The Don formation, Toronto, Canada: a record of the sangamonian interglacial and early wisconsinan (warm part of MIS 5e to a MIS 5 cold substage)

 
Quaternaire
                         Revue de l'Association française pour l'étude du
                         Quaternaire
                         vol. 27/4 | 2016
                         Volume 27 Numéro 4

The Don formation, Toronto, Canada: a record of
the sangamonian interglacial and early
wisconsinan (warm part of MIS 5e to a MIS 5 cold
substage)
La formation de Don, Toronto, Canada, de l’interglaciaire sangamonien au début
du wisconsinien (de l’optimum du MIS 5e à un stade froid du MIS 5)

Serge Occhietti, Martine Clet and Pierre J.H. Richard

Electronic version
URL: http://journals.openedition.org/quaternaire/7746
DOI: 10.4000/quaternaire.7746
ISSN: 1965-0795

Publisher
Association française pour l’étude du quaternaire

Printed version
Date of publication: 1 December 2016
Number of pages: 275-299
ISSN: 1142-2904

Electronic reference
Serge Occhietti, Martine Clet and Pierre J.H. Richard, « The Don formation, Toronto, Canada: a record
of the sangamonian interglacial and early wisconsinan (warm part of MIS 5e to a MIS 5 cold
substage) », Quaternaire [Online], vol. 27/4 | 2016, Online since 01 December 2016, connection on 01
May 2019. URL : http://journals.openedition.org/quaternaire/7746 ; DOI : 10.4000/quaternaire.7746

© Tous droits réservés
Quaternaire, 27, (4), 2016, p. 275-299

                   THE DON FORMATION, TORONTO, CANADA: A RECORD OF
                   THE SANGAMONIAN INTERGLACIAL AND EARLY WISCONSINAN
                   (WARM PART OF MIS 5e TO A MIS 5 COLD SUBSTAGE)

                   n

                   Serge OCCHIETTI1, Martine CLET2 & Pierre J.H. RICHARD3

                                                                                ABSTRACT

                          Regarded as a reference unit of the Sangamonian Interglacial in North America, the Don Formation was deposited however
                   during a longer interval of time, including the interglacial climatic optimum of MIS 5e followed by an erosive and cool phase (intra-
                   MIS 5e or MIS 5d), a boreal phase with a fir forest (late MIS 5e transition or MIS 5c), erosive episodes and the early part of a cold
                   stadial (MIS 5d or MIS 5b). From the planar geometry of the beds exposed at the former Don Valley Brickyard in Toronto, the forma-
                   tion comprises five continuous allozones with lateral variations of thickness. Each allozone corresponds to dominant conditions of
                   sedimentation in a shoreface of Lake Coleman within a limited accommodation space. Allozone D2 is correlated to other interglacial
                   units of Eastern Canada, with ages between 128 and 115 ka. The interglacial climatic optimum is interrupted in the area by two cool
                   events, the first one similar to the Tunturi event of Finland, the second one probably related to a Greenland Stadial. The heterogeneous
                   upper Allozone D5 was deposited in shallow waters when a Northern Boreal Forest prevailed in the watershed. This zone is corre-
                   lated to the Deschaillons Varves of the central St. Lawrence River Valley, deposited prior to the first regional Wisconsinan glacial
                   advance in the central St. Lawrence River Valley and the resulting glacial Lake Scarborough Formation. From the 80 ka minimal
                   U/Th age of the Deschaillons Varves and the 98 ± 8 ka TL age of the later marine La Pérade Clay, Allozone D5 was deposited during
                   the beginning of one of the cold episodes of MIS 5.

                   Keywords: Interglacial, MIS 5, Sangamonian, pollen analysis, Lake Ontario basin

                                                                                 RÉSUMÉ

                   LA FORMATION DE DON, TORONTO, CANADA, DE L’INTERGLACIAIRE SANGAMONIEN AU DÉBUT DU WISCONSI-
                   NIEN (DE L’OPTIMUM DU MIS 5e À UN STADE FROID DU MIS 5)
                          Unité de référence de l’Interglaciaire Sangamonien en Amérique du Nord, la Formation de Don a été en fait déposée pendant
                   un plus long laps de temps, incluant l’optimum climatique interglaciaire du MIS 5e suivi d’une phase fraîche avec érosion, une phase
                   boréale à sapinière (transition à la fin de MIS 5e ou MIS 5c), suivie de phases d’érosion et du début de l’un des stades subarctiques
                   MIS 5d ou MIS 5b. À partir de la géométrie planaire des affleurements de l’ancienne carrière Don Valley à Toronto, la Formation
                   de Don est subdivisée en cinq allozones d’épaisseur variable latéralement. Chaque allozone correspond à des conditions de sédi-
                   mentation dominantes sur une avant-plage du lac Coleman, dans un espace d’accommodation restreint. L’Allozone D2 fossilifère
                   est corrélée aux autres unités interglaciaires de l’est du Canada, d’âge compris entre 128 et 115 ka (MIS 5e). L’optimum climatique
                   interglaciaire est interrompu dans la région par deux refroidissements, le premier similaire à l’événement Tunturi de Finlande, le
                   second probablement en relation avec un Stade Glaciaire du Groenland. L’Allozone supérieure D5, hétérogène et déposée dans des
                   conditions subarctiques et de bas niveau lacustre, succède à une phase érosive. Elle est corrélée avec les Varves de Deschaillons de la
                   vallée centrale du Saint-Laurent, et précède la première invasion glaciaire wisconsinienne de la vallée et la Formation glaciolacustre
                   de Scarborough. D’après l’âge U/Th minimal de 80 ka de ces varves et l’âge TL de 98 ± 8 ka de l’Argile marine de La Pérade posté-
                   rieure à l’invasion glaciaire, l’Allozone D5 a été déposée au début de l’un des épisodes froids du MIS 5.

                   Mots-clés: Interglaciaire, MIS 5, Sangamonien, analyse pollinique, bassin du lac Ontario

                    1 - INTRODUCTION                                             In Europe, this time scale is applied to several terrestrial
                                                                                 sequences, being aware that the duration of continental
  The time scale of the worldwide climatic fluctuations                          climatic episodes is variable and depends on the geographic
during the last interglacial Marine Isotope Stage 5e (MIS 5e)                    settings of latitude, elevation and continentality.
and following episodes of MIS 5d to 5a, is now preci-                               In North America, MIS 5 continuous terrestrial
sely delimited by the marine and glacial isotopic records.                       sequences are rare and with variable climatic accuracy

1
  Département de géographie, Université du Québec à Montréal, C.P. 8888 succursale Centre-ville, MONTREAL, QC, H3C 3P8, Canada.
Email: serge.occhietti@gmail.com
2
  Retraitée du Laboratoire Morphodynamique Continentale et Côtière M2C CNRS-UMR 6143, 24 rue des Tilleuls, FR-14000 CAEN.
Email : martine.clet@orange.fr
3
  Département de géographie, Université de Montréal, C.P. 6128, succursale Centre-ville, MONTREAL, QC, H3C 3J7, Canada.
Email: pierrejhrichard@sympatico.ca

