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Architecture and dynamics of a Triassic/Jurassic carbonate platform-basin transition in the Sciacca area, South Central Sicily: implications for the Neogene accretion of the Maghrebian orogen

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Cacciatore M. , Di Stefano P.

Volumina Jurassica

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2006

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tom Vol. 4, no. 1

81-82

EN

The Sciacca area, in Southwestern Sicily, belongs to the external zone of the Neogene Maghrebian thrust and fold belt. Two different groups of south-verging thrust sheets crop out in this area: the so called "Saccense" units that consist of thick Mesocenozoic neritic and pelagic platform carbonates; the "Sicanian" units made of Permian to Cenozoic deeper-water sediments. The tectonic boundary between Saccense and Sicanian units runs NW-SE from Monte Genuardo to Caltabellotta. This boundary is orthogonal to the main thrust fronts and nearly parallel to the direction of thrust propagation. Thrust-top-basin deposits of Pliocene age obscure the tectonic relationships along this alignment leaving different solutions open for its structural interpretation and for the palinspastic restorations between platform and basin-derived units. Recent sedimentological and stratigraphical studies focused in this zone document the presence of Upper Triassic reef limestones in the Saccense units (Pizzo Telegrafo unit), close to the tectonic alignment. The macro and microfacies analysis reveal a typical Dachstein-type reef composition of these deposits. As consequence they can be interpreted as markers of platform edges facing high-energy, open marine basins. The collected data are thus consistent with the presence of a Late Triassic platform-basin transition close to the present-day tectonic boundary. An intense Jurassic paleotectonic activity along this margin is proved by in situ brecciation and the presence of large polyphase neptunian dykes crosscutting the reef deposits and the overlying Lower Jurassic platform limestones (Inici Formation). The dykes are filled up by Middle to Upper Jurassic Rosso Ammonitico type condensed limestones. Basaltic pillow lavas occur as thick wedges intercalated to the Jurassic pelagic limestones. They indicate repeated episodes of (trans)tensional stresses along the paleomargin. An anomalous thin Cretaceous to Miocene sedimentary cover (Scaglia type calcilutites and glauconitic sandstones) is punctuated by deep erosional truncations and megabreccias. These sediments fill up later generations of neptunian dykes confirming the paleotectonic activity in this zone throughout the Jurassic-Miocene times. In the Sicanian basinal units flanking the tectonic alignment the influence of the platform paleomargin is recorded by extensive Lower Jurassic carbonate aprons interbedded to cherty calcilutites. Upper Triassic reef-derived elements are common constituents of these clastics as recently documented at Campofiorito and Monte Triona. Looking at the present day structural relationships in the studied area we can conclude that the Triassic/Jurassic paleomargin has played an important role as major transpressional dextral escape during the Neogene Sicanian mountain building.

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The Jurassic biosiliceous sediments from the Sicanian basin in Western Sicily: new data

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Chiari M. , Di Stefano P. , Parisi G.

