Climate changes during the Early–Middle Triassic transition in the E. Iberian plate and their palaeogeographic significance in the western Tethys continental domain

Abstract

Until recently the climate of the Early–Middle Triassic at low latitudes was broadly considered as generally temperate-warm with no major climate oscillations. This work examines the climate of this period through a detailed study of the sedimentary, plant, soil and mineral records of continental rocks (Buntsandstein facies) in eastern Iberian basins. Our findings indicate temporal climate variations for these near equator (10°–14°N) regions and unveil the significance of such variations in the southern Laurasian domain.

The climate of Iberia's Early Triassic was mainly dominated by alternating brief (< 0.4 ma) arid and semi-arid climate periods, with two main arid periods documented at the end of the Smithian and middle Spathian. However, an initial short subhumid to semi-arid period was also observed in the late Spathian. Remarkably, this latter period appears just after an unconformity related to the tectonically induced Hardegsen Event in western Europe. It is also of interest that this short subhumid climate period is concurrent with the beginning of faunal and floral recovery in the basins examined. The Early Triassic ended again with a short very arid period.

Although the beginning of the Anisian (Aegean) was represented by alternating arid and semi-arid to subhumid intervals, during the Bithynian and Pelsonian clearly wetter climates are recorded by the succession consisting of alternating semi-arid to semi-humid intervals. This general tendency was interrupted by three short but marked intervals, two humid intervals in the late Bithynian, and one arid period near the Bithynian/Pelsonian boundary.

Iberia was crossed by prominent irregular highs separating marked corridors or isolated areas. This palaeogeography, prevailing since Variscan tectonics, clearly conditioned dominant climates and their geographical distribution. No clear climate belts developed in these conditions. However, isolated internal climate zones separated by elevated areas are identified. This palaeogeographic configuration and the low latitudinal position of Iberia determined central Iberia highs in the southernmost border of Laurasia, beyond which more humid conditions clearly extended towards the equator reaching the present-day Moroccan Meseta and Argana Basin.