Bird’s-eye view of an Ediacaran subglacial landscape

Abstract

Depositional evidence for glaciation (dropstones, diamictites) is common in Neoproterozoic strata, and often debated, but erosional evidence (e.g., unconformities cut directly by ice) is rare. Only two such unconformities are known to have been well preserved globally from the Ediacaran Period (in western Australia and central China). This paper provides the first full description of a spectacular subglacial landscape carved beneath ice masses in the Shimengou area of central China, with classical subglacial bed forms including general faceted forms, müschelbruche, cavetto, spindle forms, and striations that testify to an abundance of meltwater during subglacial erosion. These features were produced during the southward, somewhat sinuous, flow of a temperate to polythermal ice mass.

The sedimentological death mask of a dying glacier

“…Using Agisoft Metashape version 1.6.3, 913 photographs were aligned, a dense point cloud generated, and both a digital elevation model (DEM, resolution 9.65 cm) and orthomosaic were produced. Following the methodology of Le Heron et al (2019), these DEM and orthomosaic data were imported to QGIS 3.12. The orthomosaic was made semi‐transparent, layered on top of the DEM, and a ‘multiply’ blending mode algorithm applied, with 20% brightness and 20% contrast additionally applied.…”

“…At a high angle to these foliations, flow-transverse ogives are also recognised, originating from the ice fall at the F I G U R E 1 Uncrewed aerial vehicle (UAV) data and sediment landform assemblage-glaciological map of the Pasterze Glacier on 12 July 2021. The UAV data at the top of the image comprise a semi-transparent orthomosaic superimposed upon a digital elevation model following the methodology of Le Heron et al (2019). Small camera symbols signify the direction from which photographs were taken, with the figure numbers in this paper indicated.…”

Palaeogeography and provenance transition of Precambrian–Cambrian unconformity at the southern margin of the North China Craton

“…We carried out sedimentary petrological, trace elements, and detrital zircon geochronological analysis on the Luoquan and Xinji formations at the southern margin of the NCC and analysed the environment and provenance of the Precambrian–Cambrian unconformity in western Henan province. The Luoquan Formation is composed of glacial and glaciowater facies (Chen et al, 2020; Guan et al, 1986; Le Heron et al, 2019; Li, Vandyk, et al, 2020; Zhang & Zheng, 2019; Zhang, Zheng, & Liu, 2019), and the Xinji Formation is composed of the shallow sea to coastal deposits (Zheng et al, 2019). According to the analysis results of the Luoquan and Xinji formations, the sedimentary petrology provides evidence for a transition in the depositional environment of the Precambrian–Cambrian unconformity between the Luoquan Formation and Xinji Formation.…”

Desequilibrio del ciclo del azufre y cambio ambiental durante el Período Ediacárico

“…These biological radiations took place after two prolonged episodes of global glaciation during the Cryogenian Period (ca.715-660 and ca. 650-635 Ma), and were accompanied by further short-lived (ca.580 Ma and ca.550 Ma) regional ice ages, interspersed with warmer intervals (Condon et al, 2005;Pu et al, 2016;Le Heron et al, 2019). The world's oceans also became episodically more oxygenated during the Ediacaran with the extent of oxygenated seafloor reaching near-modern levels at times by the early Cambrian (Chen et al, 2015).…”