The geology of the western part of the Northern range of Trinidad

The results of geological mapping in the western part of the Northern Range of Trinidad are shown on 1:25,000 maps. The stratigraphy of the Caribbean group, low grade metamorphics more than 2500 m thick, has been revised. Type sections of the Maraval, Maracas and chancellor formations are established. Correlation with neighbouring area is suggested. The Maraval formation is the oldest in the area, probably Upper Jurassic; it consists of more than 500 m marbles and limestones. The base is not seen. The Maracas formation, also probably Upper Jurassic, lies above the marvel formation. It is approximately 1500 m thick and consists of slates, quartzites and phyllites. Rare volcanic ashes are found. Sedimentary structures suggest palaeocurrent directions from north to south and deposition as turbidites. The chancellor formation lies above the maracas formation and is probably lower cretaceous in age. It is approximately 500 m thick and consists of bedded limestones and phyllites with rare quartzites. It has been divided into four members. On the island of Monos it contains channels of conglomerates in the upper limestones member. The laventille formation, lower cretaceous, lies along the south flank of the Northern Range and is less metamorphosed than its equivalent the chancellor formation. There are two facies – massive limestones and a predominantly shale succession. Evaporates occur. Autobrecciation occurs in the limestones and a zone of contemporaneous dislocation lies along the eastern edge of the massive limestones. The morvant beds consist of shales, sandstones and exotic blocks. They are probably the extension of the upper cretaceous galera formation. Recumbent anticlines overturned to the north form the main part of the Northern Range. Three phases of folding can be recognised. Thrusting occurs parallel to the exes of the folds. The El Pilar fault and similar major E-W faults developed later. These have been described as wrenches but horizontal displacement is unclear, although major vertical movement is described. The main metamorphism is believed to be tectonic, contemporary with the major folding at the end of the Lower Cretaceous. Further deformation occurred in Upper Cretaceous time. Faulting continued through the Tertiary