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Important Stratigraphic and Geomorphic Concepts. Facies. Facies. A sediment body or sedimentary rock distinguished by its lithology, geometry, sedimentary structures, proximity to other sediments or sed rocks, and fossil content.
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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)
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
What is this facies Sequence? Shallow water facies overlie deeper water facies. A regressive sequence "shallowing upward" SS SH Lime SH LS
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 (1638-1687) 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
E.E. Gamble Two till units that sandwich an outwash; MN
soil geomorphic analogue 2Holocene alluviums; fragipan (dryer altithermal), vs. humid environment. MS Wysocki
Steno’s principle of Original Continuity
Badlands, SD E.E. Gamble
Cross-cutting Relations 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 RelationshipsArray features A, B, C, D, E by age. D A E B C
A B Converging, backwearing side slopes St. Peter Sandstone (Boone soil) over Prairie Du Chein dolomite; River Falls, WI Wysocki
Inset Relationship ( type of cross-cutting relationship )
inset relationship; northeast KS Wysocki
channel fill; note lack of surface expression. / Big Nemaha R., NE Wysocki
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)
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