Gypsum speleogenesis: a hydrogeological classification of gypsum caves

Abstract

Abstract:This article reviews the state of the art of speleogenetic investigations in gypsum karsts from numerous studies carried out over the past 50 years in Spain. A classification of gypsum karsts is proposed based on the hydrogeological, tectonic and stratigraphic criteria that decisively control the evolution of gypsum karsts. In this respect, lithological aspects of Messinian and Triassic-Permian gypsum series in south-eastern Spain are considered, such as the alternation of rhythmic levels of marl and gypsum, as well as geodynamic aspects. The influence of the hydrogeological characteristics of evaporite aquifers on gypsum cave speleogenesis is discussed; this includes speleogenetic processes in confined, semi-confined or free aquifers controlled by regional and local base levels. Also, the importance of intense saline diapiric uplift is examined. To illustrate our classification, examples of gypsum caves developed in Spain are presented. Their similarities and differences with gypsum karsts in other regions (Italy, Ukraine, and USA) are discussed. A first general division addresses: (1) caves controlled by stratigraphic factors and (2) caves controlled by tectonic factors. Several typologies can be described, including (A) multilayer caves with confined hydrogeological origin, (B) confined hypophreatic caves with linear or maze configurations, (C) caves controlled by the variation or remanence of regional or local base-levels, and (D) caves controlled by the halokinetic evolution of salt/gypsum diapirs. The proposed classification is flexible and adaptable to each case, because different genetic mechanisms can coincide in time and space. Likewise, most considerations stated in this work about gypsum karst are valid for speleogenesis in other rock types.caves, gypsum, karst, speleogenesis

Structural control on epigenic gypsum caves: evidences from Messinian evaporites (Northern Apennines, Italy)

“…Gypsum karst is globally widespread with individual caves strongly influenced by past and present variations in local geology, climate, and hydrology. Three epigenic gypsum areas were compared with observations from the Northern Apennines to extend the scope of this work; Sorbas evaporites, Spain (Calaforra et al, 1990;Calaforra and Gàzquez, 2017), Castile evaporites, USA (Stafford et al, 2008), and Sicilian Messinian evaporites, Italy (Cucchi, 1989;Madonia and Vattano, 2011).…”

“…Following the classification proposed by Calaforra and Gàzquez (2017), the epigenic gypsum caves can be divided in two main groups: those controlled by stratigraphy/lithology ("multi-strata" caves) and those controlled by tectonics ("multi-base levels" caves). The first group is characterized by a high-frequency alternation of evaporitic and non-evaporitic strata with very low dip in a geological setting where tectonic activity is weak or absent.…”

“…Phreatic and vadose conditions (and associated morphologies) are mainly linked to this lithologic control: tubes and proto-conduits are developed inside the gypsum beds in phreatic conditions, where dissolution is predominant on erosion. The non-evaporitic beds, on the other hand, were eroded during vadose conditions and formed specific morphotypes (Calaforra et al, 1990;Calaforra and Gàzquez, 2017).…”

“…This kind of epigenic karst is typical for medium to high dipping evaporite beds, with uplift that controlled speleogenesis and cave development on different sub-horizontal levels. Hydrological regime, base level fluctuations (usually downward), and climatic variations control the evolution of epiphreatic and vadose passages (Calaforra and Gàzquez, 2017). Using this classification, Castile Formation, Sicilian and Northern Apennines karsts (Columbu et al, 2015) can be classified as multi-base level caves, whereas the Sorbas area shows epigenic karst systems connected to both models.…”

“…As remarked by Billi et al (2007), a small number of field-based geomechanical, quantitative and structural studies describing the importance of fractures in the development of karst processes are available in the literature. Some of these studies were carried out in carbonate rocks (Rodet, 1999;Billi et al, 2007;Gale and Gomez, 2007), while others mention the importance of structures in the development of karst in gypsum rocks (Bertolani and Rossi, 1972;Finotelli et al, 1985;Belvederi and Garberi, 1986;Cucchi, 1989;Forbes and Nances, 1997;Hill, 2000;Bentini, 2003;Stafford et al, 2008;Ghiselli et al, 2011;Klimchouk et al, 2009;Klimchouk, 2013;Reitman et al, 2014;Calaforra and Gàzquez, 2017). Ghiselli et al (2011) also describe the importance of structural analysis in gypsum caves to reconstruct the deformation chronology at both local and regional scale.…”