Carta Geologica d'Italia alla scala 1:50.000 e note illustrative del foglio 594-585 PARTINICO-MONDELLO.

The 594-585 ”Partinico-Mondello” Map Sheet 1:50.000 includes marine and land areas of the topographic map sheet “Partinico” and “Mondello”. The map sheet “Partinico-Mondello” (Palermo Province) covers a part of the Sicily Fold and Thrust Belt (FTB) which has developed along the plate boundary between Africa and Europe in the central Mediterranean. The Sicily FTB links the African Maghrebides to the Calabrian arc and the Southern Apennines. The fTB and its submerged western and northern exten- sions are partly located between the Sardinia block and the Pelagian-Ionian sec- tor, and partly beneath the central southern Tyrrhenian Sea. In this sector of the Mediterranean area, the main compressional movements, after the Paleogene Alpine orogeny, began with the latest Oligocene-Early Mio- cene counterclockwise rotation of Corsica-Sardinia, believed to represent a volca- nic arc, and its collision with the African continental margin. Thrusting occurred in connection with the westward subduction of the Adriatic and Ionian lithosphere beneath the Corsica-Sardinia block. Today, a westward subduction is indicated by a North-dipping Benioff zone, as deep as 400 km, west of Calabria and the Apennines, and the related calc- alkaline volcanism in the Eolian Islands. Subduction and thrusting are contempo- raneous with a back arc-type extension in the Tyrrhenian Sea. 237lAND AREAS geomorphology The geomorphological evolution of the studied area has been controlled by strong down-cutting and dismantling processes that have produced both the ero- sion of thick volumes of very recent terrigenous deposits and the exhumation of older rocks. Due to tectonic uplifting, these deepening processes are developed intensively on “soft rocks” (Numidian fysch clayey deposits), producing large river valleys whose slopes are affected by water erosion and surfcial landslides (Nocella and Oreto rivers); erosion has slowed down considerably along the more resistant Mesozoic-Tertiary carbonate rock units of the wide ranges of the Palermo Mountains. In the present-day, relicted planation surfaces and abandoned valleys, fault/fault-line scarps and karst “dolines” and “poljes” occur in the mountainous areas. On the other hand, the geomorphological setting of the coastal areas has been infuenced by important Quaternary extensional tectonics that were at the origin of the lowering of the northern sectors of the Sicilian chain submerged by the Tyrrhenian Sea and invaded by coastal marine depositions (Marsala synthem). Uplifting, involving also the subsided blocks, together with sea level variations, has led to the progressive withdrawal of the sea that originated a succession of marine terraces, Tarantian-Latest Pleistocene in age, followed by the emersion of the present-day coastal depressions (Partinico, Carini and Palermo plains). Du- ring the Upper Pleistocene to Holocene, the uplifting rates reach values between about 0.08 and 0,15 m/kyr. stratigraphy The carbonate and terrigenous rock facies analysis and stratigraphy has led to the reconaissance of large Paleozoic to Miocene sedimentary units pertaining to different crustal paleogeographic domains; the former developed along the Pela- gian (African) passive continental margin and the adjacent Tethyan Ocean. The “Tethyan” successions correspond to the deep sea, clayey carbonate and volcanoclastic rocks known to have been deposited in the Sicilide Domain. The passive continental margin, rock units are Meso-Cenozoic shallow water carbo- nates, deep water carbonates and siliceous rocks that were deposited in some domains, locally known as Panormide, Trapanese and Imerese. The terrigenous evaporitic and clastic-carbonate rocks, Miocene to Pleistocene in age, formed during the foredeep evolution of the Sicilian fTB. A detailed stratigraphy of the rock-successions is summarized in the next paragraph (see map Legend of the sheet). 238Quaternary continental (mostly) and marine deposits have been mapped as unconformity-bounded, stratigraphic units limited by lower and upper uncon- formity surfaces, locally marked by palaeosols, due to erosion/depositional phe- nomena, marine/sub-aerial processes or non depositional events. In place, the upper boundary is the present-day topographic surface. The detection of some unconformity surfaces of regional extent allowed us to defne several synthems here described from the older ones. The Marsala synthem is a lower Pleistocene rock unit of marine/coastal deposits, with abundant fossils; its lower boundary is a marine erosion surface cut into pre-Quaternary rocks. The Piana di Parti- nico synthem is made up of marine/coastal