ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

ture and other thermodynamic parameters to make reconstructions
of past karstification rates. For this purpose we
obtained several paleotemperature records from Duhlata
cave, Bosnek karst region, Bulgaria. They are covering last
1 Myr with resolution of about 10 years for most of the the
time span. Paleoclimatic records has been derived from
speleothem luminescence, calibrated by actual climatic records
from near climatic stations. We estimated the precipitation
residues and the size of karst aquifer. The sample
was dated by 6 mass spectroscopy U/Th and 9 Tams radiocarbon
dates.
In result we obtained first quantitative reconstruction of
karst denudation in the past (during last 1 Myr), Obtained
data are important for estimations of the significance of the
contribution of karst denudation to global C02 amount
and cycle.
JOHN F. SHRaDER. IR. & MICHAELP. BISHOP
Nanga Parbat Himalaya: tectonics and denudation
Department of Geography and Geology, University
of Nebraska at Omaha, Omaha, NE 68182, U.S.A.
Assessments of relationships between extraordinarily rapid
tectonics and denudation of the Nanga Parbat massif in
the western Himalaya require detailed geomorphologic
mapping, 14C and cosmogenic radionuclide dating of landforms,
and interpretation of stratigraphy and structure to
elucidate uplift and erosional history in the Quaternary period.
Establishment of the rich Quaternary history of denudation
of the Nanga Parbat Himalaya provides control
for the understanding of suspected associations with deep
crustal processes, including decompression melting through
rapid unroofing of the orogen, and concommitant injection
of young leucogranites and high-grade metamorphism.
Studies of such hypothesized unusual feedback mechanisms
between surficial and deep-Earth processes have the
potential for important new understandings of crustal dynamics.
Two of the oldest glacial deposits in the Nanga Parbat Himalaya,
the J alipur and Gorikot tillites, are preserved along
the Raikot and Stak faults between which the rapid uplift
of the Nanga Parbat massif (8125 m) is taking place. The
Jalipur units have been known from the 1930's but understood
unequivocally as glacial only recently. The dominance
in the Jalipur tillite of mafic-rich clasts from the Kohistan
island arc, to the exclusion of Nanga Parbat gneisses,
is thought to show glacial unroofing of the rising massif in
which the uppermost mafics were removed first. The Jalipur
valley-fill cover sediments directly overlying the maficrich
J alipur tillite contain the first Nanga Parbat gneiss clasts,
thus recording the initial unroofing event. Preservation
of the J alipur tillite in the Indus river trench at the base of
Nanga Parbat is thought to be the result of protection in
part by down faulting, but especially by the thick cover sediments
derived from rapid erosion of the massif. The
newly discovered Gorikot glacial tillites and other related
deposits upstream from the Stak fault in Astor valley contain
Nanga Parbat lithologies so the nearby glacial unroofing
at this time had progressed sufficiently to expose the
gneisses from beneath the island arc lithologies. Perservation
of the Gorikot units on the downthrown side of the
fault was facilitated by the Nanga Parbat massif rising
across the Astor river valley, forcing deposition of thick cover
sediments over the Gorikot and hindering deep erosion
that would have removed the older units. Downstream
within the massif, all evidence of Gorikot ice has
been eroded.
Cosmogenic radionuclide dating of high moraines at about
4300 m shows that at --55,000 yr an eight-fold ice expansion
from the condition of the present allowed ice to descend
from the north Raikot face of Nanga Parbat to fill
the Indus valley to a depth of 3 km. Catastrophic flood flushing
of sediment from such huge ice dams has been recognized
as a significant denudation agent. Some of the
Punjab erratics and other deposits in the Peshawar basin
in the Himalayan foothills are now known to be products
of these glacier breakout floods. Emplacement of Last Glacial
Maximum (Lgm) moraines on NangaParbat was at
about 17,000 yr B.P. Since Lgm time the prime denudational
processes have been slope failures, glaciers and rivers,
which we recognize are episodic, differential, scale-dependant,
and generally high magnitude and moderate to high
frequency compared to less active landscapes. Slope failure
is strongly controlled by bedrock geology, especially along
the plate terrane boundary near the Raikot fault, altough
climatic and seismic controls are important as well. Several
major events have recurred at the same sites. Measurements
of basin volumes, fan volumes, and recurrence interval
of debris flows from dendrogeomorphic assessments allow
reconstruction of denudational process rates associated
with some alpine fans. Assessment of glacier debris
loads and velocities enables sediment discharge denudation
calculations. Bankfull river discharge and sediment
load estimates similarly enable calculation of basin denudation
rates. Numerous catastrophic breakout floods from
slope failure and small glacier dams have now been identified
and used to calculate denudation as well.
In these multiple assessments of past and present process
rates, a comprehensive investigation of the complex relations
between tectonics and denudation of the Nanga Parbat
massif is being made in the interdisciplinary Nanga
Parbat project. Access to new high-resolution satellite
imagery, state-of-the-art digital elevation models, and com";
puter-generated terrain-evolution models are providing
sound bases for geomorphological mapping where prior
topographic map control is deficient. This collaboration
between tectonicists and geomorphologists is proving to
be a highly fruitful and mutually rewarding enterprise. '
353