GEOMORPHOLOGY, TECTONICS AND SEDIMENTOLOGY OF LATE QUATERNARY FANS BETWEEN GUARDIA PIEMONTESE AND PAOLA (TYRRHENIAN COAST OF CALABRIA, SOUTHERN ITALY)

Abstract

An integrated geomorphological, preliminary structural and sedimentological study has been carried out, in order to investigate the role of tectonic and geological setting on the Late Quaternary evolution of the landscape.
The study area represents a portion of the onshore belt located on the eastern margin of the Tyrrhenian extensional basin (Coastal
Range). This sector of Calabria consists of a thrust-pile (Calabrian Arc Auct.), including both metamorphic and non-metamorphic rocks.
Structural analysis evidences four sets of major fault systems; they affect a monocline consisting of a complex folded morphostructure.
The NNW-SSE trending faults are dip-slip and oblique extensional faults, as suggested by superimposition of the striations. The relative
chronology suggests that the youngest kinematics is represented by right-lateral normal faults. The NE-trending faults are oblique normal and dip-slip faults; the latter are compatible with the kinematics of the right-lateral NNW trend.
Geomorphological analysis allows three generations of alluvial-fans to be distinguished; furthermore, valley-side perched alluvial terraces occur in the lower reaches of the valley descending from the Coastal Range. The three generations of alluvial fans are telescopically arranged, and the apexes of the piedmont fans (1st generation) are entrenched in respect to perched alluvial terraces. The fans at issue derived from steep catchments, developed as consequent and/or subsequent river valleys debouching from the mountain front.
The piedmont zone comprises the 1st generation of alluvial-fans, bordered to the West by a nearly N-S striking scarp commonly reaching up to 80 m in height to the South. The present-day coastal plain comprises the 2nd generation of alluvial-fans which lie upon and interfinger with Late Pleistocene coastal and eolian deposits; the latter sail the foot-zone scarp of piedmont fans. A tephra layer has been recognised within eolian deposits.
On the basis of preliminary structural and morphotectonic data, the last tectonic phase responsible for the latest landscape fragmentation, was probably characterised by a NW-SE trending extension direction. Moreover, morphometric measurements and pre-existing offshore data support the hypothesis that, since Middle-Late? Pleistocene time, weak tectonic subsidence, coupled with marine base level rise, constitute the main mechanisms promoting the creation of the accommodation space for fan aggradation.
The Quaternary alluvium is characterised by a variety of coarse-grained facies coming to be regarded as alluvial-fan facies. In particular, detailed facies analysis revealed the presence of 4 facies associations, mainly represented by debris flow, debris avalanche deposits and sheetflood facies; facies associations also allow different alluvial fan evolutionary stages to be outlined. In addition, the lithology of the bedrock outcropping within fan catchments, have been also identified as the main factors which played important roles in controlling the different depositional processes and consequently facies assemblages.