HEINRICH LAYERS: MAJOR QUATERNARY CONTINENTAL EVENTS

The quasi-periodic, millennial oscillations of the glacial interval from about 60 to 10 thousand years ago are interrupted by extreme events in the North Atlantic which are inferred to be the product of massive armadas of icebergs from the Laurentide ice sheet. These Heinrich events are associated with dramatic dips in the d¹⁸O of surface water in the North Atlantic and Nordic Seas. They are also marked by extreme d¹³C of benthic foraminifera that implies virtual shutdown of North Atlantic Deep Water formation, and thus dramatic changes in thermohaline circulation. Strong evidence exists for a Northern Hemisphere-wide climate impact associated with these events. Heinrich layers were deposited over very short intervals of approximately 500 ± 250 years, although the exact duration has yet to be well constrained. The flux of Heinrich detritus was at least five times higher than ambient glacial values, and it has a distinctive provenance indicating derivation from the region around Hudson Strait.

Heinrich layers offer a great example of application of multiple provenance methods to constrain sediment sources, and specifically to use marine sediment cores to understand major Quaternary continental events. Many different measures of their provenance have been applied in the North Atlantic’s ice-rafted detritus belt (Ruddiman, 1977, GSAB), and it is the cumulative result that allows such a unique estimation of their derivation from the Hudson Strait. Particularly diagnostic indications of their provenance include detrital carbonate concentration, magnetic susceptibility, K/Ar ages of the fine fraction, Nd and Pb isotopes in bulk sediments, Pb isotopes in feldspar grains and ⁴⁰Ar/³⁹Ar ages of hornblende grains. Although less diagnostic, XRD mineralogy and Sr isotopes also add to the case for their provenance. Together the data require a source region where Paleozoic sedimentary rocks overlie a basement that has an Archean heritage and a strong Paleoproterozoic metamorphic overprint. The detrital carbonate concentrations in the open ocean approach those off the entrance to Hudson Strait, and this combined with the limited age spectrum indicated by the radiogenic isotopes yields the conclusion that Hudson Strait is the dominant contributor.