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Quartzite dissolution: Karst or pseudokarst?
Abstract and Figures
A wide range of landforms of great similarity to limestone karst is found on many of the world's quartz sandstones and quartzites. These landforms have often been dismissed as pseudokarst, but recent investigation shows that the dissolutional removal of silica, even quartz, under earth-surface conditions is a critical process in their formation. They must therefore be regarded as true karst features. Recognition of these genetically similar forms on quartzose rocks now demands the worldwide adoption of a less restrictive, process-based, karst definition. Direct evidence for this near-surface dissolutional weathering is not common. Examples of this process are reviewed here, along with further evidence for the dissolution of silica from within the quartz sandstones of the Sydney Basin in temperate south-eastern Australia. Some of the complex processes by which dissolution attacks the rock remain unclear. However the solubility, thermodynamics, fluid throughput and physical removal of detritus are all critical factors in the formation of what can only be termed karst on quartzites and quartz sandstone.
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... Also, sandstone karst is used [5,6] and silicate karst [7]. As karstification occurs in nearly all silicate rocks there is high agreement to consider silicate karst as true karst phenomenon though silicate karst differs in many respects from carbonate karst [8][9][10]. ...
... The main difference to carbonate karst is the intergranular dissolution of quartz, which decreases the strength of the rocks [10]. Silikarst is widely spread with well exposed karst forms, best visible for example in Australia [8] and Africa [11,12]. In Germany, it occurs only locally, e.g., as tube-shaped caves in the western Pfälzer Wald up to good 40m in depth [5]: (Figures 1-5). ...
... Admittedly, the quartzite hole forms show a parallelism to forms of quite different origin. However, the major difference of silikarst to all the other mentioned forming processes is the transformation of the rock structure of quartz sandstones and quartzites [8,10,27]. This transformation is the decay of the rock solidness toward arenization [11] by quartz dissolution and porosity augmentation. ...
... The process operates in the subsurface and proceeds through the dissolution of crystal boundaries and grain contacts by the undersaturated meteoric water percolating through the cracks and tight vertical discontinuities in the rock mass (e.g., Mecchia et al., 2019). While arenization is not capable of removing the majority of rock bulk, it causes increase in rock porosity and reduction of its mechanical coherence (e.g., Wray, 1997). The altered portion of rock turns into loose sand, which is subject to erosional processes operating at depth, particularly along various lines of weakness in the host rock (e.g., Jennings, 1983;Galan and Lagarde, 1988). ...
... Extensive corrosion of quartz has been observed in A horizons of acidic soils developed upon sandy parent material (Little, 1978;Asumadu et al., 1988;Wilson, 2020). The effects of this process inspected in the microscale closely resemble those described elsewhere in quartzite/quartz sandstone tablelands, including severely etched silica cement (syntaxial overgrowths) as well as the abundance of distinctive embayments and crystalographicallycontrolled v-shaped pits on the surface of syntaxial overgrowths (e.g., Chalcraft and Pye, 1984;Young, 1986Young, , 1988Wray, 1997;Sauro, 2014;Sauro et al., 2019). The latter serve as a good indication of surfacereaction-controlled dissolution (Burley and Kantorowicz, 1986), i.e., the effect of slow dissolution kinetics, which might be interpreted as resulting from chemical weathering in subaerial conditions (e.g., Wilson, 1979;Wray, 1997;Sauro, 2014;Mecchia et al., 2019;Sauro et al., 2019). ...
... The effects of this process inspected in the microscale closely resemble those described elsewhere in quartzite/quartz sandstone tablelands, including severely etched silica cement (syntaxial overgrowths) as well as the abundance of distinctive embayments and crystalographicallycontrolled v-shaped pits on the surface of syntaxial overgrowths (e.g., Chalcraft and Pye, 1984;Young, 1986Young, , 1988Wray, 1997;Sauro, 2014;Sauro et al., 2019). The latter serve as a good indication of surfacereaction-controlled dissolution (Burley and Kantorowicz, 1986), i.e., the effect of slow dissolution kinetics, which might be interpreted as resulting from chemical weathering in subaerial conditions (e.g., Wilson, 1979;Wray, 1997;Sauro, 2014;Mecchia et al., 2019;Sauro et al., 2019). Such micromorphological features were found to be most widespread within quartz overgrowths of the grains of sand already detached, which might suggest that their erosional removal was preceded and facilitated by cement dissolution. ...
