A STRATIGRAPHIC STUDY OF THE LIMESTONE ROCKS ON THE ISLAND OF ANGUILLA

Two detailed stratigraphic columns were produced from two locations in the northeastern part of Anguilla (Road Bay and Crocus Bay). In addition, samples from a location in the northwestern part of the island (Anguilla Quarry) were inspected and compared with the rocks from the northeastern side of the island. The texture and composition of the rocks were studied in hand samples and in thin sections. The limestone rocks studied were named as the Anguilla Formation by Van Den Bold (1970) and the corals present in them were identified by Budd et al. (1994). Based on lithology and stratigraphy the depositional environments represented by the rocks were interpreted. Also, the measured sections were divided in parasequences based on Sequence Stratigraphy principles. Significant differences in texture and composition of the limestone rocks were found between the eastern and western side of the island. The upper twenty meters of limestone rocks along the eastern side (Quarry location) are highly altered by karst and have dolomite at the base of the altered interval. The rocks on the western show much lesser sing of alteration by karst. Two hypothesis can explain the documented lateral changes in the rocks: (1) A fault zone present located along the center of the island, exposed limestones with different texture and composition on the western and eastern sides; (2) uplift on the north that produced tilting of the island (north to south) occurred with an east-west oblique lateral component exposing the eastern parts of the island for a longer period. Most preliminary observations seem to support the second hypothesis.