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
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
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
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
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
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
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
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 (??)
Iridium concentration K/T boundary Clay layer Maximum concentration at K/T boundary Quartz structure Shocked quartz Metamorphic quartz
Volcanic hypothesis Regression Unfavorable condition for survival Global effect Prolonged darkening Acid rain Temperature drop
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
Paleodepth of CCD Subsidence Sediment sequence Clays Calcareous Basalt Sea-floor subsidence Well-preserved calcareous sediments Deep-sea karst Dissolution of carbonate
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
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