Oligocene Neritic Foraminifera in Southern Australia: Spatiotemporal Biotic Patterns Reflect Sequence-Stratigraphic Environmental Patterns
Published:January 01, 2003
Graham Moss, Brian Mcgowran, 2003. "Oligocene Neritic Foraminifera in Southern Australia: Spatiotemporal Biotic Patterns Reflect Sequence-Stratigraphic Environmental Patterns", Micropaleontologic Proxies for Sea-Level Change and Stratigraphic Discontinuities, Hilary Clement Olson, R. Mark Leckie
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Quantitative analysis of Oligocene assemblages in cool-water carbonates suggests a two-tiered response by benthic, neritic foraminiferal faunas to a succession of glacioeustatic fluctuations. One response appears at lower-frequency or second-order cycles and is marked by more substantial, nonreversible, taxic change at the Eocene–Oligocene boundary, at the Rupelian–Chattian (Early–Late Oligocene) boundary, and during a Late Oligocene transgressive phase. These faunal changes were responses to climatic changes forced by glaciations signaled by oceanic oxygen-isotope maxima. The second response is seen in fluctuations in the abundances of benthic neritic taxa. Rapid changes in infaunal-to-epifaunal ratios appear to chronicle reversible “short-term” local paleoenvironmental shifts forced by third-order cycles. Sequence stratigraphic packages and bounding surfaces are easier to decipher in sequences characteristic of the warmer and more sluggish Priabonian ocean than in the cooler and better-ventilated Rupelian ocean. The major (second-order) physical event at the Rupelian–Chattian boundary is recorded faunally but shows a relatively muted impact on the regional succession of neritic foraminifera compared to the sequence boundary coinciding with glaciation Oi1 in the very earliest Oligocene. We interpret, from graphic correlation and cluster analysis, that patterns of faunal change reflect endemism that developed on a broad neritic zone with wide variation in intensity of oceanic influence.
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Micropaleontologic Proxies for Sea-Level Change and Stratigraphic Discontinuities
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.