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