The Dakota sandstone Pierre Shale are two formations dating from this period, during which the Tethys Ocean became a shallow sea. Chalk deposits left by the Western Interior Seaway during this period formed the Smoky Hills Chalk in America, and the Dover Cliffs chalk in Europe was also formed at the same time. This period closed with the eruption of the Deccan Traps in India, which may be related to an impact that resulted in a thin layer of iridium forming between this period and the one that follows it. The Alvarezes posited that the KT boundary marks the stratigraphic border between this period and the Tertiary. For 10 points, name this period in which the T. Rex lived, the last period of the Mesozoic era that probably ended with a big meteor impact at Chixtulub. 
The Dakota sandstone Pierre Shale are two formations dating from this period, during which the Tethys Ocean became a shallow sea. Chalk deposits left by the Western Interior Seaway during this period formed the Smoky Hills Chalk in America, and the Dover Cliffs chalk in Europe was also formed at the same time. This period closed with the eruption of the Deccan Traps in India, which may be related to an impact that resulted in a thin layer of iridium forming between this period and the one that follows it. The Alvarezes posited that the KT boundary marks the stratigraphic border between this period and the Tertiary. For 10 points, name this period in which the T. Rex lived, the last period of the Mesozoic era that probably ended with a big meteor impact at Chixtulub. 
The Dakota sandstone Pierre Shale are two formations dating from this period, during which the Tethys Ocean became a shallow sea.
 Cretaceous period