FORAMINIFERAL BIOSTRATIGRAPHY OF THE MIOCENE CICUCO FIELD, NW COLOMBIA

This study presents the results of the biostratigraphic analysis of cores from the Cicuco Field, NW Colombia. The Field is composed of shallow-water carbonates, and associated siliciclastics developed on basement paleo-highs. Four cores (C11, C20, C21, and C22) ranging in thickness from ~15 to 58m, were meticulously examined to identify larger benthic and planktonic foraminifera species. This in turn, resulted in the development of an integrated foraminiferal zonation for taxonomic age determinations. Eight species of benthic foraminifera including Amphistegina lessonii, Borelis melo melo, Cyclocypeus carpenteri, Lepidocyclina (Eulepidina) formosa, Miogypsina irregularis, Lepidocyclina (Nephrolepidina) sumatrensis, Lepidocyclina (Nephrolepidina) parva, and Operculina complanata, and ten planktonic foraminifera species including Globigerinella aequilateralis, Globigerinoides bollii, Globoquadrina dehiscens, Globorotalia obesa, Globorotalia siakensis, Globigerinoides subquadratus, Orbulina bilobata, Orbulina suturalis, Orbulina universa, and Sphaeroidinellopsis seminulina seminulina were identified. The biostratigraphic intervals were determined by comparing contemporaneous ranges of well-preserved planktonic foraminifera with age diagnostic benthic foraminifera. Based on the foraminiferal assemblages, the age of the marine carbonate units is determined to be late-early to middle Miocene. This study is the first in-depth examination of the Miocene biostratigraphy to species level in the area. Identification of foraminifera species provides valuable data useful for determination of depositional environments, water depths and conditions under which the Cicuco carbonate rocks were deposited. In addition, the resulting late-early to middle Miocene age refines previous ages and allows for evaluation of time-equivalent local, regional, and global factors that may have influenced deposition.