DIVERSITY OF A LOWER CRETACEOUS PRE-ANGIOSPERM FLORA IN THE CLOVERLY FORMATION, WY

The Lower Cretaceous Cloverly Formation in the Bighorn Basin, WY documents the arrival of flowering plants into the region. Sites in the upper part of the formation contain angiosperm leaves and pollen, whereas sites in the lower part lack angiosperms. A pre-angiosperm flora is preserved in a laterally extensive laminated mudstone deposit in the lower part of the Cloverly Fm., near Ten Sleep, WY. Algal remains, caddisfly casings and barite nodules and are all consistent with a lacustrine facies interpretation. The macroflora is dominated by the cycadophyte Nilssoniocladus, and includes conifers and diverse ferns. The palynoflora includes spores and gymnosperm pollen consistent with an Hauterivian age of the unit and a pre-Aptian model of the onset of Cloverly deposition.