The geomorphology of solution cave sequences in the Kalk Bay Mountains, southern Cape Peninsula. BSc thesis, 1996, Shearer, H.

The Kalk Bay Mountains of the southern Cape Peninsula, South Africa, show marked development of pseudokarstic features such as caverns, dolines and grikes. These features have formed over at least 100 million years on supposed inert quartzitic sandstones of the Peninsula Formation of the Table Mountain Group. Pseudokarst on sandstone is relatively rare world-wide and various aspects of cave genesis are highlighted in the Cape Peninsula. Cape Peninsula pseudokarst is relict, occurs at high altitudes above the present water table and could provide clues to palaeoenvironmental conditions during the African erosion period.
The cave systems in the Kalk Bay Mountains occur in at least three levels in the thickly-bedded sandstone. These different levels are the result of differential uplift during the Miocene and Pliocene. The Cape Peninsula Mountains are tabular and blocky, as opposed to the fold mountains of the rest of the South Western Cape. Much more of the overlying sedimentary layers in the Cape Peninsula have also been removed by weathering and erosive processes. The caves can be compared to similar pseudokarst features on sandstone in areas such as Gran Sabana, Venezuela. The acidic water chemistry in Venezuela contributes to a very intensive weathering environment. Present day humid tropical conditions in Venezuela are likely to be similar to palaeoclimatic conditions in the Kalk Bay Mountains, contributing to sandstone cave genesis.

Karst-like landforms and hydrology in quartzites of the Venezuelan Guyana shield: Pseudokarst or 'real' karst?, 1999, Doerr Sh,

The surfaces of table mountains (Tepuis) in southeastern Venezuela display well-developed karst topography including caves, sinkholes and karren-features. Although the rock (orthoquartzite of the Precambrian Roraima Formation) has a very low solubility, active cave systems are present with passages more than one kilometre in length, descending to more than 300 metres depth. These dimensions are greater than any so far reported in quartzitic rocks. There is strong evidence that corrosive rather than erosive processes are responsible for the karstification. Thin-sections of rock samples show dissolution not only of the amorphous silica cement, but also of the crystalline quartz grains themselves. Together with field observations in and near an active cave system on the Kukenan Tepui, this indicates a close similarity between the processes active on the Venezuelan table mountains and karstification processes in rocks of greater solubility. A combination of factors including high precipitation (4000-7000 mm/year), rock of very high purity (98 % silica) and the absence of other significant geomorphological processes prevailing for at least several million years are thought to have enabled a spectacular karst landscape to evolve in a rock that in the past has been regarded as almost immune to chemical weathering

Review: What is karst?, 2000, Goede, Albert

A review of a paper by Doerr, S.H., 1999, Karst-like landforms and hydrology in quartzites of the Venezuelan Guyana shield: pseudokarst or "real" karst? Zeitschrift fur Geomorphology, 43(1), 1-17. The erosion process appears to involve solution of the silica, not just weathering of the cement.

Zum Gedenken. Eugenio de Bellard Pietri (1927-2000)., 2002, Trimmel, H.

[Venezuela]

AGRAPHORURA CALVOI n. sp. from Venezuelan caves (Collembola: Onychiuridae), 2005, Arbea J, I.

A new species of Agraphorura (Collembola: Poduromorpha: Onychiuridae) from caves in the North-West of Venezuela is described. A. calvoi n. sp. can be distinguished from its congeners by the following combination of characters: antennal organ III with four papillae, 32/133/33343 dorsal pseudocellar formula, 3/000/0112 ventral pseudocellar, subcoxae each with two pseudocelli, postantennal organ with 7-9 vesicles, unguiculus with a basal lamella, tibiotarsi I-III with 19,19,18 setae (distal whorl of 9 setae). A table with the differential characters, as well as an identification key for all of the known species of Agraphorura are provided.

Panstrongylus geniculatus (Heteroptera: Reduviidae: Triatominae): natural infection with Trypanosoma cruzi under cavernicolous conditions in Paraguana´ Peninsula, Venezuela, 2007, Molinari J. , Aldana E. , And Nassar J. M.