deposits located above a number of marine terrace surfaces, related to sea-high, stand phases of the Middle Pleisto- cene (Oxygen Isotope Stages – OISs - 17-7); its lower boundary is a wave cut platform carved into the Marsala synthem or some pre-Quaternary rocks. The Polisano synthem is made up of aeolian sandstones and sands with intercalations of breccia talus, late Middle Pleistocene in age (OIS 6); its lower boundary is a non-depositional surface at the top of the Piana di Partinico synthem or older rocks. The Oreto and Jato synthems are made up of Middle – Upper Pleistocene mainly fuvial deposits located on river terrace surfaces; their lower boundary is a stream erosion surface. The Monreale synthem consists of Middle Pleistoce- ne carbonate speleothems (mainly travertines); its lower boundary is a subaerial erosion surface cut both into the Marsala synthem or into the pre-quaternary rocks. The Barcarello synthem encompasses marine/coastal conglomerates and arenites, with a rich warm-temperate “Senegal fauna” including Strombus bubo- nius; the unit is located above two orders of marine terrace (OISs 5e and 5c or 5a) and laterally passes into welded colluvial deposits whose age is correlated to the oIS 5. The lower boundary of the Barcarello synthem is a marine abrasion surface, laterally extending into a continental erosion surface; the latter cuts the Polisano synthem or older rocks. The Raffo Rosso synthem consists of aeolian sandstones and sands, colluvial or gravitational deposits and thick stratifed slope deposits of the last glacial climatic event (OISs 4-2); the lower boundary is a non- depositional surface located at the top of the Barcarello synthem or older rocks. The capo Plaia synthem is made up of coastal to continental deposits of the last glacial climatic event end – Holocene age (OISs 2-1); it is comprised in the lower boundary, formed by variously originated erosion or non-depositional surfaces and the topographic surface. struCtural grain The geological map has been compiled following stratigraphic and structural criteria, suggested by the CARG rules. Following the carbonate and terrigenous 239facies analysis, already carried out in western Sicily during the eighties and nine- ties, large Paleozoic to Cenozoic sedimentary units were identifed. These bodies, detached from their basement, progressively accreted in a pile of tectonic units and are now exposed in the Sicilian FTB. To defne the extension and setting of the mentioned units versus their internal facies pattern, we have used the term Structural – Stratigraphic units (USS). The USS are bounded by clear mappable tectonic features (faults, thrust surface, etc.) and each one is characterized by ho- mogeneous lithologies and similar structural behaviours and settings. The outcropping tectonic edifce in the “Partinico-Mondello” geological map sheet is formed by some USS that, locally, can be subdivided into tectonic units of minor order mapped on the basis of their tectonic relationships. The following USS have been identifed from the geometrically highest and most internal ones in the “Partinico-Mondeòlo” tectonic edifce: 1) the USS deriving from the deformation of the Imerese Domain and its overlying Numidian fysch basin. The units outcrop in the central southern sector of the geological sheet and are Meso-cenozoic deep water carbonates deformed together with their Oligo-Miocene Numidian fysch cover. The latter is detached from its carbonate substrate. Among them: - USS Meccini; - USS Sagana – Belmonte Mezzagno. The latter has been separated into three subunits based on the occurrence of some décollment surfaces (low and high angle) that put in evidence the deforma- tion (thickening) of the rock succession: a) Cuccio-Saraceno is the highest in the stack; b) Gradara and c) Pizzuta-Santa Cristina are widespread in the southern sectors. The lowest in the stack (the Pizzuta-Santa Cristina unit) overthrusts the Trapanese carbonate Platform units as is clearly shown in the Monte Kumeta Ridge located to the south in the adjacent corleone sheet map. 2) The USS deriving from the deformation of the Panormide Domain con- sist of Meso-cenozoic shelf to pelagic carbonates including their unconformably overlying ,Numidian fysch cover that is, often detached from its substrate. Three main USS have been distinguished and divided, in turn, into subunits: - gallo- Palmeto USS consisting of the Palmeto and gallo subunits - Cozzo di Lupo USS, formed by the shelf to margin carbonates of the Panor- mide Platform, is geometrically underlying the Gallo-Palmeto unit. It has been divided into: the Cala Rossa subunit, occurring in the coastal zone of Terrasini and the Vuturo subunit outcropping in the hilly neighbourhood of Palermo and Torretta. - Pecoraro-colombrina USS. The Unit outcrops in the hills of Monte Pecora- io, Montagna Longa, Monte Colombrina, Cozzo Muletta, Torre Pozzillo near the town of carini. 