Daeareg Dyffryn Clwyd the Geology of the Vale of Clwyd
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Microfossil Contribution to the Vale of Clwyd Geology G. Wyn Hughes PhD, DSc, MSc April 2018 Applied Microfacies Ltd. Llanbedr DC [email protected] Introduction to the Vale of Clwyd feature Review of the different rock types Ordovician to Triassic stratigraphy and fossil use Physiography of the Vale of Clwyd Denbigh Moel Famau Moors (554m) http://en-gb.topographic-map.com/places/River-Clwyd-130735/ Geological map of the region (William Smith, 1828) http://www.strata-smith.com/map/ Darwin’s visit to Rhuthun (5-29 August, 1831) With Professor Sedgwick (Prof. of Geology at Cambridge) Shrewsbury Llangollen Ruthin Conwy Bangor Anglesey The route of Darwin and Sedgwick "This tour was of decided use in teaching me a little how to make out the geology of a country," (Roberts 2001) North Wales geological map http://www.largeimages.bgs.ac.uk/iip/mapsportal.html?id=1004587 North Wales structural trends Caledonian http://www.largeimages.bgs.ac.uk/iip/mapsportal.html?id=1004587 North Wales structural trends Caledonian Hercynian http://www.largeimages.bgs.ac.uk/iip/mapsportal.html?id=1004587 Llanelidan Fault Bala Fault Clues to the various rock types in the Valley • building stone • walls • exposures • place names How many different rock types are in the valley ? Dolhir Formation shales, (Ur. Ordovician, Ashgill) (Mynydd Cricor) Elwy Formation – crumpled shales, Silurian (Penycloddiau) https://www.denbighshire.gov.uk/en/your -council/...and.../decision.aspx?.. Elwy Formation mudstones, Silurian (Ludlow) (roadside wall near Llanfwrog) Berwyn Slates, metamorphosed Silurian (Ludlow) Red Basement Beds (Lower Carboniferous, Chadian) Galltegfa Dingle, west of Llanfwrog Limestone (Carboniferous), Ty Brith, Pentrecelyn Limestone (Carboniferous), Rhuthun Castle Clues of red rocks in the region (Llanfwrog Catholic Church) Clues of red rocks in the region (Rhuthin castle hotel) Kinnerton Sandstone Formation (Llanrhydd) Clues of red rocks in the region Ysgol Frongoch, Dinbych Clues of red rocks in the region Clues of red rocks in the region Clues of red rocks in the region Clues of red rocks in the region Rocks of the Vale of Clwyd Sandstone • Kinnerton (Permian) • Basement Beds (Carboniferous) Limestone • Carboniferous Slate • Silurian shales metamorphosed during the Devonian (Caledonian orogeny) Shale • Upper Silurian (Ludlovian) • Upper Ordovician (Ashgillian) Palaeoenvironments of the Vale of Clwyd succession Deep Coral Desert Sea Reef Palaeoenvironments of the Vale of Clwyd succession Deep Coral Desert Sea Reef Silurian Carboniferous Permian mudstones limestones sandstones Ordovician mudstones STRATIGRAPHY Macrofossils for age and palaeoenvironment Ammonoids Corals Brachiopods but typically poorly preserved Examples of various sections through Kurnubia sp. – think 3D Microfossils for age and palaeoenvironment Foraminifera Calcareous alga Palynomorphs Conodonts Stratigraphic summary of the Vale of Clwyd Global temperature Polar ice Phanerozoic time scale, sea-level variations (Haq & Al-Qahtani, 2005; Haq & Shutter, 2008), and icehouse (cold) and greenhouse (hot) conditions. Stratigraphic summary of the Vale of Clwyd Dolhir Formation Stratigraphic summary of the Vale of Clwyd Elwy Formation Dolhir Formation Stratigraphic summary of the Vale of Clwyd Caledonian orogeny Elwy Formation Dolhir Formation Stratigraphic summary of the Vale of Clwyd Erbistock Fm. Coal Measures Millstone Grit Clwyd Limestones Basement Beds Caledonian orogeny Elwy Formation Dolhir Formation Stratigraphic summary of the Vale of Clwyd Hercynian orogeny Erbistock Fm. Coal Measures Millstone Grit Clwyd Limestones Basement Beds Caledonian orogeny Elwy Formation Dolhir Formation Stratigraphic summary of the Vale of Clwyd Kinnerton Fm. Hercynian orogeny Erbistock Fm. Coal Measures Millstone Grit Clwyd Limestones Basement Beds Caledonian orogeny Elwy Formation Dolhir Formation Geological map of the Vale of Clwyd (North) Geological map of the Vale of Clwyd (Central) Geological map of the Vale of Clwyd (South) Llanelidan Fault – southern VoC limit Graigfechan Clawddnewydd Llanelidan Fault Llanelidan Vale of Clwyd structural x-section West Vale of East Clwyd Fault Kinnerton Fm. Erbistock Fm. Minera Fm. Cefn Mawr Fm. Loggerheads Fm. Leete Fm, Llanarmon Fm. Foel Fm. Basaement Beds Elwy Fm. Nantglyn Flags Fm. http://www.largeimages.bgs.ac.uk/iip/mapsportal.html?id=1001596 Ordovician named by Charles Lapworth (1879) after the Ordovices, an ancient Celtic tribe - palaeogeography - stratigraphy Gondwana in the Latest Ordovician (Hirnantian: 445 Ma), showing the extent of the glacial ice cap Where was the Vale of Clwyd” during the Latest Ordovician ? Laurentia Iapetus Ocean Avalonia “Vale of Clwyd” Where was the “Vale of