Aeolian sand sea development along the mid‐Cretaceous western Tethyan margin (Spain): erg sedimentology and palaeoclimate implications

The existence of a mid‐Cretaceous erg system along the western Tethyan margin (Iberian Basin, Spain) was recently demonstrated based on the occurrence of wind‐blown desert sands in coeval shallow marine deposits. Here, the first direct evidence of this mid‐Cretaceous erg in Europe is presented and the palaeoclimate and palaeoceanographic implications are discussed. The aeolian sand sea extended over an area of 4600 km². Compound crescentic dunes, linear draa and complex aeolian dunes, sand sheets, wet, dry and evaporitic interdunes, sabkha deposits and coeval extradune lagoonal deposits form the main architectural elements of this desert system that was located in a sub‐tropical arid belt along the western Tethyan margin. Sub‐critically climbing translatent strata, grain flow and grain fall deposits, pin‐stripe lamination, lee side dune wind ripples, soft‐sediment deformations, vertebrate tracks, biogenic traces, tubes and wood fragments are some of the small‐scale structures and components observed in the aeolian dune sandstones. At the boundary between the aeolian sand sea and the marine realm, intertonguing of aeolian deposits and marine facies occurs. Massive sandstone units were laid down by mass flow events that reworked aeolian dune sands during flooding events. The cyclic occurrence of soft sediment deformation is ascribed to intermittent (marine) flooding of aeolian dunes and associated rise in the water table. The aeolian erg system developed in an active extensional tectonic setting that favoured its preservation. Because of the close proximity of the marine realm, the water table was high and contributed to the preservation of the aeolian facies. A sand‐drift surface marks the onset of aeolian dune construction and accumulation, whereby aeolian deposits cover an earlier succession of coastal coal deposits formed in a more humid period. A prominent aeolian super‐surface forms an angular unconformity that divides the aeolian succession into two erg sequences. This super‐surface formed in response to a major tectonic reactivation in the basin, and also marks the change in style of aeolian sedimentation from compound climbing crescentic dunes to aeolian draas. The location of the mid‐Cretaceous palaeoerg fits well to both the global distribution of other known Cretaceous erg systems and with current palaeoclimate data that suggest a global cooling period and a sea‐level lowstand during early mid‐Cretaceous times. The occurrence of a sub‐tropical coastal erg in the mid‐Cretaceous of Spain correlates with the exposure of carbonate platforms on the Arabian platform during much of the Late Aptian to Middle Albian, and is related to this eustatic sea‐level lowstand.     

EVIDENCES FROM HISTORICAL DOCUMENTS OF LANDSCAPE EVOLUTION AFTER LITTLE ICE AGE OF A MEDITERRANEAN HIGH MOUNTAIN AREA,SIERRA NEVADA,SPAIN (EIGHTEENTH TO TWENTIETH CENTURIES)

The Sierra Nevada is the highest mountain system on the Iberian Peninsula (Mulhacén 3482 m; Veleta 3308 m) and is located in the extreme SE region of Spain (lat 37°N, long 3°W). Bibliographic resources, particularly from the eighteenth to twentieth centuries, provide insights into the changing summit landscape as the effects of cold, ice, snow and wind shaped its morphology. The selected references emphasize the Sierra's evolving climate reflected in the glaciers and snow hollows, and in the sparse vegetation above certain altitudes. Scientists had established bioclimatic conditions for the entire range in the early nineteenth century, and their works reflect the progression of ideas, particularly in the area of natural sciences, that influenced the period chosen for this study. This information, in addition to current knowledge about the morphogenetic dynamics of the Sierra Nevada, provides the basis for a comparison of the dominant environments from the Little Ice Age to the present, using the most significant high mountain morphological features as a guide. The most relevant findings indicate that cold climate processes (soli‐gelifluction, frost creep and nivation) were more predominant during the eighteenth and nineteenth centuries than they are today.