Changes

===K-T Boundary (65.5 Ma)===

===K-T Boundary (65.5 Ma)===

At the end of Cretaceous times the present-day continents were completely defined ([[:file:M106Ch01Fig10.jpg|Figure 10]]). Only the northernmost Atlantic Ocean was not completely opened (rifting was still active between Greenland and Canada). Africa detached from Antarctica and India, which began its northern flight that would eventually lead to the Himalayan orogeny. The Alpine Tethys and related basins, which linked the Central Atlantic Ocean with Neo-Tethys, were in a convergent plate regime. The large and complex puzzle of blocks of Adria, Greece, and Turkey were approaching the southern margin of Eurasia, after the almost complete subduction of the Neo-Tethys Ocean. The collision between these complex assemblages of different microplates would produce the Alpine-Dinaric and Turkish orogenic belts. In the Alpine area the lower plate was represented by Eurasia, whereas east of the Alps Laurasia represented the upper plate. This change can be ascribed to the different age and origin of the subducting oceanic crust (Alpine Tethys in the Alps, Neo-Tethys in the east). The possible occurrence of minor oceanic basins (Vardar, Pindos, and Lycian oceans; Stampfli and Borel, 2002) north of the Mesogea Ocean between the Alpine Tethys and Neo-Tethys accounted for the presence of multiple verging subduction zones. To the north of the subduction-collision belt it was still possible to recognize the occurrence of backarc basins, from the Black Sea to the Caspian Sea. The progressive closure of the Neo-Tethys also affected the evolution of the passive margin of Arabia, where the Peri-Arabian Massif high delivered sediments both northward (toward the Neo-Tethys) and southward. The origin of this high was related to the approach of the lower plate (Arabia) to the southern margin of Laurasia (represented by the Sirjan blocks of central Iran) or, alternatively, to an intra-oceanic subduction zone (Stampfli and Borel, 2002). The southern margin of Arabia was probably represented by a transform separating this plate from India. South of the Peri-Arabian Massif, on the Arabian plate, sedimentation was represented by prevailing deep-sea clastics and shallow-water carbonates passing to a large coastal plain with deposition of alluvial sediments. Extensional basins with deep-sea carbonates (Sirt Basin) developed along the northern passive margin of Africa and into the Sirt gulf. Rift basins (filled by continental clastic deposits) were also present across the interior of central-eastern Africa to the south.

At the end of Cretaceous times the present-day continents were completely defined ([[:file:M106Ch01Fig10.jpg|Figure 10]]). Only the northernmost Atlantic Ocean was not completely opened (rifting was still active between Greenland and Canada). Africa detached from Antarctica and India, which began its northern flight that would eventually lead to the Himalayan orogeny. The Alpine Tethys and related basins, which linked the Central Atlantic Ocean with Neo-Tethys, were in a convergent plate regime. The large and complex puzzle of blocks of Adria, Greece, and Turkey were approaching the southern margin of Eurasia, after the almost complete subduction of the Neo-Tethys Ocean. The collision between these complex assemblages of different microplates would produce the Alpine-Dinaric and Turkish orogenic belts. In the Alpine area the lower plate was represented by Eurasia, whereas east of the Alps Laurasia represented the upper plate. This change can be ascribed to the different age and origin of the subducting oceanic crust (Alpine Tethys in the Alps, Neo-Tethys in the east). The possible occurrence of minor oceanic basins (Vardar, Pindos, and Lycian oceans<ref name=Stampfliandborel_2002 />) north of the Mesogea Ocean between the Alpine Tethys and Neo-Tethys accounted for the presence of multiple verging subduction zones. To the north of the subduction-collision belt it was still possible to recognize the occurrence of backarc basins, from the Black Sea to the Caspian Sea. The progressive closure of the Neo-Tethys also affected the evolution of the passive margin of Arabia, where the Peri-Arabian Massif high delivered sediments both northward (toward the Neo-Tethys) and southward. The origin of this high was related to the approach of the lower plate (Arabia) to the southern margin of Laurasia (represented by the Sirjan blocks of central Iran) or, alternatively, to an intra-oceanic subduction zone.<ref name=Stampfliandborel_2002 /> The southern margin of Arabia was probably represented by a transform separating this plate from India. South of the Peri-Arabian Massif, on the Arabian plate, sedimentation was represented by prevailing deep-sea clastics and shallow-water carbonates passing to a large coastal plain with deposition of alluvial sediments. Extensional basins with deep-sea carbonates (Sirt Basin) developed along the northern passive margin of Africa and into the Sirt gulf. Rift basins (filled by continental clastic deposits) were also present across the interior of central-eastern Africa to the south.

