The significance of pollen‐rich inorganic lake sediments in the Cratére du Nouveau‐Quèbec area, Ungava, Canada

Abstract

Unexpectedly high pollen concentrations characterize the basal, silty part of the postglacial sediments accumulated in two lakes from the Cratère du Nouveau‐Quebéc area, Ungava. These lacustrine silts and their pollen content result from early postglacial washing of a pollen bearing till. The till must therefore ahve incorporated pollen that relates to events prior to the last glacial event. The matrix of the till deposits surrounding the lakes shows outstandingly high pollen concentrations. It is hypothesized that because of the proximity of the ice divide during the last (and earlier) ice advance(s) in Ungava, the previously depoisited till and the pollen that haad accumulated in its matrix during the interglacial interval(s) were preserved in relict till plains or recycled into the till of teh last glaciation. The crater's age has been established at 1.4 Ma and holds a minimum thickness of 95 m of sediments. It is very likely filled with successive tills or related glacigenic deposits perhaps representing the whole length of time since the crater was formed. Alike the most recent till, these deposits should pollen. there is thus the prospect ofr a 1.4 Ma old pollen record for Ungava.

Last interglacial lake sediments preserved beneath Laurentide and Greenland Ice sheets provide insights into Arctic climate amplification and constrain 130 ka of ice‐sheet history

“…Similar details characterise Unit 2 in Lakes AKL, BRO and GNR. Richard et al (1991) reach a similar conclusion of reworked older pollen in deglacial sediment from Ungava, Canada. We consider the depositional age of Unit 2min in all settings to be early Holocene, only a few decades to centuries older than the base of Unit 1.…”

Microfacies and microstructures of subglacial and deglacial sediments from the Pingualuit Crater Lake (Ungava Peninsula, Canada)

“…grains (Girard-Cloutier, 2010). The pollen of these two species are found in the nearby and exceptionally pollen-rich tills (Richard et al 1991;Fréchette et al 1996) and reflect their remobilization and incorporation from former interglacial/interstadial periods at the base of the ice sheet and their deposition in the lake during later deglaciation . A few diatoms were also observed around 820 cm and at the top of the facies (Black et al 2010) and mainly correspond to Aulacoseira spp., a diatom genus known to be able to grow under a thin ice cover (Bondarenko et al 2006).…”

Variabilité des enregistrements polliniques en montagne et reconstitutions paléoécologiques

“…La persistance de ces taxons pendant la période glaciaire ne peut être envisagée en raison de l'enregistrement différé d'une courbe continue d'Abies et Picea au milieu de l'Holocène. De nombreuses études ont souligné l'abondance d'éléments remaniés à la base des enregistrements sédimentaires, (voir entre autres Richard et al, 1991). Dans le bassin du lac d'Annecy, les traces de Picea proviennent de lignites datées du Würm moyen (Brun, 1995) alors que celles d'Abies indiquent des sédiments plus anciens encore (Brun & Hanss, 1987).…”