The Bucegi Conglomerate: a Romanian Carpathian submarine slope deposit

Abstract

THE Bucegi Conglomerate, a thick conglomerate-sandstone unit of Albian age (Cretaceous), is well exposed in the Eastern Carpathian Chain near Sinaia, Romania. This unit occupies more than 5,000 km² in the vicinity of the change in structural–stratigraphic trend of the mobile belt from E–W to N–S (Fig. 1a). The thickness of this remarkably coarse series is regionally variable and locally exceeds 2,000 m. To the west the conglomerate overlies, with angular unconformity, Middle and Upper Jurassic platform carbonate rocks which in turn unconformably overlie crystalline basement. To the east, over a distance of approximately 10 km, the Bucegi rests with local unconformity on Neocomian and Barremian–Aptian flysch several kilometres thick (Fig. 1b and c). This unconformity post-dates pre-upper Aptian to post-lower Aptian folding ^1,2. Previous work has alluded to the shallow marine and nearshore origin³ of this formation, and it has been frequently referred to as a molasse, or para-molasse⁴, mainly due to its coarse nature, its pebble shape^3,5, its stratigraphic position above sandstone-shale turbidite-rich formations, and presumably also to its ‘post-tectonic’ position within the mobile belt. Here we consider an alternative, that is that the Bucegi Conglomerate accumulated in an infra-neritic to deep marine environment and that it records progradation of coarse material directly onto the slope and base of slope of a turbidite basin. The field observations we made in conjunction with Romanian colleagues in selected sections of the Sinaia region (Jepi Valley, Chindichiu road cuts) and an evaluation of previous reports provide a plausible basis to reconsider the depositional origin of the Bucegi.