The Danish Cretaceous-Tertiary boundary sequences have three unique claims: a shelf sea setting, rich benthonic faunas, and an insignificant stratigraphic break at the boundary. Outcrops in the central Danish Basin (northern Jylland) are the most complete while the boundary in the classical Stevns Klint section is marked by a minor disconformity.

Detailed data from Danish sections reveal a very complex biotic turnover. Long term changes of a number of Cretaceous taxa do not appear to be directly connected with boundary events but are due to evolutionary trends of different types. Short term boundary changes partly manifest themselves by increased turnover rates in both latest Maastrichtian and Early Danian times (planktonic taxa), partly by a collapse of the extremely diverse white chalk shelf benthos at the very end of the Cretaceous, when a majority of species (but few genera) became extinct. Also, the very last ammonoids and belemnoids became extinct during this collapse. The collapse is further manifested by a peculiar fauna in the earliest Danian deposits: a soft bottom stress fauna of extremely low diversity, apparently not reflecting anoxic conditions or abnormal salinity.

These data, together with δ¹⁸O/¹⁶O and δ¹³C/¹²C anomalies below and above the boundary, cannot be explained by a single catastrophic event but point to a complex boundary scenario.