An article to be published in the journal “Proceedings of the National Academy of Sciences” reports the discovery of a fossil deposit in North Dakota, USA, which contains the remains of animals and plants that died as a direct consequence of the impact of a large meteorite that about 66 million years ago it caused the mass extinction that wiped out dinosaurs. A team of researchers led by Robert DePalma of the University of Kansas examined the site, which was named Tanis, finding what they consider evidence of the direct connection to the impact, the extremely strong earthquake that followed it with tsunamis and a debris rain.
The extinction of the dinosaurs is one of the events that raised the greatest discussions among paleontologists and geologists for decades. In the late 1970s, physicist Luis Alvarez suggested that the impact of a huge meteorite could be the cause. The evidence of the impact that happened at the time of that extinction with the crater in the Yucatan, called Chicxulub, and the anomalous presence of iridium in the geological layers of the whole world supported that theory but various scientists still had doubts. Traces of exceptional volcanism in India, in the territory known as the Deccan Traps, contributed to the discussions and it’s possible that the violence of the meteorite impact increased those phenomena.
According to the reconstructions, debris were pushed into the sky and then fell back even at considerable distances. The earthquake caused by the impact was extremely violent and caused tsunami not only in today’s Gulf of Mexico but also in other very distant seas like the one that existed at the time in today’s North Dakota. According to the researchers, two huge seiches flooded the area leaving a considerable layer of deposits that covered the organisms struck by the catastrophe, creating that sort of graveyard. There’s also a layer of clay enriched with iridium coming directly from the meteorite.
Among the authors of this research there’s also Walter Alvarez, Luis Alvarez’s son, who commented that he and his father relied only on the discovery of an anomalous concentration of iridium and that since then more evidence slowly piled up. He would never have thought that they could have discovered a sort of graveyard like the Tanis site, so full of detailed information on what happened because of the impact.
On the Tanis site, the researchers also found tektites, glassy objects that were generated as a result of meteorite impacts. In this case, the tektites were pushed away from the impact area with such force that they reached today’s North Dakota. Many tektites are in excellent condition because they got preserved in amber thanks to the fact that at the time it was malleable resin. Others were found in the gills of the fish that lived in the sea that existed at the time. Jan Smit of the Vrije Universiteit in Amsterdam is a world expert on tektites and examined the ones found at the Tanis site, establishing that they date back to the K-T boundary, also known as K–Pg boundary.
Tektites are useful to link the Tanis site to the impact that caused that mass extinction but there are many fossils not only of dinosaurs and fish but also of other animals and plants. The researchers claim that this is the richest site dating back to the K-T boundary found so far. If that’s confirmed, it brings further evidence to the theory of the impact of a huge meteorite as a cause of dinosaur extinction.
Even before the article was published, controversy began. In particular, those who already had access to the research stated that only one fragment of dinosaur bone is mentioned. For the characteristics of the Tanis site the study was multidisciplinary but for that reason some believe that there are not enough facts to confirm the value of the discovery. Certainly further comments will come after the publication of the article and perhaps others will be published because the study is far from finished. The authors of the research called it a unique site but precisely for this reason such claim need more than ever to be checked with further studies.
