The Tamana Formation of the Central Range of Trinidad was studied in order to determine its importance in the stratigraphical and structural development of north‐eastern South America. Biostratigraphical, petrological and mineralogical data, combined with field mapping show that the Tamana sediments are composed of five distinct lithofacies: inner to outer shelf, burrowed shaley mudstone; outer shelf, Fe‐rich sandy limestone; submarine channel, conglomeratic mudstone; middle shelf to nearshore, algal‐foram packstone/grainstone; and intertidal to nearshore, algal‐stromatolite‐coral boundstone with coral bioherms. Maximum thickness of the Tamana Formation is 244 m. Deposition of the Tamana limestones occurred between the Praeorbulina glomerosa (latest early Miocene) and Globorotalia fohsi robusta (middle part of the middle Miocene) planktonic foraminiferal zones, and in a more continuous trend than is seen in the current outcrop belt. Detailed biostratigraphy shows that the Tamana Formation is a facies equivalent of the shallow‐ and deep‐water shales of the Brasso Formation, and the deep water turbidites of the Herrera Member of the Cipero Formation. The early diagenetic history of the Tamana limestones was dominated by the precipitation of authigenic glauconitic smectite, and the dissolution of skeletal grains and carbonate matrix. Late burial diagenesis was dominated by the precipitation of illite and illite/smectite. Comparative mineralogy and textural analyses indicate a minimum range of burial depth for the Tamana Formation at 800–1500m, with a maximum of 2400 m. Alteration of Fe‐bearing minerals to geothite and late fracturing occurred during post‐Pliocene tectonic uplift and unroofing of the Central Range. The Tamana Formation sediments can be used as a structural and stratigraphical event marker within the Late Tertiary geological history of Trinidad. These units record a phase of the tectonic interaction between the Caribbean and South American plates in the south‐eastern Caribbean, and reflect the onset of contractile deformation in the Central Range.

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The Nariva Formation comprises mostly non-calcareous rocks with few calcareous foraminifera, but it is sandwiched geographically in a narrow (<10 km wide) band between the richly calcareous Brasso and Cipero Formations to the north and south respectively. Sixty-one samples were collected from the Nariva Formation at nine transient exposures along a transect trending NNE-SSW across southwestern Central Trinidad. The sparse planktonic foraminiferal assemblages showed the exposures to range in age between Oligocene and early middle Miocene, though many of the samples were of earliest middle Miocene age and coincident with a tectonically-induced transgressive-regressive cycle in the Brasso Formation. The Nariva assemblage at the most southerly exposure, at which the Nariva and Cipero Formations interfingered, was calcareous and of lower bathyal aspect, containing many Planulina wuellerstorfi. The assemblage at this exposure did not differ statistically between the two formations, and was thus said to be of "Cipero aspect", although the presence of rare Elphidium sp. in the Nariva parts of the exposure attests to some downslope transport. Recovery from most other exposures was typically small. Richer, predominantly agglutinated assemblages, however, were obtained from the Tarouba Community Centre, Ben Lomond Quarry, Raphael Street, and Tabaquite Heights. The assemblages were of "Brasso aspect", comprising species illustrated previously from the Brasso Formation. Three exposures were sampled at the Raphael Street site, which covered about ten hectares and had been cleared for development. The rocks at this site are patchily but richly stained with hematite and possible manganese derived from hydrothermal activity. Exposure 1 (13 samples) was subdivided into an almost barren interval (Exposure 1a, 8 samples) and an interval containing abundant Cribrostomoides carapitanus and Trochammina cf. pacifica and lesser Jarvisella karamatensis, Arenogaudryina flexilis and Glaphyrammina americana (Exposure 1b, 5 samples). This assemblage is thought to indicate low dissolved oxygen concentrations at middle to lower bathyal paleodepths. That the Brasso Formation was deposited at neritic to shallower middle bathyal paleodepths, while the Cipero Formation at lower bathyal to abyssal depths, demonstrates that the Nariva Formation was deposited on an eastward-facing paleo-slope. Exposures 2 (9 samples) and 3 (5 samples) are dominated by Simobaculites saundersi Wilson and Kaminski, n. sp., the walls of which do not incorporate calcareous particles. Many samples yielded large quantities of gypsum that, in view of (a) the paleodepth and (b) the rich planktonic foraminiferal recovery from the adjacent Brasso and Cipero Formations, is thought to reflect syndepositional dissolution of foraminiferal calcium carbonate and its precipitation as calcium sulphate. Because both the Nariva Formation and the upper Miocene to lower Pliocene Lower Cruse Member (southern Trinidad) yield primarily organically-cemented agglutinated foraminifera, a comparison is made between them. SHE analysis and different mean values of the Assemblage Turnover Index (ATI) shows the community structures in the two formations to differ. Because there is no sign of hydrothermal activity associated with the Lower Cruse Member, despite their taxonomic similarity we conclude that the agglutinated assemblages in the Nariva and Cruse Formations lived in markedly different paleoenvironments.