The Monti Ernici Miocene-Quaternary stratigraphy: An attempt for the definition of new stratigraphic units in the sheet 377 "Trasacco"

A portion of the sheet 377 "Trasacco", in the Simbruini-Ernici Ridge, has been mapped in the frame of the CARG Project. Here we describe the uppermost Miocene to Quaternary siliciclastic deposits covering the Meso-Cenozoic carbonate succession (Latium-Abruzzi Carbonate Platform). The conglomerati di Monte Prato (PTY) consist of polygenic heterometric conglomerates bearing exotic clasts such as «pietra paesina», pelagites, metamorphic and granitoid rocks. Clayey intervals with freshwater gastropods and ostracods crop out locally. PTY records latest Miocene-Early Pliocene thrust top sedimentation in coastal, deltaic environments (Cosentino & Cipollari, 2012). Maximum thickness is >250 m. The Plio-Quaternary continental deposits have been grouped in UBSUs. Two synthems characterize the Tiber/Aniene basin: i) the sintema della Val Granara (VGR), cropping out upslope of Filettino. VGR is bounded at the base by an erosional surface carved on the pre/syn-orogenic units. Within the VGR, two subsynthems, subsintema di Vaglie (VGR1) and subsintema di Pezze della Macchia (VGR2), are separated by an erosional unconformity. Both represent a gravel-dominated alluvial systems. Compositional differences (VGR2 bears clasts of PTY) and morphological clues, prove that VGR2 refers to a younger drainage system comparable to the Recent one. The age is Early (VGR1) to Middle (VGR2) Pleistocene (Delchiaro et al., 2021). Total thickness is >150 m; ii) the Sintema Fiume Tevere (SFT), developed above the last glacial lowstand erosional surface. It includes the subsintema dei Monti Simbruini (SFT1), which groups all the glacial and periglacial deposits related to the Aniene basin such as >30-40 m thick moraines. Locally, glacial derived plurimetric erratic boulders occur. Backwards of the moraines, flat morphologies suggest sedimentation in small barrage basins. Two synthems characterize also the Liri/Sacco Basin: i) the sintema di Guarcino (GUR), consisting of ?Upper Pliocene polygenic breccias and conglomerates made up of heterometric carbonate clasts, siliciclastics and PTY boulders. Development of GUR is related with the extensional activity of the Guarcino fault; ii) the Sintema di Isoletta (ISL), developed above the last glacial lowstand erosional surface. It includes the subsintema dei Monti Ernici (ISL1) which groups all the glacial and periglacial deposits related to the Sacco basin, i.e., disorganized heterometric angular carbonate clasts related to the reworking of moraines through debris-flows, alluvial transport, and avalanches. Maximum thickness is a few tens of meters.