Date of Award
Doctor of Philosophy (PhD)
Paleoenvironment exerted control on the distribution of 133 palynomorph taxa from the Ludlow and Slope Formations and Boyce and Three V Tongues of the Cannonball Formation (Fort Union Group, I Paleocene) of southwestern North Dakota. The strata represent fluvial deltaic systems that prograded eastward into the Cannonball Sea. Depositional environments include distributary channels, crevasse splays, crevasse-splay feeder channels, lignite-producing swamps and/or marshes, lakes, brackish to slightly brackish bays, lake and bay fills, and marshes
Paleoenvironmentally sensitive palynomorph taxa were identified by subjective examination of pollen diagrams and objective analysis using detrended correspondence analysis. Two paleoenvironmentally restricted palynomorph associations were recognized. The Acritarch association, composed of Ovoidites cf. O. ligneolus, Micrhystridium Type-2, Psiloschizosporis cf. S. spriggii, Cymatiosphaera sp., and three unidentified acritarch taxa, is restricted to slightly brackish to lacustrine paleoenvironments. The Pediastrum association is dominated by Pediastrum, but contains additional algal taxa including Psilainaperturites sp. 2, Ovoidites cf. 0. ligneolus, Botryococcus sp., Micrhystridium Type-1, and several species of dinoflagellates. The Pediastrum association occurs in lacustrine strata and in the basal portions of brackish-water strata, indicating that brackish-water conditions were preceded by less saline environments. Palynornorph assemblages within lignite beds are characterized by sphagnaceous spores (Stereisporites spp.), Gleicheniidites spp., Toroisporis sp., Reticuloidosporites pseudomurii, Fraxinoipollenites variabilis, Rousea cf. R. parvicolpata, Rousea sp. 1, Rousea sp. 2, Retitrescolpites anguluminosus, Cyrillaceaepollenites cf. c. exactus, and Myrtipites? sp. 2. A possible early successional association also occurs in lignites, characterized by Nyssapollenites sp., Quercoidites cf. Q. spissus, Wilsonipites sp., Foveotricolporites pachyexinous, Cranwellia subtilis, Triatriopollenites subtriangulus, Dicotetradites rallus, Cricotriporites plektosus, Sparganiaceaepollenites? sp., and Biretisporites furcosus.
Kurtzipites spp., Syncolporites cf. S. minimus, and Wilsonipites sp. are typical of the progradational marsh deposits. Rossipollis scabratus, Corollina sp., Sparganiaceaepollenites cf. s. globipites, Jarzenipollenites trinus, Triporopollenites granilabratus, Rousea sp. 4, and Striatopollis cf. S. trochuensis may represent members of salt marsh floral communities. Dinoflagellate cysts, especially Deflandrea cf. D. flounderensis are typical of brackish-water strata, although some taxa have wider paleoenvironmental tolerance.
Kroeger, Timothy J., "The paleoecologic significance of Paleocene palynomorph assemblages from the Ludow, Slope, and Cannonball formations, southwestern North Dakota" (1995). Theses and Dissertations. 168.