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OLIGOCENE- LOWER MIOCENE GEOLOGICAL EVENTS IN THE EASTERN CARPATHIANS AND THE IMPACT ON HYDROCARBON ACCUMULATION

Mihaela Melinte‐Dobrinescu

Abstract

The first isolation of the Paratethys from the Tethys Ocean (that included the Mediterranean region), at the beginning of the Oligocene Epoch, at around 33 My (million years) led to significant palaeobiogeographical changes in Europe. The present day Romanian territory belongs, since the Oligocene and up to the Middle Miocene, to the Central Paratethyan domain and afterwards was included in the Eastern Paratethys. The palaeogeographical isolation, produced in the Eastern Carpathians at the Eocene-Oligocene boundary, implied the instauration of a dysoxic to anoxic setting in the whole Carpathian bend. These conditions lasted during the whole Oligocene, including the Rupelian and Chattian stages and also in the Early Miocene, overlapping the Aquitanian and Burdigalian stages. Lithologically, the anoxic palaeoenvironment is expressed by the deposition of bituminous rocks, including bituminous marls, silicolites and clays. These are the main source rocks for hydrocarbons in Romania, being located not only in the Eastern Carpathians, but also in the Foredeep of the Southern Carpathians (i.e. the Getic Depression), in the Transylvanian basin and in the Black Sea structures, where the bituminous Oligocene-Lower Miocene deposits were described as the Maikopian Facies. During the Oligocene-Lower Miocene interval, the depositional regime of the Eastern Carpathians was not entirely anoxic. Hence, not only anoxic and dysoxic hemipelagites accumulated, but also turbiditic sediments. The Oligocene-Lower Miocene turbidites, including rhythmically alternating thick sandstones and clays, along with massive sandstones, represent the main reservoir rocks of the Eastern Carpathian bend.

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DOI resolver: doi.org/10.5593/sgem2018/1.1/s01.046

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