Studying the boundary stratotypes of the Paleocene of the Western Pyrenees

1999/03/01 Nuñez-Betelu, Koldo Iturria: Elhuyar aldizkaria

• Paleontologia
• Arkeologia

Sedimentary rocks emerge everywhere in Euskal Herria. To know their origin and classify them, that is, to establish their relationship, geologists use the principles of stratigraphy. Through these principles we can know which rock has been formed for the first time and which later, at what time, where,...

Take Paleocene as an example, a season that began 65 million years ago and ended 55 million years ago. Paleocene is a very interesting period of time. At that time Euskal Herria and most of the Pyrenees were under the sea. Between the Iberian peninsula and Europe there was a deep sea. This sea was closed by the east, since in the current area of Catalonia the Pyrenees rose. Paleocene began after the destruction of many creatures, including the Ammonites and the dinosaurs, after a giant cataclysm. The climate was mild all over the world, without ice at the poles and, in addition, the temperate increased by the end of the Paleocene. The North Atlantic expanded and Greenland separated from Europe due to strong volcanism.

Through stratigraphy we know which rocks were accumulated in Euskal Herria and its surroundings, as is the case of the Western Pyrenees. Most of these rocks are limestone, but they were formed in different areas. Some, like those located in Zumaia, are the production of sediments accumulated in the sand of the sea of about 1,000 m of depth. Others, near the coast, are indicators of the marine platform in shallow waters that we can find in Urbasa. Moreover, in the Pyrenees we find rocks originating on the coast itself. To do this, a group of researchers works in the Department of Stratigraphy and Paleontology of the UPV. Doctoral theses, scientific articles and presentations at congresses are the result of many years of work of this group. The road has been long, but has not yet finished. After knowing the main characteristics of the Paleocene, the project presented here and other projects are underway to work on the characteristics of the interior divisions of the Paleocene.

It is necessary to define the rocky set, stratotype, which serves as an example to each epoch, in order to determine each stratigraphic distribution. Most stratotypes are defined. However, many stratotypes of boundaries between epochs are not yet defined. This is what happens with the boundaries between the three inner divisions of Paleocene and the final limit of Paleocene. The stratotypes of these limits have not yet been defined. That is what the International Stratigraphy Commission is working on right now. The objectives of this project of the Department of Stratigraphy and Paleontology are framed within this context, so it has addressed the micropaleontological study and stratigraphy of sequences of the Paleocene of the Western Pyrenees, since in this region the rocks of then emerge very well and, therefore, can serve to define the stratotypes of the borders.

The micropaleontological study is mainly based on planktonic foraminifers, although it also uses palinomorphs and lime nanofossils. As in other research, this type of microfossils can provide new data to define the limits of the Paleocene, Danish/Selandiar and Selandiar/Tanetian stations. Moreover, the biozonation models being developed for border determination can be compared with classic biozonations with other microfossil groups to determine latitudinal, paleogeographic changes, etc. To this can be added qualitative changes of sea level and populations, changes in the rounding directions of foraminifera, etc. Therefore, the project has on the one hand stratigraphic objectives around the definition of borders within the Paleocene and on the other hand paleoclimatic, paleogographic and paleontological objectives.

• Project title: Micropaleontological study for the characterization of the boundary stratotypes of Western Pininy Paleocene and sequence stratigraphy.
• Objective: Determination of micropaleontological groups and stratigraphic distribution within the Paleocene of the Western Pyrenees by stratigraphy of sequences.
• Financing: DCICYT.
• Director: Xabier Orue-Etxebarria.
• Research team: Professors: Xabier Orue-Etxebarria and Victoriano Pujalte Navarro (UPV/EHU).Teaching staff: Estibaliz Apellaniz Ingunza, Koldo Núñez Betelu and Aitor Payros Agirre (UPV); Juan Ignacio Baceta Caballero (University of Huelva). Alejandro Robador Moreno (ITGME).Doctoral fellow: Gilen Bernaola Bilbao (UPV/EHU).
• Department: Department of Stratigraphy and Paleontology.
• Centre: Faculty of Sciences of Leioa.