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U.S. DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY


Petroleum Systems of the Po Basin Province of Northern Italy and the Northern Adriatic Sea: Porto Garibaldi (Biogenic), Meride/Riva di Solto (Thermal), and Marnoso Arenacea (Thermal) 

by 
Sandra J. Lindquist 
ABSTRACT
The Porto Garibaldi total petroleum system dominates the Po Basin Province of onshore northern Italy and offshore Italy and Croatia in the northern Adriatic Sea. Porto Garibaldi contains Pliocene (primarily) and Pleistocene (secondarily) biogenic gas – approximately 16 TCF (2.66 BBOE) ultimately recoverable – accumulated in co-eval siliciclastic reservoirs. This area was the northwestern edge of the Gondwanan (African) continental plate in pre-Hercynian time until the assembly of Pangea, a dominantly carbonate passive continental margin during the Mesozoic breakup of Pangea, and a Cenozoic collision zone with siliciclastic foredeep and foreland regions surrounded by thrust belts. At least two other petroleum systems, with Triassic (Meride / Riva di Solto) and Miocene (Marnoso Arenacea) source rocks, contribute oil and thermal gas reserves (nearly 1 BBOE) to the province. The major time of hydrocarbon expulsion of the thermal systems was Late Neogene during the Alpine and Apennine orogenies. Local Mesozoic oil expulsion from Triassic rocks also occurred, but those oils either were not trapped or were leaked from faulty traps through time.

INTRODUCTION
The majority of hydrocarbons in the Po Basin Province (Figure 1) are Pliocene and Pleistocene (with minor Miocene sourced and reservoired) biogenic/diagenetic gas. Additional hydrocarbon contributions are from thermogenic, Mesozoic- and Miocene-sourced and reservoired gas and oil. Two of the three total petroleum systems are assigned numbers in order of volumetric importance (406001=biogenic Plio/Pleistocene (Porto Garibaldi) and 406002=thermal Triassic (Meride / Riva di Solto)). The third small total petroleum system (thermal Tertiary (Marnoso Arenacea) is combined with 406001 for the purposes of quantitative resource assessment. That composite total petroleum system retains the number 406001 and the name Porto Garibaldi in the U.S. Geological Survey data base.

Within the body of this report, discussions of geology or petroleum system components occasionally occur in an order reflecting geologic age instead of volumetric significance. References listed in this report include a limited selection of those most recent and most pertinent to this document. Not all are specifically cited in the text. The stratigraphic equivalents chart (Figure 2) is composited from many references to approximately equate the range of stratigraphic nomenclature in use. It is not intended to be precise with respect to absolute geologic age. All stated reserves are derived from Petroconsultants (1996), unless referenced otherwise, and are "ultimate recoverable" volumes rather than "in place" numbers.

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U. S. Geological Survey Open-File Report 99-50M