A journey across 400 million yearsA journey 400 million years across The story of geology & landscape 610 570 510 440 410 360 290 245 210 145 65 0 Ediacaran Cambrian Ordovician Silurian Devonian Carboniferous Permian inTriassic SouthJurassic GloucestershireCretaceous Caenozoic Era 1 Palaeozoic Era Mesozoic Era Skull and front flipper of an Ichthyosaurus © Copyright South Gloucestershire Council (x0.2) � � All rights reserved LA100023410, 2007 � One of the early Jurassic marine reptiles � � ��������� known as ‘Sea Dragons’ (Bristol Museum) � �������� �������� � �� A journey 400 million years across � ��������� N � ��������� � �� � � ��������� �� �� � � � � � � � ������������ �������� �������� � � � ���� � � ������� � � � �� �� ����������� �� �� ���������� ������ ����� ����� ������� ����������� � � � � � ���� � Introduction ����� �������� � ��������� � ������� ��� � �������� � � ��������� ������� � ������� This booklet tells the story of Some sites, such as Aust Cliff, will �� ����� ������������ �� the geological history of South require an hour or two to explore �������� ���� � � � � ������� � ����� �������������� Gloucestershire, spanning some fully. Others – where the rocks � ����� � ������� � � ��������� 400 million years. are physically inaccessible or in a ����� � � dangerous location, like a working ������ � � �������� � �� � � It involves vast, almost unimaginable quarry – can only be viewed from a � � ������������ ������� �������� earth movements and dramatic, specific, safe vantage point. ����� radical changes in continents, ������ ���� climate and the landscape. A 6-figure Ordnance Survey Map grid ��������� � � ���� � � The evidence for these processes lies reference (NGR) for each of the sites ��� � ���� ������� all around us, albeit unobtrusive and, is provided in the text. ��� ���������� �������� � more often than not, overlooked – ������ ����� in the rock of quarries, road cuttings, Sites mentioned in the text are � ��� stone walls and buildings; and in the shown on the map opposite. There ������ mud of the Severn Estuary. is also a geology map on pages 22 and 23. The booklet directs you to a Sites mentioned in the text series of specific sites in South Please visit the web site Must see sites Information boards Other sites Gloucestershire, some of which have www.avonrigs.org.uk which provides their own geological information greater detail on the geology and 1 Aust Cliff 4 Brandy Bottom, Shortwood 10 Brinkmarsh Quarry boards. landscape of South Gloucestershire. ST565895 ST683773 ST674913 2 Huckford Quarry Local 5 Chipping Sodbury Car Park 11 Buckover Road Cutting Nature Reserve ST724823 ST665906 ST657799 6 Codrington Quarry 12 Cullimore’s Quarry 3 Wick Golden Valley Local ST727783 ST721927 Nature Reserve 7 Cromhall village 13 Hawkesbury Quarry ST709729 ST698905 ST772873 A journey 400 million years across 8 Slickstone Quarry 14 Pithay, Thornbury ST703915 ST633906 9 Tytherington Road Cutting 2 ST655876 3 Geology fieldwork tools of the trade Follow the Rock Cycle A journey 400 million years across volcanic extrusive weathering and erosion of all eroded material IGNEOUS rocks exposed at transported towards the sea ROCKS Earth’s surface (eg lava, basalt) sediments deposited sedimentary, (eg mud/sand/lime) metamorphic or igneous rocks may be exposed Basics… at Earth’s surface burial, compaction, cementation by uplift and In geology, as in all other sciences, erosion there are some important SEDIMENTARY ROCKS (eg mudstones, sandstones and principles that underpin limestones) everything else. One of these is the Rock Cycle (see opposite). may then be subjected to deeper burial with considerable heat and pressure Plate Tectonics - the Earth’s crust Asia is divided into plates composed of North Europe may cool and recrystalise into a lighter rocks, the continents and America METAMORPHIC ROCK shallow seas, which float on heavier, PANGAEA (eg slate and marble) South America Africa denser rocks beneath the oceans. India Australia Antartica may cool at may be subjected to even greater depth to form heat and pressure to melt, deep in Continental Drift - throughout The position of the continents 280 an intrusive Earth’s crust geological time, the position of the million years ago IGNEOUS ROCK continents has shifted slowly but (eg granite) dramatically – for example, some of the rocks now making up South Gloucestershire may have been MAGMA formed south of the equator. deep in Earth’s crust, magma provides the ‘raw material’ for new rocks. Rocks - are formed from minerals and may be extremely hard like granite or soft like clay. A journey 400 million years across 4 5 Wenlock limestone showing corals and brachiopods (x1.3) A journey 400 million years across Complex Geology Revealed Red rocks