Floor-age constraining of a tectonic paroxysm of the Pyrenean orogen. Late Middle Eocene mammal age of a faulted karstic filling of the Quercy phosphorites,south-western France

Breaking effects of a Pyrenean compressive tectonic phase are recognised in northern Pyrenean foreland, such as in the Quercy Jurassic limestone platform. The age of this phase still remains poorly constrained. In the so-called Quercy phosphorites area, within the Prajoux–Mémerlin paleokarst system near the city of Cajarc, a clay filling shows a strike slip fault effect, close to N–S direction. According to an analysis of the mammal fauna and inferred chronology of the polyphased paleokarst infilling, the age of the faulted clay is late Middle Eocene, with a mammal age estimate of 41.5 Ma. This provides reliable precise floor-age constraining for the involved sismo-tectonic paroxysm, seemingly related to the Pyrenean tectonic compressive phase.     

Proposition of dating a Miocene Alpine tectonic event using mammal biochronology: example of the Four karst filling

Abstract

Although the general tectonic history of the Ile Crémieu area (southern Jura) is known, establishing the chronology of events that have influenced the tectonic evolution seems to be much more difficult. A newly discovered layered karst filling in the Bajocian limestone, in the town of Four (Isère), is a synsedimentary evidence of a Tertiary tectonic activity. Actually, only the lower part of the filling has been folded by the movement of the fault in which the karstic network was made. Fossil mammals date the last movement on this fault plane, between 13.0 and 13.4 Ma. At a larger scale, the last activity of this fault could be correlated with a change in the paleo-stress could generated by the Alpine orogen, dating with precision an Alpine tectonic event. © 2002 Editions scientifiques et médicales Elsevier SAS. All rights reserved.