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AUTHORS: Riva A., Nereo P., Marian M.

YEAR: 2014

AAPG 2014, Naples

Title: An outcrop analogue for the subsurface margin of the Adriatic Carbonate Platform (Cansiglio/Cavallo area, NE Italy)
Session: Regional facies distribution in the Meso- Cenozoic carbonate platforms of the Neo-Tethys Ocean
Alberto Riva, G.E.Plan Consulting, via Ariosto 59, 44121 Ferrara, Italy, email alberto.riva@geplan.it
Nereo Preto, Department of Geosciences, University of Padova
Mara Marian, , G.E.Plan Consulting

The Adriatic Carbonate Platform outcrops from Montenegro to Northeastern Italy, crossing Bosnia, Croatia and Slovenia. It is a well know carbonate platform, now subject to hydrocarbon exploration especially focusing on the margin and on structural traps in the thrust belt.
The platform margin is present in the subsurface of the Adriatic sea, it crops out in very few places and is often heavily deformed. One of the most important hydrocarbon discoveries of the eastern Adriatic was the JJ-3 well, located in Montenegrine waters, and drilled within the platform margin.
Only in the Cansiglio/Cavallo Area of Northeastern Italy, the margin is well preserved, with preserved depositional geometries. This area is historically well-known, but geological studies applying modern methods of sedimentology and stratigraphy are missing. A detailed geological mapping, coupled with a sedimentological characterization, was performed across an area of more than 200 km2.
This platform was characterized by a gravitational slope with the angle decreasing trough time, with megabreccias and turbidites directly onlapping an erosional surface on the muddy facies of the platform interior. Locally oolitic shoals and metazoan reefs of the margin and upper foreslope are preserved. Since the Cenomanian, the platform interior switched from mud dominated to grain dominated, boasting strong slope progradation and a a decrease in slope dip. The margin is often karstified, with high-frequency cyclic exposure events. Small fault-bounded anoxic intraplatform basins with fossil fishes and plants document synsedimentary tectonics within the platform interior.
The facies distribution identifies the marginal and the foreslope areas, characterized by grainstone shoals and low-angle clinoforms, as the best potential reservoirs in the system. These facies belts are normally unaffected by meteoric diagenesis.
Outcrop analogue studies at Cansiglio contribute to the interpretation of seismic lines in the Adriatic subsurface and may help to disentangle current uncertainties in the seismic facies interpretation to better focus on the possible traps.