The interstratified breccias and conglomerates in the Cretaceous flysch of the northern Basque Pyrenees: submarine outflow of diapiric mass

Abstract

In the Cretaceous flysch of the Northern Pyrenees, polymict conglomerates interbedded in the flysch are described from the vicinity of Orio (near San Sebastián). These contain components derived from rocks of all periods from Paleozoic to Lower Cretaceous. During Late Maastrichtian times a diapir, originated in Keupez evaporites, penetrated the deep-sea Cretaceous flysch which was still undergoing deposition. This resulted in the expulsion of large quantities of diapiric mass. After the solution of the evaporites the pebbles, which had been dragged along with the diapiric masses, slumped into a neighbouring marginal depression where they were redeposited. The reddish strata of Late Maastrichtian and Danian age in this region are interpreted as being out-thrust and transported Keuper shales. It will be shown that the other breccias and conglomerates described by Feuillé and Mathey (1972) from the Late Cretaceous of the Basque Pyrenees probably have the same origin. The comprehensive name “Vascongadian Diapir Zone” is suggested for the diapir field on the northern edge of the Basque sedimentary trough.