L'importanza dello studio delle superfici di erosione nell'approccio allostratigrafico alla geologia del Quaternario

Abstract

In a continental environment, evolution can be seen as a succession of deposstional and erosionai episodes, in which the former give rise to 3-dimensional sedimentary bodies, whereas the latter produces 2-dimensional surfaces ("forms"). Obviously sedimentary bodies are more evident to study and as such they usually attract the attention of researchers as the only source of information regarding the environmental conditions (setting and climate) under which they formed and - above all - the time of their formation. In contrast, surfaces ("forms") are generally ignored. A series of examples, however, clearly demonstrate that depositions episodes are largely subordinate to erosionai episodes in terms of duration. Hence the importance of studying "forms", which are at the same time the sign of erosion and the proof of its occurrence. In chronological terms, to reconstruct the spatial development of a form, to identify its origin and its relationships with either sedimentary bodies or other forms (and thus their relative temporal position) and, finally, to identify deformations which possibly occurred after it was first created, are important aspects of the evolutionary history of a region. Thus, a stratigraphic sequence which represents a given time-span is composed of a succession of both bodies and erosionai forms. The aliostratigraphic approach, recently proposed as a surveying procedure of surface formations, is essentially based on the above-mentioned concepts: a geomorphological reconstruction that is based on deposits only is inevitably incomplete, in that it only gives information about brief events which occurred between much longer erosion-dominant periods. Because the scope of geomorphology is to study landforms, it follows that its role in Quaternary geological studies, and more generally, in geology as a whole, is of primary importance. Despite to this obvious observation geomorphological investigations are commonly confined to outcropping erosionai forms, without systematic analyses of the relationships between forms or forms and sedimentary bodies.