British Cambrian to Ordovician Stratigraphy

Title page and preliminaries

A.W.A. Rushton Palaeontology Department, Natural History Museum, London, UK

A.W. Owen Division of Earth Sciences, University of Glasgow UK

R.M. Owens Department of Geology National Museum of Wales, Cardiff, UK

and J.K. Prigmore Equipoise Solutions Ltd, Croydon, UK

GCR Editor: L.P. Thomas

Published by the Joint Nature Conservation Committee. Monkstone House, City Road, Peterborough, PE1 1JY, UK

First edition 1999

© 1999 Joint Nature Conservation Committee

Typeset in 10/12pt Garamond ITC by JNCC. Printed in Great Britain by Hobbs the Printers Ltd. on 100 gsm Silverblade Matt. ISBN 1 86107 4727.

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Contents

The Authors

Acknowledgements

Access to the countryside

Preface

1 General introduction A.W.A. Rushton

Introduction

Scope

Overview

Palaeogeography

The significance of fossils

2 Introduction to Cambrian stratigraphy A.W.A. Rushton

History

Distribution

Boundaries of the Cambrian System

Divisions of the Cambrian

3 Cambrian of North Wales A.W.A. Rushton and I.K. Prigmore

Harlech Dome

Barmouth Hillside

Trwyn Carreg-y-tir

Porth Ceiriad

Afon Llafar

Nant y Graean and Nant Ganol

Rhobell-y-big and Foel Gron

Ogof Ddû (Rhiw-for-fawr)

Arfon area

Llyn Padarn

Moel Tryfan

Cwm Graianog

4 Cambrian of South Wales: St David's area J.K. Prigmore and A.W.A. Rushton

Introduction

St Non's Bay and Caerfai Bay

Trwyncynddeiriog

Porth-y-rhaw

Dwrhyd Pit

SoIva Harbour

Treffgarne Bridge

5 Cambrian rocks of England A.W.A. Rushton

Introduction

Ercall Quarry

Comley Quarry

Gullet Pass Pit

Boon's Quarry

Woodlands Quarry

Illing's Trenches, Hartshill Hayes

Mancetter Quarries

Charnwood Forest area, English Midlands

Stable Pit, Bradgate Park

The Brand

6 Introduction to Ordovician stratigraphy A.W.A. Rushton

History

Distribution

Boundaries of the Ordovician System

Divisions of the British Ordovician

7 Tremadoc Series in Wales and England J. K. Prigmore, A.W.A. Rushton and R.M. Owens

Introduction

Wales

Bryn-llin-fawr

Dol-cyn-afon

Tyn-llan

Pen Benar

Wern Road

Amnodd-bwll

Y Garth

Cwm Crymlyn

England

Cherme's Dingle

Sheinton Brook

Coundmoor Brook, Evenwood

Granham's Moor and Eastridge Wood, and Linley Big Wood

River Calder, Latter Barrow

8 Arenig to Ashgill in South Wales R.M. Owens

Introduction

Ogof Hên and Road Uchaf

Dan-lan-y-castell

Glan Pibwr

Allt Pen-y-Coed

Cwm yr Abbey

Pwlluog (Whitesand Bay)

Pontyfenni, Whitland

Llanfallteg Cutting

Abereiddi Bay

Abergwaun (Fishguard Old Harbour)

