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GUERNSEY has a geological history stretching further back into the past than most of Europe. The majority of rock exposures on the Island may be found along the coastlines, with inland exposures scarce and usually highly weathered . There is a broad geological division between the north and south of the Island. The SOUTHERN METAMORPHIC COMPLEX is elevated above the geologically younger, lower lying NORTHERN IGNEOUS COMPLEX. Guernsey
Guernsey
has experienced a complex geological evolution (especially the rocks of the southern complex) with multiple phases of intrusion and deformation recognisable.

CONTENTS

* 1 Geological History

* 1.1 Precambrian
Precambrian
* 1.2 Cambrian
Cambrian
* 1.3 Quaternary

* 2 Lihou
Lihou
Island * 3 Quarrying * 4 References

GEOLOGICAL HISTORY

PRECAMBRIAN

The southern part is largely composed of ICART GNEISS. The Icart Gneiss
Gneiss
is an augen gneiss of granitic composition containing potassium feldspar . This was formed from a granite dated at 2,061 million years ago using U-Pb dating on zircon grains. A foliated Perelle quartz diorite (also called PERELLE GNEISS), occurs in the centre and west of the island. This is a calc-alkaline tonalitic rock. The foliation was formed at around 600 million years ago during the Cadomian Orogeny
Cadomian Orogeny
. Rafts of metamorphosed sediments, older than the Foliated Perelle Diorite
Diorite
are embedded between them.

The Pleinmont Formation consists of metamorphosed sediments is of unknown age, although it has been proposed that these belong to the Brioverian group that outcrop on nearby Jersey
Jersey
It is named after Pleinmont Point on the south west tip of the Island.

The older rocks were deformed during the Cadomian Orogeny. The Icart Gneisses formed the basement to an outboard terrane that was subsequently accreted to Armorica
Armorica
.

CAMBRIAN

The COBO GRANITE was formed at approximately 570 million years ago , named after Cobo Bay on the mid west coast. The north end of the island is an unfoliated calc-alkaline pluton of the Bordeaux Diorite Complex consisting of diorite , tonalite , and granodiorite . This is also dated at 570 million years ago .

On the central east coast around Saint Peter Port is the St Peter Port Gabbro containing layers with olivine , hornblende and two kinds of pyroxene . The igneous plutonic intrusion is 2.5 km from north to south and is 0.8 km thick. It dips shallowly to the west. The lower and upper portions are layered on the scale of a meter, while millimeter scale layering is found on the uppermost parts. This is also dated at 570 million years ago . Near Vale Castle the rock is of a type called bojite with interlocking hornblende and plagioclase crystals.

QUATERNARY

During the Quaternary Devensian
Devensian
glaciation, loess was deposited, blown in by wind from the west. The island was only separated from the continent of Europe by rising sea levels at about 5000 BC during the new stone age.

LIHOU ISLAND

Tight folds at the contact between Icart Gneiss
Gneiss
(light) and mylonitised quartz diorite (dark), western end of Lihou
Lihou
Island.

Many of the rocks present in the south of Guernsey
Guernsey
may also be observed on Lihou
Lihou
Island . At the western coast of the island, a shear zone is exposed at the contact between the Perelle Foliated Quartz Diorite
Diorite
and the Icart Gneiss. The younger quartz diorite is mylonitised , where field evidence suggests that it was most likely deformed synchronously with its intrusion. The contact between the two rocks is tightly folded , as are the mylonitic fabrics in the two rocks.

Dykes are abundant on the Island, largely of doleritic composition.

QUARRYING

Guernsey
Guernsey
has had an active quarrying industry over the years, largely removing rock for use as building materials. Many local houses are constructed of either blue-grey Bordeaux Diorite, or red-brown Cobo Granite. The only remaining active quarry is Les Vardes on the west coast of the Island, operated by Ronez . Here the Bordeaux Diorite
Diorite
is extracted and crushed on site to produce aggregate .

Many of the disused quarry sites have been allowed to fill with water, such as St. Andrews Reservoir, now used by the States of Guernsey
Guernsey
water board. Mont Cuet is another former quarry, now used as a landfill site to dispose of the majority of the Island's non-recyclable waste.

