Justin L. Shawler,ab Christopher J. Hein,a Elizabeth A. Canuel,a James M. Kaste,b Gregory G. Fitzsimons,c Ioannis Y. Georgiou,d Debra A. Willarde aVirginia Institute of Marine Science, William & Mary, P.O. Box 1346, Gloucester Point, VA 23062, USA. bDepartment of Geology, William & Mary, P.O. Box 8795, Williamsburg, VA 23185, USA. dDepartment of Earth and Environmental Sciences, University of New Orleans, New Orleans, LA 70148, USA. eU.S. Geological Survey, 926A National Center, Reston, VA 20192, USA.