Observations on the Neogene of Northwestern Ecuador

Resumen

A micropaleontological study of Neogene samples from the region of Esmeraldas defines ages and sheds light on depositional settings and regional history. The late Middle to early Late Miocene Borbon Formation consists mostly of tuffaceous diatomites and mudstones, best dated by their radiolarian component. The overlying Esmeraldas (Punta Gorda) tuffaceous mudstones yield a rich foraminiferal fauna of Pliocene (Zanclean) age, but few siliceous remains. The benthonic foraminifera of the Miocene are typical of a Caribbean/East Pacific tropical province. The Pliocene foraminiferal fauna is distinct, allied to that of California. Miocene sediments were deposited in mid-bathyal depths. The Pliocene foraminiferal fauna suggests deposition in the upper bathyal zone. A wide bathymetric range of molluscan species is attributed to taphonomic dispersal of molluscan shells by large predators. Presumably these sediments were emplaced on top of a progressively shoaling accretionary wedge, which underwent faulting as sediments accumulated and which emerged in the latest Pliocene or in Pleistocene time.