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WAS THERE AN IBERIAN DESERT DURING THE MID-CRETACEOUS?

Abstract : Since about a decade several works developed the concept of desert environments at the origin of the thick 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 extended beds, interlayered in the stratigraphic succession yielded a palynoflora and a palaeoflora which are among the richest and most diversified in the world for this time span, and comprise several taxa of clearly hygrophyte character. This is why we present here a critical review, based on field observations, of the various sedimentologic clues put forward to claim an arid climate. None of the sand-bodies studied showed a typical organization of aeolian deposit, whether it be sand sheets or dunes. Thus, largest structures, where clay drapes and intraclasts are frequent, are reinterpreted as those of subtidal bars (mostly ebb-dominated) and hydraulic dunes. Occasionally they contain quartz and quartzite dropstones, probably came there by stump-rafting from a fluvial watershed, as suggested by the proximity of silicified tree trunks. Pebbles and cobbles show no unequivocal clue of aeolian corrasion. In the western part, where they are abundant, their arrangement (especially segregation and lenticularity) is in some cases typical of wave-worked beach face deposits. In other places, well-sorted sands form upper flow regime plane-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 phase preceding the next marine transgression. As for the rare occurrences of small gypsum rosettes, they can be attributed to a telogenetic origin, via the oxidation of iron sulphides present, not only in the underlying coals and 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 regional palaeoenvironmental interpretations previously advanced, and with most of the current global palaeoclimatic inferences.
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Conference papers
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https://hal-insu.archives-ouvertes.fr/insu-01718016
Contributor : Isabelle Dubigeon <>
Submitted on : Tuesday, February 27, 2018 - 9:02:26 AM
Last modification on : Tuesday, May 26, 2020 - 11:50:04 AM

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Marc Durand, Sylvie Bourquin, José Bienvenido Diez, Luis Miguel Sender, Uxue Villanueva Amadoz. WAS THERE AN IBERIAN DESERT DURING THE MID-CRETACEOUS?. International Meeting of Sedimentology 2017, Oct 2017, Toulouse, France. pp.259. ⟨insu-01718016⟩

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