Robert W. Hook

AN EARLY PERMIAN FLORA WITH LATE PERMIAN AND MESOZOIC AFFINITIES FROM NORTH-CENTRAL TEXAS

Abstract Early Permian (late Leonardian Series) plant assemblages from King, Knox, and Stonewall Counties of North-Central Texas are dominated by seed plants, some apparently congeneric with taxa heretofore known only from the Late Permian or the Mesozoic. Conifers are the dominant elements, including one or more species of Ullmannia, Pseudovoltzia liebeana, both known from the Late Permian Zechstein flora of Germany and England, Podozamites sp., characteristic of the Mesozoic, and Walchia sp., abundant in Early Permian floras. Locally common are Taeniopteris cf. eckardtii, a Zechstein species, an unidentified plant represented by pinnule-like laminae with fine parallel veins, similar to pinnules of some Mesozoic cycads, and calamite stems. Rarely encountered are leaf fragments of the Paleozoic ginkgophyte Dicranophyllum, flabellate ginkgophyte leaves, leaves with a broad midvein and narrow, fimbriate lamina, and Wattia, typical of the Early Permian. Associated with these foliar remains are ovulate reproductive structures including the presumed cycad megasporophyll Dioonitocarpidium, known only from the Mesozoic, a voltzialean cone scale similar to Swedenborgia, and a variety of seeds, some remarkably similar to Agathis, of Cretaceous age. The assemblage includes only rare scraps of foliage and seeds possibly attributable to the pteridophyllous elements (gigantopterids, callipterids, and ferns) that dominate the Permian. The fossil plants occur in multistorey, fining-upwards, tidal-channel deposits that also include pelecypods and fragmentary palaeoniscoid fish. The occurrence of derived lineages in xeric habitats during the Early Permian indicates that some supposed Mesozoic groups actually preceded and survived the end-Permian extinction, reappearing in basinal lowlands during the mid-Mesozoic.

AN UNUSUAL MIDDLE PERMIAN FLORA FROM THE BLAINE FORMATION (PEASE RIVER GROUP: LEONARDIAN-GUADALUPIAN SERIES) OF KING COUNTY, WEST TEXAS

Abstract A new Middle Permian plant assemblage from South Ash Pasture in King County, Texas, may be the youngest and is certainly the most unusual flora known from the Permian of either West Texas or adjoining north-central Texas. Found serendipitously in the evaporite-rich upper Blaine Formation (Pease River Group, Guadalupian Series), the flora is of very low diversity despite intensive collecting efforts, and the affinities of nearly all taxa are enigmatic. The most common elements are parallel-veined leaves that resemble cordaites but that could be isolated pinnules of a pinnate leaf. Gigantopterid foliage is present but not assignable to any known taxon. A single foliar conifer specimen is too incomplete for assignment. Numerous reproductive organs, however, and an abundance of axes may represent conifers. Conchostracans, palaeoniscoid fish scales, and small heteropolar coprolites also occur in the deposit, which originated as a small, claystone-dominated channel fill in a coastal plain setting.

An Early Permian Coastal Flora from the Central Basin Platform of Gaines County, West Texas

Abstract Fossil plants are abundant in dolomite of the Clear Fork Group (Leonardian; late Early Permian) in the North Robertson Unit of the Robertson Clear Fork oil field of Gaines County, West Texas. The unit is a portion of the larger Robertson field. Thirty-seven separate collections were made from drill cores taken in three wells, spanning an interval 300 m thick from a depth below the surface of > 2000 m. The flora is depauperate, comprised of Comia sp. (most abundant), Taeniopteris sp., Delnortea abbottiae, callipterid-like foliage of uncertain affinity, calamite stems, and unidentified foliage of cycad-like character. Plants occur in discrete intervals that are a few cm to 3 m thick and have limited lateral continuity (less then 0.5 km). Plant-bearing dolomites contain interspersed fossil roots and burrows, weakly developed soil horizons, thin coaly accumulations of organic material, and pedogenic and collapse breccias. Fusain is common throughout. Between the plant-bearing layers are heavily bioturbated dolomites with anhydrite-filled burrows, interpreted as lagoonal to shallow subtidal in origin, up to 50 m thick. Contacts between marine units and plant-bearing beds are sharp. The North Robertson Unit and the field is believed to be internal to the Central Basin Platform and bordered by a shallow seaway to the east. The Central Basin Platform probably represented a broad peninsula between the Midland Basin to the east and the Delaware Basin to the west. The site probably consisted of innumerable little islands separated by a network of waterways. Plants occur in “island complexes” consisting of deposits formed in ponded water, beach fronts, and lagoons. Vegetation must have been tolerant of salt or salt spray, seasonal drought, wind, and storms; all species were robust in construction, with either thick leaves or heavy cuticles. This flora, although clearly allied with other Early Permian floras from western North America, is sufficiently peculiar to indicate that habitat differentiation was well developed within the tropical lowlands during the Late Paleozoic.

