THE INFLUENCE OF GLACIAL ISOSTATIC ADJUSTMENT ON MARINE STRATIGRAPHIC CORRELATION

Glacial isostatic adjustment (GIA) alters the amplitude and timing of ‘glacioeustatic’ sea level maxima and minima around the globe. We developed synthetic (computer-generated) marine stratigraphic records to examine the distance that glacial-interglacial sequences correlate across continental shelves subject to varying amounts of GIA. We selected seven shelf-perpendicular transects along the west coast of North America from Vancouver Island to Baja California. Along each transect we extracted the lat./long. of 9 sites between 1 and 250 m modern depth and obtained relative sea-level (RSL) histories for these 63 sites from the output of a gravitationally self-consistent GIA model run from MIS 11 to present (Raymo and Mitrovica, 2012). RSL varies both across individual transects and along the coastline. At Vancouver Island , the last glacial maximum (LGM) RSL low stand varies by ~30 m as a result of differential loading of the shelf due to gravitational attraction; between Vancouver and Baja, LGM sea level low stand varies by 100 m (-53 m to -153 m), largely from crustal deformation in response to peripheral bulge growth. Because accommodation reflects the interaction between RSL and sedimentation, GIA should produce different stratigraphies near, intermediate, and far from former ice sheets. We confirm this by pairing the aforementioned RSL histories with a high mean/low variance annual sedimentation model (Trampush and Hajek, 2017). The 63 400 kyr-duration synthetic stratigraphic columns vary both up-dip across individual transects and at specific depths parallel to the coastline. Sedimentary packages differ systematically in their thicknesses and facies, while bounding surfaces vary in their age and duration. Correlation is most difficult between sites proximal to the former ice sheet and those on the inner flank of the peripheral bulge. Correlation is easier among sites trending southward across the outer flank of the peripheral bulge.