The biostratigraphic and palaeoenvironmental significance of foraminifera in the Middle Miocene Upper Concord Calcareous Silt Member (Tamana Formation) near Gasparillo West Quarry, central Trinidad

The Tamana Formation has previously been suggested to have been deposited in the Middle Miocene Globorotalia mayeri planktonic foraminiferal Zone (N14) and to succeed the Brasso Formation. A 24 m section of the Upper Concord Calcareous Silt Member of the Tamana Formation was sampled every 1 m in the Gasparillo West Quarry, western central Trinidad, straddling the Early to Middle Miocene boundary (Praeorbulina glomerosa to Globorotalia fohsi fohsi planktonic foraminiferal Zones [N8-N10]). Abundant benthonic foraminiferal species reveal a transgressive-regressive (T-R) cycle that brought the seafloor into contact with an oxygen minimum zone (OMZ). Middle and outer neritic rocks above the OMZ were occupied by Amphistegina gibbosa and Cibicidoides crebbsi respectively. The outer neritic to upper bathyal, upper margin of the OMZ was dominated by Uvigerina subperegrina gr., while Brizalina alazanensis venezuelana dominated the upper bathyal OMZ core. The section is correlated with the Brasso Formation at Guaico-Tamana Road. The greatest palaeodepth calculated for the T-R cycle within the Brasso Formation was ~470 m, while that for the Upper Concord Calcareous Silt was ~215 m. The difference in palaeodepth is ascribed to the Upper Concord being deposited on a pop-up structure south of the Brasso piggyback basin.