Volumina Jurassica

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2006

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tom Vol. 4, no. 1

153-154

EN

Detailed stratigraphic analyses on Jurassic radiolarites from centralwestern Sicily provide new data on the onset of the biosiliceous sedimentation in the Sicanian Basin. Studies were performed in two structural units of the Maghrebian chain that crop out south of Corleone, i.e. the Monte Barraců and the Campofiorito units. The radiolaritic unit at Monte Barraců consists of radiolarian-bearing cherty calcilutites alternating with cherts and levels of siliceous marls. The lower zone is green-grey coloured, while the upper one is red. This unit covers uppermost Triassic – Lower Jurassic cherty calcilutites through a large-scale stepped unconformity of submarine origin. The upper boundary (affected, in places, by synsedimentary deformations) is transitional to a thin unit of red wackestones with Saccocoma grading upwards to pink to whitish calpionellid cherty wackestones. The radiolarians from samples collected in the radiolaritic unit (lower zone) indicate a Late Bajocian to latest Bajocian – Early Bathonian age (UAZ. 4-5) for the presence of Ares cylindricus flexuosus (Takemura) and Parahsuum(?) magnum Takemura. The transitional zone between green and red radiolarites contains a radiolarian assemblage which indicates a Middle-Late Oxfordian age (UAZ. 9) for the presence of Emiluvia pentaporata Steiger & Steiger and Saitoum levium De Wever. Samples collected in the uppermost zone yielded Podocapsa amphitreptera Foreman and Hexasaturnalis minor (Baumgartner) that indicate a Middle-Late Oxfordian to Late Kimmeridgian – Early Tithonian age (UAZ. 9-11). In the Campofiorito section the radiolaritic unit covers a 20 m thick unit of basaltic pillow lavas and hyaloclastites, resting in turn on Lower Jurassic cherty calcilutites and marls. The lithologies of the radiolaritic unit are well comparable to the Monte Barraců ones. In this section samples from the basal zone could be dated as Early-Middle Bajocian to Middle Bathonian (UAZ. 3-6) for the coexistence of Paronaella kotura Baumgartner with Unuma echinatus Ichikawa and Yao. In the upper part of the section a poor preservation of radiolarians in the studied samples prevents further biostratigraphic evaluations. The new data fit well the biostratigraphic evaluations already available from the adjacent structural units of Monte Genuardo and Giuliana. They indicate that the onset of the biosiliceous sedimentation, in a large sector of the Sicanian Basin, can be “bracketed” between Late Bajocian and Early-Mid Bathonian times.

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New biostratigraphic data on the Oxfordian from Roccapalumba (Western Sicily)

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D'arpa C. , Melendez G. , Di Stefano P.

Volumina Jurassica

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2006

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tom Vol. 4, no. 1

144-144

EN

The small locality of Roccapalumba, in western central Sicily, is one of the most classical Jurassic localities described by G. G. Gemmellaro in his numerous monographs on the Jurassic faunas of Sicily. The Jurassic sequence by the village, crops out along an overturned carbonate succession overthrusting clastic deposits of Neogene age. Within this sequence the white massive limestones of Tithonian age form a characteristic escarpment on the landscape, which gives the name (“The Rock”) to the village. The earliest deposits cropping out at this point are Middle Jurassic, Bajocian to Early Callovian in age. Bathonian to Lower Callovian deposits are represented by light grey, micritic massive limestones. A sharp irregular surface marks the Middle/Upper Jurassic boundary level: a centimetric irregular limestone bed contains scarce Callovian ammonites, preserved as fragmented internal moulds showing evidence of taphonomic reelaboration (Paralcidia, Hecticoceras, Grossouvria). The Upper Jurassic sequence above this level comprises a first, lower succession of well defined grey-brownish, somewhat nodular limestone intervals (c. 20 m) of Oxfordian-Kimmeridgian age, and a second, upper succession of light grey massive micritic limestones (over 30 m) of presumably Tithonian age. A first lithological interval 7 to 7.5 m thick may be assigned to the Middle Oxfordian Transversarium Chronozone, Luciaeformis Subchronozone: some 1.5 to 2 m above the Middle/Upper Jurassic boundary level, the age of the deposits is evidenced by the presence of several specimens (fragmented shells) of Gregoryceras close to the G. riazi (Grossouvre) group. This first recorded association is followed by a second one including few specimens of Gregoryceras closer to G. transversarium (Quenstedt) group. This interval is topped by a clear discontinuity surface underlined by a yellow limestone level. The next interval, 3 m thick, may represent the middle-upper Transversarium Chronozone Schilli Subchronozone, by the record just above this level of a well preserved, resedimented (i.e. non-reelaborated) incomplete specimen of Sequeirosia (M) cf. brochwiczi (Sequeiros) and several fragmentary specimens of Passendorferia (m) erycensis Meléndez. Phylloceratina (Holcophylloceras, Sowerbyceras) are also common, whilst Lytoceratina are slightly scarcer. Above a new discontinuity marked by a second yellow limestone level, the next interval (about 3 m thick) has yielded few incomplete specimens of early Ataxioceratinae (Orthosphinctes) and Epipeltoceras gr. bimammatum (Quenstedt) that indicate Late Oxfordian, Bimammatum Chronozone age. Above a sharp, irregular truncational discontinuity surface, the sequence forms a 10-12 m thick interval of grey-brownish bioclastic, slightly nodular, well bedded limestones stratified in massive banks 40 to 50 cm thick. The Early Kimmeridgian age of this interval is evidenced by the frequent record of Ataxioceratinae (Lithacosphinctes spp.), “Aspidoceras” and a well preserved specimen of Nebrodites (M) close to the N. peltoideus (Quenstedt) group.

