Paleoenvironmental reconstruction of late Cretaceous (Maastrichtian) dinosaur-bearing formations of Romania

Paleoenvironmental reconstruction of the contemporaneous Late Cretaceous (Maastrichtian) dinosaur-bearing Sanpetru and Densus-Ciula formations, Pui beds, and Red Continental Strata of Romania is accomplished through stratigraphic, sedimentological, and paleopedologic studies. The Sanpetru Formation consists of repetitive fining-upward cycles displaying sedimentary facies indicative of deposition by braided streams. The middle member of the Densus-Ciula Formation includes pedogenically-modified red mudstones interbedded with thick channel deposits displaying facies indicative of deposition by braided streams. The Red Continental Strata and Pui beds are dominated by red mudstone sequences and exhibit highly variable paleocurrent direction as well as inclined heterolithic strata suggesting deposition by meandering rivers.; Paleosols of the Red Continental Strata, Densus-Ciula Formation, and Pui beds are brown-to-red calcareous paleosols containing carbonate nodules intergrown with iron oxides, rhizocretions, slickensides, and geochemically well-differentiated horizons; indurated calcareous horizons are occasionally present in the Pui beds and Red Continental Strata. Pedogenic features and paleosol geochemistry indicate that the mature paleosols formed on moderately-to-well-drained floodplains in a subhumid climate characterized by alternating wet and dry periods.; Study of the Sanpetru overbank deposits reveals the presence of different habitats: ponds, wetlands, seasonal wetlands, and proximal and distal dry floodplains. Pedogenic features, such as carbonate nodules with intergrowth of iron oxides, slickensides, and deeply-penetrating roots, characterize the better drained environments, while hydromorphic and redoximorphic features characterize the poorly-drained habitats. The better drained paleosols are similar to those described in the other three formations, suggesting formation under similar paleoclimatic conditions.; The distribution of overbank deposits in the Sanpetru stratigraphic section reveals that an important paleoenvironmental change from a mosaic of wetlands and dry floodplains to exclusively wetlands occurs in the upper Sanpetru Formation. Such dramatic changes coincide with an increase in river competence and a change in paleocurrent directions, presumably induced by tectonism. Magnetic polarity stratigraphy of the Sanpetru Formation suggests that the deposits are probably early-to-middle Maastrichtian in age; therefore, the paleoenvironmental changes and coincident dinosaur "disappearance" did not occur at the K/T boundary. These results suggest that the apparent disappearance of dinosaurs in the Sanpetru Formation is not associated with the terminal Cretaceous extinction but rather reflects a preservational artifact.