240Structural evolution The tectonic edifce outcropping and buried beneath the “Partinico-Mondel- lo” map sheet is the result of several deformational events that have taken place since the Triassic, deforming the sedimentary successions deposited during the Mesozoic-Pleistocene in different ways. Two main events took place during the Miocene and Pleistocene time interval. They are respectively characterized by compression and transpression. Contraction, originally involved internal domains of the continental margin whose deep water mesocenozoic carbonates formed the structurally highest tectonic units in the chain. The occurrence of intrastratal decollement gave origin also to the duplex geometries. Since the Messinian, the deformation has gone into depth, progressively involving the carbonate platform rock body in large E-W antiforms that were successively (during Late Pliocene) folded by NE-SW structures. The transpressional event is proved by NNW-SSE and NE-SW transcurrent and transpressive structures (dextral); it involves the deep-seated carbonate platform-forming fold structures and severe uplifting that induces reimbrication in the overlying Imerese deep-water units. This transpres- sive event accompanies the paleomagnetically evidenced thrust rotations between the late Miocene and the Early Pleistocene. An abruplt change in the tectonic transport direction of the two compressional structure systems is explained taking in account the 120° clockwise rotation based on the paleomagnetically results of Channell et alii (1980, 1990); speranza et alii (2000). As a consequence the present day outcropping structural attitude of the structures (and consequently of the deformation felds) do not coincide with the original trends. The compressio- nal and traspressional structures are down faulted northwards by the extensional tectonics. After the detachment from their crystalline basement, the original sedimenta- ry bodies were progressively accreted in a pile of tectonic units now exposed in the Sicilian fold and Thrust Belt. MARINE AREAS The morphological environments from the beach and the foreshore, through to the outer shelf, upper slope and confned slope basin settings are part of the marine area. The area shows a lateral gradation from the fuvially – (i.e. small mountainous rivers) dominated Castellammare Gulf shelf to the sediment – starved Carini Bay. Important physiographic changes, as shelf width and gradient and different coast orientations, characterize the continental shelf and slope and infuence the 241hydrodynamic processes (wave activity and shelf current patterns). The physiographic sectors that have been recognised are, from the West: 1) the eastern parts of the gulf of Castellammare, 2) the shelf of the Carini Bay and 3) the inner shelf of the Mondello Bay. The shelf shows width values ranging from the 8,0 km of the gulf of Castel- lammare to the 10 km of the Carini Bay, whereas gradient values range between 0,4° and 1,35°. The shelf edge, located at water depths between 120 m and 160 m, rises to lower depths at the canyon heads. The continental shelf has been subdivided into an inner infralittoral domain down to a 30 – 35 m water depth and an outer shelf domain, extending to the shelf edge. Off Cape Rama, the seaward boundary between the inner and the outer shelf is marked by a break of slope and by the occurrence of several small wave – cut marine terraces; in the Carini Bay, a paleoshoreline, between a depth of 100 m - 110, divides the shelf into an outer smooth sector and in an inner rough area, where paleoriver valleys occur. Dominant morphological features within the eastern castellammare gulf are the submarine erosive conduits that intercept the dominant littoral drift from the west to the north-west. The heads of the castellammare conduits are characteri- zed by severe episodes of retrogressive failure and incised by small gullies. Ero- sional chutes deeply cut the sedimentary cover of the carini slope. seismostratigraphy and stratigraphiC setting The Plio – Pleistocene buried sedimentary succession has been investigated by means of a close grid of single and multichannel seismic lines. Overall, three seismic units (PL, PQ and STDQ) have been distinguished. The PL seismic unit unconformably overlies a pronounced, erosive unconfor- mity (refector Y) that has been correlated to the extensive Messinian horizon, ge- nerated during the last phases of the Mediterranean Salinity Crisis (5.5 Ma b. P.). The Pl seismic unit has been interpreted as being