Berti, C.

This study aimed at the reconstruction of magnitude and timing of uplift of a wide sector of the Central Apennines (Italy) by means of morphometric and morphostructural analyses. In the internal portion of the chain (where stratigraphic and geomorphological markers of past sea-level positions are lacking) the study was based on analysis of erosional landforms and river valleys. A large-scale topographic analysis was performed, processing 90-m and 230-m DEMs. The spatial distribution of several morphometric parameters, together with characteristic wavelengths of relief, allowed the distinction of three main regions affected by different cumulative surface uplift and tectonic/erosional fragmentation: a Peri-Tyrrhenian Belt; an Axial Belt; a Peri-Adriatic Belt. Particular attention was devoted to fluvial landforms, with analysis of longitudinal profiles and geometric pattern of the main stream-trunks and their relations with major structures. Major differences occur between the Tyrrhenian and Adriatic valley systems, the former being generally longitudinal and showing overall concave-upward longitudinal profiles, whereas the latter are generally transverse and possess less regular longitudinal profiles. Topographic features and river valleys architecture seem related to different styles and amounts of uplift in the three Belts. Within the study area, a narrower coast to coast transect (Gaeta-Vasto Transect, GVT) was investigated in detail, devoting particular attention to its axial sector, lying around the Apennines main divide (main divide area: MDA), and a possible scheme of the Quaternary surface uplift inside this transect was proposed. In the MDA, the main stages of landscape evolution and river network organization were reconstructed by analysis of paleosurfaces coupled with analysis of relic and present-day hydrographic network. This allowed recognition of a major phase of surface uplift (exceeding 1500 m in the Meta-Mainarde massif) occurred in response to thrusting during the Pliocene, whereas for the Quaternary uplift a minimum value around 400 m was estimated. Our study suggests that, during the Quaternary and in the GVT, the Peri-Tyrrhenian Belt suffered a subdued uplift operating over small wavelengths (10-15 km), while Axial and Peri- Adriatic Belts were subject to a stronger and long-wavelength (90 km) surface uplift, with maximum values (about 700 m) shifted NE of the Axial Belt and tapering to zero towards the Adriatic coast. The reconstructed pattern of uplift is coherent with the topographic properties of the three Belts and with the observed drainage features.

The principle of carbon-14 dating is well known (1): the content of this radioisotope in a sample of an animal or a plant origin is assessed and the time elapsed from the formation of the organic material to the moment of assessment is calculated comparing the present content of carbon- 14 to that at the time the plant or animal was alive. This last is assumed at equilibrium with the atmospheric concentration of carbon-14, which, in turn, is assumed to have been constant through the ages. Knowing the decay constant of carbon-14, the time elapsed is deduced. Then this calculated age is entered in calibration diagrams that account for the actual variable atmospheric content through the years, to obtain the age of the sample, or more precisely, a time interval in which the age falls. Thus, the main idea behind the technique is that the atmospheric concentration of carbon-14 marked CO2 is essentially constant, or slowly variable, from year to year. To this, one word of caution needs be added: after WW2, and particularly from the 1950s, the concentration of carbon-14 in the atmosphere has become quite erratic due to nuclear weapon tests, and hence this technique is not used for dating samples from that time on.In the present work, the whole carbon-14 idea has been reused in a somewhat different context, and with a different purpose in mind.Afact to be kept in mind is thatCO2 contained in vast amounts within the Earth’s crust beneath the volcanic apparatus, the so-called fossil CO2, either degassed by the mantle or having been formed by metamorphic reactions in the crust, contains no trace of the carbon-14 isotope. Fossil CO2 release is often associated to seismic and volcanic activity: the question may then arise whether, on occasion of such major releases and in the presence of landscape conformation conducive to slow mixing (narrow valley bottoms, canyons, and the like), the carbon-14 contents of local vegetation may be affected by the presence of spent CO2. The Solfatara at Pozzuoli presented both the above-mentioned conditions: it has the required shape and it has endured large releases of fossil CO2 in the early 1980s. It presented itself as an ideal location to test this hypothesis. There are pine trees planted in the 1930s, as part of a reforestation plan: it was possible to select two recently dead trees, one in the Solfatara area and presumably as affected by the CO2 release as could be possible, and the other immediately outside and upwind of the area, constituting an ideal blank. Sections were taken from the two trees and analysed to determine the carbon-14 content of several rings corresponding to the years of interest. In the following sections, the method and the results will be presented and commented upon.

This work presents the morphotectonic map of the Tasso Stream-Sagittario River valley, located in the Central Abruzzo area (Marsica region), in one of the areas of highest average elevation in the Apennines chain between two main intermontane basins (i.e. the Sulmona basin and Fucino basin). It is bounded by one of the main drainage divides of Central Italy, separating the Adriatic side of the Apennines from the large endorheic Fucino area. The morphotectonic map of the Sagittario River valley is the result of an geomorphological analysis of the drainage at the basin scale in Central Italy and incorporates three main sections: orography and hydrography (upper right on the map), the main morphotectonic map (center and left on the map), and the morphotectonic profile section (lower on the map). This map provides a basis for the recognition of morphotectonic features at the basin scale, the detection of tectonic vs. surface processes’ control on the landscape, and the reconstruction of the landscape evolution of the Sagittario gorges, one of the main gorges incising the carbonate ridges of the Apennines. It contributes to defining the main phases of the Quaternary landscape evolution of the inner mountain landscape of the Apennines, resulting from the combination of alternating morphotectonics (i.e. rock uplift and local tectonics) and surface processes (i.e. slope, karst, glacial and fluvial processes).

Topography of the Apennines chain resulted from the combined action of tectonic displacements (related to thrusting and high-angle faulting), large-scale uplift and surface processes. In such mountainous settings, where strong erosion is often responsible for incomplete stratigraphic records of surface evolution of thrust belts, geomorphological analysis helps quantify these processes and provide a framework for interpreting the geologic history of these regions. We studied a 400 km2 area of the Central-Southern Apennines, covering Abruzzo, Lazio and Molise regions, by means of morphostructural analysis. This sector of the chain emerged during the Lower Pliocene and suffered a long-lasting erosion. Our study reveals a high relief landscape dominated by high-standing, resistant carbonates forming structure-controlled landforms (morphosculptures), and valleys underlain by erodible siliciclastics. Quaternary deposits are few and scattered, and they give poor constraints for the recognition of ancient base-levels. However, this study defines and identifies several upland erosional surfaces (paleosurfaces) that may be linked to ancient base-levels. On the basis of cross-cut relationships between paleosurfaces and structural landforms, we outlined a possible long-term geomorphological evolution of the study area. Most of the local tectonic displacements in this sector of the chain took place during Miocene and Pliocene, by means of thrusting and strike-slip faulting, whereas only localized extensional tectonics occurred during Quaternary times. Since the Pliocene, differential erosion promoted exhumation of carbonates and deep incision of pre-existing erosional surfaces. This strong erosion can be related to a regional base-level lowering promoted by large-scale uplift of the axial sector of the Central-Southern Apennines.