GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 82-10
Presentation Time: 9:00 AM-5:30 PM


RYAN, Deirdre D., LACHLAN, Terry J. and MURRAY-WALLACE, Colin V., School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia,

Studies of subsiding coastlines or those uplifting at a rate slower than relative sea-level rise often conclude that depositional features contain a reworked component of an analogous, older feature. Quantifying the contribution of reworked material into younger deposits is seldom attempted. This research is a preliminary investigation into the use of Amino Acid Racemization (AAR) for this purpose. AAR has been applied in Quaternary studies with geochronological and taphonomic purposes e.g., whole-rock analysis, aminostratigraphy, identification of mixed-age populations, and both relative and numerical age estimation. In this research foraminifera of the Genera Elphidium and Lamellodiscorbis retrieved from the ≤500 µm fraction of multiple modern beach sediment samples of a barrier coastline are analyzed using AAR to identify grains reworked from older deposits. Individual tests of foraminifer, equivalent in size to sand grains, could serve as a measurable indicator of sediment reworking in successive interglacial periods. Two subsamples of foraminifera were hand-picked from modern beach sediments having variable carbonate content and antecedent morphologies. The first subsample was selected for the robustness of the individual tests, biased for color and level of preservation, to establish a representation of Holocene foraminifera. The second subsample was collected ‘blind’ to produce a representation of the whole sediment. Individual tests are now being analyzed using AAR. Holocene foraminifera are identified as exhibiting a lesser extent of valine racemization than of glutamic acid. It is expected that the average racemization extent of accepted individual Holocene tests will not exceed the whole-rock result, which represents an integrated average of all biominerals within that sample. Older, reworked tests will plot as outliers to the Holocene values. Preliminary results show: 1) individual foraminifera of Holocene-age exhibit extents of racemization above and below the whole-rock value but the calculated average does not exceed the whole-rock value, 2) reworked foraminifera of late to middle Pleistocene are identifiable, and 3) the quantity of reworked grains is variable along the length of the coastline with a relationship to antecedent morphology and sediment source.
  • Ryan et al. 2016 GSA Poster.pdf (1005.1 kB)