Molecular systematics of the North American chub genus Macrhybopsis (Teleostei: Cyprinidae)

The North American fish genus Macrhybopsis (Teleostei: Cyprinidae) as presently conceived comprises 12 species and occurs in much of interior eastern North America. Variation in the mitochondrial ND2 gene and the nuclear S7 intron 1 reveal conflicting gene-tree relationships for deeper nodes, which are assumed to represent past introgression and heterospecific mitochondrial fixation. The results support monophyly for the wide-ranging M. aestivalis complex with successive sister relationships to M. gelida, M. meeki, and M. storeriana. The current species-level taxonomy of Macrhybopsis is generally supported. Species status is supported for the morphologically distinct M. australis and M. tetranema, both of which are genetically introgressed by M. hyostoma. The results agree with previous suggestions that the wide-ranging M. hyostoma harbors cryptic species. Similar crypticity is indicated for the poorly sampled M. storeriana; a sample from the Pearl River shows 8% ND2 divergence from two Mississippi River populations. Within the M. aestivalis complex, there are only two examples of geographic overlap among mtDNA phylogroups. One involves co-occurrence of the highly divergent M. marconis and M. cf. hyostoma, and the other is the detection of the apparently anthropogenic occurrence of mitochondrial DNA from a Red River form, either M. cf. hyostoma or M. australis, in the Cimarron River of the Arkansas River basin.

Enigmatic Red Beds Exposed at Point of Rocks, Cimarron National Grassland, Morton County, Kansas

Point of Rocks, a high-relief bluff overlooking the Cimarron River valley in Morton County, Kansas, is capped by distinct white beds of Neogene Ogallala Formation calcrete that overlie red beds of shale, siltstone, and sandstone. These unfossiliferous red beds are currently assigned to the Jurassic System; however, their age has long been debated due to a lack of marker beds, index fossils, and nearby correlative outcrops. As a result, geologists over the years have assigned the rocks to systems ranging from the Permian to the Cretaceous. In this study, four stratigraphic sections were measured in the red beds and three bulk samples were collected to determine the uranium-lead age distributions of detrital zircon (DZ) populations. Red-bed strata composed of fissile shale and sandstone are interpreted as alluvial overbank deposits, while dominantly trough cross-bedded and planar-laminated sandstones are interpreted as tidally influenced fluvial deposits. Detrital zircon age peaks can be grouped into at least seven subpopulations with a youngest single zircon age of 263.8 ± 12.1 Ma, a more conservative age of 293.0 ± 6.95 Ma based on the youngest grouping of three grain ages overlapping at 2σ, and a complete absence of Mesozoic age zircons. In addition, copper oxides along partings and fractures suggest that the red beds once hosted copper sulfides, a common constituent of regional Permian-Triassic red beds. The DZ data--in conjunction with the identification of the Permian Day Creek Dolomite marker bed in logs of nearby drilling tests--strongly suggest that the enigmatic red beds cropping out at the base of Point of Rocks should be assigned to the Guadalupian Big Basin Formation, the uppermost Permian unit in Kansas.

Forces driving late Pleistocene (ca. 77–12 ka) landscape evolution in the Cimarron River valley, southwestern Kansas

This study presents stratigraphic, geomorphic, and paleoenvironmental (δ13C) data that provide insight into the late Pleistocene landscape evolution of the Cimarron River valley in the High Plains of southwestern Kansas. Two distinct valley fills (T-1 and T-2) were investigated. Three soils occur in the T-2 fill and five in the T-1 fill, all indicating periods of landscape stability or slow sedimentation. Of particular interest are two cumulic soils dating to ca. 48–28 and 13–12.5 ka. δ13C values are consistent with regional paleoenvironmental proxy data that indicate the prevalence of warm, dry conditions at these times. The Cimarron River is interpreted to have responded to these climatic changes and to local base level control. Specifically, aggradation occurred during cool, wet periods and slow sedimentation with cumulic soil formation occurred under warmer, drier climates. Significant valley incision (~ 25 m) by ca. 28 ka likely resulted from a lowering of local base level caused by deep-seated dissolution of Permian evaporite deposits.