important stratigraphic and geomorphic concepts facies
TRANSCRIPT
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.
• 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 sequenceDeeper 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 PrinciplesNicolaus 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 PrinciplesSuperposition
limey mudstone over coal; ND E.E. Gamble
E.E. GambleTwo 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
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.
A
B C
D
E
Cross Cutting Surface
Converging, backwearing side slopes
St. Peter Sandstone (Boone soil) over Prairie Du Chein dolomite; River Falls, WIWysocki
AB
Inset Relationship
( type of cross-cutting relationship )
Wysockiinset 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