Tenby Field Trip 5 9 May 2017 Area Map Geological Overview South - PowerPoint PPT Presentation

Tenby Field Trip 5 – 9 May 2017

Area Map

Geological Overview • South Pembrokeshire • Mainly sedimentary upper Palaeozoic rocks • Devonian to Permian • ESE – WNW trending tracts • Conformable and unconformable transitions from marine Silurian to continental Devonian red sandstones • Sandstones, limestones, mudstones and coal measures • Rich variety of fossils • Older sedimentary and igneous strata exposed along major fault lines and cores of anticlines • Precambrian to Silurian • Mainly in the North of the region • Oldest (643 MYA) is the Johnston Complex of metamorphosed plutonic igneous rocks • Diorites; Granodiorites and granites

Plate Tectonics Setting for Deformation of South Wales Rocks • Early Palaeozoic Deformations • Caledonian Orogeny • Avalonia docks with Laurentia closing the Iapetus Ocean (Late Silurian) • Acadian Orogeny • Closing of the Rheic Ocean (Mid Devonian) • Later Palaeozoic Deformations • Variscan Orogeny • Progressive convergence of Gondwana with Larussia (Upper Carboniferous) • Eventual formation of Pangea supercontinent • South Wales lies in the ‘ Forebold Edge’ of the thrust • Uplifting, folding, faulting and erosion over 50 – 100 MY

From: Geology of South Wales, second edition - Gareth T. George

Day 2 – 6 May 2017 • Morning • Skrinkle Haven • Afternoon • Manorbier

Skrinkle Haven

Skrinkle Haven • Late Devonian to Early Carboniferous • Transitional contact visible between: • Pembroke Limestone Group • Lower Limestone Shales • Skrinkle Sandstone • Ridgeway Conglomerate • Freshwater West Formation • ‘Cavern Collapse’ Breccia • Visible along coast line • Fossiliferous

The Geo eology of f Shrinkle Haven From: Geology of South Wales, second edition - Gareth T. George

Skrin inkle Haven

Im Impressive Natural Arch in in th the Bla lack Rock Lim imestone Forming th the Horseback

Coprolit ite

Crin inoid Stems

Chertified Lim imestone

Humocky cr cross - Str tratifi fication

Bry ryozoa

Skri rinkle Carboniferous Fossil il Assemblage: Crinoids, , Fenestella Bry ryozoa, , Rugose Corals

Mic ichelinia Tab abulate Co Coral

Pala laeocasts

Draught - Lydstep Penin insula la

Th The Group at th the Lydstep Peninsula

At Draught on Lydstep Peninsule – Showing Blo lowhole and Coll llapsed Breccia

Manorbier

Manorbier • Devonian • Freshwater West Formation • Old Red Sandstone (ORS) • Near Vertical Strata in Cliffs above high water mark • Fining up • Six cycles visible each capped with fine mudstones containing Calcretes • Interpreted as fills of ephemeral meandering fluvial channels

Th The Geolo logy of Manorbie ier From: Geology of South Wales, second edition - Gareth T. George

Manorbie ier Bay

Red Beds wit ith Many Trace Fossil ils

ORS S - with ith Whit ite Ca Calc lcrete and Halo los Around th the Bu Burr rrows

Beaconit ites Trace Fossil

ORS - With White Calcrete an and Halo los Around th the Burrows

Trace fossil - A Sin ingle Mil illipede in in Cross Sectio ion

Mud Aggregate in in Mudstone

Matu ture Soil il Profile le

Beaconit ites Trace Fossil

Dis ispla lacement on Fault lt

Erosio ional Base of f Sandstone

Buria ial l Chamber at t Kin ing's Quoit it

Sit itting on th the Burial Chamber at t Kin ing's Quoit

Tuff Band

Townsend Tuff

Tuff Band at t Rooks Cave

Tuff Band at t Rooks Cave

Possib ible le Faecal Pelle llets

Day 3 – 7 May 2017 • Morning • Freshwater West • Afternoon • West Angle Bay

Freshwater West

Freshwater West • Lower Limestone Shales • Upper ORS • Skrinkle Sandstone • Lower ORS • Ridgeway Conglomerate • Freshwater West Formation • Moor Cliffs Formation • Chapel Point Calcretes • Townsend Tuff Bed • Silurian Shales (Wenlock) • Ordovician Shales (Llanvirn)

Freshwater West From: Geology of South Wales, second edition - Gareth T. George

Freshwater West

Gareth Exp xplains Rock Types and Deposition Str tructures

Using th the Str tream to Demonstrate Deposition Str tructures in in Flo lowing Water

Standin ing Waves

Alm lmost Anti ti-Dune

Mudstone in in Silt ilt - Lower Ordovician - Lla lanvirn Ser eries

Lava Bread Seaweed

Freshwater East Formatio ion - Upper Silu ilurian

Porphyry ry - From Outside of f This Area

Red Beds of f th the Moor Cli liffs Formation

Fault lt - Silu iluria ian / / Devonia ian Unconformit ity

Fossili liferio ious Rock A

Fossili liferio ious Rock B

Chapel l Poin int Calc lcrete at t th the Fault lt

Chapel l Poin int Calc lcrete - at t th the Fault lt

Chapel l Poin int Calc lcrete

Freshwater West Formation

Rip ipple les at t Top of f Formation

Fin inin ing up Sequence

Trace Fossil of f Large Worm Tube

Laminatio ions Approaching Beaconites Beds

Orthocone - Long Shore Dri rift

Beaconit ites Trace Fossil ils

Beaconit ites Trace Fossils

Green Sand

Beaconites Trace Fossils in in Green Sand

Mult lti Story Orig igin inal l Erosional l Surface

Rid idgeway Conglomorate A

Rid idgeway Conglomorate B

West Angle Bay

West Angle Bay • Formed by erosion of lower Carboniferous (Dinantian) Limestone within the Angle Syncline • Main Rock Types • Blackrock Limestone • Avon Group (Limestone Shales) • Very Fossiliferous

West Angle Bay From: Geology of South Wales, second edition - Gareth T. George

Lower Lim imestone Shales of f th the Avon Group

Crin inoid Debris in in th the Sandy Lim imestone

Slic lickensid ides Min inerali lised wit ith Calc lcit ite

Zaphrentis is – A Rugose Coral

Worm Burrow

Approachin ing North Cove

Sili ilicifie ied Worm Burrows

Mappin ing th the Peric icli lines - North Cove

Dynamite Cracks fr from Previous Quarrying - North Cove

Sty tylo loli litic ic Contact in in North Cove

Gla lacial l Ti Till ll - Dia iamic icton

Gastropod

Day 4 – 8 May 2017 • Morning • Tenby South beach • Tenby North beach • Afternoon • Amroth • Ladies Cave

Tenby South Beach

Tenby South Beach • Rock Types • Bioclastic and Oolitic (Hunts Bay) Limestone • Crowded with Brachiopods • Caswell Bay Mudstone • Thinly bedded with Hunts Bay Limestone • Dipping steeply in cliffs • Blackrock Limestone • Dolomitised Bioclastic Limestone • High Tor Limestone

Geology of Tenby From: Geology of South Wales, second edition - Gareth T. George

Slic lickensid ides on South Beach Clif liffs

Small ll Cave at t th the Start of f South Beach

Large Calc lcit ite Vein ins - South Beach

Observing the Dip at the Start of the South Beach Cliffs

Jell llyfish