Abstract

In the Loranca Basin, sediments are exposed ranging in age from the Middle Eocene to the Turolian. The fossil micromammal record of this considerable time interval is, however, not continuous. For paleoecological study we have chosen a composite section in the Rio Mayor valley where stratigraphical control allows us to superpose six faunas, dating from the Late Oligocene to the Early Miocene. In this interval, which covers some 4–5 million years, two relatively dry, and two relatively humid, periods are recognized.

Introduction

A first attempt at a paleoecological approach to Spanish micromammal faunas was made by Van de Weerd & Daams (1978), who recognized an alternation of relatively humid and dry periods during the Neogene of the Calatayud–Teruel Basin. Daams & Van der Meulen (1984) further developed the model, and constructed relative humidity and temperature curves for part of the Neogene of North Central Spain. Additional information and the application of principal component analysis subsequently resulted in the construction of more-detailed relative-humidity and temperature curves (Van der Meulen & Daams, 1992) for part of the Neogene of the Calatayud–Teruel Basin.

The Upper Oligocene and Lower Miocene of the Loranca Basin also yielded numerous micromammal faunas, but our taxonomical study is unfortunately not advanced enough for principal component analysis or the construction of detailed climatic curves. For this study, we have chosen a succession of six localities, which are all located in the Rio Mayor valley and whose stratigraphic position can be controlled lithostratigraphically (Fig. 1).