Glaciation in the Eastern Pyrenees between NGRIP/GRIP GS-9 and GS-2a stadials: 25,000 years of palaeoenvironmental record in the

Valira Valleys (Principality of Andorra) Valentí Turu and Guy Jalut

Marcel Chevalier Earth Science Foundation, Ed. sociocultural La Llacuna, AD500 Andorra la Vella, Principality of Andorra. Corresponding author (E-mail: igeofundacio@andorra.ad

AMS 14C dating and δ13C Total carbon (bulk) from •  Pure colluvial •  Colluvial-alluvial mixture •  Supraglacial-colluvial m. •  Subglacial till •  Gl-Fl over bedrock δ13C from vegetation average and can be used as a proxy

•  No laminites has been dated (aquatic plants), only subaerial sediments except subglacial tills (mixture)

Glaciolacustrine geochemistry

•  232 stratigraphical descriptions •  Basin analysis using sequence

stratigraphy (Turu et al., 2016). •  Chronostratigraphic benchmark for

paleoenvironmental studies •  Online database

•  Depicting the paleolake alkalinity using 21 samples •  Major elements (Al, Si, Ca, Ti, ..) •  Proxys: Ca, Fe, Al, Ti •  Al/Ti ratio as detrital proxy

La Massana paleolake

TURU. V., CALVET, M., BORDONAU J., GUNNELL, Y., DELMAS M., VILAPLANA J.M. & JALUT, G. (2016) Did Pyrenean glaciers dance to the beat of global climatic events? Evidence from the Wurmian sequence stratigraphy of an ice-dammed palaeolake depocentre in Andorra; HUGHES P.D. & WOODWARD J.C. (eds) Quaternary Glaciation in the Mediterranean Mountains. Geological Society, London, SP 433. DOI: 10.1144/SP433.6

Stratigraphy

Stratigraphy based on the study of proglacial deltas

Arinsal tributary stratigraphy

Sequence Stratigraphy classification by identifying unconformity surfaces

Chronostratigraphy

TILL ---> TILL ---> TILL ---> TILL ---> TILL --->

Glacier front unstability is recorded on the basin (subglacial till sedimentation)

δ13C data

Rythmic trend & decreassing δ13C values in each one

Fast Fourier Transform

Wave length of 6.1 and 4.0 Kyrs are depicted

!13C Valira Nord FFT

-8

-7

-6

-5

-4

-3

-2

-1

0

0 2 4 6 8 10 12 14

Ka

Magnitud d

e l'a

rmonic

-!13C

All data

Climate

Aride

Cold &

Moist

Moister

Warmer

Aridity

Cold and moist

Moister

Warmer conditions

Conclusions

•  Five aridity cycles, one each 4 Ka (FFT) •  Three Heinrich events, one each 6.1 Ka (FFT) •  These climatic events may be independent but

their interference produce abrupt climatic shiftings between 17 and 36 Ka (19,000 yrs)

•  For that reason He are barely recognizable

Thank you

Where is the key?