FROM WETLANDS TO WET SPOTS: THE FATE AND SIGNIFICANCE OF CARBONIFEROUS ELEMENTS IN EARLY PERMIAN COASTAL PLAIN FLORAS OF NORTH CENTRAL TEXAS

The paleoecologic demise of the last Paleozoic wetlands known in North America is recorded in the Early to Middle Permian floras of North-Central Texas. Within an approximately 1000 m-thick continuous continental section that begins with regionally persistent coal deposits and ends with bedded evaporites, wetland environments shrink from mappable coal seams that offer innumerable sampling opportunities to a few map dots, or wet spots, that provide unique collections. The morphological and mineralogical characteristics of associated paleosol profiles also show a similar ecological and climatic trend. Numerous earliest Permian floras (Wolfcampian) differ little from those found in the underlying latest Carboniferous (Virgilian). Sedimentologic features and paleosols indicate widespread, regionally wet to ever-wet conditions typical of wetland environments. Carboniferous elements diminish upwards in the redbeds of the Wichita Group (lower Leonardian Series), where plants are preserved in abandoned to slack-water channel settings that formed under seasonal climates. Humid or wet paleosol morphologies become progressively restricted and replaced by morphologies consistent with drier, semi-arid conditions through the Lower Permian until wet areas are limited to "riparian corridors." The last vestige of Carboniferous wetland taxa occurs in a very small number of fluvial-channel deposits in the middle Clear Fork Group (upper Leonardian Series) that yield abundant tree ferns and broad-leaf seed plants, along with rare tree lycopsids and sphenophylls, all of which required wet conditions. Vertebrate aestivation assemblages in the middle Clear Fork indicate periods of seasonal drought and underscore the exceptional, geographically and temporally restricted aspect of these plant assemblages. Despite the loss of Carboniferous floral elements in the middle Clear Fork Group, restricted wetland environments remain a small but floristically important component of the Permian landscape in the overlying Pease River Group. Such environments yield the region's youngest Permian floras, which have a distinctly Mesozoic aspect.