An Ediacaran glacial deposit in southern margin of the North China Craton: The Luoquan Formation—sedimentology, geochronology and provenance

Abstract

The end of the Neoproterozoic global ice age has promoted the evolution of the Earth's surface system and initiated the ‘Great Explosion of Life’. Glaciation deposits provide valuable insights into the extreme climate conditions. In the southern margin of the North China Craton (NCC), an Ediacaran glacial deposit named ‘Luoquan Formation’ has been recently described in Luonan County, Shaanxi Province. It has significant characteristics of dark grey and black glacial deposits. Through extensive research in sedimentology, geochemistry and geochronology, the glacial sedimentary evolution sequence of the Luoquan Formation has been established. This research also help to define the age of the formation and reveal its provenance and sedimentary environment. The study reveals that four lithofacies associations were identified in the Luoquan Formation: diamictites, carbonates, dropstone-bearing rock and black shale. The Luoquan Formation has experienced three cycles of glacial advance–retreat. Sedimentological evidence suggests that the sedimentary environments of the Luoquan Formation evolved from subglacial (diamictite) to intertidal, then to intertidal lagoon, or from subglacial deposits to shoreface (inner shelf, subtidal), then to deep water basin and fine-grained turbidite and ice-rafting. The age of the Luoquan Formation is estimated to be 562–550 Ma constrained by indirect chronological and paleontological data, maybe representing an Upper Ediacaran glaciation that occurred later than the Gaskiers glaciation. The overall age profile of detrital zircons from the Luoquan Formation can be divided into six groups, ranging from 1.1 to 1.6, 1.85 to 1.95, ~2.1, ~2.3, ~2.5 and 2.65 to 2.9 Ga. These age groups are consistent with the Archean to Meso-Neoproterozoic magmatic–tectonic events in the southern margin of NCC, indicating they are ascribed to an origination directly from the southern margin of NCC. The Luoquan Formation exhibits the characteristics of isochronous and different sedimentary facies, with the glacial front moving from north to south. The discovery of Luoquan Formation in Lianshuigou section not only reflects the important significance of the restoration and reconstruction of the Ediacaran ice age, paleoenvironment and palaeogeography of the NCC but also provides significant evidence to support the further subdivision and correlation within the Ediacaran glacial deposits globally.