Graphic Logs of Sedimentary Rocks

I.G.Kenyon

Graphic Logs are a method used to record details of sedimentary successions to scale

The vertical scale is used to record bed thickness to scale, typically the scale will be between 1:10

(1 cm to 10cm) and 1:100 (1 cm to 1 metre)

The horizontal scale uses particle sizes of the Wentworth Scale, on the left hand side is Clay, then moving to the right is Silt, Sand, Granules, Pebbles, Cobbles and finally Boulders

A variety of symbols are used to indicate the presence of sedimentary structures including graded bedding, cross bedding, laminations, desiccation cracks,

ripple marks, flute casts and erosion surfaces

Symbols Used on Graphic Logs

Typical Glacial Sequence

Typical Fluvial (Meandering River Channel) Sequence

Desert Sequence

Deltaic Sequence – Coal Measures Cyclothem

Turbidity Current Sequence (Bouma Sequence-5 Units)

Exam questions using graphic logs of sedimentary sequences

The End