Important Stratigraphic and Geomorphic Concepts 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.

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.

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)

time line

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 Beach sands Nearshore silt Offshore Clay

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

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

Basic Stratigraphic Principles Nicolaus Steno ( ) fossil descriptions first stratigrapher Steno's Principles Superposition Original Horizontality Original Lateral Continuity

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

Superposition Younger

Steno's Principles Superposition

limey mudstone over coal; ND E.E. Gamble

Two till units that sandwich an outwash; MN

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

Pleistocene Loess Deposits Eastern WA Gamble

Original Continuity Steno’s principle of

Lateral Continuity

Badlands, SD E.E. Gamble

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

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).

Cross-cutting Relationships Array features A, B, C, D, E by age. A B C D E

Cross Cutting Surface

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

Inset Relationship ( type of cross-cutting relationship )

Wysocki inset relationship; northeast KS

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

Cross-Cutting Relations and Inclusions

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

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

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

Relative Time

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

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