Late Eocene to Early Miocene calcareous nannofossil biostratigraphy from the ANH-San Jacinto- 1 well: Stratigraphic implications for the Sinú-San Jacinto basin in the Caribbean region of Colombia

Calcareous nannofossils were analyzed in 73 samples collected from the ANH-San Jacinto-1 cored-stratigraphic section drilled in the Sinú-San Jacinto Belt (SSJB) along the tectonic boundary of the South American and Caribbean plates in Colombia. Our quantitative results show that calcareous nannofossils were commonly abundant and moderately preserved. A total of 75 morphotypes, representing 13 genera and 55 species, were quantified. Calcareous nannofossil assemblages were dominated by Reticulofenestra spp., Sphenolithus spp., Coccolithus spp. and Helicosphaera spp. We recognized the standard biostratigraphic events highest occurrence (HO) of Reticulofenestra reticulata, HO of Discoaster saipanensis, lowest common occurrence (LCO) of Clausicoccus subdistichus, HO of Coccolithus formosus, HO of Reticulofenestra umbilicus, lowest occurrence (LO) of Sphenolithus distentus, LO of Sphenolithus ciperoensis, and LO of Discoaster druggii. This indicates that the studied deposits cover a stratigraphic range from zones NP19-20 (CNE19) to NN2 (CNM1) and encompass the 35.2 Ma to 22.5 Ma, interval from late Eocene (Priabonian) to Early Miocene (Aquitanian). The distribution patterns and age model show that the Eocene–Oligocene transition can be traced in the core and overlapping of bioevents as well as reworking of taxa suggest deep-sea stratigraphic unconformities formed during the late Eocene, early Oligocene and the Oligocene/Miocene. According to the duration of the hiatuses, ∼0.8 Myr, ∼2.2 Myr and ∼4.4 Myr, respectively, and the sedimentary context of the studied deposits, we suggest that these stratigraphic gaps represent downslope mass erosional episodes triggered by tectonic events and/or mud diapirism.