Year: 2019
Type: dissertation
Abstract: The Gwna Group contains chaotic, disrupted mélange of unknown genetic history. Publications that speculate on Gwna Group formation often cast the mélange in a pivotal role: the regional co-location of blueschist and greenschist with the Gwna Group has inspired hypotheses of tectonic mélange formation during accretionary orogen subduction, yet no specific published studies of the Gwna Group exist. \nDetailed field study of the Gwna Group has distinguished primary features from those overprinted by later events, over four defined outcrop belts within which combined stratigraphic relationships are determined. \nThe Gwna Group is emphatically redefined as a sedimentary, gravity flow deposit; \n• Four basal unconformities demonstrate sedimentary superposition. \n• Pre-Sturtian molar tooth microspar is described in abiotic Neoproterozoic dolo-limestone clasts within the Gwna Group – the first account in Britain. \n• A regionally ubiquitous, internally conformable coherent sedimentary system of three main lithofacies is interbedded within repeated megacycles. \n• The sediments record early Palaeozoic passive margin evolution. \nNew U-Pb zircon investigations and meta-analysis of published ages show the Gwna Group began to accumulate near the Gondwanan margin during early Cambrian rifting and crucially demonstrate no genetic relationship with the Penmynydd Zone as Gwna Group deposition followed exhumation of the blueschists at 560 - 550 Ma.
Author: Rosemary Dartnall
Language: English
Subfield: Earth-Surface Processes
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2975629002