                                                                                                   Manuscrit reçu le 27/05/2016, accepté le 05/09/2016
276

(see section 5.10). However, tens of units are related to
the climatic optimum of MIS 5e, the Sangamonian Inter-
glacial sensu stricto, equivalent to the Eemian in conti-
nental Europe. The lower beds of the Don Formation,
in the Toronto area (fig. 1 and 2), described as early as
1894 by Coleman and in 1895 by Chamberlin, are the
most studied continental sediments of this interglacial
in North America (review by Kelly et al., 1987). The
entire Don Formation rests on the York Till, related to
the Illinoian (Saalian) Glacial Stage and is overlain by
the Scarborough Formation deposited in a glacial lake.
Some valleys are carved into these two formations, partly
filled in by the Pottery Road Formation (fig. 3 and 4).
This succession is then overlain by several stadial and
interstadial units of Wisconsin age (Karrow & Occhietti,
1989; Karrow, 2004).
   The Don Formation was deposited as lower shoreface                            Fig. 1: Location of Toronto and USA sites with Sangamonian soil,
                                                                                 beds or speleothems referred to in Section 5.10. The limits of inter-
beds (Eyles & Clark, 1988), near the mouth of a paleo-                           glacial Lake Coleman changed during the interglacial and transi-
river named the Laurentian River (White & Karrow,                                tional time; the limit on the figure is tentative.
1971), in the non-glacial Lake Coleman (Terasmae, 1960;                          Fig. 1 : Localisation de Toronto et des sites aux USA avec un sol, des
                                                                                 lits ou des spéléothèmes du Sangamonien cités dans la section 5.10. Les
Karrow, 1990). Most of the studies conducted before                              limites du lac interglaciaire Coleman ont changé au cours de l’inter-
1950 on the exposures of the Don Valley Brickyard                                glaciaire et de la transition postérieure. La limite indiquée est très
                                                                                 approximative.
in Metropolitan Toronto (fig. 5) focused on the lower
fossiliferous beds, with a fauna including Bison, Ursus,
Castoroides and two types of Cervidae (Coleman, 1933,                            the Non Arboreal Pollen (NAP) and the spores were not
1941). These lower beds correspond to the interglacial                           counted, and the number of samples was limited. Eyles &
climatic optimum. Gray (1950) was the first to describe                          Clark (1988, 1989) made a detailed facies analysis before
all the lithologic parts of the Don Formation. His unpu-                         the closure of the Don Valley Brickyard in 1984, without
blished thesis, difficult to access and with obsolete corre-                     stratigraphy. Some of their conclusions were debated by
lations, contains original lithologic and lithostratigraphic                     Karrow (1989). Thus, up to now, the studies after 1950
data that have not been subsequently taken up. Later,                            did not use nor define a lithostratigraphic framework for
the climatic sequence constructed by Terasmae (1960)                             the Don Formation.
from the pollen content and other fossils of the forma-                             Based mostly on the sequence of Terasmae (1960),
tion became the reference frame for numerous further                             climatostratigraphic charts have been used for several
studies and remained so. However, the pollen content of                          decades. A long hiatus between the Don Formation and the
the lowermost and uppermost beds was not identified,                             overlying glaciolacustrine Scarborough Formation was

            James Bay
                                                 75°W                     70°W                        65°W                     60°W
      Moose R.                    Nottaway R.

  50°N
                                                           Sangamonian sites                                                                      50°N
                                                                                                      y
                                                                                                  ua r
                                                                                               Est
       Ontario                          Québec                   Sag                      er
                                                                    uen
                                                                       ay R            low                       Gulf of    Newfoundland-
                                                                           .
                                                                                                              St. Lawrence           Labrador
                                                                            e                                    Magdalen  I.
     L.                                        Ile aux Coudres            dl                               Le
                                                                       id                                 Bassin                    Woody
   Superior                                                           m
                                                        Orléans I.                                                                  Cove
                              Ott                            .     Rivière    Plante                         Green   Point    Cape Breton I.
                                  aw           Deschaillons
            Georgian                 aR    Montréal
                                       .                    Chaudière R.                                                              East bay
                              Pointe-Fortune               .
 L.                Bay                                    R                                                                     Addington Forks
 Michigan
                                                     en
                                                       ce
                                                                            USA      Miller
                                                                                                                    t ia
                                                                                                             S co
   45°N        L.                                 wr                                 Creek                                 Milford           45°N
                            Laurentian R.      L a
             Huron                         St.          L. Champlain                          va
                                                                                Salmon No                                  Atlantic Ocean
               Toronto L. Ontario Moh                                           River                                      0                300
                                           awk R                                                                               kilometers
                       80°W       Fernbank         .                70°W                    65°W                               60°W
                              L. Erie                Hudson R.

Fig. 2: Simplified path of the ancestral Laurentian River and location of Toronto and other sites with Interglacial Sangamonian beds in eastern
Canada (from Richard et al., 1999) including the Moose River site (Mott & Dilabio, 1990), and in New York State (Karrow et al., 2009).
Fig. 2 : Tracé simplifié de l’ancienne Rivière Laurentienne et localisation de Toronto et des sites de l’Interglaciaire Sangamonien de l’est du Canada
(d’après Richard et al., 1999) incluant le site de Moose River (Mott & Dilabio, 1990), et de l’État de New York (Karrow et al., 2009).
277

                                              VIII                                                             Sunnybrook Drift
                               VII                                                                                                 Pottery R.Fm
                             VI                                           Scarborough Fm
                    IV        V
                                                                                                                                       Don Fm
                                III                           York Till
                                          II I

Fig. 3: Upper part of the Don Valley Brickyard working face, Toronto (enlargement of a color photo of Paul Karrow, 1957): planar geometry of
the Don Formation with continuous allozones and a gentle slope from the East (right) to the West (left).
Pale bands (even numbers) indicate more sandy and drier groups of beds. Darker bands correspond to moister groups of beds. The continuous and thin
pale band IV is related to an erosional discontinuity and indicates the upper limit of the climatic optimum of the Sangamonian Interglacial.
Fig. 3 : Partie supérieure de la carrière de Don Valley, Toronto (agrandissement d’une photo couleur de Paul Karrow, 1957): géométrie planaire de la
Formation de Don, avec des allozones continues et une pente douce d’Est (à droite) en Ouest (à gauche). Les bandes pâles (chiffres pairs) indiquent des
groupes de lits plus sableux et plus secs. Les bandes foncées correspondent à des groupes de lits plus humides. La bande claire continue et peu épaisse
IV marque une discontinuité d’érosion et la limite supérieure de l’optimum climatique de l’interglaciaire Sangamonien.

                                                                                                              TORONTO area

                                                                                         Hu
                                                                                           mb
                                                                                             er
                                                                                                                                               401

                                                                                               R.
                                                                                                                                           Y

                                                                                                                           E.
                                                                                                           W.                           HW

                                                                                                                                                     2
                                                                                                                            Do

                                                                                                                                                     Y
                                                                                                              D

                                                                                                                                                HW
                                                                                                                on

                                                                                                                                nR
                                                                                           *                          R.
                                                                                  Woodbridge                                           Brimley

                                                                                                                                   .
                                                                                                                                       Road
                                                                                                             Leaside                             *
                                                                                                      Sun Brickyard *                       Scarborough
                                                                                                        Don Valley *

                                                                                                                           Don R
                                                                                                        Brickyard *                         Bluffs
                                                                                            HW

                                                                                                                             .
                                                                                               Y
                                                                                               427

                                                                                                                                                           N
                                                                                                                                                           N

                                                                                                           Lake Ontario
                                                                                                                  0                                      20 km
Fig. 4: Lower units of the Toronto Quaternary sequence and Allo-                                                  0                                      20 km
zones D1 to D5 of the Don Formation, at the Don Valley Brickyard
(enlargement of a color photo of Paul Karrow, 1984).                           Fig. 5: Location of the local sites in the Toronto area, referred to in
Fig. 4 : Unités inférieures de la séquence quaternaire de Toronto et           the text.
Allozones D1 à D5 de la Formation de Don, carrière de Don Valley               Fig. 5 : Localisation des sites de Toronto et des environs cités dans le
(agrandissement d’une photo couleur de Paul Karrow, 1984).                     texte.

inferred, which corresponds to an interval between                             concern the climatic variations and the inception and
respectively the Sangamonian Interglacial and related                          fluctuations of the Laurentide Ice Sheet during MIS 5.
transitional episode equivalent to MIS 5e, and an early                        Regarding the major influence of the continental glacier
Wisconsinan cold stage attributed either to MIS 5b or                          of North America on global change, the significance of
to MIS 4 (Prest, 1970; Terasmae et al., 1972; Karrow &                         the Don Formation is of international importance, and
Occhietti, 1989). Karrow et al. (2000) propose an event                        clear litho- and biostratigraphy of this formation are
chart with the same long hiatus for the Eastern and                            prerequisites for any additional dating and finer corre-
Northern Great Lakes area (see chapter 5.8). Conversely,                       lations.
based on facies analysis, Eyles & Clark (1988) conclude                           The objective of this paper is to provide a renewed look
to a continuous sedimentation in a deepening Coleman                           at the published data and present new field observations
Lake. Without reference to other regions, the Don and                          and biological data on the Don Formation. The first part
Scarborough Formations are then related to the entire                          applies an allostratigraphic approach to the formation,
MIS 5 (Eyles & Williams, 1992). Later, based on the                            followed by a detailed pollen analysis including NAP
same facies analysis, a contradictory chart is proposed                        countings. After the reassessment of the biotic content
by Berger & Eyles (1994) from thermoluminescence                               established by previous studies and of the sedimentation
(TL) ages: the Don Formation, with calculated ages                             processes involved, the different allozones of the forma-
circa 80 ka is related to substage MIS 5a, and the Scar-                       tion are correlated to dated units of the St. Lawrence
borough Formation with calculated ages circa 68 ± 9 ka                         River Valley and Estuary, and alternative chronologies
corresponds to MIS 4. All those divergent interpretations                      are proposed. Variations of the level of lakes Coleman
278

