1. SACRAMENTO
STATE
Geology 103 Sedimentology and Stratigraphy Tim Horner Geology Department, CSU Sacramento
Lecture #2:
Siliciclastic rock identification (shale, siltstone and conglomerate)
Reading assignment:
Boggs, 5th ed., pp

2. composition with age of sediment
Changes in clay
composition with age of sediment
Figure 5.12 from Sedimentology and Stratigraphy, 4thed., by Boggs, p. 142

3. Siltstone and shale classification
Table 5.7 from Sedimentology and Stratigraphy, 5thed., by Boggs, p. 121

4. Effect of grain size on composition
From Blatt, Middleton and Murray, Origin of Sedimentary Rocks, 1980

5. From Table 5.1 (Boggs, 4th edition, p. 121):
Quartz = 65% of the average sandstone and
30% of the average shale
Feldspar = 10-15% of the average sandstone and
5% of the average shale
- Is less stable
- Includes potassium feldspar (orthoclase,
microcline... and plagioclase (albite through anorthite)
Rock fragments = 10-15% of the average sandstone
- are rare in shale

6. From Table 5.2 (Boggs, 4th edition, p. 128):
Average chemical composition of a sandstone:
SiO2 = 55-65%
Al2O3 = 5-15%
Fe2O3 = 2-5%
Na2O, K2O, CaO, P2O5 = 1-2%
Others: (trace metals, rare earth elements, etc) <<1%

7. Conglomerate classification
Figure 5.10 from Sedimentology and Stratigraphy, 5thed., by Boggs, p. 116