WJEC A2 Geology

BGS Mapwork

I.G.Kenyon

BGS 1:50.000 scale maps

1mm on the map represents 50m on the ground

Grid squares are 1 km² and have sides of 2cm on the map

BGS 1:25,000 scale maps

1mm on the map represents 25m on the ground

Grid squares are 1 km² and have sides of 4cm on the map

BGS Maps are produced in solid and solid and drift editions

Solid maps show only the fully lithified rocks

Solid and drift maps show the lithified rocks plus any recent sediments deposited on top

Solid Geology – Cockermouth Sheet 23 1:50.000

Recent drift deposits such as alluvium and boulder clay not shown

Carboniferous rocks

Permo-Triassic Rocks

Solid and Drift Geology – Clitheroe Sheet 68 1:50,000

Alluvium

River Terrace Deposits

Solid Geology

Structures to Identify on BGS Maps 1

Beds – direction of dip/angle of dip

Beds – strike direction/orientation

Anticlines/synclines/monoclines

Fold axes/axial plane of folds

Domes/basins

Symmetrical/asymmetrical folds

Plunging folds

Open/tight/recumbent/overturned folds

Structures to Identify on BGS Maps 2

Normal faults/reverse faults/thrust faults

Tear faults – sinistral/dextral/step faults

Graben/rift valley/Horst/block mountain

Unconformities-angular/parallel/heterolithic

Inliers/outliers

Lava flow/sill/dyke/pluton/mineral veins

Metamorphic aureole

Inverted relief

Symbols on BGS Maps 1

Drift Symbols on BGS Maps

Generalized vertical sections are given on BGS Maps

This is a vertical log of all the rock types present in chronological order with the oldest

at the base and the youngest at the top

On 1:50,000 maps the scale is often 1:10,000

On 1:25,000 maps the scale is often 1:4,000

However scales can vary-check carefully on each map that you are studying

Part of generalized vertical section from Cheddar Sheet ST45 1:25,000

Part of the generalized vertical section from Hawes

Solid and Drift 1:50,000

Note that rock types and ages of beds are given

Unconformities are clearly indicated in the section

It is vital that the vertical section is studied carefully in conjunction with the map

in order to interpret all of the geological structures

Cross sections are also included on BGS maps and should be studied carefully along with the vertical section and map

From Hawes Solid and Drift 1:50,000

You do not have to construct cross sections from BGS maps at A2!

In addition to geological structures, you will be asked questions with a GL3 bias

These could include evaluating the suitability of certain locations for the construction of roads, landfill sites, housing estates, reservoirs, power

stations, dams or tunnels

Questions relating to the causes of landslips are also a possibility

Sometimes additional maps are included on the BGS geology maps

These may include magnetic, gravity, radon, isostatic or mineralogical data

Questions related to this additional data may be asked

in relation to the geological map

Okehampton/Dartmoor Map Geology and Gravity Anomalies

Gravity anomalies (contoured in milligals). The negative gravity anomaly is due to the granite being of lower density than the surrounding rocks

Okehampton/Dartmoor Map Geology and Magnetic Anomalies

Aeromagnetic anomalies (contoured in nanoteslas) Magnetic disturbances skirting the granite are due to mineralisation

in the Lower Carboniferous rocks and basic intrusions at depth

The End

Ash deposits of the Las Canadas Volcano, Tenerife, Canary Islands