Seafloor topography, paleodepth and bottom water conditions in the Miocene Cipero Formation, Southern Trinidad, SE Caribbean Sea

Abstract

Six well logs and two seismic lines are used to reconstruct the paleo-seafloor surface onto which was deposited the Middle Miocene age Golconda Marl Member (Globorotalia fohsi peripheroronda to G. fohsi robusta planktonic foraminiferal Zones, = Zones N9/M6 to N12/M9) of the Cipero Formation of Trinidad, western tropical Atlantic Ocean, The reconstruction reveals five N-S oriented, south-vergent, reverse thrust fault sheets within the underlying Princes Town Marl Member (Catapsydrax dissimilis through Globigerinatella insueta Zones, N5/M2 – N7/M4) and Retrench Sandstone Member (Globigerinatella insueta planktonic foraminiferal Zone, N7/M4) onto which the Golconda Marl Member was deposited. The occurrence of sandy sections, determined from well-log signatures and illustrated on the reconstructed surface, can be used as an aid in locating potential hydrocarbon reservoirs within the Golconda Marl Member. Micropaleontology is used to infer (a) paleodepth and (b) changing paleoenvironmental conditions throughout the Cipero Formation. Foraminiferal investigation of 21 Cipero Formation samples collected at the La Fortune Anticline (LFA) places the Golconda Marl Member of the Cipero Formation at this site in the Globorotalia fohsi peripheroronda planktonic foraminiferal Zone (N9/M6). Planulina wuellerstorfi, recovered in abundance, places the LFAsection and remaining Golconda Member at water depths >700 m. The statistical similarity of the benthic foraminiferal assemblages in the >63 um and >106 um fractions suggests winnowing of the LFA section, which is thus hypothesized to comprise a contourite. The statistical similarity of previously published data from Zones N6/M3 and N12/M9 (Shannon’s H, the Berger-Parker Dominance Index, Evenness E, a Nutrient Flux Index [NFI = sum of proportional abundances of Bolivina + Bulimina + Uvigerina], and the Benthic Foraminiferal Dissolved-Oxygen Index [BFOI]) suggests that these were deposited in comparable paleoenvironments with, in contrast to Zone N9/M6 at the LFA, relatively little bottom current action.