Seasonal Distributions of Foraminifera and their Implications for Sea-Level Studies, Cowpen Marsh, U.K.
Benjamin P. Horton, Robin J. Edwards, 2003. "Seasonal Distributions of Foraminifera and their Implications for Sea-Level Studies, Cowpen Marsh, U.K.", Micropaleontologic Proxies for Sea-Level Change and Stratigraphic Discontinuities, Hilary Clement Olson, R. Mark Leckie
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Analyses of total abundance of dead foraminifera from a twelve-month study of surface samples (0–1 cm) from Cowpen Marsh shows no definite seasonal pattern, but significant seasonal variations are evident in the relative abundance of agglutinated and calcareous taxa. Agglutinated species are most dominant in the winter months whilst calcareous foraminifera reach their peak relative abundances during the summer. We identify three cluster zones: a high-marsh and middle-marsh zone of Jadammina macrescens and Trochammina inflata; a low-marsh zone of Miliammina fusca and Jadammina macrescens; and a mudflat zone of calcareous foraminiferal species, notably Elphidium williamsoni, Haynesina germanica, and Quinqueloculina spp. The variations of contemporary foraminiferal distribution across the intertidal zone during an annual cycle modify the elevation of the zonal boundaries by as much as 0.9 m. Consequently, a contemporary sample taken in one month can significantly underestimate (0.35 m) or overestimate (0.48 m) the elevation range of a zone. Hence, the value of cluster zones as indicators of former sea levels can be assessed only following a consideration of the elevation errors induced by the seasonal variability in saltmarsh foraminiferal distributions.
We developed monthly and annual foraminifera-based transfer functions using weighted averaging regression and calibration. Results suggest that precise reconstructions of former sea levels are possible (r2 ≥ 0.82) but that the accuracy of these reconstructions varies during the course of the year. Greatest precision is achieved using samples collected in the winter months (± 0.29 m) and weakest during the summer (± 0.35 m) because the foraminiferal assemblages are dominated by agglutinated and calcareous species, respectively. We conclude that an investigation of contemporary saltmarsh foraminifera that recovers a complete set of samples in the winter, spring, summer, and autumn will provide the best-quality data for use in sea-level investigations (error = ± 0.21 m). If only one set of measurements can be obtained, sampling in the winter months may represent the most reliable alternative.
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Micropaleontology and biostratigraphy play vital roles for deciphering the stratigraphic record produced by changes in relative sea level, interpreting the history of global sea-level change, and testing models for the causes of sea-level fluctuations due to the variable influences of tectonics, glacio-eustasy, and climate. The stratigraphic architecture developed in response to changing eustasy, accommodation space, and sediment supply along continental margins, in epicontinental seas, and on carbonate platforms can be interpreted using the tools of marine micropaleontology. Microfossils provide chronostratigraphic control and a wealth of paleoenvironmental information about depositional environments as well as post-depositional changes to those environments. This volume demonstrates clearly that micropaleontologic proxies of environmental change provide a powerful dimension to the interpretive potential of stratigraphic sequences produced by changes in relative sea level and eustasy. Studies in the volume range from paralic to bathyal environments, span Pennsylvanian through Holocene stratigraphy, encompass a variety of microfossil groups and include a wide spectrum of techniques and paleoenvironmental proxies. The volume has been designed for graduate students and professionals interested in a wide range of subjects.