Foraminiferal-algal nodules, 2 to 15 cm in size, are actively growing in depths of 30 to 60 m on insular shelves in the eastern Caribbean. These nodules are characterized by two-part internal structures: an outer envelope, 1 to3 cm thick, of well-preserved, concentrically laminated crusts of Gypsina and/or coralline algae, and an inner core of coral, or, more commonly, an altered nodule that has been extensively bored, infilled, and lithified. The outer envelopes are less than 600 years old; the cores are variable in age-some are modern, others may be relict. The internal structure and ages of shelf nodules in the eastern Caribbean are similar to those of deep-water nodules in a number of other locations. Abrupt transitions from well-preserved outer envelopes to altered cores in all of these nodules suggest hiatuses in growth, possibly related to burial; the transitions are not as previously interpreted, related to a change from shallow to deep water associated with the Holocene transgression. Re-evaluation of aspects of nodules that have been proposed as paleoecologic indicators (shape, coralline-algal growth form, biotic assemblages, and diagenetic alteration) shows that, in the eastern Caribbean, these parameters have little predictable relationship with specific environmental conditions.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics