Archeomagnetism of potsherds from Grand Banks, Ontario: a test of low paleointensities in Ontario around A.D. 1000

Previous investigations of postglacial sea levels around Laurentia in a non-linear earth without ambient stress found that non-linear uniform mantle models cannot explain the relative sea level data around the ice margin. In this study, a 3D finite element model of postglacial readjustment is used to calculate the Earthʹs response due to realistic ice and eustatic water loads on stratified mantle with non-linear rheology and ambient tectonic shear stress. By varying the creep parameter A* and the ambient stress level in a uniform mantle, it is found that the combination A* around 3×10-35 Pa-3 s-1 and ambient stress level around 10 MPa is able to explain the sea level data both outside and inside the Laurentian ice margin ¯ although for certain sites inside, a slightly thicker ice is required to improve the fit to the data. Other geophysical and geodetic observables ¯ namely uplift rate, horizontal velocity, free air gravity and the rate of change of gravity ¯ have also been calculated for this model.