Evoluzione stratigrafica, analisi delle biofacies e storia diagenetica di depositi Tortoniani - Messiniani: ricostruzione dell’architettura deposizionale dell’area di Monte Poro (Vibo Valentia, Calabria meridionale)

Dottorato di Ricerca in Scienze della Terra, XXI Ciclo,a.a.2005-2008Università della Calabri

Geological map of the Middle Triassic Latemar platform (Western Dolomites, Northern Italy)

The Latemar is a Middle Triassic isolated carbonate buildup with a diameter of approximately 3 km, that crops out in the western Dolomites, northern Italy. The platform is an important case study and potential analogue for carbonate hydrocarbon reservoirs. Detailed field mapping of the platform has been carried out on a high-resolution topographic base extracted from airborne LIDAR to produce a geological map at 1:5000 scale. Remote sensing was used for the recognition of structural features and then validated in the field. In addition, high-resolution digital photographs were used to interpret the geology of inaccessible rock walls. This work represents a up-to-date detailed geologic map of the Middle Triassic Latemar platform that enhances its internal units subdivision and highlights its complex shape, characterized by gulfs and internal basins and strongly controlled by synsedimentary tectonics

The Latemar: A Middle Triassic polygonal fault-block platform controlled by synsedimentary tectonics

Detailed field mapping of a Middle Triassic carbonate buildup, the Latemar in the western Dolomites, northern Italy, has been carried out. The Latemar is an isolated carbonate buildup that nucleates on a fault-bounded structural high (horst) cut into the underlying late Anisian carbonate bank of the Contrin Fm. This study demonstrates that extensional synsedimentary tectonics is the main factor controlling its geometry and provides an age for this tectonic phase. In an early phase, slopes were mostly composed of well bedded, clinostratified grainstones and rudstones. In a later stage, the deposition of grainstones was accompanied by the emplacement of clinostratified megabreccias. The upper portion of slopes is a microbial boundstone with abundant Tubiphytes and patches or lenses of grainstone. Boundstones may occasionally expand into the platform interior and downward to the base of the slope. The depositional profile was that of a mounded platform. The buildup is dissected by a dense framework of high angle fractures and faults, and by magmatic and sedimentary dikes, exhibiting two principal directions trending NNW\u2013SSE and ENE\u2013WSW. Faults trending WNW\u2013ESE were also observed. Magmatic dikes are related to the emplacement of the nearby Predazzo intrusion and are thus upper Ladinian. Kinematic indicators of strike-slip activity were observed on fault planes trending NNE\u2013SSW and NNW\u2013SSE, that can be attributed to Cenozoic Alpine tectonics. Faults, magmatic dikes and sedimentary dikes show systematic cross-cutting relationships, with strike-slip faults cutting magmatic dikes, and magmatic dikes cutting sedimentary (neptunian) dikes. ENE\u2013WSW and WNW\u2013ESE faults are cut by all other structures, and record the oldest tectonic activity in the region. Structural analysis attributes this tectonic phase to an extensional stress field, with a direction of maximum extension oriented ca. N\u2013S. Several lines of evidence, including sealed faults and growth wedge geometries allow us to recognize this old tectonic phase as syndepositional, and to date it to the latest Anisian (avisianum and crassus ammonoid biochronozones). The horse-shoe shape of the platform and its margins, rectilinear for long tracts, are explained by the existence of a network of extensional faults, whose activity lasted for part of the growth of the platform. The Latemar is thus a polygonal, fault-block platform controlled by synsedimentary tectonics. The resulting sedimentary architecture is that of a growth wedge, deposited probably on the uplifted side of a submerged half graben. Continuous reactivation of faults at platform margins locally determined anomalous facies transitions, with well layered platform interior directly in contact with the clinostratified slopes

Ostracoda and Mollusca biodiversity and hydrochemical features in Late Miocene brackish basins of Italy

Late Miocene brackish ostracods and molluscs collected in three Italian basins show noticeable differences in their taxonomic composition, despite their capability of dispersing across wide geographic areas. In the Venetian-Friulian Basin (northern Italy), the upper Tortonian sediments contain oligotypic ostracod assemblages including Hemicyprideis dacica dacica, Hemicytheria pejinovicensis, and Loxoconcha cf. L. josephi and few gastropods referable to Planorbidae and Stenothyroides, which are typical of the central Paratethys. In central Italy, the brackish ostracods and molluscs recovered from upper Tortonian-lower Messinian deposits from four Tuscan basins (Volterra-Radicondoli, Velona, Baccinello-Cinigiano, and Valdelsa) display high affinity at a generic level but strong endemicity at a specific level. At Cessaniti (southern Italy), the upper Tortonian unit contains oligotypic brackish ostracods and molluscs: Mediocytherideis (Sylvestra) posterobursa, Cyprideis ruggierii, Loxoconcha cf. L. biformata, and Zonocypris membranae quadricella characterise the ostracod fauna, while Granulolabium bicinctum and Hydrobia frauenfeldi are the dominant molluscs. The recovered ostracods have a strong affinity with brackish species from central and eastern Palaeo-Mediterranean areas, whereas the molluscs present a Paratethyan origin. Despite the fact that the basins are all brackish and partly coeval, the systematics of these assemblages highlights the absence of common species among the three studied areas. Geochemical analyses (stable isotopes and trace elements) are performed on ostracods, and 87Sr/ 86Sr ratios are established in molluscs and echinoids. The results suggest brackish environments with different compositions and origins of solutes in the three different areas. The Tuscan basins are characterised by brackish waters, with NaCl-enriched waters coming from aquifers of Triassic evaporite bedrock. The brackish deposits of the Venetian-Friulian Basin and Cessaniti are true marginal marine environments, although the northern basin may have been influenced by both the Paratethyan Sava Basin and the northern portion of the Palaeo-Mediterranean water bodies. © 2012 Elsevier Masson SAS