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Géomorphologie : relief,processus, environnement4/2014 (2014)Quaternary Geomorphology

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Cristian Scapozza, Claudio Castelletti, Linda Soma, Stephan Dall’Agnoloet Christian Ambrosi

Timing of LGM and deglaciation in theSouthern Swiss Alps................................................................................................................................................................................................................................................................................................

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Référence électroniqueCristian Scapozza, Claudio Castelletti, Linda Soma, Stephan Dall’Agnolo et Christian Ambrosi, « Timing ofLGM and deglaciation in the Southern Swiss Alps », Géomorphologie : relief, processus, environnement[En ligne], 4/2014 | 2014, mis en ligne le 01 janvier 2016, consulté le 14 janvier 2016. URL : http://geomorphologie.revues.org/10753 ; DOI : 10.4000/geomorphologie.10753

Éditeur : Groupe français de géomorphologiehttp://geomorphologie.revues.orghttp://www.revues.org

Document accessible en ligne sur : http://geomorphologie.revues.org/10753Ce document est le fac-similé de l'édition papier.© Groupe français de géomorphologie

Version française abrégée

Après le travail pionnier de A. Penck et E. Brückner (1909),plusieurs recherches se sont focalisées sur l’extension desglaciers de piedmont et sur la déglaciation dans les Alpes.Avec ces études, le schéma développé au début du XXe siècle

comprenant seulement trois stades principaux (Bühl, Gsch-nitz et Daun) est devenu plus complexe. Il comprend aujour-d’hui au moins six stades majeurs reconnus dans plusieurs ré-gions des Alpes (Müller et al., 1980 ; Maisch, 1982; Schoe-neich et al., 1997 ; Coutterand et Nicoud, 2005). Grâce à ladétermination des âges d’exposition à l’aide des isotopes

Géomorphologie : relief, processus, environnement, 2014, n° 4, p. 307-322

Timing of LGM and deglaciation in the Southern Swiss AlpsChronologie du DMG (Dernier Maximum Glaciaire) et de la

déglaciation dans les Alpes Suisses Méridionales

Cristian Scapozza*, Claudio Castelletti*, Linda Soma*, Stephan Dall’Agnolo**, Christian Ambrosi*

* Institute of Earth Sciences – University of Applied Sciences and Arts of Southern Switzerland (SUPSI) – Campus Trevano – 6952 Canobbio – Switzer-land ([email protected]).** Swiss Geological Survey – Federal Office of Topography swisstopo – Seftigenstrasse 264 – 3084 Wabern – Switzerland (Stephan.Dall’[email protected]).

AbstractDetailed mapping of Quaternary formations in Southern Switzerland (Mendrisiotto and neighbouring regions in Italy) and a compila-tion of radiocarbon dating make it possible to reconstruct the geometry and chronology of the Last Glacial Maximum (LGM) in theSouthern Swiss Alps. A detailed chronostratigraphy of the main recessional stadials during the Lateglacial and beginning of the Holocenecan also be obtained. The defined glacial stadials were correlated with the NGRIP Greenland isotopic record. An analysis of the cali-brated maximum and minimum ages of the LGM allows this episode to be limited to between 28,500 and 22,900 cal BP (24,500–19,00014C BP). The LGM advance could then tentatively been correlated with the GS-3, between 27,400 and 22,700 cal BP. For thePleniglacial and the Pleniglacial/Lateglacial transition, the first recessional phases after the LGM were positioned between ca. 22,500and 21,000 cal BP, and may correspond to the two first cold events of the GS-2c. The first Lateglacial stadial was the Melide stadial,and may match with one of the two cold events at 20,450 or 19,850 cal BP in NGRIP stratigraphy. In the Leventina and Bedretto Val-leys (Ticino glacier), five glacial stadials have been proven for the Oldest Dryas (Biasca, Faido, Airolo, Fontana and All’Acquastadials), two for the Younger Dryas (Maniò and Alpe di Cruina stadials) and one (Val Corno stadial) corresponding to GreenlandHolocene event GH-11.2.

Key words: deglaciation, LGM, Lateglacial, radiocarbon dating, Ticino glacier, Swiss Alps.

RésuméLa cartographie géologique minutieuse des terrains du Quaternaire dans la Suisse méridionale (Mendrisiotto et régions italiennesenvironnantes) et la compilation de plusieurs datations radiocarbone ont permis de reconstituer la géométrie et la chronologie du Der-nier Maximum Glaciaire (DMG/LGM) dans le Sud des Alpes Suisses. Ces résultats ont aussi permis d’obtenir une chronostratigraphiedétaillée des principaux stades glaciaires qui ont marqué le Tardiglaciaire et le début de l’Holocène. Les stades glaciaires définis ontété corrélés aux évènements de l’enregistrement isotopique du sondage NGRIP au Groënland. L’analyse des âges radiocarbone cali-brés maximaux et minimaux du DMG permet de placer cet épisode entre 28500 et 22900 cal BP (24500-19000 14C BP). L’avancéeglaciaire attribuée au DMG a donc été corrélée de manière hypothétique avec le GS-3, compris entre 27400 et 22700 cal BP. Pour lePléniglaciaire et la transition Pléniglaciaire/Tardiglaciaire, les premières phases de régression glaciaire après le DMG ont été placéesentre ca. 22500 et 21000 cal BP, et peuvent correspondre aux deux premiers épisodes froids du GS-2c. Le premier stade du Tardigla-ciaire a été le stade de Melide, qui peut correspondre avec l’un des deux épisodes froids de 20450 ou 19850 cal BP. Par la suite, dansles vallées de Leventina et de Bedretto (glacier du Ticino), cinq stades glaciaires ont été mis en évidence pour le Dryas ancien (stadesde Biasca, Faido, Airolo, Fontana et All’Acqua), deux pour le Dryas récent (Maniò et Alpe di Cruina) et un (Val Corno), en corres-pondance avec l’épisode froid holocène du Groënland GH-11.2.

Mots clés : déglaciation, DMG, Tardiglaciaire, datations radiocarbone, glacier du Ticino, Alpes Suisses.

cosmogéniques, la chronologie du dernier cycle glaciaire aégalement été affinée de manière considérable depuis la findu XXe siècle, en particulier dans les Alpes Orientales (Ivy-Ochs et al., 2007, 2008 ; Reitner, 2007).

Jusqu’à ce jour, il a été admis notamment par des cher-cheurs du Nord de l’Italie (Bini, 1997 ; Bini et al., 2009) quele Sud des Alpes Suisses présentait une histoire des glacia-tions quaternaires différente par rapport au reste des AlpesSuisses. Ceci est dû probablement à l’absence de datationsdes âges d’exposition à l’aide d’isotopes cosmogéniques etde la sous-exploitation des datations radiocarbone dispo-nibles. Pour ces raisons, le versant sud des Alpes a souventété négligé dans les synthèses concernant la déglaciationdans les Alpes Suisses (Schlücher, 1988 ; Schoeneich, 1998 ;Ivy-Ochs et al., 2008).

