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Dinoflagellate assamblages and sea-level fluctuations in the Maastrichtian of southwest Georgia.
| Firth, J.V. | |
| 1993 | |
| Review of Palaeobot. and Palynol., 79, p.179-204 | |
| Dinoflagellate assamblages and sea-level fluctuations in the Maastrichtian of southwest Georgia. |
Firth, J.V., 1993: Dinoflagellate assamblages and sea-level fluctuations in the Maastrichtian of southwest Georgia. Review of Palaeobot. and Palynol., 79, p.179-204 Analysis of Maastrichtian dinoflagellate assemblages from the upper Ripley and Providence Formations in two cores from southwestern Georgia show changes that can be related to fluctuations in relative sea-level and in depositional environments. Sediments in the USGS Ft. Gaines Core were deposited in transitional zone to nearshore and cstuarine environments close to a major fluvial source, whereas co-eval sediments in the USGS Albany Core were deposited in middle to outer shelf environments, laterally displaced away from any fluvial source. Lower Maastrichtian assemblages in the Ft. Gaines Core contain common Senegalinium ohscurum and Cerodinium pannuceum. These point to overall transgressive conditions in the lower Providence, whereas decreases in percent marine phytoplankton indicate individual progradational episodes. The upper Providence of the Ft. Gaines Core shows a marked decrease in dinoflagellate species abundance and percent and absolute abundances of marine phytoplankton, with a concurrent increase in relative abundance of Achomosphaera-Spiniferites cysts. These indicators point to a relative regression and shoreward movement of facies through the upper Maastrichtian. Lower Maastrichtian assemblages in the more seaward Albany Core are dominated by Chatangiella? robusta, Exochosphaeridium bifidum, and Cerodinium pannuceum, and have a very high percent marine phytoplankton signal. These are interpreted to represent transgressive conditions with no progradation of the shoreline. The upper Providence shows high species abundance, increasing dominance by Achomosphaera Spiniferites cysts, individual abundance peaks of several different species, and a decrease in percent marine phytoplankton, indicating an overall relative sea-level regression through the upper Maastrichtian. Comparison with dinoflagellate assemblages from Maryland suggest that high abundances of Areoligera cysts at about the lowerjupper Maastrichtian boundary may reflect the level of maximum transgression in the middle of the Maastrichtian. Three new species are described: Florentinia perforata, Yolkinigymnium expansum, and Palambages trilicius.