1. From latest Cretaceous to middle Eocene, unusually shallow subduction produced uplift and basin formation in the Rocky Mountains

2. Beginning in Miocene time, the subducting margin of California was replaced with transform faulting.

3. India collided with Asia to form the Himalayas.

4. Australia and South America rifted apart from Antarctica.

5. Africa collided with Europe to form the Alps.

6. The great Tethyan seaway closed, leaving the Mediterranean Sea as a remnant.

7. Land mammals diversified rapidly in the Paleocene following the extinction of dinosaurs.

8. Paleocene and Early Eocene jungles were inhabited by archaic leaf-eating and tree-dwelling mammals.

9. Antarctic glaciation began in the middle Eocene to Oligocene time.

10. During the early Cenozoic, vegetation changed from jungles to grassy savannas

11. Within this new environment, mammals became adapted for rapid running and for eating newly evolved grasses.

1. At the end of the Cretaceous, arc volcanism ceased in California and Nevada while deep basement folding occurred in Wyoming, Colorado and New Mexico, due to unusually shallow (almost horizontal) subduction. Deformation due to this shallow subduction is collectively regarded as the Laramide Orogeny.

2. The Laramide orogeny was characterized by broad anticlinal upheavals of basement rocks and overlying strata as opposed to the earlier Sevier Orogeny that was characterized by thin-skinned thrusting in the foreland. Laramide deformation also occurred farther east than the Sevier belt due to the shallower subduction.

3. Laramide tectonism continued throughout the Paleocene and early Eocene.

4. Figure 15.3: Between Laramide uplifts, intermontane basins collected huge volumes of sediment (up to 3,000 meters thick) eroded from adjacent uplifted regions.

5. Sediments within intermontane basins were deposited by rivers, floodplains, freshwater lakes and swampy river deltas (coal deposits). Important intermontane basins include the Green River and Uinta basins.

6. Gigantic freshwater lakes in some Intermontane basins deposited freshwater limestone. The middle Eocene Green River Formation (large lake deposit) contains shale (some oil bearing), sandstone, freshwater limestone and evaporites. Fossils of fish, frogs, birds and plants are remarkably preserved in Green River shale.

7. Figure 15.3: Laramide intermontane basins were filled to the top by the Miocene. River drainage systems were oblivious to the buried mountains beneath them. Mountain peaks that emerged above the sediments were deeply eroded and beveled off during the Oligocene and Miocene, producing flat-topped features seen today throughout Rocky Mountains.

8. Renewed uplift subsequently occurred which increased erosion such that much of the basin fill was eventually stripped away. Rivers cut down through the hard cores of mountains, creating spectacular water gaps.

9. Figure 14.32a: In California, the Sierran volcanic arc went extinct in the Late Cretaceous and underwent erosion during the Cenozoic to expose the granitic batholiths which today comprise the Sierra Nevada Mountains of California. Marine turbidites and deltas deposited sediments in the adjacent forearc basin.

10. Outside of the Laramide tract, extensive arc volcanism continued to the north in Idaho and eastern Washington and to the south in Arizona and Mexico during Paleocene and Eocene time.

1. Figure 15.5: In the late Eocene, volcanic activity increased all along the Cordilleran belt, suggesting that shallow subduction had ceased. The downgoing plate was returning to its normal dip, possibly even collapsing, thus triggering crustal melting along the entire extent of western North America.

2. The ancestral Cascades erupted green volcanic ash in central Oregon during the late Oligocene and earliest Miocene. Extensive volcanism also occurred in central Idaho and northwestern Wyoming where huge volumes of ashflow were deposited in Yellowstone National Park.

3. Volcanism broke across the Laramide "magmatic lull" region by the early Oligocene, resulting in significant eruptions in central Nevada, western Utah, southwestern Colorado, New Mexico and Arizona.

4. Figure 15.7: The cessation of shallow subduction also ended Laramide tectonism as evidenced in western Wyoming where thrust faults deform Paleocene sediments but do not affect middle Eocene deposits. Pliocene sediments overlie normal faults in this region, suggesting that extensional tectonics began around Pliocene time.

5. Figure 15.8: In the Rocky Mountain Ranges, sedimentation in basins was accompanied by pulses of deformation until the Eocene. Post-Eocene sediments were not significantly deformed, suggesting Laramide tectonism had largely ceased by this time.

6. Resumption of normal subduction also spurred further development and/or uplift of forearc basins along the Pacific Coast. Sedimentation in the Central Valley forearc basin of California changed from marine to shallow marine/nonmarine sedimentation in the Oligocene.

