Terrigenous Sandstones

• quartz arenite - 34%,
• lithic arenite - 26%
• graywacke - 20%,
• arkose - 15%
• hybrids and others - 5%

Carbonate Sandstones

• mixed composition
• requires special environment and/or rapid deposition
• not very common
• intrabasinal cabonate sands
• calcarenites
• special case

Pyroclastic Sandstones /Tuffaceous Sands

• pyroclastic detritus
• glass shards or igneous material
• special case

Glauconitic Sandstone

• special case
• peak abundance in Cambrian & Cretaceous
• glauconite needs some agitation in sea water
• glauconite is a soft bright green mineral
• last depositional site was poorly sorted
• glauconite indicates shallow marine environment
• genesis time
• two types of glauconite
• examples

Quartz Arenite

1. >95% quartz grains

2. most common sandstone

3. minor amount of matrix

4. light colored

5. well sorted

6. well rounded

7. rare fossils

8. cross bedded

9. bimodal size distribution

10. blanket shaped bodies often interbedded with shale

11. peak abundance

• Late Precambrian-Cambrian
• Cretaceous

12. age maturity relations

13. very few modern quartz arenites

14. currently examples in deserts

15. desert sands are missing 0.1-0.3 mm size grains

16. flume experiments

17. recycling quartz arenites

Summary

• prolonged abrasional history
• stable tectonics
• wind history
• time of favorable conditions

Arkose

1. 15% of sandstones

2. abundant feldspar

3. color

4. types of feldspar

5. matrix & grain size distribution

6. coarse grained

7. accessory minerals

8. mica flakes

9. feldspars breakdown

10. temporal distribution

11. wedge shaped deposits

12. areal extent of deposits

13. continental deposits

14. depositional environment

15. climate/tectonic balance

Summary

• continental with granite source
• dry depofacies or rapid deposition
• close to source
• fault basins

Lithic arenites

1. light colored

2. supracrustal rock fragments

3. feldspar

4. quartz

5. mica flakes

6. mineralogy & chemistry

7. pore space or pore filling cement

8. moderately sorted

9. 20-25% of sandstones

10. most modern sands are lithic arenites

11. modern lithic arenites & sublith-arenites

12. associated geology

13. occurrence

• geosyncline
• miogeosyncline
• eugeosyncline
• inter-cratonic basins

14. immature

15. no prolonged transport

16. local provenance indicators

17. mixed lithology terrane denudation

18. large rivers deposition

19. alluvial process deposition

20. graywacke precursor?

21. temporal distribution

22. Appalachian Mountains

Summary

• diverse origins
• take individually
• rivers & turbid currents in history
• associated with plate collisions & arc subduction

1. 20-25% of sandstones

2. tough

3. color

4. complex mineralogy

• major minerals
• feldspars
• rock fragments
• minor minerals

5. immature

6. size continuum

7. matrix

8. intergrown grain framework

9. hazy margins

10. sedimentary structures & turbid deposition

11. cyclic deposition

12. marine

13. active tectonics

14. eugeosyncline

15. temporal distribution

16. recent examples

17. graywacke matrix problem

• origin
• lab study

some possible matrix origins

• matrix recrystallization
• clay flocculation
• mechanical introduction
• authigenic & diagenetic alteration of labile components
• graywackization

Summary

• petrologically complex
• matrix problem
• turbid deposition with active tectonics

GEL 3510 page

RBJ 10/99