ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

ANNETTE KADEREIT & ANDREAS LANG
Colluvial sediments as a key to the holocene landscape
evolution of early settled areas: a case study from the
Kraichgau-Hills, southern Germany
Forschungsstelle Archaometrie, Heidelberger Akademie der
Wissenschaften, Max Planck Institut fur Kernphysik,
Saupfercheckweg 1, D-69117 Heidelberg, Germany
The loess areas of Middle-Europe have undergone enormous
geomorphical changes since the onset of agriculture
(ca. 7000 a BP), documented by partially or completely
truncated soils in localities prone to erosion and thick colluvial
and alluvial sediments in the depressions. Yet still
unsolved is the question whether these changes were triggered
dominantly by climatic or human impacts. Results
from studies of large drainage basins can often not be
interpreted in order to answer this question satisfyingly
due to the great variety of the controlling factors and the
complexity of the responding system at that scale of investigation.
In this respect small scale geomorphological studies in the
direct neighbourhood of archaeological sites have become
increasingly relevant in the context of palaeoecological and
geoarchaeological analyses. Colluvial sediments on the
lower hillslopes and in the drainage lines of zero order basins,
as well as, alluvial sediments of first order basins represent
important archives for the reconstruction of the
Holocene landscape evolution. However, apart from geomorphological
and palaeoecological analyses, high-resolution
chronologies are required for precise correlations of
these sediments to human activities or climatic fluctuations.
The application of luminescence dating promises to
being a powerful tool to close the chronometric gaps for
the sediment layers free of organic material or archaeological
finds. Especially the recently achieved progresses in optically
stimulated luminescence (Os1) are of great advantage
for the reliable dating of sediments with only short transportation
distances.
First results of geoarchaeological investigations at the locality
'Bauerbach' in the loess covered Kraichgau-Hills in
southern Germany will be presented and their possible implications
for the human impact on the Holocene landscape
evolution will be discussed. The test area stretches from
the drainage divide down to the outlet of the first order to
the second order basin. It is located between two archaeological
sites: at the upper end remnants of Neolithic and
Bronze to Iron age settlements and at the lower end remnants
of roman buildings. While the younger Wurmian
loess has been eroded on the upper slopes, not only the
prehistoric concavities are filled with colluvial material but
also the hill-foot and the drainage lines are buried deeply
by colluvial and alluvial sediments up to several metres
thickness. The colluvial sediments typically show coarsening
upward with clay rich material borne from the Holocene
climax luvisol at the bottom and loess-rich material
on top. Apart from 14C-dating of the available organic ma-
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terials, infrared stimulated luminescence (Ir-Os1) dating
provides the chronology for the feldspar rich, mainly fine
grained, loessic sediments.
HIROSHI KADOMURA
Morpho-ecological response to recent climatic
variations and human impacts in the Sahel:
an overview for a geomorphological contribution
to the convention to combat desertification
Department of Geography, Rissho University, 4-2-16 Osaki,
Shinagawa-ku 141, Tokyo, Japan
In the tropical semi-arid areas on the south side of the
Sahara, i.e. the Sahel Zone, desertification/land degradation
has not occurred by the spreading of the Sahara but
occurred in close connection with the local physical conditions'
in particular landform types and superficial materials
and/or underlying rocks, as well as kind and intensity of
human impacts. Relative importance of wind or water erosion
depends on both regional climatic and edaphic conditions.
Gently sloping lands such as pediments and glacis,
and plateau surfaces covered with hard ferrugineous cuirasses'
gravels or sealed silty soils, are the landform types
which are particularly prone to degradation processes. On
these habitats, while the regression of woody vegetation is
rapid, the recovery of it is very slow.
As observed in many areas of the Sahel Zone, the regrowth
of natural woody vegetation in response to the return of
good rains after the severe drought years has shown in
good correlation with edaphic conditions, rather than the
amount of rainfall. Sandy terrains, such as semi-fixed sand
dunes and sand sheet areas with studded nebkhas, even if
they are located in more arid area with less rainfall, have
revealed rapid regeneration of woody species than cuirasscapped
landscape in the area with more rainfall. The role
of sandy soils, that can store viable seeds and sustain the
rapid regrowth of vegetation, should deserve special attention.
In contrast, it is the latter type of terrain where the
continuous removal of top soils tends to result in a severely
devastated landscape which is equalled to stony desert, i.e.,
reg landscape, and even to rocky desert.
Spatial differentiation in land degradation is more complicated
in the dissected terrain composed of a variety of
landform units, as exemplified by the dissected, cuirasscapped
plateau of Ader Doutchi, near Keita Valley, Central
Niger. In this area, types and intensity of degradation
differ by landform/superficial material units, along with
the topographic positions from the plateau surface through
the scarp and glacis to the valley bottom. This segregation
in degradation patterns has provided important information
for planning the integrated rehabilitation works. In
facts, much of the erosion control and water conservation
works (e.g., Sombroek, 1992) have been carried out in clo-