Palynological indicators of palaeoenvironmental perturbations in the Basque-Cantabrian Basin during the latest Cretaceous (Zumaia, northern Spain)

The latest Cretaceous palynological assemblages from the southern margin of the Basque-Cantabrian Basin (northern Spain, Zumaia) are dominated by black opaque equidimensional phytoclasts, black opaque blade shaped phytoclasts and translucent gold-orange to brown phytoclasts. Deep water dinoflagellate cysts Cannosphaeridium Utinensis and Pterodinium spp. constitutes a part of the assemblages throughout the whole succession. This record and previous study suggest deposition of the Zumaia section in the marine bathyal conditions, in relative close proximity to the land. Palynofacies analyses yields increased abundance of Leiosphaeridia spp. and some changes in the palynomorph proportions just before the significant lithological change near the lower/upper Maastrichtian. This signal may either be primary and record an environmental change, or taphonomic. Nevertheless, environmental interpretation of the upper Maastrichtian palynological assemblage seems to be more consistent with the late Maastrichtian marine regression, and in consequence, a reduction of the distance from the nearby land. Such conditions may have caused transport of leiosphaerids from shallower water sites.