Le levé des formes et dépôts du Quaternaire de la feuille1373/Mendrisio pour l’Atlas géologique de la Suisse au1:25 000 (Ambrosi et al., 2014), et la compilation de 26 da-tations radiocarbone pour les glaciers du Ticino et de l’Ad-da au Pléistocène récent (fig. 1) a rendu possible la recons-titution d’une nouvelle géométrie et chronologie du DMG etde définir les principales étapes de la déglaciation dans leSud des Alpes Suisses. À l’aide de la chronologie de la dé-glaciation élaborée en combinaison avec le calcul de la Dé-pression de la Ligne d’Equilibre des Glaciers (DLEG) pourles principaux stades glaciaires reconnus, un essai de cor-rélation des stades glaciaires définis dans la vallée du Tici-no avec le modèle des Alpes Orientales est proposé ici. LaDLEG a été calculée par soustraction de la LEG déterminéeen utilisant la méthode de partage des surfaces et considé-rant un AAR (Accumulation Area Ratio) de 0,67 (Kerschner,1976 ; Gross et al., 1977) du niveau de référence de la findu Petit Age Glaciaire (Dorthe-Monachon et Schoeneich,1993). Sur la base de cette approche, il est également pos-sible de corréler les fluctuations glaciaires mises en éviden-ce avec l’enregistrement isotopique groenlandais du sonda-ge NGRIP (North Greenland Ice Core Project ; voir NGRIP-Members, 2004a) sur la base de la stratigraphie INTIMATE(INTegration of Ice core, Marine and TErrestrial records ofthe last termination ; voir Blockley et al., 2012).

Toutes les données radiocarbone compilées (tab. 1 et fig. 2A)ont été calibrées grâce au logiciel OxCal 4.2 (Bronk Ram-sey, 2014) sur la base de la courbe de calibration IntCal13(Reimer et al., 2013) et avec un intervalle de confiance de2σ (95,4% de probabilité).

D’un point de vue chronologique, les datations des dépôtsrecouverts, respectivement couvrant ceux relatifs à l’EpisodioCantù, défini comme l’avancée maximale des glaciers du Suddes Alpes pendant le dernier cycle glaciaire (Bini 1987; Fel-ber, 1993; Bini et al., 2001), ont permis de déterminer un âgedu DMG pour les glaciers du Ticino et de l’Adda comprisentre 28500-22900 cal BP (24500 et 19000 14C BP). Il a doncété possible de proposer une corrélation du DMG avec lestade isotopique GS-3, compris entre 27400 et 22700 cal BPsur la courbe du forage NGRIP (fig. 2B). Ce résultat est co-hérent avec l’âge du DMG déterminé au Nord des AlpesSuisses, qui est généralement compris entre 26800-21250 calBP (22000 et 18000 14C BP) pour les glaciers du Rhône (lobe

Suisse), de la Linth et du Rhin (Schoeneich, 1998 ; Preusser,2004 ; Ivy-Ochs et al., 2008), ce qui permet de le placer entreles interstades GI-3 et GI-2.

Les premières phases de la déglaciation ont été détailléesen particulier pour le sous-lobe de la Faloppia, partie dulobe du Lario du glacier de l’Adda (fig. 3A), permettant de dé-terminer les équivalents des phases de Cucciago et Ca’Mortadéfinies par Felber (1993) et Bini et al. (2001). La corrélationhypothétique de ces phases avec la stratigraphie isotopique duGroënland a permis de proposer un âge compris entre 22500et 21000 cal BP (fig. 3B, C).

Pour les stades suivants, seul celui de Melide du lobe du Ce-resio est bien précisé, avec un âge minimal d’environ 18000 calBP permettant de proposer une corrélation avec l’un des deuxpics froids placés entre 20450 et 19850 cal BP sur la courbeNGRIP. Celui-ci pourrait correspondre au stade de Cugnascodéfini sur le lobe du Verbano du glacier du Ticino (fig. 4).

Le premier véritable stade tardiglaciaire à l’intérieur desvallées supérieures est celui de Biasca (fig. 5). Sur la based’arguments paléoclimatiques et d’une DLEG comprise entre1 080 et 1 200 m, Scapozza et Fontana (2009) ont proposéune corrélation avec le stade de Weissbad défini par Keller(1988a) dans le massif du Säntis, en Suisse Orientale, cor-respondant à l’ancien stade de Bühl II des Alpes Orientales(tab. 3), qui aujourd’hui n’est plus considéré comme un stademais plutôt comme une phase de décroissance glaciaire dudébut du Tardiglaciaire (Reitner, 2007).

Pour la suite du Dryas ancien, quatre autres stades gla-ciaires (Faido, Airolo, Fontana et All’Acqua) ont été définis.Les datations disponibles permettent de conclure que lesstades de Biasca, Faido et Airolo sont plus anciens que16500 cal BP. Si l’on tient compte également des corréla-tions avec les Alpes Orientales, les stades de Biasca et deFaido seraient antérieurs à 19000-18000 cal BP (âge mini-mal du stade de Steinach dans les Alpes Orientales ; voirvan Husen, 1999 ; Ivy-Ochs et al., 2006) et le stade d’Airo-lo serait probablement compris entre 18000 et 17000 cal BP(fig. 2B). Pour les stades de Fontana et All’Acqua, un âgeminimal de ce dernier de 12575–11620 cal BP (rd-24) per-met de conclure qu’ils sont antérieurs à l’interstade du Bøl-ling/Allerød et qu’ils peuvent donc être attribués au stadeisotopique GS-2a.

Les trois derniers stades définis dans le Val Bedretto, ceuxde Maniò, Alpe di Cruina et Val Corno (fig. 6), peuvent êtrerespectivement corrélés avec une bonne certitude avec lesstades de l’Egesen I (Egesen maximal), Egesen II (Bock-tentälli) et Egesen III (Kartell) des Alpes Orientales. Lesâges minimaux de ces stades permettent d’attribuer ceux deManiò et de l’Alpe di Cruina au stade isotopique groenlan-dais GS-1 (Dryas récent) et celui de Val Corno est associé àl’épisode froid holocène GH-11.2 (Préboréal).

La corrélation des stades glaciaires définis au Sud desAlpes avec ceux des Alpes Orientales a permis de soulignerune chronologie de la déglaciation assez similaire entre leSud et le Nord des Alpes Suisses. Cela n’a rien de surpre-nant si l’on considère une zone d’accumulation communeentre les glaciers de vallée provenant de la région du Go-thard constituée par des dômes de glace situés dans la par-

308 Géomorphologie : relief, processus, environnement, 2014, n° 4, p. 307-322

Cristian Scapozza et al.

tie supérieure de la Vallée du Rhône (dôme de glace duRhône) et dans la Haute Surselva (dôme de glace du Vor-derrhein ; Florineth et Schlüchter, 1998 ; Bini et al., 2009).En effet, cette géométrie des zones d’accumulation des gla-ciers pendant le DMG, ainsi que les évidences géomorpho-logiques de diffluences glaciaires (du nord vers le sud) auxprincipaux cols (Cols du Nüfenen, du Gothard, du Lukma-nier et de la Greina) de la région du Gothard (Florineth etSchlüchter, 1998 ; Scapozza et Fontana, 2009 ; Scapozza etal., 2011), indiquent une alimentation partielle du glacier duTicino par des glaces provenant du côté Nord des Alpes.

