K/Pg Boundary And An Emerging Database Of The Terrestrial Cretaceous From China

Nature News has an article by Jane Qiu detailing an ambitious drilling project ultimately aimed at recovering 10 km of core from a Cretaceous sedimentary section deposited in the Songlia Basin, northeast China. The Songlia basin is a rift basin that saw establishment of very long lived lakes fed by rivers throughout the Cretaceous, a geological period which saw great fluctuations in temperature, atmospheric carbon dioxide and sea / lake levels. Much of our understanding of the Cretaceous comes from marine sediments. Scientists have started analyzing portions of a two km core of terrestrial sediment in the hope of understanding how dramatic shifts in temperature and CO₂ content affected conditions on land.

Here is an interesting bit:

Other as-yet-unpublished results also point to a possible position for the K/Pg boundary. But it is about 100 meters below the depth determined by Wan Xiaoqiao, a palaeontologist at the Beijing-based China University of Geosciences who used fossils of spores, pollen, phytoplankton and ostracod to locate the boundary. The researchers are trying to determine why the estimates differ, and to nail the boundary down to 2–3 metres, so that detailed geochemical analysis can be performed to look for rare elements, such as iridium, that are common in meteorites and were spread around the globe by the cosmic impact.

The article doesn't say how the K/Pg boundary has been identified but one cannot help speculating on a topic like the end Cretaceous mass extinction.

Some scenarios:

1) The boundary has been incorrectly located and more detailed work will place it near the palaeontologically determined K/Pg boundary.

2) The physical location of the K/Pg boundary is correct and more detailed studies will show that it temporally coincides with the palaeontological boundary. This will imply that the intervening 100 meter or so of sediment was deposited very rapidly.

3) The identified boundary is indeed an event pointing to a large environmental perturbation caused by a meteorite impact but palaeontological evidence for a mass extinction occurs a considerable amount of time after this event as evidence in the 100 meter or so of intervening sediment will tell us. This is a scenario similar to what Gerta Keller and colleagues have been arguing using late Cretaceous sections from Texas and near the Chicxulub impact site i.e. the Chicxulub impact took place a few hundred thousand years before the mass extinction.

This might turn out to be an important section in the context of the mass extinction debate. Cretaceous geology is never dull.