Projects / Programmes
Biogenicity of fibrous microcrystalline calcite in vadose terrestrial settings
| Code |
Science |
Field |
Subfield |
| 1.06.03 |
Natural sciences and mathematics |
Geology |
Sedimentology |
| Code |
Science |
Field |
| P005 |
Natural sciences and mathematics |
Geology, physical geography |
| Code |
Science |
Field |
| 1.05 |
Natural Sciences |
Earth and related Environmental sciences |
Calcium carbonate, terrestrial settings, speleothems, moonmilk, biomineralization, EPS
Researchers (1)
| no. |
Code |
Name and surname |
Research area |
Role |
Period |
No. of publicationsNo. of publications |
| 1. |
36049 |
PhD Andrea Martin Perez |
Geology |
Head |
2016 - 2017 |
99 |
Organisations (1)
Abstract
Fibrous microcrystalline calcite (FMC) is one of the most common and widespread forms of secondary calcium carbonate in vadose terrestrial environments (caves, soils, surficial sediments, etc.). FMC is characterized by two basic habits: needle fiber calcite (NFC) and nanofibers, both varieties composed of low-Mg calcite. The origin of FMC crystals has generally been attributed either to purely physicochemical processes or to microbial biomineralization. The current biogenic hypotheses are largely based on common co-occurrence of fibrous calcite and microbial features, and the similarity in dimensions and morphology of calcite fibers with fungal hyphae and filamentous bacteria. Morphological arguments for biogenicity have been supported by geochemical and petrographic data, considered as biosignatures preserved in certain forms of FMC.
There is a considerable evidence that deposits of FMC make specific microbial ecosystems in the vadose zone, i.e., many studies have shown positive association of diverse microbial communities with fibrous calcite, what is particularly evident in soft, hydrated cave sediments known as moonmilk. However, the controversy remains regarding the role of microorganisms in carbonate mineralization.
The purpose of the proposed project is to test the hypothesis of biogenic precipitation of FMC using in-situ and laboratory investigation of calcite moonmilk from actively precipitating sites in four Slovenian karst caves. The project is primarily aimed at evaluating the mechanisms of biologically-induced vs. biologically-influenced vs. inorganic precipitation. The main objectives are: 1) to define the physicochemical parameters of the FMC precipitation microenvironments in caves through systematic, regular in-situ measuring, sampling, and analysis (optimally, through a one year period); 2) to characterize organic and inorganic chemistry of water from moonmilk deposits; 3) to extract and characterize organic polymeric substances from the moonmilk interstitial waters; 4) to examine the structure of FMC precipitating microenvironments; and 5) to undertake in-situ precipitation experiments of calcite crystallization in natural cave environment but under controlled conditions.
The proposed study sites in Slovenian caves are targeted because they include all different microenvironments of FMC precipitation. One of the caves is close to the lab and easily accessible throughout the year and will be used as a main field site for regular sampling of water and mineral precipitates, as well as for continuous microclimate determination.
The study will contribute to the understanding of fundamental principles of calcium carbonate deposition in near-surface terrestrial settings. Apart from the broad field of sedimentology, the results will bear significance for geomicrobiology and materials science.
Significance for science
Our research has contributed to the understanding of fundamental principles of calcium carbonate deposition in near-surface terrestrial settings, an inherent subject of sedimentology. The addressed problems are on the interface of several scientific fields from geomicrobiology, cave & karst studies, soil science, and crystallography: results thus bear significance in all these disciplines. The approach of the proposed project has been specific in entering a largely unexplored gap between pure biogenic and inorganic models of precipitation of fibrous microcrystalline carbonates. The results have strengthened the perception of non-classical crystallisation mechanisms in natural, geological settings. Methodologically, we have put special emphasis to the preparation techniques for the study of complex materials, such as calcite moonmilk, which are predominantly composed of water and with only minor inorganic hard matter, embedded in diluted organic matrices. The preparation of good quality thin sections of such material, and the use of cryogenic techniques, has shown excellent results in the observation of these highly hydrated structures.
Significance for the country
The results have provided a basis for the evaluation of geological sites in studied caves in terms of their conservation, protection and educational value. These have been focused on identification and conservation of cave sediments of specific scientific importance. During our regular visits to the caves, we have noticed damages in the moonmilk deposits, which have been scratched and excavated, showing the urgent need to establish physical measures of cave protection. The project’s results will be primarily applied for educational purposes. Snežna jama na Raduhi is a turist cave with considerable number of visitors, however, spectacular moonmilk deposits in the cave have been only briefly mentioned in guided tours and publications. Although the mechanisms of formation of moonmilk speleothems are a very specific and complex topic, they can be used to illustrate the fascinating interface of processes operating in geosphere, hydrosphere and microbial biosphere.
Most important scientific results
Final report
Most important socioeconomically and culturally relevant results
Interim report,
final report
