Important Stratigraphic and Geomorphic Concepts

1. Important Stratigraphic and Geomorphic Concepts Facies

2. Facies • A sediment body or sedimentary rock distinguished by its lithology, geometry, sedimentary structures, proximity to other sediments or sed rocks, and fossil content. • Formed by and characteristic of a particular depositional environment.

3. Facies refers to various sediment characteristics you might refer to a "tan, laminar-bedded, beach sandstone facies". Rock unit characteristics result from depositional environment (energy). Depositional setting imprints a distinctive sediment characteristics.. facies is a distinct kind of rock for that environment and area.

4. Each depositional environment grades laterally into other environments. We call this facies change when dealing with the rock record. A = Sandstone facies (beach environment) B = Shale facies (offshore marine environment) C = Limestone facies (far from sources of clastic input)

6. time line

7. Walther's Law – (continuous deposition) Sedimentary environments that start out side-by-side will overlap one another over time due to transgressions or regressions. A vertical sequence of beds results. The vertical sequence of a facies matches the original lateral distribution of sediments and sedimentary environments. Transgressive sequence Deeper water facies overlie shallow water facies. A "deepening upward“ or “fining upward” sequence. Offshore LS Offshore Clay Nearshore silt Beach sands

8. What is this facies Sequence? Shallow water facies overlie deeper water facies. A regressive sequence "shallowing upward" SS SH Lime SH LS

10. Laws of Stratigraphy • Superposition- youngest on top • Original lateral continuity- erosion cuts valleys • Original horizontality- most sediments deposited in horizontal layers, or nearly so. • Cross-cutting relations- A feature must be younger than the rock, sediment, or surface it cuts • Inclusions- must be older than their host

11. Basic Stratigraphic Principles Nicolaus Steno (1638-1687) fossil descriptions first stratigrapher Steno's Principles Superposition Original Horizontality Original Lateral Continuity

12. Principle of Superposition youngest material on top; except if inverted Fundamental principle for age relationships in sedimentary rocks (sediments) and extrusive volcanics

13. Superposition Younger

14. Steno's Principles Superposition

15. limey mudstone over coal; ND E.E. Gamble

16. E.E. Gamble Two till units that sandwich an outwash; MN

17. soil geomorphic analogue 2Holocene alluviums; fragipan (dryer altithermal), vs. humid environment. MS Wysocki

18. Pleistocene Loess Deposits Eastern WA Gamble

19. Steno’s principle of Original Continuity

20. Lateral Continuity

22. Badlands, SD E.E. Gamble

23. Cross-cutting Relations relative age relationships A feature is younger than the rock, sediment, surface, or other feature that it cuts.

24. Relative Age Tools: Cross-Cutting Relations A rock unit must always be older than any feature that cuts or disrupts it (e.g., faults, metamorphism, igneous intrusions).

25. Cross-cutting RelationshipsArray features A, B, C, D, E by age. D A E B C

26. Cross Cutting Surface

27. A B Converging, backwearing side slopes St. Peter Sandstone (Boone soil) over Prairie Du Chein dolomite; River Falls, WI Wysocki

28. Inset Relationship ( type of cross-cutting relationship )

29. inset relationship; northeast KS Wysocki

30. channel fill; note lack of surface expression. / Big Nemaha R., NE Wysocki

31. Cross-Cutting Relations and Inclusions

32. Facing of Strata:how some sedimentary structures indicate if beds are overturned..

33. Hutton’s “Great unconformity” at Siccar point, eastern Scotland

34. Relative Time Superposition (Steno) Lateral Continuity (Steno) Original Horizontality (Steno) Inclusions (Lyell) Cross-cutting Relationships (Lyell)

35. Relative Time

36. Quiz - Array by age: Faults A & B, Dikes A & B, the Batholith, and the Limestone and Shale units.

37. Shale Youngest Dike A Dike B Batholith Fault B Fault A Limestone Oldest