title: Conservatism of Late Pennsylvanian vegetational patterns during short-term cyclic and long-term directional environmental change, western equatorial Pangea.
abstract: Patterns of plant distribution by palaeoenvironment were examined across the Pennsylvanian-Permian transition in North-Central Texas. Stratigraphically recurrent packages of distinct lithofacies, representing different habitats, contain qualitatively and quantitatively different macrofloras and microfloras. The species pools demonstrate niche conservatism, remaining closely tied to specific habitats, during both short-term cyclic environmental change and a long-term trend of increasing aridity. The deposits examined principally comprise the terrestrial Markley and its approximate marine equivalent, the Harpersville Formation and parts of lower Archer City Formation. Fossiliferous deposits are lens-like, likely representing fill sequences of channels formed during abandonment phases. Palaeosols, represented by blocky mudstones, comprise a large fraction of the deposits. They suggest progressive climate change from minimally seasonal humid to seasonal subhumid to seasonal dry subhumid. Five lithofacies yielded plants: kaolinite-dominated siltstone, organic shale, mudstone beds within organic shale, coarsening upward mudstone-sandstone interbeds and channel sandstone. Both macro- and microflora were examined. Lithofacies proved compositionally distinct, with different patterns of dominance diversity. Organic shales (swamp deposits), mudstone partings (swamp drainages) and coarsening upward mudstone-sandstone interbeds (floodplains) typically contain Pennsylvanian wetland vegetation. Kaolinite-dominated siltstones and (to the extent known) sandstones contain taxa indicative of seasonally dry substrates. Some kaolinite-dominated siltstones and organic shales/coals yielded palynomorphs. Microfloras are more diverse, with greater wetland-dryland overlap than macrofloras. It appears that these two floras were coexistent at times on the regional landscape.
authors.affiliation: Huffington Department of Earth Sciences, PO Box 750395, Dallas, TX 75275-0395, USA.
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Tabor
authors.affiliation: Department of Earth and Environmental Science, University of Pennsylvania, 240 South 33rd Street, Philadelphia, PA 19104, USA.
authors.forename: Charles M
authors.initials: CM
authors.lastname: Romanchock
authors.affiliation: Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, CA 94720, USA.
authors.forename: Cynthia V
authors.initials: CV
authors.lastname: Looy
authors.affiliation: Department of Paleobiology, NMNH Smithsonian Institution, Washington, DC 20560, USA ; National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Carol L
authors.initials: CL
authors.lastname: Hotton
authors.affiliation: Department of Paleobiology, NMNH Smithsonian Institution, Washington, DC 20560, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Dimichele
authors.affiliation: Department of Paleobiology, NMNH Smithsonian Institution, Washington, DC 20560, USA.
authors.forename: Dan S
authors.initials: DS
authors.lastname: Chaney