THE INFLUENCE OF GLACIAL ISOSTATIC ADJUSTMENT ON CONTINENTAL SHELF STRATIGRAPHIC CORRELATION (Invited Presentation)

Continental shelf stratigraphy offers an unparalleled archive of Phanerozoic Eon glacial oscillations (e.g., Miller et al., 2004, 2012; Isaacson et al., 2008; Rygel et al., 2008; Loi et al., 2010; Hoffman, 2011). Yet, tectonics, dynamic topography, and sedimentation can distort the preservation of depositional sequences, erosional surfaces, or the apparent water-depth changes within facies juxtapositions, leading to discrepant reconstructions of the number and magnitude of glacial cycles inferred from shelf stratigraphy (Jervey, 1988; Einsele, 1993; Catuneanu et al., 2009). Here we explore how glacial isostatic adjustment (GIA)—the response of the solid earth, rotation axis, and gravity field, to ice sheet and ocean loading and unloading—induces spatially variable accommodation and distorts the inference of glacial cycles and scale (Farrell and Clark, 1976; Milne and Mitrovica, 2008; Tamisiea and Mitrovica, 2011; Creveling et al., 2018).

We modeled how GIA manifests in the stratigraphic record across four shelf-perpendicular transects moving progressively more distal to the Quaternary North American ice complex, subject to varying amounts of GIA during glacial-interglacial cycles (King and Creveling, 2022). Along each transect, we obtained local sea level (LSL) histories for nine sites between 1 m and 250 m water depth from the output of a gravitationally self-consistent GIA model run from marine oxygen isotope stage (MIS) 11 to the present. We paired each site’s unique LSL history with 50 identical annual sedimentation models to create a library of 400-k.y.-duration synthetic stratigraphic columns (each assuming no tectonics). For a given bathymetric depth, the comparison of the suite of synthetic stratigraphic columns between transects reveal latitudinal differences in the stratigraphically determined number, magnitude, and age of glacial-interglacial cycles, as inferred from stratigraphic sequence count, apparent water-depth change, and age of preserved deglacial transgression, respectively. We conclude that robust inferences of glacial sea-level change demand an assessment of the geographic gradient of vertical lithospheric motion across a shelf’s sequence stratigraphic architecture.