ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉Earth analogs are indispensable to investigate mineral assemblages on Mars because they enable detailed analysis of spectroscopic data from Mars and aid environmental interpretation. Samples from four sites in the Iberian Pyrite Belt (El Villar, Calañas, Quebrantahuesos, and Tharsis) were investigated using mineralogical, chemical, and spectroscopic techniques, with a focus on clay minerals and alteration environments. They represent Earth analogs of areas on Mars that underwent acidic alteration. X-ray diffraction and transmittance mid-infrared data indicate that the rocks were subjected to several degrees of acid alteration corresponding to assemblages characterized by the following mixtures: (1) illite, chlorite, interstratified chlorite-vermiculite, kaolinite-smectite, and kaolinite; (2) illite, kaolinite, and alunite; and (3) jarosite and goethite. According to mineral stability data, these three assemblages correspond to pH values 7–5, 5–3, and 〈3, respectively. The lack of goethite in the illite-kaolinitealunite assemblage suggests an alteration in reducing conditions. Illite was progressively dissolved by acidic alteration but is sufficiently resilient not to be diagnostic of the intensity of the alteration. Illite and kaolinite were the two most abundant phyllosilicate minerals observed, and the main reaction involving phyllosilicates was the alteration of illite to kaolinite. Mixed-layer phases appeared mainly in the mildest degree of acid alteration, with few exceptions. This suggests a transition from a mechanism dominated by transformation to a mechanism dominated by dissolution-precipitation as the intensity of the acid alteration increases. Our results highlight the sparse kaolinite-alunite occur-rences on Mars as worthy of specific investigation. Acid alteration on Mars is expected to be patchy and/or consisting of fine alteration rims. Alunite occurrences on Mars in the absence of goethite may indicate an acid alteration in reducing conditions. Kaolinite produced through acid alteration on Mars is expected to exist mainly as an end-member phase of low crystallinity, which would enhance IR absorption and increase its visibility.〈/span〉

Description: Land colonization by plants and their fungal and bacterial symbionts during the Paleozoic was fundamental to the evolution of terrestrial ecosystems, but how these early communities influenced mineral weathering and soil development remains largely unknown. We investigated cryptogamic ground covers (CGCs) in Iceland to identify modern analogous communities and to characterize soil structure and biologically mediated weathering features. Using a novel application of X-ray microcomputed tomography, we show that moss-dominated CGCs and their soils are not adequate analogues of early communities. Comparisons with the 407 Ma Rhynie Chert (Scotland) biota indicate that modern CGCs dominated by lichens, liverworts, and their associated symbionts (fungi, cyanobacteria) are more representative of early soil-forming communities. Liverwort and lichen soils are thin, and their depth and complexity are constrained by the size and growth form of the dominant plants or lichens. They are aggregated and stabilized by cyanobacteria, mycorrhizal and lichenized fungi, rhizoids, and associated exudates. Smectite was associated with liverwort but not with moss CGC soils. Soil grain dissolution features are diverse and attributable to different organisms (e.g., bacteria, fungi) and types of interaction (e.g., symbiosis). We postulate that such features provide a novel indirect means of inferring biotic interactions in paleosols.

Description: Most glacier forefields of the European Alps are progressively exposed since the glaciers reached their maximum expansion in the 1850s. Global warming and climate changes additionally promote the exposure of sediments in previously glaciated areas. In these proglacial areas, initial soils have started to develop so that they may offer a continuous chronosequence from 0 to 150 yr-old soils. The build-up of organic matter is an important factor of soil formation, and not only autochthonous but also distant sources might contribute to its accumulation in young soils and surfaces of glacier forefields. Only little is known about black carbon in soils that develop in glacier forefields, although charred organic matter could be an important component of organic carbon in Alpine soils. The aim of our study was to examine whether black carbon is present in the initial soils of a proglacial area, and to estimate its relative contribution to soil organic matter. We investigated soil samples from 35 sites distributed over the whole proglacial area of Morteratsch, covering a chronosequence from 0 to 150 yr. BC concentrations were determined in fine-earth using the benzene polycarboxylic acid (BPCA) marker method. We found that the proportion of BC to total Corg was related to the time since the surface was exposed. Soils on surfaces exposed less than 40 yr ago contained the highest proportion of BC. The absolute concentrations of BC in fine-earth were generally low but increased in soils that had been exposed for more than 40 yr. Charred organic matter occurred in the whole area, and it was a main component of soil organic matter in young soils, where total Corg concentrations were very low. Specific initial microbial communities consequently may profit from this additional C source during the first years of soil evolution and potentially promote soil development in its early stage.

Description: Most glacier forefields of the European Alps are being progressively exposed since the glaciers reached their maximum expansion in the 1850s. Global warming and climate changes additionally promote the exposure of sediments in previously glaciated areas. In these proglacial areas, initial soils have started to develop so that they may offer a continuous chronosequence from 0 to 150-yr-old soils. The build-up of organic matter is an important factor of soil formation, and not only autochthonous but also distant sources might contribute to its accumulation in young soils and surfaces of glacier forefields. Only little is known about black carbon in soils that develop in glacier forefields, although charred organic matter could be an important component of organic carbon in Alpine soils. The aim of our study was to examine whether black carbon (BC) is present in the initial soils of a proglacial area, and to estimate its relative contribution to soil organic matter. We investigated soil samples from 35 sites distributed over the whole proglacial area of Morteratsch (Upper Engadine, Switzerland), covering a chronosequence from 0 to 150 yr. BC concentrations were determined in fine earth using the benzene polycarboxylic acid (BPCA) marker method. We found that charred organic matter occurred in the whole area, and that it was a main compound of soil organic matter in the youngest soils, where total Corg concentrations were very low. The absolute concentrations of BC in fine earth were generally low but increased in soils that had been exposed for more than 40 yr. Specific initial microbial communities may profit from this additional C source during the first years of soil evolution and potentially promote soil development in its early stage.