Abstracted/indexed

Orakei Basin, a former maar lake in Auckland, New Zealand provides an outstanding sediment record over the last ca. 130,000 years but an age model is required to allow the reconstruction of climate change and volcanic eruptions contained in the sequence. To construct a relationship between depth in the sediment core and age of deposition, we combined tephrochronology, radiocarbon dating, luminescence dating, and the relative intensity of the paleomagnetic field in a Bayesian age-depth model.

This contribution present a new reference material, ASH-15 flowstone with an age of 2.965 ± 0.011 Ma (2σ), to be used for in-situ U-Pb dating of carbonate material. The new age analyses include the use of the EARTHTIME isotopic tracers and a large number of sub-samples (n = 36) with small aliquots (1–7 mg) each that are more representative of laser-ablation spot analysis. The new results could improve the propagated uncertainties on the final age with a minimal value of 0.4 %.

Unetched and etched apatites of five samples were dated by U–Pb with laser ablation inductively coupled plasma mass spectrometry. Our experiment demonstrates that the etching, needed for the apatite fission track dating, has no important effect on the obtaining of U–Pb ages; and therefore, the laser ablation-based technique can be used for apatite fission track and U–Pb double dating.

We characterize three natural carbonate samples with elevated uranium/lead (U/Pb) ratios to demonstrate techniques for characterizing carbonates for U/Pb dating. With the rapidly accelerating application of laser ablation analyses, there is a great need for well-characterized standards. The three samples we describe have good potential as standards. In addition to U/Pb data, we present strontium (Sr) isotope analyses to demonstrate that these could be dual standards for U/Pb and Sr isotopes.

This manuscript describes a new method of U-Pb calcite dating by laser ablation using a new detector array that allows for higher precision and lower limits of detection. This method thereby increases the likelihood of success in dating any given sample. I also explore how concentration of U and Pb, laser spot size and repetition rate, and mass spectrometer selection influence the final precision on the age, as to make recommendations for those interested in dating such samples.

Luminescence properties of samples from the northern foreland of the Swiss Alps are assessed. While signal loss is observed for the feldspar and polymineral, correction leads to feldspar ages that are consistent with those derived from quartz. In general, ages of the coarse-grained quartz and feldspar as well as the fine-grained polymineral fractions are in agreement. Ages indicate sedimentation of ca. 17 m during MIS 6 with a rapid transition from a lacustrine to a colluvial landscape.

Potassium-based geochronology, including the ⁴⁰Ar/³⁹Ar and K-Ar methods, provides critical constraints on the timing and duration of many events and processes in earth history. These methods assume that a key parameter, the fraction of potassium with a mass of 40, does not vary in some relevant materials. Some recent work has identified some variability in these materials. This work examines the effects of this variability on calculated K-Ar and ⁴⁰Ar/³⁹Ar ages.

The North American Varve Chronology is a sequence of 5659 annual sedimentary layers that were deposited in proglacial lakes adjacent to the retreating Laurentide Ice Sheet ca. 12,500 - 18,200 years ago. We attempt to synchronize this record with Greenland ice core and other climate records that cover the same time period by detecting variations in global fallout of atmospherically-produced beryllium-10 in NAVC sediments.

We investigate the timing and rate of retreat for 3 alpine glaciers in the S. Rocky Mountains to test whether they followed the pattern of global climate change or were majorly influenced by regional forcing mechanisms. We find that the latter is most likely the case for these glaciers. Our conclusions are based on a new ¹⁰Be chronology of alpine glacier retreat. We quantify retreat rates for each valley using the BACON program in R, which may be of interest for the audience of Geochronology.

We compare two published U-Pb and ⁴⁰Ar/³⁹Ar geochronologic datasets used to produce different eruption rate models for the Deccan Traps LIP. We conclude that differences in eruption rates arise not from inaccuracy of dates, but instead from the way the data were presented. Applying the same statistical approach to each dataset, the resulting models agree well, but the higher precision U-Pb dataset generates a more nuanced eruption model that is untestable with the lower precision ⁴⁰Ar/³⁹Ar data.