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Sedimentary Environments and Facies
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
The deposits (‘drifts’) produced out of glacial action are of two types: stratified and unstratified. Varves, outwash deposits and eskers are examples of stratified drifts. Unsorted mixtures of morainic gravel, sand and mud (designated as ‘till’ in older literature) are called ‘diamicts’. Lithified equivalents of diamicts are ‘diamictites’ (meaning a thorough mixture of mud and gravel, from Greek: diamignymi—to mix thoroughly). Glacial facies are described here under two headings: continental and marine, following Eyles and Miall (1984).
Strong tides during Cryogenian glaciations: tidal rhythmites from early and late Cryogenian glacial successions and interglacial beds, South Australia
Published in Australian Journal of Earth Sciences, 2023
In the Depot Flat area NNE of Port Augusta (Figure 1), a regolithic breccia that formed on stromatolitic dolomite of the Tonian Burra Group is unconformably overlain by 150 m of interbedded, locally ankeritic diamictite, breccia, conglomerate, sandstone and shale of the Sturt Formation (Hopton, 1983; Preiss, 1993). There, sandstone, shale and diamictite forming the lowermost 6–8 m of the Sturt Formation are succeeded by a unit of yellowish brown, well-bedded to rhythmically laminated, fine- to coarse-grained sandstone with scattered small pebbles. This arenaceous unit was termed the ‘varve unit’ by Hopton (1983). The unit is 38 m thick in Hopton’s northernmost section 5 (32°14′49.02″S, 137°57′10.02″E) and thins southwards to 6 m over a distance of 1 km, wedging out further south. In the north, the ‘varve unit’ is followed by 70 m of interbedded clast-rich diamictite with clasts up to 1 m in diameter, clast-poor diamictite, shale with dropstones ≤5 cm in diameter, sandstone and conglomerate. The ‘varve unit’ was deposited during early glacial advance.
Reconciling the onshore/offshore stratigraphy of the Canning Basin and implications for petroleum prospectivity
Published in Australian Journal of Earth Sciences, 2023
C. T. G. Yule, J. Daniell, D. S. Edwards, N. Rollet, E. M. Roberts
By far the thickest unit in this study, the Grant Group is mapped across the onshore Canning, offshore Canning, Browse, Roebuck and Northern Carnarvon basins (Figure 6c). It consists of several units composed of sandstone, siltstone, mudstone, diamictite and minor conglomerate. The Grant Group has a large time range where the top of the unit varies between −278 and –8074 ms (TWT), where it is above sea-level farther inland of the Canning Basin and deepest in the Roebuck Basin near the Argo Abyssal Plain. It is also thick, reaching up to ∼1000 ms (TWT); however, it may be thicker in the Roebuck Basin, but the lower boundary is unclear (Figure 5c). The Grant Group displays shallow dips in the Canning Basin, whereas it is steeply dipping in the Browse and Roebuck basins. There are more subtle trends including being found deeper in the Fitzroy Trough than in the rest of the Canning Basin and an anomaly in a depocentre southeast of the Bedout High. The Grant Group is not present where the Bedout High is prominent and on shallower parts of the Browse Basin. The Grant Group can be easily identifiable in seismic data because of its strong reflectors, and the top boundary is commonly marked by a regional-scale unconformity where it is unconformably overlain by Mesozoic strata (Figure 3a).
Re-visiting the structural and glacial history of the Shackleton Glacier region of the Transantarctic Mountains, Antarctica
Published in New Zealand Journal of Geology and Geophysics, 2022
The type section of the Bennett Platform Formation lies along the flanks of the Shackleton Glacier, suggesting a protracted time interval followed deposition of the Shackleton Glacier Formation. During this interval a landscape with incised glacial valleys, not too dissimilar to today’s topography, was developed (Hambrey et al. 2003). Old glacial deposits, first reported and illustrated by McGregor (1965), are perched high on the south-facing valley wall of the Shackleton Glacier at Dismal Buttress (Figure 6). The deposits, sitting about 200 m above Shackleton Glacier and plastered on a steep slope of Fremouw strata, comprise weakly bedded diamictite, containing dolerite and sandstone clasts, overlain by unstratified till (McGregor 1965, Figures 3 and 4). These Sirius strata represent glacial sedimentation on essentially modern topography but at an early stage in the carving of the glacial valley. From the perspective of the topographic setting and the presence of dolerite clasts, the strata should be assigned to the Bennett Platform Formation. However, it seems improbable that they were contemporaneous either with the type section of the Bennett Platform Formation, which is located about 25 km to the north and up to about 100 m above ice level, or with the Bennett Platform Formation beds documented by Hambrey et al. (2003) at a higher elevation overlying dolerite on the northern flank of Dismal Buttress.