regional geology and tectonic history of wyoming geological field techniques course
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Regional geology and tectonic history of Wyoming
Geological Field Techniques Course
Wyoming geologic history
See the summary chart in your guidebook Begin to place events
in proper context
Regional physiography
Wyoming straddles the Great Plains and Rocky Mountains
Regional tectonic provinces
Central craton surrounded by orogenic belts NuNA = nucleus of
North America
Basement rocks
Subdivided by age and tectonic affinity
Tectonic history of the U.S. Cordillera
Seven major periods of tectonism Antler (Mississippian) Ancestral Rockies (Mississippian – Permian) Sonoma (Permian) Nevadan (Jurassic) Sevier (Cretaceous) Laramide (Late Cretaceous - Eocene) Cenozoic tectonics (continuing today!)
Basin and Range extension San Andreas fault Volcanism
Cambrian paleogeography
Maps from Dr. Ron Blakey’s web sitehttp://jan.ucc.nau.edu/~rcb7/globaltext.html
Early Paleozoic stratigraphy
Reflects passive margin and shallow continental sea deposition Sandstones, shales and carbonates Global sea level changes exert dominant control
Uplifts of the Ancestral Rockies
Mississippian – Permian Earliest motion on
some classic Rocky Mountain ranges
Colorado Front Range Uncompaghre
New Mexico Sangre de Cristo
West and North Texas
Marathon Llano
Permian paleogeography
Ancestral Rockies related to continent-continent collision Assembly of Pangaea Only minor deformation in Wyoming Major transition in depositional environments
begins
Permian – Jurassic is tectonically quiet
Little deformation in Wyoming Sonoma and Nevadan orogenies to west
Major fall in global sea level
Early Cretaceous paleogeography
Accretion of exotic terranes Creation of Andean style subduction margin
The Sevier orogeny
Sevier – Laramide stratigraphy
Sevier orogeny
Creation of continental magmatic arc Extensive thin-skinned deformation Foreland basin deposition
Sevier deformation front
Great Valley
Foreland fold and thrust belt
Sevier orogeny deformation style
Thin-skinned Sedimentary
“cover” detached from basement
Idaho – Wyoming thrust belt
Cross sectional view
westwest easteast
Tectonic configuration – Late Sevier
Foreland basin of the Sevier orogeny
Western Interior Basin
Formation of foreland basins
Thickening and loading of crust causes flexure Creates accommodation space to capture debris
eroded from mountains
Cretaceous foreland basin
Sediment sources and crustal loading patterns revealed by stratigraphic thickness and facies variations
Late Cretaceous paleogeography
Two major tectonic changes Shut down of magmatic arc Change in deformation location and style
Laramide orogeny
Tectonic configuration - onset Laramide
Laramide basement uplifts
A distinctly different structural style In a very different place
Colorado plateau Laramide uplifts
Capitol Reef National Park
After Billingsley, Huntoon and Breed (1987)
Black Hills Laramide uplift
Laramide sedimentary basins
Basement uplifts subdivide the Sevier foreland basin into many smaller basins Intermontaine
basins
Geometry of Laramide basins
Asymmetric Basin axes close
to uplift margins Facies and
thickness changes indicate uplifts were sediment sources
Regional structure of Wyoming
Regional structure of Wyoming
Detailed structure of basement arches
Flexing of crustal rocks creates many smaller scale basement-involved folds
Erslev et al. (2001)
Why the change in structural style?
Change in plate convergence Direction Rate
Younger, hotter, more buoyant crust begins to subduct more rapidly
Sevier to Laramide transition
Related to change in subduction angle
Consequences of shallow subduction
Causes reactivation of old crustal weaknesses Laramide uplifts resulted from inversion of
Proterozoic extensional faults
Marshak et al. (2000)
Cenozoic tectonics30 Ma 20 Ma 10 Ma Present
Magmatic shift
Laramide magmatic gap closes and migrates southward
Miocene paleogeography
Basin and Range extension
Basin and Range extension
Basin and Range faulting
Alternating mountain ranges and basins Horst and graben
systems
Basin and Range faulting
Basin and Range faulting in Wyoming
Teton National Park
Cenozoic volcanism
Columbia River flood basalts Yellowstone hot spot