CORDILLERAN SEDIMENTS IN THE LABRADOR SEA: DETRITAL EVIDENCE FROM THE SAGLEK BASIN FOR THE OLIGOCENE-PLIOCENE TRANSCONTINENTAL BELL RIVER

The Saglek Basin in the Labrador Sea contains nearly 10 km of clastic strata that are inferred to be the product of an Oligocene-Pliocene transcontinental river system called the Bell River. The Bell River drainage basin is thought to have extended as far west as the Canadian Rockies, which if true, would suggest this system was responsible for a large influx of freshwater to the Labrador Sea prior to growth of the Laurentide ice sheet. In an effort to test the Bell River-Saglek Basin hypothesis and better understand Cenozoic sediment delivery pathways in northern North America we examined the provenance and detrital record of the Mokami and Saglek formations from subsurface samples of the Saglek Basin. Strontium (Sr) isotopes (⁸⁷Sr/⁸⁶Sr) were measured in marine bivalve shells from the upper Mokami and Saglek formations, yielding values of 0.708122–0.708567. Calibrated with the LOWESS 5 marine Sr isotope curve, the ⁸⁷Sr/⁸⁶Sr values result in ages ranging from 18.08 to 25.63 Ma. Detrital zircon uranium-lead (U-Pb) age populations of the Mokami and Saglek Formation include clusters at <250 Ma, 950–1250 Ma, 1600–2000 Ma, and 2400–3200 Ma. The population of <250 Ma detrital zircons in the Saglek Basin match those from coeval fluvial deposits in western Canada and are interpreted to be derived from the North American Cordillera. Neodymium (Nd) isotopes in shell material from the Saglek Basin range from εNd= -10.2 to -12.0 (average= -11.2; SD= 0.5). These εNd values overlap with those reported from Paleozoic miogeocline strata in western North America (εNd≈ -6–-14), and importantly, are more radiogenic than the modern Labrador Current, Labrador Sea Water, and North Atlantic Deep Water (εNd ~-12–-25). From the U-Pb detrital zircon age distributions and Nd isotopes we suggest that a large portion of the Bell River’s detrital and dissolved sediment load was derived from western North America including the Cordillera. This supports the postulation that the Bell River was transcontinental and of a scale comparable to the modern Mississippi River prior to development of the Laurentide ice sheet. Preliminary reconstructions of the Bell River drainage basin suggest efflux from the river would have likely influenced Oligocene–Miocene chemistry, salinity, and density stratification in the Labrador Sea; as such, the Bell River and its ultimate demise was a consequential component for the Neogene evolution of thermohaline circulation in the Atlantic Ocean.