Gröcke, D., Ludvigson, G., Witzke, B., Robinson, S., Joeckel, R., Ufnar, D., & Ravn, R. (2006). Recognizing the Albian-Cenomanian (OAE1d) sequence boundary using plant carbon isotopes: Dakota Formation, Western Interior Basin, USA. Geology, 34(3), 193-196. https://doi.org/10.1130/g21998.1