ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

Rondonia, Southwestern Amazonia, near the bords of Brazil
and Bolivia. The range is formed by sedimentary Precambrian
rocks of the Pacaas Novos Formation and bordered
by Precambrian crystalline rocks of the Brazilian
Shield. The range has an elongate arch shape in the WSW­
WNW to WNW-WSW direction, forming a broad syncline.
The research focused on piedmont geomorphology and
some deep weathering profiles in the rocks of the Brasilian
Shield.
The landscape sequence begins with the occurrence of
thick saprolites that developed through chemical weathering
in the granitic rocks of the shield.
The septentrional flank of the range shows a 150 m high
cliff and a continuous detrital talus with a thickness of 70­
80 m and a declivity of 34° along the piedmont. The base
of the talus is related to a pediment which was developed
on the strongly chemically weathered of the crystalline
rock basement. The formation of the detrital talus and a
pediment level in the piedmont area indicates a change
toward a semiarid climate. The thin alluvial sediments «in
transit» of the pediment suffered laterization which resulted
in a duricrust during a subhumid climate. A new climatic
change activated the linear erosion of the drainage
networks encasing the pediment and dismantling the duricrust.
During a subsequent semiarid period, alluvial fans
were deposited on the piedmont. Today, the rain forest
inhibits the development of all paleoforms.
The geomorphologic analysis of the Pacaas Novos range
provides strong evidence that the morphogenetic systems
changed drastically in Amazonia during the Quaternary.
STANISLAV A. LAUKHIN
Relief evolution of Asia continent's margin in connection
with forming amerasian subbasin of the Arctic Ocean
in the Cenozoic
Institute of Geography RAS, Staromonetny 29, Moscow 109017, Russia
In a continental part of Amerasian subbasin traces of the
Palaeocenic riftogenetic are reflected less clearly, than in
Eurasian one, where structures of rift penetrated a long
way into continent in Verkhoyanye.
Before neotectonic stage a continental regime predominated
on the outer shelf. The sea almost did not penetrate to
the South of 75(N in the Paleocene (although world ocean
level was 150-300 m higher than at present) high plains
predominated and mountainous relief spreaded most widely
on outer shelf (on continent to the North from the
Polar Circle it was spreaded least widely) on the Cenozoic
in the whole. Already in the Early Eocene a sea spreaded
to 72(N and its gulfs penetrated the recent dryland till
68(N. On the whole, risings predominated during the Eocene.
On outer shelf lowlands spreaded, mountainous relief
narrowed his spreading on the shelf and widened on
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the dryland. In the 1st half of the Eocene weathering crusts
formed South from 70 N. In the conditions of warm climate
(annual temperatures near 71° N were 15-19° C). Reliefforming
role of the crust is not clear. Mainly inner shelf
was drawn in subsidence the subbasin.
In the Oligocene, at the beginning of neotectonic stage, the
subsidence area shifted to the North from the flexure separating
hershelf from the outer one. On the outershelf lowerings
along sublatitudinal faults leaded to multiple sea
transgressions, which penetrated into recent dryland in
Yakutia even in end of the Oligocene, when the world
ocean level was 100-150 m lowerthan the recent one. A differentiation
of relief abruptly gorew . Mendeleev Ridge (in
subbasin) and his morphostructural and its orogenic continuation
on the shelf and continent formed. In the North of
continent in end of the Oligocene high mountain relief
spreaded, and the alpine of relief appear forthe first time.
Till middle of the Oligocene on continent low and middle
mountains predominated.
In the Neogene on the outershelf subsidence continued,
sea transgressions penetrated in to the recent dryland not
less than 7 times. In middle of the Miocene relief of
Chukotka was a like to recent; Momo-Selennyakh rift lays
(it's northern offshoots penetrates to NE Yakutya). In the
Late Miocene-Pliocene to the North from the Polar Circle
rising activated in mountains, the high mountainrelief formed,
on E Chukotka basalts outlawed. In the end of the
Miocene on continental lowlands landscapes of tundra raised
to the first time; permafrost becomes reliefforming factor.
In middle of the Pliocene mountain-valley glaciers in
the first time went out on the lowlands of Chukotka (and
lowlands of Eurasia in the whole).
In the Pleistocene a relief is arming under an influence of
differented tectonic movements, glaciations (sea regression-transgressions,
isostasy etc., producing by ones) and
arctic-subarctic climate.
STEIN-ERIK LAURITZEN
A simple growth model for limestone pedestals:
determination of surface karst denudation
Department of Geology, Bergen University,
Allegaten 41, N-5007 Bergen, Norway
Limestone pedestals (Karrentische) are believed to develop
by differential corrosion beneath and around the protecting
boulder. The height of the pedestal is a function of time
and of the shielding effect of the perched boulder. This
work develops mathematical models for the size (i.e, height)
of limestone pedestals as a function of time and the
properties of the perched boulder. These properties are
the shortest horizontal axis of the boulder (x), its shape
factor (.B) and the amount of condensation corrosion be-