Lecture 18 Paleoceanography 2

Transcription

1 Lecture 18 Paleoceanography 2 May 26, 2010 Trend and Events Climatic evolution in Tertiary Overall drop of sea level General cooling (Figure 9-11) High latitude (deep-water) feature Two major step Middle of Miocene E/O boundary Internal feedback/change of geography

2 Cooling trend in the Cenozoic Sea level curve Overall regression Oxygen isotope Planktonic Benthic MM & EO major cooling steps Great Partitioning Change in geography due to plate motion configuration of exchange between ocean basins Gateways (Figure 9-12) Arctic Ocean (east and west Greenland) Equator (Tethys Ocean, Panama strati, Indonesian seaway) Circumpolar Current (Tasmanian passage, Drake passage) Difference Closing of tropical gateways Opening of poleward gateways

3 Geography in the Eocene Tropical valve - closing High latitude valve - opening Grand Asymmetries Increased compartmentalization Broad range of T & S Increased displacement of the ITCZ Whitening of Antarctic Northward movement of continents Monsoonal heat transfer Collision of Indian and Eurasian plate Uplift of Tibet and Himalayas Deflection of westward-flowing equatorial current Strength of western boundary Current

4 Grand Asymmetries Heat asymmetry North Atlantic Heat pump: warm water in, cold water out Nordic Heat Pump Chemical asymmetries between Pacific and Atlantic Basin-basin fractionation Onset of Ice Age Nordic heat pump operation North-south strong asymmetry Overall cooling in NH Plio-Pleistocene cooling Figure 9-13 Mountain building Northward drift of land masses Panama seaway

5 Onset of ice age Sudden increase in detrital mineral grains Change from a low variability to a high variability Mid-Miocene Cooling Step Silica switch - Figure 9-14 Large-scale transfer of dissolved silicate from the Atlantic to Pacific Major reorganization of deep circulation (Figure 9-11) Growth of ice on Antarctica Worldwide cooling Carbon isotope excursion Indonesian Seaway

6 Silica switch Turning of Nordic heat pump At 15 Ma End-of-Eocene Cooling Enigmatic Oligocene Low planktonic diversity Strange Braarudospharea bloom Eocene - Chert in the world Communicated ocean basin Less temperature gradient Positive feedback Thermal isolation Internal feedback process

7 K-T Boundary Sudden Extinction Cause of Extinction Age of mammals from reptile Sudden Extinction Major biostratigraphic event Boundary between M & C Age of mammals from reptile Worldwide extinction K/T boundary Figure 9-15

8 Cause of Extinction Radiation from a supernova Poison gas from comet Volcanism Meteorite colliding Impact scenario Alvarez and Alvarez (1980) Iridium (noble rare metal) Shocked quartz Impact crater 200-km Chicxulub structure Volcanism (??)

9 Iridium concentration K/T boundary Clay layer Maximum concentration at K/T boundary Quartz structure Shocked quartz Metamorphic quartz

10 Volcanic hypothesis Regression Unfavorable condition for survival Global effect Prolonged darkening Acid rain Temperature drop

11 Plate Stratigraphy & CCD Backtracking CCD fluctuation Backtracking Original latitude and depth at the time of deposition Horizontal backtracking paleolatitude Vertical backtracking paleodepth Example Figure 9-16, Figure 9-17

12 Paleodepth of CCD Subsidence Sediment sequence Clays Calcareous Basalt Sea-floor subsidence Well-preserved calcareous sediments Deep-sea karst Dissolution of carbonate

13 CCD Fluctuations Deep circulation Regional productivity Sharing of carbonate between shelf and deep sea sea level Figure 9-18 Global and regional Pacific and Atlantic - similarity CCD Fluctuations High in late Eocene Drop near the E/O boundary Rise in Miocene High sea level Shallow CCD Warm

14 Possible Causes Sea level to CCD Basin-shelf-fractionation Not temperature, but sea level Biological productivity High productivity, shallow CCD Erosion and dissolution hiatus End of Lecture 18 Quartz grains and the carbonate shells of single-celled animals called foraminifera. x100