Shocked quartz in polymict impact breccia from the Upper Cretaceous Yallalie impact structure in Western Australia

Abstract

Yallalie is a ~12 km diameter circular structure located ~200 km north of Perth, Australia. Previous studies have proposed that the buried structure is a complex impact crater based on geophysical data. Allochthonous breccia exposed near the structure has previously been interpreted as proximal impact ejecta; however, no diagnostic indicators of shock metamorphism have been found. Here we report multiple (27) shocked quartz grains containing planar fractures (PFs) and planar deformation features (PDFs) in the breccia. The PFs occur in up to five sets per grain, while the PDFs occur in up to four sets per grain. Universal stage measurements of all 27 shocked quartz grains confirms that the planar microstructures occur in known crystallographic orientations in quartz corresponding to shock compression from 5 to 20 GPa. Proximity to the buried structure (~4 km) and occurrence of shocked quartz indicates that the breccia represents either primary or reworked ejecta. Ejecta distribution simulated using iSALE hydrocode predicts the same distribution of shock levels at the site as those found in the breccia, which supports a primary ejecta interpretation, although local reworking cannot be excluded. The Yallalie impact event is stratigraphically constrained to have occurred in the interval from 89.8 to 83.6 Ma based on the occurrence of Coniacian clasts in the breccia and undisturbed overlying Santonian to Campanian sedimentary rocks. Yallalie is thus the first confirmed Upper Cretaceous impact structure in Australia.

Seismic Efficiency for Simple Crater Formation in the Martian Top Crust Analog

“…The iSALE-2D code (Collins et al, 2004(Collins et al, , 2005Wünnemann et al, 2006) is a multirheology, multimaterial extension to the finite-difference hydrocode (Amsden et al, 1980). The iSALE shock physics code is validated against laboratory experiments (Güldemeister & Wünnemann, 2017;Wójcicka et al, 2020) at low-and high-strain rates, as well as other impact simulation codes (Pierazzo et al, 2008) and has been widely used to numerically simulate terrestrial impact crater formation (e.g., Collins et al, 2005;Cox et al, 2019;Wünnemann et al, 2006).…”

Identification of the ejecta deposit formed by the Australasian Tektite Event at Huai Om, northeastern Thailand

“…According to the data of Cox et al. (2019) and Reimold et al. (2019), quartz grains with single sets of PDFs oriented in π{102} are present in porous sandstone targets in Yallalie crater and Cerro do Jarau crater, although the number of the measurement was small (only nine sets in six grains and ten sets in nine grains were measured with respect to their orientation, respectively).…”

The variation and visualisation of elastic anisotropy in rock-forming minerals

“…Also shown is a 3D representation surface of Δs 11 ', which emphasises the anisotropy of favoured directions for Dauphiné twins in α-quartz. The significance of Dauphiné twinning in quartz has recently been described for sandstones compacted during diagenesis (Mørk and Moen, 2007), deformed in fault damage zones (Olierook et al, 2014), and deformed by meteorite impact (Wenk et al, 2011;Timms et al, 2019;Cox et al, 2019), and granitoid protomylonites (Menegon et al, 2011). In all cases, Dauphiné twins can be used to infer palaeostresses from deformed microstructures.…”