On the mid-Atlantic Coastal Plain of the United States, Paleocene sands and silts are replaced during the Paleocene-Eocene Thermal Maximum (PETM) by the kaolinite-rich Marlboro Clay. The clay preserves abundant magnetite produced by magnetotactic bacteria and novel, presumptively eukaryotic, iron-biomineralizing microorganisms. Using ferromagnetic resonance spectroscopy and electron microscopy, we map the magnetofossil distribution in the context of stratigraphy and carbon isotope data and identify three magnetic facies in the clay: one characterized by a mix of detrital particles and magnetofossils, a second with a higher magnetofossil-to-detrital ratio, and a third with only transient magnetofossils. The distribution of these facies suggests that suboxic conditions promoting magnetofossil production and preservation occurred throughout inner middle neritic sediments of the Salisbury Embayment but extended only transiently to outer neritic sediments and the flanks of the embayment. Such a distribution is consistent with the development of a system resembling a modern tropical river-dominated shelf.

Where present, numerical counts of putative eukaryotic magnetofossils are based upon the number of particles in a magnetic extract observed under SEM on a single Cu grid within a ~40 micron by 50 micron frame. Observations of conventional magnetofossils are based on TEM. + indicates presence; ++ indicates high abundance; - indicates absence; blanks and ? indicate missing or inconclusive observations.

Supplement to: Kopp, Robert E; Schumann, Dirk; Raub, Timothy; Powars, David S; Godfrey, Linda V; Swanson-Hysell, Nicholas L; Maloof, Adam C; Vali, Hojatollah (2009): An Appalachian Amazon? Magnetofossil evidence for the development of a tropical river-like system in the mid-Atlantic United States during the Paleocene-Eocene thermal maximum. Paleoceanography, 24(4), PA4211