Mauro Agate

WALKING ALONG A CRUSTAL PROFILE ACROSS THE SICILY FOLD AND THRUST BELT

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A multidisciplinary approach to reveal the Sicily Climate and Environment over the last 20 000 years

We present a thorough review of the knowledge on the climate and environment in Sicily over the last 20 000 years, taking into account results of several studies carried using terrestrial and marine records. We obtain a coherent framework of the most important changes succeeded in the island, even if some points need further investigation.All the reconstructions of surface temperatures of the seas and the air surrounding Sicily point out severe climatic conditions during the last glacial period. The steppe- and semisteppe-like vegetation pattern testifies, together with additional evidence from geochemical data of lacustrine evidence, markedly arid conditions. Fi-nally, significant episodes of sea level drop connected Sicily to the Italian Peninsula and favoured the dispersion of faunal elements from southern Italy.The transition between the last glacial and the Holocene was not characterized by a gradual warming but was punctuated by two abrupt suborbital climatic fluctuations: Bølling-Allerød (warm) and Younger Dryas (cold), as recognized in the sediments recovered close to the northern and southern coast of Sicily. A denser arboreal cover is possibly indicated by the occurrence of dormouse and Arvicola remains.Finally the sensitivity of Sicily to climate perturbations is demonstrated by the occurrence of repeated subtle climatic anomalies during the Holocene, including the Little Ice Age, also known from historical chronicles. Forests, woods and Mediterranean maquis developed in the early-middle Holocene. Thereafter was a general decline of arboreal vegetation, following a general aridification trend that seems to be a common feature in southern Europe and North Africa. Science Greek colonization (7th century before Christ), the landscape was intensively modelled for agriculture and breeding, leading to a significant loss of vegetation cover.

Middle Miocene–Early Pliocene wedge-top basins of NW Sicily (Italy): constraints for the tectonic evolution of a ‘non-conventional’ thrust belt, affected by transpression

The study of geological evolution of a multiphase orogenic belt is complex, expecially when the tectonic events are superimposed in a coaxial fashion. The Sicilian fold-and-thrust belt represents an interesting case study, as a non-coaxial superimposition of structures is recognizable, owing to large synkinematic clockwise rotations during each of two subsequent compressional events. These rotations involved also the syntectonic basins that developed in the wedge-top depozone. This study aims to constrain the tectono-depositional evolution of the NW Sicily fold-and-thrust belt and the associated wedge-top depozone between the middle Miocene and the early Pliocene. Integrated analyses of stratigraphic, sedimentological and structural field data allow us to better constrain the transition between the two tectonic events. The syntectonic basins developed during the first (late Serravallian–early Tortonian) tectonic event were relatively wide and characterized by marine sedimentation. The onset of the second (latest Tortonian) transpressional event induced localized deformation into the wedge-top depozone and the syntectonic successions were accommodated as basin fill in progressively narrower and laterally discontinuous basins, bounded by transpressional structures. The lateral correlation of the wedge-top successions suggests a latest Miocene regional palaeoslope with a present-day WSW dip, which fits well with the tectonic transport calculated for the early compressional event.

Tectono-stratigraphic evolution of a basin generated by transpression: the case of the Early Pliocene Lascari Basin (northern Sicily)

In the present paper integrated stratigraphy and structural analyses are aimed at the description of a synsedimentary transpressional tectonic event, driving the onset and development of the Early Pliocene Lascari Basin, located NW of the Madonie Mountains(northern Sicily). Our data show that the transpressive tectonics generated a morphostructural high flanked by a deep and narrow tectonic depression, bounded by steep and tectonically controlled slopes. Within this depression an Early Pliocene fining and deepening upward sedimentary succession was deposited, unconformably overlying the already deformed substrate. The succession is made up of «base-ofslope» breccias, cross-stratified calcarenites, and bathyal limestones deposited in a high-energy palaeostrait setting. The growth geometry that characterizes the stratal pattern of the deposits suggests the activity of a synsedrimentary transpressional event during the Early Pliocene time. The roughly E-W trending Lascari Syncline, where the Early Pliocene syntectonic basin is hosted, belongs to a system of north verging folds, deforming the pre-existing, originally flat thrusts, generated in Langhian-Serravallian time. This paper presents an original interpretation of the stratigraphic and structural evolution of the study sector of the Sicily Fold and Thrust Belt. Our data contribute also to both define the structural style and constrain the timing of transpressional tectonic event in northern Sicily. A brief comparison performed between the data here presented and those coming from adjacent sectors of northern Sicily suggests that the transpressional tectonics in these sectors of the chain was active at least since the latest Tortonian till at least the Late Pliocene.

Quaternary marine and continental unconformity-bounded stratigraphic units of the NW Sicily coastal belt

ABSTRACT In the coastal sector of NW Sicily, the regional correlation of relevant unconformities recognised within the Quaternary sedimentary successions allowed the mapping of seven unconformity-bounded stratigraphic units (UBSUs). The regional unconformities are marine or subaerial erosional surfaces, as well as non-depositional surfaces, locally marked by paleosoils. The erosional surfaces were produced from marine abrasion, surface water overland/concentrated flow, river erosion, karst solution, mass movement, or wind erosion. The main lithofacies of the Quaternary UBSUs consist of: (a) marine and coastal bioclastic calcarenites, (b) aeolian sandstones, (c) river deposits, (d) colluvial deposits, (e) talus slope deposits, (f) landslide deposits, and (g) chemical carbonates (travertines and speleothems). Quaternary environmental changes, due to tectonics, climate, and sea-level oscillations, are the causes that favoured the development of erosion/deposition processes responsible for the genesis of unconformities and deposits. As a result, through the UBSU map of the NW Sicilian coastal belt, it is possible to: (i) recognise stratigraphic units controlled by tectonic, climatic, and environmental processes (and their interplay) and (ii) detect Quaternary sedimentary evolution.

