Hertzian Fractures in the Sub-Dwyka Nooitgedacht Striated Pavement, and Implications for the Former Thickness of Karoo Strata Near Kimberley, South Africa

Master, Sharad

doi:10.2113/gssajg.115.4.561

Cited by 5 publications

(5 citation statements)

References 39 publications

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“…Hertzian fractures are explained by a complex stress field that is set up when a spherical indenter is pressed onto the surface of an isotropic material. The stresses under and around the indenter contact are compressive; however, outside the contact circle, a radially directed tensile stress is created (Frank & Lawn 1967;Master 2012). Results are consistent with deformation band development within Navajo Sandstone sequences with varying grain size and porosity values at Buckskin Gulsch, Utah, USA .…”

Section: Distribution-localization Of Deformation Bands As a Functionmentioning

confidence: 63%

Deformation band development as a function of intrinsic host-rock properties in Triassic Sherwood Sandstone

Griffiths

Faulkner

Edwards³

et al. 2016

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Deformation bands significantly alter the local petrophysical properties of sandstone reservoirs, although it is not known how the intrinsically variable characteristics of sandstones (e.g. grain size, sorting and mineralogy) influence the nature and distribution of deformation bands. To address this, cataclastic deformation bands within fine-and coarse-grained Triassic Sherwood Sandstone at Thurstaston, UK were analysed, for the first time, using a suite of petrographical techniques, outcrop studies, helium porosimetry and image analysis. Deformation bands are more abundant in the coarse-grained sandstone than in the underlying fine-grained sandstone. North-and south-dipping conjugate sets of cataclastic bands in the coarse-grained sandstone broadly increase in density (defined by number/m 2 ) when approaching faults. Microstructural analysis revealed that primary grain size controls deformation band density. Deformation bands in both coarse and fine sandstones led to significantly reduced porosity, and so can represent barriers or baffles to lateral fluid flow. Microstructural data show preferential cataclasis of K-feldspar grains within the host rock and deformation band. The study is of direct relevance to the prediction of reservoir quality in several petroleum-bearing Lower Triassic reservoirs in the near offshore, as deformation band development occurred prior to Carboniferous source-rock maturation and petroleum migration.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.

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Section: Distribution-localization Of Deformation Bands As a Functionmentioning

confidence: 63%

Deformation band development as a function of intrinsic host-rock properties in Triassic Sherwood Sandstone

Griffiths

Faulkner

Edwards³

et al. 2016

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“…• A first period of accelerated denudation of the margins of the plateau followed, at ~150-120 Ma, tied to continental breakup and post-rift erosion of the rift shoulders, as indicated by thermochronometric data (e.g., Gallagher and Brown, 1999;Brown et al, 2002;Tinker et al, 2008b;Kounov et al, 2009Kounov et al, , 2013Stanley et al, 2013Stanley et al, , 2015Stanley et al, , 2021Wildman et al, 2016Wildman et al, , 2015aGreen et al, 2017). A second pulse of denudation took place at ~100-70 Myr and coincides with acceleration of offshore sediment flux (Walford et al, 2005;Tinker et al, 2008a;Rouby et al, 2009;Guillocheau et al., 2012;Said et al, 2015;Baby et al, 2020). This second pulse of denudation likely resulted from the tilting of the plateau to the west that steepened the slopes across the sub-continent and enhanced a widespread and fast erosion response, notably of the passive margins escarpments (Braun et al, 2014;Baby et al, 2018b;Ding et al, 2019;Stanley et al, 2021).…”

Section: Post Gondwana-breakup History Of the Southern Africa Plateaumentioning

confidence: 94%

“…Here, the Nooitgedacht glacial pavement records a WSW glacial movement (Fig. 6; Slater et al, 1932;Du Toit, 1954;Visser and Loock, 1988;Master, 2012). The western flank of the valley is steep (up to 11%), 100-200 m-high and cut into Paleoproterozoic dolomites of the Griqualand West Basin forming the karstified Ghaap plateau, over which no glaciogenic sediments are mapped.…”

Section: The Cargonian Highlandmentioning

confidence: 96%

The Glacial Paleolandscapes of Southern Africa: the Legacy of the Late Paleozoic Ice Age