The flagellate protozoan, Trypanosoma cruzi, causes Chagas disease, a zoonosis affecting millions of humans in the Americas. The triatomine insect, Panstrongylus geniculatus, a well known vector of this disease, inhabits and is infected with T. cruzi in Cueva del Guano, a limestone cave in Paraguana´ Peninsula, Venezuela. P. geniculatus probably feeds on the blood of four rare or endangered bat species roosting in this cave, infecting them with T. cruzi. It is recommended that (1) any epidemiological activity at this cave be designed to minimize bat mortality, and (2) speleologists visiting tropical caves avoid contact with triatomine insects and their feces.

Sandstone caves on Venezuelan tepuis: Return to pseudokarst?, 2011, Aubrecht R. , Lanczos T. , Gregor M. , Schlogl J. , Smida B. , Liscak P. , Brewercarias C. H. , Vlek L.

Venezuelan table mountains (tepuis) host the largest arenite caves in the world. The most frequently used explanation of their origin so far was the "arenization" theory, involving dissolution of quartz cement around the sand grains and subsequent removing of the released grains by water. New research in the two largest arenite cave systems - Churi-Tepui System in Chimanta Massif and Ojos de Cristal System in Roraima Tepui showed that quartz dissolution plays only a minor role in their speleogenesis. Arenites forming the tepuis are not only quartzites but they display a wide range of lithification and breakdown, including also loose sands and sandstones. Speleogenetic processes are mostly concentrated on the beds of unlithified sands which escaped from diagenesis by being sealed by the surrounding perfectly lithified quartzites. Only the so-called "finger-flow" pillars testify to confined diagenetic fluids which flowed in narrow channels, leaving the surrounding arenite uncemented. Another factor which influenced the cave-forming processes by about 30% was lateritization. It affects beds formed of arkosic sandstones and greywackes which show strong dissolution of micas, feldspars and clay minerals, turning then to laterite ("Barro Rojo"). The main prerequisite to rank caves among karst phenomena is dissolution. As the dissolution of silicate minerals other than quartz appears to play not only a volumetrically important role but even a trigger role, these arenitic caves may be ranked as karst.

Dokumentation von zwei Quarzithöhlen am Roraima Tepui (Brasilien, Guyana) , 2011, Plan L. , Hölzel M. , Auler A.

The Gran Sabana extends over the area between the Amazonas and Orinoco River in the northern part of South America. There about hundred table mountains (locally named Tepuis) are rising above the wet savannah plain. One of these, the Roraima Tepui, is situated at the triple border junction of the states of Brazil, Guyana and Venezuela. The plateau is built up of sandstones and quartzites of palaeoproterozoic age (c. 1.9 Billion years). Several caves which have mainly developed due to mechanical erosion of not or just partly lithified sandstone layers have been explored. The aim of a Brazilian Austrian expedition in November 2010 was to visit caves in the southern part of the Roraima Tepui and search for new caves in the less accessible northern part. The Cueva Ojos de Cristal (or Sistema Roraima Sur) was visited. With a mapped length of 16.1 km it is the biggest quartzite cave known in the world. Two caves were mapped, the Hotel Coati and the Lake Gladys Cave, which are the highest lying documented caves of Guyana and Brazil respectively. The Hotel Coati is situated in the north of the Tepui and is a cave often used as a bivouac. It is a shaft, acting as ponor, which is accessible through galleries aligned at rectangularly arranged fissures. North of that cave, in the Guyanese part, the single lake on the plateau, the Lake Gladys is situated at 2665 m a.s.l. There, the Lake Gladys Cave with a total length of 68 m is draining the lake. The entrance lies behind a boulder fall and water disappears into a sump. At the Roraima Tepui there are other not docu - mented objects so far, as the shaft ponor El Fosso (The Pit). Even though no major systems were found during this short expe - dition, the potential of finding further caves in the northern part seems still good.

Solutional Weathering and Karstic Landscapes on Quartz Sandstones and Quartzite, 2013, Wray, R. A. L.

Landscapes on highly quartzose bedrock that exhibit almost identical scale and morphology to those on karstified limestones occur under a range of climates and on most continents. These include ruiniform towers, grikes, stone cities, caves, dolines, smaller surface karren, and silica speleothems.

However, these rocks are much less soluble than most carbonates, and the weathering processes are quite different. However, because chemical solution is demonstratively a critical component in the genesis of these landforms, they may be regarded as karst. This chapter summarizes the processes of karstification in quartz sandstones and then reviews the incidence of these landforms around the world.

