Guano-related phosphate-rich minerals in European caves

Abstract

Guano is a typical deposit found in caves derived from the excretions of bats and in minor cases of birds. These organic deposits decompose and form a series of acid fluids and gases that can interact with the minerals, sediments, and rocks present in the cave. Over sixty phosphates are known and described from caves, but guano decay also often leads to the formation of nitrates and sulfates. In this study twenty-two European caves were investigated for their guano-related secondary minerals. Using various analytical techniques, seventeen phosphates, along with one sulfate (gypsum), were recognized as secondary products of guano decay. Among those minerals, some are very rare and result from the interaction of guano leachates with clays, fluvial deposits, or pyrite. Some of these minerals are even found only in the studied caves (spheniscidite, robertsite). The most common minerals belong to the apatite group. The common mineral association present in fresh decaying guano is brushiteardealite-gypsum, minerals that usually are not present in older deposits because of their higher solubility. Most minerals are in hydrated form because of the wet cave environment; however, some specific dry conditions may favor the presence of dehydrated minerals, such as berlinite, formed during guano combustion. Investigation on the acidity of guano piles shows pH values as low as 3.5 with an increase of acidity with age and depth. Finally, cave guano deposits should be better studied in the future because of their role in paleoenvironmental and paleoclimatic reconstructions and because it is important to better understand the origin of guano-related minerals, especially the phosphates and sulfates. Among all of the caves studied, Corona 'e sa Craba (Italy) and Domica-Baradla Cave (Slovakia-Hungary) are considered to be outstanding sites with respect to their phosphate mineralogy. secondary cave minerals, phosphates, minerogenesis, limestone caves, bat guano

Bats as ecosystem engineers in iron ore caves in the Carajás National Forest, Brazilian Amazonia

“…In the active or inactive bat caves with deposits of guano, the speleothems are larger more abundant and more diversified. A variety of complex reactions takes place in the guano, especially bacterial decomposition, liberating nitric, phosphoric and sulphuric acids which react with the rock or the sediments to form secondary minerals [36, 37].…”

“…The high temperatures identified in bat caves have been pointed out to potentialize air convection and condensation of acid-rich corrosive aerosols on cooler walls and ceilings, contributing to the dissolution of the surrounding rock [37, 58, 62]. In Carajás, another important thermal factor operates: the water percolating the caves is heated when crossing the iron ore layer above.…”

Epigenic vs. hypogenic speleogenesis governed by H2S/CO2 hydrothermal input and Quaternary icefield dynamics (NE French Pyrenees)

“…Cave sediments were probably first weathered in phreatic conditions before the complete retreat of the glacier, and was followed by a partial dissolution and destabilization through sub-aerial condensationcorrosion in vadose conditions that dissolved the carbonate part (15 to 20%) and led to the hydrolyze of the clay fraction (e.g. Audra et al, 2016). Then, the sandy residual sediments (not easily altered by condensation-corrosion) could be evacuated by sudden hydraulic purge during late melting phases of perched residual glaciers, either directly to the cave outlet toward the Ariège Valley or to the base of the caves, thus clogging a part of the sump.…”

Application of Line of Sight and Potential Audience Analysis to Unravel the Spatial Organization of Palaeolithic Cave Art

“…Furthermore, the same sedimentary and erosive processes can completely alter the topography of a cave over a short (Van Gundy & White, 2009) or long period (Laureano et al, 2016). To these issues, one might add the taphonomic problems of biological (Audra et al, 2019;Bruxelles et al, 2016) and human origin, including prehistoric morphological changes (e.g. Geneste, 2001;Balbín-Behrmann et al, 2003;Arias et al, 2004).…”