Research Description:

The Onset of Alpine Glaciation in the Wrangell Volcanic Field, Alaska

It has long been known that glacial conditions existed in Eurasia and North America prior to the Pliocene, though exact timing and location of permanent ice fields is not known.  By better constraining these two, hypotheses can be tested examining the interaction between climatic deterioration and tectonic processes in Alaska (Jaeger et al., 2001  Gulick et al., 2004).
        
Fifteen to 10 Ma, Alaska was characterized by a warm and wet climate (White et al., 1997).   Since then there has been a shift to the cool, wet, glacial conditions of modern times.  During the change, Alaska’s coastal mountain ranges began to rise due to subduction of the Yakutat microplate triggering volcanism in the Wrangell volcanic field (WVF) (Plafker, 1994).  When the mountains reached a sufficient elevation to trap moisture from storms in the Gulf of Alaska, alpine glaciation would have begun in earnest (Lagoe 93).  My goal is to establish a more precise indicator through the use of geochemical, mineralogical, and textural proxies for a shift in weathering environment of the mountains present at the time.  Once done, the proxy records of weathering can be examined in DSDP and proposed IODP samples from the Gulf of Alaska continental margin to establish the timing of this climatic change.

The aforementioned hypothesis will be tested by examining the physical and chemical weathering of andesitic/dacitic WVF lavas whose elemental composition has remained constant for 11 Ma (Trop et al., 2005).  Miocene-age fluvial mudstone and lava samples are from the Frederika Formation of the northeastern flank of the Wrangells (supplied by Dr. Jeff Trop, Bucknell Univ.) and modern glacially derived samples collected from rivers and glaciers draining the WVF.  Elemental composition will be found through x-ray fluorescence. Mineralogical studies will be done using thin section analysis and x-ray diffraction.  Textural analysis of silt grains will be done with SEM analysis.  The three analytical methods will therefore provide a means of establishing the weathering products from the same source rock but subjected to two very different weathering regimes.