Original paper

Petrography and mineral chemistry of Bessarabian siliciclastic rocks in the Eastern Carpathians Foreland Basin (Romania and Republic of Moldova)

Dill, Harald G.; Iancu, Gabriel O.; Ionesi, Viorel; Sârbu, Smaranda; Balintoni, Ioan; Botz, Reiner

Abstract

Bessarabian sedimentary rocks contributed much to the filling of the arcuate foreland basin, extending in front of the Eastern Carpathians. In this foreland basin, during the Bessarabian, a nearshore marine depositional environment developed in what is called today the Romanian-Moldavian border region. The depositional environment deepened towards the east from brackish beach, through shoreface to upper shelf deposits. The continental impact on the depositional environment was almost negligible and is only detectable by isotope studies of the carbonate cement of the siliciclastic rocks. The redox conditions fluctuated around Eh = 0 depending upon the local environment. The diagenetic alteration was rather moderate, with temperatures of near-ambient conditions. The pore water solutions had a pH ≥ 7 (≈ 9). Most of the carbonate, including the minor amounts of aragonite, is of biogenic origin. The mineralogy of Bessarabian sediments indicates a great variety, of source rocks lithologies, comprising mainly high-grade metamorphic paragneisses, granitoids, ultramafic and mafic magmatic rocks, manganiferous metasomatites and meta(saprolites). Provoked by the late Neogene tectonic movements in the East Carpathians, five units, comprising three terranes, one nappe and one massif which are listed in order of decreasing intensity of erosion of the hinterland, contributed to the debris of the siliciclastic rocks during the Bessarabian: Tulgheş Terrane, Bretila Terrane, Wildflysch Nappe, Rebra Terrane, and Ditrău Alkaline Massif.

Keywords

foreland basinbessarabianmiocenesiliciclastic sedimentsheavy mineralsprovenancedepositional environmenteastern carpathiansromaniarepublic of moldova