Sediment accumulation, stratigraphic order, and the extent of time-averaging in lagoonal sediments: a comparison of Pb-210 and C-14/amino acid racemization chronologies

Carbon-14 calibrated amino acid racemization (¹⁴C/AAR) data and lead-210 (²¹⁰Pb) data are used to examine sediment accumulation rates, stratigraphic order, and the extent of time-averaging in sediments collected from the One Tree Reef lagoon (southern Great Barrier Reef, Australia). The top meter of lagoonal sediment preserves a stratigraphically ordered deposit spanning the last 600 yrs. Despite different assumptions, the ²¹⁰Pb and ¹⁴C/AAR chronologies are remarkably similar indicating consistency in sedimentary processes across sediment grain sizes spanning more than three orders of magnitude (0.1–10 mm). Estimates of long-term sediment accumulation rates range from 2.2 to 1.2 mm yr⁻¹. Molluscan time-averaging in the taphonomically active zone is 19 yrs, whereas below the depth of final burial (~15 cm), it is ~110 yrs/5 cm layer. While not a high-resolution paleontological record, this reef lagoon sediment is suitable for paleoecological studies spanning the period of Western colonization and development. This sedimentary deposit, and others like it, should be useful, albeit not ideal, for quantifying anthropogenic impacts on coral reef systems.