CRUSTACEAN-BEARING CONTINENTAL DEPOSITS IN THE PETROLIA FORMATION (LEONARDIAN SERIES, LOWER PERMIAN) OF NORTH-CENTRAL TEXAS

Abstract Numerous pygocephalomorph crustaceans occur with conchostracans, plants, fishes, amphibians, and amniotes in the Petrolia Formation (Leonardian Series, Lower Permian) of Baylor and Archer counties, Texas. Two pygocephalomorph species are represented; Mamayocaris serendipitous, new species, by hundreds of specimens that appear to be molted exoskeletons, and Paulocaris schrami, new species, by only a few specimens. Mamayocaris has been reported previously from the Lower Permian of Texas and South Dakota and the Upper Carboniferous of Illinois; Paulocaris was previously known only from South America. Associated plant assemblages are dominated by conifers accompanied by other Early Permian and some Late Carboniferous elements. Accompanying vertebrate remains include aquatic to fully terrestrial forms with close taxonomic ties to genera or families recorded in Upper Carboniferous deposits. The fossils are preserved in local deposits of thin (<2 cm), lenticular to nodular beds of limestone and thin (<15 cm) intervals of dark-gray claystone. These deposits accumulated in abandoned, standing-water segments of suspended-load fluvial channels. The archaic nature of these plant and animal assemblages supports previous interpretations that the Permian Petrolia Formation contains paleoenvironmentally isolated biotic elements characteristic of the Carboniferous and underscores prior depictions of the assemblages as relictual.

Amphibian eggs from the Lower Permian of north-central Texas

ABSTRACT Masses of small (up to 0.8 mm in diameter) oviform bodies were found in association with fossil plants as well as freshwater and terrestrial invertebrate and vertebrate remains in the Waggoner Ranch Formation (Wichita Group, Leonardian Series, Lower Permian) of Baylor County, Texas; this is the first record of fossilized amphibian eggs. The eggs occur as compact, rounded masses and as irregular sheetlike or unilayered aggregates, some of which cover plant remains to which they may have been attached originally. Individual eggs consist of a compressed central body surrounded by a thin, apparently flexible membrane, and an outermost halolike covering. Characteristics of the egg masses and the morphology of individual eggs are indistinguishable from those of modern anuran amphibians. Because dissorophoid temnospondyls are phylogenetically related closely to Recent amphibians and are well represented in the Lower Permian of north-central Texas, dissorophoids are the most probable source of the eggs.

Petrography, geochemistry, and depositional setting of the San Pedro and Santo Tomas coal zones : anomalous algae-rich coals in the middle part of the Claiborne Group (Eocene) of Webb County, Texas

Two coal zones, the San Pedro and the overlying Santo Tomas, are present for nearly 35 km in outcrop, surface and underground mines, and shallow drill holes along the strike of the middle part of the Claiborne Group (Eocene) in Webb County, Texas. A sandstone-dominated interval of 25 to 35 m separates the two coal zones, which range up to 3 m in thickness. Each coal zone contains carbonaceous shales, thin (<0.75 m) impure coal beds, and thin (<0.85 m) but commercially significant nonbanded coal beds. The nonbanded coals are different from other Tertiary coals of the Gulf of Mexico Coastal Plain: unlike lignites that are typical of the older Wilcox Group (Paleocene-Eocene) and younger Jackson Group (Eocene), nonbanded coals of the Claiborne Group have high vitrinite-reflectance values (0.53 Rmax) and high calorific yields (average 6670 kcal/kg or 12,000 Btu, dry basis). The coals are weakly agglomerating (free-swelling index is 1.5–2.0) and have an apparent rank of high-volatile bituminous. The coal-bearing portion of the middle Claiborne Group in the Rio Grande area represents a fining-upward transition from sandstone-dominated, marine-influenced, lower delta plain depositional environments to more inland, mudstone-rich, predominantly freshwater deltaic settings. Discontinuities within the San Pedro coal zone are attributed mainly to the influence of contemporaneous deposition of distributary mouth-bar sand bodies. The less variable nature of the Santo Tomas coal zone reflects its origin in the upper part of an interlobe basin that received only minor clastic influx. Petrographic attributes of the nonbanded coals indicate that they formed subaqueously in fresh to possibly brackish waters. A highly degraded groundmass composed of eugelinite is the main petrographic component (approximately 71%, mineral-matter-free basis). An enriched liptinite fraction (approximately 23%) probably accounts for unusually high calorific values. There is negligible inertinite. Petrographic study of polished blocks indicates that approximately 10 percent of the nonbanded coal from both coal zones is composed of green algae fructifications, which also occur in clastic rocks of the coal-bearing interval. Such algal material cannot be identified or quantified by conventional coal petrographic techniques that utilize particle pellets or by palynological analyses that include acid preparation.