The Neogene sedimentary basins of the Colombian Pacific coast were formed in forearc basins associated with the uplift of the Andes. In this area, some marine sequences remain unexplored and are marked by a lack of biostratigraphic information. Additionally, available high-resolution biostratigraphic and biochronologic data from this region are limited almost exclusively to open sea research conducted by the Integrated Ocean Drilling Programs (IODP). The Ladrilleros-Juanchaco section is a continuous and well-exposed marine terrigenous sedimentary sequence with abundant Miocene microfossils. Biostratigraphic and biochronologic studies with calcareous nannofossils, planktonic foraminifera and diatoms carried out there revealed the presence of seventeen astronomically calibrated and standard calcareous microfossil biohorizons as well as two tropical diatom biozones. Such information enabled the establishment of a chronologic framework between the Base of Praeorbulina glomerosa and Catinaster coalitus Base, corresponding to 16.27 and 10.79 Ma, respectively (Burdigalian-Tortonian). The proposed biozonation favoured the observation of a high correlation between low-latitude planktonic foraminifera and calcareous nannofossil bioevents whereas diatom biozones and calcareous nannofossil biohorizons are marked by variations since the lowest occurrence of diatoms around 12.2 Ma. Furthermore, by means of interpolating age between the Sphenolithus heteromorphus Top and Fohsella praefohsi Base bioevents, the fact that the Reticulofenestra pseudoumbilicus (>7 µm) Base common took place around 13.6 Ma is interpreted and correlated with other sites, therefore revealing that it can be considered a good bioevent for the base of the Serravallian in these tropical areas.
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Vol. 53 • No. 6