and Scarborough through time are then tentatively                               sampling had to be applied to beds with silt and clay when
reconstructed. Finally, the interglacial and transitional                       possible. Therefore, the sampling intervals in the open
sequence of units of the Toronto area and St. Lawrence                          part of the Don Formation are not regular, with most of
Valley is compared to other sequences in North America.                         them close to 10 cm. Gravel beds and several sandy beds
                                                                                were not sampled (fig. 8). The sandy upper part, poorly
                                                                                studied so far, was closely sampled, every 5 cm or less.
                    2 - METHODOLOGY                                             The lower part of the overlying Scarborough Formation
                                                                                was sampled every 10 or 20 cm, for a total of 18 samples.
2.1 - LITHOSTRATIGRAPHY                                                            The samples (20 g) were sieved between 100 µm and
                                                                                10 µm after removal of carbonates with hydrochloric acid
   This study takes into account the various approaches                         and removal of silica with hydrofluoric acid. They were
developed in previous work (Occhietti, 1990; Richard,                           prepared without acetolysis. The concentrations (number
1994; Clet-Pellerin & Occhietti, 2000) and in the studies                       of pollen grains per gram of sediment) were calculated
of other authors (Gray, 1950; Karrow, 1967, 1990;                               using the weighted aliquot method of Jørgensen (1967).
Eyles & Clark, 1988; Kelly & Martini, 1986; Lamothe,                            The pollen percentages were calculated using a standard
1989). Given that the Don Formation accumulated                                 sum of all the pollen of terrestrial vascular plants counted
at the margin of a fluvial system, we propose a strati-                         (300-400 grains per sample). The representation of spores
graphy of the formation based on allostratigraphic and                          (Pteridophyta, Sphagnum) was expressed over this Pollen
sequence analyses (Bhattacharya, 2001) coupled with                             Sum. Identification was made according to the criteria
biostratigraphy. From the sequence stratigraphy prin-                           of Richard (1970); however, because of morphological
ciples (see Catuneanu et al., 2011) and their application                       uncertainties, Pinus banksiana/divaricata and Pinus resi-
to sequences of the Toronto area by Martini & Brookfield                        nosa pollen grains were grouped within the Diploxylon
(1995), attention is given to discontinuities (fig. 3, 4, 6                     pines and Pinus strobus was specified as an Haploxylon
and 7) and sedimentary system tracks. The paleoenvi-                            pine. Besides, identification of spruce pollen to the species
ronmental interpretations and paleoclimatic reconstruc-                         level is tentative: Picea glauca type is nevertheless distin-
tions are based on converging facts at local, regional and                      guished from Picea mariana/rubens type. Regarding alder
global scales.                                                                  identification, Alnus incana ssp. rugosa type is clearly
                                                                                distinguished from Alnus viridis ssp. crispa type. The
                                                                                pollen taxa are grouped into the following categories: ther-
                                                                                mophilous trees, other trees, shrubs, herbs, spores (fig. 8).
                                                                                The diagram was prepared with Tilia, version 1.7.16
                                                                                (2011), and plotted with TGView, version 2.0.2 (2004),
                                                                                developed by Dr Eric C. Grimm, from the Illinois State
                                                                                Research and Collections Center at Springfield, Illinois.
                                                                                   The climatic significance of the Late Pleistocene units
                                                                                is assessed according to the pollen and spore content,
                                                                                the inferred past vegetation and its evolving trend. The
                                                                                pollen and spore assemblages are compared to the Holo-
                                                                                cene assemblages and their associated climatic signifi-
                                                                                cance, as expressed in modern vegetation (Ritchie, 1987;
                                                                                Anderson et al., 1991; Richard, 1994).
                                                                                   From our previous work mostly in the St. Lawrence
                                                                                River Valley and Basin (Clet & Occhietti, 1994; 1995;
                                                                                Occhietti & Clet, 1989; Richard et al., 1999), distinct
                                                                                pollen and spore assemblages occurred during Late Pleis-
Fig. 6 : Detailed view of the Don Formation at the Don Valley
Brickyard (sample log by S. Occhietti, 1998). The lower Allozones
                                                                                tocene and characterized the regional paleoenvironmental
D1 and D2a were covered by debris.                                              dynamics (Clet-Pellerin & Occhietti, 2000). These are as
Fig. 6: Détails de la Formation de Don, carrière de Don Valley (coupe           follows, from warm temperate to subarctic assemblages
échantillonnée par S. Occhietti, 1998). Les Allozones inférieures D1 et
D2a étaient couvertes d’éboulis.                                                (tab. 1): 1) the Mixed Hardwoods (MW) assemblage
                                                                                (MWa, MWb, MWc) which contains trees and shrubs
                                                                                found in temperate deciduous forests; 2) the Southern
                                                                                Boreal Forest (SBF) which is subdivided into SBFa: a
2.2 - POLLEN ANALYSIS                                                           balsam fir (Abies balsamea) dominated assemblage, and
                                                                                SBFb: a pine (Pinus diploxylon e.g. P. banksiana and/
  Former pollen analyses by members of our team,
                                                                                or P. resinosa) dominated assemblage; 3) the Northern
mainly on the Scarborough Formation, revealed the
                                                                                Boreal Forest (NBF): a spruce (Picea cf. mariana)
necessity to tally the NAP grains and to analyse more
                                                                                dominated assemblage; 4) the Forest Tundra (FT) with
samples within a given unit (Richard et al., 1999). With
                                                                                evidences of an open tree canopy with a subarctic
sandy and gravelly beds of the Don Formation usually
                                                                                character: Alnus cf. crispa, Ericaceae, Sphagnum. These
sterile in pollen and spore grains, a close and selective
                                                                                pollen and spore assemblages are related to vegetation
279

   Visual          silt gravel                                       Allozones               Pollen                 Other fossils      Units
   bands       clay sand cobble                                                            assemblages                                Gray 1950
                                                          Erosional
                                                       discontinuities
                            rhythmites                                               Forest Tundra R
                                                                      Scarb.         Northern Boreal Forest T, R
                           brown sand                                g
                            sand shale cobbles                           f
   VIII                    white sand and fine gravel                e                                                  no
                                                                                                                                      Unit C
          6                                                                  D5
                            green sand                               d              Northern Boreal Forest              fauna
                              pavement shale wood
                                      green sand                     bc                    Don 5
                              green shale clasts                       a
   VII                                                                d
                             fine sand
   VI 5                        and
                                                                      c
                                                                                                                     poor fauna
                                                                             D4     Southern Boreal Forest T, R                       Unit B
   V                         silt beds
                                                                      b
                                                                                            Don 4

          4                  fine sand                                a
                                                                                      cold event       Don 3
                             g ravel                                                                                                “pebble
   IV                        sand
                                                                             D3                       no pollen        sterile
                                                                                                                                    conglomerate”

                           fine sand                                  e                                               diatoms
          3                                                                                                           ostracods
                                                                                    Mixed Hardwood Forest T, R        insects
   III                      silt and sand                             d                     Don 2.5                   molluscs

                                                                                                       no pollen

                              fine sand                                               cool event       Don 2.4
          2                                                                                                                          Unit A
                                and
                                                                      c                                                abundant
                              silt beds
   II                                                                        D2      Deciduous Forest T, R             molluscs
                               with
                                                                                       with Liquidambar                insects
                               shells
                                                                                           Don 2.3
          1                                                                          cool event        Don 2.2                  “pebble
                               gravel                                 b
                                                                                                                      diatoms   conglomerate”
                                                                      a             Mixed Hardwood Forest T           ostracods
                              sand
   I                                                                                       Don 2.1                    insects
                                                                                                                      molluscs
                                                                 ?                                                                  Lower Clay
                              lower clay and stones                          D1      (Don 1)      ?          (HK)     cladocera
          0
          m
                                                                     York Till

Fig. 7: Log of the section of the Don Formation sampled in 1998: allozones, pollen zones and fossil assemblages from other studies referred to
in tab. 4.
The covered basal part of the section (D1 and D2a) is simplified from Karrow (1969). HK: Hann & Karrow, 1993; R: Richard et al., 1999; T: Terasmae,
1960.
Fig. 7 : Log de la Formation de Don échantillonnée en 1998: allozones, palynozones et assemblages de fossiles d’études citées dans le tab. 4. La partie
inférieure masquée de la formation est redessinée d’après Karrow (1969). HK: Hann & Karrow, 1993; R: Richard et al., 1999; T: Terasmae, 1960.

