Rend. Online Soc. Geol. It., Vol. 21 (2012), pp. 1004-1006, 3 figs. © Società Geologica Italiana, Roma 2012
Middle Triassic carbonate platform-basin system from Sicily. New evidence from the Madonie Mountains PIETRO DI STEFANO (*), CHRISTOPHER MCROBERTS (**), PIETRO RENDA (*), ANGELO TRIPODO (*), GIUSEPPE ZARCONE (*) Key words: Triassic, Ladinian, Sicily, Diplopora, Daonella.
INTRODUCTION AND GEOLOGICAL SETTING New findings of Middle Triassic shallow and deep-water carbonate sediments from the Madonie Mountain confirm the presence of an originally pre-Carnian sedimentary substrate in the Panormide and Imerese paleogeographic units (DI STEFANO et alii, 2012, in press). The tectonostratigraphic setting and the preliminary sedimentological and stratigraphical data collected from these sediments are here summarized. The studied area is located in the southern zone of the Madonie Mountains near the village of Petralia Sottana along the eastern slope of Monte San Salvatore (Fig. 1). The structural setting of this area consists of a complexly deformed thrust pile which is the result of the Neogene compressional and transpressional stacking of a Mesozoic carbonate platformbasin system (known as the Panormide Platform and the Imerese Basin) and its Cenozoic, mostly terrigenous, covers (RENDA et al. 1999). Neo (or Alpine) Tethyan-derived allochtons known as Sicilidi units (OGNIBEN 1960) are also involved in the collisional complex. In the Monte San Salvatore area several thrust sheets that are considered to be derived from the slope between the Panormide Platform and the Imerese Basin outcrops (RENDA et al. 1999). The stratigraphy of these thrust-units consists of Carnian calcilutites and marls (Mufara Fm.) overlain by slope dolostones (known as the Quacella Formation, CERETTI & CIABATTI 1965). Numidian Flysch sediments follow on a deep _________________________
(*)Università di Palermo - Dipartimento di Scienze della Terra e del Mare – Via Archirafi, 20 – 90123 Palermo (Italy).
[email protected],
[email protected],
[email protected],
[email protected]. (**)State University of New York at Cortland, Geology Department, Cortland, New York, 13045 (U.S.A.).
[email protected] This research was supported through the MIUR-COFIN 2008 project on “Upper Triassic carbonate systems from Sicily: Stratigraphic architecture, depositional dynamics and paleogeographic setting” (grants to P. Di Stefano).
Fig. 1 – Structural sketch of the Central Mediterranean area showing the location of the Madonie Mountains.
erosional surface. The Numidian sediments contain thick intercalations of platform-derived carbonate megabreccias (Wildflysh di Monte San Salvatore, OGNIBEN 1960).
THE SANT’OTIERO SUCCESSION The Middle Triassic sediments occur at the base of a thrust sheet with a similar sedimentary succession in the Sant’Otiero locality near Petralia Sottana (Fig. 2). The studied section exposes from the base about 60 m of dark grey coarse calcareous breccias with centimeter to decimeter-sized angular pebbles surrounded by a calcilutite matrix. The breccia outcrops along the nearly vertical slope of the Sant’Otiero peak and is followed upward by about 50 m of thick parallel-bedded dark-grey calcilutites. Between the calcareous breccias and the calcilutites a détachement surface can be observed. The lowermost part of the calcilutitic zone, consists of wedge-shaped beds with pebbly mudstones. Upsection, beds of thin-shelled bivalve lumachella are irregularly intercalated to the calcilutites.
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Fig. 2 – Outcrop view of the calcare di Sant’Otiero. The section shows the brecciated zone (right) and the overlying well bedded calcilutites.
Upward the dark gray calcilutites are overlain by the typical Mufara sediments consisting of alternations of brown clays and platy calcilutites. They are in turn overlain by the Quacella dolomites and by the Numidian Flysch containing thick megabreccia intercalations. The microfacies analysis of samples collected along the section shows that the elements of the megabreccia consists of different microfacies types such as dasycladalean grainstone with Diplopora annulatissima Pia, peloidal grainstone with
Fig. 3 – Daonella tyrolensis Mojsisovics, 1874 from calcare di Sant’Otiero, Sant’Otiero section, Monte San Salvatore, Sicily.