7. Laramide Basins were filling rapidly by the end of the Eocene. The Rocky Mountains, exposed today as tall jagged peaks, were nearly buried beneath their own debris during most of the Oligocene and Miocene.

8. During this period when the Rockies were mostly buried, isolated highlands continued to shed sediments eastward into Nebraska, eastern Wyoming and the Dakotas (Badlands of S. Dakota).

9. Late Oligocene volcanism in Colorado and Nevada deposited wind-blown ash towards the east into Nebraska.

10. Fluvial sands and gravels of the Ogallala Group, which today serve as an important aquifer along the High Plains, were deposited during the upper Miocene and Pliocene.

1. Since the early Mesozoic, the Cordilleran margin had been a subduction zone. From the Cretaceous until the early Miocene, the Farallon Plate was obliquely subducting underneath the North American Plate.

2. Figure 15.12: In the late Oligocene or early Miocene, a segment of the Farallon-Pacific spreading ridge came in contact with the subduction zone and the Pacific Plate touched the North American Plate for the first time. Along the zone of ridge subduction, eastward subduction of the Farallon was replaced by northwesterly movement of the Pacific Plate. The Pacific Plate along this zone was not subducting like the Farallon Plate, but rather was moving sideways such that the boundary changed from a subduction zone to a transform fault (San Andreas Fault).

3. When the Pacific Plate first touched North America in the early Miocene, the San Andreas fault was a short segment between the long subduction zones to the north and south. The San Andreas has since grown much larger as more of the Farallon Plate was subducted. Today it runs from the Gulf of California to northern California, transporting the Pacific Plate northwest relative to the North American Plate.

4. As more of the subduction zone was being replaced by transform faulting, arc volcanism in southern California and Arizona ceased since melting of downgoing lithosphere was no longer occurring in these regions.

5. Figure 15.15: During the Miocene, Arizona was being stretched apart by extensional forces into a series of fault-bounded mountains and graben basins in between (Basin and Range tectonics). Miocene extension began in the south during which time the rest of Nevada experienced continued arc volcanism. Basin and Range tectonics, however, gradually extended towards the north.

6. Today, the Basin and Range province extends from Nevada all the way into southern Oregon. The crust of Nevada has been stretched to twice its Miocene width.

7. Figures 15.12 & 15.17: In eastern Washington and Oregon during the middle Miocene, the Columbia River plateau basalt spewed out of crustal fissures from sources deep in the mantle, probably as a result of movement of the region over a large hot spot. Extensive flows eventually covered 300,000 square kilometers of land over a 3.5 million year period, filling former valleys with flow after flow of basaltic rock that eventually achieved a stacked thickness of up to 4,000 meters.

8. In the late Miocene and Pliocene, similar flood basalt erupted in the Snake River plain of Idaho, suggesting that hot spot activity was migrating eastward as the North American Plate rode westward over it. Today, the hot spot resides beneath Yellowstone National Park and is responsible for the geysers, occasional earthquakes and overall general uplifting of the area. Much of Yellowstone Park resides within a large caldera.

9. Throughout the late Miocene, Basin and Range stretching and the shutoff of the Nevada volcanic arc continued as the boundary between the subduction zone and the San Andreas transform moved north. By the end of the Miocene, the San Andreas reached north of San Francisco.

10. Figure 15.18: Paleomagnetic evidence suggests that the Sierra Nevadas, Cascades, Klamath Mountains and Great Valley rotated southwestward along a hinge in western Washington (triangle) since the middle Miocene. This enormous rotation stretched the crust like an opening fan to form the Basin and Range Province behind it.

11. Figure 15.17: Late Miocene-Pliocene tectonism extended east of the Basin and Range Province into the four corners region of Arizona, Utah, Colorado and New Mexico where uplift of the Colorado Plateau occurred. Mantle upwelling uplifted the Colorado Plateau block about 1.5 km, causing the Colorado River to cut the Grand Canyon.

12. Uplift of the Colorado Plateau was accompanied by exhumation of the Rocky Mountains by erosion possibly due to uplift or climatic changes. The long-buried Rockies were resurrected again, the sedimentary cover was stripped away, and rivers were forced to downcut rapidly and carve deep canyons such as the Royal Gorge in Colorado and Flaming Gorge in Utah.

13. In the Late Miocene, the Rio Grande rift opened along the eastern edge of the Colorado Plateau and was eventually filled with Miocene and Pliocene sediments.