types which correspond in most cases to the canadian                               2.3 - CORRELATION
biomes (Strong et al., 1989; Dyke, 2005).
  Pollen or spores from species living along the banks of                             Using a system track approach, the correlations between
lakes and rivers were grouped in an azonal group labelled                          the Don Formation and units of the St. Lawrence River
RB (River Banks). It comprises mainly Alnus rugosa, and                            Valley are based on the stratigraphic relative position, the
part of Cyperaceae, Poaceae, other herbs and Pterido-                              nature of the units and their elevation, the climatic condi-
phyta. This group is present throughout the sedimentary                            tions deduced from the biotic content, and the inferred
sequence but Sphagnum is however best represented in                               sea level at the time of deposition established from the
the overlying Scarborough Formation.                                               global climatic conditions.
Thermophilous trees                                                           Other trees                                                                    Shrubs                       Herbs                                 Out of Sum

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                                   rc         an                                                      a a a                      s s                        l                                                                                                     p o   es un gin po a dive div entr
  ep         ol sa qu r                               ta in a s            us in es s                                                                        a la la s s x ce ylu ica ica ice o rn ea e ra lif lif m ro nop op ce go ta iac lic ha ha ole
 D       i th ys Li Ca          ue        u gl ilia as arp sug agu cer lm rax upr bie arix ice ice ice                       i nu inu                     tu tu tu nu nu li ica or yr yr n em bu ac p bu gu te b e ry ia ly an m a p up on                     ly ilet sm la co Sph ree erb onc
        L N                    Q         J T C C T F A U F C A                            L P P P                          P P                          Be Be Be Al Al Sa Er C M M Lo N Vi Po Cy Tu Li Ar Am Ch Ca Ap Po Pl La Th Ty N M                    Po Tr O Se Ly             T H C          Zones
  0

 50

100

150

200                                                                                                                                                                                                                                                                                                        Scar 1b

250

300

350
                                                                                                                                                                                                                                                                                                           Scar 1a
                                                                                                                                                                                                                                                                                                st_2       Don 5.3
400
                                                                                                                                                                                                                                                                                                st_5
                                                                                                                                                                                                                                                                                                st_3       Don 5.2
450
                                                                                                                                                                                                                                                                                                           Don 5.1
                                                                                                                                                                                                                                                                                                                     280

                                                                                                                                                                                                                                                                                                           Don 4.3
500
                                                                                                                                                                                                                                                                                                  n.s.     Don 4.2
550
                                                                                                                                                                                                                                                                                                           Don 4.1
600

                                                                                                                                                                                                                                                                                                  n.s.
                                                                                                                                                                                                                                                                                                           Don 3
650                                                                                                                                                                                                                                                                                               n.s.
                                                                                                                                                                                                                                                                                                st_1
700
                                                                                                                                                                                                                                                                                                           Don 2.5

750

                                                                                                                                                                                                                                                                                                  n.s.
                                                                                                                                                                                                                                                                                                           Don 2.4
800

                                                                                                                                                                                                                                                                                                  n.s.
850
                                                                                                                                                                                                                                                                                                st_3       Don 2.3

900
                                                                                                                                                                                                                                                                                                           Don 2.2
                                                                                                                                                                                                                                                                                                           Don 2.1
                         20    40    20   40                                20             20                 20   40   60          20   40   60   80             20                                                                                  20                  20   400   20 20       40 80
                                                                                                                                                                                                                                                                                     N   N 1000 grains/g
                                                                                    Blank levels are either not sampled (n.s.) or proved sterile (st); the number of sterile samples is indicated (st_3).
                                                                                                                                                                                                                                                                                 Analysis: Martine Clet, 1995-2001
               Silt           Sand   Gravel/Cobble                                 Except for Carya, Quercus, Picea cf. mariana and Pinus diploxylon, low percentages are amplified 10 times (hollow curves).

Fig. 8: Pollen and spore diagram of the sampled parts of the Don and Scarborough Formations at the Don Valley Brickyard, Toronto.
Fig. 8 : Diagramme sporopollinique de la partie échantillonnée des Formation de Don et de Scarborough exposées à la carrière de Don Valley, Toronto.
281

                           Vegetation Type                                Pollen assemblages

                                                         Milder                    Zonal                   Harsher

                                  MW             MW-a = Deciduous                  MW-b                     MW-c
                                                      Forest                   Acer, Ulmus,           Tsuga, Pinus cf.
                          Mixed Hardwood
                                                Liquidambar, Nyssa,          Fraxinus, Fagus,         strobus, Betula,
                                Forest
                                                  Celtis, Quercus,          Pinus cf. strobus,       Picea cf. rubens,
                                                Carya, Juglans, Tilia,      Corylus, Viburnum        Pinus cf. resinosa
                                                    Castanea, …
                                  SBF                                             SBF-a                     SBF-b
                          Southern Boreal       Tsuga, Pinus strobus,        Abies balsamea,         Pinus cf. resinosa
                              Forest            Betula lutea, Picea cf.      Betula papyrifera
                                                        rubens
                                 NBF                                               NBF
                           Northern Boreal                                   Picea cf. mariana
                               Forest                                        Pinus cf. banksiana

                                  FT                                       FT-a Forest Tundra               FT-b
                            Forest Tundra        Pinus cf. banksiana       Picea mariana, Picea          Sphagnum
                                                  Betula papyrifera        glauca, Betula, Alnus
                                                                                   crispa
                                  HT             HT-a Shrub Tundra          HT-b Herb Tundra                HT-c
                                Tundra           Alnus crispa, Betula         Salix herbacea,            Sphagnum
                                                glandulosa, Salix spp.       Oxyria, Dryas…,
                                                                           Lycopodium and other
                                                                             Herbs (Poaceae,
                                                                               Cyperaceae,
                                                                                Ericaceae)
                                                                                Present at
                                                                            Scarborough Bluffs
                                  RB
                                                 Larix, Alnus rugosa, Myrica, Pteridophyta, various herbaceous and
                             River Banks                                   aquatic plants.

Tab. 1: Upper Pleistocene pollen assemblages identified in Eastern Canada, from Clet-Pellerin & Occhietti (2000).
Tab.1: Types d’assemblages polliniques du Pléistocène supérieur identifiés dans l’est du Canada, de Clet-Pellerin & Occhietti (2000).

2.4 - PARADIGMS                                                                 applied for example to the late-glacial Younger Dryas
                                                                                “event” on both sides of the Atlantic Ocean, even if this
   Changes in orbital forcing is the primary mechanism of                       cold episode is not directly linked to orbital forcing. The
climate changes, at the scale of thousands of years. Due                        reassessed continental record of the Don Formation can
to changes of the insolation through time and latitudes,                        therefore be compared to the European, Greenland and
to complex retroactions of the global climatic system                           marine series, using an unambiguous terminology.
and to variable inertia, the climatic responses in oceans,
continents and glaciers are not perfectly synchronous
                                                                                2.5 - STRATIGRAPHIC DEFINITIONS: WHAT IS
(see the report of Wohlfarth, 2013). Nevertheless, signifi-
                                                                                THE SANGAMONIAN?
cant climatic changes are recorded within a defined time
span. For example, continental beds with markers of the                           Marine Isotope Stage 5 (MIS 5) occurred between
climatic optimum of the last interglacial can be correlated                     135-130 and 72-70 ka (Shackleton et al., 2003; Sánchez
with marine beds with benthic foraminifers and pollen                           Goñi et al., 2012; Capron et al., 2014; Simon et al.,
which indicate a marine high stand and elevated surface                         2016). From 18O and other markers, in concordance with
temperature. Despite some differences in ages given to                          the orbital forcing, this stage comprises five main climatic
the limits of MIS 5e and clear differences in the dura-                         substages: the interglacial climatic optimum (MIS 5e)
tion and representation of the Eemian - Sangamonian                             and subsequent colder or mild substages (MIS 5d to 5a).
Interglacial according to the regional setting, a careful                       In Europe, the pollen content of several continuous conti-
correlation between the continental and oceanic strati-                         nental series, mainly from peat bogs (La Grande Pile,
graphic systems gives a global significance to local data.                      Woillard, 1978; Les Echets, de Beaulieu & Reille, 1984)
The Clear Lake pollen record in California (Adam et al.,                        and lake fillings (Reille & de Beaulieu, 1990), and from
1981) and the reassessed chronology of the Devils Hole                          discontinuous fluvio-deltaic accumulations (Rhine delta,
samples of calcite (Moseley et al., 2016) are examples                          Zagwijn, 1996), indicates the same climatic pattern. The
of the global response within North America. Shorter                            climatic optimum is related to the Eemian, considered as
climatic events (in broad sense), identified on conti-                          the interglacial sensu stricto, and the subsequent substages
nents and in Greenland ice cores may be related, or at                          are referred to the Early Weichselian. Nevertheless, as
least compared as similar types of events. This is usually                      mentioned, the boundaries of the continental and oceanic
282

