A time-depth scale for Owens Lake sediments of core OL-92; radiocarbon dates and constant mass-accumulation rate

Abstract

Results of radiocarbon analyses of carbonates and humates from the upper 31 m of OL-92 indicate coherent and linear progression of dates with depth down to about 24 m and 30 ka. Scatter of results below this depth indicates that the practical limit of radiocarbon dating in this core is about 30 ka. The average mass-accumulation rate (MAR) for the top 24 m is 52.4 g/cm 2 /k.y. calculated from radiocarbon dates and bulk density reconstruction. A similar calculation for the entire core down to the Bishop ash bed (304 m, 759 ka) gives a MAR of 51.4 g/cm 2 /k.y., suggesting a constant MAR throughout the past 760 k.y. A time-depth curve for the entire core was then constructed from this constant value and using pore-water content to correct for sediment compaction. The resulting curve is remarkably coincident with a similar plot independently derived from 10 within-Brunhes paleomagnetic events identified by Glen et al. (this volume). That MAR remained relatively constant through the glacial/interglacial cycles may imply that the increased sediment supply during the high runoff of glacial times was balanced by increased size of the depositional area and vice-versa during interglacials. Surface area of the lake is approximately proportional to river discharge, but only up to the spill point of the lake. The constant MAR suggests, therefore, that spilling of Owens Lake was relatively infrequent during the past 800 k.y., as independently inferred from the sediment geochemistry (Bischoff et al., this volume, chapter 4).