FACIES MODELS

1. FACIES MODELS Pages 241-243 Sedimentology 340

2. Previous Work • Majority of the semester has been largely descriptive, identifying; • Lithology & mineralogy • Sedimentary fabric and texture • Sedimentary structures • Scales of observation • Now a “Story to tell” and “puzzles to solve” • Sediments are products of sedimentary processes • Snapshot of the environment of deposition

3. Sedimentary Facies • Facies analysis • The interpretation of rocks and sediments for the purpose of reconstructing the processes that were responsible for the original deposition • Multi-pronged approach • Physical • Chemical • Biological • Lithofacies and Biofacies Example of sedimentary facies modal: Delta distributary channel

4. Pardon me, what are facies? • In the field of geology, facies is often misused and misunderstood • AGI (1984) Definition: • The aspect, appearance, and characteristics of a rock unit, usually reflecting the conditions of its origin; especially as differentiating it from adjacent or associated units • Facies! • Refers to the lithologic and biologic characteristics of a sedimentary deposit imparted by the processes collectively operating in the depositional environment

5. Facies defined • Deposits that evolve in a specific depositional environment are considered to be sedimentary facies • Ex. Arid desert lakes/salt flats Bonneville Salt Flats, Utah

6. Facies defined • For this class and facies will be defined as… • A description of physical, chemical and biological properties of a sedimentary unit • Main criteria in facies definition are: • Lithology, sedimentary structures, paleontology, and sediment body geometry

7. Sediment body geometry is the 3-D shape of deposit barrier island

8. Question? What are you looking at? How can you describe it in the framework of its depositional environment? This is a delta How do we know? ?

9. Delta Delta is at the end of a river and is the sedimentary record of deposition into deeper water

10. Nile Delta Example Modern examples are used to gather data on processes and deposits (cores) Facies model - a 3-D block diagram

11. Facies model – 2-D vertical succession diagram Delta depositional environment?

12. So question was….…how do we know ? Answer: facies associations • Depositional environments are generally composed of multiple subenvironments • Ex. Delta • Thus, we can expect that facies will vary throughout the environment to reflect the transition between subenvironments • We must assume that adjacent facies represent adjacent environments

13. Delta components and facies

14. So how are they related? The association of certain facies near or adjacent to each other are characteristic of distinct depositional environments Based on observations from modern environments of deposition and parallels to past environments By understanding these associations, we can generate facies models

15. 4-D models add understanding of processes 3-D Block daigram facies associations in a delta distributary channel environment

16. Facies Models • General summary given to a depositional system • 2-D Vertical successions of sediment that represent facies relationships expected in the geologic record • 3-D Block Diagrams • 4-D Models detailing sedimentary processes

17. Walther’s Law of Correlation of Facies Facies that occur in comformable vertical successions of strata also occur in laterally adjacent environments Thus, facies boundaries may shift so that the deposits of an adjacent environment may lie directly atop those of a laterally related environment

18. Takeaway Message: For any sedimentary package you can examine the facies and their relationships to each other, apply a facies model and assign a depositional environment So, what is this?

19. Catskill Delta (Devonian) Catskill Delta builds westward through time with sediment delivered by rivers fluvial delta marine Regressive- sediments coarsen upwards

20. 3-D Barrier Island Facies Model barrier island

21. Environments are dependent on sediment supply, • subsidence and changing sea level Conditions (tectonics or climate) usually change with time With rise in sea level ….. The shoreline shifts landward and fine grained marine sediments will overly coarser beach sediments Transgressive – sediments fine upwards,

22. Facies Changes • Transgressive and Regressive systems can be identified by observing facies and lithological changes in rock/sediment • Transgressive – sediments fine upwards, represent deeper water environments • Regressive- sediments coarsen upwards, represents shallowing effect

23. Facies Distribution • What factors control the nature and distribution of facies? 1. Sedimentary Processes 2. Sediment Supply 3. Climate 4. Tectonics (subsidence or uplift) 5. Sea level change

24. Summary – using an example What facies would you expect to find from this depositional environment? • Fluvial Environment • Meandering River • Cross bedded sandstones • Coarse gravel deposits • Broad sheets of silty shale with root casts and plant debris • Isolated Shale bodies • Beds of peat and coal • Facies models help solve the puzzle of depositional environment