Tafoni are one of the most interesting weathering features developed in many areas of the world from tropical areas to polar ones such as Antarctica. Here, we present the results on 4 tafoni in similar conditions (aspect, slope, distance from the sea, elevation) and in the same granite close to the Italian Antarctic station at Mario Zucchelli Station (74°42′S). These tafoni were thermally monitored through infrared thermography and in situ thermistors for an austral summer (2018/19). They were also mineralogically characterized through the image analyses in each tafone sectors (Top, Ceiling, Side and Floor). Salts concentration on the weathered material removed through the scratching was also detected through chemical analyses. Moreover, the weathering rate was calculated through periodic sample weightings of the scratched material from the different tafone sectors. Our results confirmed the importance of the fractures inclination that seem to favor the vertical development of the cavities where basal fractures occurred and the backward development where fractures are vertical. The weathering rates shown that vertical development was always faster than the backward (except for O4) and that the former is statistically linked with the size of the tafone. At mineralogical scale, the higher weathered removal of the quartz concentration could be more closely related to the higher cryogenic weathering of intra-crystal fractures that occur at very low temperatures (−20 °C) in winter than to the thermal stress, thermal shock, or potential freeze-thaw cycles during the summer. Among the different salts, the strong relationship between weathering removals and chlorides suggests that chlorides in this climate are more effective than sulphates. The seasonal trend of weathering matches well with the breaking up of sea ice towards the Tethys Bay and can provide a supply of sea spray that is richer in chlorides (halite) than in sulphates (thenardite, mirabilite). From the analyses of the spatial thermal variability, we could argue that the thermal stress during the summer is not relevant except for the tafone O4. The fact that higher weathering removal were recorded in the innermost (C and S) of the tafoni where thermal variability and AMP were lower suggests that higher moisture content is the crucial factor for a high evaporation flux that can enhance the salt action.

The development of Antarctic tafoni: Relations between differential weathering rates and spatial distribution of thermal events, salts concentration and mineralogy

Pezza M.;
2021-01-01

Abstract

Tafoni are one of the most interesting weathering features developed in many areas of the world from tropical areas to polar ones such as Antarctica. Here, we present the results on 4 tafoni in similar conditions (aspect, slope, distance from the sea, elevation) and in the same granite close to the Italian Antarctic station at Mario Zucchelli Station (74°42′S). These tafoni were thermally monitored through infrared thermography and in situ thermistors for an austral summer (2018/19). They were also mineralogically characterized through the image analyses in each tafone sectors (Top, Ceiling, Side and Floor). Salts concentration on the weathered material removed through the scratching was also detected through chemical analyses. Moreover, the weathering rate was calculated through periodic sample weightings of the scratched material from the different tafone sectors. Our results confirmed the importance of the fractures inclination that seem to favor the vertical development of the cavities where basal fractures occurred and the backward development where fractures are vertical. The weathering rates shown that vertical development was always faster than the backward (except for O4) and that the former is statistically linked with the size of the tafone. At mineralogical scale, the higher weathered removal of the quartz concentration could be more closely related to the higher cryogenic weathering of intra-crystal fractures that occur at very low temperatures (−20 °C) in winter than to the thermal stress, thermal shock, or potential freeze-thaw cycles during the summer. Among the different salts, the strong relationship between weathering removals and chlorides suggests that chlorides in this climate are more effective than sulphates. The seasonal trend of weathering matches well with the breaking up of sea ice towards the Tethys Bay and can provide a supply of sea spray that is richer in chlorides (halite) than in sulphates (thenardite, mirabilite). From the analyses of the spatial thermal variability, we could argue that the thermal stress during the summer is not relevant except for the tafone O4. The fact that higher weathering removal were recorded in the innermost (C and S) of the tafoni where thermal variability and AMP were lower suggests that higher moisture content is the crucial factor for a high evaporation flux that can enhance the salt action.
Granite weathering
Infrared thermography
Salt weathering
Tafoni
Thermal stress
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12079/65729
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