Results of a comparative study on the recent and fossil periglacial forms on the Iberian Peninsula

Abstract

Article in German.

ORIGINAL TITLE: Ergebnisse einer vergleichenden studie zum rezenten und vorzeitlichen periglazialen formenschatz auf der Iberischen Halbinsel

Thls study describes the recent periglacial microforms of the Iberian Peninsula, in so far as they are represented by solifluction forms and patterned ground. Mesoforms (rectilinear slopes) are also dealt with. It was shown that certain forms and form-distributions are connected with certain rocks and their particular weathering characteristics (Table I). Since, however, not all rocks on the Iberian Peninsula rise up to heights where free solifluction forms dominate withln wide areas, thls is probably only an incomplete list of form-distributions as linked to rock-type. The microforms found here are comparable to those in the Alps, Pyrenees and Apennines. Due to the lack of glacial forefields and other favourable factors, meso- and macroforms of patterned ground are almost non-existent on the Iberian Peninsula. Compared to the high mountains in Greece, the periglacial microforms of the Iberian Peninsula seem to be much more plentiful. The transition from dominant bound (gebundene) solifluction in the north to dominant impeded (gehemmte) solifluction in the south corresponds to the climatic change from the wet oceanic climate region in North and Northwest Spain to the dry-summer Mediterranean climate south of the main watershed in the Asturian-Leonesian mountains. A N-S and E-W rise of important periglacial altitudinal limits occurs largely in the same direction as the course of the lower limit of the glacial snow-line and timber-line but not parallel to it. The course of the lower limit runs parallel to climatic variations. The investigations seem to be a suitable basis for more extensive studies on the reconstruction of glacial climatic conditions.

Investigations into pre-recent periglacial forms on the Iberian Peninsula concentrated on unstratified detrital material (Hangschuttdecken) and unstratified coarse waste (Blockschuttdecken), both covering slopes with inclinations of 5-30°, symmetrical and climatically-caused asymmetrical valleys, as well as cryoturbation forms. Various evidence (including alignment measurements using the same method as Poser & Hövermann, 1951) led to the Hangschuttdecken and Blockschuttdecken being classified as periglacial solifluctional sheets, in so far as they occur on medium-steep slopes and are unstratified and superposed by a Holocene soil formation. Whilst the pre-recent Hangschuttdecken (solifluctional talus covers) occur as low as sea-level in N Spain and N Portugal, in S Spain and S Portugal they are found within large areas up to heights of 150-200-300 m above sea level, when rock conditions are favourable. Whilst periglacial symmetrical trough valleys are found on the entire Iberian Peninsula, climatically caused periglacial asymmetrical trough valleys and periglacial cryoturbational formations are only found north of a line running from Galicia through Toledo to Barcelona.

The climatic-morphological interpretation of the pre-recent periglacial forms permits us to conclude that a glacial temperature depression of at least 8 -10° must be reckoned with in N Spain during the maximum of the Würm glacial epoch. Values of 8 -10° for the glacial temperature depression may be inferred for the rest of Spain.