A reappraisal of postglacial decay times from Richmond Gulf and James Bay, Canada
Decay times inferred from relative sea-level (RSL) histories of previously glaciated regions provide a potentially important constraint on mantle rheology. We present a new compilation of RSL data from Richmond Gulf and James Bay, Canada. This recompilation reveals errors in previous compilations that led to inaccurate estimates for the Richmond Gulf decay time in a series of recently published articles. We derive updated estimates for the decay time at Richmond Gulf and James Bay using a methodology that incorporates errors in both the age and the height of the sea-level markers. This exercise is guided by a series of synthetic RSL calculations that show that decay time estimates in the region can be significantly biased if the RSL time-series are not corrected for global eustatic sea-level trends, or if the estimates are based on composite RSL histories derived by combining data from both the Richmond Gulf and the James Bay regions. Our decay time analysis for Richmond Gulf applies the pioneering approach of Walcott (1980) to a large database and we derive a value of 4.0-6.6 kyr, where the range is defined by a misfit tolerance 10 per cent higher than the minimum. Our analysis for James Bay is based on the uplift curve derived by Hardy (1976), and we estimate a decay time of about 2.0-2.8 kyr. The difference between our estimates for Richmond Gulf and James Bay may be due to errors in the observational record from these regions, but could also be influenced by lateral variations in lithospheric structure associated with the assembly of Laurentia.
Additional Information© 2000 RAS. Accepted 2000 March 30. Received 2000 March 10; in original form 1999 October 15. We thank two anonymous reviewers for their comments regarding the original manuscript. Part of this work was performed while JXM was on sabbatical leave at Caltech, and he thanks the Division of Geological and Planetary Sciences for financial support during the visit. JXM and AMF are funded, in part, from individual NSERC Operating Grants. Contribution number 8710 of the Division of Geological and Planetary Science, California Institute of Technology.
Published - Mitrovica_2000.pdf