School of GeoSciences

School of GeoSciences

Siccar Point Field Excursion Preview

Sedimentary structures in the Silurian greywackes

In the field, examine the grey vertical beds in detail. You are looking for way-up criteria - features that tell you which was the original top and bottom. You might see grading - variation in grain size from top to bottom, and ripples - laminations produced by current flow. It can be quite difficult - you need to search! More below...

Greywacke sedimentary structures

In the field look closely at the hard and soft bands. In each case you are looking for:

  • Grain size: can you estimate the size of the largest grains in millmetres?

    If the grains are large enough to see (with a hand-lens) look for:

  • Sorting: are the grains all the same size or is there a complete range of sizes?

  • Angularity: are the grains angular or rounded or somwhere in between?

  • Composition: are the grains made of quartz or fragments of rock or...?