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