14. Figure 15.21: Along coastal California, northwesterly shearing caused fault-bounded crustal blocks to slide northward, shearing past one another. In the Transverse Ranges, fault blocks got caught between shear zones and were rotated clockwise about 90o since the mid-Miocene.

15. Figure 15.22: As rotation proceeded, deep structural chasms opened up between pivoting crustal blocks to form narrow, steep-walled basins. These basins accumulated great thicknesses of sediments. Examples include the Los Angeles Basin and Ventura Basin, both accumulating several km of sediment in only a few million years. The Ridge Basin, north of Los Angeles, contains 13.5 km of sediment yet is only 10-15 km wide.

16. Figure 15.25: A second triple junction moved southward and reached the southern tip of Baja California about 5 million years ago, causing the entire peninsula to tear away from mainland Mexico. The East Pacific Rise began to spread in the Gulf of California.

17. Figure 15.23: Most of the events initiated in the Miocene have continued to this day.

1. There is a coincidence in timing between the growth of the San Andreas Fault System and opening of the Basin and Range Province.

2. Hypothesis #1: The subducted portion of the East Pacific Rise lies under Nevada and the sub-crustal spreading causes mantle upwelling and crustal extension. Some scientists dispute this, claiming that the East Pacific Rise ends abruptly at the transform fault.

3. Hypothesis #2: The Basin and Range was produced by backarc spreading. However, regions of the Basin and Range which were no longer behind an arc continued to spread.

4. Hypothesis #3: Following the onset of transform faulting along the plate boundary, a detached portion of the subducted Pacific Plate continued to be subducted and melted beneath Nevada. This, however, would produce volcanism and not cause significant crustal rifting.

1. Figure 15.24: A "slab gap" forms between subducting remnants of the Farallon Plate. Within this gap, North America lies directly over upwelling mantle which, in turn, causes Basin and Range rifting.

2. Figure 15.25: The Dickinson and Snyder hypothesis explains why the Basin and Range opened progressively from south to north since the expanding gap would generate a northward exposure of the mantle.

3. As the northern edge of the gap moved north, the Cascade arc was shut off in the south. The current northern edge of the gap lies just south of the southernmost active Cascade volcanoes (e.g. Mt. Lassen and Mt. Shasta).

4. In addition, the expansion of the slab gap underneath the Colorado Plateau region is predicted to have occurred 10-5 million years ago, around the time that uplift actually occurred.

1. Figure 15.26: Chains of volcanic islands and submerged seamounts comprise the Emperor -Hawaiian chain of the Pacific Ocean. This volcanic chain may represent the trace of a mantle plume (or hotspot).

2. The plume of hot material rises from the lower mantle and inpinges on the base of the lithosphere, producing basaltic eruptions on the surface. The chain of volcanoes and seamounts are produced when the lithosphere moves over this fixed hot spot.

3. Fossils and isotopic ages from dredged sedimentary and volcanic rocks indicate that the northernmost Emperor Seamounts are Late Cretaceous in age, seamounts near the bend are 46 Ma, Midway Island is 18 Ma and the Hawaiian Islands were formed from 6 Ma to the present. The chain therefore becomes progressively younger towards the southeast, suggesting that plate motion is towards the north-northwest. The sharp bend indicates a change of direction of plate motion areound 35 to 40 Ma.

4. Figure 15.27: Each volcanic center was built upon abyssal sea floor 6,000 meters below sea level and developed into an emergent seamount in only a few million years. Each island then moved off the hot spot, subsided beneath sea level, and eroded to form flat-topped seamounts, many rimmed with coral reefs.

1. Figure 15.26: The mid-Cenozoic date for the change in direction of motion of the Pacific Plate corresponds to the initial collision between the American Plate and the East Pacific ridge as well as a time of renewed volcanic activity in the Aleutians and all the western Pacific island arcs.

2. During this mid-Cenozoic plate reorganization, Japan and several other western Pacific island arcs formed from continental slivers that tore away from mainland Asia, opening small marginal ocean basins behind them.

1. On the southeastern Pacific margin, the last Gondwana separation was completed in mid-Cenozoic time.

2. Figure 15.29: Until the Miocene, South America and Antarctica were connected by the Antarctic Peninsula. Separation of Antarctica and South America occurred in early Miocene time (23 m.y. ago) and represented the last stage in the breakup of Gondwanaland.