Comment on “Sandstone caves on Venezuelan tepuis: Return to pseudokarst?” by R. Aubrecht, T. Lánczos, M. Gregor, J. Schlögl, B. Smída, P. Liscák, Ch. Brewer-Carías, L. Vlcek, Geomorphology 132 (2011), 351–365, 2013, Sauro F. , Piccini L. , Mecchia M. , De Waele J.

In the recent work of Aubrecht et al. (2011) the presence of “unlithified or poorly-lithified beds” of sands in the quartz-sandstone stratigraphic succession is proposed as a key factor for speleogenesis in the Venezuelan tepuis.In this comment we observe that in the cited work the geologic history of the region, in terms of sedimentation environment, diagenesis and low grade burial metamorphism, has not been considered. Furthermore, the peculiar “pillar flow” columns that Aubrecht et al. describe as a proof of the unlithification are lacking in many other different cave systems in the same area.

Four critical points are discussed: the burial metamorphism of the Mataui Formation, the significance of the Schmidt Hammer measurements, the cave morphologies and the role of SiO2 dissolution. Finally we suggest that weathering, in its wider significance, is probably the triggering process in speleogenesis, and there is no need to invoke a differential diagenesis of the sandstone beds. ©

Comment on “Sandstone caves on Venezuelan tepuis: Return to pseudokarst?” by R. Aubrecht, T. Lánczos, M. Gregor, J. Schlögl, B. Smída, P. Liscák, Ch. Brewer-Carías, L. Vlcek, Geomorphology 132 (2011), 351–365, 2013, Sauro Francesco, Piccini Leonardo, Mecchia Marco, De Waele Jo

In the recent work of Aubrecht et al. (2011) the presence of “unlithified or poorly-lithified beds” of sands in the   quartz-sandstone stratigraphic succession is proposed as a key factor for speleogenesis in the Venezuelan tepuis.   In this comment we observe that in the cited work the geologic history of the region, in terms of sedimentation   environment, diagenesis and low grade burial metamorphism, has not been considered. Furthermore, the   peculiar “pillar flow” columns that Aubrecht et al. describe as a proof of the unlithification are lacking in   many other different cave systems in the same area.   Four critical points are discussed: the burial metamorphism of the Mataui Formation, the significance of the   Schmidt Hammer measurements, the cave morphologies and the role of SiO2 dissolution. Finally we suggest   that weathering, in its wider significance, is probably the triggering process in speleogenesis, and there is no   need to invoke a differential diagenesis of the sandstone beds

Structural and lithological guidance on speleogenesis in quartz–sandstone: Evidence of the arenisation process, 2014,

A detailed petrographic, structural and morphometric investigation of different types of caves carved in the quartz–sandstones of the “tepui” table mountains in Venezuela has allowed identification of the main speleogenetic factors guiding cave pattern development and the formation of particular features commonly found in these caves, such as funnel-shaped pillars, pendants and floor bumps. Samples of fresh and weathered quartz–sandstone of the Mataui Formation (Roraima Supergroup) were characterised through WDS dispersive X-ray chemical analyses, picnometer measurements, EDAX analyses, SEM and thin-section microscopy. In all the caves two compositionally different strata were identified: almost pure quartz–sandstones, with content of silica over 95% and high primary porosity (around 4%), and phyllosilicate-rich quartz–sandstone, with contents of aluminium over 10% and low primary porosity (lower than 0.5%). Phyllosilicates are mainly pyrophyllite and kaolinite. SEMimages on weathered samples showed clear evidence of dissolution on quartz grains to different degrees of development, depending on the alteration state of the samples. Grain boundary dissolution increases the rock porosity and gradually releases the quartz grains, suggesting that arenisation is a widespread and effective weathering process in these caves. The primary porosity and the degree of fracturing of the quartz–sandstone beds are the main factors controlling the intensity and distribution of the arenisation process. Weathering along iron hydroxide or silt layers, which represent inception horizons, or a strata-bounded fracture network, predisposes the formation of horizontal caves in specific stratigraphic positions. The loose sands produced by arenisation are removed by piping processes, gradually creating anastomosing open-fracture systems and forming braided mazes, geometric networks or main conduit patterns, depending on the local lithological and structural guidance on the weathering process. This study demonstrates that all the typical morphologies documented in these quartz–sandstone caves can be explained as a result of arenisation, which is guided by layers with particular petrographic characteristics (primary porosity, content of phyllosilicates and iron hydroxides), and different degrees of fracturing (strata-bounded fractures or continuous dilational joints).