A Look at the Assselian Permian fluvial deposits of West Virginia Suggests More Humid Climate

A paleopedological and ichnological approach to interpreting spatial and temporal variability in Early Permian fluvial deposits of the lower Dunkard Group, West Virginia, U.S.A.

Authors:

Hembree et al

Abstract:

Lower Permian (Asselian) deposits of the Washington Formation (Dunkard Group) in West Virginia (U.S.A.) represent proximal to distal expressions of a migrating, anastomosing river and associated floodplain environments. These deposits are part of the upper fluvial plain province of the Dunkard Basin characterized by thick-to-thin sandstone bodies, shales, and paleosols. The paleosols and associated ichnofossils record a wealth of paleoenvironmental, paleoecological, and paleoclimatic data which improve our understanding of the autogenic and allogenic processes that result in the spatial and temporal variability of ancient fluvial systems. This study integrates field and laboratory analysis of paleosols and ichnofossils including macro- to micromorphology, bulk geochemistry, and clay mineralogy to better understand variations in soil-forming processes across this Early Permian floodplain. Nine different pedotypes were identified including proximal, poorly developed Entisols and Inceptisols, poorly drained Histosols, and thick, moderately to well-drained Inceptisols and Vertisols. Lateral differences in paleosol properties were minor compared to the diversity of paleosols present in the vertical exposure and were largely a result of localized variations in drainage and topography. Differences in the properties of the paleosols in the vertical succession could not be explained by variable drainage due to position on the floodplain. Cyclicity was largely controlled by avulsion, but was overprinted by changes in climate. While climatic drying during the Early Permian as a general trend is well established, smaller scale fluctuations between wet and dry intervals contributed significantly to observed paleosol properties. Dominance by calcareous Vertisols in the upper fluvial plain facies province and their representation of strongly seasonal conditions are consistent with previous research; however, thorough investigation of the paleosols suggests that more humid conditions existed than the arid to semiarid climate that has been suggested.

The Flora of Asselian Permian Equitorial and Seasonally dry Pangea...From Las Cruces, NM

Early Permian (Asselian) vegetation from a seasonally dry coast in western equatorial Pangea: Paleoecology and evolutionary significance

Authors:

Falcon-Lang et al

Abstract:

The Pennsylvanian–Permian transition has been inferred to be a time of significant glaciation in the Southern Hemisphere, the effects of which were manifested throughout the world. In the equatorial regions of Pangea, the response of terrestrial ecosystems was highly variable geographically, reflecting the interactions of polar ice and geographic patterns on atmospheric circulation. In general, however, there was a drying trend throughout most of the western and central equatorial belt. In western Pangea, the climate proved to be considerably more seasonally dry and with much lower mean annual rainfall than in areas in the more central and easterly portions of the supercontinent. Here we describe lower Permian (upper Asselian) fossil plant assemblages from the Community Pit Formation in Prehistoric Trackways National Monument near Las Cruces, south-central New Mexico, U.S.A. The fossils occur in sediments within a 140-m-wide channel that was incised into indurated marine carbonates. The channel filling can be divided into three phases. A basal channel, limestone conglomerate facies contains allochthonous trunks of walchian conifers. A middle channel fill is composed of micritic limestone beds containing a brackish-to-marine fauna with carbon, oxygen and strontium isotopic composition that provide independent support for salinity inferences. The middle limestone also contains a (par)autochthonous adpressed megaflora co-dominated by voltzian conifers and the callipterid Lodevia oxydata. The upper portions of the channel are filled with muddy, gypsiferous limestone that lacks plant fossils. This is the geologically oldest occurrence of voltzian conifers. It also is the westernmost occurrence of L. oxydata, a rare callipterid known only from the Pennsylvanian–Permian transition in Poland, the Appalachian Basin and New Mexico. The presence of in situ fine roots within these channel-fill limestone beds and the taphonomic constraints on the incorporation of aerial plant remains into a lime mudstone indicate that the channel sediments were periodically colonized by plants, which suggests that these species were tolerant of salinity, making these plants one of, if not the earliest unambiguous mangroves.

