New evidence of the outer Dinaric deformation front in the Grado area (NE-Italy)

Abstract

A well Grado-1 was drilled down to 1108 m reaching mesozoic shelf carbonates which occur in the structural highs in the Lignano – Grado area. The well was completed with geophysical logs in the open hole interval from -700 to -1108 m. The drilling bit met the nummulitic shelf paleogenic limestones at -616,5 m and Mesozoic (Upper Cretaceous) platform around -1007 m. About 400 m thick Palaeogene interval appears affected by open fractures which we consider linked up to a reverse fault and a tectonic duplex of the Palaeogene limestone interval is hypothesized. The feature corresponds to the outer deformation front of the Dinaric thrusts system and looks still active. Palaeogene limestone sequence is analogous to the outcrops in the northern Istria and in the stratigraphy in the oil wells offshore northern Dalmatia. The drilling target was the characterization of the nature of the geothermal resources in the Friuli lower plain and lagoons region, following the long-term investigations of the Department of Civil and Environmental Engineering of the Trieste University.\ud The geothermal resource was found in correspondence of the above mentioned open fracture zone and below it, with salty hot waters at a temperature of 42°C, increasing with depth, and a flow of 25 l/s arriving to the surface with 2,8 pressure bars

Thickness of marine Holocene sediment in the Gulf of Trieste (northern Adriatic Sea)

“…1b and consists of Quaternary alluvial sediment (grey) of the Friuli plain in the north, Cretaceous-Paleogene carbonates (green) of the Classical Karst in the northeast and Paleogene marls and sandstones of the flysch (orange) of the Istria peninsula and Trieste coastline in the southern and eastern parts of the gulf. A similar geological sequence can be observed in geophysical data offshore from the gulf area where the carbonate platform is followed by a flysch succession which is overlain by a few hundred metres of Quaternary sediment deposited during the transgressive-regressive cycles (Busetti et al, 2010a, b;Cimolino et al, 2010;Vrabec et al, 2014). The youngest sedimentary sequence in the Gulf of Trieste is represented by Holocene marine sediment which has been depositing for the last 10 000 years since the onset of the Holocene transgression following the Younger Dryas (Ogorelec et al, 1981(Ogorelec et al, , 1997Lambeck et al, 2004;Covelli et al, 2006;Trincardi et al, 2011b;Zecchin et al, 2015).…”

“…While the exact cause of the basin formation exceeds the scope of this paper, we suspect it represents an interplay between different tectonic, sedimentologic, climatic and oceanographic factors that need to be further examined in order to better understand the distribution of Holocene marine sediment in the Gulf of Trieste. Additionally, thicker Holocene marine sequences can be observed above paleochannels, in the Trezza Grande area and in the internal parts of bays and in close proximity to the shoreline, where the thickness is probably governed by increased amounts of available sediment transported by rivers and surface run-off from rocky coasts of the southeastern part and due to increased amounts of fluvially transported sediment from the alluvial plains of the northern and northwestern coasts of the gulf (Covelli et al, 2004;Mandac Soczka and Faganeli, 2015). In the central part of the gulf the Holocene marine sequences are very thin or even absent (unresolvable on geophysical profiles).…”

Wave equation datuming applied to marine OBS data and to land high resolution seismic profiling

“…The reflector at about 650 m (Fig. 10a) can be associated to the top of the Paleogene platform carbonates (horizon "c") thickening at roughly 380 m. These data were calibrated by the well Grado 1 (Cimolino et al, 2010), which was drilled to 1108 m, reaching the Mesozoic limestones close to 1000 m depth. The well confirmed that the carbonates are folded and disrupted by thrust faults, which are propagated in the Miocene terrigenous molasse (interval "m") until the near surface deposits.…”

“…The study was commissioned by Regione Friuli Venezia GiuliaGeological Service for the inventory of the local geothermal resources. The primary objective was to identify aquifers of geothermal interest, through the characterization of the geological and hydro-geological structures of the subsoil, constituted by an alternation of aquifers and aquitardes, typical of the lower Friuli Plain, and the identification of the top of the Paleogene-Mesozoic carbonates basement (Cimolino et al, 2010).…”

Broadband Q-Factor Imaging for Geofluid Detection in the Gulf of Trieste (Northern Adriatic Sea)

“…In the Adriatic Sea, the occurrence of fluids within the sediment and fluid seeps at the sea floor are well known. Source of these fluids have been identified in the buried several kilometer thick Meso-Cenozoic carbonate reservoir, with salty water occurrence (Cimolino et al, 2010), and within the overlying Late Cenozoic terrigenous sedimentary units bearing biogenic gas (e.g., Casero, 2004). Fluids upward migration from several km deep rocks and feeding local seeps have been documented in the central and northern Adriatic (Geletti et al, 2008;Busetti et al, 2013;Donda et al, 2019).…”