ABSTRACT

Quartzose sandstone and mudstone turbidites of Cenozoic and possibly older age constitute a large proportion of strata in the accretionary complex of the Lesser Antilles arc exposed at its structural high on Barbados. The Chalky Mount succession is the thickest (> 628 m) and best exposed of structurally continuous turbidite sequences on the island. Four classes of layer types are distinguished among Chalky Mount beds: single sandstones (between 0.2 and 12 m thick), amalgamated sandstones, multilayers of sandstone (< 20 cm thick) and mudstone, and thick mudstone units. Layer types are divided among 65 types based on Bouma sequences, grading within sandy divisions, and sand to mud gradation. Of these, less than a dozen types occur frequently. Although many layer types cannot be in erpreted uniquely as turbidites, the occurrence of classic turbidites throughout the section indicates the succession is of subsea sediment-gravity flow origin.

The vertical succession of layer types can generally be interpreted as reflecting lateral facies migration of a radial fan, and includes from bottom to top: basin plain, distal outer fan, proximal outer fan, midfan, inner fan (?), midfan, abandoned fan, proximal outer fan. The sequence indicates initial progradation, followed by retrogradation and abandonment, then rejuvenation of the former fan. Paleocurrent directions at several horizons in the section indicate transport mainly between north and east relative to present coordinates. The applicability of the radial fan model to the Chalky Mount and other turbidite successions of Barbados suggests that a base-of-slope configuration of the depositional sites was likely.