Sea–land geology of Marettimo (Egadi Islands, central Mediterranean sea)

ABSTRACT We present a 1:10,000 scale geological map of Marettimo Island and its offshore (Egadi Archipelago, central Mediterranean Sea). The map was achieved by integrating a new geological survey with data from recent, marine, geological and geophysical surveys acquired along the adjacent continental shelf. The island is composed of a Mesozoic, mostly carbonate platform succession, which is overlain by continental to coastal marine Quaternary deposits. Extensional tectonics have affected the carbonate platform since the Late Triassic producing an initial increase of accommodation space that was filled by interbed breccias, marls and calcareous marls. During the Jurassic, a NE-SW-directed normal fault-bounded structural lows where thick beds of megabreccias accumulated followed upwards by cherty limestone and bedded cherts. During the building of the chain, the compressional tectonics generated a southeast-verging tectonic wedge, displaced by subsequent transpression. During the Quaternary, repeated sea-level changes shaped a rough erosional surface along the inner shelf and controlled the lateral facies variation of the continental and marine coastal deposits along the present day coastline.

Geoacoustic Inversion with Drifting Buoys: Enverse 1997–98 Experiments (Marettimo Is.)

Acoustic buoys were developed to allow the rapid determination of range-dependent bottom properties in a shallow water environment from the inversion of propagation measurements. The main features of the buoys are the large dynamic range, digital signal conditioning unit, global positioning system receiver and reliable radio data link. The buoys drift away from a broadband source receiving its pings at known positions. Single hydrophone, matched waveform, inversion techniques are applied to the received signals to invert for geoacoustic parameters. Eight prototypes were tested over the southern continental shelf off the island of Marettimo (Sicily) during the EnVerse 97 sea trials. Calibrated measurements of medium impulse responses were obtained between a controlled source and a field of receivers drifting over carbonate bioclastic sediments with outcropping rocky substratum. Inversion results agree with ground truth data obtained during the EnVerse 98 geophysic survey.

Mountain building in NW Sicily from the superimposition of subsequent thrusting and folding events during Neogene: structural setting and tectonic evolution of the Kumeta and Pizzuta ridges

ABSTRACT We present a 1:25.000 scale geological map of the Kumeta-Pizzuta ridge in north-western Sicily (Italy), achieved by integrating stratigraphic, structural and geophysical data. In this area, the tectonic edifice results from the piling-up of deep-water-, carbonate platform- and pelagic platform-derived tectonic units (Imerese and Sicilide, Panormide and Trapanese domains, respectively) resulting from deformations of the former southern Tethyan continental margin. The structural setting shows interference of tectonic events, different types of structural styles and different scales of deformational patterns. Early overthrust of the Imerese on the Trapanese units (since the late Serravallian) was followed by wedging at depth of the Trapanese units (after the Tortonian). The wedging implied re-embrication and shortening into the overlying Imerese tectonic units and so produced the main folding and compressive to transpressive structures along the Kumeta-Pizzuta Ridge. Seismic reflection profiles integrated with field data reveal that the main E-W-trending anticlines have been offset by high-angle reverse faults flattening at depth until they connect with low-angle, regionally widespread, decollement surfaces with a northward tectonic transport. This setting supports backthrusting along transpressional faults in the study area, ruling out that the Kumeta ridge is a positive flower structure related to a near-vertical deep, crustal, shear zone as formerly suggested.

Biostratigraphy, chronostratigraphy and paleonvironmental reconstruction of the Palermo historical centre Quaternary succession

Marine deposits from the Palermo Plain were historically relevant for the Quaternary Period definition. Here we show lithostratigraphic, biostratigraphic and chronostratigraphic data collected on three boreholes in the Palermo historical centre that recovered 36.8, 42.0 and 52.0 metres of sediments overlaying the Numidian Flysch. Marine sedimentary sequences span from the Calabrian Stage (calcareous nannofossil Zone MNN 19d) to the Middle Pleistocene (dominance of medium-sized gephyrocapsids within the MNN 19f Zone) and also include a short Holocene depositional event. Calcareous nannofossil, benthic and planktonic foraminifera assemblages point to a shallow coastal environment, possibly < 50 m deep. This study highlights the need of a modern and reliable stratigraphic interpretation of lithotypes, to identify stratigraphic gaps and to draw deep geological structures in an area extremely vulnerable to seismic and hydrogeological hazard.

Submarine slope failures along the Northern Sicilian Continental Margin (Southern Tyrrhenian Sea) and possible implications for Geo-hazard

In this study we present an overview of the mass wasting features (e.g.: submarine canyons, landslides, debris flows) and downslope movements that have contributed to shape the northern Sicily continental margin (southern Tyrrhenian Sea) since the Late Quaternary. The study is based on Multibeam data and high-resolution seismic reflection profiles, which allowed to define the morphology and the stratigraphy of the mass transport deposits and related failures of the area. We distinguished slope failures related to different mechanisms. In the Palermo Gulf and in the eastern sector of the northern Sicily margin tectonic activity, fluid escaping and oversteepening triggered downslope turbiditic currents and concurrent up-slope retrogressive mass failures. In the Ustica offshore gravitational collapse of volcanic edifices is mainly linked to neotectonic activity and volcanism. These data allow us to understand geological features and processes which may represent a threat for coastal areas of the northern Sicily margin.