Wilson M.A.,U.S. Department of Agriculture |
Indorante S.J.,U.S. Department of Agriculture |
Lee B.D.,University of Kentucky |
Follmer L.,Illinois Geological Survey |
And 6 more authors.
Geoderma | Year: 2010
Fragic soil properties often develop in thin loess units overlying residual parent materials in the midwest USA. Morphologic indicators of these fragic properties are often weakly expressed, making consistent mapping of soils difficult. This study was initiated in a small watershed in Union County, Illinois to determine location and degree of development of fragic materials and fragipans on the landscape. We also sought to assess factors influencing the degree of expression of these features, and document accessory soil properties that reflect the presence of these fragic soil materials. Nine pedons from two catenas were sampled and selected chemical, physical, and mineralogical analyses were conducted. Results indicate that loess thickness across the watershed ranged from about 2 to 4 m. Fragic soil properties were observed in argillic horizons on side slope and head slope geomorphic components at depths ranging from 51 to 111 cm. Depths to horizons meeting fragipan criteria ranged from 140 to 175 cm. Discontinuity between two loess units (Peoria and Roxana Silts) was verified by both particle size analysis (fine:coarse silt ratios, clay-free fine and coarse silt) and magnetic susceptibility. These data suggest that the development of fragic soil properties is not controlled solely by the discontinuity between loess deposits. Fragipans are weakly developed based on rupture resistance, morphological features such as structure, bulk density < 1.5 Mg m- 3, and a uniform depth function of citrate dithionite-extractable Fe. The best developed fragipan occurs where loess is thinner (~ 2 m) overlying less permeable material suggesting that loess thickness does influence degree of development of fragic properties. Horizons above fragipans do have increased kaolinite, a greater noncrystalline proportion of the Fe oxyhydroxides, and redoximorphic features suggesting some perching of water. These features suggest that fragic soil properties and fragipans in these soils, though weakly expressed, impact water movement within landscapes. © 2009.
Goldman D.,University of Dayton |
Bergstrom S.M.,Ohio State University |
Sheets H.D.,Canisius College |
Pantle C.,Illinois Geological Survey
GFF | Year: 2014
The Middle and Upper Ordovician rocks of Baltoscandia have been divided into spatially distinct, composite litho- and biofacies units called confacies belts. The precise regional correlation of outcrops and boreholes, which is necessary for biodiversity analyses, has always been problematic due to the pronounced biogeographical differentiation of macrofossils and horizontal lithofacies changes. We used a computer-assisted numerical sequencing program (CONOP9) to construct a correlation model and composite range chart from the stratigraphic range data of 159 conodont species in 24 boreholes and outcrops in Baltoscandia. We converted the composite section into a timescale in which to calculate the biodiversity, extinction, origination and fossil sampling probabilities through the Ordovician Period. Rates of extinction and origination were calculated using both simple approaches which do not incorporate estimates of sampling probability, and also more complex maximum-likelihood approaches based on Capture-Mark-Recapture (CMR) models. Our data show that overall biodiversity increases steadily from the base of the Paltodusdeltifer Zone to the uppermost Baltoniodusnorrlandicus Zone and then maintains an uneven diversity plateau until the earliest Sandbian. Diversity then declines dramatically throughout the remainder of the Ordovician. CMR analyses suggest that extinction rates remain constant throughout most of the Ordovician indicating that the dramatic late Middle and Late Ordovician decline in conodont diversity in Baltoscandia is attributable to depressed origination. © 2014 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint, 2013.