Graduate Thesis Or Dissertation

 

The Influence of Glacial Isostatic Adjustment on Marine Stratigraphic Correlation Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/v118rm50v

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  • 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 (modelled) 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, a difference in last glacial maximum (LGM) RSL of ~30 m across transect 1 (northernmost transect) arises from a cross-shelf gradient in the gravitational attraction of water to the proximal ice sheet whereas this RSL amplitude difference is only ~1 m across transect 7 (southernmost transect) owing to differential loading of the shelf. A LGM sea level low stand of -53 m at transect 1 and -153 m at transect 2 contributes to a maximum RSL difference of ~100 m along the coastline, and the former low stand occurred over 7 kyr later than the eustatic. The majority of far-field sites exhibit similar timing of RSL change to that of the eustatic, though the glacial amplitude differs by one to tens of meters. The greater similarity in RSL between transect 2–7 versus transect 1 sites arises from the former’s relative distance from the ancient ice complexes; at transect 2–7 the physics of the peripheral bulge far exceed the contribution from gravitational attraction that dominates transect 1. 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 stochastic models for annual sediment depositional and erosional events: high mean/low variance vs. low mean/high variance (Trampush and Hajek, 2017). We visually assessed the similarities of both sedimentary packages, and their bounding surfaces, for the 63 site-specific 400 kyr synthetic stratigraphies. We found that the sedimentary packages varied systematically in their thickness and duration of model time represented both up-dip across individual transects and at specific depths parallel to the coastline; the age and duration of bounding surfaces similarly varied, and showed most pronounced differences between transect 1 and transects 2–7. Correlation of synthetic stratigraphic columns differently affected by GIA over several glacial-interglacial cycles is most difficult between sites proximal to the former ice sheet (transect 1) and those on the inner flank of the peripheral bulge (transects 2 and 3). Correlation is easier with respect to sites trending southward across the outer flank of the peripheral bulge (transects 4-7). The maximum distance where dissimilar stratigraphic records impacted by GIA can be correlated is between 600 and 1300 km from the former ice sheet (between transect 3 and 4).
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