3. Figure 15.28: Gondwanaland apparently collided with a spreading-ridge triple junction and this collision broke the narrow continental connection to form the Drake Passage, creating several microcontinents which then drifted eastward.

4. The final separation of the Gondwanan continent allowed full development of the Circum-Antarctic ocean current. This cold current encircled Antarctica and prevented any warmer waters from reaching the continent, therefore triggering glaciation on Antarctica by Oligocene and Miocene time.

5. Figure 14.6: Meanwhile, the northern end of South America continued separating from North America and the Caribbian widened.

6. During the Pliocene, volcanism built a continuous Isthmus of Panama between the two continents.

7. The Caribbean region was fragmented by major faults during the late Cenozoic, moving Cuba, Hispaniola and Jamaica eastward. During this same period, the Lesser Antilles in the eastern Caribbean were formed as an island arc complex.

1. Figure 15.29: In Paleocene time, Greenland separated from Europe as the northern mid-Atlantic ridge formed.

2. India had separated from Africa by this time and was migrating northward towards Asia.

3. India, Africa and Australia were soon to collide with Eurasia.

1. During the Late Mesozoic and Cenozoic, the Tethyan region between Godwanaland and Eurasia underwent closure and deformation, culminating in late Cenozoic time with the upheaval of the Alps, Himalayas, and mountain ranges in Asia Minor. These events are identified as the Alpine-Himalayan orogeny.

2. During this orogeny, old continental crust along southern Eurasia were deformed. Mesozoic Tethyan oceanic crust were thrust northward onto the Eurasian continental margin and crushed together with Hercynian basement.

3. Erosion of deformed uplifts along the northern side of the shrinking Tethyan seaway generated clastic debris (flysch) which was then deposited by turbidity currents into adjacent deep-water basins

4. Figure 15.30: The culmination of compressive deformation occurred in Oligocene and Miocene time Complex thrust faulting in the Alps generated immense recumbent folds called nappes. Alpine granites formed 30 m.y. ago and metamorphism continued locally untill 11 m.y. ago. Uplift continues today.

5. In general, parts of northern Africa collided with Europe to form the Alps. India collided with Asia to produce the Himalayas. Arabia and Iran collided with Asia to produce the Taurus, Zagros and other mountain belts of Asia Minor.

1. Figure 15.32: The effects of the collision of India with Asia bagan about 25-30 m.y. ago.

2. The collision was so violent that the Tibetan plateau in southern China was elevated and several blocks of continental crust (including South China and Indochina) were squeezed towards the Pacific. Extension along the Baikal Rift in Siberia and Shansi Rift in North China may be due to collision of India.

1. Figure 15.33: By early Miocene time, the northward drift of Africa toward Europe was restricting circulation in the western Tethys Sea. Mountain building had closed most of the eastern seaway and split the western Tethys into two parts, The Mediterranean Tethys and a Paratethys (the latter encompassing the Black, Aral and Caspian Seas).

2. About 6 m.y. ago, collision temporarily closed the main connections between the Mediterranean and Atlantic Ocean, causing the Mediterranean to dry up. Thick evaporite deposits formed over virtually the entire basin with maximum thicknesses reaching 1,000-2,000 meters. The evaporites indicate that for a time, the Mediterranean experienced restricted circulation with the Atlantic with as many as 40 fillings and dryings occurring over a period of only 1-2 million years.

3. Lowering of the Mediterranean caused the Nile river to cut a very deep gorge that later filled with alluvium when the sea returned in Pliocene time.

4. About 5 million years ago, the Strait of Gibraltar opened and Atlantic water gushed in to refill the Mediterranean and eventually to reconnect it with the Black Sea.

5. Northward subduction of oceanic crust continues today beneath Italy and Greece along the southern Eurasian continent, and in Indonesia where deep-focus earthquakes and andesitic earthquakes are still active.

1. While Pacific arcs were being rejuvenated and the Alpine-Himalayan orogeny was in progress, extensive Neogene rifting and accompanying lava outpouring occurred on the cratons of Africa, southern Siberia (Baikal rifts), central Europe (Rhine graben) and Antarctica.

2. Rifting in East Africa began in Oligocene or Miocene time and continues today. The rifts average 50 km in width and associated volcanism produces oceanic basalts together with alkaline volcanics. The East African Rift System may represent a failed arm of a triple junction at the Red Sea-Aden junction.

1. After Appalachian-Ouachita mountain building ceased in Triassic time, Gondwanaland split from North America during the Jurassic, forming the Gulf of Mexico.

