Depositional and microfaunal response to Pliocene climate change and tectonics in the eastern Gulf of Alaska

Abstract

The Yakataga Formation provides an excellent record of Pliocene paleoclimate in the Gulf of Alaska and northeastern Pacific Ocean. Evidence for glaciomarine influence and paleoclimatic change includes the distribution of ice-rafted debris and diamictite, planktic and benthic foraminiferal biofacies, and variable sediment accumulation rates. Three paleoclimatically defined intervals within the Pliocene Yakataga Formation are recognized in onshore and offshore sections. Interval P1 (5.35 to 4.2 Ma) contains the first evidence of Neogene glaciomarine deposition in the form of ice rafted debris and rare diamictite. Interval P2 (4.2 to 3.0–3.5 Ma) exhibits a reduction in glaciomarine influence and warming to cool temperate conditions. Interval P3 (3.0–3.5 to 1.8 Ma) contains massive amounts of glaciomarine diamictite and correlates with other evidence indicating the onset of major northern hemisphere glaciation. Sediment accumulation rate and foraminiferal based paleobathymetric curves show some correlation to the above paleoclimatic subdivision, but also significant independent relationships, indicating a strong tectonic influence on those parameters. Comparison of the Yakataga record to ODP sites in the North Pacific shows that there is good agreement in the ice-proximal (Yakataga) and deep-sea records of Pliocene paleoclimate change.