Despite recent major advances, complex factors contributing to the development of sandstone ruiniform relief still require recognition, particularly with respect to environmental controls and the character of the weathering processes responsible for the formation of corridors. The discovery of a small cave and roofed slots in one of ruiniform terrains in the Stołowe Mountains tableland, SW Poland – with active weathering and erosional processes – allowed us to tackle the problem. Our study confirmed earlier claims that the formation of corridors might lead through the speleogenesis. We showed that the process is geologically- and environmentally-controlled and is facilitated by cement dissolution. Thick sandstone beds of subhorizontal alignment, well-developed vertical jointing, high porosity and coarse grain size account for preferential groundwater drainage and the susceptibility to erosional removal of mass. The dominance of quartz and kaolinite in mineral composition, together with the present-day temperate climate and the dense vegetation cover, result in the development of permeable and very acidic soils upon the plateau surface. Such soils support efficient rainwater percolation, produce acidic solutions and create room for fungi dominance among soil microorganisms. The development of corridors of ruiniform relief is associated with structure-controlled topographic lows upon the plateau surface, which act as sinks. There, the throughput of acidic solutions, enriched with microorganisms, is the highest and over prolonged period of time causes dissolution of clay and quartz cement. Since its content is small, the dissolution results in the reduction of rock cohesion and the susceptibility to grain-by-grain detachment. Yet, dissolution is only a facilitator, with various mechanical processes (frost weathering, wetting-weakening, dilation) earlier recognized taking part in sandstone deterioration and upward propagation of voids, until the emergence of an unroofed corridor. The remaining bedrock compartments – hardened by protective surface crust – are also subject to dissolution, but at slower pace.
... Erosional landscapes in clastic sedimentary successions, especially in areas dominated by quartz arenites, had long been believed to be very far from karst, with the implication that subsurface processes are of negligible geomorphological significance (see reviews by Wray, 1997aWray, , 1997b. Insolubility of quartz was a dogma and hence, concepts developed in carbonate or gypsum karst were thought of as hardly applicable to sandstone terrains. ...
... Thus, dissolution of quartzite was convincingly demonstrated, initially in South Africa (Martini, 1979), then in Australia (Jennings, 1983;Young, 1986Young, , 1988Wray, 1997a) and the Guyana Shield (Doerr, 1999;Piccini and Mecchia, 2009;Sauro, 2014). These studies provided foundations for the concept of silicate karst (Wray, 1997b), now elaborately presented in karst global overviews (De Waele and Gutiérrez, 2022). The phenomenon of arenization, involving dissolution of siliceous cement and release of individual grains, is now an accepted mechanism of sandstone and quartzite breakdown (Wray and Sauro, 2017). ...
... Some plazas and corridors with remnants of a boulder fill show similarities to unroofed caves reported from many karst areas worldwide Slabe, 2002, 2023). Moreover, similar landform inventories have been described from quartz-rich lithologies and interpreted in terms of silicate karst phenomena (e.g., Briceño and Schubert, 1990;Piccini, 1995;Wray, 1997aWray, , 1997b). Yet, with the exception of enclosed depressions, the latter tended to be dismissed as only 'pseudokarst' or 'karst-like' features, since neither they bear signs of corrosion as the dominant weathering factor, nor have originated directly as a result of replacement of surface drainage by the underground one (e.g., Doerr, 1999;Aubrecht et al., 2011). ...
... Also, sandstone karst is used [5,6] and silicate karst [7]. As karstification occurs in nearly all silicate rocks there is high agreement to consider silicate karst as true karst phenomenon though silicate karst differs in many respects from carbonate karst [8][9][10]. ...
... The main difference to carbonate karst is the intergranular dissolution of quartz, which decreases the strength of the rocks [10]. Silikarst is widely spread with well exposed karst forms, best visible for example in Australia [8] and Africa [11,12]. In Germany, it occurs only locally, e.g., as tube-shaped caves in the western Pfälzer Wald up to good 40m in depth [5]: (Figures 1-5). ...
... Admittedly, the quartzite hole forms show a parallelism to forms of quite different origin. However, the major difference of silikarst to all the other mentioned forming processes is the transformation of the rock structure of quartz sandstones and quartzites [8,10,27]. This transformation is the decay of the rock solidness toward arenization [11] by quartz dissolution and porosity augmentation. ...
Demonstrating recent and paleo Silicate Karst (silikarst)
... When still capping the mesa, the quartz arenite is subject to efficient disintegration at depth by percolating water, with the critical, preparatory role of silica and clay minerals dissolution (Fig. 11A) and the removal of residuum outside the caprock (Fig. 11B) Migoń et al., 2023). This phenomenon, known as 'arenization', is typical for quartz sandstone/ quartzite-capped tablelands and is mainly confined to the discontinuity zones (e.g., Wray, 1997;Sauro, 2014). It leads to the development of underground passages and a ruiniform relief (e.g., Wray and Sauro, 2017), the latter particularly common in the studied tableland (Migoń et al., 2023). ...
