Calcareous microfossil biostratigraphy of Upper Miocene to Pliocene deposits of the Sinú-San Jacinto Belt, Caribbean region of Colombia

A compilation of previous biostratigraphic studies conducted in Upper Miocene to Pliocene deposits from the Caribbean region of Colombia reveals a predominant reliance on mollusks and benthic foraminifera for age determinations, with planktonic microfossils being less explored. To contribute to this biostratigraphic background, we have performed biostratigraphic analyses of calcareous nannoplankton, an oceanic planktonic micropaleontological group, on 71 mudrock samples from two stratigraphic sections located in the Sinú-San Jacinto Belt (SSJB). The Canalete stratigraphic section, outcropping in the southwestern portion of the belt, yielded the biostratigraphic markers Discoaster bergenii, Discoaster berggrenii, Discoaster surculus, and Reticulofenestra pseudoumbilicus. This assemblage, typical of the Zone NN11, indicates that the 50-m-thick section was accumulated during the Late Miocene, sometime between the late Tortonian and late Messinian. The ANH-Conuco-1 well, a cored stratigraphic section drilled in the northeastern area of the belt, also contained the above-mentioned biostratigraphic markers as well as Amaurolithus primus-delicatus, Ceratolithus acutus, Discoaster quinqueramus, Helicosphaera sellii, and Reticulofenestra rotaria. These taxa suggest that the stratigraphic interval between 754.1 m and 58.4 m in this cored section is enclosed within the zones NN11 and NN12, ranging in age from Late Miocene to Early Pliocene (late Tortonian to earliest Zanclean). Reworked nannofossils Cyclicargolithus floridanus, Discoaster deflandrei, Sphenolithus disbelemnos, and Sphenolithus heteromorphus were observed in both localities, implying the redeposition of Lower to Middle Miocene and, possibly, Paleogene marine sediments. This is supported by previous documentation of reworked planktonic foraminifera in Upper Miocene to Pliocene deposits from the Caribbean region of Colombia. The identified calcareous nannoplankton assemblages not only provide additional constraints on the existing biostratigraphic data of planktonic foraminifera in this region, but also aid in the correlation of both analyzed stratigraphic sections with other Upper Miocene deposits in northwestern South America.