Introduction

Following the pioneering work by A. Penck and E. Brück-ner (1901-1909), many studies have focused on piedmontglacier extension and on the history of the last deglaciation inthe European Alps, during Quaternary. In the course of thelast century, there have been considerable developments inthe level of understanding regarding the morphostratigraph-ical sequence of deglaciation during the Lateglacial. Thescheme developed by A. Penck and E. Brückner (1909) con-tained only three glacial stadials (Bühl, Gschnitz and Daun),but at the beginning of the 1980s six stadials were identifiedin different regions of the Alps (Müller et al., 1980; Maisch,1982; Schoeneich et al., 1997; Coutterand and Nicoud, 2005).Thanks to the application of surface exposure-dating with cos-mogenic nuclides, the chronology of the last glacial cycle wassignificantly improved, particularly in the Eastern Alps (e.g.,Ivy-Ochs et al. 2007; Reitner, 2007; Ivy-Ochs et al., 2008,and references therein).

However, the evolution and chronology of Quaternary glacia-tions in the Southern Swiss Alps were often considered as dif-ferent from those in the Northern or Eastern Alps (Bini, 1997;Bini et al., 2009), and the southern face of the Alps was omittedfrom overviews of the Swiss Alps deglaciation (Schlüchter,1988; Schoeneich, 1998; Ivy-Ochs et al., 2008). Presented hereis a reassessment of deglaciation timing based on a compilationand re-evaluation of existent radiocarbon dates.

This revision of the LGM chronology and of the lastdeglaciation in the Southern Swiss Alps was conductedduring the realisation of the 1:25,000 Quaternary geologicalmap of Sheet 1373/Mendrisio (Ambrosi et al., 2014), cov-ering the southern part of Canton Ticino and the northernpart of Italy, between Como and Varese (fig. 1). Detailedmapping of the glacial and glaciofluvial deposits and land-forms, and the compilation of several radiocarbon dates forthe Ticino and Adda glaciers, makes it possible to establishthe extent and chronology of the Last Glacial Maximum(LGM) in the Southern Swiss Alps. Moreover, the calibra-tion of radiocarbon dates, together with the glacial reces-sional stadials specified in the literature, can be used to ob-tain a detailed chronostratigraphy of the main recessionalstadials during the Lateglacial and at the beginning of theHolocene. The chronological assessment of the deglacia-tion, and the definition of the Equilibrium Line Altitude(ELA) depression, makes it possible to attempt to correlatethe glacial stadials defined in the Ticino Valley with the

Eastern Alps model. This assessment means that climaticfluctuations indicated by the glacial stadials can thereforebe correlated with the NGRIP Greenland isotopic record(North Greenland Ice Core Project; NGRIP-Members,2004a).

Methods

Radiocarbon dating compilation andcalibration

26 radiocarbon dates generated from Ticino (Switzerland)and Lombardy (Italy) were compiled from previous works(tab. 1), and plotted in a graph in accordance with the timeperiod covered for every date, and with their respective po-sitions in the morphostratigraphy of the glacial deposits ofthe Ticino and Adda glaciers, from the Po plain to the high-er part of the Bedretto Valley (fig. 2A). All the radiocarbondates reported here were calibrated using OxCal 4.2 soft-ware (Bronk Ramsey, 2001, 2014), in accordance with theIntCal13 calibration curve (Reimer et al., 2013), and with a2σ confidence interval (95.4% probability). The calibrateddates are expressed in calendar years before present (cal BP),while the conventional ages are expressed in radiocarbonyears before present (14C BP; Miallier and Lefèvre, 2013),with the present corresponding to AD 1950.

Morphostratigraphy of the glacial stadials

The morphostratigraphy of deglaciation is based on thedefinition of the former-ELA, with the ELA depression cal-culated from a reference altitude. The ELA was calculatedusing the Accumulation Area Ratio (AAR) hypsometricmethod, based on 0.67 ratio for the accumulation surface/totalsurface of a glacier (Kerschner, 1976; Gross et al., 1977), cor-responding to a ratio of 2:1 between the accumulation surfaceand the ablation surface of a glacier. The ELA depressionwas calculated on the basis of the difference in altitude be-tween the former-ELA and the ELA calculated for the end ofthe Little Ice Age (1850/60 AD in the Central and SouthernSwiss Alps), considered as the last important glacial stadialwith the glaciers in a condition of climatic equilibrium (Dorthe-Monachon and Schoeneich, 1993).

Greenland isotope stratigraphy

The general climatic framework for the northern hemi-sphere is supplied by the oceanic and Greenland isotopecurves, which make it possible to establish the volumetricvariations in the continental ice sheets, and the air tempera-ture variations in the northern Atlantic (Johnsen et al.,2001). Since the Alps contributed relatively little to theglobal ice masses during past glaciations, a more detailedclimatic proxy is supplied by the Greenland isotopic stratig-raphy. Variations in δ18O reflect variations in temperatureand in the circulation of moisture. More negative δ18O val-ues reflect colder air temperatures, and more positive δ18Ovalues therefore reflect warmer air temperatures. A δ18O

309Géomorphologie : relief, processus, environnement, 2014, n° 4, p. 307-322

Timing of LGM and deglaciation in the Southern Swiss Alps



Fig. 1 – Localisation of the study area, representation of the glacial extent during the LGM (modified from Bini et al., 2009) and positionof the discovered organic material supplying the radiocarbon dating presented in tab. 1 and in fig. 2A. The radiocarbon dating numbercorresponds to the numbers in the first column of tab. 1. The positions of dating rd-1, rd-4, rd-7, rd-11 and rd-13 are not represented becausethey lie outside of the map frame. 1: main pass; 2: radiocarbon dating; 3: Faloppia sub-lobe. Equidistance of the contour lines: 200 m.

Fig. 1 – Localisation du secteur étudié, représentation de lʼextension glaciaire pendant le DMG (modifié dʼaprès Bini et al., 2009) etposition des découvertes de matériel organique ayant permis les datations radiocarbone présentées dans le tab. 1 et dans lafig. 2A. L'identifiant de la datation radiocarbone correspond à l'identifiant de la première colonne de la tab. 1. La position des datations rd-1,rd-4, rd-7, rd-11 et rd-13 nʼest pas représentée parce quʼelle se situe en dehors du cadre de la carte. 1 : col principal ; 2 : datation radiocar-bone ; 3 : sous-lobe de la Faloppia. Equidistance des courbes de niveau : 200 m.



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onda

scia

(B

iasc

a)W

ood

/ B

ois

12,3

70 ±

85

14,9

00 –

14,

085

18

rd-2

1B

-2,8

49B

edrin

a (D

alpe

)G

yttja

/ G

yttja

12,1

70 ±

110

14,5

45 –

13,

745

19

rd-2

2LH

GI*

S. A

bbon

dio

(Com

o)W

ood

/ B

ois

11,7

30 ±

180

14,0

05 –

13,

210

11,

20

rd-2

3U

Z-4

,722

/ET

H-2

5,35

5(L

avor

go,

Fai

do)

Woo

d /

Boi

s11

,690

± 8

513

,735

– 1

3,35

021

rd-2

4U

Z-1

67P

lidut

scha

Gyt

tja /

Gyt

tja10

,325

± 1

3012

,575

– 1

1,62

022

, 23

rd-2

5U

Z-3

48V

al T

orta

Pea

t / T

ourb

e9,

995

± 11

011

,960

– 1

1,22

022

, 23

rd-2

6U

Z-2

22A

lpe

di C

ruin

aP

eat

/ Tou

rbe

6,37

0 ±

857,

460

– 7,

025

22,

23

Tab.

