Investigating the origin and biogenicity of spheroidal carbonate particles within an Argentinean Puna plateau travertine system

MORS, R. AGUSTIN; GOMEZ, FERNANDO J.; MLEWSKI, CECILIA E.; ASTINI, RICARDO A.; PETRYSHYN, VICTORIA A.; CORSETTI, FRANK A.

San Francisco

Congreso; AGU 2019 Fall Meeting; 2019

American Geophysical Union

Millimeter to centimeter scale spheroidal carbonate particles were documented in the Terma Los Hornos active travertine system (Puna of Catamarca, Argentina) and investigated to determine their origin and the role microorganisms may have played in their formation. Two different types of spheroidal particles were observed: a) spheroids (0.1 ? 1.6 cm in diameter) with rough outer surfaces and an internal microstructure composed of dendriform micrite-rich clumps; and b) pisoids (0.3 ? 3.9 cm in diameter) with smooth exteriors and concentrically laminated interiors that alternate between micrite and sparite laminae that grew upon a detrital or intraclastic nucleus. As a result of episodic transport and recycling within the travertine system, spheroids and pisoids can occur together. For example, it is common to find the spheroids as a nucleus of the concentrically laminated pisoids.The dendriform spheroids developed under low-energy flows immediately downstream of hot springs within shallow micropools (< 10?s cm size) between microterracettes. Petrography, scanning electron, and confocal laser scanning microscopy of spheroids reveal that carbonate minerals are intimately associated with microbial life. Filamentous bacterial and diatoms form an intricate network with microcrystalline calcite aggregates immersed in exopolymeric substances. When spheroids serve as pisoid nuclei, filamentous forms are truncated by the concentric layering.Pisoids are typically associated with either deeper (10 ? 100 cm deep) and larger (> 100 cm wide) highly turbulent pools or the base of waterfalls. They do not display an obvious relation with microorganisms or organic remains. The laminated outer crust is typically affected by dissolution and recrystallization that moves progressively toward the nucleus preferentially through incipient radial fissures. Such alteration produces characteristics reminiscent of columnar micro-stromatolites, which in this case are not primary textures.Preliminary results suggest that dendriform micrite-rich spheroid microtextures may be biogenically influenced under low-energy conditions, while pisoids development is mostly controlled by physio-chemical processes in a high-energy setting.