records are not exactly synchronous. From Shackleton et                              to 2) was debated mostly in Canada (Dreimanis, 1977;
al. (2003), the base of the Eemian is younger than the                               Karrow & Occhietti, 1989; Grant, 1989; Occhietti et al.,
base of MIS 5e and falls within the isotopic “plateau” of                            1995), and the extent of the glaciers in North America
the marine isotope stage (tab. 2).                                                   during substages 5d and 5b is still to be assessed from
  In continental North America, the direct equivalent to                             direct continental evidence. Sangamonian Stage sensu
MIS 5, both in time span and climate, was the Sanga-                                 stricto was also used by some authors in order to distin-
monian Stage in its former definition. This period was                               guish the warmer interglacial phase equivalent to the
defined, in Illinois, from a paleosol developed in Illi-                             Eemian. Richmond & Fullerton (1984) proposed to use
noian drifts and related colluvial deposits, and overlain                            Sangamonian Stage as the equivalent to the Eemian, and
by Wisconsinan till or loess (Willman & Frye, 1970).                                 Eowisconsinan Stage as the equivalent to MIS 5d to 5a
According to this definition, which was in use for a long                            substages. The Sangamonian sensu stricto is now used as
time (Fulton, 1989; Zhu & Baker, 1995), the Sangamo-                                 the interglacial stage (see 6. Delineation of the Last Inter-
nian Stage (sensu lato) was equivalent to the European                               glacial - Last Glacial stage boundary, in Otvos, 2015).
Eemian and Early Weichselian altogether. The usage of                                Using a diachronic nomenclature, Karrow et al. (2000)
Sangamonian Stage in its broad sense came also from                                  distinguishes the Sangamon Episode related to MIS subs-
a tacit assessment that the development of glaciers in                               tage 5e, and the Ontario Subepisode of the Wisconsin
North America was limited during substages MIS 5d                                    Episode as the equivalent of MIS substages 5d to 5a and
and 5b, and very limited or even close to interglacial                               MIS 4, in the eastern and northern Great Lakes area.
conditions during respectively substages MIS 5c and 5a.                                In this paper on continental deposits, the climatic
Nevertheless, this model with a short glacial time (MIS 4                            optimum of the last interglacial is related to the beds

                           Toronto area                            Estimated Central and Southern Time                  Greenland Marine Isotope
                                                                    duration     Europe           scale                 Phases    Stages
               (names of units by Karrow, 1990)
                                                                                   Guiot et al.., 1993                NGRIP, 2004    Shackleton
     Sunnybrook                                                        ka                                       ka                  et al..,. 2003
      Drift                                                                                                    50
       Pottery
       Rd Fm
                                                                                                                                      MIS 3
      erosion

       Scar.                  Sunnybrook Drift                                                                                        MIS 4

       Don 5                   proglacial beds                                                             71-70
                                                                       2     Interstadial                         GI 19
         ?                                                                                                     72
                                                                       1.5   Stadial II                        74       GS 20        **
      erosion              fluvial lower beds of Pottery               3     Ognon
                                                                                                               77  GI 20
                                                                       1     Stadial I
                                   Road Formation                                                              78       GS 21         MIS 5a
       Don 4                                                          5-7    St. Germain II
                           erosional valleys and gullies
                                                                                                          85-82.5 GI 21
      Don 3               Scar.                         Scar.       3-4.5    Melisey II                                               MIS 5b
      erosion             Don 5                         D5defg                                              88-87         GS 22
       D2/D3                                            D5c ?                                                          GI 22
                                                                                                                            GS 23
                          Don 4                         erosion     12-16    St. Germain Ic
      Don 2.5                                                                                                                         MIS 5c
                                                              ?                                                        GI 23
                                                                                                               100

                                                                      2.5                                102
                                  Don 3       Scar.                          Montaigu    St. G. Ib       ***
                  Don 3       erosion D2/D3
                                                        D5b                                              105                GS 24
      Don 2.4     erosion      Don 2.5                                 3     St. Germain Ia                            GI 24
                  D2/D3             ?         Don 5     D5a           2-3                                109                          MIS 5d
                               Don 2.4                                       Melisey I                   *** 110           GS 25
                                    ?         erosion   erosion                                          112                        Sanchez Goñi
                                                                                      cooler                           GI 25        et al., 2012
                               Don 2.3             Don 4
                                                   Don 3                                                       115          GS 26
      Don 2.3 Don 2.5                         erosion D2/D3         12-18
                                                                             Eemian
                  Don 2.4                     Don 2.5                                                          120
                                              Don 2.4 GS event ?
                 Don 2.3                      Don 2.3                               climatic optimum                                  MIS 5e
                            Don 2.2 Tunturi event?
                            Don 2.1                                                                             128
                  Don 1?       D1 ?                                            ?
                                                                                                               130
         A           B              C           D             E
                                                                                                                        (135 ka) * Sanchez Goñi
                                                                                                                                    et al ., 2012

Tab. 2: MIS 5 chronology in Europe and Greenland, and age hypotheses of the allozones of the Don Formation.
* 135 ka: MIS 5 lower limit by Sánchez Goñi et al. (2012). ** Lower limit of MIS 4 above Ognon proposed by Sánchez Goñi et al. (2013).***Limits of
cold events Melisey I and Montaigu from Drysdale et al. (2007).
Tab. 2 : Chronologie du MIS 5 en Europe et au Groenland. Hypothèses de l’âge des allozones de la Formation de Don. * 135 ka: base du MIS 5 d’après
Sánchez Goñi et al. (2012). ** Base du MIS 4, après la phase Ognon, proposée par Sánchez Goñi et al. (2013).***Âges des épisodes froids Melisey I
et Montaigu d’après Drysdale et al. (2007).
283

with indicators of climatic conditions warmer than today               thickness reaches 7.6 m, but the thickness of each unit
and to the beds which directly precede and follow those                is variable. Gray (1950) stated (p. 12) that “sections fail
beds with indicators of climatic conditions as warm as                 to correlate in detail; no on (one?) stratum can be said
today. Some beds or palynozones which record very short                to extend completely around the quarry in a consistent
cooler events can be included in the series of beds or paly-           fashion, except for the basal clay”. According to Coleman
nozones of the climatic optimum. The climatic optimum                  (1941), the “basal blue clay with logs of wood and unios
beds are attributed to the main part of the Sangamonian                (clams)... are of warm climate”. From Karrow (1969), the
Interglacial and to the “plateau” of MIS 5e (Shackleton                top of the Don Formation slopes southeasterly from 102 m
et al., 2003). Without a complete series such as the one               a.s.l. in central Toronto to 93 m at the Don Brickyard
at La Grande Pile (Woillard, 1978) and because of the                  and 70 m a.s.l. below the Scarborough Bluffs along the
homotaxy of beds with interstadial or stadial markers                  present Lake Ontario shore. The sedimentary structures
(Karrow, 1989; Occhietti, 1990), the overlying units or                and changes of facies were related to a river entering
beds with transitional and colder indicators of climate                the shallow interglacial Lake Coleman and the position
have an equivocal stratigraphic position, as observed by               of the river channel (Terasmae, 1960). Eyles & Clark
Mott & Dilabio (1990) in the James Bay Lowlands. In this               (1988) described the “Don Beds” as sands interbedded
study, all the transitional beds of the Don Formation are              with bioturbated peaty muds. They stated that “Most sand
revealed to have an equivocal position. For this reason,               beds are composite in origin,… each in erosional contact
they are temporarily not related to the Sangamonian                    with the underlying unit.” These beds were deposited in a
(sensu stricto), until univocal evidence can be obtained.              lacustrine lower shoreface environment subject to episodic
   In many papers, Last Interglacial (LIG), Eemian,                    storms and to increasing depth, from 2 to about 18 m,
Sangamonian and MIS 5e refer to the same event. Never-                 that is 12 to 28 m above present level of Lake Ontario.
theless, the given limits of the last interglacial and transi-         They did not recognize any major erosional discontinuity
tional phases which precede the major glaciation related               within the Don Formation or between the top of it and the
to MIS 4 are somehow changing from one reference to                    overlying Scarborough Formation.
the other. For example, the age given to the lower limit of               Numerous studies of the biotic content were done
Stage 5e varies from 135 ka (Sánchez Goñi et al., 2012)                (reviewed in Kerr-Lawson et al., 1992). Terasmae (1960)
to 132 ka (Shackleton et al., 2003), and to the widely                 established the pollen sequence of the Don Formation
used value of 130 ka (Simon et al., 2016). Usually,                    from 33 pollen assemblages. According to his sequence
MIS 5d is related to the Melisey I continental cold phase,             and reassessing previous works (Coleman, 1933; Gray,
from 115-112 ka to 105 ka, but covers also the end of the              1950; Watt, 1953), the lower part of the Don Formation
Eemian in Sánchez Goñi et al. (2012), from 120 ka to                   was deposited during the climatic optimum of the Sanga-
105 ka. From a wide compilation including Antarctic ice                monian Interglacial, and the upper part of the formation
cores, Capron et al. (2014) define the LIG period between              is related to a change towards a boreal climate. This is
129 and 116 ka, and Veres et al. (2013) develop a time                 confirmed by other biota (see chapter 5.3), by a stratigra-
scale for the last 120 ka. Establishing formal limits to               phic diagram of prominent tree pollen by McAndrews (in
MIS 5 and to the ice core and continental phases/episodes              Westgate et al., 1999), and by a preliminary study of the
is out of the scope of this study. In tab. 2, the data from            pollen content of a part of the Don Formation by Richard
the Toronto lower sequence of units are compared to a                  et al. (1999).
perfectible climatostratigraphic and chronostratigraphic                  The stratified sand beds with some pebbles and cobbles,
framework based on several sources, keeping in mind                    located at the top of the unit (Gray, 1950; Terasmae, 1960)
that the limits given to the different phases/events can               were interpreted as evidence for a further shallowing
vary by some thousands of years (see Tables 6-2 and 8-1                of the lake accompanied by a cooling of the climate
in Wohlfarth, 2013). Toronto is located at the same lati-              (Terasmae, 1960). Their significance has been controver-
tude than Nice, France; therefore, despite some continen-              sial. Gray (1950) concluded to a low lake level and even
tality buffered by the proximity of the Great Lakes, the               to the exposure of the formation, while Terasmae (1960)
Toronto units are compared to the climatostratigraphic                 proposed a considerable hiatus between the Don and
chart of central and southern Europe (tab. 2).                         the Scarborough Formations. Karrow (1969) concluded
                                                                       there were deposition in shallow waters and a disconfor-
                                                                       mity. During the study of fossil caddishflies, Williams &
     3 - REVIEW OF THE DON FORMATION                                   Morgan (1977) identified the following sequence of
            IN THE TORONTO AREA                                        sediments: lowermost beds deposited on the substrate,
                                                                       lower quiet-water deposits with current-bedding struc-
3.1 - DON FORMATION                                                    tures and some large logs, a buff-grey coarse cross-
                                                                       bedded sand unit which suggests a more littoral facies,
  In the Don Valley Brickyard, Gray (1950) recognized                  clay laminae and ripple-marked structures with detrital
a decimetric Basal Clay and three other units in the Don               organics related to deeper water conditions, and at the
Formation, a lower deltaic sand (Unit A) up to 5.4 m thick,            top of the sequence, limonite stained sands. One of two
an intermediate lacustrine unit up to 1.4 m thick, with                groups of caddishflies is similar to assemblages found
some stones, deposited in deeper waters (Unit B), and an               on exposed shores of large lakes, the second group is
upper weathered sand (Unit C) up to 1.8 m thick. The total             related to large rivers. Morgan (1979) evoked a signifi-
284

