Nl Introduction Nl Method of study N3 Stratigraphy N3 Micropaleontology N4 Whitewater Arroyo Tongue N4 Lower Member of the Mancos Shale at Laguna N6 Hartland Member-lower member, Chama Basin N7 Significance of planktonic foraminifers N8 Faunal and environmental interpretations N9 Paleogeographic theories Nil Late Cenomanian stratigraphy and ammonite zones N12 Conclusions N13 Taxonomic notes on selected species N14 References cited N16 Appendix Description of localities N17 PLATES [Plates follow text] 1-3. Scanning electron microscope photomicrographs of selected specimens from study area. 14, 15. Maps showing general positions of shorelines: 14. Late Cenomanian N13 15. Middle Cenomanian N13 16. Chart showing foraminiferal zones and subzones, ammonite zones, and stratigraphic nomenclature of study area N14 IV Contents