No abstract

The petroleum industry has always been pursuing highly exploitable gas fields, which are often hosted in carbonate rocks. However, carbonates are highly heterogeneous and show different fabrics and structures as the result of sedimentation in various environments, and subsequent diagenesis and deformation. In this study, a multi-scale and multidisciplinary approach has been performed on classical reservoir rocks from the subsurface of the Hyblean Plateau (Sicily, Italy). We aim at unravelling the important and debated role of tectonic and diagenetic structures (mainly fractures as well as stylolites) in enhancing or reducing the porosity. Black shales, limestones, and laminites of intertidal environment represent the main lithologies. Structure cross-cutting relationships record different stages of the basin geological history, which are related to the tectonic evolution of the area. Our results show that porosity is uncommonly lightly affected by fractures and faults, because of their mineralization, whereas stylolites, which are often considered as barriers to fluid flow, show a certain porosity. Therefore, we want to highlight the importance of a multi-scale and multidisciplinary approach in the analysis of heterogeneously porous, fractured- and stylolite-rich carbonate rocks, and our study aspires to boost other similar gas reservoir studies in energy transition times.

Tectonic, paleoenvironmental, and paleoclimatic unstable conditions preceding the onset of the Messinian Salinity Crisis (MSC) highly affected marine life. Changes in calcareous plankton association are overall registered in the Mediterranean. They consist of a general transition from abundant and well-diversified planktonic associations to strictly oligotypic assemblages that precede their total disappearance at the onset of evaporitic precipitation. In this work, an accurate quantitative analysis of calcareous plankton, both foraminifers and nannofossils, has been carried out in the Torrente Vaccarizzo Section of Sicily (southern Italy). The aim is to independently define a chronostratigraphic pattern of bioevents preceding the MSC in the absence of magnetostratigraphic or radiometric constraints. The fluctuating abundance of the genus Orbulina fits well with the 100 ky Eccentricity maxima, and it is successfully applied to build an astronomically calibrated age-model for the section. On this basis, all the biohorizons have been recalibrated and discussed with regard to the previous literature. Abundant influxes of selected species demonstrated to be of local significance since they are highly affected by paleoenvironmental and paleoclimatic conditions. A chronological sequence of foraminifers and nannofossils events marks the onset of the MSC with a derived age of 5.957 My, which agrees well with previous findings from other Mediterranean sections. This methodology and the new biostratigraphic events may be useful for future studies on pre-evaporitic successions of the Mediterranean.

<p>Ancient coastal carbonate depositional systems provide exceptional records of past changes in relative sea level– globally and locally (tectonics) – and of paleoenvironmental variations. Here we present new work on carbonate outcrops within the UNESCO Rocca di Cerere Geopark in central Sicily (Caltanissetta and Enna districts). They show superb sub-vertical cliffs made of Pleistocene packstones with clinoforms which provide a high-resolution record of relative sea-level changes that correlate with precession cycles. Regionally these successions deposited during Plio-Quaternary forced regression caused by late-orogenic uplift. However, their deposition within local thrust top basins was modulated by local uplift and tectonic tilting. Collectively these global, regional, and local processes are recorded by offlapping of successive depositional cycles. Moreover, the high-resolution photogrammetric surveys we developed, revealed that the underlying anticlines tilted the original beds of almost 20°. The packstones are derived from fauna: micro-habitat variations have been here traced by changes in sediment provenance, fossil assemblages, and preservation. The resultant stratal architectures reflect the interplay between the efficiency of this carbonate factory, the environmental conditions, the minute siliciclastic input, and the evolution of accommodation space. Bio- and magneto-stratigraphy were fundamental to date, the parasequences, while organic and inorganic chemistry, benthic foraminifera assemblages, as well as stable isotopes analyses (δ<sup>18</sup>O and δ<sup>13</sup>C) are used as environmental and climatic proxies (where possible) to reconstruct coastal dynamics (physical and biological), in relation to the tectonic history and sea-level change.<br />These outcrops provide analogues to interpret stratal patterns in subsurface examples where these types of strata form important aquifers – and shallow gas reservoirs.</p>