Marci M. Robinson (a), Jean M. Self-Trail (a), Gregory A. Wandless (b) & Debra A. Willard (a)
(a) Eastern Geology and Paleoclimate Science Center, United States Geological Survey, Reston, Virginia 20192, USA. E-mail: mmrobinson@usgs.gov
(b) Eastern Mineral and Environmental Resources Science Center, United States Geological Survey, Reston, Virginia 20192, USA.