Cenozoic Modernization

Eastern Cratonic Margin

• Passive margin with minimal uplift
• Stream entrenchment
• Coastal plain, thickening wedges
• Reduced terrigenous clastics, carbonate sediments to thicknesses > 2500m (subsiding, elongate coralline platforms).

Gulf Coast

• Evidence for 8 major transgressions/ regressions.
• Interfingering offshore muds with nearshore sands provide hydrocarbon reservoirs. Coastal plain sediments near the northern border of the Gulf exceeds 10,000 m.

Rocky Mountains

• Interior continental terrestrial deposition; one marine transgression in the Paleocene
• Early Tertiary deposits within lowlands and intermontane basins.
• Late Cretaceous tectonism into the Paleocene
• Tectonic style includes western igneous volcanic belt and eastern fold and thrust belt
• Some Cretaceous seaway rocks exhibit compressional tectonics.
• Palaeocene deposits include gray siltstones and sandstones, carbonaceous shales, lignite and coal (e.g., Fort Union Formation).
• Eocene deposits include the Wasatch & Green River Formations (fluvial fining upwards; Bryce Canyon badlands and shallow lake deposits).
• Green River Fm. Limestones and varved shales over 600 m in thickness.
• Varves record over 6.5 million years.
• Some lakes rich in waxy hydrocarbons (oil shale)
• Eocene and Oligocene record active volcanism and extensive alluvial plain deposits (White River Fm. -Badlands of South Dakota)
• Uplifts and erosion resulted in Oligocene -Pliocene sands, shales & lignites to the east of the mountains.
• Terrestrial deposits are interspersed with volcaniclastics ( Great Plains ).
• Terrestrial sedimentation interspersed with volcaniclastics into the Pliocene Ogallala Group.
• Present topography of area the result of erosion following Miocene uplift.

Basin and Range Province

• Late Tertiary tensional faulting (e.g., Death Valley ).
• Early Tertiary structural arch (a result of Mesozoic tectonics).
• Early Miocene subsidence between sets of normal faults resulted in horsts (uplifted blocks) & grabens (down faulted basins).
• Coarse alluvial fan deposits are intermixed with lacustrine and evaporite deposits

Basin-n-Range Causes

• Westward-moving North American plate
• Crustal adjustment due to oblique shearing of the continental edge during the Miocene ;
• Developed in response to earlier subducted ocean plate;
• Convectional movements beneath the plate.

Colorado Plateau

• Undeformed block uplifted during the early to middle Pliocene (5-10 MY BP). Faults provide routes for magma to escape forming volcanoes (San Francisco Mts -AZ).
• The Grand Canyon is a feature of the Colorado Plateau.

Columbia Plateau

• Columbia Plateau result of Tertiary & Quaternary volcanic activity erupting basaltic lava.
• More than 50,000 km2 of land buried up to depths of 2800 meters.
• West of the Plateau is uplifted belt where volcanic activity began about 4 MY BP - the Cascades
• Mt. St. Helens - 1980; Mt. Lassen - 1915;, Mt. Ranier -2000 YR BP, Mt. Hood; Mt. Baker
• Surface manifestations of ongoing eastward collision

West Coast Tectonics

• Cenozoic eastward-dipping subduction of the Farallon and Juan de Fuca plates.
• Cenozoic consumption at subduction zone exceeded material at the spreading center.
• Subduction of Farallon Plate and East Pacific rise
• Remnants now include:
• Juan de Fuca plate near Oregon/Washington;
• Cocos plate off Mexico.
• North American plate contacted with the northeast-moving Pacific plate.
• Pacific plate changed direction and slipped laterally along continental (San Andreas fault).
• Baja California sheared away from mainland Mexico (5 MY BP).