The Geology of the Cenozoic Era

Introduction The Cenozoic began ~65 mya and continues until the present –Cenozoic rocks are more easily accessible and less deformed than older rocks –divided into the Tertiary and Quaternary

Early Work on the Cenozoic Charles Lyell England’s foremost geologist of his day. Author of Principles of Geology (1830) Supported James Hutton's concepts of Uniformitarianism Teacher of Charles Darwin Charles Lyell studied the Tertiary and Quaternary fossils of France Defined the Eocene, Miocene, Pliocene, Pleistocene, and Holocene Paleocene and Oligocene were added later

Geologic Events Cenozoic Laramide uplifts eroded away Mantle upwelling Colorado Plateau Rockies Washington (Longest Tertiary Epoch)

Cenozoic Tectonic activity concentrated in two areas –Alpine-Himalayan belt deformation began in the Mesozoic and remains geologically active. Isolation of Tethys to form the modern Mediterranean Sea –circum-Pacific belt deformation occurred throughout the Cenozoic

Cenozoic Pacific realm 1.Subduction of the Farallon Plate and its Mid Ocean Ridge 2. Formation of Andean Cordillera San Andreas forms

Geologic Events Cenozoic Mantle upwelling Colorado Plateau Rockies Washington (Longest Tertiary Epoch), Basin & Range San Andreas Fault

Circum-Pacific Orogenic belt –Laramide Lt. Jur - E Tertiary –further inland than most - CLUE –deformation was vertical uplift, with little volcanism –shallow subduction angle –“buoyant subduction” Cordillera

Laramide Orogeny K to T Buoyant Subduction One possible result of shallow angle of subduction and the drag that it causes with overlying lithosphere is uplift - Rocky Mountain formation. Renewed normal subduction would restore normal volcanism within the western part of the mountains – Basin and Range

Uplift of the Rocky Mountains Rockies Basin and Range shear stress

Teton Range Laramide uplifts eroded away in Oligocene, renewed uplifts Late Mio – Pleist.

Basin and Range of Cordillera Beginning in the Miocene, 2 mechanisms 1.lessening of the subduction angle allows dewatering volcanism further west. 2.Farallon pieces under the lithosphere cause uplift, lithosphere cracking and buoyant decompression magmas. Basin and Range Columbia River Basalts

Basin and Range terminology Extensional Feature w/ Normal Faults DISCUSSION, SHIP HULLS

Geologic Events Cenozoic Mantle upwelling Colorado Plateau Rockies Washington (Longest Tertiary Epoch) San Andreas Fault, Basin & Range

San Andreas transform Ridges Change Orientation15 mya SAF forms

The Interior Lowlands Sediments eroded from the Laramide highlands were deposited in the Cannonball Sea Early Paleocene south to North Dakota. –Terrestrial deposits are also found, but much of this area was experiencing erosion –Igneous activity was significant in some areas - New Mexico, Colorado, Wyoming, and others –East of the Great Plains, deposits other than glacial are rare until the eastern coastal plain.

The Gulf Coastal Plain The Tejas epeiric sea transgressed briefly over the southeastern coastal plains E. Tertiary –eight minor transgressive- regressive sequences are recognized as sea level fell in general – reduced rifting

East Coast Passive margin sedimentation dominates –rocks form a seaward thickening wedge that dips gently seaward –Cenozoic uplift and erosion produced the present topography of the Appalachians –Coastal Plain a thick clastic wedge –Florida Carbonates Pliocene - Recent

Eastern North America Appalachians rejuvenated recently, probably glacial rebound Allegheny Orogeny still high Erosion due Transgression Coastal Plain streams and marshes

1.Alpine Orogen 3. Vocabulary: Nappe Large recumbent folds in thrust-fault zones where orogenic belts impinge craton margins Flysch alternating thin shales and sandstones. Sandstones turbidites prior orogenic collision. Molasse non-marine deposits accompanying the uplift of a mountain belt. 4.Closing of the Tethys Sea Apennine Balkan Carpathian Caucasus Pyrenees Atlas Isolation of the Mediterranean Basin: Evaporites 2. Eocene to Miocene

Nappe-folded mountains

New Orogen, Nappes still visible

source

Arabian-African Rift 1. The underside of Europe collided with numerous microplates rifted from Africa Closing of the Tethys Sea between late Mesozoic and early Cenozoic time 4. Thrusts not Subduction 3. Messinian Salinity Crisis ~ 5.5 mya 2. Pliocene three way rift. 3. Arabia Microcontinent collision -> Zagros Mts

Himalayan Orogeny Thin-skinned tectonics Partly subducted so under AW Subduction

Himalayan Orogeny AW FAB Zoomed-in Views

Generalized Cross-Section South North

Décollement Décollement (from the French 'to detach from') is a gliding plane between two rock masses, also known as a basal detachment fault. Décollements result in independent styles of deformation in the rocks above and below the fault. Both compressional settings (involving folding and overthrusting) and extensional settings.

