Optical dating of cobble surfaces determines the chronology of Holocene beach ridges in Greenland

Abstract

We constrain the age of a cobble beach ridge system in Greenland using Optically Stimulated Luminescence (OSL) dating of buried cobble surfaces. Luminescence signals from six cobbles are measured using infrared (IR) stimulation at 50 °C (IR50) and 180 °C (pIRIR180); these cobbles represent four progressively younger beach ridges lying between ~35 and ~6 m above present sea level. Luminescence–depth profiles show that the IR50 signals in all the samples and pIRIR180 signals in four out of six samples are well bleached to depths >1.2 mm into the cobble surfaces. Equivalent doses in well‐bleached cobble surface slices (i.e. <1.2 mm) are measured and divided by the effective environmental dose rate to the cobble surfaces in order to derive burial ages. Both IR signals are corrected for anomalous fading using the sample‐specific ratio of the field to the laboratory saturation levels. Our results are consistent with a depositional model predicting that the investigated portion of the beach ridge system built out continuously during relative sea level fall between ~5.3 and ~1.9 ka ago. The optical ages suggest that the rate of construction varied considerably, with the highest rates ~3.4 ka ago. Additionally, the lowest‐elevation beach ridge investigated here provides the first evidence for a higher‐than‐present relative sea level, between 1.5 and 2 ka ago, in the Disko coastal region.

Sedimentary Coastal Cliff Erosion in Greenland

“…This cliff is exposed to waves, both sea and swell waves coming over a relatively large embayment (Qeqertarsuup Tunua) with associated high‐energetic waves and wave run‐up during the ice‐free season. Similar settings were found in western Qeqertarsuaq (Souza et al., 2021).…”

“…at a decreasing rate (Rasch, 2000). Around 3 ka B.P., sea level reached the present level, and little is known about relative sea‐level changes since then (Rasch & Nielsen, 1994; Souza et al., 2021). GNSS measurements between 2006 and 2012 from the town of Qeqertarsuaq 25 km west of the study area show present‐day uplift of 7.7 (±0.4) mm y −1 (K. Nielsen et al., 2013).…”

Rock surface luminescence dating of prehistoric rock art from central Iberia

“…The resulting best‐fit parameter values (see Table S2 in the additional supporting information) were then inserted in the following model for one exposure event only: Equation () predicts the shape of the profiles at the time of deposition (Freiesleben et al, 2015; Sohbati et al, 2015). Following Rades et al (2018), we calculate the ratio of the predicted pre‐burial profiles (the dashed lines in Figure 4a–d) to the corresponding present‐day profiles (the solid lines in Figure 4a–d) and characterize a signal as well‐bleached if the pre‐ to post‐deposition signal ratio is < 5% (Souza et al, 2021). As shown in the insets to Figure 4 (a–d), the IR 50 pre‐ to post‐burial signal ratio in sample PE2.2 is < 5% up to a depth of 1.6 mm.…”

Supplemental Material: Rock surface luminescence dating of gravel determines the age of a glacial outburst megaflood, Glacial Lake Missoula, Montana, USA

“…After Souza et al (2021) we define a surface as well-bleached if the ratio of the predicted pre-burial profile to the observed post-burial profile is < 5%. The bottom side of C-3, the top surface of C-4, and both sides of C-1-11 are identified as well-bleached prior to burial (Fig.…”