Biosignatures in Subsurface Filamentous Fabrics (SFF) from the Deccan Volcanic Province, India

Jens Götze,Beda Hofmann,Berthold Ottens,Hermann Ehrlich,Mikhail V Tsurkan,Reinhard Kleeberg,Tomasz Machałowski,Teofil Jesionowski

doi:10.3390/min10060540

Abstract

The morphology, chemical, and mineralogical composition of subsurface filamentous fabrics (SFF) from the Deccan Volcanic Province (DVP) were investigated to determine the origin of these spectacular aggregates. SFF occur in a wide variety of morphologies ranging from pseudo-stalactites to irregular fabrics and are classified as SFFIr (irregular) or SFFMa (matted). The SFF samples exhibit a thread-like (or filament-like) center from which mineral precipitation starts to form the final macroscopic morphologies. Detailed investigations revealed organic material (fungal chitin) in the innermost filamentous core, which may have acted as an initial nucleus for the mineralization processes. The morphometric characteristics of certain filamentous fabrics are very similar to those of microbial filaments and the fabrics formed from them but are clearly distinct from similar types of non-biological precipitates (fibrous minerals, speleothems, and “chemical gardens”). These features indicate that the filamentous cores might be products of microbial communities that were active in the basaltic cavities. The SFF cross-sections display similar concentric layers of the mineral succession and reach thicknesses of several centimeters with spectacular lengths up to 100 cm and constant diameters. The typical mineralization sequence points to temporal variation in the chemical composition of the mineralizing fluids from Fe(Mg)-rich (Fe-oxides/-hydroxides, Fe-rich sheet silicates such as celadonite and di-/tri-smectite) to Ca-dominated (Ca-rich zeolites) and finally pure SiO2 (opal-CT, chalcedony, and macro-crystalline quartz). Assuming biological activity at least during the early mineralization processes, circumneutral pH conditions and maximum temperatures of 100–120 °C were supposed. The formation of filamentous cores including Fe-bearing phyllosilicates probably occurred near the surface after cooling of the lava, where the elements necessary for mineral formation (i.e., Si, Mg, Al, Fe) were released during alteration of the volcanic host rocks by percolating fluids.

Highlights

The Deccan VolcanicProvince (DVP; isamong amongEarth’s largest continental flood (DVP;Figure Figure 1)1) is thethe continental flood
The subsurface filamentous fabrics (SFF) occur in the open space of cavities and exhibit a wide variation in macroscopic The SFF occur in the open space of cavities and exhibit a wide variation in macroscopic morphology morphology
We have shown that the following morphometric parameters of the filamentous fabrics are consistent with the same parameters that were obtained from certain microbial filaments, while they are strongly different from the same parameters as obtained from a range of non-biological filament-like objects: diameter of the innermost filaments; variability of the diameter of the innermost filaments; tortuosity; degree of bending; number of direction changes

Summary

Methods

Most of the sample material (SFF and secondary minerals) was collected during several field trips from large, freshly opened cavities within the flow core zone in the quarry complex of Savda near. The cavities here contain a large number of valuable mineral specimens resulting in careful mining of crystals including SFF over the last 20 years. These mining activities allowed long-term observations and thorough geological and mineralogical studies of the SFF and related mineralization, which could be used for the present study. Polarizing microscopy in transmitted light on polished thin sections was performed on a ZEISS Axio Imager A1m microscope (ZEISS, Thornwood, NY, USA). Luminescence images were recorded by a Peltier cooled digital video-camera (OLYMPUS DP72, OLYMPUS Deutschland GmbH, Hamburg, Germany) and CL spectra measured with an Acton

Results

Discussion

Conclusion