Geological map of the eastern foothills of Majella at 1:25.000 scale
The Geological Map of the eastern piedmont area of Majella at 1:25,000 scale has been realized by the Department for the Geological Survey of Italy - ISPRA within an Agreement stipulated on 5/4/2016 (disp. 1090/DG/2015) with the Abruzzo Region - Department of Public Works, Government of the Territory and Environmental Policies, for the development of forms of collaboration and exchange of data aimed at the prevention and mitigation of seismic risk, due to the high level of seismic hazard of the regional territory.
The map covers the foothills to the east of the Majella carbonate massif, extending about 220 km2, which falls within the Guardiagrele Sheet 370 of the Geological Map of Italy in scale 1:50,000, starting from its northern limit and approximately up to the alignment Taranta Peligna - Colledimacine - Roccascalegna.
The studied area is included in the hydrographic basins of the Aventino and Foro Rivers, it is characterized by hilly morphologies and by the outcrop of silicoclastic terrigenous deposits and of the Molise allochthonous succession, as well as by quaternary continental deposits.
SUBSTRATE
For the substratum, a geological map at 1:10,000 scale, drawn up on a lithostratigraphic basis, was created, which included the execution of extensive field surveys and the collection of about 120 samples for supporting biostratigraphic analyses (foraminifers and nannofossils). The main bibliographic references were the Geological map of the Aventino river valley (ACCOTTO et alii, 2014) at a scale of 1:25,000, the sheets attached to D'AMBROGI's doctoral thesis (1998), and the Geological map of the Majella mountain (PATACCA & SCANDONE, 2021).
A large part of the study area has been the object of new original surveys; particular in-depth studies have concerned the sectors located in correspondence of the geological structures where inconsistencies or dissimilarities persisted, highlighted by the overlapping of the various bibliographic references, and all the areas that stood out for their particular geological complexity. Detailed studies were also carried out where new lithostratigraphic units were introduced and tectonic lineaments of considerable importance were identified at local and regional scales.
On the basis of the original data deriving from the study in question and the bibliographic works cited, several main tectono-stratigraphic units have been recognized and within these lithostratigraphic units have been mapped that are consistent in terms of abbreviation, lithological analogy and chronostratigraphic location, with those already used in the CARG sheets at 50,000 already published (393 Trivento, 372 Vasto, 361 Chieti, 369 Sulmona, 360 Torre de' Passeri). This was done in order to ensure complete geological homogeneity between the cartography object of this study and the sheets already produced. In particular, along the areas of contact with Sheet 361 Chieti, a check was made on the lateral continuity of the geological bodies mapped. In some areas, however, where the data collected through field surveys suggested the presence of lithofacies and formations different from those reported in the literature, new lithostratigraphic units were preliminarily identified; moreover, the chronostratigraphic position of some already known formations was partially redefined, also through the support of the results of new samplings carried out for biostratigraphic analysis. In the studied sector the overlapping of different tectono-stratigraphic units has been recognized, represented by the outermost units of the central Apennine chain (Morrone-Porrara, Majella and Casoli-Bomba units) and by the allochthonous Molise units. The result is a complex structure, characterized by the extreme variability of the facies in time and space, both in carbonate and silicoclastic successions, but also by the problematic interpretation of the contacts between the various tectono-stratigraphic units. These contacts are largely obliterated by the subsequent terrigenous deposits of the thrust-top basins, by the Plio-Pleistocene deposits of the regressive cycle of the Adriatic basin, as well as by vast layers of quaternary detrital deposits, which make their analysis particularly complex. After the emersion from the sea, in fact, the area has been affected by an intense and rapid continental morphogenesis, which has produced large amounts of glacial, alluvial and gravitational deposits, determining its uniqueness and beauty from the landscape point of view, but also its vulnerability and geological hazard.
Although the geological cartography of the studied area has been realized with high detail, using also the biostratigraphic support, some stratigraphic and structural aspects represent problems still open, that will have to be object of integrations and deepenings in occasion of future works, in particular for an eventual project of realization of the CARG 370 Sheet Guardiagrele.
QUATERNARY CONTINENTAL DEPOSITS
In the sector under investigation in discordance on the units of the marine substrate extensively outcrop continental deposits in conoid and floodplain facies and in slope facies, referable to different phases of sedimentation framed between the Middle Pleistocene and the Holocene, in agreement with what recognized by previous authors (MICCADEI et alii, 2013; ACCOTTO et alii, 2014; CRESCENTI, 2015). An in-depth study was conducted on these deposits, according to a consolidated working methodology, including the ex-novo survey at 1:10,000 scale of the whole territory and the analysis of aerial photos of the base flight (GAI Flight 1954-55 B/W, nominal scale 1:33. 000) supplemented by the study of the most recent aerial photographs, orthophoto maps, the Digital Terrain Model 10 x 10 m of the Abruzzo Region and the LiDAR images available for the upper basin of the Foro River and for the fluvial shaft of the Aventino River.
Due to the relevance of Quaternary deposits for application purposes, particular attention was paid to the characterization of facies, according to the CARG guidelines.
The reference of the deposits to the different stratigraphic units, of a preliminary nature, is based on correlations, with geomorphological criteria, of the accumulation forms and of the basal support surfaces of the units, paying particular attention to the characterization of relict and buried soils and on some radiometric dating, which will have to be integrated for the realization of the CARG Sheet.
For the stratigraphic classification, the same units with unconformity limits defined in other sheets of the Abruzzo Region were used, in order to guarantee the necessary homogeneity with the neighboring Sheet 361 Chieti, whose southern edge is largely in contact with the study area, establishing new subunits of local significance where necessary. In particular, reference was made to the Catignano synthema of the upper Middle Pleistocene and the Valle Majelama synthema of the Upper Pleistocene.
In the course of the study, some new features emerged with respect to what was already known. In particular: 1) between Fara San Martino and Lama dei Peligni, in the Corpi Santi area, torrential and debris flow deposits attributable to different lithosomes, progressively embedded, were recognized; 2) along the piedmont strip between Fara San Martino and Pennapiedimonte, some strips of ancient alluvial conglomerates were identified; 3) in the valleys of the Avello and Verde rivers, terraced alluvial deposits have been mapped, arranged at different levels along the sides of the valleys, which were not represented in the previous maps; 4) in the areas between S. Eusanio and Piano Ascendente, terraced alluvial deposits have been mapped. Eusanio and Piano di Ascigno, a substantial difference emerged in the interpretation of the Quaternary gravels outcropping along the sides and at the top of the hills, referred in this work to the ruditic lithofacies of the Mutignano formation and classified instead as alluvial facies of the Middle Pleistocene in the literature. Other dissimilarities with respect to what is mapped in Sheet 316 Chieti will merit further investigation during the realization of the geological sheet 370 Guardiagrele.
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