Mercy to a sequence stratigraphy study of the Delta d’Erts proglacial complex, a roboust correlation across the basin has been obtained.

1. Para ver esta película, debe
disponer de QuickTime™ y de
un descompresor TIFF (LZW).
ESTUDIO GEOQUÍMICO DE LOS SEDIMENTOS
GLACIOLACUSTRES DE LA MASSANA Y ORDINO (ANDORRA,
PIRINEOS ORIENTALES): INFLUJO SEDIMENTARIO ENTRE LAGOS
DE OBTURACIÓN YUXTAGLACIAR E INTERPRETACIÓN
PALEOAMBIENTAL
Valentí Turu i Michels
Fundació Marcel Chevalier
Av. Príncep Benlloch 66. D-0500 Andorra la Vella
Jaume Bordonau i Ibern
RISKNAT. Dpt. Geodinàmica i Geofísica
Universitat de Barcelona. C/ Martí i Franquès (S/N). 08028-Barcelona

2. Para ver esta película, debe
disponer de QuickTime™ y de
un descompresor TIFF (LZW).
Palaeogeography of the glacial dammed lake
Three glacial tongues converged on the La Massana site during the local
glacial maximum prior to the LGM. A post maximum glacial retreat occured
followed by a glacial advance and stabilisation (post maximum stabilisation).
At that moment the glacial tongues converged several times at La Massana
damming intermittently the lake. A final disjunction phase gave way to an icefree lake until its final drainage.
Idealized palaeoreconstruction of
the dammed lake by Marta
Vilaplana (1981)
Sketch map of the palaeolake at the post-maximum phase
Outcrop at the Hortals proglacial delta

3. Para ver esta película, debe
disponer de QuickTime™ y de
un descompresor TIFF (LZW).
Sequence Stratigraphy: A key tool to study palaeolake
sediments
Mercy to a sequence stratigraphy study of the Delta d’Erts proglacial complex,
a roboust correlation across the basin has been obtained.
Erts delta sequence stratigraphy
(Arinsal valley). Relative position
of the glaciolacustrine samples for
geochemical analysis and AMS
available data (from all valleys).
More than 150 outcrops were
described in the Arinsal valley
AMS data and geochemical
samples taken at different places
in the basin. Because a robust
correlation is avaiable is now
possible to locate such data in a
chronostratigraphic section

4. Para ver esta película, debe
disponer de QuickTime™ y de
un descompresor TIFF (LZW).
Accumulation-related mechanical denudation for the paleolake
In this slice the denudation rate is shown evaluating the sediments deposited in the
paleolake that acted as a a sediment trap. The age model model is based on bulk
sediment 14C-dating and cosmogenic-datingversus glacial extention
Glacial extent curve obtained from the volume of
the stored sediments in the lake. More than 250
outcrops were used. Some analogies can be observed
if it is compared with the results obtained in the
Southern Pyrenees glaciolacustrine deposits.
Bordonau (1992)

5. Para ver esta película, debe
disponer de QuickTime™ y de
un descompresor TIFF (LZW).
Geochemistry: A key tool to study palaeoclimate
changes
Geochemistry studies give all its potential if a good chronostratigraphic model
has been previously stablished. Data about weathering, chemical conditions in paleolake
waters and its relationship with paleoclimate are available with this kind of studies.
Chemical denudation in mountains is an important process in
humid conditions, particularly when water pH low values
appears by sulfide alteration from metamorphic rocks, or/and
humid soils (histosols) and stagnant waters cover extended
areas of the basin.
Titanium is an immobile element and is used to illustrate the
relative input of terrestrial materials.
Aluminium may be partly transported in soil waters with a pH
value below four.
We try to estimate the weathering patterns comparing the Al/Ti
ratio of sediments and the unaltered bedrock. In that sense we
think that aluminium comes form the hand of weathered pyrite
rich metamorphic rocks.
.
Basement weathering seems to follow climatic favourable
conditions that promote Al leaching.
Attention should be placed at GS-2b stadial, were Al/Ti ratio
overflow the basement mean value.

6. Para ver esta película, debe
disponer de QuickTime™ y de
un descompresor TIFF (LZW).
Isotope analysis: A key tool to reconstruct
palaeoenvironments
In proglacial palaeoenvironments, pollen can be distroyed by the energy of the glacial
meltwaters. In such cases it is possible to reconstruct the palaeovegetation from the
δ13C ratio. In continental environments less depletion in δ13C values are correlated
with an increasing presence of aquatic plants and also arid zone plants (C4), on the
other hand high depleted values are related to terrestrial (C3 plants).
C3 plants
C4 plants
Positive correlation between both variables are observed. During the LGM, δ13C shows a very low depletion value. At the same time the
weathering Al/Ti ratio is low. How should we interpret this evidences?, cooling?, high amount of metwaters?, increasing of aridity?... We
interpret that the paleolake receive highs amounts of meltwater and drive to desestabilize the sulfurs of the metamorfic terrains.

7. Para ver esta película, debe
disponer de QuickTime™ y de
un descompresor TIFF (LZW).
Decoding the sedimentological record of the palaeolake
A similar glacial evolution was previously proposed (Bordonau, 1992) from
sedimentological studies of glacial paleolakes from Southern Pyrenees.
However a more complete chronological reconstruction can be stablished here.

8. Para ver esta película, debe
disponer de QuickTime™ y de
un descompresor TIFF (LZW).
Thank you