Marine ecosystem response and restitutions across the Cretaceous-Paleogene boundary - Correlation of marine and terrestrial microfossils
At the Cretaceous-Paleogene boundary (known as the K-T, or K-Pg boundary) circa 65.5 million years ago, the Earth experienced one of the largest mass extinction events in its history. Approximately 50-70% of all organisms living on the planet died. One of the most famous groups going extinct at the Cretaceous-Paleogene boundary was the non-avian dinosaurs, fossils of which are only found below the boundary.
In 1980 the Alvarez group published a theory where they linked this global mass extinction with an extra-terrestrial event - a meteorite impact. Globally, it is now well established by geochemical, mineralogical, morphological, and paleontological evidences that an impact of a celestial body with a diameter of 10km, in what is today Yucatan peninsula in Mexico, caused this sudden ecological catastrophe 65.5 million years ago.
In distal locations from the impact site, such as the New Zealand Region and Denmark, the Cretaceous-Paleogene (K-Pg) boundary event left its imprint as a thin layer of circa 1-5 cm in thickness - the so-called K-Pg boundary layer (Fig. 1). One of the most famous Northern Hemisphere outcrop K-Pg sections is the coastal cliff locality at Stevns Klint in Denmark, where the boundary - a dark clay layer - can be traced for kilometres within a sequence of white chalk deposits.
Even though the K-Pg boundary mass-extinction has been the focus much debate and research, we still need to know how life in different regions was influenced by the impact and in which tempo different types of ecosystems recovered after the event. The overall aim of this project is therefore to study and correlate the immediate influence and how ecosystems on land and in the marine realm recovered from the K-Pg event.
It is known that in the marine realm the K-Pg boundary event caused an abrupt and widespread mass extinction of large as well as microscopic plant and animal groups such as ammonites, marine reptiles, foraminifera and coccoliths. But one major phytoplankton group, the organic-walled cyst producing algae or dinoflagellates, did not go extinct at the K-Pg boundary. Instead, fossils from this group reflect the oceanographic and climatic changes that took place around the time of the impact event.
We have studied rock samples taken in centimetre resolution across the K-Pg boundary transition in sections from both the Southern and Northern Hemisphere. By treating the rock samples with acids, the so-called palynological content - fossil algal, spore, pollen and woody remains - becomes available for study, making it possible to deduct biological signals stored inside the mineral matrix.
Palynology is one of the few micropaleontological disciplines where one can study minute remains from both terrestrial and marine fossils in the same preparation. This technique was developed in America after World War II when oil exploration intensified. Today, it is widely used in biostratigraphic and paleoenvironmental assessments of sediments ranging from circa 250 Million years BP (the Triassic period) to the present.