Abstract

During sedimentation of stage 2 of the ‘Upper Unit’, four saline units developed in the central part of the Loranca Basin. These deposits occur associated with the palaeogeographic limits of the Tortola and Villalba de la Sierra fluvial fans. Analysis of facies, sequences and their distribution through time permit examination of the evolution of saline environments during fan evolution. Saline facies distribution is asymmetric and controlled by fan activity. Primary gypsum is the dominant lithology of the saline deposits. The absence of anhydrite or more-soluble minerals reflects low salinity of the brines. Triassic and Cretaceous gypsiferous source rocks, basin configuration, and progressive aridity were the controls on the development of these saline environments.

Introduction

The Loranca Basin is located in the central part of Spain and it was filled by continental deposits from Late Oligocene to Miocene (Turolian) times. During ‘Upper Unit’ deposition, from Late Oligocene to Early Miocene (Agenian), three different ‘stages’ can be distinguished in the evolution of the Tórtola and Villalba de la Sierra depositional systems (Diaz Molina et al., 1989; see also Chapters C5 and C7). The first stage corresponds to the most active time interval of the Tortola and Villalba de la Sierra humid fans, when the Loranca Basin was connected to the Madrid Basin. During the following stage, syn-sedimentary folding started to plug the area connecting the Loranca Basin with the Madrid Basin, and local base levels were being established with development of wet areas of around 600 km2 (Fig. 1).