GSC Exam 4 - Cenozoic
Basin and range
continental rift zone area where continental crust is extending series of normal fault blocks extensions began approx. 20 MY
Coast ranges
crust in this region is divided into sliver shaped blocks by numerous faults including San Andreas plate boundary is a large transform fault associated with subduction of the east pacific rise rift
Younger dryas
dramatic and rapid cooling event
Formation of circumpolar current and Antarctic ice sheet
widespread marine extinctions from Eocene-Oligocene transition foraminifera, calcareous nanoplankton, molluscs extinction forests shrink, grasslands expand, terrestrial flora and terrestrial mammal extinction
Northern hemisphere glaciation timing and conditions
Pliocene around 3.5 MY Closure of central american seaway/gateway Warm waters able to go up to arctic in early Pliocene because salinity is a bit less then what we sea today Salinity gradient is more pronounced Once close off seaway, no longer exchanging warm salty water, salty water comes through gulfstream, more saltier water cools down and sinks, leaves Arctic more isolated, cools and cools and develops sea ice and ice sheets
Laramide orogeny
Precambrian uplifts east of Sevier orogenic activity eastward migration is associated with an increased rate of western migration of North America and a lower angle of subducting slab
Cenozoic climate
major climatic cooling after early Eocene climates became cooler and seasonally arid during Miocene
Sierra Nevada range
major uplift of fault block uplift and tilting from faults on the eastern margin exposes extensive granitic (Nevadan) and younger andesitic rocks
4 major groups mammals originate in Cretaceous
monotremes multituberculates marsupials placentals
Antarctica glaciation timing and conditions
Developed around Eocene Oligocene boundary, again in Miocene Circle diagram, breakaway of Australia from Antarctica Further expand in late Miocene Due to further expansion and strengthening of circum volar current (in southern hemisphere only) Deep sea foraminifera record
Paleocene reefs
100% of rudist bivalves extinct at KT boundary 97% of scleractinian corals extinct at KT boundary surviving corals are azooxanthellate
Cause of younger dryas
A freshwater pulse into the north Atlantic and shutdown of the global conveyor belt As Glaciers retreated back, freshwater lakes drained out into North Atlantic into very abrupt drainage event Freshened up north Atlantic enough so that it sits on top, stops thermohalene circulation climate plunges back into another ice age until fresh water can be removed from North Atlantic
Other mammal groups
Gires (rabits, rodents) Creodonts and Carnivora Pinnipeds (sea lions, seals, walruses) Archonta (primates, bats, tree shrews) Insectivores (shrews, moles, hedgehods) Ungulates (hoofed mammals)
Middle Miocene paleogeography
Himalayas fully formed Middle east and central americas still open
Middle Eocene paleogeography
breakup of Antarctica and Australia Atlantic and Arctic oceans connect
Growth of Antarctic ice cap
as Australia and south America rifted away, circumpolar current strengthened cold dense water spread northward cooling surface waters in many regions
marine survivors of KT mass extinction
benthic foraminifera, sea urchins, cheilostome bryozoans, crabs, snails, bivalves, teleost fish
Glacial cycles driven by
earth's rotational movement, milankovitch cycles
evidence for past glaciation
erratic boulders, glacial tills and morraines, depression of the land, glacial scouring, lowering of sea level, migration of species
Calcareous nanoplankton and planktonic foraminifera
few species survived KT mass extinction paleogene radiaiton later cenozoic declines due to temperature and Mg/Ca ratio
Columbia plateau, snake river plain and yellowstone hot spot
for approx. 15 MY during late Miocene and Pliocene, huge outpourings of flood basalts engulfed a region of roughly 63,000 square miles in northwest US as lava came to surface, the earth's crust subsided forming the broad depression of Columbia plateau igneous activity related to Yellowstone hot spot
Rocky mountains and colorado plateau
secondary uplift following late Cretaceous and Paleogene Laramide uplift Colorado plateau - 8 MY Rockies - 20 MY Rockies uplifted 1-2 miles and valleys carved by glaciers in Pleistocene