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- 저자 : Tamara B. Afanasyeva (검색결과 1 건)
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New Maastrichtian oxygen and carbon isotope record: Additional evidence for warm low latitudes
Yuri D. Zakharov,Alexander M. Popov,Yasunari Shigeta,Olga P. Smyshlyaeva,Ekaterina A. Sokolova,Ragavendra Nagendra,Tatiana A. Velivetskaya,Tamara B. Afanasyeva 한국지질과학협의회 2006 Geosciences Journal Vol.10 No.3
The Cretaceous period was generally characterizedby greenhouse conditions. Nevertheless, our data on isotopic com-position of biogenic carbonates from the Koryak Upland andSakhalin (Russian Far East) show that during the Maastrichtian,temperatures dropped sharply at high and middle latitudes, withonly a slight warming in the early Late Maastrichtian. At the sametime, there is contradictory evidence on climatic conditions for lowlatitude areas during Maastrichtian time. The new and previouslypublished isotopic data on Maastrichtian molusks in the WesternInterior Seaway (North America) (WIS) and some other areas sug-gest that tropical deep-sea surface temperatures calculated from theoxygen isotopic composition of the majority of investigated Maas-trichtian planktic foraminifera are, obviously, underestimated. Unusu-aly low isotopic temperatures were obtained for tropical plankticforaminifera. This probably reflects both local conditions provoked,first of all, by the influence of tropical upwelling zones, and the abil-ity of Maastrichtian planktic foraminifera to migrate within a largevertical interval in the tropical zone in conditions of weakly strati-fied (well-mixed) ocean. The average tropical deep-sea surface pale-otemperature estimates for the Maastrichtian could have beenabout 26.630.2°C, but, apparently, did not reach the level denotedfor the Late Albian and Turonian (32±3°C). Negative carbon-iso-topic shifts at the end of the early Maastrichtian and the Creta-ceous-Tertiary boundary time seem to be conected with the fall oftemperature and eventual reduction of oxygen content in theatmosphere and hydrosphere.
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