Tubiphytes and benthic foraminifers, algal boundstone with the problematic Zornia obscura Senowbari-Daryan & Di Stefano. Additionally among the elements pelagic wackestones with calcispheres and filaments are found.
The upper part of the Sant’Otiero section shows muddominated microfacies types such as dark-gray mudstone or wackestone with thin-shelled bivalves and rare calcispheres. In places a shelter porosity can be observed that increases in the lumachella beds. Among the thin shelled bivalves Daonella tyrolensis Mojsisovics, 1874 has been recognized (Fig. 3).
DISCUSSION The carbonate megabreccias with Diplopora annulatissima, Zornia obscura, Tubiphytes and benthic foraminifers in the lower part of the calcare di Sant’Otiero, support a provenance from the dismantling of an Anisian? or early Ladinian carbonate shelf. The micritic matrix with thin-shelled bivalve fragments between the elements indicate a deep-water (slope or toe-of-slope) environment for the megabreccia accumulation. Moreover, the presence of lithoclastic grains with the same microfacies, suggests the presence in the source areas of already litified pelagites. The age of the overlying Daonella beds is well constrained by the presence of D. tyrolensis. This species is among the most widely distributed Ladinian Daonella in Alpine Europe and is a well-established biostratigraphic marker of the early late Ladinian Protrachyceras longobardicum ammonoid zone (BRACK & RIEBER 1993; SCHATZ 2004; MCROBERTS 2010). An early late Ladinian age for the Daonella beds requires that the megabreccia emplacement took place in the early Ladinian or to the earliest late Ladinian.
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CONCLUSIONS The finding in the Madonie Mountains from Sicily of a Ladinian lumachella with daonellids including Daonella tyrolensis, associated with a megabreccia formed by neritic elements with Diplopora annulatissma, provide new data permitting a more precise reconstruction of the pre-Carnian sedimentary basins of Sicily during the early-Alpine stage. The presence of pelagic limestones of Ladinian age and their tectonostratigraphic location, reinforce previous data on the existence of a Middle Triassic carbonate platform to basin system which more or less corresponds to the Panormide and Imerese paleogeographic zones. REFERENCES BRACK P. & RIEBER H. (1993) - Towards a better definition of the Anisian/Ladinian boundary: New biostratigraphic data and correlations of boundary sections from the southern Alps. Eclogae Geologicae Helvetiae, 86 (2), 415-572.
CERETTI E. & CIABATTI M. (1965) – rilevamento geologico delle Madonie nord-orientali (Sicilia). Giorn. Geol. Ser 2, 33, 51-57. DI STEFANO P., MCROBERTS C., RENDA P., TRIPODO A., TORRE A. & TORRE F. (2012) - Middle Triassic (Ladinian) deepwater sediments in Sicily. New findings from the Madonie Mountains. Riv. It. Paleont. Str., 118(2). MCROBERTS C.A. (2010) - Biochronology of Triassic bivalves. In: Lucas, S.G. (Ed) - The Triassic Time Scale. Geological Society of London Special Publication, 334, 201-219. OGNIBEN L. (1960) - Nota illustrativa dello schema geologico della Sicilia nord-orientale. Riv. Min. Sic., 64-65, 183-222. RENDA P., TAVARNELLI E. & TRAMUTOLI M. (1999) - La distensione tetidea e il suo controllo sulle strutture compressive del sistema appenninico-maghrebide: l’esempio dei Monti delle Madonie (Sicilia centrosettentrionale). Boll. Soc. Geol. It., 188,179-190. SCHATZ W. (2004) - Revision of the subgenus Daonella (Arzelella) (Halobiidae; Middle Triassic). Journal of Paleontology, 78 (2), 300-316.
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