Close Geochemistry of Upper Cambrian-Lower Ordovician black shale along a northeastern Appalachian transect,
Fyffe, L. R., R. K. Pickerill (1993) (1993),
Bulletin of Geological Society of America, 105 p. 897–910,
10.1130/0016-7606(1993)105%3C0897:GOUCLO%3E2.3.CO;2.