Bat guano minerals and mineralization processes in chameau cave, Eastern Morocco

Philippe Audra, Vasile Heresanu, Lionel Barriquand, Mohamed El Kadiri Boutchich, Stéphane Jaillet, Edwige Pons-Branchu, Pavel Bosák, Hai Cheng, R. Lawrence Edwards, Michel Renda

Research output: Contribution to journalArticlepeer-review

Abstract

The decay of bat guano deposits in caves produces mineral accumulations, mainly phosphates and secondary sulfates. Chameau Cave, Eastern Morocco, is located in the semi-arid Bni Snassen Mountains. It is composed of semi-active and dry passages, and is featured by strong condensation-corrosion on the walls, presence of fluvial sediments, and old corroded flowstones. Due to forced and convective airflow, the cave is generally very dry, with some damp sites related to condensation. Samples collected on the surface of different passages and along two sediment profiles yielded minerals related to bat guano decay. On recent or fresh guano, precursor minerals correspond to sulfate (gypsum), phosphate-sulfate (ardealite) and phosphate (brushite). Phosphates (hydroxylapatite, fluorapatite) occur at the interface with host rock or carbonate speleothems. At the contact of phyllosilicates contained in allogenic fluvial deposits or shale partings, or with pyrite-rich sediments, various phosphates occur (Al-rich strengite, Fe-rich variscite, phosphosiderite, leucophosphite, spheniscidite, crandallite, minyulite, variscite, and strengite), the latter two minerals being the stable end-members. Black seams of oxyhydroxides (goethite, hematite, birnessite) line the contact between carbonate host rock and weathered fluvial deposits. After “digestion” by acidic guano leachates, fluvial deposits only display the most resistant minerals (quartz, muscovite, K-feldspars, and Na-plagioclases) and weathering byproducts (kaolinite). We discuss the origin of a pure gypsum particle cone, possibly related to evaporation at the edge of a wet cupola and subsequent detachment of sulfate particles. Among environmental conditions, humidity is required for decay. In this dry cave, most of the damp originates from either permanent or seasonal condensation. Dust particle advection seems to be essential in providing compounds that are not present on fresh guano (quartz, clay minerals). Bat guano phosphatization has probably occurred since >100 ka. The Chameau Cave appears as an outstanding site for bat guano-related minerals (n = 12), including rare phosphates (spheniscidite and minyulite).

Original languageEnglish (US)
Pages (from-to)91-109
Number of pages19
JournalInternational Journal of Speleology
Volume50
Issue number1
DOIs
StatePublished - 2021

Bibliographical note

Funding Information:
This study was granted by the Fondation de la Vallée de Zegzel. Pavel Bosák was supported by the Institutional financing of the Inst. Geol., Czech Acad. Sci. no. RVO6798531. We particularly thank Christian Dodelin, “Bat delegate” of the French Federation of Speleology (FFS), for identification of the bat species; Jean-Jacques Bahain, Yann Callot, and Jacques Martini for fruitful discussions; Daniel Borschneck for XRD analyses of samples Cham 3 to 9b at CEREGE; Roger Notonier for MEB images and EDX analyses at PRATIM; Olivier Grauby for the SEM-TEM analysis at CINaM, all three at Aix Marseille University; Daniel Chailloux for participating at the survey of Chameau Cave; Hubert Camus for providing Morocco’s cave inventory. The inhabitants of Zegzel village are especially acknowledged for their warm welcome during each field session. Finally, we are grateful to an anonymous reviewer, Carol A. Hill, Paolo Forti, and Bogdan P. Onac, for their insightful comments and suggestions.

Publisher Copyright:
© 2021, Societa Speleologica Italiana. All rights reserved.

Keywords

  • Cave dust
  • Condensation/evaporation
  • Phosphates
  • Sulfates
  • “Candy-floss” gypsum

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