Turonian–Santonian Calcareous Nannofossil Biozonation for La Luna Formation, Middle Magdalena Valley Basin, Northern Colombia

A well site biostratigraphic study was carried out in the Chuira-2 ST-1 well, through the Umir and La Luna Formations in the Middle Magdalena Valley Basin (MMVB), north of Colombia. Results of the calcareous nannofossil analysis are presented and compared to local biozonations for planktonic foraminifera and palinomorphs for La Luna Formation in the MMVB and calcareous nannofossils for the Maracaibo Basin. Biostratigraphic analyses result in the identification of different time intervals and sediment thickness of an inverse fault traversed by the well. Six local calcareous nannofossil biozones, based on eleven dissolution-resistant taxa bioevents, for the lower to the upper part of the La Luna Formation in the MMVB are proposed—Micula adumbrata Interval Biozone, comprising the early Turonian; Eprolithus moratus Interval Biozone, for the middle Turonian to the latest Turonian; Micula staurophora Interval Biozone, for the early Coniacian to the early late Coniacian; Micula adumbrata–Micula concava Interval Biozone, of late Coniacian age; Micula concava Interval Biozone, of early Santonian age; and Zeugrhabdotus scutula Interval Biozone, which corresponds to the early Santonian to late Santonian.