Microfósiles neógenos de la Diatomita de Santiago, Baja California Sur, México

A biostratigraphic study of the Santiago Diatomite -the diatomaceous outcrops in southernmost Baja California- was carried out using benthic and planktonic foraminifera and calcareous nannoplankton. The Santiago Diatomite is considered to be latest Miocene to middle Pliocene in age and to be associated with nearby upper Pliocene beds. The sediment was deposited during a transgressive event which resulted from local tectonic spreading of the Gulf of California. A paleobasin with its major depocenter at the Santiago site was formed. Micropaleontological information suggests an upper bathyal paleodepth for the Santiago Diatomite, with an assemblage characteristic of transitional water masses -California current and the North Equatorial System- converging at this site. In general, normal marine conditions existed, with the exception of some levels of laminated sediments that suggest decreased oxygen content. Dissolution of calcareous microfossils could be indicative of deposition near the carbonate compensation depth, or local upwelling. Reconstruction of the evolution of the Santiago paleobasin suggests a probable association with a subaerial canyon that existed prior to this time, with later submersion and, finally, a regressive event during late Pliocene-Pleistocene time.