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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 ice-free lake until its final drainage.

Palaeogeography of the glacial dammed lake

Sequence Stratigraphy: A key tool to study palaeolake sediments

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. The relation between immobile (Ti) and mobile (Al) elements is shown. Basement weathering by climatic favourable conditions promote Al leaching.

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 (C4), on the other hand high depleted values are related to terrestrial plants (C3 plants), frequently a mixture of them is recorded in such environments. 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?...

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.

Sequence stratigraphy is a toolkit that allows us to study more efficiently the geometry of the glaciolacustrine sediments.

Glacial extent curve obtained from the volume of the stored sediments in the lake. More than 250 outcrops were used in order to obtain this curve

Outcrop at the Hortals proglacial delta

Valentí Turu (FMC) & Jaume Bordonau (UB)

The La Massana and Ordino Palaeolake (SE Pyrenees)

Glaciolacustrine record chronology

Idealized palaeoreconstruction of the dammed lake by Marta Vilaplana (1981)

Sketch map of the palaeolake at the post-maximum phase

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

Relationships between Al/Ti and isotope ratio -13C/12C ‰ (AMS)

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Age (Cal BP)

Al/Ti

Al/Ti d13C

GS-2c

He1

GS-5

GIS-4GIS-3

GS-2bGIS-1ad GIS-2 GS 3 GS-4

NGRIP (2bk)

GS-2a

GS-1

He2

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