A Comparison of Clast Fabric and Shape in Late Precambrian and Modern Glacigenic Sediments

Dowdeswell, Julian A.; Hambrey, Michael J.; Ruitang, Wu

doi:10.1306/212f87bf-2b24-11d7-8648000102c1865d

Cited by 28 publications

(2 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The exotic nature of clasts, the clast shapes and the striated surfaces (cf. Dowdeswell, Hambrey & Wu 1985) all suggest that the material had undergone a phase of glacial transport before its final translation as debris flows to the valley floor. Such material could be envisaged as lateral dump moraines (cf.…”

Section: IImentioning

confidence: 97%

Post-glacial mass flow and associated deposits preserved in palaeovalleys: the Late Precambrian Morænesø Formation, North Greenland

Collinson,

Bevins,

Clemmensen

1989

Meddr Grønland. Geosci.

View full text Add to dashboard Cite

The Morænesø Formation is of Late Proterozoic age and is preserved as the fills of a series of palaeovalleys. The formation is made up of conglomerates and sandstones of fluvial and aeolian origin and of a series of breccias which resulted almost entirely from gravitational mass movement down the sides of the palaeovalleys. At the most extensive exposure, examples of local rock-fall, rock-slide and matrix-poor breccia flows are observed close to the valley side. Their movement was probably favoured by freeze-thaw mechanisms. More widespread diamictites overlie valley-floor sands and were deposited under water-saturated conditions as a series of mass flows apparently from the sides of the palaeovalleys. The diamictites contain far-travelled clasts, some of which show striated surfaces suggesting a phase of glacial transport prior to final emplacement. Only at one locality does diamictite directly overlie the basal unconformity and suggest possible in situ till. The diamictite sheets are overlain by a widespread but thin dolomite unit which shows spectacular stromatolitic domes. At other localities in the area, valley fills show evidence of floating lake ice with dropstone pebbles occurring in thin bedded sandstones and mudstones. The palaeovalleys are thought to have been eroded by valley glaciers which, on retreat, left substantial volumes of till on the valley sides and possibly in tributary valleys. Any moraine deposited on the valley floor was eroded by fluvial activity priorto a phase of alluvial and aeolian aggradation which coincided with local mass movement in cold conditions. Catastrophic rainfall, probably related to a generally wetter palaeoclimate, remobilised lateral moraines and other deposits and emplaced them on the valley floor. Deep weathering of dolerites at the unconformity suggests an ameliorated climate and a substantial time gap prior to these mass flows. A body of shallow water, established on the valley floor soon after these events, led to deposition of stromatolitic dolomite. The Morænesø Formation represents remarkable preservation of a complex series of local glacial and post-glacial deposits in an upland setting compared with the more widespread lowland or marine tillites of Late Proterozoic age in other areas.

show abstract

Section: IImentioning

confidence: 97%

Post-glacial mass flow and associated deposits preserved in palaeovalleys: the Late Precambrian Morænesø Formation, North Greenland

Collinson,

Bevins,

Clemmensen

1989

Meddr Grønland. Geosci.

View full text Add to dashboard Cite

show abstract

“…Even differentiating samples visually is difficult because populations associated with very different process domains commonly have substantial overlap in particle shape when plotted on conventional diagrams (e.g. Dowdeswell et al, 1985;Bennett et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

New statistical methods for the comparison and characterization of particle shape

Graham

Gadsden

2019

Earth Surf Processes Landf

View full text Add to dashboard Cite

This paper presents novel methods for robust statistical testing of particle shape data. Shape (the relative lengths of three orthogonal axes) is a key property of sedimentary particles, providing information on provenance, transport history and depositional environment. However, the usefulness of shape data, including the ability to make robust comparisons between samples, has been constrained by the absence of a satisfactory definition of the mean shape for a sample of particles. Such a definition is proposed and used to develop confidence regions for the population mean shape using both parametric (theoretical) and computational (bootstrap) methods. These techniques are based on a transform that permits multivariate statistical methods for the analysis of compositional data to be extended to shape. These techniques are validated with reference to a dataset of 169 clast samples and found to perform well. A statistical test on the mean – using the multivariate extension of Student's t‐test, Hotelling's T2 – is presented. The benefits of the methods presented are demonstrated with reference to a case study. © 2019 John Wiley & Sons, Ltd.

show abstract

Neoproterozoic Glaciated Basins: A Critical Review of the Snowball Earth Hypothesis by Comparison with Phanerozoic Glaciations

Etienne¹,

Allen

Rieu

et al. 2007

Glacial Sedimentary Processes and Products

View full text Add to dashboard Cite

The Neoproterozoic is widely considered to have experienced some of the most severe climatic perturbations recorded in Earth history, with extensive glaciations often referred to as 'Snowball Earth' events. The Snowball Earth and competing hypotheses seek to explain a wide range of geological data on Neoproterozoic pre-, syn-and post-glacial successions including glacial sedimentology, chemostratigraphy, palaeoceanography, geochronology, palaeomagnetism and palaeogeography, geodynamics, tectonics, palaeontology and palaeobiogeochemistry. However, our understanding of the Phanerozoic and particularly the Cenozoic and contemporary glacial geological record is often relatively neglected when evaluating the evidence for apparent severe and prolonged periods of globally synchronous glaciation. This paper presents a review of the available geological data for Neoproterozoic glacial successions in the light of what we know about the Cenozoic and recent glacial record. Most Neoproterozoic successions are shown to exhibit spatial and temporal variability, with sediment stacking patterns and facies associations indicative of dynamic ice masses. These characteristics are typical of sedimentary sequences deposited along glaciated continental margins throughout Earth history, without the need for global synchroneity or necessarily severe climatic excursions. Although recurrent very widespread glaciation is envisaged in the Neoproterozoic, the presence of analogous glacigenic and interglacial successions in the Neoproterozoic and Cenozoic suggest the operation of a similar set of processes across a similar range of depositional environments. Consequently, an unambiguous sedimentary record of hydrological shutdown during a prolonged global glaciation appears to be lacking. This indicates either a preservational bias in Neoproterozoic successions of the advance and recessional stages of glacial epochs, or the occurrence of dynamic, non-global glaciations during the Neoproterozoic.

show abstract

A Comparison of Clast Fabric and Shape in Late Precambrian and Modern Glacigenic Sediments

Cited by 28 publications

References 0 publications

Post-glacial mass flow and associated deposits preserved in palaeovalleys: the Late Precambrian Morænesø Formation, North Greenland

Post-glacial mass flow and associated deposits preserved in palaeovalleys: the Late Precambrian Morænesø Formation, North Greenland

New statistical methods for the comparison and characterization of particle shape

Neoproterozoic Glaciated Basins: A Critical Review of the Snowball Earth Hypothesis by Comparison with Phanerozoic Glaciations

Contact Info

Product

Resources

About