Abstract: M. Ivarsson, T. Sallstedt, J. Lundberg, 2011. Biogeology and speleothems in Tjuv-Antes grotta, N. Sweden: A preliminary report. Presentation at the 2nd International Congress on Granite Caves, June 1, 2011, Nynäshamn, Sweden. [PDF]
Tjuv-Antes grotta (Tjuv-Ante's Cave; Sjöberg 1982) is one of several caves in Storrisberget, Nordmaling, northern Sweden. It is a large round-abraded sea-cave (tunnel cave), about 30m in length and formed along a dolerite dyke in granitegneiss. The width of the cave forming crevice is about 0.5 to 1.5m. The inner part of the crevice has a dolerite roof (forming a cave proper), while the outer part is open. Much of the crevice, especially in its outer part, is filled with dolerite boulders from the collapsed roof. The crevice with the cave shows clear signs of abrasion, forming a beautiful tunnel cave, and rounded boulders, which aided in the polishing of the cave, are still to be found in the interior. The entrance is situated approximately 90 masl. The shoreline reached this altitude about 7000 years ago, and it was around this time that the abrasion and polishing of the walls shaped the crevice into the typical pear profile.
The cave was (re)discovered by Rabbe Sjöberg in 1966, and already at that time he noticed the coralloid speleothems covering areas of the dolerite in the innermost part of the cave. A more careful investigation of the speleothems was however initiated by Sjöberg in August 2010, in collaboration with Juan Ramón Vidal Romaní. In contrast to the better known karst caves, where speleothems normally are calcitic (CaCO3), the speleothems investigated from granitic cavities, have so far been found to consist of biogenic opal-A (SiO2•15H2O; Vidal Romaní & Vaqueiro 2007, Vidal Romaní et al. 2010). However, the sample of the coralloids surprisingly turned out to be composed of calcite, and SEM images taken by Vidal Romaní showed the presence of partly calcified microorganisms, though not in the amounts normally present in the opal-A speleothems. These images were sent to Sjöberg, who forwarded them to us.
In early May 2011 we visited Tjuv-Antes grotta to sample the coralloids for studies using the facilities at the Swedish Museum of Natural History (NRM) and Stockholm University. We also sampled some of the biofilm present at the cave wall close to the speleothem. Our working-hypothesis is that the speleothem is fairly recent, at most 7000 years but possibly much younger, and that the microorganisms present may play some role in the precipitation of calcite and build-up of speleothems. Whether the microorganisms are inducing calcite precipitation actively by metabolically altering the chemistry of their microenvironment leading to calcification, or simply influence the precipitation by providing suitable crystal nucleation sites, presumably related to the biofilm extracellular polymeric substances (EPS), is an ongoing investigation. The source of calcium is presently unknown but may be related to meteoric water seepage leading to the leaching of dolerite plagioclase. We are currently investigating these questions using fluorescent microscopy, environmental SEM (ESEM) and confocal microscopy. We have further sampled the interior of the speleothem for DNA analysis in collaboration with the Ancient DNA lab at NRM for a metagenomic study, and a stable isotope study is planned for the summer/fall 2011.
Sjöberg, R. 1982. Tunnelgrottor i södra Västerbotten: morfologiska och morfogenetiska studier. Gerum Rapport A:31. Umeå.
Vidal Romaní, J.R. & Vaqueiro, M. 2007. Types of granite cavities and associated speleothems: genesis and evolution. Nature Conservation 63: 41-46.
Vidal Romaní, J.R., Sanjurjo Sánchez, J., Vaqueiro, M. & Fernández Mosquera, D. 2010. Speleothems of granite caves. Comunicações Geológicas 97: 71-80.