Calcrete morphology and karst development in the Upper Old Red Sandstone at Milton Ness, Scotland

Abstract

The Upper Old Red Sandstone at Milton Ness, Scotland, is notable for its excellent preservation of calcrete textures, which are comparable with some of the best Quaternary examples. It is also significant for the implications that can be drawn from the association between karst and calcrete, with this example interpreted to have formed entirely within a semi-arid environment. Karst cavities were developed in a mature hardpan calcrete, generated in sandy fluvial sediments with associated aeolian deposits. Subsequent to karst cavity generation, clasts derived from the subaerially exposed hardpan were locally transported and deposited as a laterally traceable bed connecting the tops of all the cavities. Both this bed and the karst infills were subsequently recalcretized in the final phase of the profile's evolution. Although calcrete-karst associations often are interpreted as the alternation between semi-arid and humid climates, respectively, this example is interpreted to be a result of water accumulating on the nearly impervious hardpan surface under fairly constant semiarid conditions, evidenced by the recalcretization of both the karst infill and the calcretederived breccia ('boulder calcrete'). Additional substrate modification also has taken place by plant roots; the remarkable development of rhizoliths in these Old Red Sandstone sediments should emphasize the need to consider plant influence on other non-marine rocks of post-Silurian age.

Review of groundwater flow and contaminant transport modelling approaches for the Sherwood Sandstone aquifer, UK; insights from analogous successions worldwide

“…Note that, the Sherwood Sandstone Aquifer in west Cumbria where cavities were detected by optical and acoustic televiewer logs is located in the proximity of the Lake District mountains and hence elevated hydraulic gradients (0.15-0.35) and intense groundwater flow occur (Black and Brightman 1996;Medici et al 2016Medici et al , 2018Medici et al , 2019b. Karst-like cavities and caves have been reported in some other sandstones with calcite cement in five continents; the Devonian in Australia (Young 1986(Young , 1988, the Carboniferous in Scotland (Balin 2000), the Permian in China (Yang et al 2011), the Jurassic in Luxembourg (Meus and Willems 2021), the Cretaceous in Czech Republic (Kůrková et al 2019), and the Miocene in Nigeria (Wray 1997). Karstlike groundwater flow velocities have been found in the Sherwood Sandstone Aquifer in England (1.6x10 -3 m/s average peak flow velocity), the Jurassic Sandstone of Luxembourg (4.4x10 -3 m/s and 9.7x10 -2 m/s as average pick and maximum flow velocities, respectively), and the Cretaceous in Czech Republic (maximum flow velocities reported 2.2x10 -2 -2.02x10 -1 m/s) by using tracer testing (Barker et al 1998;Kůrková et al 2019;Meus and Willems 2021).…”

Earliest Triassic Claystone Breccias and Soil-Erosion Crisis

“…Permian-Triassic boundary pedoliths of the Karoo Basin include abundant redeposited caliche nodules, with diagnostic replacive-micritic and displacive-sparry internal fabrics, like nodules within underlying fossil Aridisols (Lootsberg, Wapadsberg, and Bethulie of Retallack et al 2003). These can be termed calcic pedoliths, which are widespread because lithified caliche nodules are stable in water (Tandon and Narayan 1981;Retallack 1991;Balin 2002). Only a few Karoo Basin clasts included pseudomorphs of gypsum (Fig.…”

Widespread freshwater carbonate in the Olduvai Basin, a precursor to a major eruption in the East African Rift System

“…Relatively low trace element concentrations suggest that the wetland waters were oxidizing, therefore, iron and manganese would not be in their reduced valency (2+) and thus be unlikely to replace Ca 2+ in calcite. The abundance of circumgranular cracks, mottles, glaebules and possible root traces indicates episodic shallowing and subaerial exposure (Balin, ). Similar deposits are described from Polish Upper Triassic freshwater limestones (Szulc et al , ).…”