Early permian depositional environments and pond bonebeds in central archer County, Texas

Abstract

The Lower Permian redbeds of North Texas contain the oldest abundant non-aquatic vertebrate fauna. In the past, collecting of fossils and study of their paleozoology has been emphasized. With the exception of the pioneering work of Olson (1958, 1977) little attention was paid to sedimentological, paleoecological, and taphonomical aspects of the fauna. This study focuses on the sedimentary framework, paleoenvironment, fossil content, and taphonomy of the most common type of fossil occurrence — the pond bonebed. Five sedimentary facies are recognized: meanderbelt sandstones, large straigt channel fill sandstones, small straight channel fill sandstone, interbedded facies, and floodplain mudstone. These are the components of small meandering river systems with local tributaries and crevasse splays. Pond bonebeds occur as gray claystone lenses in red floodplain mudstones, deposited in oxbow lakes or swamps. The fauna is largely aquatic ( Orthacanthus, Ectosteorhachis, paleoniscoids, Sagenodus) or semiaquatic ( Eryops, Trimerorachis, Archeria, Edaphosaurus) with subordinate terrestrial elements ( Diadectes, Dimetrodon). Fossil plants, found as impressions, petrifactions, and charcoal, are indicative of swamps ( Psaronius) and well drained soils (conifers). All of the organic debris accumulated gradually by biological and physical processes. Occasional isolated but complete vertebrate skeletons are found in the floodplain mudstones.