... En estos lugares los paisajes son creados tanto por la composición geológica como por los procesos de disolución, y se denominan paisajes cársticos (Culver y Pipan, 2013). Sin embargo, cuando se desarrollan paisajes similares a los cársticos, pero sobre áreas que poseen rocas diferentes a las anteriormente mencionadas, estos se denominan pseudocarst (Wray, 1997). ...
El sistema cárstico de La Paz, ubicado en el municipio de La Paz, forma parte integral de la formación Rosablanca de la provincia santandereana de Vélez, en el departamento de Santander. Esta zona cuenta con gran cantidad de ambientes hipogeos, como cuevas, cavernas, hoyos y grutas, que en total contabilizan a la fecha 21 unidades. Sin embargo, reportes de habitantes locales sugieren que este número puede aumentar hasta algo más de 30 cavidades subterráneas en todo el municipio. Se actualiza en este trabajo la información de los principales grupos taxonómicos de fauna subterránea como un aporte al conocimiento de la biodiversidad colombiana en la que la biología subterránea juega un papel muy importante por su marcada tendencia a los endemismos y registros de especies con algún riesgo de extinción. El estudio incluye información obtenida en campo, así como la revisión y valoración de información válida. Los resultados de este trabajo indican la presencia de diferentes grupos taxonómicos, como aves, murciélagos, peces, crustáceos e insectos. Se registran al menos dos especies endémicas (un cangrejo y un pez) en los ambientes de cavernas en el municipio de La Paz
... Esses caminhos da água podem ser úteis também para o trânsito da fauna subterrânea (TRON-TELJ et al., 2009), favorecendo a conformação das identidades. Além disso, os diferentes recortes geológicos apresentam solubilidades distintas (FORD, WILLIAMS, 2007;WRAY, 1997). Isso faz com que haja variação na frequência e tamanho das cavernas (AULER, 2019) e, consequentemente, na conectividade entre sistemas subterrâneos. ...
Although several biogeographic clippings have already been proposed in the world, only one deals with subterranean ecosystems, being focused on subterranean aquatic habitats in Germany. In this sense, the existence of biogeographic identity in Neotropical subterranean ecosystems is tested here and an attempt is made to understand the factors that drive these identities. For this, data from communities of 249 caves in southeastern Brazil were used. Considering all arthropod species (3469 spp.), 23 regions with distinct biogeographical identities were obtained. Considering only troglobitic species (184 spp.) 17 regions were obtained. The determining factors were different for each region, demonstrating that landscape and climate attributes have different influences in each unit, depending on the species pool. This reinforces the idea that efficient measures for the conservation of subterranean ecosystems must, as a priority, respect regionalisms and their respective faunal identities.
... Calcite and gypsum are minerals that are commonly found in the karst environment (Chalmin et al. 2017). Likewise, SiO 2 might also be found in karst as dissolved minerals (Wray 2003). ...
Recent research on black pigment rock art reported on various prehistoric image sites globally consisting of carbon compounds and manganese oxides. In this paper, we report the unprecedented use of hematite as a black pigment material in rock art. Combination of scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM–EDS), X-ray fluorescence (XRF), synchrotron radiation X-ray diffraction (SR-XRD), X-ray absorption near-edge spectroscopy (XANES), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy was able to provide detailed information on the physicochemical characteristics of red, purple and black pigment materials from Jufri Cave, Sangkulirang, East Kalimantan. The results show that the mineral hematite is the main component of all pigment materials. However, the hematite crystals in each pigment possess different properties of crystallinity and octahedral symmetry of the Fe³⁺ ion. The characteristic differences in hematite compounds are possibly due to the high-temperature heating process and could be caused by natural geological or anthropological factors. Besides, the discrepancy of crystallinity and distortion of octahedral symmetry in the hematite structures are presumably responsible for the color variety among hematite crystals in the pigment material. The information on the physicochemical properties obtained from this research certainly adds new insights into the characteristics of pigments in the diversity of rock art in Indonesia.
... However, its investigations are significantly less intense than of true karst. Moreover, the conceptual understanding of pseudokarst and the related terminology remain debatable [1][2][3][4][5][6][7][8]. Undoubtedly, advance in the understanding of pseudokarst needs representative factual basis, and, thus, it depends strongly on reporting pseudokarstic features from many regions of the world with different geological and geomrophological settings. ...