End-Cretaceous time recorded the last of the Big Five mass extinctions (e.g., Ward, 1990; Bambach et al., 2004), so drastic and so close in time to leave a biogeographic imprint even on modern biota (Krug et al., 2009). Extinctions happened both in the sea (marine reptile, cephalopods, foraminifers, brachiopods, sharks) and on land (dinosaurs, pterosaurs, some bird groups, marsupial mammals). However, the pattern of this extinction is still disputed, with some groups interpreting gradual decline before the K-Pg boundary, and others catastrophic die-off (Ward, 1990; Benton and Little, 1994; MacLeod et al., 1997). One of the first proposed causal mechanisms was a major asteroid impact (Alvarez et al., 1980; Ocampo et al., 2006) with proposals of craters, such as Chicxulub Crater, Yucatan (Hildebrand et al., 1991). Among other suggested triggering mechanisms are global warming and flood basalts (Deccan Traps) (Courtillot, 2005).

End-Cretaceous time recorded the last of the Big Five mass extinctions (e.g., Ward,<ref name=Ward_1990>Ward, P. D., 1990, The Cretaceous/Tertiary extinctions in the marine realm: A 1990 perspective: Special Paper of the GSA v. 247, p. 425–432.</ref> Bambach et al.<ref name=Bambachetal_2004>Bambach, R. K., Knoll, A. H., and Wang, S. C., 2004, Origination, extinction, and mass depletions of marine diversity: Paleobiology, v. 30, p. 522–542.</ref>), so drastic and so close in time to leave a biogeographic imprint even on modern biota.<ref name=Krugetal_2009>Krug, A. Z., Jablonski, D., and Valentine, J. W., 2009, Signature of the end-Cretaceous mass extinction in the modern biota: Science, v. 323, p. 767–771.</ref> Extinctions happened both in the sea (marine reptile, cephalopods, foraminifers, brachiopods, sharks) and on land (dinosaurs, pterosaurs, some bird groups, marsupial mammals). However, the pattern of this extinction is still disputed, with some groups interpreting gradual decline before the K-Pg boundary, and others catastrophic die-off.<ref name=Ward_1990 /> <ref name=Bentonandlittle_1994>Benton, M. J., and Little, C. T., 1994, Impact in the Caribbean and death of the dinosaurs: Geology Today, v. 13, p. 222–227.</ref> <ref name=Macleodetal_1977>MacLeod, N. et al., 1997, The Cretaceous-Tertiary biotic transition: Journal of the Geological Society, v. 154, p. 265–292.</ref> One of the first proposed causal mechanisms was a major asteroid impact<ref name=Alvarezetal_1980>Alvarez, L. W., Alvarez, W., Asaro, F., and Michel, H. V., 1980, Extraterrestrial cause for the Cretaceous-Tertiary extinction: Science, New Series, v. 208, no. 4448, p. 1095–1108.</ref> <ref name=Ocampoetal_2006>Ocampo, A., Vajda, V., and Buffetaut, E., 2006, Unraveling the Cretaceous-Paleogene (KT) catastrophe: Evidence from flora fauna and geology, in C. Cockell, C. Koeberl, and I. Gilmour, eds., Biological Processes Associated with Impact Events: Springer-Verlag Series, p. 197–219.</ref> with proposals of craters, such as Chicxulub Crater, Yucatan.<ref name=Hildebrandetal_1991>Hildebrand, A. R., Penfield, G. T., Kring, D. A., Pilkington, M., Camargo, A., Jacobsen, S. B., and Boynton, W. V., 1991, Chixulub crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico: Geology, v. 19, p. 867–871.</ref> Among other suggested triggering mechanisms are global warming and flood basalts (Deccan Traps).<ref name=Courtillot_2005>Courtillot, V., 2005, Evolutionary catastrophes: Cambridge University Press, 173 p.</ref>

[[file:M106Ch01Fig11.jpg|thumb|300px|{{figure number|11}}Global paleogeography (top) and major depositional settings in the southern margin of the Tethys (below) at the time of the Eocene-Oligocene boundary (about 34 Ma).]]

[[file:M106Ch01Fig11.jpg|thumb|300px|{{figure number|11}}Global paleogeography (top) and major depositional settings in the southern margin of the Tethys (below) at the time of the Eocene-Oligocene boundary (about 34 Ma).]]