What is Luminescence? Optically Stimulated Luminescence (OSL) Sediment Context Collection Procedures

OSL geochronology of Strandplains adjacent to the Great Lakes

Michigan, USA

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luminescence graph
Chronologic control on the deposition of individual beach ridges in strandplains adjacent to the Great Lakes is required to determine the rates and magnitudes of late Holocene water level fluctuations, and to reconstruct records of regional isostasy and climatic variability. This study compares optically stimulated luminescence (OSL) ages for littoral ridge sediments against conventional and AMS 14C ages obtained from inter-ridge organic material for strandplain sequences at Manistique, Grand Traverse, and Tahquamenon Bays, Michigan, USA. Analyses of modern littoral and eolian sediments collected from beaches at Grand Traverse and Au Train Bays, MI and at Batchawana Bay, Ontario, Canada indicate that quartz grains are completely solar reset and that analogous paleo-sediments are suitable for OSL dating using the single aliquot regeneration (SAR) approach. In general, SAR ages on paleo-littoral sediments are within 1 ? of conventional and AMS 14C data for the past 2 ky. Independent chronologic constraint is provided by the extent of podzolization observed with beach ridge excavation and by tide gauge rebound rates at Tahquamenon Bay. Prior to 2 kya direct comparison of SAR and 14C ages is hindered by scatter > 1000 yrs. observed in the 14C data. Comparatively, SAR ages are internally consistent across individual strandplains with few age reversals, and exhibit less scatter than 14C results for corresponding ridges. Moreover, SAR ages of 4260 450 yr B.P. and 4280 390 yr B.P. for ridges 72 and 77, respectively, at Tahquamenon Bay are chronologically consistent with an elevated platform of prograding beach ridges associated with lake level fall post the Nipissing II Phase. Overall, the results indicate that SAR is a suitable alternative for dating strandplain sequences when isolating organic material suitable for 14C dating proves problematic. SAR provides the advantage of producing discrete ages for littoral and eolian sediments rather than for associated landforms, i.e. swale organics. Consequently, each SAR age must be interpreted in accordance with the stratigraphic context (e.g. upper shoreface, foreshore, dune). Ultimately the multi-decadal to century scale resolution of the SAR method may also provide an opportunity to identify primary and secondary eolian activity across strandplains.
Erin Argyilan, S. L. Forman, T. Thompson (Indiana Geol. Survey), John Johnston (Indiana Geolo. Survey), Stephen Jackson (Univ. of Wyoming), Robert Booth (Univ.of Wyoming) and Douglas Wilcox ( USGS).