New investigations in the Western Caucasus contribute to the understanding of granite pseudokarst (sensu lato) and megaclasts linked to river erosion. A plot on the bank of the Belaya River (Mountainous Adygeya, Western Caucasus) was selected to examine diverse and abundant pseudokarst features (small rock basins, hollows, potholes, and channels) and large clasts. Morphological analysis of these features clarifies their general characteristics and genetic interpretations. Pseudokarst features can be classified into two major categories, namely the relatively small (<1 m) and large (>1 m) features. Potholes, which are usually 1–3 m in size, are the most characteristic features occurring on two levels, i.e., on steep walls of the gorge (half-filled with river water) and on slightly inclined surfaces of a terrace-like landform (subaerial exposure). In both cases, their walls from the side of the river are broken. Apparently, these potholes were formed on the river bottom. Subsequent incision of the gorge elevated potholes and the river has eroded them from one side. Apparently, some pseudokarst features are related to macroturbulent flood flows and granite weathering. Due to its scientific uniqueness and aesthetic attractiveness, this granite pseudokarst constitutes geoheritage, which can be exploited for the purposes of geoscience research and geotourism development.
Caves and rockshelters occur in dolomite, siliciclastic and granite rocks of varying ages in Botswana and this leads to an interesting variety of entrance, passage and cavern types controlled by fracturing, bedding, groundwater levels, springs and slope processes. The dolomitic caves include the Gcwihaba Caves in northwestern Botswana and Lobatse Caves in southeastern Botswana. The siliciclastic caves/rockshelters occur at: Tsodilo Hills in northwestern Botswana; Tswapong Hills and Shoshong in eastern Botswana; Molepolole, Lekgolobotlo (Mmalogage), Manyana, Otse and Lobatse in southeastern Botswana. The granitic caves occur within the Lepokole Hills in eastern Botswana. The formation of the caves/rockshelters and their deposits are overviewed along with description of previous studies and the potential for further research is outlined in terms of landscape evolution and geoarchaeology.KeywordsGeodiversityCaveRockshelterBotswanaDolomiticSiliciclasticGranitic
Cement-porosity relationships are described from the Lower Triassic Sherwood Sandstone Group and the Middle Jurassic Ravenscar Group in the United Kingdom. Calcite cemented sandstones display a variety of replacement textures, with preferential replacement of grains and of overgrowth faces with high free-surface energy. Dolomite and siderite cemented sandstones display similar textures but replacement is less specific and euhedral overgrowth surfaces are commonly embayed by carbonates. Examination of the more porous sandstones with the scanning electron microscope reveals a range of pitting and embayment textures in authigenic overgrowths and in detrital grains. These range from small ‘v’-shaped notches and pits, through regular and irregular shaped embayments, into large depressions. These textures appear to be morphologically similar to the quartz surfaces seen in thin sections of carbonate cemented sandstones, and are interpreted to have been formed by the dissolution of pore-filling and grain replacive authigenic carbonates. This is confirmed by examination of experimentally exhumed overgrowth surfaces from carbonate cemented sandstones. These textures indicate that part of the intergranular porosity in these sediments is secondary in origin, and has been generated by the dissolution of carbonate cements. The identification of such textures may lead to a more confident interpretation of the nature of intergranular porosity in the subsurface.
Difficulties of attempting to measure loads of dissolved silica in rivers are discussed, particularly in relation to their use in assessing rates of catchment denudation. The evidence suggests that humid tropical landform studies need to pay attention to finer detail and to acknowledge that variation between one part of the humid tropics and another is possibly greater than variation between the humid tropics and other humid areas. -Editors
Under humid tropical conditions durite has a high degree of solubility that leads to the development of karst landforms similar to those found in limestone karst from temperate regions. Weathering characteristics of durite also show great similarity with limestone. -EditorsEnglish
Considering karst morphogenesis, there are no thresholds in the aqueous processes, but there are well-defined limits of mineral solubility. Because karst is rock specific and the other geomorphic systems are not, there is a situation of competition between karst processes and those of the zonal system. There is a threshold of effective competition which, if exceeded, results in other landforms or a polygenetic mix. Caves are the longest lived elements in our landscapes.-from Author
The largest karst-related landforms in sandstone are a number of scarpfoot-depressions which are the sites of all the oases in the region. They have been sunk below the level of late Pliocene pediments by 40 to 60m. Depressions are thought to have been formed by chemical deep weathering and subterranean export of solutes through the karst water system at a time when the climate was already too dry for etchplain formation in general in the southern Sahara. -from Authors
Les hauts plateaux greso-quartzitiques de la formation Roraima presentent, dans la region de La Gran Sabana, au sud-est du Venezuela, des caracteristiques macro et micro-geomorphologiques particulieres. D'une part, cette couverture sedimentaire precambrienne comporte des reliefs spectaculaires de hauts plateaux structuraux affectes par de grands anticlinaux, synclinaux et mono-clinaux en partie demanteles par l'erosion ; d'autre part, dans le detail, des formes pseudo-karstiques se sont developpees tant sur les silcretes de surface (lapies, guillochages, etc...) que dans les structures profondes (cavernes, gouffres). Diverses hypotheses sont avancees en conclusion, pour tenter une approche d'explication sur la genese des pseudo-karsts.