Volume 28 (2022): Edizione 2 (August 2022)

The Gondwana Late Palaeozoic Ice Age is probably best represented by the Dwyka Group in South Africa. Striated and grooved surfaces or pavements are commonly considered to have formed subglacially, as are diamictites which have been interpreted as in-situ or reworked tillites. These interpretations were tested by investigation of outcrops in formerly well-studied areas, throughout South Africa. Detailed analyses have focused on striated surfaces/pavements and surface microtextures on quartz sand grains in diamictites. The sedimentological context of four pavements, interpreted to be glaciogenic, display features commonly associated with sediment gravity flows, rather than glaciation. A total of 4,271 quartz sand grains were subsampled from outcrops that are considered mainly to be tillites formed by continental glaciation. These grains, analysed by SEM, do not demonstrate the characteristic surface microtexture combinations of fracturing and irregular abrasion associated with Quaternary glacial deposits, but mainly a mix of surface microtextures associated with multicyclical grains. The Dwyka Group diamictites warrant reinterpretation as non-glacial sediment gravity flow deposits.

The north-east sector of the Himalaya is one of the most active tectonic belts, with complex geological and tectonic features. The b-value and spatial correlation dimension (D_c) of earthquake distribution in the north-east Himalaya and its adjacent regions (20–32°N and 88–98°E) are estimated in the present study. Based on seismicity and faulting pattern, the region is divided into five active regions, namely the (i) South-Tibet, (ii) Eastern-Syntaxis, (iii) Himalayan-Frontal Arc, (iv) Arakan-Yoma belt and (v) Shillong-Plateau. A homogeneous catalogue of 1,416 earthquakes (mb ≥ 4.5) has been prepared from a revised catalogue of the ISC (International Seismological Centre). The b-value has been appraised by the maximum likelihood estimation method, while D_c values have been calculated by the correlation integral method; b-values of 1.08 ± 0.09, 1.13 ± 0.05, 0.92 ± 0.05, 1.00 ± 0.03 and 0.98 ± 0.08 have been computed for the South-Tibet, Eastern-Syntaxis, Himalayan-Frontal Arc, Arakan-Yoma belt and Shillong-Plateau region, respectively. The D_c values computed for the respective regions are 1.36 ± 0.02, 1.74 ± 0.04, 1.57 ± 0.01, 1.8 ± 0.01, and 1.83 ± 0.02. These values are > 1.5, except for the South-Tibet (1.36 ± 0.02). The b-values around the global average value (1.0) reflect the stress level and seismic activity of the regions, while high D_c values refer to the heterogeneity of the seismogenic sources.

The present paper investigates the colour dependence of mineral compositions in clay-rich sedimentary strata, mainly clayey silts, the emphasis being on iron-bearing minerals (rather than clay minerals) by using powder X-ray diffraction (PXRD) and ⁵⁷Fe Mössbauer spectroscopy (⁵⁷Fe-MS). The PXRD-based phase analysis has demonstrated the variable compositions of samples, consisting of, inter alia, quartz, calcite or gypsum, and admixtures of potassium feldspars and plagioclase. Hematite + goethite (sample D1, dark red), goethite (sample D2, pinkish brown), poorly crystalline goethite (sample D3, orange) and jarosite (sample D4, yellow) have been distinguished. A very low jarosite content was detected in sample D5 (light grey); this did not affect its colour. The potential yellow/brown shades in sample D6 (dark grey), coming from trace amounts of jarosite, are masked by macroscopically visible organic matter. In the case of the two last-named samples (D5 and D6), with trace amounts of Fe-bearing minerals, it is most likely that the organic matter was effective in influencing the light and dark grey colour of the sediment, respectively.

Elements of geodiversity evaluated for scientific value should be protected, conserved and promoted as potentially important for geotourism. The Divjakë-Karavasta National Park is a large natural area that comprises six geosites along the Adriatic coastline of Albania. Geosites are elements of the geosphere that should be preserved for geoeducation of the present and future generations, in view of the fact that they yield significant data on Earth’s history. By means of the Geosite Assessment Method (GAM) and the SPSS program (version 20), we have analysed the geotouristic values of the Divjakë-Karavasta geosites and interpreted the importance of each subindicator. A correlation analysis, performed through SPSS and Pearson’s correlation coefficient as a test statistics, has been carried out as well. The Pearson’s correlation coefficient reflects the strong relationship between the scientific/educational values (i.e., representativeness and scientific knowledge) and touristic values (promotion, number of visitors, interpretative panels, hostelry services, restaurant services, touristic infrastructure). These coefficients express the importance of the dependence of additional values in the development of geotourism at protected sites.

Nature is never at a steady state. Natural history is generated by ever-new and ever-interacting forces that produce continuous changes. At virtually all timescales, the geological record shows that these changes do not cancel each other out and, thus, that the steady state is utopic. However, we need a state of equilibrium as a starting point for modelling Nature, and the steady-state condition is widely used as a reference in idealisations aimed at understanding natural processes. The present contribution is meant as an epistemological note of caution − from Earth scientists to Earth scientists − aimed at discouraging the use of theoretical models as true evidence instead of terms of comparison.