The coastal cliff site, Stevns Klint is arguably the most famous, scenic and best exposed K/T (Cretaceous-Tertiary) boundary section in the world with the exceptional K/T boundary layer easily recognisable immediately beneath a pronounced topographic overhang separating the underlying soft Cretaceous chalk from the overlying, harder Tertiary limestone.
The K/T boundary coincides with one of the most pronounced faunal mass extinction known in the geological record, a turnover that affected both terrestrial and marine faunas 65.5 million years ago. The recovery after the extinction event lead to the life we know on Earth today. At the same time the boundary represents the only mass extinction and change of the global ecosystems which has been related to an extraterrestrial impact.
Stevns Klint is a 14.5 km long coastal cliff located about 45 km south of Danish capital, Copenhagen on the east coast of the Danish island of Sjælland. The exposed succession is about 45 m thick and shows the stratigraphic evolution from the latest Cretaceous, across the K/T boundary and into the early Tertiary.
Stevns Klint is a classical K/T boundary site and is one of the three discovery localities of the famous iridium anomaly, which formed the basis for the asteroid impact hypothesis of Alvarez et al. (1980) proposed to explain the end-Cretaceous mass extinction. Stevns Klint is therefore a key locality in the ongoing debate about mass extinction in general and the K/T boundary in particular. In addition Stevns Klint is type locality of the Danian Stage. The Danian is represented by bryozoan limestone mounds outlined by thick black flint bands which illustrate the geometry, dimensions and architecture of one of the finest, ancient cool-water carbonate mound complexes in the world.
Stevns Klint is a world-class K/T boundary site for the description of the mass extinction and recovery of the fauna and one of the best localities to document changes in sea level, surface and bottom sea-water temperature, and ecological and evolutionary conditions and changes in the last phases of the Late Cretaceous greenhouse world. A large number of detailed palaeontological, biostratigraphical, geochemical and sedimentological studies have been thus undertaken at the locality.
Stevns Klint is the most outstanding K/T boundary site found to date, showing the evidence of one of the most remarkable events of Earth history - the mass extinction at the end of the Cretaceous 65.5 million years ago, where more than half of the all faunal and floral species, including the dinosaurs, disappeared. The K/T boundary extinction is one of the biggest and most controversial mass extinction since it is related to an extraterrestrial impact. Stevns Klint is the prime locality to study the faunal turnover at this event and the recovery after the extinction as both micro- and macrofaunas are well preserved in the complete succession across the boundary. Stevns Klint is a key locality in the ongoing discussion of the trigger mechanism for the K/T mass extinction as it is one of the discovery localities of the famous iridium anomaly, which lead to the hypothesis of an asteroid impact as a cause of the extinction. International researchers have flocked to Stevns Klint to sample from the iridium-rich boundary layer. Furthermore, Stevns Klint is the type locality of the Danian Stage and the cliff exposes along its length of 14 km a unique, Danian, cool-water bryozoan limestone mound complex formed shortly after the mass extinction.
Stevns Klint exposes a complete succession across the K/T boundary with an easily recognised boundary layer. The boundary layer presents evidence of an extraterrestrial impact and the Late Cretaceous and Early Danian sediments contain a rich and well preserved fauna and nannoflora that documents the impact and associated extinction event at the K/T boundary. The nominated site thus includes all elements necessary to express its outstanding universal value and most of the key interrelated and interdependent elements in their natural relationships represented by the lithological succession.
Stevns Klint is a 14 km long coastal cliff and is the longest and best exposed, complete K/T boundary site known. The coastal position makes sure that the site is subject to natural continuous erosion which will keep a high exposure of the site, a high potential to continuously yield new finds in future research, and a high permanency, since there is no risk of oversampling or overgrowth. The site therefore does not suffer from adverse effects of development or neglect.
Stevns Klint does not resemble other World Heritage sites already inscribed on the list under criteria viii. They represent different periods of geological time and none represents the evolution of life after a mass extinction caused by an extraterrestrial impact.
Of sites not currently on the World Heritage list, 16 other sites representing the K/T boundary event with a complete succession across the boundary and a boundary layer which are enriched in iridium and other elements considered to be mainly or partly of meteoritic origin. Stevns Klint is unique compared with these 16 sites in having an easily recognised boundary layer, a high diversity of major biota groups offering information about the mass extinction and subsequent recovery, a high lateral extent of the boundary layer, and a high degree of exposure and permanency of the K/T boundary succession.
The 16 other K/T boundary sites includes well known localities like Caravaca, Gubbio, Brazos River, Woodside Creek, and the stratotype site El Kef. Gubbio and Woodside Creek are the two other discovery localities for the iridium anomaly. They both have an easily recognised boundary layer, but a low diversity of major biota groups, and a low degree of permanency as they are located in a valley and along a road respectively. Gubbio has a very short lateral extent as the succession is tilted. Caravaca, Brazos River, and El Kef all have a relative high diversity of major biota groups. Caravaca has an easily recognised boundary layer, whereas it is more difficult to locate the boundary at the other two sites. They all have relative short lateral extents of the boundary layer compared to Stevns Klint and El Kef and Caravaca have a low permanency due to their location in a valley and along a road respectively.
None of the 16 sites have a better exposed and easily recognised boundary layer compared to Stevns Klint and only one site, Seymour Island, have a higher diversity of major biota groups. Hell Creek is the only site which has a higher lateral extent compared to Stevns Klint and Seymour Island is the only other site with same degree of permanency and erosion as it is also a coastal cliffs, but remotely located in Antarctica.
There is therefore no comparison of any of these 16 sites to Stevns Klint to show and tell the amazing story of the Late Cretaceous impact event and associated mass extinction.