Ffairfâch Railway Cutting and Afon Cennen

Dynevor Park

Talar Wen

Meidrim Road section

Bryn-banc Quarry, Llan-mill

Mylet Road

Sholeshook

Robeston Wathen

Crûg Farm

Birdshill Quarry

Builth–Llandrindod Inlier

Howey Brook

Newmead

Bach-y-graig

Llanfawr Quarry

Gwern yfed fâch, Builth Road

9 Arenig to Ashgill of North Wales R.M. Owens, A.W. Owen and A.W.A. Rushton

Introduction

Bryn Glas Quarry

Hafotty Ffilltirgerig and Amnodd-wên

Trwyn-llêch-y-doll

Wîg

Nant y Gadwen

Afon Seiont

Llynnau Cregennen

Treiorwerth and Ty-hên

Nantannog Ravine

The Gynfor outliers

Fferam-uchaf

Trilobite Dingle

Nant Aberderfel

Gelli-grîn

Cadnant Cutting

Gwern-y-Brain

Cynwyd

Rhiwlas

Deganwy Quarries

Cwm Hirnant

10 Arenig to Caradoc of Shropshire A.W. Owen, R.M. Owens and A.W.A. Rushton

Introduction

Shelve area

Mytton Dingle and Snailbeach

Bergam Quarry

Shelve Church

Hope Valley

Betton Dingle

Meadowtown Quarry

Spywood and Aldress Jingles

Caradoc area

Coston Farm

Coundmoor Brook, Harnage

Hope Bowdler Road Section

Soudley Quarry

Marshwood

Onny River

11 Arenig to Ashgill of northern England A.W. Owen and A.W.A. Rushton

Introduction

Main Outcrop: Skiddaw Group

Trusmadoor

Blaze Bridge and Scawgill Quarry

Barf

Randel Crag

Outerside

Main Outcrop: Dent Group

Stile End

Ashgill. Quarry

Cross Fell Inlier

Harthwaite Sike

Pus Gill

Melmerby Road

Swindale Beck

Keisley Quarry

Cautley inliers

Sally Beck and River Rawthev

Backside Beck

Ecker Secker Beck

12 Scotland: Cambrian and Ordovician of the Hebridean Terrane J.K. Prigmore and A.W.A. Rushton

Introduction

Ductless and Balnakeil

An t-Sròn

Fuaran Mor

Loch Awe Quarry

Ord

13 Scotland: Cambrian and Ordovician of the Grampian Terrane and Highland Border Sub-terrane A.W.A. Rushton and A.W. Owen

Introduction

Leny Quarry

Lime Craig Quarry

14 Scotland: Ordovician of the Midland Valley Terrane A.W. Owen and A.W.A. Rushton

Introduction

Balcreuchan Port–Bennane Head

Aldons Quarry

Laggan Burn

Girvan foreshore

Craighead Quarry

South Threave

15 Scotland: Ordovician of the Southern Uplands Terrane A.W.A. Rushton and A.W. Owen

Introduction

Raven Gill

Corsewall Point

Morroch Bay and Port of Spittal Bay

Glenkiln Burn

Dob's Linn

References

Glossary

Fossil index

General index

The Authors

Dr A.W.A. Rushton, formerly with the British Geological Survey, Keyworth, Nottingham, NG12 5GG (present address: Department of Palaeontology, the Natural History Museum, London SW7 5BD).

Dr A.W. Owen, Division of Earth Sciences, Department of Geography, University of Glasgow, Lilybank Gardens, Glasgow 612 8QQ.

Dr R.M. Owens, Department of Geology National Museum of Wales, Cardiff CH 3NP

Dr J.K. Prigmore, formerly with the British Geological Survey, Keyworth, Nottingham NG12 566 (present address: Equipoise Solutions Ltd, 2B Rathbone Square, 28 Tantield Road Croydon, CR0 1BT).

Acknowledgements

The compilation of this volume has been very much a co-operative effort, and many colleagues have assisted with the project by giving us their advice and supplying information, either unpublished or in advance of publication. We have benefited particularly from the help of Dr A. J. Beckly, Dr R. Bettley, Dr P J. Brenchley, Dr J. N. Carney, Dr R. Cave, Mr A. F. Cook, Dr D. H. Evans, Dr T. P Fletcher, Dr M. Y. Huselbee, Dr J. K. Ingham, Dr R. Kennedy, Dr. M. Lewis, Mr R. J. Merriman, Dr. P Smith, Dr P Stone, Dr P. G. Tanner and Dr A. T. Thomas. Dr R. A. Fortey read the whole typescript and made very many valuable suggestions for its improvement. Adrian Rushton acknowledges the help of Mr S. P Tunnicliff (British Geological Survey) and Dr D. Lees (Natural History Museum) for technical assistance. The authors thank Dr Susanne White of Xipress for skilfully converting their rude sketches into finished drawings, and are grateful to many colleagues who lent illustrative matter, as listed below. The Council of Palaeontological Association freely gave us permission to reproduce figures used in Fossils of the Upper Ordovician (ed. Harper and Owen, 1996). Some of the most striking scenes are from copyright photographs in the Cambridge University Collection of Aerial Photographs, and are reproduced by the permission of the Curator of that collection. Many other photographs are from the extensive collection of photographs (some of which are of notable historical and archival value) held by the British Geological Survey. They are reproduced by kind permission of the Director, British Geological Survey (0 NERC, all rights reserved; IRP/23–27). We are particularly grateful to Neil Ellis, Neil Cousins and Anita Carter of JNCC for their patience and assiduity during editorial and production work on this volume; we also thank Larry Thomas, GCR Editor.

Photographs of fossils

Many contributors supplied photographs of fossils for this book, and the authors are glad to acknowledge their assistance below.

