Palynological and organic geochemical analyses of the Upper Cretaceous Bozeș Formation at Petrești (southwestern Transylvanian Basin) – biostratigraphic and palaeoenvironmental implications

Abstract

A palynological and organic geochemical study of the Upper Cretaceous deposits cropping out in the southwestern part of the Transylvanian Basin (Petreşti section) has been carried out. The samples were collected from the marine Bozeş as well as from the overlying continental Sebeş formations, with main focus on the Bozeș Formation. The recovered palynomorph assemblages are represented mainly by early angiosperm pollen and by fern spores. Phytoplankton taxa are either absent or were recorded only as rare occurrences in the upper part of the Bozeş Formation.The identified terrestrial palynomorph assemblages document the co-occurrence of taxa from plant communities typical for fluvial to coastal habitats with other palynofloral elements derived from areas of higher altitude and/or cooler–wetter conditions. The occurrence of a diversified Normapolles assemblage including Trudopollis cuneolis, Oculopollis principalis and O. praedicatus, in association with fern spores such as Klukisporites pseudoreticulatus and Vadaszisporites sacali, supports a mid-late Campanian age for the analyzed section of the marine Bozeş Formation. Palynofacies constituents, combined with organic geochemical data, were used to reconstruct the depositional environments represented in the studied deposits. According to these data, the lower and middle sections of the Bozeş Formation sampled in the Petrești succession were deposited in a distal, outer neritic area of the Late Cretaceous basin. This outer neritic succession is followed by a nearshore/inner neritic sequence corresponding to the topmost part of the Bozeş Formation, as indicated by the presence of a palynofacies containing lath-shaped opaque phytoclasts mixed with large translucent biostructured phytoclasts.