Geology topics

Jenifer Amy Leidelmeijer

Publications and source records attributed to Jenifer Amy Leidelmeijer.

2 recordsLinked to original sources

USGS2026

The influence of surface crust dynamics and sediment availability on aeolian dust emission from ephemeral lake beds: Evidence from Etosha Pan, Namibia

Ephemeral lake beds (playas) are major global sources of atmospheric mineral dust, yet controls governing sediment availability and emission potential at fine spatial scales remain poorly constrained. This study presents the first in situ measurements of surface erodibility and potential PM 10 emission fluxes from Etosha Pan, Namibia. Threshold shear velocities and PM 10 emission fluxes were quantified using a Portable In-Situ Wind ERosion Laboratory (PI-SWERL) across five surface types spanning highly emissive hotspots to non-emissive consolidated salt crusts. Threshold shear velocities ranged from 0.38 m s −1 on deflated clay-rich surfaces to >1.14 m s −1 on recently inundated or cemented salt crusts, and PM 10 fluxes at u ⁎ = 0.56 m s −1 varied by more than three orders of magnitude. Emissions were highest where degraded efflorescent crusts exposed fine sediment, whereas halite-rich crusts exhibited greater mechanical strength and resisted wind erosion despite low surface moisture. X-ray diffraction analyses confirmed spatial variability in evaporite and silicate mineral assemblages, with halite abundance inversely related to dust emission potential. Antecedent hydrological conditions regulated sediment availability. Moderate wetting–drying cycles promoted weak, emissive crusts, whilst persistently wet or dry conditions were associated with continuous, resistant crusts and reduced emissions. Distinct emission regimes arose from differences in crust failure and saltation feedbacks, highlighting sub-landform-scale variability in dust sources. Crust dynamism, driven by spatial variability in surface conditions and antecedent hydrological regime, is identified as a key, under-represented control on dust emission. The relationships quantified here provide new empirical constraints for improving the representation of sediment availability in global dust modelling.

Etosha Pan↗

USGS2024

Inbuilt age, residence time, and inherited age from radiocarbon dates of modern fires and late Holocene deposits, Western Transverse Ranges, California

Radiocarbon dates of sedimentary deposits include the elapsed time between formation of the organic material and deposition at the sample site, known as the inherited age. Long inherited ages reduce the accuracy of estimates of the timing of depositional events used to infer paleoclimate change, fire histories, and paleoearthquake timing. An inherited age distribution combines the inbuilt age distribution, which reflects the age composition of the vegetation of the source area, and the residence time distribution, which includes transport and interim storage prior to final deposition. Differentiating residence time and inbuilt age is difficult given typical dispersion of ages in a sedimentary deposit. We address this problem by comparing charcoal dates from two modern fires in southern California, the 2020 Bobcat and the 2013 Grand Fire, with a well-dated late Holocene deposit in the Pallett Creek watershed. The modern fire deposits have negligible transport time (<1 year), and 56 radiocarbon dates indicate a median age of 25 years (300-year 95% range) provides an estimate of inbuilt age for the San Gabriel Mountains. The inherited age calculated from the paleodeposits is older with a median age of ~90 years and has a positive skew (850-year 95% range). A modeled inherited age, calculated by applying the pre-bomb radiocarbon calibration curve to the modern fire age distribution, is shorter than the paleodeposit inherited age by only 21 years, indicating samples with long residence times are not common in the deposit. Comparison of inherited ages calculated from organic-rich and clastic paleodeposits indicate a slight facies dependence that may reflect longer residence time in clastic deposits. The results provide insight into the transport of charcoal through the landscape are useful for refining estimates of past environmental and tectonic events.

California↗