Details of localities, museum numbers etc. of the figured fossils are given, together with the names of individuals who supplied prints. Unattributed photographs are from the authors' collections. National grid references are in square brackets. The repositories most commonly cited are abbreviated as follows: BGS = British Geological Survey, Keyworth; BU = Lapworth Museum, University of Birmingham; GLAHM = Hunterian Museum, Glasgow; NHM = Natural History Museum, London; NMW = National Museum of Wales, Cardiff; SM = Sedgwick Museum, Cambridge.

(Figure 3.8) (a, h) Ptychagnostus punctuosus, cephalon BGS RU6441, pygidium, RU6440, from the Clogau Formation (punctuosus Zone), Afon Llafar [SH 7342 3673]. (c) Olenus micrurus, cast of BGS RU4317, Maentwrog Formation (Olenus Zone, cataractes Subzone), Nant Ganol [SH 7659 3285]. (d) Peltura scarabaeoides scarabaeoides, BGS RU4762, Dolgellau Formation (scarabaeoides Zone, bisulcata Subzone), Rhobell-y-big [SH 7859 2845].

(Figure 4.8) (a) Onymagnostus davidis, NMW 80.346.787a, parvifrons Zone, Solva Harbour [SM 8014 2411]. (b) Eodiscus punctatus, cast of NMW 80.34G.333b, parvifrons Zone, Porth-y-rhaw [SM 7849 2426]. (c) Bailiella lyelli, cast of NMW 80.34G.841, Trwyncynddeiriog [SM 7468 2382]. (d), Plutonides hicksii, cast of NMW 80.346.881b, fissus Zone, Dwrhyd [SM 7913 2476]. All photos by Dr M. Lewis.

(Figure 5.2) (a, h) Mobergella cf. radiolata BGS RU3870, 3871, basal Comley Sandstone (Tommotian), Ercall Quarry [SJ 6445 0955] (c) Tomagnostus fissus, cast of BGS GSM57850, Abbey Shales (fissus Zone) Hartshill Hayes [SP 3240 9425]. (d) Olenus gibbosus, SM A59066a, Outwoods Shales (Olenus Zone, gibbosus Subzone), Purley Quarry [SP 3051 9606].

(Figure 7.5) Rhabdinopora flabelliformis cf. parabola, Legrand collection W 98a1, Dol-cyn-afon Formation, basal Tremadoc, Bryn-llin-fawr [SH 7906 30701]. Drawing supplied by Dr P Legrand.

(Figure 7.7) Tremadoc fossils from the site at Wern. (a) Niobella homfrayi smithi, NMW 97.57G.1, roadside east of Wern [SH 5442 3965]. Photo by Mr J. Wild. (b) Rhabdinopora flabelliformis socialis, BGS GSM37500, lower Tremadoc, Cefn Cyfanedd near [SH 544 394].

(Figure 7.9) Fossils from Tremadoc sites. (a) Adelograptus tenellus NMW 77.26.17, tenellus Zone, Cwm Crymlyn [SN 3477 1735]. (b) Shumardia (Conophrys) salopiensis, cast of BGS Zs 6188, Shineton Shales (salopiensis Zone), Sheinton Brook [SJ 6075 0372]. (c) Beyrichona triceps, BGS RX2277, Arenaceous Beds of the Shineton Shales (salopiensis Zonc), Coundmoor Brook, Evenwood [SJ 5549 0152]; photo (c) supplied by Dr Mark Williams.

(Figure 8.4) Fossils from Arenig and Llanvirn sites in South Wales. (a) Falcatodonta costata NMW 78.17G.976, from the Bolhaul Member (Moridunian) at Dan-lan-y-castell I [SN 3640 1639]; photo supplied by Dr. J. C. W Cope. (b) Merlinia selwynii NHM It14033, Pibwr Member (Moridunian), Glan Pibwr [SN 4183 1795]. (c) Portolieldia punctata NHM It 14001, Cwm yr Abbey Member (Moridunian), Cwm yr Abbey [SN 5011 1950]. (d, e) Hyolithid conch and operculum, NMW 84.17G.332a, and Bergamia rushtoni NMW 21.306.64a, from the Pontyfenni Formation (Fennian), Pontyfenni [SN 239 169]. (f) Undulograptus austrodentatus, NHM Q5802, Llanfallteg Formation (basal Abereiddian), Llanfallteg cutting [SN 1574 2019].

(Figure 8.12) Didymograptus murchisoni, NMW 27.110.G404, Caerhys Shale Formation (murchisoni Zone), Abereiddi Bay [SM 796 300].