cant interval of weathering. On the west side of the Don
Valley Brickyard, Poplawski & Karrow (1981) observed                                                     Laurentian River:
coarse, rust-coloured sand and gravel below 1 m of iron-              L. Superior                        interglacial outlet
stained deposits. According to Hann & Karrow (1984),                                                                   sill   > 120 m
the organic matter content of about 4 % in the lower fossi-                         183 ? m
                                                                                                                                 St. Lawrence
liferous part decreases abruptly to 1 and 2 % upwards.                                                           Georgian                    R.
The percentages of carbonate content decrease slowly,                                                            Bay          L. Simcoe
                                                                                                     176 - ? m
from 12 to 8 %, in the lower beds, and rapidly to 2 % in                                               L.
the overlying part. Conversely, for Eyles & Clark (1988)                                             Huron                       75 + 18 m
                                                                                                                                        L.
the rusty upper sand bed is related to post-sedimentation                                                              Niagara     Coleman
                                                                          L.
underground waters and the sedimentation is continuous
between the Don and Scarborough units.                                  Michigan                                    174 ? m
                                                                                                                                                  N
                                                                                                                              L. Erie
                                                                                                                               500 km
3.2 - EXTENT OF THE DON FORMATION AND
FLUVIAL NETWORK OF THE LAURENTIAN RIVER                             Fig. 9: Inferred drainage pattern between the Great Lakes during
                                                                    the Last Interglacial and transitional phase, from Spencer (1890),
   Scattered findings indicate that a large sedimentary             White & Karrow 1971) and Westgate et al. (1999).
                                                                    Fig. 9 : Mode présumé de drainage entre les Grands Lacs pendant
body of the order of one hundred to several hundred km2             le Dernier Interglaciaire et la phase de transition suivante, d’après
was deposited in the Toronto area, in the lower reaches of          Spencer (1890), White & Karrow (1971) et Westgate et al. (1999).
the Laurentian River valley at the edge of Lake Coleman.
The Don Formation was exposed naturally in the banks                ment on offshore seismic profiles (Eyles & Clark, 1989;
of the Don River and widely accessible in the former                Anderson & Lewis, 2012). Upstream from the Don Valley
Sun Brickyard (Coleman, 1933) and, since 1899, in the               Brickyard, shallower shoreface deposits are observed on
now abandoned Don Valley Brickyard (fig. 5). From the               the Leaside site (Hann & Karrow, 1993) (fig. 5), and
presence of abundant mollusc shells, and sometimes                  further northward in the Toronto vicinity, sandy facies
large pieces of wood, the part of the formation deposited           correspond to fluvial deposits. If not erased by the
during the interglacial climatic optimum was recognized             Wisconsinan glaciers, concealed fluvial sediments of the
in many temporary excavations downtown Toronto                      interglacial Laurentian River are potentially present in
(Karrow, 1990). The largest excavations were done during            the middle and upper reaches toward the Georgian Bay,
the construction of subways in the 1950 and 1960’s in               as suggested by the interglacial beds of the Woodbridge
Metropolitan Toronto. These data and subsequent excava-             Cut, 21 km northwest of the Don Brickyard (Sharpe,
tions were compiled by Sharpe (1980) and Eyles (1987)               1987; Karrow et al., 2001) (fig. 5).
as a series of cross sections with a total length of nearly            The status of the Don beds has changed since the early
105 km. In the Scarborough area, downstream the Metro-              works of Coleman (1894, 1933) and Chamberlin (1895),
politan Toronto on the North shore of Lake Ontario, the             regarding the interpretation given to the Don-Scarbo-
Don Formation was reached by coring (Terasmae, 1960)                rough succession of formations (Eyles & Clark, 1989;
and by drilling (Hann & Karrow, 1993) under the Scar-               Karrow, 1990). Either, the two units are in continuity
borough Formation.                                                  (Coleman, 1933, who maintained the name of Toronto
   A major interglacial and early stadial river, with no            Formation; as reused by Eyles & Clark, 1988), or they
modern equivalent, is inferred from this large sedimen-             represent distinct units (Don and Scarborough Forma-
tary body (White & Karrow, 1971; Eyles, 1987; Martini &             tions, Karrow, 1967, 1990).
Brookfield, 1995) and from the biotic studies. The river
flowed along a topographic low in the bedrock identified            3.3 - CHRONOLOGY
as the Laurentian River channel by Spencer (1890). The
                                                                       In the Toronto area, a set of thermoluminescence dates
bedrock contours of the buried valley are established
                                                                    by Berger & Eyles (1994) gives an age of 80 ± 19 ka at the
from drilling and water wells (White & Karrow, 1971;
                                                                    base of the Don Formation, 78 ± 17 ka in the middle part,
Westgate et al., 1999). From quartzite cobbles in the Don
                                                                    and 67.6 ± 9 ka near the top of the formation. The same
Formation, the interglacial drainage is thought to have
                                                                    set provides also TL ages of 59.8 ± 8.5 and 54.1 ± 8.2 ka
connected Lake Huron to the Lake Ontario basin (Gray,
                                                                    at the base of the Scarborough Formation.
1950), over an approximate distance of 110 km (fig. 9;
see Fig. 1 in Eyles, 1987).
                                                                    3.4 - CORRELATIONS
   Most of the knowledge of the Don Formation is based
on the exposures followed through time at the Don Valley              Several early correlation charts between the units of the
Brickyard. The distal part of the sedimentary body was              Lake Ontario Basin and the St. Lawrence River Valley,
deposited in deeper waters, as suggested by cladocerans             referred to in the introduction, were based on the 14C
in logs of the Brimley Road site (Hann & Karrow, 1993)              age (see discussion in Dreimanis, 1977) of the St. Pierre
(fig. 5). This part, equivalent to prodelta and bottom              Sediments found in the central St. Lawrence River Valley
deposits, was eroded during subsequent glacial phases               (Gadd, 1971; Ferland & Occhietti, 1990a). From the age
(Martini & Brookfield, 1995) and the post-glacial Lake              of 74.7 ka + 2.7/-2.1 (Stuiver et al., 1978), these sedi-
Iroquois low phase, as indicated by a prominent escarp-             ments are related to MIS 5a. The contradictory charts
285

