Late Miocene to Early Pliocene chronostratigraphic framework for the Dacic Basin, Romania

Abstract

New magnetostratigraphic results and calcareous nannofossil data of seven sections in the Dacic Basin of southern Romania, covering the Latest Maeotian to Early Romanian time span (6.4–4.0 Ma), allow a correlation with the current Astronomical Polarity Time Scale. This establishes a chronological framework for the Pontian and Dacian stages of the Paratethys and facilitates to correlate the Paratethys stages with those of the Mediterranean. The Maeotian–Pontian boundary is estimated at 6.15 ± 0.11 Ma, within subchron C3An.1n, while the age of the Pontian–Dacian boundary is 5.30 ± 0.1 Ma, within subchron C3r. The Odessian–Portaferrian and Portaferrian–Bosphorian substage boundaries can be placed at about 6.0 and 5.6 Ma, at the base and near the end of chron C3r, respectively. Consequently, the Pontian stage has a duration of approximately 0.85 Myr and is coeval with the upper half of the Messinian stage. The base of the Dacian stage corresponds to the onset of the Pliocene and is coeval with the Pontian–Kimmerian boundary of the Euxinic (Black Sea) Basin. The Dacian–Romanian boundary is recorded either at 4.58 ± 0.05 Ma, in subchron C3n.2n (Nunivak), or at 4.25 ± 0.05 Ma in subchron C3n.1n (Cochiti). The length of the Dacian stage is therefore about 0.7 Myr or approximately 1 Ma. The transition of the Getian into the Parscovian substage can be dated at ∼ 4.83 Ma within subchron C3n.3n (Sidufjall), or at ∼ 4.55 Ma within subchron C3n.2n (Nunivak). The occurrence of calcareous nannofossil assemblages in the lower Portaferrian and near the Portaferrian–Bosphorian transition, belonging to the upper part of the Discoaster quinqueramus–NN11 Zone, and in the middle Bosphorian, belonging to the Amaurolithus tricorniculatus–NN12 Zone, indicates the presence of ephemeral marine connections between the Paratethys Basin and the Mediterranean during the Late Messinian. Another marine influx, inferred from nannofossil species characteristic of the NN12 Zone and found in lower Dacian sediments near the top of subchron C3n.4n (Thvera), post-dates the basal-Pliocene transgression of the Mediterranean Basin.