(Figure 8.18) Marrolithoides simplex, NMW 83.31G.219, Talar Wen, Bethlehem [SN 7012 2660].

(Figure 8.23) (a) Normalograptus sp., BGS JZ6424, Mydrim Shales at Pengawse Hill [SN 1698 1599]; photo supplied by Dr J. A. Zalasiewicz. (b) Kuckersella borealis, NHM PD8236a, Slade and Redhill Beds, Pengawse Hill [SN 164 170]; photo by Dr C. J. Bugler. (c) Eucystis pentax, cast of SM A31814, Sholeshook Limestone, Sholeshook about [SM 967 171]; photo by Prof C. R. C. Paul. (d) Archegocystis stellulifera cast of BGS GSM102374, locality as for (c): photo by Prof C. R. C. Paul. (e) Atractopyge verrucosa, Oxford University Museum B106, holotype, presumed to he from the Crûg Limestone, Crûg [SN 627 2311.

(Figure 9.9) Merlinia selwynii, NHM It21220, Moridunian, Nant y Gadwen [SH 2120 2680]. Isograptus caduceus gibberulus, BGS AW24, west side of Nant y Gadwen, adjacent to old level about [SH 211 267].

(Figure 9.15) Salterolithus caractaci paucus, SM A46414 Trilobite Dingle Formation, Trilobite Dingle [SJ 221 080].

(Figure 9.18) Dorsal valve of Dolerorthis duftonensis prolixa, BGS GSM103307, Gelli-grîn [SH 944 339].

(Figure 9.21) Gravicalymene arcuata, latex cast of NMW 84.86.51a, Ddolhir Formation, Cynwyd about [SJ 092 399].

(Figure 9.22) (a, b) Vellamo sp., BGS GSM11357 and BGS GSM11316, Cynwyd about [SJ 092 399]. (c, d) Tetraeucystis munita, BGS GSM74229, 102382, Rhiwlas Limestone, Rhiwlas [SH 923 372]; (c) and (d) by Prof C. R. C. Paul. (e–g) casts from loose block of Hirnant Limestone, Aber Hirnant [SH 9529 2995]. (e) Eostropheodonta hirnantensis, BGS RU9805. (I) Hirnantia sagittifera, RU9804. (g) Plectothyrella crassicostis, BGS RU9806.

(Figure 10.12) (a, b) Harknessella vespertilio NHM BC 56809, 56808 Coston. (c, d) Dinorthis flabellulum NHM BB 30641, 30644 Coston. (c, Heterorthis alternata NHM BB 28903, 28905, Alternata Limestone, Soudley. Photos by Prof. A. I). Wright.

(Figure 10.20) Onnia gracilis, NHM In49032, Wistanstow Member, Acton Scott Formation (Streffordian, Onnian Substage), Onny River [SO 4255 8540].

(Figure 11.3) Araneograptus inurrayi, BGS RX3099, top of Watch Hill Formation (murrayi Zone), Trusmadoor [NY 2782 3360].

(Figure 11.10) (a, h) Trematis corona, SM A32864, Caradoc (Longvillian Substage), Pus Gill about [NY 704 260]. (c, d) Tretaspis moeldenensis, BGS PC4604, Ashgill (Pusgillian Stage), Pus Gill [NY 6973 2569].

(Figure 11.17) (a) Sphaerocoryphe kingi, GLAHM HUD7.6a, Cautley Mudstones (Zone 6), loc.W12, Wandale Beck [SD 7099 9851]. (b, c) Mucronaspis mucronata, NMW.99.39G.1and GLAHM HUD10.4, Ashgill Shale Formation (Zone 8), Fairy Gill (loc.T16) [SD 7056 9614].

(Figure 13.2) Pagetiid cephala BGS 714078, Zf3873, 714675, pygidium BGS 713897, Leny Limestone, Leny Quarry [NN 6153 0984]. Photos supplied by Dr J. W. Cowie.

(Figure 14.4) Tetragraptus approximates, Grant Institute of Geology, Edinburgh, no. 47 503, Balcreuchan Group, unit 1 of Figure 14.3 (basal Bendigonian, lower Arenig), Balcreuchan Port [NX 0968 8750].

(Figure 14.13) Fossils from the Craighead Limestone, Craighead Quarry. (a, b) Lyopora favosa, longitudinal and transverse sections of SM A6382 (photo by Dr D. E. White). (c, d) Rostricellula lapworthi, no.NHM BB 15038 (photo by Prof. A. D. Wright).

