Cold feet: Trackways and burrows in ice-marginal strata of the end-Ordovician glaciation (Table Mountain Group, South Africa)

Davies, Neil S.; Shillito, Anthony P.; Penn-Clarke, Cameron R.

doi:10.1130/g47808.1

Cited by 3 publications

(2 citation statements)

References 24 publications

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“…Influence of glacial dropstones persisted, as seen in (H) where Diplichnites trackway on true substrate is forced to skirt around exposed part of dropstone (direction of travel arrowed: dropstone is that which is arrowed in (G). Late Ordovician Table Mountain Group, Matjiesgoedkloof, Western Cape, South Africa (see Davies et al ., 2020b for further details; measuring stick is 20 cm long).…”

Section: Classification Of Bedding Surfacesmentioning

confidence: 99%

True substrates: The exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces

Davies

Shillito

2021

Sedimentology

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Rock outcrops of the sedimentary-stratigraphic record often reveal bedding planes that can be considered to be true substrates: preserved surfaces that demonstrably existed at the sediment-water or sediment-air interface at the time of deposition. These surfaces have high value as repositories of palaeoenvironmental information, revealing fossilized snapshots of microscale topography from deep time. Some true substrates are notable for their sedimentary, palaeontological and ichnological signatures that provide windows into key intervals of Earth history, but countless others occur routinely throughout the sedimentary-stratigraphic record. They frequently reveal patterns that are strikingly familiar from modern sedimentary environments, such as ripple marks, animal trackways, raindrop impressions or mudcracks: all phenomena that are apparently ephemeral in modern settings, and which form on recognizably human timescales. This paper sets out to explain why these short-term, transient, small-scale features are counter-intuitively abundant within a 3.8 billion year-long sedimentary-stratigraphic record that is known to be inherently time-incomplete. True substrates are fundamentally related to a state of stasis in ancient sedimentation systems, and distinguishable from other types of bedding surfaces that formed from a dominance of states of deposition or erosion. Stasis is shown to play a key role in both their formation and preservation, rendering them faithful and valuable archives of palaeoenvironmental and temporal information. Further, the intersection between the time-length scale of their formative processes and outcrop expressions can be used to explain why they are so frequently encountered in outcrop investigations. Explaining true substrates as inevitable and unexceptional by-products of the accrual of the sedimentary-stratigraphic record should shift perspectives on what can be understood about Earth history from field studies of the sedimentary-stratigraphic record. They should be recognized as providing high-definition information about the mundane day to day operation of ancient environments, and critically assuage the argument that the incomplete sedimentary-stratigraphic record is unrepresentative of the geological past.

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Section: Classification Of Bedding Surfacesmentioning

confidence: 99%

True substrates: The exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces

Davies

Shillito

2021

Sedimentology

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“…No major relict glacial erosion landforms are associated to this glacial episode. Although renown for topping the iconic Table Mountain overhanging the city of Cape Town, the sedimentary record of the Ordovician glacial episode is spatially restricted to the Cape Fold Belt in South Africa (Thamm and Johnson, 2006;Ghienne et al, 2007;Fourie et al, 2010;Meadows and Compton, 2015;Davies et al, 2020).…”

Section: The Late Ordovician Glacial Episodementioning

confidence: 99%

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 Ordovician System of South Africa: a review

Penn-Clarke

Browning

Harper

2023

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Outcrops of the Ordovician System in South Africa are extensive; covering significant portions of the Northern, Western and Eastern Cape provinces as part of the Cape Fold Belt as well as the KwaZulu-Natal Province as supracrustal cover overlying the Natal sector of the Palaeoproterozoic Namaqua-Natal metamorphic province. Within the Cape Fold Belt, Ordovician-aged rocks of the Table Mountain Group (Piekenierskloof, Graafwater, Peninsula, Pakhuis and Cedarberg formations as well as the enigmatic Sardinia Bay Formation) outcrop extensively whilst pre-Cape rocks of the Kansa Group (Vaartwell, Uitvlug, Gezwinds Kraal and Schoongezigt formations) and Schoemanspoort Formation are present within the Kango Inlier encapsulated by the fold belt. The Natal Group (Durban and Mariannhill formations) is entirely located within KwaZulu-Natal. For the most part, these metasiliciclastic rocks are markedly unfossiliferous except for world class fossil deposits of the Cedarberg Formation and important trace fossil sites in the Graafwater, Peninsula and Pakhuis formations. The lack of palaeontological material and other accurate geochronological proxies in these successions (as well as those of the Kansa and Natal groups and Schoemanspoort Formation) makes estimations of relative age constraints tenuous at best and difficult to correlate with global Ordovician chronostratigraphic frameworks. Regardless of the challenges faced in correlating these rocks within global frameworks, these rocks provide a unique low latitude glimpse into Earth surface processes and the feedback loops that ensued with the biological realm along the southern margin of Gondwana.

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Cold feet: Trackways and burrows in ice-marginal strata of the end-Ordovician glaciation (Table Mountain Group, South Africa)

Cited by 3 publications

References 24 publications

True substrates: The exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces

True substrates: The exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces

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

The Ordovician System of South Africa: a review

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