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New data on the Jurassic evolution of the Panormide Carbonate Platform (Sicily)

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Zarcone G. , Mindszenty A. , Di Stefano P.

Volumina Jurassica

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2006

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tom Vol. 4, no. 1

107-107

EN

The Jurassic of the Panormide Carbonate Platform records several discontinuity surfaces reflecting a complex sedimentary dynamics at a time of general extension in the western Tethyan realm. Previous studies documented subaerial exposure with karst bauxites between Upper Triassic and Upper Jurassic in the internal sector of the platform. On the contrary, at same time the marginal sectors of the platform record Rosso Ammonitico type sedimentation and the subsequent progradation of a new, Upper Jurassic platform. Latest sedimentological and stratigraphical studies added new data on these discontinuity surfaces in the Palermo Mountains. The succession of Mt. Castellaccio is characterized by Upper Triassic peritidal dolostones crosscut by various generations of neptunian dykes filled by pelagic limestones with crinoids, brachiopods, ammonites and filaments (Pliensbachian to Middle Jurassic). They are covered by red sediments rich in ferric ooids and lithoclasts enclosed in a red, argillaceous matrix. Petrographics and X-ray analyses have confirmed the presence of boehmite, kaolinite and hematite in these rocks, on the basis of which they may be qualified as low-grade bauxites. Above, with an angular unconformity, there follow Kimmeridgian loferitic limestones interbedded to bioclastic grainstone/packstone with Clypeina sulcata (Alth). At Punta Raisi, a stratigraphically equivalent, but sedimentologically different succession has been studied. The Upper Triassic peritidal dolostones are overlain by Lower Jurassic cyclic peritidal limestone with very poor microfauna. It is repeatedly interrupted by yellow to browinsh paleosoil levels. The top of this succession is red-coloured and is marked by a complex dissolution surface, with pinnacles and grooves. It is capped by a thick Fe-Mn crust with Foraminifera, small ammonites and filaments [Bajocian-Callovian(?)]. Based on preliminary petrographical and geochemical analyses a brief subaerial event may be hypothesized. However, the very same petrographic analyses revealed the effects of undoubtedly submarine bioerosion (action of sponge, fungi and bacteria), too. So even if we accept the idea of a transient subaerial phase, a strong submarine overprint during subsequent drowning, possibly contributing to the development of the pinnacle-and-groove topography can not be excluded, either. The Fe-Mn-crust is overlain by pelagic sediments displaying a coarsening upward trend and gradually passing into bioclastic grainstones/packstones with abundant carbonate platform elements (Kimmeridgian). This work is intended to add new arguments to the stratigraphic evolution and, consequently, to the subsidence history of the Panormide Carbonate Platform. Results are as follows: * evidence for an Early Jurassic shallow water depositional environment; * restriction of the size of the hiatus between Lower and Middle Jurassic; * verification of the presence of a submarine dissolution surface analogous to that of the Trapanese Platform; * increase of the areal extension of bauxites on the Panormide Platform; * confimation of the synchroneity of the re-establishment of the shallow-water carbonate sedimentation during the Late Jurassic. This data moreover allow a better paleogeographic reconstruction and a key to understand the combined effects of sea-level changes, tectonics and thermal (?)updoming at the time of an overall extensional regime.