The Composition and Layout of a Wolfcampian/Lower Permian Woodland

Plant architecture and spatial structure of an early Permian woodland buried by flood waters, Sangre de Cristo Formation, New Mexico

Authors:

Rinehart et al

Abstract:

Natural molds of 165 stems were found in life position in a 1 m-thick sandstone bed, lower Permian (Wolfcampian), Sangre de Cristo Formation, northern New Mexico. The sandstone represents a single flood event of a river sourced in the Ancestral Rocky Mountains. Most of the flood-buried plants survived and resumed growth. The stem affinities are uncertain, but they resemble coniferophytic gymnosperms, possibly dicranophylls. Stem diameters (N = 135) vary from 1 to 21 cm, with three strongly overlapping size classes. Modern forest studies predict a monotonically decreasing number (inverse square law) of individuals per size class as diameter increases. This is not seen for fossil stems ≤ 6 cm diameter, reflecting biases against preservation, exposure, and observation of smaller individuals. Stems ≥ 6 cm diameter obey the predicted inverse square law of diameter distribution. Height estimates calculated from diameter-to-height relationships of modern gymnosperms yielded heights varying from ~ 0.9 m to greater than 8 m, mean of ~ 3 m. Mean stand density is approximately 2 stems/m2 (20,000 stems/hectare) for all stems greater than 1 cm diameter. For stems greatre than than 7.5 cm or greater than 10 cm diameter, density is approximately 0.24 stems/m2 (2400 stems/hectare) and 0.14 stems/m2 (1400 stems/hectare). Stem spatial distribution is random (Poisson). Mean all-stem nearest-neighbor distance (NND) averages 36 cm. Mean NND between stems greater than 7.5 cm and greater than than 10 cm diameter is approximately 1.02 m and 1.36 m. NND increases in approximate isometry with stem diameter, indicating conformation to the same spatial packing rules found in extant forests and other fossil forests of varying ages. Nearest-neighbor distance distribution passes statistical testing for normality, but with positive skew, as often seen in extant NND distributions. The size-frequency distribution of the stems is similar to those of Jurassic, early Tertiary, and extant woodlands; the early Permian woodland distribution line has the same slope, but differs in that the overall size range increases over time (Cope's rule). The early Permian woodland is self-thinning; its volume versus density relationship shows a self-thinning exponent between − 1.25 and − 1.5, within the range seen in some extant plant stands (− 1.21 to − 1.7).

Broiliellus reiszi: A New Dissorophid Temnospondyl From Early Permian New Mexico

A new dissorophid (Temnospondyli, Dissorophoidea) from the Early Permian of New Mexico (United States)

Authors:

1. Robert Holmes (a)
2. David S. Berman (b)
3. Jason S. Anderson (c)

Affiliations:

a. Department of Biological Sciences, University of Alberta, Alberta T6E 1A2, Canada

b. Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA

c. Faculty of Veterinary Medicine, University of Calgary, 3330 Hospital Drive, Calgary, Alberta T2N 4N1, Canada

Abstract:

An amphibian skull and partial skeleton found from the El Cobre Canyon Formation of New Mexico, USA, is identified as a new species of the dissorophoid temnospondyl genus Broiliellus. Significant anatomical features include: a relatively long, narrow preorbital region, with both nasals and vomers no more than half as wide anteriorly than posteriorly; extended ventral projection of the postorbital; a unilaterally retained lateral exposure of the ectopterygoid (in addition to the normally present lateral exposure of the palatine); supratemporal lacking a semilunar flange; highly vaulted vomers forming a median internasal septum; and an angular with a swollen posteroventral keel. Phylogenetic analysis strongly supports a sister group relationship with Broiliellus brevis and clearly distinguishes it from another dissorophoid, ‘B.’ novomexicanus from New Mexico. The medially restricted supraneural osteoderms are more similar to those seen in Cacops than Broiliellus, which reinforces the importance of avoiding using single ‘key features’ to discriminate taxa.