ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

JORGE RABASSA 1, MARCELO ZARATE 2,
TIMOTHY C. PARTRIDGE 3, RODNEY MAUD 4,
MARCELA CIOCCALE 5 & CLAUDIO CARIGNANO 5
Gondwanic relict palaeolandscapes in cratonic areas
of Argentina
1 Cadic-conicet, C.C.92, 9410 Ushuaia, Argentina
2 Conicet-Universidad Nacional de Mar del Plata,
C.C.722, 7600 Mar del Plata, Argentina
3 University of Witwatersrand, p.o. box 1050, Parklands,
Johannesburg 2121, South Africa
4 University of Natal, 68 Ridge Road, Durban 4001, South Africa
5 Conicet-Universidad Nacional de C6rdoba, Av.Velez Sarsfield 299,
5000 C6rdoba, Argentina
Relict landforms (peneplains, pediplains, bornhardts,
rocking stones, core rocks, palaeoweathering profiles, etc.)
of Late Mesozoic-Early Tertiary age, have been identified
since long ago in South Africa and Brazil. Similar
landforms have been recognized in Argentina, following
the South African methodology as summarized by Partridge
& Maud (1987). The works ofDu Toit (1927) and KING
(1967), among many other South African and Brazilian
authors, have been used in the preparation of the theoretical,
conceptual framework for this paper.
During Early Cretaceous times, the present territories of
Argentina, as well as the rest of South America, were still
physically linked to South Africa as part of the Gondwana
Supercontinent. Dominant climate was humid tropicalsubtropical
for most of its emerged lands. Relict landscapes
in Argentina would have been generated during Jurassic-Cretaceous,
up to Palaeocene times, under climatic
conditions which were very different from those existing
today. These relict landforms have been observed in the
Tandilia hills (core stones, rocking stones, palaeoweathering
profiles), the Ventania ranges (silcretes and silicified
slope breccias), the Northern Patagonian Massif (erosional
surfaces, deep palaeoweathering profiles, kaolinization
processes), the Sierras de Cordoba (high «pampas» or erosional
surfaces, core stones, bornhardts, palaeoweathering
profiles) and the Deseado Massif of Southern Patagonia
(extensive erosional surfaces). In Ventania, the densely silicified
Cerro Colorado Breccia fills a drainage network eroded
into the Late Palaeozoic sedimentary rocks. These
breccias have been tentatively correlated with Du Toit's
«High Level Gravels» and their associated siliceous duricrusts
of the Southern Africa Cape region, which age is
bracketed between 63-54.8 Ma, thus providing a minimum
age for the underlying fluvial palaeolandscape. However,
due to other regional interpretations, the breccias may be
even older (Cretaceous). The Pampean intracratonic tectonic
basins, such as the Colorado, Parana, and Macachfn
basins, were initially filled by Cretaceous basalts, related to
the Southern Atlantic rifting process. In the western margin
of the Northern Patagonian Massif, the Jurassic(?)-Cretaceous
erosional surfaces were fluvially eroded and the resulting
drainage landscape was infilled by Palaeocene-Early
Eocene (ca. 55 Ma) volcanics and highly-siliceous pyrocla-
sties, The Sierras de Cordoba high «pampas» are locally
covered by Cretaceous basalts and sedimentary rocks, which
fill shallow depressions carved into the relict erosional
surfaces. However, in the Sierras Pampeana region, the palaeolandforms
have been severely affected by Tertiary Andean
tectonism, and their reconstruction is more difficult.
The preservation of these ancient, relict palaeolandscapes,
which were never buried afterwards and remained as portions
of positive elements since then, is interpreted as a
consequence of their development over hyperstable regions
of Argentina. Their recognition in the field and subsequent
interpretation is of high relevance because: (1) it
explains the cratonic morphogenesis as part of Gondwana
and its persistency for at least 60 Ma; (2) it provides a new
approach in the interpretation of the Pampean and present
submarine-platform, Cretaceous-Early Tertiary tectonic
basins; (3) it offers an appropiate conceptual scheme for
mineral exploration of such ores as kimberlites or bauxites;
(4) it favours the geomorphological interpretation of the
Argentine cratonic regions with a «Gondwanic vision»
that should replace the «Andean vision», until now dominating
the Argentine geological literature.
ZOFIA RACZKOWSKA
Nivation in the Tatras in comparison
with other mountain areas
Department of Geomorphology, Institut of Geography
and Spatial Organization, Polish Academy of Sciences,
cew.Jana 22,30-918 Krac6w, Poland
The geomorphic processes operating around the snow patches
on the high-mountain slopes are presented.
The studies of nivation in the Tatras were carried out on
the northern slopes of the High Tatras, above the timberline
(1500 m a.s.l.), on the slopes developed on granite bedrock.
The studies mainly concerned thermal conditions of
weathering, meltwater runoff, material transport and the
impact of snow patches on the accumulation processes developed
on debris slopes. It is concluded that the key factor
in the intensification of processes is increased moisture
availability rather than the microclimatic effects of snow
patches. If compared with weathering, present-day transport
processes and deposition appear to be more active.
Nevertheless, the activity of the above processes varies
with the meteorological situation.
Erosional effects of snow patches are considerable on slopes
mantled by debris devoid of vegetation cover. The nival
niche backwall retreats 1 to 5 em per year due mainly
to frost action and needle ice. In the lower part of niche
bottom sheet wash and rill erosion was observed.
On debris slopes «accumulation niches» are developing in
places occupied by snow patches, most often in the apex
part of the slope. They are formed due to accreation on de-
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