2. Figure 14.5: The first deposits formed in the young Gulf of Mexico rift were evaporites. By the end of the Jurassic, normal marine deposition ensued and considerable carbonate deposition occurred throughout the Cretaceous Period. Cenozoic deposites are largely terrigenous sands and shales characteristic of a passive continental margin.

3. The Mississippi and other modern river systems brought immense volumes of sediment to the northern Gulf and began building the great deltas of today.

4. Throughout the Cenozoic, the axis of maximum sedimentation in the basin continuously shifted southward while subsidence of the crust produced a broad, regional downbending accompanied by faulting. As sediment loading increased, the underlying Jurassic evaporites were squeezed and forced to intrude the overlying sediments as salt diapirs (salt domes).

5. The northern margin of the Gulf of Mexico today contains almost 12,000 meters of sediments near the Mississippi Delta.

6. The Gulf Coast Region has the largest petroleum reserves in North America.

1. The Atlantic coastal plain is another example of a modern passive margin.

2. Figure 15.36: In the present Appalachian Mountains, there is topographic evidence that, after Mesozoic beveling, regional upwarping caused rivers to reexpose the buried old landscape. As the area rose, gradients of major rivers were rejuvenated and early Cenozoic and Cretaceous strata were stripped off, exposing the harder, deformed rocks of the old orogenic belt.

1. Cretaceous climate was much warmer than today and areas like Greenland and Siberia were covered by temperate vegetation instead of snow and ice. Most of this warming was attributed to abundant CO2 in the atmosphere.

2. Figure 15.37: The cooler oceans and atmosphere present during the K/T extinction were soon returned to a warm, greenhouse state in the Paleocene. Temperate zone plants occurred above the Arctic Circle during the Early Cenozoic and Alligators and tortoises lived above 77^o N latitude. Astronomical phenomena, such as a shallower tilt in the Earth's axis of rotation, were cited as possible reasons for the Paleocene warming.

3. The beginning of the Eocene was marked by a major warming event and the global temperature increased by as much as 5oC, marking the warmest interval of the Cenozoic.

4. One reason for the Eocene warming may have been that ocean circulation became sluggish. The limited ocean-water circulation allowed seawater to warm significantly.

5. The collision of India with the Asian continent and the beginning of closure of the Mediterranean during the early Eocene were possibly accompanied by acceleration in sea-floor spreading rates, resulting in a rise in sea level. The greater surface area of water around the globe and increased eruption of greenhouse gases by rapidly erupting midocean ridges may have contributed to the Eocene warming.

6. The Eocene warming was soon followed by a dramatic decline of more than 10oC in mean global temperature during the late Eocene and Oligocene, possibly resulting from Antarctic glaciation. The earth changed from a warm greenhouse world to an icehouse world of polar glaciers and large temperature differences between the poles and equator. This major cooling event occurred both in the oceans and on land, resulting in many extinctions of warm-water microfossils as well as many land plants and animals.

7. The late Eocene-Oligocene cooling was accompanied by dryer climates. As a result, dense forest vegetation turned into a mixture of forests and grasslands. Water-loving crocodiles and turtles were replaced by land tortoises and other species that were more tolerant of drought-like conditions.

8. Climate deterioration reached its low point by the middle Oligocene and major glaciations in Antactica locked enormous amounts of seawater in ice caps, resulting in a global drop in sea level.

9. Figure 15.39: The onset of late Eocene-Oligocene cooling may have been due to establishment of the Circum-Antarctic current. Prior to the Eocene, Antarctica, Australia and South America were connected such that the South Pacific, South Atlantic and Indian Oceans were forced to mix with warmer waters from the subtropics.

10. In the early Oligocene, separation between Australia and Antactica allowed the Circum-Antacric current to flow eastward between the continents. This new current trapped cold water around the Antarctic, preventing it from mixing with equatorial waters. As a result, Antarctica became glaciated. The Circum-Antarctic circulation was complete when the Drake Passage between Antactica and South America opened in the early Miocene.

11. A major expansion of the Antarctic ice sheet caused another dramatic cooling at the Miocene/Pliocene boundary. During the late Pliocene, the Arctic ice caps began to form and soon glaciers were advancing in the northern continents.

12. Late Cenozoic glaciation may have been aided by closure of the Panama gap between North and South America, thus preventing mixing of Atlantic and Pacific waters. The Atlantic Gulf Stream intensified, bringing more moisture to eastern North America and northwestern Europe, ultimately leading to Pleistocene glaciation.