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摘要
This study shows that successions of Pleistocene carbonate aeolian deposits can be placed successfully in a geochronologic framework using magnetostratigraphic and susceptibility stratigraphic analysis supplemented by luminescence dating, studies of wave-cut platforms, and biostratigraphic evidence. The investigated aeolian system covers a significant part of southernmost Mallorca and is exposed in impressive coastal cliff sections. At the study site at Els Bancals the aeolian system has a maximum thickness of 16m and is composed of alternating dark red colluvial deposits and greyish red aeolian dune and sand-sheet deposits forming seven cyclo strati graphic units. Each cyclostratigraphic unit represents landscape stabilisation, colluviation, and soil formation followed by dunefield development, when marine carbonate sand was transported far inland by westerly or north-westerly winds. The aeolian system is located on top of a wave-cut marine platform 12-14m a.s.l. This platform probably formed during a sea-level highstand in Marine Isotope Stage (MIS) 11 (427 364 ka), and renewed marine activity probably later in MIS I I is indicated by the formation of beach deposits. Two sections at Els Bancals were sampled for a paleomagnetic study; additional samples were taken to detect variations in magnetic susceptibility (MS). The characteristic remanent magnetisation has been recovered for the most part of the succession in spite of diagenetic overprinting. There is evidence for two probably three reversal polarity excursions, possible connected to the Levantine, CRI and CR0/Biwa III episodes. If this correlation is correct, the sampled succession represents a time interval in the Middle Pleistocene between ca 410 and ca 260ka. This age estimate is supported by the MS study and by luminescence dates of 333 +/- 70 ka (aeolianite from lower part of the succession) and 275 +/- 23 ka (aeolianite from the top of the succession). The nature of the succession suggests deposition during alternating warm and moist (colluvial deposition; soil formation) and cold, dry and windy conditions (dunefield formation). The susceptibility signal can be correlated with the insolation signal at 65degreesN suggesting that environmental variation on Mallorca was linked to orbitally forced climate change, and it seems that aeolian activity and dunefield formation were linked to glacial or stadia] periods.
- 出版日期2004-9
