Manganese stromatolites in caves: El Soplao (Cantabria, Spain)

Abstract

In the dark regions of caves, the formation of stromatolites is virtually unknown. Although Mn oxide crusts presumably induced by bacteria have been described in some caves, they lack stromatolite features, and the evidence of microbial origin is normally inconclusive. Here we describe for the fi rst time the occurrence of extensive Mn oxide stromatolites formed in the deep interior of a cave. The stromatolites are of decimeter thickness and kilometer extent and show features extremely similar to typical CaCO 3 stromatolites. However, unlike most stromatolites, their biogenicity is supported by the exceptional abundance of fossil microbes. Our data support that the stromatolites were mainly induced by chemolithotrophic Mn-oxidizing microbes, and were formed in a low-gradient water-table stream passage at least ~1 m.y. ago. The El Soplao stromatolites (Cantabria, Spain) may contribute to increasing our understanding of microbial life in extreme environments, as well as the role of bacteria in the genesis of modern and ancient Mn deposits.

Paleoflood events recorded by speleothems in caves

“…Spectacular helictites, anthodites and huge speleothems are the most relevant aesthetic features of this mine show‐cave. Other unusual speleothems have also been described in this cave, including the dark amberine speleothems whose colour is related to lixiviates from a carbonaceous stratum located above this speleothem formation (Gázquez et al ., ), black ferromanganese crusts (Gázquez et al ., ) and ferromanganese stromatolites (Rossi et al ., ).…”

“…Topography courtesy of El Soplao S.L and cross‐section modified from Rossi et al . (). This figure is available in colour online at wileyonlinelibrary.com/journal/espl…”

Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs

“…The mechanisms controlling their genesis have been extensively studied, trying to shed light on the evolution of early metabolisms (Allwood et al, 2010;Bontognali et al, 2012). Although most microbialite studies focus on processes occurring in the photic zone of marine and lacustrine environments (Bosak et al, 2013), a growing number of works also deals with biomineralization processes that take place in subsurface environments (Jones, 2001(Jones, , 2011Melim et al, 2001;Olivier et al, 2003;Baskar et al, 2007Baskar et al, , 2011Baskar et al, , 2014Blyth and Frisia, 2008;Lisker et al, 2009;Rossi et al, 2010;Florea et al, 2011;Lundberg and McFarlane, 2011;Gradzíński et al, 2012;Lozano and Rossi, 2012;Léveillé et al, 2000;Pacton et al, 2013;Tisato et al, 2015). It has often been hypothesized that life originated in the dark, protected from the strong UV radiation that characterized the surface environments of the early Earth and other planets (Homann et al, 2016).…”

In situ Raman characterization of minerals and degradation processes in a variety of cultural and geological heritage sites

“…The precipitation of this metal oxide in the El Soplao Cave is related to the mobilization of manganese from the host rock probably under phreatic anaerobic conditions and subsequent precipitation on the walls and floors of the cave as oxides when the water table fell and conditions were again oxygenic [15]. The oxidation of manganese was probably mediated by microorganisms (as suggested by the presence of fossil bacteria inside ferromanganese speleothems discovered in this cave in previous studies [16]). …”

“…Spectacular helictites and huge speleothems are the most relevant aesthetic features of this mining show-cave [12]. Other unusual speleothems have also been described, including amberine stalactites [13], flowstones containing layers of cemented detrital materials [14], black ferromanganese crusts and stromatolites [15,16], frostwork-type speleothems and moonmilk deposits [17], some of which were studied in our in situ survey.…”