proposed by Eyles & Clark (1988); Eyles & Williams                 the York Till at the bottom of the lowermost beds D1 or
(1992), and Berger & Eyles (1994) do not take notice               D2a (fig. 7).
of stratigraphic successions of other areas. Meanwhile,
the stratigraphy of the central St. Lawrence River Valley             4.2.2 - Allozone D2
was revised, with the identification of an early Wiscon-              The lower Allozone D2a is mainly sandy and corres-
sinan glacial and non glacial succession and the reassess-         ponds approximately to the lower grey band I (fig. 4),
ment of several units (Lamothe, 1985, 1989; Occhietti &            with an irregular erosional upper limit with ripples and
Clet, 1989; Occhietti, 1990; Besré & Occhietti, 1990;              lenses of gravel (Allozone D2b; the unconsolidated
Ferland & Occhietti, 1990b; Bernier & Occhietti, 1991).            “pebble conglomerate”of Gray, 1950; see also the lower
Preliminary correlations between the lower units of the            Gr beds in Fig. 5 of Eyles & Clark, 1988). Just above,
two areas were proposed by Clet & Occhietti (1994) and             Allozone D2c (fig. 4 and 6) comprises the sequence
by Richard et al. (1999).                                          of sand beds related to the pale band II. Allozone D2d
                                                                   (fig. 6) corresponds to the conformable grey band III
                                                                   (fig. 3 and 4) composed of planar silt and fine sand beds,
                     4 - RESULTS                                   and is overlain by the pale grey sand beds of Allozone
                                                                   D2e (fig. 6). The erosional upper limit is irregular.
4.1 - TABULAR GEOMETRY OF THE DON
FORMATION: METRIC TO SUBMETRIC VISUAL                                 4.2.3 - Allozone D3
BANDS                                                                 Allozone D3 is limited to coarser beds with gravel
                                                                   related to the end of a major erosional hiatus in the pale
   On the working face of the former Don Valley Bric-
                                                                   band IV. This allozone represents a continuous marker
kyard, the formation presented eight distinct metric to
                                                                   unit on the faces of the brickyard (fig. 3 and 4). On the
submetric continuous bands, either pale or dark grey
                                                                   sample log (fig. 6), the thickness of these beds varies
(fig. 3, 4 and 6). Light bands are composed of drier sandy
                                                                   between 20 and 40 cm. This unit corresponds to the
beds (bands with even numbers II to VIII ; fig. 3 and 4).
                                                                   horizon with unconsolidated “pebble conglomerate” and
The darker bands (bands with odd numbers) are more
                                                                   gravel described on several sections by Gray (1950) at
clayey and moister, the basal water-saturated sandy band
                                                                   the top of his Unit A. Allozone D3 is overlain by distinct
I being the exception. In the Don Formation, the mois-
                                                                   finer deposits.
ture varies within a range of 22 to 6 % of water content
(Hann & Karrow, 1984). The bands show a progressive
thickness variation at the scale of a single working face            4.2.4 - Allozone D4
(fig. 3) and stronger variations at the scale of the past            Allozone D4 comprises the sequence of silt and fine
working faces and between working faces with different             sand beds of the grey bands V and VII (fig. 4), and the
orientations (Gray, 1950). The visual bands are approxi-           intermediate sandy beds of pale band VI which is thin-
mate and informal units, as the moisture limits are only           ning from the West to the East on the brickyard working
indicative of the dominant grain size and may vary with            face (fig. 3). This unit corresponds to the ‘’lacustrine’’
the seasons. Thus, this visual approach provides only a            Unit B of Gray (1950).
schematic view of the tabular geometry and gentle slope
of the Don Formation. From a detailed analysis, each                  4.2.5 - Allozone D5
continuous band corresponds to a sequence of disconti-                At the top of the formation, Allozone D5 (fig. 4 and
nuous beds with roughly the same dominant grain size or            6) is over 1.2 m thick, heterogeneous and corresponds
same dominant lithofacies.                                         roughly to the upper visual band VIII (fig. 4 and 6).
                                                                   During sampling, we observed a basal bed (10 cm) with
4.2 - DON FORMATION: ALLOSTRATIGRAPHY                              green shale fragments (D5a) (uppermost part of grey
                                                                   band VII, fig. 4 and 6), covered by a thin bed of green
  Based on this general geometry, together with sampling           sand (D5b). Above it (fig. 7), a pavement of green shale
logs and published detailed studies, the Don Formation             flat cobbles and wood fragments (D5c) underlies beds
can be subdivided into five allozones (D1 to D5), sepa-            of greenish sand (D5d) and white sand and fine gravel
rated mostly by erosional limits (fig. 3,4 and 6).                 beds (D5e). The uppermost beds (D5f and D5g) consist
                                                                   respectively of grey sand with frequent flat cobbles of
   4.2.1 - Allozone D1                                             green shale and of strongly weathered coarse brown
   The lowermost Allozone D1 corresponds to the discon-            sand.
tinuous “Basal Clay” described by Coleman (1933) and                  The seasonal, annual or multi-year beds of the forma-
Gray (1950), and mentioned by Terasmae (1960). The                 tion are discontinuous, as stated by Gray (1950) and Eyles
unit is composed of layered clay, interbedded with coarse          & Clark (1988). These inner discontinuities are the rule
dark sand. The thickness is decreasing (40 to 15 cm)               in every log of the formation and every continuous allo-
from the early working faces of the brickyard to those             zone. For this type of sediments, the thickness of the five
observed by Gray (1950). On the late exposures, the clay           allozones and their subdivisions varies within the entire
beds were apparently discontinuous. This zone belongs              sedimentary body. Nevertheless, despite these lateral thic-
to the lower grey band I. Some cobbles and blocks lay on           kness variations, the relative position of each allozone is
286

constrained within the formation, as it can be pointed out                             changing taphonomy throughout the record. An excep-
in all the photos of the former Don Valley Brickyard (see                              tion may be found in the behavior of the Monolete spores
photos by Coleman, 1941, p. 74; Coleman in Eyles &                                     (most probably derived from erosion of river banks occu-
Clark, 1988; Eyles, 1987; Karrow, 1990; this study).                                   pied by ferns) that parallels the total pollen concentration.
                                                                                       However this does not affect the sequence of changes in
4.3 - POLLEN STRATIGRAPHY: VEGETATIONAL                                                the mainland vegetation, as translated by the successive
AND CLIMATIC INTERPRETATION                                                            pollen assemblages.

   The exposed middle and upper parts of the Don Forma-                                  4.3.1 - Virtual Palynozone Don 1 (from Hann &
tion (Allozones D2b to D5) were resampled (1994 and                                    Karrow, 1984)
1998), resulting in 16 sterile samples and 42 pollen                                     Terasmae (1960) did not sample the basal clay, and
assemblages. From this analysis, five palynozones can                                  these beds were buried in 1994 and 1998. Therefore,
be distinguished in the formation, with a close but not                                the pollen content of Allozone D1 is unknown, but
perfect relationship between allostatigraphy and biostra-                              Hann & Karrow (1984) identified in the lowermost
tigraphy (tab. 3; fig. 7 and 8).                                                       beds of the Don Formation a cladoceran fauna that
   The pollen assemblages are essentially interpreted                                  can be found today in glacial lakes and boreal to
as indicating climatic changes. Given the fact that the                                subarctic habitats. This cladoceran biozone and the
sedimentological sequence represents shoreface depo-                                   equivalent virtual pollen zone Don 1 would corres-
sits and is not deposited in an enclosed lake basin, the                               pond to a transition after the Illinoian glaciation.
pollen and spore content of the formation should be                                    Nevertheless, trunks and branches of red cedar and
affected by changes of catchment size in the river system                              Unio shells with both valves united observed in the
feeding the shoreface, or by changes in discharge resul-                               lowermost blue clay by Coleman (1941) correspond
ting in sorting. In such a situation, it may appear unwise                             to warm interglacial conditions. This contradiction is
to attribute change in palynological assemblages directly                              not resolved.
to climatic change when variations arising from changing
taphonomy could potentially explain much of the identi-                                 4.3.2 - Palynozone Don 2
fied variability. The interpretations of climate instability                            Palynozone Don 2 corresponds to a deciduous and
from our record, presented below, are nevertheless valid                               mixed hardwood vegetation, with harsher episodes.
because there is no evidence of a reaction to obvious