1 –

Co

mp

ilati

on

of

rad

ioca

rbo

n d

atin

g, m

akin

g it

po

ssib

le t

o r

eco

nst

ruct

th

e d

egla

ciat

ion

in t

he

So

uth

ern

Sw

iss

Alp

s. *

LHG

I = L

abor

atoi

re d

e H

ydro

logi

e et

de

Géo

chim

ie Is

otop

ique

,U

nive

rsité

Par

is-S

ud.

1: B

ini (

1997

); 2

: B

ini e

t al

.(2

001)

; 3:

Fel

ber

(199

3);

4: D

a R

old

(199

0);

5: R

ossi

et

al.

(199

1);

6: A

less

io e

t al

.(1

975)

; 7:

Ale

ssio

et

al.

(197

8);

8: O

rom

belli

(19

74);

9:

Oro

m-

belli

(19

83a)

; 10

: O

rom

belli

(19

83b)

; 11

: C

omer

ci e

t al

.(2

007)

; 12

: S

chne

ider

(19

78);

13:

Por

ter

and

Oro

mbe

lli (

1982

); 1

4: N

iess

en a

nd K

elts

(19

89);

15:

Oes

chge

r et

al.

(197

0);

16:

Zol

ler

and

Kle

iber

(19

71);

17:

Mül

ler

(197

2);

18:

Sca

pozz

a et

al.

(201

2);

19:

Küt

tel (

1977

); 2

0: C

aste

lletti

and

Oro

mbe

lli (

1986

); 2

1: A

ntog

nini

and

Vol

pers

(20

02);

22:

Ren

ner

(198

2);

23:

Kel

ler

(198

8b).

Tab.

1 –

Co

mp

ilati

on

des

dat

atio

ns

rad

ioca

rbo

ne

per

met

tan

t la

rec

on

stit

uti

on

de

la d

égla

ciat

ion

du

Su

d d

es A

lpes

Su

isse

s. P

our

les

sour

ces,

voi

r la

lége

nde

angl

aise

.

value is based on the difference (in ‰) between the isotopicratio of the oxygen contained in the ice (18O/16O ratio or Ri =ice ratio) and the isotopic ratio of a reference standard (Rs =standard ratio):δ18O = [(Ri – Rs) / Rs] * 1,000 (1)

In accordance with the variations of δ18O, it is possible todefine several Greenland Isotope Stages (GIS), includingcold stadials (GS) and interstadials (GI) for the Pleistocene,

and the main Holocene cold events (GH), in line with theINTIMATE stratigraphy (INTegration of Ice core, Marineand TErrestrial records of the last termination; Blockley etal., 2012).

It is cleat that the proposed correlations between Green-land stadial and glacial advances in the Alps are highly spec-ulative, since high levels of dating uncertainty do not permitsafe correlations (e.g., Blaauw et al., 2010). In particular, it



Fig. 2 – Correlation of the main deglaciation stadials in the Southern Swiss Alps with the Greenland isotopic stratigraphy. A: Boxplot of the radiocarbon dates compiled in tab. 1. 1: organic material within the tills of the Episodio Cantù (= minimum age of the LGM andminimum deglaciation age of the Como area, Mendrisiotto and lower Lake Verbano); 2: sediments buried by lodgement till of the EpisodioCantù (= LGM) and palaeosoils of the Allogruppo di Besnate (precedent the Episodio Cantù); GL-2: radiocarbon dating of the P-level on ageomagnetical profile. B: Correlation hypothesis between the LGM and the main Lateglacial stadials of the Ticino/Adda glaciers, and the Eas-tern Alps analogues and with the isotope stratigraphy of the Greenland ice core NGRIP (numerical data from NGRIP-Members, 2004b).

Fig. 2 – Corrélation des principaux stades de déglaciation du Sud des Alpes Suisses avec la stratigraphie isotopique du Groen-land. A : Graphique des datations radiocarbone compilées dans le tab. 1. 1 : matériel organique dans les tills de lʼEpisodio Cantù (= âgeminimal du DMG et de la déglaciation de la zone de Como, du Mendrisiotto et du bas Lac Verbano) ; 2 : sédiments enterrés par les tills defond de lʼEpisodio Cantù (=DMG) et paléosols de lʼAllogruppo di Besnate (précédant lʼEpisodio Cantù) ; GL-2: Datation radiocarbone duniveau P dans un profil géomagnétique. B : Hypothèses de corrélation du DMG et des principaux stades tardiglaciaires des glaciers du Tici-no et de lʼAdda avec les analogues des Alpes Orientales et avec la stratigraphie isotopique groenlandaise du forage NGRIP (donnéesnumériques dʼaprès NGRIP-Members, 2004b).

δ18O

is not possible to determine the impact of (win-ter) air temperature over Greenland on the ac-cumulation balance of glaciers, which is main-ly governed by summer temperature and win-ter precipitation, particularly for the southernside of the Alps.

Regional setting

LGM in the Southern Swiss Alps

In the Southern Swiss Alps, the equivalent ofthe LGM extent as defined by A. Bini (1997)has been named Episodio Cantù and corre-sponds to the paroxistic phase of the last glacia-tion, known as Glaciazione Cantù in the re-gional allostratigraphy (Bini, 1987; Felber,1993; Bini et al., 2001). The deposits relatedto this glaciation are grouped in the Allofor-mazione di Cantù, corresponding to the Allo-formazione di Bodio as defined by O. Da Rold(1990), and includes weakly weathered glacial,glaciofluvial, deltaic, lacustrine and glaciola-custrine deposits, with well-preserved mor-phology, without loess cover, and very locallycemented. During the LGM advance, the Tici-no and Adda glaciers reached a limited exten-sion compared to the previous glaciations (inparticular, the Glaciazione Daverio precedingthe Glaciazione Cantù). The Verbano lobe ofthe Ticino glacier occupies only half of LakeVarese and its front was positioned upslope ofSesto Calende. The Ceresio lobe reached Vareseby means of the Porto Ceresio diffluence, andStabio (in confluence with the Adda glacier)by means of the Capolago diffluence, whereasthe Lario lobe of the Adda glacier reached theComo-Chiasso region (Bini et al., 2009;fig. 1).

In the Mendrisiotto and Luganese areas(southern part of Canton Ticino), during thePleniglacial the front of the Ticino and Addaglaciers underwent several oscillations that leadto the deposition of numerous moraines locatedinside the LGM advance moraine complex(fig. 3). These glacial fluctuations were studiedand grouped by M. Felber (1993), and later byA. Bini et al. (2001), in the Rancate-Casate-Cuc-ciago and in the Capolago-Roncaccio-Ca’Mortaphases. These phases and the followings reces-sional stadials are listed in figure 2B.

Reference stadials for the Ticinoglacier

The first well-defined stadial following thedeglaciation of the Mendrisiotto correspondsto the Melide stadial as defined on the Ceresio



Fig. 3 – First deglaciation phases following the LGM advance: example of theFaloppia sub-lobe of the Adda glacier in the Chiasso region. A: Simplified Qua-ternary geological map. 1: moraine ridge; 2: kame terrace; 3: moraine ridge number.Coordinates: Swiss Grid system CH1903 / LV03. B: Synthetic sketch of the degla-ciation of the Faloppia sub-lobe, based on the glacial positions determined by theprogression or main stagnation moraines (the numerical code of the moraine ridgesrefers to the enumeration reported in A). 1: glacial position; 2: kame terrace; 3: im-portant glacial recession. C: Essay of correlation between the Faloppia sub-lobe de-glaciation and the isotope stratigraphy of the Greenland ice core NGRIP (numericaldata from NGRIP-Members, 2004b).

