A Geochemical Review of Carbonate Source Rocks in Italy

Abstract

Field sampling of potential source rock units in Italy, and detailed geochemical characterization of Italian petroleum (surface seeps and reservoired oils), have provided insights into the origins of the resource base. Organic‐rich, oil‐prone intervals have been identified in Middle to Upper Triassic, lower Toarcian, Lower Cretaceous, Upper Cretaceous and Oligo‐Miocene strata. The hydrocarbon generation potential of these intervals can be signipcant. For example, the weighted mean generation potential of the Upper Triassic in southern Italy is ˜47 mg HC/g rock, with the net source rock representing about 20% of the exposed stratigraphic sequence. Comparable richnesses exist in the other intervals noted above, although the Toarcian and Late Cretaceous intervals, including those associated with the “Bonarelli Event” (a brief period straddling the Cenomanian‐Turonian which is thought to represent an oceanic anoxic event) appear to be much more volumetrically restricted. There is sedimentological evidence that these organic‐rich intervals were deposited in both shallow‐water intraplatformal settings, and in deep‐water interplatformal basinal settings. The stacking of sequences as a result of evolving platform bathymetly and changes in sea level enhanced the volumetric importance of intraplatformal source rocks, and may explain some of the minor geochemical differences observed among the region s oils. There is a sharp contrast in the stable isotope composition of the organic matter contained in the different source intervals. The Triassic and Toarcian organic matter is isotopically light (δ13Cbitumen lighter than ‐26%o), while Cretaceous and Oligo‐Miocene OM is isotopically heavy (δ13Cbitumen heavier than ‐26%o). Although the oils share characteristics associated with carbonate source rock systems, two distinct populations exist. These are an isotopically light population (δ13 Coil, lighter than ‐26%o, typically lighter than ‐27. 5%o), which includes the oils at Rospo Mare, Malossa and the degraded oil at Maiella; and an isotopically heavier (δ13 Coil heavier than ‐26%o) population, including the oils at Monte Alpi, Bagnolo and at the Tramutola seep. The stable carbon isotopic compositions provide the strongest evidence for stratigraphic affinity. Biomarker data permits further refinement of these two “mega‐families”.

The Role of Pleistocene Strike‐slip Tectonics in the Neogene‐quaternary Evolution of the Southern Apennine Orogenic Belt: Implications for Oil Trap Development

“…Apulian carbonates include both source and reservoir rock intervals. Two principal source rocks have been identified (Katz et al, 2000). Most of the hydrocarbons in the Agri Valley and Tempa Rossa fields ( Fig.…”

First evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event) from the Ionian Zone, western continental Greece

“…In a local geographical context, the upper Cenomanian black shale of the Ionian Zone is a stratigraphically discrete lithologic unit which, like the lower Albian black shale representing the 'Paquier' event, appears to be unrelated to the Vigla shale member spanning the Aptian-lower Albian (Tsikos et al 2004b). The Vigla shale member is known to contain a series of at least 20, decimetre-thick organicrich marly units, which despite having relatively low TOC contents (1-6 wt%) are volumetrically clearly more significant than the two black shales representing OAEs (see also Katz et al 2000 shales in the Ionian strata and, by extension, their source-rock potential for substantial petroleum generation in the wider area (Rigakis and Karakitsios 1998).…”

Petroleum Geology and Hydrocarbon Potential of the Adriatic Basin, Offshore Croatia

“…(Jenkyns, 1988;Mattavelli and Novelli, 1990;Zappaterra, 1994;Cota and Baric, 1998;Grandić et al, 2001;Katz et al, 2000;Casero and Bigi, 2013). Analogous Triassic source rocks are also identified in the Central Adriatic offshore and the Sicilian Channel (Anelli et al, 1996) (Fig.…”