ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

vations (continuous cross sections), drillings and cores.
The intercomparison of morphosedimentary data with
other data supplied by archaeology, palynology, malacology,
and palaeosoil (micromorphology) sciences enables
us to analyse the reactions of the river dynamics to climate
and human activities. The time frame is based on 14C dates
and on the stratigraphy of archaeological sites.
The Late-glacial evolution is largely controlled by climatic
variations, and is characterized by very sharp events. It
consists of two important sedimentation phases, approximately
dated Oldest Dryas/beginning of the Bolling and
Younger Dryas. Both phases are separated by a vertical
cutting which occurred during the second half of the Bolling
(approx. 12,500 BP), followed by an episode of dynamic
stability and the Allerod soil formation. Locally, cryoturbations
show the magnitude of the cooling at the beginning
of the Younger Dryas.
The Post-glacial started with a deep incision during the first
half of the Preboreal.
During the Boreal and the Atlantic, the erosion/sedimentation
dynamics decreased with the growth of the vegetation
cover. The stream channels were progressively filled by organic
matter-rich sediments and the watershed did not
supply any more clastic material. During the second half of
the Atlantic, the various indicators do not show any particular
modification of the environment. However, the pollen
data reveal, during Middle Neolithic times, the development
of agriculture together with the scarce opening of
the landscapes.
During the second half of the Subboreal, the increasing
erosion of the slopes, favoured by the human activities, led
clayey silts to fill the mean water channels; the increase of
the river discharges generated numerous channels which
were very active during the Bronze Age. Most of these
channels were filled during the Second Iron Age (La Tene,
beginning of the Subatlantic),
During Roman times, the main river valley floors continued
to be filled with silts; the clastic sedimentation
slowed down during the Middle Ages.
Finally, a big erosion crisis, marked by a thick silty fill in
the valleys of the small contributors, is evidenced during
the Little Ice Age.
This general scheme admits numerous fluctuations in relation
with geomorphological and phytogeographical parameters;
it will be detailed by a research programme aiming
at precising and quantifying the various elements.
NATALIA G. PATYK-KARA ', NINA V. GORELIKOVA 1
& JOSEF PLAKHT 2
Rock varnish in the geomorphological levels dating
(Makhtesh Ramon depression in the Negev Highland)
1 Institute of Geology of Ore Deposits, Petrography, Mineralogy & Geochemistry,
Russian Academy of Science,
Staromonetny per., 35, 109017 Moscou, Russia
2 Ramon Science Center, p.o. box 194, 80600 Mitzpe Ramon, Israel
Rock varnish is a widespread feature of stony desert landscapes
throughout the wourd. It is the product of complicated
and specific physical and chemical processes under
arid and semi-arid environments. It was revealed that chemical
composition of these desert coatings, especially relationship
between separate group of chemical elements, is
age-dependent, therefore these ones have attracted considerable
attention from archeologists and quaternary geologists
when solving a challenge of both artifacts and native
phenomena dating. As a rule, the object of such investigations
are «mature» rock varnish coatings of considerable
thickness (up to 0.5 mm) and of zonal structure.
Rock varnish patina occures widely on the different surfaces
of the Negev Highland, but, as opposed to well known
ones from the Death Valley in California, varnish coatings
are here extremely thin (vanishingly thin in places), no more
than 1 mk, which hampers their analysis by electron
mictoprobe method, dating assessement and revealing
aged relations with initial surface. The main objects of our
investigation are different-age denudational levels within
Makhtesh Ramon cirque, the unique structural-erosional
depression formed in the Ramon anticline in the central
part of the Negev desert. The highest of these levels (the
ancient Makhtesh bottom) is propably of the Late Pliocene
age. The stair of 6 terraces related to vadi Ramon and the 5
pediments connected to them are of the Quaternary age.
Some of them have been dated by TL method (Kulikov)
and were used as markers for the rock varnish dating and
absolute age scale creating.
Rock varnish chemistry was studied by electron microprobe
analysis (Camebax) with the special technic developed
by Nechelustov for unpolished surface because of extreme
thinness of patina. The distribution of chemical elements
forming the basis of rock patina, Na, Mg, AI, Si, K, Ti, Cr,
Mn, Fe, was determined; among them such elements as Fe,
Mn,Si,AI,Mg are the most varied in content and can be
viewed as indicators. Mineral composition identified by
electron microscopy technique (Tem) with microdiffraction
(Sivtsov) is the following: kaolinite, montmorillonite,
chlorite, goetite, hematite, litioforite, Mg-AI asbolan, Tiaugite,
etc.
Creating of foolproof methods of rock-varnish dating assessmant
and revealing and aged relations between geomorphological
levels was in the focus ofour unvestigation.
Because primary signs ( element contens ) dont show clearcut
change tendency from age, not only elemental concentrations
but their ratios and products were.taken into accont.
products were used. The using of the original algorithm
(put forward by Chizova) gives minimal determination
error of calculated parameters. The generalized geochemical
index, GI rv, for absolute dating of geomorphologicallevels
based on this calculating model was suggested.
The calculated RV-age scale has been tested on the selected
independent samples from the different-age levels of
the Makhtesh Ramon (from 30 t.y to 1 mIn y.), It can be
used for dating of the varnished geomorphologic surfaces
(river terraces, fans, pediments, slopes) in the Central Negevarea.
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