The distribution of Pyrenean erosion material, deposited by eocene sheetflood systems and associated fan-deltas: a fossil record in the Monllobat and adjacent Castigaleu formations, in the drainage area of the present Rio Noguerra Ribagorzana, provinces of Huesca and Lérida, Spain

Abstract

Sedimentological investigations of the Eocene Monllobat and adjacent Castigaleu Formations in the Southern Pyrenees followed two main lines. In the first place the interrelationships of the coarse and the fine members were studied and detailed sedimentation models were developed. In the second place the distributions of the coarse members and the sedimentary facies were recorded, in order to obtain detailed models of the palaeogeography and the ancient sedimentation processes. The approach to the study comprised three elements: 1- Objective observation of rock characteristics, as much as possible represented in a manner which enables repetition. The field study was based on: a Centimetre-decimetre scale facies observations in three-dimensional exposures of several 100' m' with a thickness of up to 20 m, and in 40 - 180 m thick vertical sections. b Metre-scale observations of the coarse member distributions in valley wall sections in the Ribagorzana drainage area, which are up to tens-o~kilometres wide. Microscopic study of sandstone thin sections supported field definitions of certain types, and was a major tool in hinterland reconstructions; 2 - Interpretation of the rock characteristics in the most logic and simple way - summarized in models of the palaeogeography at a large-scale, and also, in some select cases, in great detail, as inferred from ancient sedimentary reliefs; 3 - Continuation of and comparison with other research.