Depositional framework of the Gwna Group mélanges of Anglesey and North-West Wales, UK

Dartnall, Rosemary ORCID: https://orcid.org/0000-0001-7643-3441 (2019). Depositional framework of the Gwna Group mélanges of Anglesey and North-West Wales, UK. University of Birmingham. Ph.D.

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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.
Detailed 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.
The Gwna Group is emphatically redefined as a sedimentary, gravity flow deposit;
• Four basal unconformities demonstrate sedimentary superposition.
• Pre-Sturtian molar tooth microspar is described in abiotic Neoproterozoic dolo-limestone clasts within the Gwna Group – the first account in Britain.
• A regionally ubiquitous, internally conformable coherent sedimentary system of three main lithofacies is interbedded within repeated megacycles.
• The sediments record early Palaeozoic passive margin evolution.
New 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.

Type of Work:	Thesis (Doctorates > Ph.D.)
Award Type:	Doctorates > Ph.D.
Supervisor(s):	Supervisor(s) Email ORCID Fairchild, Ian J. UNSPECIFIED orcid.org/0000-0003-4822-2895 Smith, M. Paul UNSPECIFIED orcid.org/0000-0002-5141-1577 Schofield, David I. UNSPECIFIED orcid.org/0000-0002-2669-5627 Wheeley, James R. UNSPECIFIED orcid.org/0000-0001-7861-8108
Licence:	All rights reserved
College/Faculty:	Colleges (2008 onwards) > College of Life & Environmental Sciences
School or Department:	School of Geography, Earth and Environmental Sciences
Funders:	Natural Environment Research Council, Other
Other Funders:	British Sedimentological Research Group, Gill Harwood Memorial Fund
Subjects:	Q Science > QE Geology
URI:	http://etheses.bham.ac.uk/id/eprint/9310

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