PALYNOLOGICAL ANALYSIS OF FLORAL CHANGES CAUSED BY REPEATED VOLCANIC ASH BURIAL OF A COAL-FORMING UPPER CRETACEOUS PEAT SWAMP, UTAH, U.S.A. (UNITED STATES)

The Ferron Sandstone C coal horizon and several outcrop samples from the upper Tununk Shale, Ferron Sandstone, and lower Bluegate Shale Members of the Mancos Shale from the Castle Valley area of east-central Utah were studied palynologically. This information was used to reconstruct the floristic assemblages of the coal-forming peat swamps, to determine the extent of destruction of the vegetation by repeated burial by volcanic ash, and the sequence of plant community paleosuccession following such events.;Both lateral (geographic) and vertical (successional) floristic trends are identified in the Ferron C. coal. Low diversity, fern dominated assemblages represent early successional communities. The mature coal swamp consists primarily of the Gymnosperm Assemblage.;Periodic volcanic eruptions had varying effects on the paleocommunity structure of the Ferron C coal swamp vegetation. The thicker ash fall accumulations were more devastating to the flora than the thin ash accumulations. Hydrologic, pedologic, and floristic changes are associated with the thickest ash fall. After a major destructive ash fall, the coal swamps were first repopulated by herbaceous ferns. A return to predisturbance palynomorph assemblages is evident within 30-60 cm of post-disturbance coal.;The Ferron Sandstone palynoflora (middle to late Turonian) is similar to other western United States Middle-Cretaceous floras. No depositional or age relationships were established between productive samples from northern and southern Castle Valley.;Seven floristic assemblages are differentiated in the coal swamps. These include an Herbaceous Fern Assemblage, Mixed Assemblage, Angiosperm Assemblage, Gymnosperm Assemblage, Wet, Fern-Gymnosperm Swamp Assemblage, Wet, Mixed, Swamp Assemblage, and the Brackish, Gymnosperm Swamp Assemblage.;The upper Tununk Shale palynoflora is characteristic of the Cenomanian-Turonian (Middle Cretaceous). The lower Bluegate Shale palynoflora is latest Turonian in age or younger. Both the Tununk Shale and the Bluegate Shale yielded palynofloras characteristic of marine depositional environments.