NERC National Environmental Isotope Facility project: Constraining the onset of northern hemisphere glaciations onshore Iceland by argon dating lavas from the Tjörnes sequence

Description

The Tjörnes sequence (TS), of onshore Iceland (Figs. 1a, 1b), holds the potential to be a globally important outcrop for assessing the timing of and controls on the intensification of the Northern Hemisphere Glaciation (iNHG; c. 2.7 Ma). In this project, we aim to constrain: (a) the onset age of lowland glaciation in Iceland, and (b) the glacial/interglacial cyclicity shortly after this onset, by generating new Ar-Ar ages from basaltic lavas intercalated within Plio-Pleistocene diamictites of the TS, and integrating them with existing high quality palaeomagnetic data. We build on a successful collaboration with Dan Barfod at NEIF (NIGL proposal: IP-1855-1118) tied to two NERC-funded PhD projects (NE/M00578X/1 completed, NE/S007350/1 ongoing) that have already Ar-Ar dated the lower TS, and sampled the key lavas in the upper TS that we propose to analyse here. Our previous work (Hall et al., 2023, https://doi. org/10.1029/2022PA004539) demonstrated that the legacy 1970s K-Ar ages underpinning published TS age models are unreliable; we proved that establishment of Pacific-to-Atlantic marine connection via the Bering Strait happened 1.3 My earlier than previously thought, and did not directly cause the iNHG. Importantly, our findings imply that the onset of lowland glaciation recorded in the lower Breiðavík Group (BG) may be up to 0.5 My older than previously thought. We will test this proposition by Ar-Ar dating of 8 already-acquired basaltic lava samples intercalated above and below the base of the BG (fEC value £38,626). The new data will also constrain the ages of six diamictites that record the lowermost cycles of glacial advance and retreat within the lower BG. This work will complete our radiometric/palaeomagnetic age model for the entire TS (high quality Ar-Ar ages already exist for the uppermost BG), adding value to this important archive of past glaciations and enabling new insights into the timing of and the mechanism(s) that drove the iNHG. As before, we aim to publish our findings in an appropriate journal, such as Paleoceanography and Paleoclimatology, upon completion.

Period	1 Jan 2023 → 31 Dec 2025
Held at	Earth and Environmental Sciences
Degree of Recognition	International