(Figure 14.14) Fossils from the Starfish Beds, South Threave around [NS 251 038]. (a) Pygecystis quadrates, NHM E23298 (photo by Prof. C. R. C. Paul). (b) Mesopalaeaster primus, NHM E 52441a (photo by Mr D. Lewis). (c) Scotiaecystis curvata, cast of NHM E 28652a (photo by Dr R. P. S. Jefferies). (d) Toxochasmops bisseti, GLAHM A4133 (photo by Dr J.K. Ingham) (Figured by Owen and Ingham in Harper and Owen 1996, p1.30, fig. 7).

(Figure 15.7) Graptolites from Glenkiln Burn (a) and Dob's Linn (b-h). All figures x2. (a) Nemagraptus gracilis (Hall), gracilis Zone. BU 1059. (b) Dicellograptus inorrisi Hopkinson, SM A19399, clinganilinearis zones. SM A19399. (c) Dicranograptus ziczac Lapworth, peltifer Zone. BU 1133. (d) Climacograptus wilsoni Lapworth, wilsoni Zone. BU 1172. (e) Dicellograptus anceps (Nicholson), anceps Zone. (Figured by Williams in Harper and Owen 1996, p1. 35, fig. 10). (1) Lasiograptus harknessi (Nicholson), wilsoni Zone. (Figured by Williams in Harper and Owen 1996, pl. 35, fig. 4). (g) Climacograptus supernus Elles and Wood, anceps Zone. GLAHM C13384/2. (h) Orthograptus calcaratus (Lapworth) sensu lato, clinganilinearis zones. GLAHM C14286/1. All photos by Prof. S. H. Williams.

Access to the countryside

This volume is not intended for use as a field guide. The description or mention of any site should not be taken as an indication that access to a site is open or that a right of way exists. Most sites described are in private ownership, and their inclusion herein is solely for the purpose of justifying their conservation. Their description or appearance on a map in this work should in no way be construed as an invitation to visit. Prior consent for visits should always he obtained from the landowner and/or occupier.

Information on conservation matters, including site ownership, relating to Sites of Special Scientific Interest (SSSIs) or National Nature Reserves (NNRs) in particular counties or districts may he obtained from the relevant country conservation agency headquarters listed below:

Countryside Council for Wales, Plas Penrhos, Ffordd Penrhos, Bangor, Gwynedd 1157 2LQ.

English Nature, Northminster House, Peterborough PE1 1 UA.

Scottish Natural Heritage, 12 Hope Terrace, Edinburgh El-19 2AS.

Preface

Britain is singularly rich in geological sites of scientific importance, not least because so many of the leading figures in geology in its early days developed their concepts on home turf These geological exposures — some of them rather modest — generated ideas that spread across Europe in the 19th century and around the world in the 20th. This is particularly true of the Lower Palaeozoic, where the discrimination of subdivisions of geological time was made on the basis of the strata cropping out in Wales and the Welsh Borderlands, the Lake District and central Scotland. 'Cambrian' and 'Ordovician' can be understood equally in Novosibirsk and Nantucket, as can many of the British subdivisions of these systems. The great men of geology in its formative years — Sedgwick, Murchison, Lapworth, Peach, Horne — have left their signatures on our geological landscape for all time. It would be a proper employment of an overused word to describe this as our geological heritage. Much of the narrative of geological time was written in the 'language' of fossils, and sites that have yielded useful or famous fossils are no less part of our legacy than the localities where formations or unconformities were recognized. Our great museums house the fruits of more than 150 years' collecting endeavour, but the 'ground truth' remains the localities where the original discoveries were made. Nor is this just a matter of history; for classic sites frequently demand re-investigation when new scientific questions arise. The geological past is not preservable in a kind of 'temporal aspic' — instead it is continually under review. Hence many sites of scientific interest relate to discoveries made since the turn of the century, and even within the last few years. Adrian Rushton and his colleagues have made an invaluable inventory of geologically significant sites in Cambrian and Ordovician strata in Britain: now for the first time we actually know what constitutes our geological heritage. The sites range in size from sea cliffs to scrapings. Some sites have been referred to only once in the literature; others are classic localities, a visit to which is considered a sine qua non for a complete geological education. All are important. In many respects this is sacred ground, and a publication that heightens public awareness is timely and welcome. Both the scientific and lay communities need to know that what may seem to be no more than an abandoned quarry may have played an important part in developing crucial scientific concepts. Documentation helps secure the respect for this kind of site that locations harbouring rare animals or plants already enjoy. Not least, this hook can provide the basis for a rational conservation policy.

Richard Fortey Spring 1999

References