Fig. 3 – Premières phases de la déglaciation suivant le DMG : exemple du sous-lobe de la Faloppia du glacier de lʼAdda dans la région de Chiasso. A : Cartegéologique simplifiée du Quaternaire. 1 : cordon morainique ; 2 : terrasse de kame ; 3 :numéro du cordon morainique. Coordonnées : système suisse CH1903 / LV03. B : Sché-ma de synthèse de la déglaciation du sous-lobe de la Faloppia basée sur les positionsglaciaires déterminées grâce aux principaux cordons morainiques de progression ou destagnation (le code numérique des cordons morainiques fait référence à lʼénumération re-portée en A). 1 : position glaciaire ; 2 : terrasse de kame ; 3 : régression glaciaire impor-tante. C : Essai de corrélation de la déglaciation du sous-lobe de la Faloppia avec la stra-tigraphie isotopique groenlandaise du forage NGRIP (données numériques dʼaprèsNGRIP-Members, 2004b).

lobe of the Ticino/Adda glaciers, characterised by the lacus-trine moraines between Melide and Bissone (Niessen andKelts, 1989). On the Verbano lobe of the Ticino glacier, Han-tke (1983) described the Cugnasco stadial as defined by lat-eral moraines located above Progero on the right side of thevalley, and above Cadenazzo on the left side (see Bächlin etal., 1974). According to C. Scapozza et al. (2012), during theCugnasco stadial, the Ticino glacier front constituted a calvingglacier on the Lake Verbano (fig. 4). The mean level of thelake lay between 215 and 220 m asl (today it lies at 193 m asl),corresponding to the maximum level reached at the beginningof the deglaciation because it was controlled by the elevationof the moraines situated north of Sesto Calende (Felber,2000; Scapozza et al., 2012).

The compilation of the glacial stadials defined by F. Ren-ner (1982) in the Leventina and Bedretto Valleys, and thedefinition of the analogues for the Blenio Valley by C. Scapoz-za and G. Fontana (2009), make it possible to identify ninemain glacial stadials following the Cugnasco stadial and lo-cated upslope of Biasca (tab. 2).



Fig. 4 – Palaeogeography of the lower Ticino Valley at the begin-ning of the Lateglacial during the Cugnasco stadial. Modified fromC. Scapozza et al. (2012). 1: moraine ridge; 2: Ticino glacier; 3: palaeoVerbano Lake; 4: iceberg.

Fig. 4 – Paléogéographie de la partie basse de la Vallée du Tici-no au début du Tardiglaciaire pendant le stade de Cugnasco.Modifié dʼaprès Scapozza et al. (2012). 1 : cordon morainique ; 2 :glacier du Ticino ; 3 : paléo Lac Verbano ; 4 : iceberg.

Ticino glacier (reference values) Glacier du Ticino (valeurs de référence)

Bedretto ValleyVal Bedretto

Blenio ValleyVal Blenio

Glacial stadialStade glaciaire

ELA 2:1LEG 2:1(m asl)

ELA dépressionDép. de la LEG

(m/1850 AD)


(m/1850 AD)


(m/1850 AD)

Val Corno C 2,470 65 70-95 -

Alpe di Cruina M 2,420 115 125-180 110

Maniò M1 2,375 235 200-250 210-290

Cassina Baggio A2 2,325 275 280-295310-420

AllʼAcqua A1 2,300 300 315

Fontana 2,165 435 470-560

Airolo 2,075 660 600-700

Faido 1,915 820 800-950

Biasca 1,535 1,200 1,080-1,200

Tab. 2 – Definition of the reference values of the ELA depres-sion for the Ticino and Brenno glaciers during the Lateglacial.The reference values (with the reference positions C, M, etc. definedby Renner, 1982) are based on the glacial positions occurring on thevalley bottom. The ELA depression values for the lateral cirques of theBedretto Valley (Scapozza, unpublished data) and for the whole Ble-nio Valley (data from Scapozza and Fontana, 2009) are also presen-ted. ELA = Equilibrium Line Altitude.

Tab. 2 – Définition des valeurs de référence de la dépression dela LEG pour les glaciers du Ticino et du Brenno pendant le Tar-diglaciaire. Les valeurs de référence (avec les positions de réfé-rence C, M, etc. définies par Renner, 1982) sont basées sur les po-sitions glaciaires caractérisant le fond de vallée. Les valeurs de dé-pression de la LEG pour les cirques latéraux du Val Bedretto (Sca-pozza, données non publiées) et pour lʼensemble du Val Blenio(données dʼaprès Scapozza et Fontana, 2009) sont également pré-sentées. LEG = Ligne dʼEquilibre des Glaciers.

For the Ticino glacier, the Biasca stadial is defined by a lat-eral moraine located at Ponte di Iragna, west of Biasca (Hantke,1983). For the Brenno glacier, a lateral moraine of this stadi-al located in Chiegnezz, north of Biasca (fig. 5A), togetherwith other morphological and geometrical elements (Scapoz-za and Fontana, 2009), make it possible to propose areconstruction of the Brenno (Blenio Valley) and Lesgiüna(Pontirone Valley) glaciers during the Biasca stadial (fig. 5B).Considering an ELA depression of between 1,080 and

1,200 m and the fact that this stadial was prob-ably the first progression stadial of the localglaciers during the Lateglacial, C. Scapozzaand G. Fontana (2009) proposed a correlationof the Biasca stadial with the Weissbad stadialdefined by O. Keller (1988a) in the Säntis mas-sif, on the Eastern side of the Alps (tab. 3). TheWeissbad stadial, with a mean ELA depressionof 950 m, probably results from a short andbrutal cooling following an important intersta-dial, characterised by a relatively long phase ofregression interrupted by several stagnationphases. The final one was the Appenzell-Kon-stanz phase (= Bühl 1) of the Rhine glacier(Keller, 1988a; Schoeneich, 1998), leading tothe conclusion that the Weissbad stadial can becorrelated with the traditional Bühl II stadial ofthe Eastern Alps (sensu Keller, 1988a), whichtoday is no longer considered as a stadial, butonly a “phase of early Lateglacial ice decay”(Reitner, 2007).

The Biasca stadial was followed by theFaido and Airolo stadials, with the front of theTicino glacier in the Leventina Valley locatedin the Piottino gorges (Hantke, 1983) and in

the region of Airolo. In this last case, the left lateral moraineis located at Valle, east of Airolo (Renner, 1982). Based onthis moraine, a past extension of the glaciers on the southernside of the Gotthard Pass was observed by Lavizzari (1859-1863) and Omboni (1861) in the second half of the 19th cen-tury. Based on the moraine morphology, on glaciological ar-guments and on an ELA depression of 660 m, Renner (1982)proposes a correlation between the Airolo stadial and theGschnitz stadial of the Eastern Alps (tab. 3).



