DETRITAL ZIRCON FROM A LARGE CENOZOIC DELTA AT THE MOUTH OF HUDSON STRAIT: EVIDENCE FOR CANADA’S AMAZON-SCALE, “PALEO-BELL RIVER” BASIN

Concordant U-Pb ages from 850 detrital zircon (DZ) grains sampled from a large Cenozoic delta at the mouth of Hudson Strait in the northern Labrador Sea indicate headwater sources in the Canadian and US Cordillera, northern Great Plains, and eastern Canadian Shield. The zircon grains were separated from Miocene and Oligocene sands from bore hole # Rut H-11 in the Saglek basin. The Miocene samples came from 1000 m above the Oligocene samples in the well. The analyses positively tested the hypothesis that the delta is the deposit of the Amazon-scale, Cenozoic “paleo-Bell River”, which had three main tributaries (McMillan, 1973; Balkwill et al., 1990). The tributaries are thought to have gathered into the main trunk stream in the present area of Hudson Bay, and flowed through Hudson Strait to the delta in the Saglek basin. Pleistocene continental glaciation covered Canada, re-arranged the giant river system, and drove crustal subsidence that sank the delta below sea level. The delta has been extensively explored for hydrocarbons with seismic reflection profiles and bore holes, and is shown to be the largest Cenozoic depositional system on the eastern seaboard of North America. The Saglek basin deposits are as thick as 9 km and cover ~200,000 km². Our results find three main DZ age-groupings that correlate with sources in the three main tributary regions. The Cordillera and northern Great Plains yielded distinctive zircons recycled from the foreland, including ones correlative with the Wopmay, Yavapai, and Mazatzal provinces, Belt Supergroup, the Triassic-Jurassic Cordilleran magmatic arc, the Idaho and Boulder batholiths, late Cretaceous bentonites, and Eocene igneous rocks of the Montana Plains and possibly Colorado Plateau. Erosion of the foreland was coeval with deposition in the delta, and Fensome (2015) reported that Oligocene and Miocene samples from the same borehole yielded recycled Upper Cretaceous dinocysts from the Cordilleran foreland. The eastern Canadian Shield likely yielded abundant zircons of Archean and Proterozoic ages. The samples imply that the paleo-Bell River had a relatively stable drainage basin from ~ 30 to 15 Ma.