Palynology and sequence stratigraphy of the Cretaceous of eastern Venezuela

Abstract

From Jurassic to Tertiary times, northeastern Venezuela represented the continental shelf of a tectonically passive margin. A dominantly marine Cretaceous sedimentary section, within an overthrusted allochthonous block and with a maximum thickness of 3658 m, is found in the subsurface in this area. Palynomorph recovery from these strata, together with planktonic foraminifera and calcareous nannofossils, indicate an age-range from at least Aptian to Maastrichtian. The palynological assemblages observed exhibit changes with time and environments, which are here related to the sedimentary evolution. Integrated analyses of palynology, lithology, and well logs are the basis for the reconstruction of the sedimentary evolution in the area. The oldest marine sediments in this section correspond to the uppermost part of the Lower Zuni Megacycle and contain a maximum flooding surface correlative with that dated at 111Ma. The rest of the sequence represents a major transgressive-regressive cycle (Upper Zuni) and contains seven sequences correlative with global eustatic cycles. The Turonian transgression dated at 91.5Ma is the most important marine transgression in the entire section and is recognizable in all sections studied, while the Maastrichtian-Paleocene boundary dated at 68Ma is not always clearly recognizable.