Gabriele Lena

The barren Messinian Tripoli in Sicily and its palaeoenvironmental evolution: suggestions on the exploration potential

New observations on the Sicily Messinian Tripoli have yielded a variably thick diatomitic, calcareous and shaly rock interval marked by an upwards disappearance of calcareous and siliceous plankton (barren lithosome), coexisting with a variability in vegetal remains and significant amounts of amorphous organic matter (AOM). Facies analysis associated with biostratigraphy and palaeoecology of the several field and borehole sections has been framed in a well-accepted chronological scheme that points to this barren interval coinciding with the stratigraphic upper and younger part of some Tripoli sections (bituminous Tripoli) located in the northern part of the study area. Biostratigraphically, the barren lithosome falls within the Non-Distinctive Zone (NDZ) and is generally younger than the First Common Occurrence (FCO) of T. multiloba. The age of its diachronous base appears older than the Messinian salinity crisis (MSC) deposits, because is well constrained by the calcareous plankton biostratigraphic markers along the underlying portions of the Tripoli. The top boundary of the barren rock interval, that is not always identifiable, could be age dated, following the proposed stratigraphic criteria. We infer that the Tripoli initial open-marine environment became, in more inner areas, progressively confined, with freshwater floodings alternating with short marine-water incursions in a shallow-water to continental domain. The collected information appears useful in addressing further exploration.

Palaeoenvironmental Evolution and Exploration Hydrocarbon Potential of the Messinian Tripoli in Sicily

With the aim to evaluate the hydrocarbon potential of the Messinian Tripoli Formation widely outcropping in the Sicily structural evaporitic basins, nineteen field sections sited mostly in Central Southern Sicily have been investigated in a cooperation program with ENI. Many of these basins are part of the Gela accretionary wedge, the highest and more recent tectonic element of the Sicily Fold and Thrust Belt. The study evidentiates the tectonic involvement of the several Tripoli-Evaporites sections, originally deposited in an area now occupied by the Tyrrhenian Sea. A restoration of the surface and subsurface setting images the Tripoli as deformed in large, buried asymmetrical synclines and surface tight anticlines with limbs eroded in outcrop. With reference to the well-known Tripoli chronology (nine bioevents constrained by cyclostratigraphy), each section has been assigned (referred) to a well defined biostratigraphic and chronologic interval. On the ground of the micropaleontological associations the palaeoenvironmental evolution has been restored in order to recognize the occurrence of openly marine to restricted domains. Finally geochemical analyses helped to recognize and evaluate an unexpected hydrocarbon potential for the exploration of the Tripoli Formation in Sicily.