Abstract

Recently developed magnetic polarity stratigraphies in the western South–Central Unit provide a more-precise temporal database for the analysis of the depositional and deformational history of the southern Pyrenean foreland basin. When combined with lithostratigraphic and structural data, the eight new magnetic sections along the Isabena and Esera valleys and in the Ainsa Basin help define the early stages of development of the Eocene foreland and illustrate the important role played by growing structures, such as the Mediano Anticline, in controlling depositional environments and patterns of subsidence.

Introduction

In an attempt to develop more precise chronological control for the depositional and deformational history of the central part of the South Pyrenean fold-and-thrust belt and its related foreland-basin deposits, several new magnetic polarity stratigraphies have been developed within the syntectonic sedimentary succession. The temporal information derived from these studies permits more detailed correlation between sections and more reliable analysis of the timing, sequencing and rates of sedimentary and tectonic processes. This work has been focused on the western part of the South–Central Unit (Séguret, 1972) and encompasses the western Tremp–Graus and Ainsa basins (Fig. 1). Whereas the majority of these studies has been concerned with late Eocene and Oligocene deposition, part of the studied record begins in the early Eocene. We report here the data and the location of each magnetostratigraphic section, the nature of the magnetic record from these sites, the chronologic significance of each section, and some of the geologic conclusions drawn from these chronologic data.