Sedimentology and fabric characteristics of subaerial slope and alluvial cone deposits in northern Calabria (Southern Italy)

This work focuses on the transport processes, sedimentology and clast fabric of slope deposits cropping out in active depositional environments, widespread between 900 and 1000 m in altitude, close to Mormanno, in northern Calabria. The climate is characterised by a mean annual temperature of about 10-12°C and a mean annual precipitation higher than 1500 mm; as a whole an upland Mediterranean climate (Csb-type) occurs. The parent rock consists of strongly fractured Meso-Cenozoic limestones and dolostones with marly intercalations; rocky slopes are deeply incised by steep flanked V-shaped gullies, outlining a badland-like drainage network. Two types of talus slope have been distinguished: (i) rock fall dominated (RF) and (ii) slope wash dominated (SW), located at the foot of rockwalls and downslope of large gullies, respectively. A talus surface survey, coupled with observations made in trenches dug in the taluses at issue, allow us to describe lithofacies and to sample deposits for fabric analysis. RF talus slopes, showing well developed fallsorting, consist mainly of alternating couplets of sheet conglomerates of pebble grade and lenticular pebbly sandstones. Clast fabric, grain size, grading and bed geometry suggest an alternation of rockfall and sediment-gravity flow processes in RF talus development. SW deposits show well developed bedding, inferred by grain-size variations; fabric, lamination and lenticular geometry have been referred to sediment-gravity flows plus fine-fraction winnowing. To test the hypothesis that slope deposits are representative of the processes above mentioned, a-axis orientation and dip were measured on sets of 40 clasts. Data were treated according to the eigenvalue method, which allows to distinguish among cluster, girdle and random fabric patterns. In addition, the spherical variance (SVAR) has also been calculated, to obtain a further measure of fabric strength. All diagrams of fabric characteristics reveal overlaps of the fields representing different sedimentary processes; although girdle fabric shapes prevail, the fabric strength is thought to be a good discriminator for sedimentary processes assessment.