Lower to Middle Miocene multiproxy biostratigraphy of the P-18 core-stratigraphic well in Sinú-San Jacinto Basin, Caribbean region of Colombia

Abstract

A Lower-to-Middle Miocene core-stratigraphic section, P-18 well, was drilled in the Sinú-San Jacinto Basin (SSJB) in the Caribbean region of Colombia, showing exceptionally well-preserved planktonic foraminifera, calcareous nannofossils, and palynomorphs. We use these micropaleontological groups to perform integrated biostratigraphic analyzes and estimate the stratigraphic record's continuity and sedimentation rates for the early Neogene of the region. Two lithological intervals were defined, the first between 423.9 m and 345.8 m and the second between 345.8 m to the top of the core. Only palynomorphs were identified for the first interval of this section, assigned to the Ciénaga de Oro Formation. We proposed an age no older than 19.49 Ma (Early Miocene, Burdigalian) based on the occurrence of Rugutricolpites intensus at 381.5 m. Although for the second interval, correlated with the Porquera Formation, we found three well-calibrated bioevents of calcareous microfossils, top of Sphenolithus belemnos at 213.2 m, base of Sphenolithus heteromorphus at 187.9 m, and top of Catapsydrax dissimilis at 141.9 m. In addition, we identified the top of uncalibrated planktonic foraminifera Trilobatus primordius, Globigerinoides altiaperturus, Paragloborotalia semivera, Paragloborotalia acrostoma, and Globoturborotalita pseudopraebulloides. Our age model along the P-18 well indicates a time range from ≥19.01 Ma (Early Miocene, Burdigalian) to ∼14.70 Ma (Middle Miocene, Langhian) equivalent to the calcareous nannofossils biozones NN3 to NN4, or, M3 to M5? Of planktonic foraminifera or palynological zones from T12 to T14? Even though we do not observe standard Middle Miocene bioevents with well-calibrated ages, the occurrence of nannofossils taxa Helicosphaera ampliaperta, and planktonic foraminifera Paragloborotalia semivera, Paragloborotalia acrostoma, and Globoturborotalita pseudopraebulloides show a distinctive biostratigraphic pattern, suggesting an age of ∼14.70 Ma to the top of the core section. Estimated sedimentation rates display high values (∼120 m/Myr to ∼219 m/Myr) during the Burdigallian (Early Miocene). They coincide with the regional subsidence increase during the Early Neogene in SSJB and Lower Magdalena Valley and the Early Miocene marine flooding event recorded in the Eastern Llanos Basin (ELB). From 17.60 Ma onwards, sedimentation rates decrease considerably, and a hiatus between 17.54 Ma and 16.96 Ma is interpreted as being tied to an abrupt change in sedimentology from calcareous mudrocks (marls) to very fine sandstones and sandy limestones. Finally, our data suggest that sedimentation rates in the basin were higher than marine sedimentation for ODP 999 during the same period.