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Grain size and SEM analyses suggest the presence of Cretaceous windblown desert sands in coeval shallow marine environments. Size distributions and microtexture data allowed us to infer a climate change to more arid conditions in the Iberian Basin during the mid-Cretaceous. The grain size of the sands in the late Aptian to early Cenomanian shallow-marine deposits in the western sub-basins of the Maestrazgo Basin (Teruel, Spain) is almost exclusively in the range between 1.5 and 3 Phi (0.35-0.125 mm), reflecting a prolonged or at least recurrent preselection of aeolian sands. The palaeolatitude of 25 degrees N showed a change from a warm humid climate during the Lower Cretaceous to an arid desert climate in the eastern sector of Iberia during the late Aptian-early Cenomanian. Winds supplied abundant desert sand to the estuarine and deltaic sedimentary environments where it was worked up in sandy sub- and intertidal facies with a striking absence of mud in cross-bedded sets which otherwise clearly reflect the influence of a semi-diurnal tidal system.