary slope processes, products and stratigraphy in southern Africa. This study integrates the existing morphological, sedimentary and dating evidence to examine mountain slope evolution in southern Africa based on the conceptual framework of sediment cascades. Application of this framework can help explain the spatial and temporal differences in sediment supply and dynamics observed in different sectors of the Great Escarpment during the late Quaternary.
山区由于其陡峭的斜坡和通常凉爽潮湿的气候,是潜在产沙量高的地区。山区沉积物通过重力驱动且通常受低温影响的过程移动,并以砾石、冲积扇/崩积扇和阶地的形式在山谷或坡脚内捕获,或以沙流片、碎屑凸角/山脊和露天矿块沉积物的形式在山坡上捕获。本研究严格审查了在东开普省(南非)和马洛蒂-德拉肯斯堡山脉(莱索托和南非夸祖鲁-纳塔尔省)大悬崖最高地段发现的受低温影响的晚第四纪斜坡沉积物的地貌、沉积、地层和年代证据。这一证据是在第四纪晚期的山脉风化和侵蚀/运输过程以及这些沉积系统的动力学背景下提出的。尽管有许多一般性的报告和观测,但关于南部非洲晚第四纪斜坡过程、产物和地层学的详细和定量证据很少。本研究综合了现有的形态学、沉积学和年代测定证据,以沉积物级联的概念框架为基础,研究了南部非洲的山坡演化。该框架的应用有助于解释第四纪晚期在大陡崖不同地段观测到的沉积物供应和动力学的时空差异。
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引用次数: 2
Lithostratigraphy of the Naros Granite (Komsberg Suite), South Africa and Namibia 南非和纳米比亚Naros花岗岩(Komsberg套件)的岩石地层学
IF 1.8 4区 地球科学 Q2 GEOLOGY Pub Date : 2021-07-24 DOI: 10.25131/SAJG.124.0040
P. Macey, R. Thomas, H. Smith, D. Frei, P. Roux
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引用次数: 1
期刊
South African Journal of Geology
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