- Quaternary (3) (remove)
- Investigations of the geomorphologic and pedologic system of sedimentary vega deposits from Lanzarote (Canary Islands) supported by luminescence dating – important steps towards their palaeoclimatic interpretation (2007)
- On Lanzarote (Canary Islands/Spain), sequences similar to loess-palaeosol-sequences from other regions developed in dammed volcanic valleys during the Middle and Late Pleistocene. Based on former investigations, we assumed that these sequences could serve as palaeoclimate archives for the NW-African region, an area characterised by a lack of investigations from continuous terrestrial palaeoclimate archives. The material deposited in the valleys consists of Saharan dust as well as of local volcanic material. Due to their location in valley positions and adjacent strongly eroded slopes it is obvious that these sequences do not represent classic loess-palaeosol-archives. Instead, they must consist of a mixture of in situ aeolian fallout as well as of sediments derived from colluvial input from the slopes. Consequently, prior to a correct palaeoclimatic interpretation the geomorphologic character of the archives and the properties of their sediments must be analysed. Thus, in this study we intensively investigate the geomorphologic and pedologic system, combining geomorphologic mapping and quantitative GIS-calculations with sedimentological-pedological methods (grain size, XRD, rock magnetic und pedologic analyses as well as investigation of micromorphologic properties). Furthermore, we built up a chronostratigraphy using different luminescence-methods (quartz coarse- and fine grain-OSL, polymineral fine grain-IRSL). Fundamental investigations on the bleaching-behaviour of recent Saharan dust and colluvial sediments on Lanzarote demonstrate, that in spite of partial insufficient bleaching of the luminescence signal a dating of the valley-bottom sediments is possible. These datings were supported by a correlation of local kaolinite-contents with iron and kaolinite contents from nearby marine cores as well as a stratigraphic correlation between different profiles. Thus, we could establish a chronostratigraphy for the last 180 ka. We demonstrate that outcropped sediments were deposited almost continuously from the Middle Pleistocen until the Holocene, wheras the uppermost sections of the profiles consist of anthropogenic colluvia which can not be interpreted in a palaeoclimatic way. The alternation of reddish-clayey and yellowish-silty layers tracks changes of soil humidity on Lanzarote rather than variations of the composition of Saharan dust. Due to the colluvial dynamics of the valleys, reddish-silty layers in the valley bottoms are no palaeosoils sensu strictu but mainly consist of colluvial soil sediments originating from pedogenesis on the slopes. These soils as well as unweathered material were eroded and deposited with high frequency and low amplitude. Thus, their sedimentation age in the valley bottoms is close to the primary time of aeolian deposition on the slopes and the formation of pedogenetic properties. These findings allow a palaeoclimatic interpretation of the sediment sequences. We could demonstrate that glacials and stadials were characterised by higher soil moisture than interglacials and interstadials. When comparing our results with other palaeoclimatic studies from a broader region, we can show that the causes for periods of enhanced humidity were westerly cyclones using a more southern way than at recent, as well as lowered sea and air temperatures in the area of the Canary Islands. During some periods, soil humidity was possibly occasionally amplified by a northward advance of the African summer monsoon up to the latitude of Lanzarote. Although we are not able to directly derive palaeoprecipitation values from soil moisture, we can show that maximal precipitation values must have been in the the range of ca. 560 mm/a. Our results demonstrate that during most of the investigated period of the Late Quaternary the climate of Lanzarote was influenced by northern high latitude processes. Furthermore, during most of the investigated period the recent aridity of the island was somewhat mitigated.
- Soil moisture fluctuations recorded in Saharan dust deposits on Lanzarote (CanaryIslands) over the last 180 ka (2010)
- Aeolian sediments trapped in volcanically dammed valleys on Lanzarote, Canary Islands, were investigated in order to reveal environmental changes over the last 180 ka. Clay content and frequency dependent magnetic susceptibility were used as proxies for pedogenesis and palaeo-soil moisture. During the last 180 ka, these proxies showed a general pattern of enhanced soil moisture during glacials and stadials and more arid conditions during interglacials and interstadials. Comparisons of these results with proxies from regional palaeoclimate studies identified a positive correlation with proxies of trade wind strength off northwest Africa and inverse correlations with both sea surface temperatures in the northeast Atlantic and the extent of Mediterranean vegetation. Possible causes for the observed pattern include a glacial enhancement of precipitation from westerly cyclones, a change in relative humidity due to fluctuating air temperatures and an occasional influence of the African summer monsoon. Although it is not yet possible to clearly differentiate among these factors, it is clear that the first two factors must have been primarily dominant. These results represent the first quasi-continuous terrestrial data testifying to environmental changes in the northwest African coastal area for the last 180 ka and complement the abundant data derived from marine cores of the region. High latitude dynamics had a major influence in this area and were intermediated by North Atlantic sea surface temperatures. A possible negative correlation can also be observed with the orbital obliquity cycle with a 10 ka time lag, which is similar to the lag recorded from North Atlantic sea surface temperatures.
- Response to the „Comment on ’Geoarchaeological and chronometrical evidence …’ ” by J.C. Carracedo et al. (2004)
- This paper is a reply to the comments made by Carracedo et al. (Quaternary Science Reviews 23, 2045-2049) to the original paper by Zöller, L., Suchodoletz, H.von & N. Küster (2003): Geoarchaeological and chronometrical evidence of early human occupation on Lanzarote (Canary Islands), Quaternary Science Reviews 22, 1299-1307. The reply copes with comments concerning chronometrical dating, the origin of investigated material and geomorphologic and geoarchaeologic problems.