Cenozoic Climates, Currents, and Volcanism Ocean current flow changes due to tectonics in Antarctic-Australian and Central American regions Dramatic changes in climate Major plume under North America Continuous cooling, culminating in on-going Ice Age

Cenozoic Cooling (Northern Hemisphere) Australia separates Central America construction Starts see Monterey Fm.

Geologic Events Cenozoic Geologic Events Cenozoic (Longest Tertiary Epoch) Circumpolar Current Antarctica Panama Closes High CO2 Mediterranean Dries Out Rockies

Antarctic Circumpolar Current Paleocene to Mid-Eocene WARM Currents from Tropics

Early Eocene Warm Green River Formation Oil Shales

Green River Formation Lake (lacustrine) silts Organic-rich (oil) shales w/ fossils

Green River Formation Tropical Plants to High Latitudes

Antarctic Circumpolar Current 4. Fauna changes. Example: Penguin relationships from S. American bird following current rich in fish. 2. Late Eocene Sudden Antarctic cooling as warm currents barred 5. Longest continuous Ice Sheets 1. Australia pulls away 3.

Fossils in volcanic tuff deposit Tree stumps, insects in Oligocene Ash, Florissant, Colorado Extensive Volcanism Late Eocene to Oligocene Cooler

Pre Gulf Stream Current Isthmus of Panama open, same salinity Atlantic and Pacific Early Pliocene

Modern Gulf Stream Current 1. Terranes, Subduction, Volcanic Arc, Isthmus of Panama closed, North Atlantic isol., higher salinity, dense cool water sinks before it reaches Arctic, polar sea freezes Late Pliocene 2. Caused Formation of the present Gulf Stream Current in the Atlantic 3. Dramatic Cooling Mediterranean Dried Out

Late Pliocene 5.96 to 5.33 mya Evaporites, Gorges, Faunal Exchanges Messinian Salinity Crisis – recall salt buoyancy, low competence

The Great Exchange Bears Camels Cats Dogs Elephants Horses Peccaries Rabbits Raccoons Skunks Tapirs Weasels Anteaters Armadillos Capybaras Glyptodonts Monkeys Opossums Porcupines Sloths Toxodonts South America Late Pliocene, Isthmus of Panama closed, migrations North and South North America

With cooling comes drought. Grasses replaced forests, mammals adapted for a diet of grass, grew larger, faster as predators pursued.

Geologic Events Cenozoic Geologic Events Cenozoic Laramide uplifts eroded away Mantle upwelling Colorado Plateau Rockies Washington (Longest Tertiary Epoch)

Pliocene 2000 m uplift of Colorado Plateau (Grand Canyon - Colorado River incised ) Evidence, Incised meanders

The Yellowstone Plume Miocene to RecentMiocene to Recent Starts with flood basalts in Columbia Plateau Washington and Oregon 15 myaStarts with flood basalts in Columbia Plateau Washington and Oregon 15 mya Continues into Snake River BasinContinues into Snake River Basin Then to Yellowstone in HoloceneThen to Yellowstone in Holocene

Basalt flows - Columbia Plateau Miocene 15 – 12 mya Start of Plume forming Snake River Plateau and recently Yellowstone Just like the Watchungs

Craters of the Moon Monument Migration of Yellowstone Park over the plume 2 mya to recent Migration of Snake River Basin over the plume 10 mya

Geologic Events Cenozoic (Longest Tertiary Epoch) Rockies

Pleistocene Glaciation The Pleistocene began about 1.8 – 1.6 mya and ended about 10,000 years ago –several intervals of widespread glaciation took place, separated by warmer intervals

Causes of Ice Ages Plate Tectonics Moves Continents to Poles Raises mountains above snowline Orbit distance, Axis Tilt and Wobble –Moderates solar radiation north of 65 N –Milankovitch Cycles ~ 100,000 years –Low summertime radiation 65 N, glaciers expand

Milankovitch Cycles 100,000 years Discussion: cool summers and wet winters Moisture content of air masses

41,000 years Cold Dry Winter Hot Summer Warm Wet Winter Cool Summer

25,700 years Discussion: Perihelion and Aphelion

Louis Agassiz Swiss Geologist Eventually Professor of Geology at Harvard Familiar with Alpine Glaciers Recognized Moraines, erratic boulders, and scoured bedrock in Europe and N.Am Proposed huge glaciations Europe and N. America

Glacial and Interglacial Stages 65 (Many) (ongoing) Glacial advances named for states C-14 works here Medieval warm Little Ice Age

Foraminifera tests - Ice Age 1. Evap. water and CO 2 removes 16 O from oceans 18 O left in oceans used to make shells 3. Also spiral direction & diversity depends on Temp. Nebraskan Kansan Illinoian Wisconsinan About 30 pulses in 4 or so major groups Cold Warm 2. Ice traps CO 2 and water with light oxygen

The Effects of Glaciation The effects of glacial erosion and deposition are evident worldwide –lowering of sea level affected base level of streams –pluvial lakes –proglacial lakes –Compression of the Crust

Pleistocene Lakes - West Pluvial Lakes Remnant of Bonneville

Lake Bonneville terraces Much deeper that GSL

Terminal Moraine (melting)