Palaeoclimatic Inferences from Clayey-Iron Palaeosols: A Weathering Event Recorded in the Middle–Upper Jurassic Unconformity (South Iberian Palaeomargin, Western Tethys)

Abstract

The study of iron crusts containing iron-coated grains from different sections of the Prebetic (SE Iberia) and the overlying marine sedimentary rocks also containing iron-coated grains in the Prebetic and the Iberian Range (NE Iberia) allowed us to determine the palaeoclimatic and palaeoenvironmental conditions under which they originated. The iron crusts are mainly composed of clay minerals (kaolinite and illitic phases) and/or goethite and hematite. The kaolinite texture indicates that it is authigenic, whereas the illitic phases are probably detrital. The mineralogy and texture of the iron crusts allow us to classify them as plinthitic palaeosols. The iron-coated grains consisting of a nucleus and a cortex, both composed of a mixture of kaolinite, goethite, and hematite, originated in situ during the plinthite development. Reworking processes caused the fragmentation and incorporation of the iron-coated grains into the overlying ferruginous oolithic limestones and terrigenous-carbonated breccia. New marine iron-coated grains formed later in the ferruginous oolithic limestones. The high Chemical Index of Alteration and Chemical Index of Weathering values and the geochemical ratios (Ba/Sr, Rb/Sr, Sr/Cu, Ga/Rb) from iron deposits reflect intense weathering under warm and humid conditions in the South Iberian Palaeomargin during the Callovian–Oxfordian, which may also take place in the East Iberian Palaeomargin (Iberian Range).