such as the Upper Old Red - the change from Silurian to Sandstone are strongly indicative of a Later, these seas grew shallower, with Devonian desert environment. coral reefs and shellfish that became fossils. These fossils enable the Buckover Road Cutting ST665906 Frequent powerful flash floods then rocks to be correlated with those at Site of Special Scientific Interest eroded these desert mountains, Wenlock Edge, Shropshire - they are (SSSI) on the A38 near Thornbury depositing large boulders, chiefly Old Rocks, mostly buried thus part of the Wenlock Series. illustrates the relationship quartzite, from the older harder - the Silurian, 440 to 410 million between rocks of two different rocks. These became cemented years ago The basalts can be seen at geological periods – the Silurian together to form the massive Quartz Cullimore’s Quarry ST721927. and Devonian. Conglomerate. The oldest visible rocks in South Fossiliferous limestones (the Gloucestershire belong to the Brinkmarsh Beds of the Wenlock A break in deposition is called an The deposited beds were once Silurian Period. Series) containing corals and other ‘unconformity’. The unconformity at horizontal but colossal earth fossils can be seen in Brinkmarsh Buckover Road represents a period movements subsequently These occur mainly in the Tortworth Quarry ST674913. of about 35 million years between caused them to become area and belong to the Llandovery the Silurian and the Devonian (Upper tilted and faulted. Old Red Sandstone). Series, so-called because similar rocks Silurian Period rock can also be seen containing the same types of fossils in walls at Tortworth, Avening Green were first recorded at Llandovery in and Damery. Wales. The Series consists of a succession Massive Quartz Conglomerate of sedimentary rocks interrupted by two bands of basalt, a fine-grained Footpath Thick bed of Quartz Conglomerate igneous rock, formed from cooled lava that was forced through the sedimentary rock. Between the two layers of basalt there is a succession of sandstones, siltstones and lime-rich rocks that Photo of Charfield Pin Mill with a variety Devonian Fault of local Silurian rock reflect the changing environments Silurian at the time that they were laid down Unconformity – shallow seas that deepened as time Buckover Road Cutting progressed. A journey 400 million years across 610 570 510 440 410 360 290 245 210 145 65 0 Ediacaran Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous 6 Caenozoic Era 7 Palaeozoic Era Mesozoic Era Palaeosmilia regia (x1) Fossilised coral from the Carboniferous Period Wick Golden Valley Local Nature Reserve There are spectacular views of the Carboniferous Limestone quarry A journey 400 million years across at Wick from the Wick Golden Valley Local Nature Reserve. Wick Rocks l l i H e b The hard rocks began as the soft, m o c h is a River Boyd lime-rich mud and the remains N Disabled of marine creatures, such as coral, Parking Entrance on a tropical sea floor. Over time, Wick layer upon layer of sediment was Parking Village Mountains and Coral Seas compressed into rock by its own MUSTVISIT Hall A420 - the Lower Carboniferous weight. Information leaflets are available from South Gloucestershire Council about 350 million years ago È Tel 01454 863592 or visit www.southglos.gov.uk All rights Council reserved South LA100023410, 2007 © Copyright Gloucestershire These beds are not, however, The limestone formed during horizontal. A massive collision of the Lower Carboniferous Period continental plates folded this part (Carboniferous Limestone) is one of the Earth’s crust into a chain of the most important rocks for of mountains that would have A section through the North Bristol Coalfield Syncline commercial purposes, because of extended across present day Europe. vertical scale exaggerated its hardness and accessibility. This chain was then ‘planed off’ by extreme weathering and erosion, This limestone is 900m thick, forming slowly and over vast periods of Almondsbury Frampton Cotterell Chipping Sodbury a ridge that extends from Cromhall time – the tilted, angled beds of to Chipping Sodbury and from rock in these limestone quarries are Tytherington to Almondsbury (see evidence of these processes. diagram on opposite page) and is extensively quarried. In South Gloucestershire the 1.3 miles See boards at Codrington Quarry rocks form a great basin, filled (2km) ST727783, Chipping Sodbury car park with younger rocks. ST 724823 and Wick Golden Valley Local Nature Reserve ST709729. Younger Rocks Upper Carboniferous Lower Carboniferous A journey 400 million years across 610 570 510 440 410 360 290 245 210 145 65 0 Ediacaran Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous 8 Caenozoic Era 9 Palaeozoic Era Mesozoic Era