Copy of `BGS - Geological terms`

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BGS - Geological terms Category: Sciences > Geology Date & country: 27/12/2017, UK Words: 324

Benthos
Animals and plants living on the bottom of a sea or lake.

Biostratigraphy
The classification of rock successions based on fossil content.

Bed
Layer of sedimentary rock. Beds are built up one on top of the next, separated from each other by bedding planes. Each bed represents a single phase of more or less continuous sedimentation, before a change in conditions or an interruption of sedimentation, forms the bedding plane.

Basin mires
Developed in a waterlogged basin which may be completely enclosed or only a very restricted through-flow of water.

Barrier reef
A coral reef that started growing close to the shore (fringing reef), but due to earth movements is now growing some distance away from it.

Atoll
A reef that formed around an island. The island sank, but the continued growth of the coral resulted in a rounded reef.

Atmosphere
The atmosphere is a thin layer of gas and suspended particles surrounding the Earth and is composed mainly of nitrogen and oxygen but also small quantities of argon, carbon dioxide, neon, helium, methane, krypton, nitrous oxide, hydrogen, xenon and ozone (in order of decreasing amounts). The atmosphere has four layers: the troposphere up to an altitude of about 18 km, the stratosphere from 18 km to about 50 km, and the mesosphere from about 50 km to 82 km, beyond which is the thermosphere. Above 80 km the gases begin to thin out eventually leaving just oxygen in its atomic form.

Arrival time
The time at which a particular wave phase arrives at a detector.

Ash
In Limestone Landscapes we use this term to mean small (less than 2 mm) fragments of rock and volcanic glass ejected during volcanic eruptions.

Aseismic area
An area that is almost free of earthquakes.

Asthenosphere
The asthenosphere is the ductile part of the Earth just below the lithosphere, including the upper mantle. The asthenosphere is about 180 km thick.

Arrival
The appearance of a seismic wave on the seismic record.

Array
An ordered arrangement of seismometers or geophones, the data from which feeds into a central receiver.

Aragonite
An unstable form of calcium carbonate which changes into calcite.

Aquitard
A rock with limited permeability that allows some water to pass through it, but at a very reduced rate.

Aquifer
One of many types of permeable rock. Pore spaces (tiny holes) between the grains, or fractures (cracks) allows water to flow through and accumulate in an aquifer rock.

Aquiclude
An impermeable layer of rock which water cannot flow through because there are no pore or fracture voids, or such voids are not connected together.

Anticline
Upwardly arched folds of Sedimentary rocks put under pressure by movement in the Earth. (See syncline)

Altitude
Height above sea level.

Alum
A chemical compound that can be processed from clays. It has been used for industrial purposes (e.g. tanning leather and dyeing) and in medicine.

Amplitude
The maximum height of a wave crest or depth of a trough.

Anglian
One of the glaciations during the last Ice Age, about half a million years ago, when glaciers reached as far south as the Severn

Aftershock
An earthquake which follows a larger earthquake or main shock and originates at or near the focus of the larger earthquake. Generally, major earthquakes are followed by a larger number of aftershocks, decreasing in frequency with time.

Albedo
The amount of solar radiation that is reflected back off a surface.