Stratigraphy of the Ponticello formation (Upper Miocene, Campanian Apennines)

The Ponticello formation is represented by a siliciclastic and calciclastic sedimentary succession, outcropping in the campaman sector of the Southern Apennines, and structured in four main sequences (lithozones) A nansition interval is localized in the upper portion of the sedimentary recordA lithozone CTS (Calcaremtic Turbiclitic Sequence), with dominant marly deposits is constituted by yellow, medium, sometimes coarse grained stratified calcarenites, occasionally weakly cemented The bed thickness varies from a few centimeters to several decimeters, with many showing the Bouma Sequence. In the Arenara and Melto Vecchia locations frequent intervals of marls, marly limestones, and rarely ("pseudo-saccharoidal" limestones crop out An intense bioturbation is present The deposits of thus interval are approximately 25 meters thick and originated by turbid the processesA lithozone SCS (Sandy-nueroConglomeratic Sequence), with dominant arenaceous-conglomeratic deposits, comprises alternations of medium-coarse grained yellow-brownish sands with quartzo-feldspathic composition, and paraconglomerates In places this Interval includes some layers of granular conglomerates, with sub-rotmded polygenic clasts, immersecl in a sandy matrix The sands are organized in layers some decimetres thick The paraconglomerates are usually organized in fining-up sequences The thickness of this lithozone is approximately 40 meters, the significant exposures being in the Vallone der Morn The deposits of this lithozone can be interpreted as formed by submarine mass flows and gravity flowsA lithozone MCS (Marly-Calcarcous Sequence), with marly-limestone dominant, consists of alternattons of marls, calcareous marls and white manly limestones, ordered in layers which generally have a maximum thickness of 10-15 centimeters, and usually contain an abundant planktonic microfauna The thickness of this lithozone seems to exceed 50 meters in the Incoronata and Felette locations The sediments of this interval can be considered as the result of depositional processes that occur alone a submarine slopeAbove the lithozone MCS lies a transitional stratigraphic interval, well exposed along the Vallone Porincello, and characterized by two dominant components a calciclastic portion (TCC), in the lower part, and a siliciclastic fraction (TSC), in the upper part The lower part, about 20 meters thick, crops out in the C Sterpara and longa:A locations, shows alternations of partially IX:Crystallized calcarenues and calcareous brecciola This last lithotype is characterized by lithoclastic (calcilutites, oolithic limestones, etc) and bioelastic (Luhothannuum and briozoarians, pectimds, etc) elements, granule to fine pebble size and frequently angular-shaped, interbedded with marly limestones and marls In the C Sterpara location, the upper transition interval (TSC), approximately 25 meters thick, also outcrops Ii is constituted by sandstones, siltstones and marls, with very frequent Intercalations of alternating of light grey muddy marls and brownish muddy silts, outcropping in Incoronata location Here a polygenetic orthoconglomerate horizon more than one meter thick is present, containing an important crystalline fraction (mostly gramtoids) The clast dimensions arc commonly larger than ten centimetres, the sorting us moderate, and a short supply of the arenaceous-microconelomeratic matrix is manifest The transition interval can be interpreted as connected to processes of detritic sedimentation in proximal sectors of the marine basin, near the coastline.A lithozone ATS (Arenaceous Turbiditic Sequence) with arenaceous-pelitic compositions dominant, consists of brownish-yellow, [or yellowish-brown(1)] medium to fine grained, quartzo-feldspathic sandstones and laminated muds Usually the complete Bouma Sequence is recognizable The best exposure is in the C Sterpara location, where this interval reaches a thickness of approximately 30 meters This interval can be interpreted as the result of submarine turbidtic flowsThe planktonic foraminifera (biozone C a extremus) and nannoplankton (biozone CN9a) associations indicate a middle-upper Tortonian ageThe calciclastic fraction originates from the erosion of several units of the Southern Apennine chain The supply areas oh the calcareous clasts are identifiable with the Mesozoic carbonate platform unit, mainly from outer positions hi the lower part of the transition interval (TCC) the presence of fragments of limestones with huholhannuum and briozoarians indicates the pi obable erosion of Miocene successions (Formazione ch Cusano and Formazione ch Loneano, SELLA, 1937) overlyme some external platformsThe source areas of the siliciclastic sediments, instead, derive from the erosion of deposits previously involved in the orogenic transport The rich presence of crystalline clasts in the upper portion of the transition interval (TSC), is due to probable reworking of inner units of the sudappennme chain (cfr Gruppo del Cilento, AmoRE et alit. 1988)The supra-Miocene deposits of the Ponncello Formation are the expression ol an mtermontane basin, carried on the Southern Apennme nappes, m thrust-top position