Resumo

SEDOV, Sergey; ZAZOVSKAYA, Elya; FEDOROV-DAVYDOV, Dmitriy  e  ALEKSEEVA, Tatiana. Soils of East Antarctic oasis: interplay of organisms and mineral components at microscale. Bol. Soc. Geol. Mex [online]. 2019, vol.71, n.1, pp.43-63. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2019v71n1a4.

The soils of Antarctic oases - coastal as well as inland ice-free areas limited by ice sheet or ice shelves attract attention as a block of one of the most extreme terrestrial ecosystems of the Earth. The knowledge about early stages of pedogenesis, solumformation and stabilization, interaction between organic and mineral components in these soils is still limited. We performed micromorphological investigation of several thin soil profiles developed under mosses and lichens on the sediments deposited by meltwater in a lake depression of Schirmacher Oasis. Mineral components are dominated by sand particles of primary minerals (mostly quartz, K-Na feldspars and micas) derived from gneiss bedrock. Quartz grains exhibit surface structures indicative of cryogenic fragmentation, whereas biotite has signs of chemical alteration: exfoliation along cleavage planes, deformation of laminae, loss of interference colours and pleochroism. Despite severe environmental conditions, incipient weathering occurs that contribute clay minerals and iron oxides to the fine material. The latter forms discontinuous coatings on the coarse grains providing a chitonic c/f related distribution pattern. Arrangement of the fine components in form of coatings on coarse grains provides their maximal interaction with soil moisture and organic matter and generation of microhabitats for the microorganisms. Common micromorphological features of the studied soils is a complex groundmass which combines well preserved organic tissues of mosses and lichens and mineral particles spread among them. We conclude that the studied soil bodies are synsedimentary: fluvial (and possibly eolian) deposition of mineral material that occurs simultaneously with the growth of primitive plants. The mineral grains are trapped between plant tissues which form a framework of the soil matrix. This interlacing provides also conservation of organic material within the soil layer. Studied soils demonstrate similarities with the biological crusts of other present and past extreme terrestrial environments.

Palavras-chave : Antarctic oasis; extreme ecosystems; weathering; biological soil crust.

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