WAS THERE AN IBERIAN DESERT DURING THE MID-CRETACEOUS?

International audienceSince about a decade several works developed the concept of desert environments at the origin of thethick sand deposits overlying coal units within the Escucha and Utrillas Formations (uppermost Aptian–uppermost Albian, Iberian Range, Eastern Spain). In the same while, silt-clay lenses, and even widely extendedbeds, interlayered in the stratigraphic succession yielded a palynoflora and a palaeoflora which are among therichest and most diversified in the world for this time span, and comprise several taxa of clearly hygrophytecharacter. This is why we present here a critical review, based on field observations, of the varioussedimentologic clues put forward to claim an arid climate.None of the sand-bodies studied showed a typical organization of aeolian deposit, whether it be sandsheets or dunes. Thus, largest structures, where clay drapes and intraclasts are frequent, are reinterpreted asthose of subtidal bars (mostly ebb-dominated) and hydraulic dunes. Occasionally they contain quartz andquartzite dropstones, probably came there by stump-rafting from a fluvial watershed, as suggested by theproximity of silicified tree trunks. Pebbles and cobbles show no unequivocal clue of aeolian corrasion. In thewestern part, where they are abundant, their arrangement (especially segregation and lenticularity) is in somecases typical of wave-worked beach face deposits. In other places, well-sorted sands form upper flow regimeplane-beds (swash-zone), while pebbles are concentrated in beach-step prisms.Conspicuous ferralitic paleosols, where clays and feldspars are transformed into kaolinite clay matrix,are expression of emersion periods. Frequent sphaerosiderite in them is indicative of a late drowning phasepreceding the next marine transgression. As for the rare occurrences of small gypsum rosettes, they can beattributed to a telogenetic origin, via the oxidation of iron sulphides present, not only in the underlying coalsand their lateral facies, but also in the uniformly grey primary clay phase of the sandy units.If compared with the “desert” hypothesis, all these elements are in better agreement with the regionalpalaeoenvironmental interpretations previously advanced, and with most of the current global palaeoclimaticinferences