Fig. 5 – The Biasca stadial in the Blenio Valley.A: Simplified geomorphological map of the lowerBlenio Valley north of Biasca (modified from C. Sca-pozza and G. Fontana, 2009). 1: river; 2: debris flowchannel; 3: alluvial fan; 4: bank erosion; 5: alluvialdeposits; 6: erosional escarpment; 7: landslide; 8:morainic ridge. B: Extent and geometry of the Bren-no (Blenio Valley and tributary valleys) andLesgiüna (Pontirone Valley) glaciers during theBiasca stadial (modified from C. Scapozza and G.Fontana, 2009). Coordinates: Swiss Grid systemCH1903 / LV03.

Fig. 5 – Le stade de Biasca dans le Val Blenio. A :Carte géomorphologique simplifiée de la partiebasse du Val Blenio au nord de Biasca (modifiédʼaprès C. Scapozza et G. Fontana, 2009). 1 :cours dʼeau ; 2 : chenal de lave torrentielle ; 3 : cônede déjection ; 4 : berge dʼérosion fluviatile ; 5 : dé-pôts dʼorigine fluviatile ; 6 : niche dʼarrachement ; 7 :glissement de terrain ; 8 : cordon morainique. B :Extension et géométrie du glacier du Brenno (ValBlenio et vallées latérales) et de la Lesgiüna (ValPontirone) pendant le stade de Biasca (modifiédʼaprès C. Scapozza et G. Fontana, 2009). Coor-données : système suisse CH1903 / LV03.



Ticino and Brenno glaciersGlaciers du Ticino et du Brenno

Eastern Alps analoguesAnalogues des Alpes orientales

Glacial stadial Stade glaciaire

ELA depressionDépression de la LEG

(m/1850 AD)

Glacial stadialStade glaciaire

ELA depressionDépression de la LEG

(m/1850 AD)

Val Corno 65-95 Egesen III (Kartell) 60-120

Alpe di Cruina 110-180 Egesen II (Bocktentälli) 100-150

Maniò 200-290 Egesen I 170-240

Cassina Baggio 275-295Daun 250-350

AllʼAcqua 300-420

Fontana 435-560 Clavadel/Senders 380-470

Airolo 600-700 Gschnitz 600-700

Faido 800-950 Steinach 700-800

Biasca 1,080-1,200 (Bühl II) – Weissbad 900-1,000

Tab. 3 – Correlation of the reference Lateglacial stadials, defined for the Ticino and Brenno glaciers in the Leventina/Bedretto andBlenio Valleys, with the Eastern Alps model developed by M. Maisch (1982). For the Ticino and Brenno glaciers, the ELA depression isbased on the integration of the values presented in tab. 2. ELA = Equilibrium Line Altitude.

Tab. 3 – Corrélation des stades tardiglaciaires de référence définis pour les glaciers du Ticino et du Brenno dans les vallés deLeventina/Bedretto et de Blenio avec le modèle des Alpes orientales développé par M. Maisch (1982). Pour les glaciers du Ticino etdu Brenno, la dépression de la LEG est basée sur lʼintégration des valeurs présentées dans le tab. 2. LEG = Ligne dʼEquilibre des Glaciers.

Fig. 6 – Reference glacial stadials moraine ridges in the Bedretto Valley. Mapping and glacial stadial attribution of the moraine ridgesfrom Renner (1982) and our own work. Glacial stadials: LIA: Little Ice Age; C: Val Corno; M: Alpe di Cruina; M1: Maniò; A2: Cassina Baggio;A1: AllʼAcqua. 1: hydrography. Coordinates: Swiss Grid system CH1903 / LV03.

Fig. 6 – Cordons morainiques de référence des stades glaciaires du Val Bedretto. Cartographie et attribution des stades glaciaires descordons morainiques dʼaprès Renner (1982) et notre travail. Stades glaciaires : LIA : Petit Age Glaciaire ; C : Val Corno ; M : Alpe di Crui-na ; M1 : Maniò ; A2 : Cassina Baggio ; A1 : AllʼAcqua. 1 : hydrographie. Coordonnées : système suisse CH1903 / LV03.

The following stadials, identified in the Bedretto Valley, arecalled Fontana and All’Acqua stadials (fig. 6). The Fontanastadial is defined by a left lateral moraine located above Soria(west of Fontana), and with an ELA depression of 435. Ren-ner (1982) correlated it with the Clavadel/Senders stadial ofthe Eastern Alps. The All’Acqua stadial presents almost twowell-defined positions (tab. 2). The first (position A1) corre-sponds to the maximum phase and is defined by a left lateralmoraine at Cioss Prato (north-west of All’Acqua), while thesecond one (position A2) is defined by a left latero-frontalmoraine just below Cassina Baggio (west of All’Acqua). TheELA depression of 300 m for A1 and of 275 m for A2 (fig. 6)allowed the All’Acqua stadial to be correlated with the Daunstadial of the Eastern Alps (Renner, 1982).

The last stadials defined for the Ticino glacier in theBedretto Valley are the Maniò, Alpe di Cruina and ValCorno stadials (tab. 2 and fig. 6). The Maniò stadial is de-fined by a maximum phase left lateral moraine (position M1)located above Maniò, and by a left latero-frontal morainefrom a following phase (position M) located just inside ofthe maximum phase (Renner, 1982). The Alpe di Cruina sta-dial is characterised by a well-defined position inside themoraines of the maximum phase of the Maniò stadial (Ren-ner, 1982). Finally, the Val Corno stadial presents a maxi-mum position (position C) marked by several lateral andfrontal moraines located between 2,200 and 2,400 m asl onthe right side and on the bottom of the Corno Valley (Ren-ner, 1982), in the uppers part of the Bedretto Valley. TheELA depression of the reference positions in the BedrettoValley are 235 m for the Maniò stadial, 115 m for the Alpedi Cruina stadial and 65 m for the Val Corno stadial (fig. 5).It was then possible for Renner (1982) to correlate thesethree stadials, respectively, with the Egesen I, Egesen II(Bocktentälli) and Egesen III (Kartell) stadials of the East-ern Alps (fig. 2B and tab. 3).

Chronological constraints

The LGM advance

The maximum age of the LGM advance is constrained by ra-diocarbon dating of sediments buried by lodgement till at-tributed to the Episodio Cantù and palaeosoils of the Allogrup-po di Besnate, preceding the Alloformazione di Cantù in the re-gional stratigraphy (fig. 2A). Considering the radiocarbon dateslisted in table 1 (with the samples identified by the ID rd-n):

- rd-7 can be used to date palustrine deposits, partiallycovered by till, located immediately outside the maximumLGM advance moraines;- rd-2, rd-10 and rd-12 were obtained on a palaeosoilburied by lodgement tills of the Alloformazione di Cantù;rd-12 is much younger than the other two dates (referringto the same sample) and may testify a contamination ofthe sample by more recent elements;- rd-8 dates a fossil wood contained in glacial depositsburied by a deltaic sequence of the Breggia river preced-ing the LGM advance;

- rd-3 was obtained on fossil wood included in glaciolacus-trine deposits buried by ablation till of the LGM advance;- rd-6 and rd-9 were measured on fossil woods containedin palustrine deposits buried by lodgement till of the LGMadvance, originating from 17.05 and 15.65-15.69 m depthrespectively, in a borehole drilled in the Lischee area ofMorbio Inferiore;- rd-4 and rd-11 can be used to date the Castelnovate Unit,whereas rd-5 can be used to date the Alloformazione diAlbusciago, both contained in the Allogruppo di Besnatepreceding the LGM advance;- Finally, rd-1 was obtained at the top of the Valle dellaCalcina Media Unit, corresponding to the oldest buriedunit of the Allogruppo di Besnate. For the minimum age of the LGM advance, radiocarbon dat-

ing of organic material above till of the Episodio Cantù makesit possible to reconstruct the deglaciation chronology in theComo area, in Mendrisiotto and in the lower Lake Verbano:

- rd-13 was obtained on branches, leafs and seeds foundwithin glaciolacustrine deposits located inside the LGMadvance moraines;- rd-14 and rd-15 obtained from two boreholes drilled inthe city of Como, making it possible to reconstruct thedeglaciation of the lower Lario Lake;- rd-16 makes it possible to obtain a minimum deglacia-tion age for the lower Lake Verbano.

