No abstract

No 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 δ13C 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.

No abstract

Upper Cretaceous carbonate sequences contain omission surfaces, hardgrounds and intercalations of ‘clays’. These ‘clays’ are largely associated with submarine biogeochemical carbonate dissolution that was caused by high biological productivity in the pelagic zone. The Maastrichtian-Danian ‘boundary clays’ probably accumulated during a maximum productivity that led to the exhaustion of nutrients, development of phenomena comparable to present-day red tides, and mass mortality of marine biota. There was a type of ecological break in the seas and oceans at the time of the Maastrichtian-Danian boundary.