SOURCE TO SINK RECORD OF EROSION ALONG A GLACIATED CONVERGENT MARGIN

Ongoing collision of the Yakutat microplate with the western margin of North America formed the St. Elias Mountains in southeast Alaska and southwest Yukon. The St. Elias Mountains are heavily glaciated and large glacial systems such as the Bagley-Bering, Seward-Malaspina and Hubbard efficiently erode and transport material into the Gulf of Alaska. Glacial erosion started by 6–5 Ma and intensified as global climate shifted to cooler temperatures during the Pliocene­–Pleistocene. The sediment eroded from the St. Elias Mountains is deposited on the Yakutat shelf and in the deep sea Surveyor fan through shelf-crossing troughs and channels. In this study, we investigate the Miocene to Recent sedimentary strata from the Gulf of Alaska to reconstruct spatial and temporal changes in source rock erosion, exhumation, and sediment routing. We use detrital apatite and zircon fission-track and U-Pb dating from sand deposited on the shelf and deep sea and compare it with the geology and thermochronology data of the St. Elias Mountains. We show that sediment deposited on the shelf, slope, and proximal deep sea in front of the Bering Glacier is sourced from the Bagley-Bering Glacier catchment with little changes in provenance since ~4 Ma. Cooling ages reveal moderate exhumation rates (<1 mm/yr) underneath the Bagley-Bering ice. This result supports the longevity of the Bering sediment transport system and indicates limited lateral sediment mixing on the shelf. Sediment deposited in front of the fold-thrust belt, south of Yakutat Bay, reveal different sediment sources including an area of very rapid (>2 mm/yr) and deep-seated exhumation that is comparable to the St. Elias syntaxis. Deposits on the shelf and in the distal deep sea reveal that a source of similarly rapid exhumation already existed at 11–10 Ma and was deposited by 8 Ma. Overall, we show that sediment transport from an active mountain range to the adjacent sink by ice streams results in very high deposition rates and limited lateral sediment mixing due to evolving structural barriers in the fold-thrust belt. We also show that the record of distinct source regions identified on land is diluted by the overall high erosion rates along the coastal mountain range.