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Accueil du site → Master → Afrique du Sud → 2021 → Biogeochemistry of the lichen-rock interface on different silica-rich rock types in the Vredefort Dome, South Africa

North-West University (2021)

Biogeochemistry of the lichen-rock interface on different silica-rich rock types in the Vredefort Dome, South Africa

Smit, B.J.

Titre : Biogeochemistry of the lichen-rock interface on different silica-rich rock types in the Vredefort Dome, South Africa

Auteur : Smit, B.J.

Université de soutenance : North-West University

Grade : Master of Science in Environmental Sciences 2021

Résumé partiel
Land colonization by plants and their fungal and bacterial symbionts was fundamental to the evolution of terrestrial ecosystems, but how their communities influenced mineral weathering and soil development in the southern hemisphere and African environments remains largely unknown. This study considers lichen colonization on the weathering crust on silica-rich rock varieties (K-feldspar rich granite, alkali granite, sub-labile arenite, ferruginous wacke and metaconglomerate) from the 2023 ± 4 Ma Vredefort impact crater, central South Africa, with an integrated approach using optical microscopy, X-ray micro-computed tomography (μCT) and scanning electron microscopy (SEM). The interaction of four recurrent saxicolous lichen genera (Acarospora sp.pl., Caloplaca s. lat. sp.pl., Buellia sp.pl. and Xanthoparmelia sp.pl.) which targeted silica-rich rock varieties were explored, thus contributing to a deeper understanding of the multifaceted lichen-induced bioweathering processes that are active within impacted regions. In particular, the potential efficacy of lichen colonization on silica-rich rock degradation were investigated. The study characterized and compared the specific biomechanical and biochemical actions of each genus and documented their expected epilithic and endolithic behavior. It was investigated whether different lichen genera could explain variations in mechanisms, patterns and degree of weathering at each site. Granitic rocks with initially low porosity became more porous as a result of impact bulking, whilst metasedimentary rocks showed a well-defined decrease in particle size and permeability, presumably related to pore collapse or impact-induced annealing. However, the heterogeneous distribution of collapsed pores, melt phases, and subsequent recrystallization, resulted in heterogeneous lichen colonization patterns. Cavities and vesicles formed during melting yielded new habitats for both cryptoendoliths and chasmoendoliths, manifested in the natural cryptoendolithic and chasmoendolithic colonization of meteor impact-shocked silica-rich rocks.

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