Dietrich,

Guillocheau,

Douillet

et al. 2024

Preprint

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Abstract. The modern relief of Southern Africa is characterised by stepped plateaus bordered by escarpments. This morphology is thought to result from stepwise uplift and ensuing continental-scale erosion of the region as it rode over Africa’s mantle ‘superplume’ following the break-up of Gondwana, i.e. since the mid-Mesozoic. We demonstrate in this contribution that this modern morphology of Southern Africa is in fact largely inherited from glacial erosion associated to the Late Paleozoic Ice Age (LPIA) that occurred between 370 and 260 Myr ago, during which Gondwana – which included Southern Africa – was covered in thick ice masses. Southern Africa hosts vast (up to 106 km²) and thick (up to 5 km) sedimentary basins ranging from the Carboniferous, represented by glaciogenic sediments tied to the LPIA, to the Jurassic-Cretaceous. These basins are separated by intervening regions largely underlain by Archean to Paleoproterozoic cratonic areas that correspond to paleohighlands that preserve much of the morphology that existed when sedimentary basins formed, and particularly glacial landforms. In this contribution, we review published field and remote data and provide new large-scale interpretation of the geomorphology of these paleohighlands of Southern Africa. Our foremost finding is that over Southern Africa, vast surfaces, tens to hundreds of thousands km² (71.000–360.000 km²) are exhumed glacial landscapes tied to the LPIA. These glacial landscapes manifest in the form of cm-scale striated pavements, m-scale fields of roches moutonnées, whalebacks and crag-and-tails, narrow gorges cut into high-standing mountain ranges, and km-scale planation surfaces and large U-shaped valleys, overdeepenings, fjords and troughs up to 200 km in length. Many modern savannahs and desertic landscapes of Southern Africa are therefore relict glacial landscapes and relief ca. 300 Myr old. These exhumed glacial relief moreover exerts a strong control on the modern-day aspect of the geomorphology of Southern Africa as (1) some escarpments that delineate high-standing plateaux from valleys and coastal plains are inherited glacial relief in which glacial valleys are carved, (2) some hill or mountain ranges already existed by LPIA times and were likely modelled by glacial erosion, and (3) the drainage network of many of the main rivers of Southern Africa is funnelled through ancient glacial valleys. This remarkable preservation allowed us to reconstruct the paleogeography of Southern Africa in the aftermath of the LPIA, consisting of highlands over which ice masses nucleated and from which they flowed through the escarpments and toward lowlands that now correspond to sedimentary basins. Our findings therefore indicate that glacial landforms and relief of continental-scale can survive over tens to hundreds of million years. This preservation and modern exposure of the glacial paleolandscapes were achieved through burial under piles of Karoo sediments and lavas over ca. 120 to 170 million years and a subsequent exhumation since the middle Mesozoic owing to the uplift of Southern Africa. Owing to strong erodibility contrasts between resistant Precambrian bedrock and softer sedimentary infill, the glacial landscapes have been exhumed and rejuvenated. We therefore emphasise the need of considering the legacy of glacial erosion processes and the resulting presence of glacial landscapes when assessing the post-Gondwana-breakup evolution of Southern African topography and its resulting modern-day aspect, as well as inferences about climate changes and tectonic processes. Finally, we explore the potential pre-LPIA origin for some of the landscapes. In the Kaoko region of northern Namibia, the escarpments into which glacial valleys are carved may correspond to a reminiscence of the Kaoko Pan-African Belt, whose crustal structures were either reactivated or where relief persisted since then. In South Africa, the escarpment bordering the paleohighland corresponds to crustal-scale faults that might have been reactivated during LPIA by subsidence processes. These inherited morphological or crustal features may have been re-exploited and enhanced by glacial erosion during the LPIA, as it is the case for some Quaternary glacial morphology.

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“…The Dwyka Group has to a large part been studied with the commonly accepted interpretation, or paradigm, that this sedimentary unit was the geological consequence of a major glaciation. In 1856 the diamictites were interpreted to be of volcanic origin (Sandberg, 1928;Norman, 2013), and later as mudflows or the result of meteorite impacts, including striated surfaces (Geophysical Discussion, 1960;Master, 2012;Rampino, 2017). The glaciogenic interpretation was first published in 1870 (Hancox & Götz, 2014), generally accepted in 1898 (Sandberg, 1928), and basically has withstood critical comments and alternative geological interpretations.…”

Section: Geology Of the Dwyka Groupmentioning

confidence: 99%

“…The pavements display striations with different appearances in distinct areas. Master (2012) identified three main sets of bearings: 225-232°, 240-256° and 203-216°. But, there is a large variation of bearings, which is partly controlled by small local highs or steep surfaces (Fig.…”

Section: Nooitgedachtmentioning

confidence: 99%

Reconsidering the glaciogenic origin of Gondwana diamictites of the Dwyka Group, South Africa

Molén

Smit²

2022

Geologos

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The Gondwana Late Palaeozoic Ice Age is probably best represented by the Dwyka Group in South Africa. Striated and grooved surfaces or pavements are commonly considered to have formed subglacially, as are diamictites which have been interpreted as in-situ or reworked tillites. These interpretations were tested by investigation of outcrops in formerly well-studied areas, throughout South Africa. Detailed analyses have focused on striated surfaces/pavements and surface microtextures on quartz sand grains in diamictites. The sedimentological context of four pavements, interpreted to be glaciogenic, display features commonly associated with sediment gravity flows, rather than glaciation. A total of 4,271 quartz sand grains were subsampled from outcrops that are considered mainly to be tillites formed by continental glaciation. These grains, analysed by SEM, do not demonstrate the characteristic surface microtexture combinations of fracturing and irregular abrasion associated with Quaternary glacial deposits, but mainly a mix of surface microtextures associated with multicyclical grains. The Dwyka Group diamictites warrant reinterpretation as non-glacial sediment gravity flow deposits.

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Hertzian Fractures in the Sub-Dwyka Nooitgedacht Striated Pavement, and Implications for the Former Thickness of Karoo Strata Near Kimberley, South Africa

Cited by 5 publications

References 39 publications

Deformation band development as a function of intrinsic host-rock properties in Triassic Sherwood Sandstone

Deformation band development as a function of intrinsic host-rock properties in Triassic Sherwood Sandstone

The Glacial Paleolandscapes of Southern Africa: the Legacy of the Late Paleozoic Ice Age

Reconsidering the glaciogenic origin of Gondwana diamictites of the Dwyka Group, South Africa

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