Outcrop-scale Environmental Heterogeneity and Vegetational Complexity in the Permo-carboniferous Markley Formation of North Central Texas

The Markley Formation of north-central Texas is composed predominantly of terrestrial rocks that span the Pennsylvanian-Permian boundary. Plant-fossil-bearing outcrops of the Markley are complex and preserve distinct environments that probably differed in position on the landscape and habitat conditions. In superpositional order, basal paleosols evidence well drained but wet conditions and supported a flora with deep rooting. The immediately superjacent kaolinite-rich, quartz mudstone beds contain a 'Termian"-type flora, dominated by seed plants, particularly conifers. Above these units there are "wet" floodplain deposits including organic shales that grade into coals. Above these are floodplain mudstones coarsening upward to sandstones. The floodplain deposits contain a typically "Pennsylvanian"-type flora. The co-occurrence of these floras in different beds within the same outcrops is strong evidence of climatic fluctuations during the time of accumulation, probably in response to the glacially controlled climatic rhythmicity, still prominent during the latest Pennsylvanian and earliest Permian.