Units           Palynozones   Vegetation cover                        Inferred climate     Estimated water depth       Dominant fluvial      Continental
                              on the watershed                                             Coleman, 1933; Gray, 1950   input                 processes
                                                                                           Eyles & Clark, 1988
                                                                                           Karrow, 1990; this study
Scarborough     Scar 1b                                                                                                                      remote ice margin
Formation                     Tundra Forest: open                     hemiarctic                                       distal input          sporadic permafrost
                Scar1b        forest with peat                                             deep water                  non glacial and       &
                              ( Richard et al ., 1999)                                                                 proglacial            seasonal ice
                Scar 1b                                                                                                debris                spring floods
                Scar1a                                                                     flooding phase
        g       Don 5.3
        f                     taiga to open taiga                                          shallow                     clasts
D5      d,e     Don 5.2                                                                                                wood fragments        seasonal ice
                              taiga: Northern                         subarctic            local exposures?                                  spring floods
     a, b, c    Don 5.1       Boreal Forest                                                littoral channels?          bedrock clasts        seasonal ice on shore
                                                                                           shallow
                              ?                                                            bottom erosion
        d       Don 4.3       harscher fir forest, deciduous                               18 m                        fine silty sand
                               decrease
D4          c   Don 4.2       fir forest:Picea
                                  forest:      cf. mariana increase   climatic change                                  fine sand
                                                                      from cooler than                                                       seasonal frost
        b       Don 4.1       fir forest: Southern Boreal Forest       today to boreal     deepening                   fine silty sand

        a       Don 3         harsher Southern Borea lForest                                                           fine sand
D3                            hiatus                                  ?                    bottom erosion              sand and gravel       ?
        e       Don 2.5       Mixed Harwood Forest                    today and cooler     shallow water               fine sand

        d       Don 2.5       mild Mixed Harwood Forest               warm                 deepening water             silty sand

        c       Don 2.4       Southern Boreal Forest                  cool event                                       cross-bedded sand

D2       c      Don 2.3       Deciduous Forest                        warmest              shallow water               sand                  weathering and
                                                                                                                                             fluvial
        b       Don 2.2       Southern Boreal Forest                  cool event           minor bottom erosion        sandy gravel

        a       Don 2.1       Mixed Harwood Forest (Terasmae, 1960)   warm                 very shallow 2 m            sand
                              hiatus                                                       bottom erosion ?
D1              (Don 1)       ?                                       late glacial ?       ?                           seasonal silt input   glacial lake ?

Tab. 3: Processes and conditions related to the deposition of the Don and Scarborough Formations, from the Illinoian/Sangamonian (MIS 6/5)
transition to an early Wisconsinan stadial (MIS 5d or b).
Tab. 3 : Processus et contextes de la sédimentation des formations de Don et de Scarborough, de la transition Illinoien/Sangamonien (MIS 6/5) à un
stade précoce du Wisconsinien (MIS 5d ou b).
287

  – Palynozone Don 2.1 (from Terasmae, 1960)                        and the Picea rubens type (Richard, 1970) is identified
  Allozone D2a was buried in the 1990’s and only one                almost exclusively in this zone. The total concentration
sample could be obtained from the top of the unit. The              lowers progressively upwards the section (13,000 to
analyses of Terasmae (1960: fig. 19) are used to define             7000 grains/g.). The uppermost assemblage with low
the type of assemblage related to these beds. The pollen            concentration (3000 grains/g.) is composed of Quercus,
content of 10 samples from Terasmae and one from this               Carya, Pinus diploxylon (cf. Pinus resinosa) and Picea
study (fig. 8; Palynozone Don 2.1) can be related to a              cf. mariana; the diversity of trees and herbaceous plants
zonal Mixed Hardwood Forest (MWb) assemblage with                   is significantly poorer than in the rest of Palynozone
Quercus, Carya, Tilia, Acer and Ulmus, and without                  Don 2 with the exception of the colder episodes Don 2.2
Liquidambar.                                                        and 2.4.

   – Palynozone Don 2.2: short colder episode                         4.3.3 - Palynozone Don 3
   The new pollen spectrum contains Southern Boreal                   The gravelly Allozone D 3 is sterile. The assem-
Forest (SBF) element with diploxylon pine pollen                    blage immediately above the gravel corresponds to
(probably Pinus cf. resinosa) and Picea cf. mariana. This           a harsher Southern Boreal Forest (SBFb) with Pinus
is related to a short cooler episode.                               diploxylon (P. cf. resinosa/banksiana), Picea cf.
                                                                    mariana and Quercus. The low concentration could
  – Palynozone Don 2.3: maximum warmth of the                       indicate leaching of the sediment, but the abundance of
interglacial stage with a Deciduous Forest                          Picea cf. mariana (34 %) would confirm real harsher
  Palynozone Don 2.3 is characterized by the occurrence             conditions for the vegetation than the overlying zonal
of Liquidambar and Nyssa along with most of the other               Southern Boreal Forest of Palynozone Don 4. Paly-
Mixed Hardwood Forest (MWa) species. The basal part                 nozone Don 3 follows a gap and represents a drastic
comprises dominant Carya (37 %) and Quercus, then                   change in comparison to the preceding zonal Mixed
dominant Quercus, Pinus diploxylon (cf. P. resinosa)                Hardwood Forest; the pollen grains were deposited
and Carya. In the upper part, the forest contains domi-             at the end of an unknown vegetation episode, but the
nant Quercus, Ulmus, Pinus diploxylon (cf. P. resinosa),            harsher assemblage is representative of an interme-
Tilia and Tsuga. The River Bank (RB) species with Larix             diate colder episode. The observed discontinuity in
and mostly fern monolete spores and herbaceous plants               the studied log may be different laterally: some beds,
(Poaceae, Cyperaceae) are present (between 7 and 10 %).             truncated at the sampled section, may be present and
Pollen and spore concentration is low (2000 grains/g.),             contain pollen assemblages from a part of the interme-
with increasing values in the upper part. The diversity is          diate vegetation between the two zonal forests.
high (fig. 8).
                                                                      4.3.4 - Palynozone Don 4
  – Palynozone Don 2.4                                                Palynozone Don 4 is characterized by Southern Boreal
  Increased representation of small size Betula pollen              Forest assemblages with Abies balsamea, Pinus diploxylon
grains (cf. Betula glandulosa), Alnus cf. crispa and Erica-         (cf. Pinus resinosa/banksiana), Picea cf. mariana, and a
ceae pollen characterize Palynozone Don 2.4, indicating             sharp decrease of deciduous trees (Quercus, Carya). The
an important cooling. The Palynozone is related to the              Palynozone is subdivided in three parts.
upper half of sandy Allozone D2c (fig. 8). In the lower
samples, elevated pollen representation of Quercus is                 – Palynozome Don 4.1
maintained along with that of Juglans, but increasing of              Palynozone Don 4.1 is characterized by a rapid increase
Picea cf. glauca, albeit low amounts, is in harmony with            of Abies (from 8 to 14 %), with Pinus diploxylon and
the presence of the mentioned shrubs. The corresponding             Picea cf. mariana, and represents the zonal Southern
vegetation may still be a deciduous forest, but experien-           Boreal Forest (SBFa) with some Tsuga. This vegetation
cing a harsher climate. Some thermophilous tree pollen              developed under wetter conditions than during Palyno-
may be reworked from underlying beds of the shoreface.              zones Don 2 and Don 3. The highest concentrations in
The upper sample is characterized by a Southern Boreal              the pollen diagram of the formation are observed in this
Forest assemblage with a low pollen representation of               palynozone (up to 70,000 grains/g.).
thermophilous trees and increasing amounts of Abies,
Pinus diploxylon (cf. Pinus resinosa/banksiana) and                    – Palynozome Don 4.2
Picea cf. mariana.                                                     A peak of Picea cf. mariana pollen, at the base of this
                                                                    Palynozone, corresponds to a more sandy band (D4c,
  – Palynozone Don 2.5                                              fig. 6 and 8), translating a vegetational response to a
  Diploxylon pine (cf. Pinus resinosa) and Quercus are              climate change promoting erosion. Opening of the forest
dominant with Carya and Ulmus of the Mixed Hard-                    cover in a colder environment is inferred.
wood Forest. Then the vegetation evolves to Quercus,
Pinus cf. resinosa, Carya, Ulmus, Fagus and Acer.                     – Palynozome Don 4.3
Palynozone Don 2.5 corresponds to a zonal Hardwood                    Abies balsamea decreases slowly (7 to 2 %), indicating
Forest (MWb). Picea cf. mariana is present (7 to 10 %)              the extent of a harsher Southern Boreal Forest (SBFb)
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