Clwyd” during the Latest Ordovician Iapetus Dea Iapetus Suture Stone, 2010 The Ordovician Period (ICS, 2015) Dolhir Ashgill Caradoc No Llandeilo Llanvirn Arenig Tremadoc Stratigraphic summary of the Vale of Clwyd Dolhir Formation Ordovician inlier at the southern Vale of Clwyd (BGS map) Llysfasi Mynydd Cricor Ordovician inlier at the southern Vale of Clwyd (BGS map) Llysfasi Dolhir Fm. Llanelidan Fault Dolhir Formation shales, Silurian (Ur. Ordovician, Ashgill) (Mynydd Cricor) Dolhir Formation shales, Silurian (Ur. Ordovician, Ashgill) (Mynydd Cricor) Ordovician fossils / microfossils : • age • palaeoenvironment Graptolites (Phyllograptus sp.) (Lower Ordovician) Stratigraphic ranges of graptolites Monograptus spp. Ordovician Phyllograptus spp. Dicellograptus spp. Dicellograptus sp. cf cambrensis (Middle Ordovician) Llanfawr Quarry Llandrindod Courtesy of Dr. Dennis Bates, University of Wales, Aberystwyth Stratigraphic ranges of graptolites Monograptus spp. Ordovician Phyllograptus spp. Dicellograptus spp. Graptolites as palaeoenvironmental indicators Basin and slope Shelf No graptolites isograptids didymograptids Silurian named by Roderick Murchison (1835) after the Silures, an ancient Celtic tribe - palaeogeography - stratigraphy Late Silurian : Continued closure of the Iaptus Ocean Laurentia Avalonia “Vale of Clwyd” Late Silurian - the Iapetus Ocean had closed in the Caledonian Orogeny. “Vale of Early Silurian Late Silurian Clwyd” The Silurian Period (ICS, 2015) Elwy Fm. Stratigraphic summary of the Vale of Clwyd Elwy Formation Dolhir Formation Geological map of the Vale of Clwyd (Central) Denbigh Silurian Silurian Ruthin Elwy Formation (Ludlow) Galltegfa Dingle, west of Llanfwrog Elwy Formation (Ludlow) Galltegfa Dingle, west of Llanfwrog Geological map of the Vale of Clwyd (Central) Denbigh Silurian Silurian Ruthin Elwy Formation, Silurian (Ludlow) (A55 roadcut) Silurian: Clwydian Range (Llanbedr DC) Elwy Formation, Silurian (Ludlow) (above Llanbedr DC) Elwy Formation, Silurian (Ludlow) (A484 quarry above Llanbedr DC) Elwy Formation, Silurian (Ludlow) (A484 quarry above Llanbedr DC) • snooker table • gravestones • building stone • dry stone walls Thin section of shale under the microscope Clay particles Quartz grains Silurian fossils / microfossils : • age • palaeoenvironment Monograptus graptolite thecal evolution Simple Hooked Isolate Lobate Monograptus sp. (Lower Silurian) Hooked theca Silurian graptolites Silurian graptolites Silurian graptolites Monograptus sp, a graptolite fossil, in black shale. Silurian. Cliffs of Veryac Stratigraphic ranges of graptolites Monograptus spp. Silurian Phyllograptus spp. Dicellograptus spp. Graptolites as palaeoenvironmental indicators Basin and slope Shelf No graptolites isograptids didymograptids Mudstones and shales of the Vale of Clwyd Elwy Striped silty mudstones & sandstones with disturbed beds Formation Nantglyn Ribbon-banded mudstones with Flags sandstones and disturbed beds Formation The Silurian Period (ICS, 2015) Elwy Fm. Early Devonian (Caledonian orogeny terminates) Bala, Bryneglwys & Llanelidan faults active • Collision of Avalonia and Laurentia continents completed • Closure of Iapetus Ocean • Uplift of the Silurian and Devonian basins • Major hiatus between the Silurian and Carboniferous in North Wales • Thermal relaxation caused extension (rift zones) e.g. Vale of Clwyd Late Ashgill Late Silurian – Early Devonian Early Devonian north-south rifting : grabens & half grabens Evidence for Caledonian Vale of Clwyd faulting (BGS Memoir, Davies et al. 2004) Note differential deposition of younger Carboniferous Llanarmon Fm. Foel Fm. Basement Beds SILURIAN Berwyn Slates, metamorphosed Silurian (Ludlow) mudstones Berwyn Slates, metamorphosed Silurian (Ludlow) mudstones Berwyn Slates, metamorphosed Silurian (Ludlow) mudstones Berwyn Slates, metamorphosed Silurian (Ludlow) mudstones Berwyn Slates, metamorphosed Silurian (Ludlow) mudstones 1.3 mm Photomicrographslate of Devonian The Devonian Period (ICS 2015) • Britain 200S • well preserved Lower Devonian in Anglesey (Lligwy Bay Sandstone Fm.) • NOT present in the Vale of Clwyd – major unconformity Devonian of North Wales – minimal / absent Anglesey Vale of Carboniferous Pembrokeshire Clwyd Carboniferous Upper Upper Devonian Devonian Middle Middle Devonian Devonian Lower Lower Devonian Devonian Silurian Silurian Lower Devonian sandstones (Lligwy Bay, Anglesey) Lower Devonian sandstones (Lligwy Bay, Anglesey) 2007 Carboniferous - palaeogeography - stratigraphy Early Carboniferous Palaeogeography “Vale of Clwyd” Rheic Ocean The Carboniferous Period (Regional subdivisions and official ICS stages) The Carboniferous Period (ICS, 2015) Coal Measures Millstone Grit Carboniferous Limestone Limestones of the Vale of Clwyd Thinly interbedded dark argillaceous limestones and