Cretaceous terrestrial and shallow marine deposits in northern South Dobrogea (SE Rumania)

Abstract

Of the regions containing Cretaceous deposits in Rumania, South Dobrogea is notable for extensive terrestrial, transitional and near-shore facies. These deposits constitute seven formations, defined by different lithologies, fossil content and environmental depositional conditions: (1) the upper Tithonian?-Berriasian-Valanginian Cernavoda Formation, consisting of four interfingering members in the late Tithonian?-Valanginian interval (the Amara Member, late Tithonian?-Valanginian in age, consisting of clastic coastal marine deposits, in places with evaporitic and freshwater interbeds; the Berriasian Poarta Albā, Member, consisting of marine deposits, mainly of a dolomitic tidal flat type; the Medgidia Member, also Berriasian in age, consisting of marginal marine deposits of a calcareous-clayey, mostly subsaline tidal flat type; and the Alimanu Member, late Berriasian-Valanginian in age, composed of calcareous marine deposits, accumulated in restricted lagoonal conditions); (2) the upper Barremian-lower Aptian Ramadan Formation, displaying clastic-terrigenous coastal marine (sandy beach-type) deposits in its lower part, overlain by pachyodont-rich marine carbonate-detrital deposits in its upper part; (3) the middle-upper Aptian Gherghina Formation, made up mainly of fluviatile and lacustrine deposits, but in places with thin marine interbeds; (4) the uppermost Aptian?-Albian Cochirleni Formation, built up of detrital-terrigenous coastal sediments deposited in brackish swamp or normal marine marsh conditions; (5) the lower Cenomanian Peştera Formation, with nearshore detrital deposits, progressively replaced upwards by offshore (chalky) deposits; (6) the middle? Turonian Cuza Vodā Formation, a lower shoreface clastic unit of an unrestricted lagoonal type; (7) the Santonian-Campanian Murfatlar Formation, a mainly chalky formation, but with some clastic nearshore members in its lowermost part. The main lithostratigraphical units are delimited by depositional or erosional gaps, corresponding to the following time intervals: Hauterivian (locally Hauterivian-Barremian), Clansayesian ( pro parte), late Albian (in places late Vraconian, only), middledate Cenomanian, Coniacian-earliest Santonian, and late Campanian. A particular feature of the Gherghina Formation is that it is characterized by the predominance of kaolinite over other clay minerals. The earliest appearance of angiosperm pollen in Rumania has been recorded from lower Aptian beds within the Ramadan Formation.