Speleothems and speleogenesis of the hypogenic Santa Barbara Cave System (South-West Sardinia, Italy)

Abstract

This paper presents t�e results of a study on t�e speleogenesis and t�e speleot�ems and secondary mineralisations of t�e Santa Barbara Cave System in t�e Iglesiente Mining District (Sout�-West Sardinia, Cagliari). This cave system, �osted in Cambrian carbonate rocks, �as a very long geological �istory and its main voids �ave formed in �ypogenic conditions. Nine speleogenetic p�ases can be recognised ranging in age between Cambrian and Holocene. Optical microscope and diffractometric analysis of active flowstone deposits �ave s�own t�em being composed of alternating calcite and aragonite layers. The textural and c�emical c�aracteristics of t�ese layers, obtained by SEM and EDAx analysis, suggest t�em to be related to variations in t�e depositional environment inside t�e cave, w�ic� in turn are probably correlated to external climatic oscillations.

Diagenesis of a drapery speleothem from Castañar Cave: from dissolution to dolomitization

“…Calcitization has been recognised in a certain number of caves (Folk & Assereto, 1976;Cabrol & Coudray, 1982;Frisia et al, 2002;Woo & Choi, 2006;Pagliara et al, 2010). This process takes place by dissolution at the microscale of metastable aragonite and precipitation of the stable phase, calcite (Perdikouri et al, 2008), when waters are undersaturated in aragonite and oversaturated in calcite (Maliva et al, 2000;Frisia et al, 2002).…”

“…Relatively Mg enriched waters, as those found in Castañar Cave, can explain the formation of this type of calcite, and they would also be responsible for the presence of aragonite in the studied drapery, since it is commonly accepted that aragonite forms in the speleothems when Mg/Ca ratios in the waters are high (Cabrol & Coudray, 1982;González & Lohmann, 1988;Frisia et al, 2002;Rowling, 2004) due to the inhibiting role of Mg 2+ in calcite growth (Berner, 1975;Lippmann, 1973;Fernández-Díaz et al, 1996). Commonly, the high Mg/Ca necessary for aragonite formation has been related to evaporation that may accompany seasonal dryness (Railsback et al, 1994) and warmer and dryer climatic conditions (Pagliara et al, 2010), although aragonite precipitation has also been reported in comparatively wet climatic conditions due to the effect of Zn 2+ or Pb 2+ in inhibiting precipitation of calcite (Caddeo et al, 2011). of the primary texture.…”

“…Conditions leading to calcitization and eventually dissolution in pathway 2 can be related with more humid climatic conditions (Denniston et al, 2000;Woo & Choi, 2006;Pagliara et al, 2010) or with seasonal events of high rainfall (Railsback et al, 1994). Another source of fluids undersaturated in calcite and aragonite can be the condensation of water from cave air (de Freitas, 2010) which can be especially aggressive if the CO 2 contents in the cave are high (Sarbu & Lascu, 1997;Sánchez-Moral et al, 1999).…”

“…They are attractive to paleoclimatologists because: i) they can grow continuously and be precisely dated through a series of techniques (Frisia & Borsato, 2010); ii) they capture the cave response to the external environment during their formation (cave temperature is around the mean annual external temperature and dripwater discharge reflects the amount of infiltration) (McDermott, 2004); and iii) they generally show little secondary alteration (Fairchild et al, 2006). However, diagenetic processes affecting speleothems have been recognised in a certain number of caves around the world (Cabrol, 1978;Frisia et al, 2002;Woo & Choi, 2006;Woo et al, 2008;Hopley et al, 2009;Martín-García et al, 2009;Aramburu Artano et al, 2010;Pagliara et al, 2010). Diagenetic processes can potentially modify the original features of speleothems, including their geochemical signatures (Frisia et al, 2002;Woo & Choi, 2006), so their use in paleoclimate studies can be problematic.…”

Speleogenesis of an exhumed hydrothermal sulphuric acid karst in Cambrian carbonates (Mount San Giovanni, Sardinia)

“…Its development must thus be placed below the water table, at least predominantly, as demonstrated by the presence of barite crystals and calcite cave clouds. During approximately the past one million years meteoric drip water has deposited large vadose calcite and aragonite speleothems making this chamber one of the most extraordinary cave environments of the world, of great scientific importance (Forti et al ., ; Pagliara et al ., ). These chemical deposits also sealed up part of the cave passages, allowing for the formation of a perched lake in the lowest part of Santa Barbara 1 cave.…”