Roberta Somma

Shallow burial and exhumation of the Peloritani Mountains (NE Sicily, Italy): Insight from paleothermal and structural indicators

We used vitrinite refl ectance and mixedlayered clay minerals to investigate levels of diagenesis of the Oligocene-Miocene basin developed on the nappes of the Alpine orogen exposed in the Peloritani Mountains (NE Sicily). Paleothermal indicators were integrated with stratigraphic and structural analyses and published apatite fi ssion-track and (U-Th-Sm)/He ages to defi ne the late evolutionary stages of the Peloritani Mountains. This multimethod approach allowed us to reconstruct the paleogeothermal gradient of the basin in Oligocene-Miocene times, to constrain its burial evolution, and discriminate between areas where it has been affected by sedimentary and/or tectonic load. In the southern area of the basin, organic and inorganic thermal parameters increase as function of depth, suggesting that their evolution was ruled by sedimentary burial. They record a decrease in paleogeothermal gradient values marking the evolution of the basin from a forearc to a thrust-top setting during the convergence-collision process between the Calabria-Peloritani Arc and the African plate. On the other hand, in the northern edge of the basin, vitrinite refl ectance values (0.46%‐0.58%) indicate that the thermal evolution of this area was controlled by tectonic burial related to late Langhian‐early Serravallian out-of-sequence thrust tec tonics. The tectonic overburden has been totally removed by extensional tectonics and/or erosion since the late Miocene. The short time span at maximum temperature (<2 m.y.) elapsing between thrust stack emplacement and the beginning of tectonic overburden removal has allowed only vitrinite refl ectance and thermochronological indicators to record this compressive reactivation.

Triassic continental rifting of Pangaea: direct evidence from the Alpujarride carbonates, Betic Cordillera, SE Spain

Abstract: Evidence is presented for Triassic rift-related palaeo-structures from the Alpujarride Complex carbonates of the Betic Cordillera, SE Spain. Direct evidence of synsedimentary extensional tectonics is provided by macro- to meso-scale normal faults overstepped by younger strata. Most faults define domino-like horst and graben structures. The faults are associated with an expanded synrift sedimentary prism in which soft-sediment deformation, gravity-flow deposits and unconformities are widely developed. Syntectonic mafic igneous intrusions also occur. The age of this phase of extension is constrained as Ladinian–Carnian (c. 237–216 Ma). From a palaeogeographical standpoint, the thick Triassic carbonates of the Betic Internal Zone, together with comparable successions in Northern Calabria (Southern Apennines), occupied a belt with elevated subsidence connecting the Neo-Tethys to the east with the eastern North American intracontinental rift system to the west. Their carbonate facies, intermediate between classical Alpine- and Germanic-type Triassic facies, recorded the main episodes of rifting affecting Central Pangaea.

The Cambrian to Aquitanian geological record of the Longi-Taormina Unit (Calabria-Peloritani Arc, southern Italy): geodynamic implications

The Longi-Taormina Unit forms the “Dorsale calcaire” of the Peloritani Alpine Belt (southern Calabria-Peloritani Arc). It is made by a thick sedimentary cover of Meso-Cenozoic age overlying a Variscan weakly metamorphosed Cambrian to Carboniferous succession. The Palaeozoic series consists of pelitic to arenaceous sediments containing layers of acidic and basic volcanics. The acidic volcanics are affected by the “Caledonian” compressional deformations and are referred to Early Ordovician. The basic rocks belong to two different volcanic cycles; the first, not dated, is ascribed to the Caledonian cycle according to its geochemical signature; whereas the second, middle-late Devonian in age, is interpreted to have formed in the framework of pre-Variscan extensional tectonics. During the Variscan Orogeny (330 Ma), the area recorded metamorphism up to subgreenschist-to-greenschist facies and two main deformation phases, marked by syn-schistose early folds (Dv1), overprinted by dominantly NW-SE trending late folds (Dv2). During the Aquitanian, deformation related to the Alpine Orogeny led to imbrication of the Palaeozoic and Meso-Cenozoic series. The sedimentary cover was affected by a series of N090° to N130° trending folds. Detailed stratigraphical and structural investigations on the tectonic contact between the Longi-Taormina Unit, and the overlying Fondachelli Unit indicate that this structure is part of a frontal thrust ramp which developed during the Aquitanian. Our geological and structural studies on the Cambrian to Aquitanian rocks of the Longi-Taormina Unit of the Calabria-Peloritani Arc enable to unravel the complex geodynamic history of the central-western Mediterranean area.

