High-resolution profile of stable isotopes and iridium across a K/T boundary section from Koshak hill, Mangyshlak, Kazakhstan

Abstract

Oxygen and carbon isotopes were measured to a high depth resolution in a nannoplankton carbonate sequence spanning the Cretaceous-Tertiary boundary at Koshak Hill, Mangyshlak Peninsula, Kazakhstan. The boundary is characterized by the presence of a ~1 cm thick clay layer having a sharp peak in iridium concentration with a maximum value of 3.7 ng g^-1. The δ¹⁸O data reveal rapid (~10³ years) excursion of sea-surface temperature at the boundary where an initial cold pulse is followed by a persistent warm period. The δ ¹³C data, in contrast, indicate only a gradual change in productivity across the boundary. The observations suggest a biogeochemical scenario for the boundary event pertaining to shallow epicontinental seas.