made up of globigerina – bearing pelagic chalk (Trubi) and the Upper (?) Pliocene slope to shelfal deposits, pertain to the “marnoso arenacea del Belice”. The Pq seismic unit has been correlated with the regressive Pleistocene depo- sits, bounded below to the x horizon, corresponding to the lower boundary of the Marsala synthem and topped by the regional-wide, erosional truncation related to the last glacioeustatic sea level fall, correlable with the δ18 o isotopic stage 2. In the stratigraphic section, transversal to the coastline, the Late Pleistocene to holocene STDq shows a sigmoidal to tabular geometry; the depositional se- quence consists of a falling Stage and a lowstand Systems Tract with a progra- dational pattern controlling a relevant outward-building of the shelf margin and 242a sedimentary wedge, of variable thickness, made up of the Transgressive (TST) and the Highstand (HST) Systems Tracts. The TST, developed during the Holocene sea level rise, shows a retrograda- tional stacking pattern of three small parasequences, well defned in the eastern sectors of the Castellammare shelf but more condensed in the Carini Bay; here, the holocene sea level stillstands have been recorded by three orders of submer- ged paleo-shorelines. The HST, deposited during the last 6 ka b.P., shows aggradational to faintly progradational geometries, related to the development of a deltaic to littoral de- positional system. In the inner continental shelf of the eastern Castellammare Gulf, seismic fa- cies, like “migrating waves” and acoustic wipe – out, suggest sedimentary insta- bility and gas expulsion phenomena. Along the upper slope, an extensive slope to turbiditic system, characterized by erosive conduits and scattered mass wasting deposits, developed during the late Pleistocene to holocene. Surfcial sediments of the continental shelf and slope The continental shelf and slope of the “Partinico – Mondello” sheet are vene- ered with unconsolidated, late Holocene in age, terrigenous and carbonate clastic and biogenic sediments. Deposits are composed of quarzose sands, relictic? Pleistocene and older car- bonate particles, abundant biogenic carbonate granules and algal-coated grains. In the outer shelf and the upper slope seafoors, deposits are predominantly fne to very fne grained (silts and silty clays). The inner shelf seafoors are vene- ered by a mixture of very coarse to fne sands, silts and clays, showing a general trend of decreasing size in a general seaward direction. According to the sedimentary and the morphological features, four different depositional systems have been distinguished: foreshore depositional systems, inner shelf depositional systems, outer shelf depositional systems and upper slope depositional systems, mapped as g8, g19, g21, m2 respectively. The systems are laterally gradational and linked by a variety of sedimentary processes. Shallow marine environments (up to 50 m of water depth) are general- ly characterized, in the Castellammare Gulf, by terrigenous and carbonate clastic sediments supplied by rivers or coastal erosion; in the carini Bay and in the inner shelf of Mondello, biogenic sediments prevail. The most important facies of the infralittoral domain consists of Posidonia oceanica and Cymodocea nodosa meadows that extensively cover the rocky sub- strate or the sandy foors the frst, muddy foors the latter. 243teCtoniC evolution of the offshore areas The present day structural setting reconstructed in the castellammare basin and Palermo salient marine sectors appears correlatable to the tectonic edifce depicted on the mainland: it has been interpreted as a consequence of a complex Neogene to Quaternary tectonic evolution. The compressive tectonics, responsi- ble for the wedging of the present day submerged thrust sheets, developed during the late Miocene span interval. This event was followed by transpressive tecto- nics that faulted and folded the Late Neogene to Pliocene infll by activation of deep, high-angle faults. During the Pleistocene, extensional tectonics accounted for opening and sub- sidence of structural lows. Present day active tectonics are still going on, as documented by compressive- transpressive focal mechanisms of shallow to deep, low amplitude earthquakes occurring along the offshore between the Sicily coast and Ustica Island. A few middle-late Pleistocene marine terraces outcropping along the coast at different levels suggest a prolonged, faintly tectonic uplift. On the whole, the Plio-Quaternary geological evolution of the offshore area appears constrained by a deep interaction between tectonics, eustatic sea level changes and sediment supply, recorded by strain features and enhanced unconfor- mities crossing the basin fll.