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Red sandstones of the Cambrian age are globally distributed and represent an important sedimentation phase during this critical time interval. Their sedimentology and geochemistry can provide key information about the sedimentation style, paleoclimatic conditions, and weathering trends during the Cambrian. In the Salt Range of Pakistan, the Khewra Sandstone constitutes the Lower Cambrian strata and consists of red–maroon sandstones with minor siltstone and shale in the basal part. Cross-bedding, graded bedding, ripple marks, parallel laminations, load casts, ball and pillows, desiccation cracks, and bioturbation are the common sedimentary features of the formation. The sandstones are fine to medium to coarse-grained with subangular to subrounded morphology and display an overall coarsening upward trend. Petrographic analysis indicates that the sandstones are sub-arkose and sub-lithic arenites, and dolomite and calcite are common cementing materials. X-ray Diffraction (XRD) analysis indicates that the main minerals in the formation are quartz, feldspars, kaolinite, illite, mica, hematite, dolomite, and calcite. Geochemical analysis indicates that SiO₂ is the major component at a range of 53.3 to 88% (averaging 70.4%), Al₂O₃ ranges from 3.1 to 19.2% (averaging 9.2%), CaO ranges from 0.4 to 25.3% (averaging 7.4%), K₂O ranges from 1.2 to 7.4% (averaging 4.8%), MgO ranges from 0.2 to 7.4% (averaging 3.5%), and Na₂O ranges from 0.1 to 0.9% (averaging 0.4%), respectively. The results of the combined proxies indicate that the sedimentation occurred in fluvial–deltaic settings under overall arid to semi-arid paleoclimatic conditions with poor to moderate chemical weathering. The Khewra Sandstone represents the red Cambrian sandstones on the NW Indian Plate margin of Gondwana and can be correlated with contemporaneous red sandstones in the USA, Europe, Africa, Iran, and Turkey (Türkiye). Full article

Glacial ripping is a newly recognized process sequence in which subglacial erosion is triggered by groundwater overpressure. Investigations in gneiss terrain in lowland Sweden indicate that ripping involves three stages of (i) hydraulic jacking, (ii) rock disruption under subglacial traction, and (iii) glacial transport of rock blocks. Evidence for each stage includes, respectively, dilated fractures with sediment fills, disintegrated roches moutonnées, and boulder spreads. Here, we ask: can glacial ripping also occur in sedimentary rocks, and, if so, what are its effects? The case study area is in hard, thinly bedded, gently dipping Cambrian quartz-arenites at Loch Eriboll, NW Scotland. Field surveys reveal dilated, sediment filled, bedding-parallel fractures, open joints, and brecciated zones, interpreted as markers for pervasive, shallow penetration of the quartz-arenite by water at overpressure. Other features, including disintegrated rock surfaces, boulder spreads, and monomict rubble tills, indicate glacial disruption and short distance subglacial transport. The field results together with cosmogenic isotope ages indicate that glacial ripping operated with high impact close to the former ice margin at Loch Eriboll at 17.6–16.5 ka. Glacial ripping thus can operate effectively in bedded, hard sedimentary rocks, and the accompanying brecciation is significant—if not dominant—in till formation. Candidate markers for glacial ripping are identified in other sedimentary terrains in former glaciated areas of the Northern Hemisphere. Full article