Holocene sedimentary sequences from Nachvak and Saglek Fjords (Northern Labrador) as a record of deglaciation of the Torngat Mountains and Hudson Bay

Abstract

Listen

Translate article

Constraining the final retreat of the Laurentide Ice Sheet offers the best opportunities to understand the impacts of glacial retreat on landscapes and sedimentary processes, and their relation to oceanography and climate variations in Eastern North America. In Northern Labrador, an area that lacks chronological constraints on terrestrial data, investigating deglacial dynamics is also important as meltwater pulses may affect the deepwater formation that takes place in the Labrador Sea. In this paper, we investigate the deglacial sedimentary sequences from Nachvak and Saglek Fjords located in the Torngat Mountains of Northern Labrador. Sub-bottom profiles reveal that both fjords contain a deglacial sequence thicker than 100 m, including important mass-movement deposits reaching thicknesses of 40 m. These events were possibly triggered by glacio-isostatically induced earthquakes during the Younger Dryas and the Early Holocene. Estimations based on well-dated gravity cores sampled in both fjords suggest a deglaciation before the Younger Dryas for the Nachvak Outer Basin, but only 2000 yr later for the equivalent basin in Saglek Fjord. Such asynchronous retreat is explained by the presence of Saglek Bay acting as a buffer zone against oceanic forcing at the entrance of Saglek Fjord. In the sediment cores, high concentrations of detrital carbonates and an equivalent of the Hudson-Strait red bed are correlated with major deglacial events occurring between 9.2 and 8.1 cal ka BP in the Hudson Bay area. A progressive postglacial transition began around 8.0 cal ka BP with a decrease of detrital carbonate inputs and an increasing influence of North Atlantic waters. This transition ended abruptly with a regional major environmental change around 6.3 cal ka BP after the end of the Laurentide Ice Sheet melting. Magnetic properties reflecting enhanced bottom oxygen consumption reveal a high primary productivity from 6.3 to 3.8 cal ka BP in Saglek and Nachvak main basins, and probably a stronger water stratification. Overall, these results indicate that the deglacial and postglacial sedimentary dynamics of Nachvak and Saglek Fjords was influenced by (1) massive mass-movement deposits possibly generated by earthquakes, (2) sediment export by deglacial processes from both the local and the Hudson Bay areas and (3) the influence of Labrador Sea waters.