NUOVI PROCEDIMENTI CARTOGRAFICI PER IL QUATERNARIO CONTINENTALE: L’ESEMPIO DELLA CARTA GEOLOGICA DELL'ALTA VALLE DELL'ATERNO

Abstract

In the field of the Italian geological cartography of the continental Quaternary deposits at present the most advanced procedures are
those used for the new Italian geological map project on a scale of 1:50.000 (CARG).
The most noticeable innovation introduced by this project is represented by the adoption of allo-stratigraphical units or unconformity
boundary stratigraphic units (UBSU). Some accomplishments in the 90’s, however, suggest the possibility of other innovations that
regard the informative content of maps, with a particular consideration to the use of geomorphological elements. In some of the procedures which until now have been adopted, these elements have in fact not been added to those stratigraphic, but have been integrated with a perspective that tends to exceed the usual separation between stratigraphy and geomorphology.
The Quaternary geological map of the upper Aterno Valley has been achieved with a process that represents a radical use of these
procedures, to such a degree that it modifies the structure of the reference unit. In fact, those cartographed are no longer stratigraphic units, but units that correspond to an integration of allo-stratigraphic units and morphosequencial units, the last agreed to be elements in a sequence of relict surfaces (due to erosion or accumulation). These units, defined as “allo-morphosequencial units” (UAM) are delimited lower down by an erosional surface buried below by the allo-stratigraphic unit and above by one or more relict surfaces. The main difference with the usual stratigraphic units is that while these are defined mainly on the basis of depositional events, the UAM also represents in an explicit way the morphogenetic events, perfecting the definition of the succession of events that have given origin to the geological evolution of the area. This difference also has consequences on the importance of the erosionial surfaces (unconformity) that delimit the stratigraphic units: they are no longer considered as simple elements of separation between allo-stratigraphic units (or UBSU), but as evidence of morphogenetic events to which is assigned a completely equal rank, as for those depositional.
In the surveyed area many units have been recognised which have been divided into three different groups, which are:
(i) a chronologically ordered succession of 8 units allo-morfosequenziali and 19 morphosequential units represented by relict surfaces.
(ii) 6 morphosequential units corresponding to a terraced succession which is at least in part older than the previous succession (iii) three stratigraphic units of which it has been impossible to define in detail its relationship with the chronologically ordered succession.
All these units have been indicated with numbers that express the relative chronological position of the constituent elements (lithosomes and shapes).
In a situation such as the one considered, dominated by the progressive embedding of shapes and lithosomes, the succession of the
allo-morphosequential unit is revealed in correspondence to the progressive deepening phases of the hydrographic network. The
distinct evolutionary valence of the map is therefore confirmed.
Other innovations adopted in the making of the map regard the geomorphological indications and the structural elements. For the first, the common indications usually referred to in the geological maps have been abandoned (terrace borders, dolines, etc.) limiting ourselves to cartographing only the geomorphological elements of direct interest in regards to the reconstruction of successive geological events in the area represented by relict surfaces. Information on the chronology of the deformation and origin of the evaluation have been provided for the structural elements.
Taking into account that the upper Aterno represents a significant sample of the intermountain valley of the central Apennines, the illustrated procedure in this text does not seem to be susceptible to only a strictly local application. The map presented can therefore be considered as a proposal to be placed in a methodological perspective as a surpassing of the present cartographic criteria for the continental Quaternary.