The deglaciation

Concerning the first steps of deglaciation, the radiocarbondate rd-17 makes it possible to establish a minimum age forthe Melide stadial, older than 16,000 cal BP. This date wasobtained on wood remains and seeds discovered at a depthof 8.05 m in a borehole drilled in the Lake Ceresio close toBissone (Niessen and Kelts, 1989). The palaeomagneticdeclination profile measured in this borehole made it possi-ble to identify the P-level at a depth of 9.50 m. Thus levelwas dated in a palaeomagnetic profile measured in LakeZurich at 18,390–17,130 cal BP (14,600 ± 250 14C BP; lab-oratory code GL-2; Giovanoli, 1979; Lister, 1985, 1988).This correlation between the two palaeomagnetic profilesmakes it possible to define a slightly older minimum age forthe Melide stadial (1-2 millennia), and to place it at around18,000 cal BP.

For the Biasca, Faido and Airolo stadials, the radiocarbondating rd-18, rd-19, rd-20 and rd-21 make it possible toplace them before 14,000 cal BP. The Fontana and All’Ac-qua stadials are older than 12,575–11,620 cal BP (rd-24).This is the age of a gyttja on the bottom of a peat bog atPlidutscha (Oberen Tavetsch, GR), making it possible to estab-lish the minimum age of the Selva stadial, corresponding to theAll’Acqua stadial in the Bedretto Valley (Renner, 1982). Theminimum age of the Maniò stadial is 11,960–11,220 cal BP(rd-25), obtained on the bottom of a peat bog in Val Torta. Forthe Alpe di Cruina and Val Corno stadials, a minimum age of7,460–7,025 cal BP (rd-26) was obtained on the bottom ofthe Alpe di Cruina peat bog.



Discussion

The LGM advance and the beginning of deglaciation

Considering the maximum and minimum ages presentedabove, it is possible to propose that the LGM advance inthe Southern Swiss Alps is aged between 28,500 and22,900 cal BP (24,500–19,000 14C BP). This result is ap-proximately the same age as that of the LGM of Alpineglaciers in the northern Alpine Foreland, which generallylie between 26,800 and 21,250 cal BP (22,000–18,000 14CBP) on the Rhone (Swiss lobe), Linth and Rhine glaciers(e.g., Schoeneich, 1998; Preusser, 2004; Ivy-Ochs et al.,2008). Radiocarbon data support the hypothesis that south-ern Alpine piedmont glaciers reached their maximum ex-tents during Marine Isotope Stage 2 (MIS 2; 29,000–14,500cal BP) (cf. Schaefer et al., 2006), as suggested for thenorthern Alpine foreland by S. Ivy-Ochs et al. (2008). Inparticular, considering the lack of radiocarbon dates be-tween 28,435 cal BP (minimum age of dating rd-10) and22,900 cal BP (maximum age of dating rd-12), it is there-fore possible to correlate tentatively the LGM advance withthe GS-3, between 27,400 and 22,700 cal BP on the NGRIPcurve (fig. 2B), therefore placing it between the GI-3 andGI-2 interstadials.

For the Faloppia sub-lobe of the Lario lobe of the Addaglacier, studied in this work (fig. 3A), the Cucciago and theCa’Morta phases can be identified by a series of morainesfollowing a substantial glacial recession at the end of theLGM (fig. 3B). The hypothetical correlation of the firststeps of deglaciation for this sub-lobe with the Greenlandisotope stratigraphy (fig. 3C) indicates that the Cucciagoand Ca’Morta phases occurred between ca. 22,500 and21,000 cal BP.

The Rancate-Castate-Cucciago and Capolago-Roncaccio-Ca’Morta phases were defined on the Ceresio lobe of theconfluent Ticino and Adda glaciers and on the Lario lobe ofthe Adda glacier. On the Verbano lobe of the Ticino glacier,it is very difficult to find unambiguous analogues for thesetwo phases. The attribution of the moraines of Oleggio andof the Lake Varese at the LGM advance (Hantke, 1983) andthe definition of the recessional stages by a correlation ofthe main phases determined on the Rhine and Linth glacier(and defined as “Primo arresto”, Sesto Calende stadial andIspra stadial, corresponding respectively with the Killwan-gen/Schaffhausen, Schlieren/Feuenthalen and Zürich/Steinam Rhein stadials defined on the Linth/Rhine glaciers byO. Keller and E. Krayss (1993) might be debatable.

In view of the lack of chronostratigraphical elements, it isvery difficult to determine if the Cugnasco stadial of theVerbano lobe of the Ticino glacier can be correlated with theMelide stadial of the Ceresio lobe of the Adda/Ticinoglaciers or if it is younger. Considering the dates presentedabove, the following chronological considerations are pro-posed for the Pleniglacial and the transition into theLateglacial (fig. 2):

- The first recessional phases following the LGM advance(Cucciago and Ca’Morta phases) can be tentatively placedbetween ca. 22,500 and 21,000 cal BP, and probably cor-responds with the two first cold peaks of first order of theGS-2 (fig. 3C);- The Melide stadial may corresponds to the first well-de-fined Lateglacial stadial, placed hypothetically in corre-spondence with one of the two cold peaks between 20,450and 19,850 cal BP (fig. 2B);- There is nothing to support a correlation between the Cug-nasco stadial and the Melide stadial; nevertheless, bothphases could probably be placed in the middle of the GS-2c.

The Lateglacial

The first well-defined stadial in the alpine valleys is theBiasca stadial, when the Ticino (Leventina Valley) and Bren-no (Blenio Valley) glaciers were already not in confluence.Considering the correlation with the traditional Bühl II sta-dial of the Eastern Alps (sensu Keller, 1988a) and the chrono-logical constraints, this stadial could be placed tentativelyin correspondence with one of the last cold peaks of the GS-2c (ca. 20,000–18,500 cal BP) at the beginning of Termina-tion I, as also suggested by J.-M. Reitner (2007) for thetype-localities of the traditional “Bühl stadial” of the Innglacier (Northern Tyrol).

The Biasca stadial, together with preceding Cugnasco sta-dial and the subsequent Faido stadial, testify the earlyLateglacial ice decay, when the Ticino glacier (and the Bren-no glacier) readvanced locally several times, as was thecase in the Eastern Alps only for small glaciers (Reitner,2007; Ivy-Ochs et al., 2008). This behaviour shows aresponse of the Ticino glacier to climatic fluctuations at thebeginning of Termination I, which at this time was not thecase for the larger dendritic glaciers of the Eastern Alps,which in the main longitudinal valleys were principallystagnant and downwasting ice bodies (Reitner, 2007; Ivy-Ochs et al., 2008).

