Geos 432-2 Cenozoic tectonism and climates; climate change Orogeny-mountain building: existing mountain belts are the result of Cenozoic tectonics Cenozoic tectonism and climate Movement of continents to higher latitudes-glaciation more favorable Changes in oceanic circulation-separation of Antarctica, S. America, Australia (35 my), Ant. Circumpolar current; closing of Isthmus of Panama (3 my), warm water to N. Atlantic: The Gateway Hypothesis Orographic barriers; Cordilleran mtn.. ranges; create deserts and semi-arid areas 1
Orogenic belts-1 Island Arc system Orogenic belt-2 Continental-oceanic Plate collision Orogenic belt-3 Continent-continent collision: India-Asia collision to form Himalayas 2
Foreland Thrusting Thin skinned; belts of anticlines & synclines with thin slices of basement rocks: low angle detachment zone; Appalachian Valley & Ridge Thick skinned; Block fault mountain ranges with basement involvement along steeper thrust faults; Central Rockies Extensional tectonics Sinai Peninsula Gulf of Suez Wadi Isla El Qaa Plain U D Gulf of Aqaba Red Sea 3
Epeirogeny Broad uplift or subsidence not associated with orogenic belts broad broad domes and basins (Michigan Basin). Cenozoic climate change Gradual Cenozoic cooling Circumantarctic current ~ 35 my Collision of India and Asia ~35 my Closing of Isthmus of Panama ~2-3 3 my Quaternary: oscillation between ice house and greenhouse conditions Cenozoic tectonism and climate Movement of continents to higher latitudes-glaciation more favorable Changes in oceanic circulation-separation of Antarctica, S. America, Australia (35 my), Ant. Circumpolar current; closing of Isthmus of Panama (3 my), warm water to N. Atlantic: The Gateway Hypothesis Orographic barriers; Cordilleran mtn.. ranges; create deserts and semi-arid areas 4
Greenhouse effect CO 2 and climate Relationship to tectonics Uplift-- more rocks exposed to atmospheric CO 2 -- CO 2 consumed-- climate cools Spreading rates: higher spreading rate, more CO 2 released to the atmosphere and climate warms; lower spreading rates and the opposite occurs. Ocean Circulation and climate Long term gradual cooling Surface Currents Ocean Circulation and climate Cenozoic pattern established 35 my BP Thermohaline circulation 5
Evaluation of the Gateway Hypothesis Climate models suggest that the circum-antarctic current and the northern deflection of the Gulf Stream did not significantly affect climate in the polar regions; therefore they may not explain the long term cooling. At this point, a more likely explanation is that uplift of the Tibetan Plateau and the Himalayas caused by the collision of India and Asia may be responsible for a decrease in CO 2 by the accelerated weathering that takes place there. The Laurentide Ice Sheet Short term heating and cooling Planetary Movements and Cimate Eccentricity Obliquity Precession 6
Eccentricity (100,000 yr) Obliquity (41,000 yr) Precession (21,000 yr) Precession Approximately 21,000 yr period Caused by wobble of the earth on its axis 7
Pleistocene Climates: Greenhouse/Icehouse fluctuations in high latitudes Milutin Milankovitch Major pulse of the ice ages Northern hemisphere summers when earth is farthest from sun Now! What about the southern hemisphere? Why should it have a glaciation at the same time (because its summers now occur when the earth is closest to the sun) CO 2 feedback-the CO 2 cycle is in sync with the ice ages, but for the northern hemisphere it may be an effect of glaciation and for the southern hemisphere it may be a cause of glaciation (positive feedback). When the earth is colder, the ocean can absorb more CO 2. During the ice ages, the ocean acts as a carbon pump and removes CO 2 from the atmosphere. So when a glaciation starts in the northern hemisphere, CO 2 levels drop and the southern hemisphere has a glaciation too?? http://www.globalwarmingart.com/wiki/image:milankovitch_variations_png 8
δ 18 O from benthic organisms δ 18 O, etc. in Ice Cores 9
Pollen records Other cycles (Dansgard( Dansgard-Oeshger) Younger dryas What about CO 2? Source: Wikipedia; Timeline of glaciation; CURRENT CO2 LEVELS 380 ppm 10
Ruddiman et al., 2005, QSR, 24; 1-10. The overdue glaciation hypothesis 11