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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 78 (1994)

Issue: 3. (March)

First Page: 333

Last Page: 354

Title: Source-Rock Distribution Model of the Periadriatic Region

Author(s): Enzo Zappaterra (2)

Abstract:

The Periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic-sedimentary cycles. Tectonic evolution progressed from a Triassic-Early Jurassic (Liassic) continental rifting stage on the northern edge of the African craton, through an Early Jurassic (Middle Liassic)-Late Cretaceous/Eocene oceanic rifting stage and passive margin formation, to a final continental collision and active margin deformation stage in the Late Cretaceous/Eocene to Holocene. This evolution occurred in a transtensional and transpressional framework resulting from the oblique separation and convergence of the African and European plates.

Extensive shallow-water carbonate platform deposits covered large parts of the Periadriatic region in the Late Triassic. Platform breakup and development of a platform-to-basin carbonate shelf morphology began in the Late Triassic and extended through the Cretaceous. On the basis of this paleogeographic evolution, the regional geology of the Periadriatic region can be expressed in terms of three main Upper Triassic-Paleogene sedimentary sequences: the platform sequence (sequence "A"), the platform to basin sequence (sequence "B"), and the basin sequence (sequence "C"). These sequences developed during the initial rifting and subsequent passive-margin formation tectonic stages.

Three distinct episodes of source-bed deposition can be identified. Middle-Upper Triassic to Lower Jurassic (Liassic) organic-rich, oil-prone and mature source beds generally are structurally controlled, and are closely associated with transtensional intraplatform basins formed in the early continental rifting stage. The principal Triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the Periadriatic region are associated with sequence "B" areas.

The second episode of organic-rich rocks deposition includes both shallow and deeper water facies of Jurassic-Cretaceous age. Thin, immature, deep-water epioceanic organic-rich marls and shales are generally bathymetrically controlled. These units are related to basin-wide anoxic events in the Tethys ocean and its submerged continental margin, and are associated with sequence "B" areas. Middle-Upper Cretaceous shallow-water, oil-prone facies occur in isolated anoxic basins within carbonate platforms; these source sequences are generally thicker and are associated with sequence "A" areas. No major hydrocarbon accumulation can be directly attributed to the Jurassic-Cretaceous epioceanic and intraplatform source rock sequences.

The third episode of source bed deposition characterizes the final active margin deformation stage, and is represented by Upper Tertiary organic-rich terrigenous units, mostly gas prone. These are essentially associated with turbiditic and flysch sequences of foredeep basins, and have generated the greater part of the commercial biogenic gases of the Periadriatic region.

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