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A new Early Silurian turbidite system in Central Wales: insights into eustatic and tectonic controls on deposition in the southern Welsh Basin

Published online by Cambridge University Press:  10 September 2008

D. I. SCHOFIELD ,
J. R. DAVIES ,
R. A. WATERS ,
M. WILLIAMS  and
D. WILSON
D. I. SCHOFIELD*
Affiliation:
British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottinghamshire, NG12 5GG, UK
J. R. DAVIES
Affiliation:
British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottinghamshire, NG12 5GG, UK
R. A. WATERS
Affiliation:
Department of Geology, National Museum of Wales, Cathays Park, Cardiff, CF10 3NP, UK
M. WILLIAMS
Affiliation:
Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, UK
D. WILSON
Affiliation:
British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottinghamshire, NG12 5GG, UK
*
†Author for correspondence: [email protected]
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Abstract

The newly recognized Nant Brianne turbidite system was a focus of laterally supplied coarse-grade sediment deposition that, along with the Caban–Ystrad Meurig system, punctuated late Hirnantian to early Telychian, mudstone-dominated slope apron deposition along the SE margin of the southern Welsh Basin. Geological mapping coupled with detailed biostratigraphy enable the depositional influence of sea-floor topography, an active Llyn Brianne Fault and eustatic sea-level changes to be tracked. The latter may represent ‘far field’ effects relating to the retreat and advance of contemporary Gondwanan ice sheets. Slope apron mudstone facies reveal a strong response to high order eustatic events; however, the response of contemporary, easterly sourced, coarse-grade turbidite systems was more complex, with some periods of increased sand and gravel input coinciding with times of rising global sea level. These anomalous relationships are explained by invoking a series of smaller-scale movements in marine base level. It was the interaction of these lower order events with the main eustatic cycles that appears to have been the primary control on sand and gravel input to the Welsh Basin. An early Telychian expansion of the Nant Brianne turbidite system records a marked increase in tectonically generated sediment at a time of palaeo-plate collision between Baltica/Avalonia and Laurentia before intra- and peri-basinal faulting led to its abandonment as a supply path to the basin centre.

Keywords

SilurianLlandoveryWalesturbidite
Type
Original Article
Information
Geological Magazine , Volume 146 , Issue 1 , January 2009 , pp. 121 - 132
Copyright
Copyright © Cambridge University Press 2008

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