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Abstract

The Holocene land uplift in regions of Pleistocene glaciation, such as Hudson Bay in Canada, is dominated by glacial-isostatic adjustment with quasi-exponential time dependence. To infer the decay time associated with the uplift, neighbouring sea-level indicators (SLIs) related to the relative sea-level (RSL) height during the Holocene are commonly grouped into a single RSL diagram assumed to be representative of the region considered. Usually, the nominal height and age of a particular SLI are the only characteristics used when determining the Holocene RSL height. However, only SLIs based on isolation basins yield a narrow range for this height, whereas SLIs based on fossil samples, such as shells, peats or drift wood, only allow the determination of an upper bound, a lower bound or a finite interval for it. To use also fossil samples objectively, we develop a classification scheme based on fuzzy logic. After the defintion of appropriate membership functions, this method leads to a more systematic interpretation of the large amount of SLIs available. We apply the scheme to SLIs from the Richmond Gulf region (SE Hudson Bay) near the Pleistocene glaciation center of Canada and derive a decay time of 5.8 ka for the exponential function best fitting the RSL diagram, and thus the Holocene land uplift, for this region.