Abstract

The Upper Miocene Cruse Formation of Trinidad yields predominantly agglutinated foraminifera. The limited assemblage has previously hampered palaeoenvironmental interpretations. Twenty-two samples taken from a basal Cruse section at 0.5 m intervals from Quinam Bay (10°05′07.7″N, 61°45′04.7″W) yielded 2938 foraminifera in 33 species, almost all agglutinated. The absence of calcite-cemented agglutinants suggests post-mortem dissolution of calcareous specimens. Dominant Spirosigmoilinella compressa indicates lower bathyal to abyssal palaeodepths, although the low values of the information function H are typical of shallower water. Subdominant Haplophragmoides carinatus and Haplophragmoides sp. 1 indicate low dissolved oxygen levels. Diversities measured using species richness S and H were especially low in the lowest 3.5 m of the section. The proportional abundance of the dominant species in each sample, max(pi), indicated three subsections, being low in the middle of the section but higher at the top and bottom. SHE analysis indicated six abundance biozones (ABs) containing one to seven samples each. Of the three ABs with more than three samples, two had Type 1 community structures and one had a Type 0 community structure. ABs with one or two samples indicate that environmental change at the top of the interval with low diversity is rapid. This is reflected in a change from abundant morphotype M3a (surficial epifauna flattened) at the base of the section to abundant M4a (shallow infauna planispiral) with M4b (deep infaunal) towards the top, which shows a downward shift in the position of the redox front part way through the section.

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