Abstract

Many carbonate sections are characterized by monotonous successions that mask subtle changes in paleoenvironmental parameters. Foraminiferal populations, however, are more sensitive to environmental parameters and commonly reflect these subtle changes. The accuracy of paleoenvironmental interpretations based on foraminiferal assemblages depends on the precise delineation and interpretation of abundance biozones (ABs). Samples rich in foraminifera were taken from four outcrops (OC1–OC4, oldest to youngest) of the Mayo limestone bioherm (Tamana Formation) that comprised 6–8 limestone-marl alternations each. Bottom-up SHE Analysis for Biozone Identification (SHEBI) indicated the samples to be from seven ABs (AB1–AB7). The percentage of the foraminiferal assemblage as planktonic specimens (%P) ranged from 5%–25% and was generally lower in AB1, AB3, AB5, and AB7 than in intervening biozones. This indicates deposition at shallow- to mid-neritic paleodepths (∼20–55 m) during a series of transgressions and regressions. Per sample (point) diversities, measured using the information function H, ranged from 1.67 to 2.86. Total within-AB diversities (α diversities), were calculated from the final value of H and expressed as the effective number of species SE [ = eH]; these ranged from 7.8 to 18.4. Changes in diversity across AB boundaries (β diversities) were calculated using the percentage change in SE, and ranged from −44% to 137%. Not all β diversities were significant, indicating that paleodepth was not the only control on α diversity. Fluctuations in the percentage abundances of Elphidium spp., Pseudononion atlanticum, and Amphistegina sp. show that changes in the organic matter flux also exerted some control, being lowest in the Amphistegina-rich AB3.

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