ABSTRACT

One of the most challenging questions in active mountain building is how climate might drive tectonic processes, in the form of mass redistribution. In other words, do climate-driven changes in erosion lead to increased exposure of mountainous belts, and perhaps influence tectonic processes, like uplift and faulting, as predicted by numerical models? The study of this question, by means of observational and analytical data is challenging because most areas where active mountain building is occurring are covered by remnant glaciers and glaciated landscapes from the end of the Neogene period (23 ? 2.5 million years ago). The St. Elias mountain belt, in southeast Alaska, is a prime location to address this question due to its extensive glaciation. The recent erosional record of this active mountain range is stored in the Gulf of Alaska and was recovered during Integrated Ocean Drilling Program (IODP) Expedition 341. Integrated analysis of deep-sea core material obtained from drilling at the continental shelf, slope, and the deep-sea Surveyor Fan will provide means to quantify the effect of global and local climate changes on the erosional and structural evolution of a mountain range. The youthfulness of the St. Elias belt, along with high rates of tectonic and erosional processes, and its close proximity of the Gulf of Alaska provide an ideal natural setting to study climate-tectonic interactions.

Long-standing debates exist in the Earth sciences on whether Neogene climate change affects rates of surface processes, such as erosion, and consequently influences tectonic processes, such as faulting, through redistribution of mass. The proposed study will test the hypothesis that an increase in glacial erosion has led to focused exhumation in the core of the St. Elias orogeny as proposed by numerical and analytical data. Two possible target regions have been suggested where a tectonic-climate feedback may have developed: in the fold-thrust belt and at the indenting Yakutat plate corner. The wealth of existing onshore geo- and thermochronological data provide a comprehensive picture of the current spatial pattern of exhumation rates, but the quantification of changes in rates and patterns through time has been challenging. The research team?s approach is to investigate the offshore sedimentary record of the St. Elias orogeny deposited in the Gulf of Alaska. This orogeny developed during a period of significant global climate change, including the intensification of Northern Hemisphere glaciation (iNHG) at the Plio-Pleistogene transition (PPT), ~2.6 Ma, and the mid-Pleistocene transition (MPT) from 1.2 to 0.7 Ma, but also a change of local climate resulting in alpine glaciers, perhaps as early as the Late Miocene/Pliocene (6.5 Ma). The high-resolution magnetostratigraphic and biostratigraphic age control from the IODP Expedition 341 cores allow close linking of changes in sedimentary lithofacies and textures, provenanace, exhumation, and sediment routing and distribution, to test the record of climate-tectonic interactions along the southern Alaska margin. The integration of Gulf of Alaska seismic reflection data with the age and provenance control from the 341 cores allow examination of sediment mass flux in the regional offshore depositional system, the Surveyor Fan, from a 3-D perspective through time.

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