Geology of Alderney
The geology of Alderney includes similarities in its rock to the neighbouring Normandy and Guernsey. Although Alderney is only five kilometers long, it has a geological history spanning half of the life of the earth. It is part of the Armorican Massif.
Geological history
Relics of sediments appear as
The next stage of geological history was the intrusion of the Central Diorite Complex that makes up the north and centre of the island. This belongs to the
In the next stage the terrane was uplifted, and eroded. Fine grained sand that formed quartzite was deposited. Further weathering ensued, with most of this deposit removed and laterite formed. Next a stream channel formed over the land, dumping coarse sand with feldspar. This formed a pink sandstone. The flow came from the northwest, with particles derived from granite and gneiss. initially this filled in the hollows in the underlying granites, but soon overflowed into a braided channel. Flood plain conditions caused layers of silt to form between the sand. These sediments deposited in the Cambrian are probably the final stage of the Cadomian Orogeny.
In the
In the Pleistocene varying sea levels caused raised beaches to form 8, 18 and 30 meters above the current sea level. As in Jersey, loess blew in as dust from the bare ground in the near glacial conditions in the ice ages. Head also formed in the periglacial circumstances by breaking off rock fragments and mixing with dirt.
References
- 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.
- N d'A Laffoley: Geological excursion guide 2: Alderney, Channel Islands in Geology Today volume 1 number 5 page 151 1985