Baffin Bay late Neogene palynostratigraphy at Ocean Drilling Program Site 645

Analyses of marine and terrestrial palynomorphs of Ocean Drilling Program (ODP) Site 645 in Baffin Bay led us to define a new biostratigraphical scheme covering the late Miocene to Pleistocene based on dinocyst and acritarch assemblages. Four biozones were defined. The first one, from 438.6 m below sea floor (mbsf) to 388 mbsf, can be assigned a late Miocene to early Pliocene age (>4.5 Ma), based on the common occurrence of Cristadinium diminutivum and Selenopemphix brevispinosa. Biozone 2, spanning from an erosional unconformity to a recovery hiatus, is marked by the highest occurrences (HOs) of Veriplicidiumfranklinii and Cristadinium diminutivum, which suggest an early Pliocene age >3.6 Ma (~4.5 to ~3.6 Ma). Biozone 3, above the recovery hiatus and up to 220.94 mbsf, corresponds to a late Pliocene or early Pleistocene age based on occurrences of Bitectatodinium readwaldii, Cymatiosphaera? icenorum, and Lavradosphaera canalis. Finally, between 266.4 and 120.56 mbsf, Biozone 4, marked by the HO of Filisphaera filifera, Filisphaera microornata, and Habibacysta tectata, has an early Pleistocene age (>1.4 Ma). Our biostratigraphy implies that horizon bl of the Baffin Bay seismic stratigraphy corresponds to the recovery hiatus at ODP Site 645, which suggests a very thick Pliocene sequence along the Baffin Island slope. Dinocyst assemblages and terrestrial palynomorphs in our records indicate that the late Miocene and (or) early Pliocene were characterized by relatively warm coastal surface waters and boreal forest or forested tundra vegetation over adjacent lands. In contrast, the early Pleistocene dinocyst assemblages above the recovery hiatus indicate cold surface waters, while pollen data suggest reduced vegetation cover on adjacent lands. Key words: Baffin Bay, dinocysts, biostratigraphy, Pliocene, Pleistocene, palynology. Des analyses de palynomorphes marins et terrestres provenant du site 645 de l'ODP dans la baie de Baffin nous ont amene a definir un nouveau schema biostratigraphique couvrant la periode du Miocene superieur au Pleistocene, a la lumiere d'assemblages de dinokystes et d'acritarches. Quatre biozones ont ete definies. La premiere, qui couvre de 438,6 m sous le fond marin (msfm) a 388 msfm, peut se voir attribuer un age miocene superieur a pliocene inferieur (>4,5 Ma), a la lumiere de la presence repandue de Cristadinium diminutivum et de Selenopemphix brevispinosa. La biozone 2, qui recouvre une discordance d'erosion et un hiatus dans la sequence sedimentaire carottee, est marquee par les occurrence superieures (OS) de Veriplicidium franklinii et de Cristadinium diminutivum, qui indiqueraient un age pliocene inferieur de >3,6 Ma (~4,5 Ma a ~3,6 Ma). La biozone 3, qui couvre du hiatus de recuperation jusqu'a 220,94 msfm, correspond a un age pliocene superieur ou pleistocene infereur a la lumiere de la presence de Bitectatodinium readwaldii, Cymatiosphaera? icenorum et Lavradosphaera canalis. Enfin, de 266,4 msfm a 120,56 msfm, la biozone 4, marquee par les OS de Filisphaera filifera, Filisphaera microornata et Habibacysta tectata, est d'age pleistocene inferieur (>1,4 Ma). Notre biostratigraphie implique que l'horizon bl de la stratig-raphie sismique de la baie de Baffin correspond au hiatus de recuperation au site 645 de l'ODP, ce qui indiquerait la presence d'une sequence pliocene tres epaisse le long du talus de la terre de Baffin. Les assemblages de dinokystes et de palynomorphes terrestres dans les sediments analyses indiquent que le Miocene superieur et/ou le Pliocene inferieur etaient caracterises par des eaux de surface littorales relativement chaudes et une vegetation de foret boreale ou de toundra arboree sur les terres adjacentes. En comparaison, les assemblages de dinokystes d'age pleistocene inferieur au-dessus du hiatus indiquent des eaux de surface froides et que les donnees polliniques indiqueraient une couverture vegetale reduite sur les terres adjacentes. [Traduit par la Redaction] Mots-cles: baie de Baffin, dinokystes, biostratigraphie, Pliocene, Pleistocene, palynologie.
Introduction Baffin Bay is an important transitional basin for heat and salt exchanges between the Arctic and North Atlantic oceans (Fig. 1); it receives more than one-third of the freshwater [...]