174 D15. Paleontology, Biogeography/Biostratigraphy (Posters)

Monday, 23 October 2017
9:00 AM - 6:30 PM
Halls 4EF

AMINOCHRONOLOGY AND TIME-AVERAGING IN QUATERNARY LAND SNAIL ASSEMBLAGES FROM THE MADEIRA ARCHIPELAGO

Paper number: 174-10
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Understanding the properties of time-averaging (age mixing) in a geologic stratum is essential for properly interpreting the paleofauna preserved in the geologic record. This work assesses the age and quantifies the scale of time-averaging in Madeira (Portugal) land-snail-rich deposits by dating individual shells using amino acid racemization (AAR) calibrated with radiocarbon. Snail shells were collected from eleven colluvial soil sites on the semi-arid and uninhabited islands of Bugio and Deserta Grande. These islands are home to a rich indigenous malacofauna with abundant Quaternary fossils suitable for further paleoenvironmental and paleoecological studies.

Analyses were performed on 20 shells of the dominant and well-preserved genus Actinella. Amino acid D/L ratios were calibrated with rapid, low-precision AMS radiocarbon at UC Irvine, using power function regression. The D/L ratios of glutamic acid showed the least variance from the calendar-year-calibrated radiocarbon age (r-squared=0.96) and were used to estimate the ages of fossil snails from Madeira. The results suggest that shells range in age from ~9200 to ~35,700 cal yr BP and show some examples of multi-millennial-scale time averaging throughout the investigated colluvial Quaternary soils. This research illustrates that time-averaging in land snail shells can be credibly quantified using AAR, which could be invaluable in future studies on taphonomy, paleoclimate and paleodiversity using these shelly assemblages.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-301548

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