Stratigrafia Plio-Pleistocenica della Conca del Fucino

Abstract

As a part of a study aimed at defining the Quaternary tectonics of the Fucino Basin, detailed field surveys have outlined a Plio-Pleistocene stratigraphy that is significantly more complex than previously assumed. The substratum of the Fucino basin consists of a Jurassic- Paleogene sequence of limestones and dolomites, overlaid with terrigenous formations mainly of Miocene age. The continental stratigraphic succession is represented by a large number of sedimentary - often lacustrine - events, separated by as many erosive events. The complexity of this situation is the result of the interaction between climatic variations and tectonic activity. Seven principal sedimentary events have been reconstructed, attributed to a time interval between the Pliocene and the Upper Pleistocene. This sedimentary sequence is covered by deposits dating to the last 30,000 years. Lacustrine or fluvial deposits mostly outcrop on the northern and eastern slopes of the basin. Sporadic breccia bodies are present on the other slopes. Of particular importance is the oldest complex (Aielli complex), present from the Fucino area to as far as the middle Salto Valley. The upper part of the complex has characteristic mega-breccia horizons, indicating a landscape that evolved (in Pliocene times) from low gentle-sloping ridges of terrigenous sediments to the initial uplift of carbonate hills. The Cupoli complex is markedly entrenched into the Aielli deposits, its top being characterised by an extensive and sub-horizontal erosion surface. While Cupoli gravels were being deposited into the depression, a characteristic generally pink matrix breccia was deposited onto the surrounding slopes. Entrenched within the Cupoli complex are the Pescina, Casoli and CoHarmele Formations, which formed along of very similar local base-levels. On the top of these formations are relics of flat surfaces, which represent the original, reshaped accumulation plane. Subsequently, the Pervole and Boscito Formations were deposited, the latter characterised by horizons consisting almost entirely of volcanic material. There is no unequivocal data in any of the described formations allowing the formulation of chronological hypotheses, nor is there any data on the structural geology of the subsurface. Consequently, the geological evolution of the basin is proposed on the basis of outcropping stratigraphic successions and the areal distribution of their outcrops. As a result of a series of events - most likely highly influenced by tectonics - the sedimentary basin was subjected to significant size variations which resulted in a series of terraces. In addition, erosive processes often affected the carbonate substratum, forming extensive relic erosion surfaces. On the basis of the scarce data available, it is practically impossible to deduce the cause of size variations in the sedimentary basin. A possible conclusion is that variations may equally be linked either to climatic or tectonic processes (namely, either size variation of the subsiding area or uplift of a "barrier") or both.