REFERENCES

* ^ citation needed

* Great Britain: Channel Islands in Encyclopedia of European and Asian Regional Geology by Eldridge M. Moores, Rhodes Whitmore Fairbridge, Published 1997 by Springer pp 276–277. * John Renouf: Geological excursion guide 1: Jersey
Jersey
and Guernsey, Channel Islands in Geology Today volume 1 number 3 1985

* v * t * e

Geology of Europe

COUNTRIES

* Albania * Andorra * Armenia * Austria * Azerbaijan * Belarus * Belgium * Bosnia and Herzegovina * Bulgaria * Croatia * Cyprus * Czech Republic

* Denmark

* Faroe Islands

* Estonia

* Finland

* Åland Islands

* France * Georgia * Germany * Greece * Hungary * Iceland * Ireland * Italy * Kazakhstan * Kosovo * Latvia * Liechtenstein * Lithuania * Luxembourg * Macedonia * Malta * Moldova * Monaco * Montenegro * Netherlands

* Norway

* Jan Mayen * Svalbard

* Poland * Portugal * Romania * Russia * San Marino * Serbia * Slovakia * Slovenia * Spain * Sweden * Switzerland * Turkey * Ukraine

* United Kingdom

* England * Northern Ireland * Scotland * Wales * Gibraltar * Guernsey * Jersey
Jersey
* Isle of Man

GEOLOGIC REGIONS

OROGENS

* Acadian * Alpine * Belomorian * Cadomian * Caledonian * Carpathian * Dalslandian * Gothian * Grampian * Hallandian-Danopolonian * Hellenic * Laxfordian * Lopian * Saamian * Scandian * Scourian * Timanide * Svecofennian * Sveconorwegian * Uralian * Variscan

MOUNTAIN RANGES

* Alps * Apennines * Caucasus * Dinaric Alps * Harz * Massif Central * Ore Mountains * Pyrenees * Urals * Western Carpathians

OCEANIC BASINS

* Atlantic Ocean * Arctic Ocean * Bay of Biscay * Black Sea * Mediterranean Sea * Norwegian Sea

Intracontinental basins and grabens

* Aquitaine Basin
Aquitaine Basin
* Barents Basin
Barents Basin
* Baltic Sea Basin * Central Lowlands
Central Lowlands
* Dnieper–Donets Rift * Ebro Basin * European Cenozoic Rift System * Limagne Graben * Mezen Basin * Molasse Basin * Moscow Basin * North Sea Basin * Oslo Rift * Pannonian Basin
Pannonian Basin
* Paris Basin
Paris Basin
* Peri- Caspian Depression
Caspian Depression
* Timan-Pechora Basin
Timan-Pechora Basin
* White Sea Rift System

Tectonic plates and microcontinents

* Adriatic Plate
Adriatic Plate
* Aegean Sea Plate
Aegean Sea Plate
* Anatolian Plate
Anatolian Plate
* Eurasian Plate
Eurasian Plate
* Iberian Plate * Jan Mayen Microcontinent * Misian Plate * Pelso Plate * Tisza Plate

TERRANES

* Armorican terrane
Armorican terrane
* Avalonia
Avalonia
* Baltica
Baltica
* Cimmeria * East European Craton
East European Craton
* Fennoscandian Craton * Sarmatian Craton * Volgo–Uralia

UNESCO WORLD HERITAGE SITES

* Aeolian Islands
Aeolian Islands
* Aggtelek * Calanques de Piana * Curonian Spit
Curonian Spit
* Dolomites
Dolomites
* Durmitor
Durmitor
* Geirangerfjord
Geirangerfjord
* Giant\'s Causeway * Glarus * High Coast * Jungfrau-Aletsch * Jurassic Coast
Jurassic Coast
* Komi * Kvarken
Kvarken
* Laponia * Messel Pit * Meteora
Meteora
* Monte Perdido
Monte Perdido
* Monte San Giorgio
Monte San Giorgio
* Mount Etna
Mount Etna
* Nærøyfjord
Nærøyfjord
* Pirin * Plitvice * Rhine Gorge
Rhine Gorge
* Scandola * Škocjan * St Kilda * Stevns Klint
Stevns Klint
* Surtsey
Surtsey
* Th

.