Considering its correlation with the Gschnitz stadial of theEastern Alps, the minimum age of the Airolo stadial can beassumed to be 15,400 ± 1,400 years ago, corresponding tothe exposure-age obtained by cosmogenic nuclides dating(Ivy-Ochs et al., 2006) of the type-locality moraines of theGschnitz stadial at Trins, in the Gschnitz Valley (Tyrol).Radiocarbon dating performed within the moraines of thetraditional Steinach stadial type-locality, which precedes theGschnitz stadial in the Eastern Alps model of the deglacia-tion (Maisch, 1982), gives an age of 19,840–17,640 cal BP(15,400 ± 470 14C BP; laboratory code VRI-484; van Husen,1999; Ivy-Ochs et al., 2006). Radiocarbon dating rd-18 andrd-19 make it possible to establish the minimum deglacia-tion age of the San Bernardino and Lukmanier Passes. It istherefore possible to conclude that the Biasca, Faido and Airo-lo stadials are older than ca. 16,500 cal BP, with the Biascaand Faido stadials perhaps older than 19,000–18,000 cal BP(i.e. minimum age of the Steinach stadial in the EasternAlps), and the Airolo stadial probably between 18,000 and



17,000 cal BP, possibly in correspondence with the first coldpeaks of GS-2b (fig. 2B). This result is consistent with thecompilation of dates and the comparison with the develop-ment of vegetation in the Alps, suggesting that the Gschnitzstadial occurred at around 17,500–17,000 cal BP, following aclearly recognizable warming phase (Ivy-Ochs et al., 2008;and references therein).

The Fontana and All’Acqua stadials are older than theBølling/Allerød interstadial. Since the minimum age of theClavadel/Senders stadial of the Eastern Alps is 18,080-15,405 cal BP (13,850 ± 490 14C BP; laboratory code UZ-301;Maisch, 1981), it is possible to hypothetically place the Fontanastadial in correspondence with one of the first cold peaks(> 15,500 cal BP) of the GS-2a. So the All’Acqua stadialprobably corresponds with the last cold oscillation of GS-2(fig.2B).

The analogue of the Eastern Alps of the Maniò stadial, theEgesen I stadial, was dated at ca. 12,300 ± 1,500 years ago(Kerschner and Ivy-Ochs, 2008), corresponding to the expo-sure-age obtained by cosmogenic nuclides dating of thetype-locality moraine stabilisation of this stadial, located inthe Schönverwall Valley, in Tyrol. Considering this correla-tion and the minimum age of 11,960–11,220 cal BP (rd-25),the maximum phase of the Maniò stadial could then beplaced in correspondence with the coldest peak of GS-1 (ca.12,500 cal BP), with the following positions placed in cor-respondence with the subsequent colds peaks. This stadial isthen attributed to the beginning of the Younger Dryas.

For the analogue of the Val Corno stadial in the EasternAlps, S. Ivy-Ochs et al. (2009) has determined an exposure-age obtained by cosmogenic nuclides dating of the type-lo-cality moraine stabilisation of the Egesen III stadial (Kartellcirque in the Ferwall Groups, Tyrol), of ca. 10,800 ± 1,100years ago. The Val Corno stadial could then be placed in cor-respondence with the Greenland Holocene event GH-11.2,chronostratigraphically positioned in the Preboreal stage(fig. 2B).

Synchronicity of deglaciation in theLepontine and Rhaetian Alps

As a result of the correlation with the NGRIP Greenlandisotopic record, it is also possible to propose a relationshipbetween the stadials defined in the Southern Swiss Alps andthe “traditional” glacial stadials model defined in the East-ern Alps. The deglaciation appears to have happen very sim-ilarly in the Lepontine and Rhaetian Alps, as was shown inthe Monte Leone–Gotthard Alps (Renner, 1982), in EasternLepontine Alps (Scapozza and Fontana, 2009) and in theGreina region (Scapozza et al., 2011). This similar behaviouris not surprising since there is a common accumulation zoneof the valley glaciers coming from the Gotthard area consti-tuted by the ice domes located in the uppermost Rhone Val-ley (Rhone ice dome) and in the Surselva (Vorderrhein icedome; Florineth and Schlüchter, 1998; Bini et al., 2009). In-deed, this geometry of the accumulation zones during theLGM, together with the geomorphological evidences of

transgressive glaciers (north to south) over the main alpinepasses in the Gotthard area (Nufenen, Gotthard, Lukmanierand Greina Passes; e.g., Florineth and Schlüchter, 1998;Scapozza et al., 2011), indicate that the Ticino glacier waspartially supplied with ice coming from the northern side ofthe Alps.

Concerning the deglaciation, the synchronicity of theirfirst phases is probably related to the collapse of these icedomes, as indicated by the cosmogenic nuclides dating per-formed on the Grimsel and Gotthard Passes (Kelly et al.,2006; Hippe et al., 2014). This synchronicity persisted alsoafter the deglaciation of the main Passes, when the accu-mulation zones became individualised between the north-ern and southern part of the Alps. This may indicate a sim-ilar climatic framework for the Lepontine and RhaetianAlps during the whole deglaciation, as also suggested bythe history of vegetation development until the Preboreal(Burga, 1988).

Conclusion

Detailed mapping of Quaternary landforms and deposits,and the compilation and calibration of 26 radiocarbon datesranging from the Po Plain to the Bedretto Valley, made itpossible to refine the chronology of the Last Glacial Cyclein the Southern Swiss Alps, and to propose a correlationwith the deglaciation model constructed for the EasternAlps. In particular, the main conclusions proposed here are:

1. The LGM advance for the Ticino and Adda glaciers wasbetween 28,500 and 22,900 cal BP (24,500-19,000 14C BP).It can be correlated with the GS-3 of the NGRIP Greenlandisotopic record. This result is very consistent with the knownages available for the LGM advance in the Northern SwissAlps, in particular on the Rhone (Swiss lobe), Linth andRhine glaciers (Schoeneich, 1998; Preusser, 2004; Ivy-Ochset al., 2008),

2. For the Pleniglacial and the transition into the Lateglacial,the early recessional phases after the LGM we placed atbetween ca. 22,500 and 21,000 cal BP. The main phases char-acterizing this period have not been well defined and furtherfield analyses are required. There are still a number of correla-tion problems between the Ceresio lobe of the Ticino/Addaglaciers and the Verbano lobe of the Ticino glacier;

3. In the Leventina/Bedretto and Blenio Valleys, eightglacial stadials are found for the period between ca. 20,000and 11,200 cal BP. Five of these stadials (Biasca, Faido,Airolo, Fontana and All’Acqua) are in the Oldest Dryas, two(Maniò and Alpe di Cruina) in the Younger Dryas and one(Val Corno) in correspondence with the Greenland Holoceneevent GH-11.2 (Preboreal). The three last glacial stadials canbe easily correlated with the Egesen I, II and III stadials de-fined in the Eastern Alps.

AcknowledgementsA special thanks to the associate editor, Prof. Dr. Margot

Böse, and to the two anonymous reviewers for their usefulfeedback, as well as Jan Hardie for proofreading the English.



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Article soumis 14 janvier 2014, accepté le 24 juin 2014.



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