HOW DOES GLACIAL ISOSTATIC ADJUSTMENT AFFECT MARINE STRATIGRAPHIC CORRELATION?

Glacial isostatic adjustment (GIA) alters the amplitude and timing of ‘glacioeustatic’ sea level maxima and minima around the globe. No study has examined the intrinsic distance that one can correlate marine stratigraphic records of glacial–interglacial sedimentation across continental shelves subject to varying amounts of GIA. Here, we seek to model how well synthetic (computer generated) marine stratigraphies of glacial–interglacial deposition correlate across space and through time. To obtain realistic relative sea-level (RSL) histories arising from GIA, we selected 7 shelf-perpendicular transects along the west coast of North America, extending from Vancouver Island to Baja California, that were variably impacted by post-glacial rebound (northern transects) and peripheral bulge subsidence (southern transects) over the last ~400 kyr. Next, we extracted the lat./long. of 9 sites between 1 and 250 m modern depth along each transect. Finally, we retrieved RSL change 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 between all 7 transects. For example, GIA imparted a difference in last glacial maximum (LGM) RSL of ~30 m across T1 (northernmost transect), but only ~1 m across T7 (southernmost transect). A LGM sea level lowstand of -53 m at T1 and -153 m at T2 contributes to a maximum RSL difference of ~100 m along the coastline, and the former lowstand occurred over 7 kyr later than the eustatic. The majority of far-field sites exhibit similar timing of RSL change to eustasy, though the glacial amplitude differs by one to tens of meters. Because accommodation is determined by the interaction between RSL and sedimentation, sites with variable RSL histories (from GIA) should produce different marine stratigraphies. Thus, we developed synthetic stratigraphies from the aforementioned RSL histories and two models for sedimentation: the first a constant positive sedimentation rate, and the second a stochastic model capable of both depositional and erosional events (Trampush and Hajek, 2017). We visually assessed the similarities in the duration of deposition and non-deposition/erosion (unconformities) for the 63 site-specific 400 kyr synthetic stratigraphies.