OUTCROP-SCALE ENVIRONMENTAL HETEROGENEITY AND VEGETATIONAL COMPLEXITY IN THE PERMO-CARBONIFEROUS MARKLEY FORMATION OF NORTH CENTRAL TEXAS

Abstract—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 pre-serve 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 accumula-tion, probably in response to the glacially controlled climatic rhythmicity, still prominent during the latest Pennsylvanian and earliest Permian