Planktonic Foraminifera in the Early to Middle Miocene 'Lower Concord Calcareous Silt Member' at Mayo Quarry, Central Trinidad, and the invalidity of the Tamana Formation
Newsletters on Stratigraphy Volume 45 Number 2 (2012), p. 105 - 114
published: Apr 1, 2012
Rocks previously included in the Lower Concord Calcareous Silt Member of the Tamana Formation of Central Trinidad have in the past been thought to be deposited during the early Late Miocene Globorotalia mayeri Zone. However, examination of planktonic foraminifera immediately south of the Mayo Limestone at Mayo Quarry indicates that rocks ascribed to the Lower Concord Silt were deposited during the Early to early Middle Miocene (Globigerinatella insueta to Praeorbulina glomerosa Zones, N7 - earliest N9). The fauna, with abundant Globigerina praebulloides and G. woodi, indicates that surface water was cooled by upwelling. On the basis of this and earlier studies, it is concluded that the whole of the Tamana Formation is of late Early to early Middle Miocene age, and not early Late Miocene as previously thought, and thus equivalent to part of the Brasso Formation of the Northern Basin of Trinidad. The Lower and Upper Concord Calcareous Silt Members cannot be distinguished lithologically from either each other or the Brasso Formation. The Tamana formation, Lower Concord Calcareous Silt member and Upper Concord Calcareous Silt member are, therefore, invalid lithostratigraphic units and must be referred to the Brasso Formation. The disjunct Brigand Hill, Biche, Tamana, Tabaquite, Guaracara, and Gasparillo Limestones, previously grouped as the Guaracara Limestone Member, must each be given member status, as must the Concord Limestone. Trinidad is renowned for its complex geology. Some of that apparent complexity may be man-made, however, early workers having subdivided some thick lithostratigraphic units into formations and members using bio stratigraphic tools. It is recommended that the Trinidadian stratigraphic column be re-examined for instances similar to the one reported here.