Chapter A4 Sr isotope record in the area of the lower miocene historical stratotypes of the aquitaine basin (France)

Abstract

This chapter discusses the Sr isotope record in the area of the lower Miocene historical stratotypes of the aquitaine basin (France). During the Miocene, the Aquitaine basin was a large embayment opening westward into the Atlantic Ocean. Several transgressions extended more or less eastward, with facies of mainly shallow to infralittoral types. These deposits are generally very fossiliferous, which led earlier authors to define the Aquitanian and Burdigalian stages there. The chapter presents the Sr isotope record of the Aquitanian and Burdigalian stratotypes area. Samples are collected in historical, as well as new outcrops described here. Among these sections, a few are protected and have been cleaned and set off in the framework of the “Réserve Naturelle Géologique de Saucats-La Brède”. Analyses are performed on well-preserved macrofossils only, preferably on aragonitic bivalves. Based on these stratigraphic datings, the recognition of the Miocene deposits in the whole Aquitaine basin (from outcrops and boreholes) led palaeogeographic interpretations. In the lower Miocene—for example, two main transgressive phases occurred, during which the sea extended far eastward.