Accretionary Wedge - Geo-Image
Tuesday, May 11, 2010 3:46:25 PM
I have chosen a picture I took some years ago in winter time (with snow). It is a picture of Stevns Klint in Denmark.
Why this choice? A. o. because it is as well an important K/T boundary site as the type locality of the Danian Stage.
On 8 January 2010 the site was submitted to the tentative list of UNESCO World Heritage Sites. Let me quote some of the reasons according to the site description:
“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.
The picture shows one of the bryozoan limestone mounds quite clearly (middle of image).
You may notice that the whole succession is chalk or limestone, also above the K/T boundary. Primarily for this reason (I suppose) the Danian (at least in Denmark and a few other countries) was considered part of the Cretacious (Cretacious is Latin for "chalky") - when I was young. The situation in today’s stratigraphy: Cretacious about 100 to 65 million years ago with Maastrichtian as last stage and Danian (65.5 ± 0.3 to 61.7 ± 0.2 million years ago) first stage of Tertiary.
Personally I find that Stevns Klint certainly deserve to be a UNESCO World Heritage Site.
See my next post for a few notes on "Bryozoan Mounds".