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Upper Cretaceous volcanoclastic deposits from the Haţeg basin, south Carpathians (Romania): K-Ar ages and intrabasinal correlation

Bojar A.-V., Halas S., Bojar H.-P., Grigorescu D., Vasile S.

Geochronometria

2011

Vol. 38, no. 2

182-188

In order to constrain the age of the Upper Cretaceous continental Densuş-Ciula Formation from the Haţeg basin, South Carpathians, and correlate it with the other continental unit that occurs in the region, the Sânpetru Formation, we separated and dated by the K-Ar method biotites and amphi-boles from volcanoclastic deposits. The mineral phases analysed are from two tuff layers and volcanic bombs cropping out near Rachitova village. Two tuff layers from the Densuş-Ciula Formation give early Maastrichtian ages of 69.8š1.3 and 71.3š1.6 Ma, respectively. The ages determined for the tuff layers constrain the age of deposition for the Densuş-Ciula Formation and enable further correlations with the available palaeomagnetic data from the deposits occurring along the Sibişel Valley that be-long to the Sânpetru Formation. The volcanic bombs collected near to Răchitova village are andesites and dacites. The age determined by K-Ar method on hornblende separated from a volcanic bomb is 82.7š1.5 Ma, which is older than the underlying Campanian marine deposits in turbidite facies. This suggests that the volcanic bombs were re-deposited during the early Maastrichtian. Thus, the volcan-ics found at Răchitova have at least two origins: one type is related to an explosive synsedimentary volcanic activity, and the other type is represented by older andesitic/dacitic bombs, which most probably originate from a volcanic centre situated in the Haţeg region.