Soft-sediment deformation in a pre-vegetation river system: the Neoproterozoic Torridonian of NW Scotland

Owen, Geraint; Santos, Maurício Guerreiro Martinho dos

doi:10.1016/j.pgeola.2014.08.005

Cited by 41 publications

(25 citation statements)

References 93 publications

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“…Downstream accretion has only been documented at Site I, although thick planar cross‐sets elsewhere in the Applecross Formation (i.e. high‐flood deposits) can be related to such processes (Nicholson, ; Owen & Santos, ; Ielpi & Ghinassi, ). Downstream accretion is a common process in modern braided rivers (Cant & Walker, ; Ashworth et al ., ; Skelly et al ., ) and is most likely during phases of high discharge (Horn et al ., ,b), when sediment bypasses (at least in the part) the upstream‐bar and central‐bar zones, and accumulates in the downstream‐bar terminus.…”

Section: Discussionmentioning

confidence: 99%

Precambrian snapshots: Morphodynamics of Torridonian fluvial braid bars revealed by three‐dimensional photogrammetry and outcrop sedimentology

Ghinassi

Ielpi

2017

Sedimentology

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Pre‐vegetation fluvial channels have long been considered predominantly sheet‐like in geometry, owing to hydraulic sections that rapidly widened rather than incise during floods. This motif has been paralleled to that of modern dryland rivers subject to sharp discharge fluctuations during ephemeral floods. However, a number of Precambrian fluvial successions have been recently appraised as the product of deep‐channelled systems characterized by relatively stable – probably perennial – discharge regimes. One such example is the ca 1·0 Ga Applecross Formation, part of the well‐studied Torridon Group of Scotland. To contribute to this debate and to provide refined morphodynamic models for the Applecross Formation, this article presents an integration of three‐dimensional photogrammetry and outcrop sedimentology applied to key exposures at Stoer Peninsula, north‐western Scottish Highlands. Analysis of selected sandbodies reveals that high‐relief fluvial sand bars, both mid‐channel and bank‐attached, evolved within deep, braided‐channel belts. These bars grew through complex mechanisms of accretion and reactivation related to different flood stages: upstream and downstream accretion probably occurred during waning‐flood stages characterized by high hydrograph levels and abundant sediment availability; lateral accretion took place during later waning‐flood stages, and it was associated in some cases with helical recirculation and increase in bend sinuosity. Overall, the depicted morphodynamics are consistent with prolonged flood events that cannot be reconciled with sharply fluctuating discharge regimes. Critical comparisons between the internal geometry of the studied bars and modern counterparts corroborate the findings herein. Thus, this study recommends stricter comparisons between the products of modern braided channels and Precambrian fluvial rock records featuring thick and well‐developed bar forms.

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Section: Discussionmentioning

confidence: 99%

Precambrian snapshots: Morphodynamics of Torridonian fluvial braid bars revealed by three‐dimensional photogrammetry and outcrop sedimentology

Ghinassi

Ielpi

2017

Sedimentology

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“…The upward transition from sub-to super-critical deposits points to increasing flow strength or water shallowing (Stear 1983). Bedform collapse, sediment liquefaction, and flow-induced lateral shear generated local soft-sediment deformation (Owen and Santos 2014). Relationships with overlying and adjacent channel-fill deposits suggest deposition controlled by processes of channel migration and aggradation, typical of fluvial bars (Miall 1994).…”

Section: Discussionmentioning

confidence: 99%

Highly Variable Precambrian Fluvial Style Recorded In the Nelson Head Formation of Brock Inlier (Northwest Territories, Canada)

Ielpi

Rainbird

2016

Journal of Sedimentary Research

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Spectacular canyon exposures of the~1 Ga Nelson Head Formation along the modern Brock River, Northwest Territories, provide a rare opportunity to assess the deposits of pre-vegetation, braided to sinuouschannelized fluvial systems. We analyze the sedimentology, architecture, and depositional evolution of 16 stacked fluvial-channel belts at this site, demonstrating greater variability in sedimentary style and morphodynamics than is typically interpreted for Precambrian rivers. Inferences on fluvial planview based on integrated analysis of depositional architecture and paleoflow reveal complex patterns of channel-planform evolution, and four depositional stages are recognized: (1) floodbasin-splay progradation with bounding episodes of eolian reworking; (2) deposition in wandering-channel belts characterized by deep anabranches and prominent lateral accretion; (3) progressive shift towards shallow, braided-channel belts confined within alluvial valleys and dominated by downstream accretion; and (4) deposition by marine-influenced braided-channel belts with mixed downstream, lateral, and upstream accretion.Overall, the studied fluvial-channel belts point to significant morphodynamic complexity and geomorphic variability, challenging the assumption that all pre-Silurian rivers shared poor channelization and low sinuosity. Observed channel bodies also have width:thickness ratios strongly overlapping with those of rivers postdating the rise of vegetation. In both wandering-and braided-channel belts, complex patterns of channel migration, bar accretion, and dissection were the result of co-acting processes such as development of transverse-velocity zones within the channels, local paleoflow disturbance induced by depositional topography, and avulsion. In concert with the regional extent and paleoflow, and increasingly distal character of correlative stratigraphic units towards the northwest, the magnitude of the observed trunk-fluvial channels is consistent with a mature drainage capable of transecting the Laurentian craton over thousands of kilometers.