Un escarpement sous-marin permanent du Lias à l'Eocène, dans la dorsale calcaire Péloritaine (Sicile, Italie)

The schistosity of the Palaeozoic basement of the Capo San Andrea unit (Peloritan Dorsale) is cut by Liassic to Eocene neptunian dykes which developed along a pelagic fault scarp exposed on the sea bottom for 140 My. The Mesozoic structures determined the location of the Alpine deformation.

The Triassic platform of the Gador-Turon unit (Alpujarride complex, Betic Cordillera, southeast Spain): climate versus tectonic factors controlling platform architecture

A litho-biostratigraphic analysis has been carried out in the Gador-Turon unit of the Sierra de Gador (Alpujarride complex, Betic Cordillera, SE Spain). The Triassic succession of this unit is composed of a lower meta-detrital formation overlain by an upper meta-carbonate formation divided in six members. In the latter, a Ladinian–Carnian-rich fossil association has been found (foraminifers, algae, bivalves, microproblematica, trace fossils). Facies analysis has enabled the recognition of 22 facies of platform origin. This succession accumulated as a subsiding margin-type carbonate platform with homoclinal ramp geometry (Anisian?–Ladinian) evolving into a fault-block-type platform with a steeper-margined geometry (Ladinian–Carnian). Slope deposits of this latter platform show a prism-like geometry with progradational patterns and include syn-sedimentary structures associated with normal faults capped by younger beds. The results of the present research indicate that the architecture of the platform studied has been controlled mainly by climate and oceanic factors during the development of the ramp, and by syn-sedimentary extensional tectonics during the development of the steeper-margined platform. The Ladinian–Carnian tectonic activity was probably also responsible for the siliciclastic input and the shift to a mixed terrigenous-carbonate platform.

Paleo-thermal and Structural Indicators for Unraveling Burial – Exhumation Paths in the Peloritani Mts., NE Sicily, Italy

We used vitrinite reflectance and mixed layered clay minerals to investigate levels of diagenesis of the Oligocene-Miocene basin developed on the nappes of the Alpine orogen in the Peloritani Mts. (NE Sicily). Paleothermal indicators were integrated with stratigraphic-structural analyses and apatite fission-track and (U-Th-Sm)/He ages to define the late evolutionary stages of the Peloritani Mts. The reconstruction of the paleogeothermal gradient in Oligocene-Miocene times was performed to constrain the burial-thermal evolution. In the southern area, thermal parameters increase with depth suggesting that their evolution is ruled by sedimentary burial. They recorded a decrease in paleogeothermal gradients which marked the evolution of the basin from a fore-arc to a thrust-top setting during convergence-collision. In the northern edge of the basin, higher vitrinite reflectance values indicate that thermal evolution was controlled by tectonic burial related to late Langhian-early Serravallian out-of-sequence thrusting. This overburden was removed by extensional tectonics and/or erosion since late Miocene. The short time span at maximum temperature (<2 Ma) elapsing between thrust stack emplacement and the beginning of its removal have allowed only vitrinite reflectance and thermo-chronological indicators to record this compressive reactivation.

The main lithoid material origin of the Temple of Hercules in San Marco d'Alunzio (Sicily, Italy)

This study compares four samples of travertine collected in the lithoid material of the Temple of Hercules (III-IV century B.C.) in San Marco d’Alunzio (Messina) and other four samples of the same lithotype collected in an outcrop found in the surroundings of Alcara Li Fusi (Messina). Analyses on sedimentary petrology, paleontology, XRay diffraction and infrared spectroscopy have been carried out on both series of samples. Chemical analyses, for the determination of the major and trace elements, were carried out too. Sedimentary petrology and paleontological studies have indicated that all samples consist of Quaternary soft and porous organic limestones with plant remains, formed in wet and warm zones. X-ray diffraction analyses have shown that studied travertines are prevalently made up of calcite. Infrared spectroscopy studies also showed small quantities of kaolinite and dolomite. Chemical analyses have confirmed the compositional homogeneity among the different samples. Data, as a whole, allow us to hypothesize that the travertines used to build the Temple of Hercules were extracted in the surroundings areas of Alcara Li Fusi, in ancient open quarries set up in Quaternary travertines.