Geoscience Reference
In-Depth Information
Appendix A6: Sedimentary
All of the following descriptors and some of the classifi cation
charts are applicable to both sediments (i.e. unconsolidated
sediments) and sedimentary rocks (consolidated
sediments).
Table A6.1
Checklist for the description of sedimentary deposits.
Property
Questions
Composition
Grains
What is the composition of the most abundant grains?
Matrix
Is there any fi ne-grained (clay-sized) fragmentary material infi lling the
spaces between larger grains? If so, what is it?
Cement
Is there any crystalline material precipitated around the edges of
grains, or in the spaces between grains? If so, what is it?
Texture
Grain size
What is the most abundant grain size present (use a grain-size card
and Figure A6.1)?
Grain sorting
Are the grains all more or less of the same size (i.e. well-sorted) or
different sizes (i.e. poorly sorted) or somewhere in between (use the
sorting scale; Figure A6.2)?
Grain morphology:
See Figure A6.3
shape or form
Are the grains long and thin or equidimensional?
roundness
Do the grains have rounded or angular corners (use roundness
scale)?
sphericity
Are the grains like spheres (i.e. high sphericity) or are they elongate
(low sphericity)?
Grain surface texture
Are any quartz grains present smooth and glassy, or are they
frosted?
Grain fabric (packing)
Are the grains orientated in any preferred direction? Are the grains
closely packed together? Are the grains matrix- or grain-supported?
(See Figure A6.4)
Fossils
Can you see the remains of any body fossils or their movements
(trace fossils)?
Sedimentary
structures
Are there any obvious layers or other structures in the rocks? (See
Figures A6.5-A6.7)
