Amino acid geochronology of individual foraminifer (Pulleniatina obliquiloculata) tests, north Queensland margin, Australia: A new approach to correlating and dating Quaternary tropical marine sediment cores

Abstract

[1] In this study, we demonstrate the utility of amino acid geochronology based on single-foraminiferal tests in Quaternary sediment cores from the Queensland margin, Australia. The large planktonic foraminifer Pulleniatina obliquiloculata is ubiquitous in shelf, slope, and basin sediments of north Queensland as well as pantropical oceans. Fossil tests are resistant to dissolution, and retain substantial concentrations of amino acids (2-4 nmol mg À1 of shell) over hundreds of thousands of years. Amino acid D and L isomers of aspartic acid (Asp) and glutamic acid (Glu) were separated using reverse phase chromatography, which is sensitive enough to analyze individual foraminifera tests. In all, 462 Pulleniatina tests from 80 horizons in 11 cores exhibit a systematic increase in D/L ratios down core. D/L ratios were determined in 32 samples whose ages are known from AMS 14 C analyses. In all cases, the Asp and Glu D/L ratios are concordant with 14 C age. D/L ratios of equal-age samples are slightly lower for cores taken from deeper water sites, reflecting the sensitivity of the rate of racemization to bottom water temperature. Beyond the range of 14 C dating, previously identified marine oxygen-isotope stage boundaries provide approximate ages of the sediments up to about 500,000 years. For this longer time frame, D/L ratios also vary systematically with isotope-correlated ages. The rate of racemization for Glu and Asp was modeled using power functions. These equations can be used to estimate ages of samples from the Queensland margin extending back at least 500,000 years. This analytical approach provides new opportunities for geochronological control necessary to understand fundamental sedimentary processes affecting a wide range of marine environments.

Carbonate eolianites, quartz sands, and Quaternary sea-level cycles, Western Australia: A chronostratigraphic approach

“…Previous studies have determined that amino acid concentration decreases exponentially with greater sample age Hearty et al, 2004a). If fossil or WR sediment samples are generally well preserved, and there is no evidence for unusual diagenesis (such as associated cavernous weathering, extreme Fe staining, complete recrystallization), then there is a threshold age at which samples yield insufficient levels of amino acids to be accurately measured.…”

Intrashell Radiocarbon Variability in Marine Mollusks

“…Sample size requirements (grams of final carbon) for conventional 14 C dating often demanded composite or bulk-sampled charcoal, mollusk shell, or large sections of human or animal bone to obtain sufficient collagen, which decreases dating accuracy by averaging or precludes 14 C dating altogether for lack of suitable material. The micrograms of final carbon required for AMS dating are now routinely derived from specific genera of foraminifera (Hearty 2004;Ingram and Kennett 1995;Roark et al 2003); annual tree-rings (Gandou et al 2004;Kaiser 1994); pollen, starch grains, and seeds (Caran et al 2001;Smith 1997;Mulholland and Prior 1993;Piperno and Flannery 2001;Piperno and Stothert 2003); small samples of bone collagen or specific amino acids (e.g. Formicola et al 2004;Stafford et al 1991;Taylor et al 1998;Tripp and Hedges 2004); single mollusk valves (e.g.…”

A New Genus and Species of Buteonine Hawk from Quaternary Deposits in Bermuda (Aves: Accipitridae)

“…A/I results on encrusting bioclastic sediment indicate a similar correlation, although the presence of the serpulid tubes on the bone indicates marine inundation and thus a probable highstand of sea level. Both MIS 5a and 5e highstands were at or above present sea level in Bermuda (Vacher & Hearty 1989, Hearty 2002, with MIS 5c being significantly lower. As the dating appears to point more toward early MIS 5 than late, we conclude the hawk bone was deposited in the cave sometime during MIS 6 and was subsequently inundated and encrusted marine with sediment and worm tubes most likely during the MIS 5e highstand.…”

“…The large error (16%) extends the age estimate across much of the last interglacial MIS 5 interval and into late MIS 6, in general agreement with D/L Glu results. The mean WR sediment AA of 0.21 ± 0.01 requires no independent scheme for comparison, as a calibrated WR bioclastic limestone database is well established for Bermuda (Hearty 2002, Hearty et al 1992. Within this framework, the value of 0.21 equates with a mid MIS 5 age estimate between about 85 and 115 ka.…”