Eocene Oligocene Transition Class Presentation By Kedar Ghimire

Global cooling at the Eocene – Oligocene transition “the world turned cold” transition “ the world turned cold Hello !, Sorry I am extinct Environmental Geosciences, class presentation IOR Prof. Dr. Andrea KoschinskyFritsche IOR Koschinsky Presented by Kedar Ghimire, May 8th, 2007 Title Image: Moeritherium

Source: http://www.williamsclass.com/images/GifImages/GeologicTime205K.gif

Eocene epoch • Timeline (55.8 ± 0.2 33.9 ± 0.1 Ma) when earth was free of large continental ice sheets • In Greek, ἠώς (eos, dawn) and καινός (kainos, new). refers to the \"dawn\" of modern ('new') mammalian fauna, appeared during the epoch CLIMATE •Extreme global warming termed PaleoceneEocene Thermal Maximum or Initial Eocene Thermal Maximum (PETM or IETM) •Deep ocean currents extremely warm. Temperate forests extend to the poles Most homogeneous global climate. •Grand Coupure the end of Eocene, causes could be due to climate change with polar glaciations, bolide impact Middle Eocene ,Scotese, C. R., 1997. Paleogeographic Atlas, PALEOMAP Progress Report 900497, Department of Geology, University of Texas at Arlington, Arlington, Texas, 37 pp

Oligocene epoch • 34 million to 23 million years ago • comes from the Greek ὀλίγος (oligos, few)& καινός (kainos, new) • the sparsity of additional modern mammalian faunas after a burst of evolution during the Eocene • increase of volcanic activity and the plate tectonic movement • The start of general cooling, glaciers forming in Antarctica for first time, fall in sea level, tropics diminished, ice covered the south pole but not north pole • Cooling trend continued, culminated into ice age of Pleistocene finally. • followed by Miocene, then Pliocene, pleistocene and then Holocene http://www.utexas.edu/opa/news/03newsreleases/nr_200312/nr_anthropology031203.html

EoceneOligocene Transition Eocene • \"greenhouse\" climates of the Eocene were replaced by the \"icehouse\" \"greenhouse\" climates of the Eocene were replaced by the \"icehou conditions that persist today. • Analysis of Sedimentary rocks. Major extinctions for gastropods, amphibians and reptiles, little change to mammals • Causes • DupontNivet et al. and Zanazzi et al. implicate it to the declining Dupont levels of atmospheric CO2 . CO • Ocean circulation hypothesis by Shackleton and Kennett . During Paleocene, Australia and Antarctica were joined. In the early Eocene Paleocene, Australia and Antarctica were joined. In the early Eo (t=~55 m.y. ago), Australia began to drift northward from Antarctica. m.y • During the Eocene (t=55 to 38 m.y. ago) the Southern Ocean was m.y relatively warm and the continent largely nonglaciated. By the late nonglaciated Eocene (t=~39 m.y. ago) a shallow water connection had developed m.y between the southern Indian and Pacific oceans and also probably the Drake passage. Substantial Antarctic sea ice began to form. the Drake passage. Substantial Antarctic sea ice began to form.

EoceneOligocene Transition Eocene • Antarctic glaciation sustained by “Antarctic “ circumpolar current”. circumpolar current ” • Thermohaline oceanic circulation was initiated. (the global densitydriven initiated. (the global density circulation of the oceans). • HOWEVER, computer models suggest something else. something else.

EoceneOligocene Transition Eocene • DupontNivet et al.(2007) applied precision dating techniques to demonstrate that climatic change in central asia occurred at the same time as the early oligocene glaciation of antarctica. • Zanazzi et al. (2007), using 18O/16O measurements in tooth enamel from mammal fossils have provided evidence of decrease in AAT of 8°C • They measured relative abundance of oxygen isotopes in ancient minerals. Depends upon the 18O/16O of water from which mineral is derived and the temperature at the time of formation. • used 18O/16O measurements of tooth enamel from mammal fossils estimated 18O/16O of body water. No temperature dependence to these isotope compositions

EoceneOligocene Transition Eocene • Findings of Zanazzi et. al • Zanazzi et. al. methods lag the determined age of eoceneoligocene eocene transition time period by approx. 400 Kyr compared to marine methods • They made sure that all taxa experimented were waterdependent. experimented were water • No resolvable change seen in mean enamel δ18O, suggests that water δ 18 composition remained unchanged. • Statistical variance (var) for Eocene vs. Oligocene teeth – Statistical variance ( var indistinguishable, suggests no major change in MART across the transition or a possibly small increase. • Shows decrease in MAT of 8°C, far larger than found in marine records Shows decrease in MAT of 8 C, far larger than found in marine records ° 23°C 2 3 ° • MAT (Eocene)=21.0±10.1°C; MAT (Oligocene)= 13.1±9.5°C; MAT (Eocene)=21.0 10.1 C; MAT (Oligocene)= 13.1 9.5 ± ° ± ° δMAT(EOT)= 8.2±3.1°C δ ± ° 8.2 3.1 • Results say that decrease in MAT rather than an increase in seasonality Results say that decrease in MAT rather than an increase in seas or aridity is the primary cause of the extinctions of gastropods, or aridity is the primary cause of the extinctions of gastropods amphibians and reptiles associated with the EOT. amphibians and reptiles associated with the EOT.

Discussion and conclusion • Asian drying and early oligocene climate change are linked. • One thing to be tested: whether the regional tectonic events caused both the observed aridification and climatic change in Antarctica. • Himalayan uplift could have caused a rain shadow , simultaneously triggering a global reduction of CO2. reduction of CO • The eoceneoligoscene transition was a turning eocene point for whole of earth and not only antarctica. antarctica .

Thank you for your kind attention! Reference: • JP Kennett Journal of Geophysical Research, 1977 • Zanazzi, A., Kohn, M. J., MacFadden, B. J. & Terry, D. O. Jr Nature Zanazzi MacFadden 445, 639–642 (2007) 445, 639 – • DeConto, R. M. & Pollard, D. Nature 421, 245–249 (2003) DeConto , R. M. & Pollard, D. Nature 421, 245 – • http://www.nature.com/nature/journal/v445/n7128/full/445607a.html http://www.nature.com/nature/journal/v445/n7128/full/445607a.htm • http://www.3dvalley.com/gallery/d/32752/moeritherium4.jpg http://www.3dvalley.com/gallery/d/3275 • http://en.wikipedia.org/wiki/Eocene http:// • http://www.mnh.si.edu/anthro/humanorigins/faq/gt/cenozoic/oligoce http://www.mnh.si.edu/anthro/humanorigins/faq/gt/cenozoic/oligoc ne.htm • http://www.palaeos.com/Cenozoic/Oligocene/Oligocene.htm http:// • http://scotese.com/oligocen.htm • http://en.wikipedia.org/wiki/Wiki • Kedar Ghimire Kedar Ghimire

Eocene Oligocene Transition Class Presentation By Kedar Ghimire

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