PLIO-QUATERNARY CONTINENTAL DEPOSITS IN THE LATIUM-ABRUZZI APENNINES: THE CORRELATION OF GEOLOGICAL EVENTS ACROSS DIFFERENT INTERMONTANE BASINS

Abstract

A stratigraphic framework valid for the Pliocene-Middle Pleistocene continental deposits of the Latium-Abruzzi Apennines has been
defined through the correlation of the depositional/erosional events (indicated by stratigraphic and morphologic units, respectively)
across seven different intermontane basins. This has been made by comparing the geological evolutions of the different basins. The
basic assumption for the correlation of the different events is that climatic factors have conditioned the geological evolution of the investigated sector in a substantially uniform way. Uniform climatic conditions have caused similar responses of the basins to the climatic changes. Continental deposition in the Latium-Abruzzi Apennines began during the Pliocene, prevalently with clayey-silty-sandy lacustrine deposits fed by the clayey-arenaceous flysch into which the landscape was carved at the time of the first continental deposition.
The formation of an indented landscape with higher slopes bordering the basins is demonstrated by huge landslide deposits of both
arenaceous and calcareous coarse material. Sediments related to the second depositional event (Early Pleistocene) are mainly characterised by a carbonate lithology in slope deposits (slope-derived breccias), in lacustrine (carbonate silts) and fluvial (carbonate gravels) sediments. This is due to the dominant carbonate lithology of the bedrock in the areas experiencing erosion during the Quaternary. The third depositional event (related to the lower Middle Pleistocene) has lithological and sedimentological characteristics comparable to those of the second event. It consists, indeed, of slope-derived carbonate breccias, carbonate silty deposits of lacustrine origin and carbonate gravels of fluvial facies. The fourth depositional event (Middle Pleistocene) is characterised by the first significant deposition of material of volcanic origin and numerous tephra levels related to the central Italy volcanic activity can be detected. Chronological constraints for the second depositional event are represented by the reverse paleomagnetic polarity of the deposits, defining ages older than 0.78 Ma and by the remains of Arkidiscon meridionalis vestinus Azzaroli in the L'Aquila basin. Chronological data for the third depositional event are represented by paleontological remains of Equus altidens Reichenau and by the association Hippopotamus antiquus Desmarest/Elephas antiquus Falc. & Cautl. and by the lack of volcanic materials which became widespread after 0.6 Ma. The age of the fourth depositional event is constrained by the presence of the tephra levels which define a deposition after about 0.6 Ma. The attribution of a Pliocene age to the deposits of the first event can only be made on a qualitative basis, since bio-chronological data or other quantitative chronological constraints are not available. In this light, the significant changes which affected the landscape between the first two depositional events seem to indicate that a very long time span passed between them.