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

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.

Mineralogy, Geochemistry and Genesis of Agate—A Review

“…The internal structure of SFF is mostly made up of a core of clay minerals (in particular smectite), celadonite and zeolites, followed by concentric layers of chalcedony. Similar results were obtained for moss agates (Figure 34e), which also show clear indications of biosignatures [33,195,213,214].…”

“…It is assumed that the stalactites have been formed simultaneously with the wall layers from a liquid that had completely filled the cavity. Recent studies on such pseudostalactitic fabrics (sub-surface filamentous fabrics-SFF; [213]) in cavities of the Deccan Trap basalts in India (Figure 34d) revealed that the growth of the SFF is not limited to vertical directions and might be initiated by microbial activities [195]. Residues of organic material (fungal chitin) in the innermost filamentous core as well as the morphometric characteristics of certain filamentous fabrics indicate a biological contribution during an early state of SFF formation.…”

“…Although the principle processes in basic and acidic volcanics are similar, the specific rock composition and the chemical environment (T, Eh, pH, CO 2 , SO 2 , water, etc.) strongly influence the alteration processes [78,[188][189][190][191][192][193][194][195]. In mafic volcanic rocks, a greenish layer of sheet silicates (celadonite) can often be observed at the interface between agate geode and host rock.…”

Occurrence and Distribution of Moganite and Opal-CT in Agates from Paleocene/Eocene Tuffs, El Picado (Cuba)

“…Both field observations, concerning the appearance of agates in the host rocks and their mineralogical characteristics, illustrate that agates in El Picado can mostly be related to the crystallization from silica-rich solutions in fissures and cavities of the volcanic host rocks. The presence of opal-CT as an intermediate silica phase between amorphous and crystalline SiO 2 is a strong indication that the agate formation processes started from noncrystalline silica; particularly, in geologically young volcanic host rocks worldwide, opal-CT is detectable, since it has not been completely transformed to quartz [20,21]. Therefore, the preservation of opal-CT in the Cuban agates can be explained by the relatively young age (~55 Ma) of the hosting tuff layers.…”

Calcium Carbonate Growth with the Ring Structure of Stalactite-Type Minerals in a Tuff Breccia

“…Stalactite minerals were analyzed by electrospray ionization mass spectrometry (ESI-MS; LC-20AD XR, Shimadzu, Kyoto, Japan) to identify the chemical substances in the stalactite minerals and identify a biosignature. The analysis was conducted based on the experiment of Götze et al (2020). The calcium carbonate in the stalactite minerals was demineralized in 6M hydrochloric acid (HCl) for 24 h at 90 • C, and the resulting solution was filtered through a 0.2 µm filter and freeze-dried to remove excess HCl [35].…”