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“…The abundant soft-sediment deformation, affecting 50-60% of beds in the two formations, suggests high deposition rates combined with a high water table (e. g. Owen and Santos, 2014); the convoluted and pinched cuspate deformation forms are generally truncated by overlying beds. Palaeocurrents are overall towards the east, but vary between SE to NE (Williams, 1969(Williams, , 2001Nicholson, 1993;Ielpi and Ghinassi, 2015).…”

Section: Torridon Groupmentioning

confidence: 96%

Tracking the evolution of the Grenvillian foreland basin: Constraints from sedimentology and detrital zircon and rutile in the Sleat and Torridon groups, Scotland

Krabbendam

Bonsor

Horstwood

et al. 2017

Precambrian Research

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The Grenville Orogen, although occupying a key position in the Rodinia supercontinent, lacks a clear foreland basin in its type area in eastern Canada. Early Neoproterozoic siliciclastic rocks in northern Scotland, however, are now interpreted as remnants of a proximal Grenvillian foreland basin. Analysis of the sedimentology and detrital zircon and rutile of the Torridon and underlying Sleat groups provide new constraints on the evolution of this basin. Youngest U-Pb detrital zircon grains yield ages of 1070-990 Ma in both groups, consistent with a Grenvillian source. The proportions of older age components vary throughout the stratigraphy. The lower Sleat Group shows a dominant ca. 1750 Ma peak, likely derived from local Rhinnian rocks in Scotland and Ireland uplifted within the Grenville Orogen. In the upper Sleat Group and Torridon Group, detrital zircon peaks at ca. 1650 Ma and ca. 1500-1100 Ma become increasingly important. These latter peaks correspond with Labradorian Pinwarian, Elzevirian and early Grenvillian protolith ages within the eastern Grenville Province in Canada, and reflect exhumation and erosion of different mid-crustal complexes within that sector of the orogen. There is no difference in detrital zircon ages across the low-angle Sleat/Torridon unconformity. Detrital rutile in the Torridon Group yields a significant ca. 1070 Ma, Grenville-age peak, but older grains (1700-1200 Ma) also occur, suggesting derivation from the cool (T<600°C) upper orogenic crust. The detrital mineral data and sedimentology suggest the following evolution of the Grenvillian foreland basin in Scotland: i) early deposition in a narrow marine foreland basin (lower Sleat Group), sourced from the Irish-Scottish sector of the Grenville Orogen, with orogen-normal fill; ii) within the narrow Sleat Group basin a gradual switch to more distal sources in the Canadian sector of the Grenville Orogen, via axial transport; iii) an abrupt switch in basin dynamics (but not in source) across the Sleat-Torridon boundary to fluvial braidplain deposition in a much wider, Torridon-Morar basin; iv) followed by a gradual retrogradation of that basin. The Torridon-Morar groups represent a major denudational event of the Grenville Orogen that we infer was linked to more distal deposits in East Greenland, Svalbard and Norway.

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Soft-sediment deformation in a pre-vegetation river system: the Neoproterozoic Torridonian of NW Scotland

Cited by 41 publications

References 93 publications

Precambrian snapshots: Morphodynamics of Torridonian fluvial braid bars revealed by three‐dimensional photogrammetry and outcrop sedimentology

Precambrian snapshots: Morphodynamics of Torridonian fluvial braid bars revealed by three‐dimensional photogrammetry and outcrop sedimentology

Highly Variable Precambrian Fluvial Style Recorded In the Nelson Head Formation of Brock Inlier (Northwest Territories, Canada)

Tracking the evolution of the Grenvillian foreland basin: Constraints from sedimentology and detrital zircon and rutile in the Sleat and Torridon groups, Scotland

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