Sigleo, Anne (1978). "Organic geochemistry of silicified wood, Petrified Forest National Park, Arizona". Geochimica et Cosmochimica Acta. 42 (9). Arizona: 1397–1405. Bibcode:1978GeCoA..42.1397S. doi:10.1016/0016-7037(78)90045-5.
Sigleo, Anne (1978). "Organic geochemistry of silicified wood, Petrified Forest National Park, Arizona". Geochimica et Cosmochimica Acta. 42 (9). Arizona: 1397–1405. Bibcode:1978GeCoA..42.1397S. doi:10.1016/0016-7037(78)90045-5.