Abstract
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 Veriplicidium franklinii 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 b1 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.
Highlights
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 discharge from the drainage of the western Greenland ice sheet (e.g., Rignot and Mouginot 2012; Rignot et al 2016)
Samples were taken in cores from two different holes: 13 samples were collected below the recovery hiatus in Hole 645D between 438.6 and 340.6 mbsf in lithological Unit IIIA; 19 samples were collected above the hiatus in Hole 645B between 302.05 and 120.56 mbsf in Units II (n = 14) and IB (n = 6)
Palynomorph concentrations are high in lithologic units IIIA and II, between 438.6 and 220.94 mbsf, and very low in lithologic unit IB, between 209.89 and 120.56 mbsf (Fig. 3, Supplementary Table S11)
Summary
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 discharge from the drainage of the western Greenland ice sheet (e.g., Rignot and Mouginot 2012; Rignot et al 2016). The Baffin Island Current, which feeds the Labrador Current, carries large amounts of freshwater from the Arctic (Aksenov et al 2010), impacting the surface water salinity and density in the Labrador Sea and, the formation of intermediate/deep water mass (Cheng and Rhines 2004) and the Atlantic meridional overturning circulation (Lozier 2012; Rhein et al 2015). In eastern Baffin Bay, the West Greenland Current carries relatively warm and saline Atlantic waters northward (Tang et al 2004; Zweng and Münchow 2006; Fig. 1).
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