Quartzose turbidites of the accretionary complex of Barbados, II: Variations in bedding styles, facies and sequences

Abstract

Barbados provides the only subaerial exposures of the Barbados Ridge, an accretionary complex lying outboard of the Lesser Antilles volcanic arc. Within nine measured sections of quartzose turbidites, five major types of sequences are recognized: 1. (1) Progradational sequences (basin plain-outer fan) of uniformly fine-grained, flat-based, base-absent turbidites that thicken upward and gradually become coarser-grained and base-present at the top of the sequence. 2. (2) A single rejuvenation (rapid progradational) sequence was identified as an abrupt progradational sequence above abandoned-lobe deposits, and is not characterized by stacked, well-developed, upward-thickening successions as many progradational sequences are. 3. (3) Channelized successions of coarse-grained, base-present turbidites arranged in packets 5–20 or 50–140 m thick which are midfan and inner-fan deposits, respectively. The distinction between predominance of base-present and base-absent turbidites seems to correspond with the interpreted change from midfan channelized to outer-fan sheet flow deposition. 4. (4) One example of a major retrogradational sequence, of midfan deposits above inner-fan (?) sandstones, has been found on Barbados. Minor sequences of facies retrogradation are relatively common in the outer-fan environment where upward-thinning sandstone beds overlie upward-thickening units to define symmetric sequences. 5. (5) Abandonment successions are: major, as indicated by massive accumulations of mudstone; minor, as indicated by abrupt reversals of upward-thickening trends in outer-fan lobe deposits; and cryptic where indicated by thick (> 4 m) bioturbated zones of massive sandstone.