Search Results (3)

Serpentinite is a common lithology in Greece with significant geotectonic and petrogenetic implications, yet its archaeometric study remains limited. This also applies to the Ras serpentinite outcrop on Tinos Island—an enigmatic ancient quarry with no prior documentation of its exploitation. This study aims to provide a holistic provenance analysis and full material characterization to establish a unique fingerprint for future comparative research. A multidisciplinary methodology was applied, including petrography, XRD, FTIR, BET, LA-ICP-MS, electron microprobe analyses, and lichenometry—the latter used to estimate the quarry’s period of activity. The Ras serpentinite consists of a dark-green, brecciated lizardite matrix cut by a pale-green chrysotile network, and notably hosts the first recorded occurrence of minnesotaite in Greece. Relict antigorite within the matrix indicates high-pressure, high-temperature metamorphism preceding a greenschist facies overprint. Geochemical data classify the Ras occurrence as a subduction-related serpentinite derived from a depleted ultrabasic protolith. The aforementioned traits distinguish it from other Greek examples. Lichenometric analysis suggests the quarry was active in the 13th century A.D., with evidence of deliberate extraction techniques. These findings offer valuable insights into archaeometric studies and the provenance of serpentinites in the Aegean. Full article

The Sencelles Fault constitutes the main extensional structure of Mallorca Island (Spain), holds a NE-SE orientation, and has been identified as the possible seismic source of the 1851 CE Palma earthquake (VII EMS.) The SE termination of the fault (Sta. Eugenia Segment) features a linear bedrock fault scarp of a maximum of 3.15 m height. The last 840 m of this rocky scarp display a significant horizontal banding, with up to five differentially weathered ribbons colonized by lichens. The lichenometric analysis is based on the measurement of 155 specimens of Aspicilia calcarea (Ac) and Aspicilia radiosa (Ar) in tombstones and funerary monuments (with inscribed dates) from the nearby cemeteries of Sta. María del Camí, Sta. Eugenia and Sencelles, to obtain the local lichen growth rates (LGR), with the two last graveyards being directly located in the fault zone. Lichens were measured on variously oriented (N, S, NE, SW, etc…) horizontal and vertical surfaces, generating differentially oriented lichen populations (DOLPs) to be compared with the Ac and Ar specimens colonizing the studied fault scarp (38 measured individual specimens). After successive trial and error regression tests, vertical DOLPs resulted in the best appropriate groups for the analysis, with LGR of 0.23–0.31 mm/yr. Horizontal ones reached widths of up to 20 cm, with LGR up to 0.84 mm/yr, which were clearly oversized. The application of the selected LGR points to a human-induced origin for the thin basal lichen ribbon of the scarp (10–13 cm), which should have developed during the middle 20th century (c. 1950–1966) because of documented ground leveling works. However, the second ribbon of the scarp (23–47 cm) shows exposure dates of 1852 ± 40 (Ar) and 1841 ± 59 (Ac), overlapping the date of the 1851 CE earthquake. The study is complemented with data from a fault trench excavated in the year 2002 at the toe of the scarp. The combined data of lichenometry, fault trenching, and the length of the analyzed fault scarp (c. 840 m) indicate that the studied segment of the fault cannot be considered a co-seismic surface faulting related to the 1851 CE event as a whole, but a relevant secondary earthquake effect on a pre-existing fault scarp (e.g., sympathetic ground ruptures). Full article

Lichenometry, a method for dating rock surface exposure mainly in high latitudes and mountain environments, is based on estimates of lichen growth rates, but over the last 70 years it has been severely criticised. Its chief limitation is its questionable reliability due to three main problems: the species belonging to the Rhizocarpon subgenus, most often used by lichenometrists, are hard to identify; growth studies have highlighted the intrinsic variability of growth both seasonally and annually, with species sensitively responding to a wide range of environmental factors; and the same sensitive dependence also applies to the time taken for colonization on fresh rock surfaces. These problems cast doubt on many absolute dating studies and critics have suggested that, at best, the technique should only be used for relative dating. This paper provides guidance on identification procedures and suggests alternative dating methods based on lichen size-frequency distributions and cross-dating with other lichen species, thus avoiding reliance on a single species or support from other methods. With appropriate development, it is hoped that these approaches can provide a way forward that allows the technique to contribute more reliably to the dating of rock surfaces in regions where there are few other dating options. Full article