A Probable Neoceratopsian Manus Track from the Nanushuk Formation (Albian, Northern Alaska)

We report a likely neoceratopsian manus track from an exposure of the Nanushuk Formation along the Colville River in northern Alaska. The track described here containts the impressions of five digits, arranged as an arc, which identify this specimen as a manus. Details of the impression suggest that it is neoceratopsian rather than ankylosaurian. The length of the chord of the arc of the track is approximately 25 cm, which is half the size of manus tracks found west of Denver, Colorado, USA attributed to the 10 m long Maastrichtian Triceratops. The Nanushuk Formation is a succession of complexly intertonguing marine and nonmarine strata interpreted as shelf, deltaic, strandplain, fluvial, and alluvial overbank deposits. Deposited in the foreland basin north f the Brooks Range, the rock unit is present throughout most of the northern foothills belt and subsurface of the central and western North Slope coastal plain. Fossil and radiometric data place outcrop within the Albian. If the identification of the track is correct, this is one of the earlies occurrences of neoceratopsians from North America. The occurrence of this track in Alaska substantiates the biogeographic model of faunal exchange between Asia and North America through a Cretaceous land bridge known as Beringia.Presentamos una probable huella de mano atribuida a neoceratopsido de un afloramiento de la Formación Nanushuk a lo largo del río Colville, en el norte de Alaska. La huella descrita contiene la impresión de cinco dígitos, dispuestos en arco, que identifican este especimen como una mano. Los detalles de la impresion sugieren que se trata de un neoceratopsido mas que de un ankilosaurio. La longitud de la cuerda del arco de la huella es aproximadamente de 25 cm, lo cual es la mitad del tamano de las huellas de mano encontradas al oeste de Denver, Colorado, EE.UU, y atribuidas a Triceratops, un taxon de unos 10 m de largo de edad Maastrichtiense. La Formacion Nanushuk es una sucesion de capas de origen marino y no marino complejamente interdigitadas e interpretadas como depósitos de plataforma, deltaicos de playas progradantes, fluviales y de overbank aluvial. Depositada en una cuenca de antepais al norte del Brooks Range, la unidad de roca esta presente a lo largo de la mayor parte de la franja septentrional de colinas, y en el subsuelo de la zona central y occidental, de la llanura costera de North Slope. Los fosiles y los datos radiometricos situan este afloramiento en el Albiense. Si la identificación de la huella es correcta, es una de las apariciones más tempranas de neoceratopsidos en Norteamaerica. La aparición de esta huella en Alaska apoya el modelo biogeográfico de intercambio faunístico entre Asia y Norteamerica a traves de un puente de tierra cretacico conocido como Beringia

Exploring the Law of Detrital Zircon: LA-ICP-MS and CA-TIMS Geochronology of Jurassic Forearc Strata, Cook Inlet, Alaska, USA

Uranium-lead (U-Pb) geochronology studies commonly employ the law of detrital zircon: A sedimentary rock cannot be older than its youngest zircon. This premise permits maximum depositional ages (MDAs) to be applied in chronostratigraphy, but geochronologic dates are complicated by uncertainty. We conducted laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) of detrital zircon in forearc strata of southern Alaska (USA) to assess the accuracy of several MDA approaches. Six samples from Middle–Upper Jurassic units are generally replete with youthful zircon and underwent three rounds of analysis: (1) LA-ICP-MS of ∼115 grains, with one date per zircon; (2) LA-ICP-MS of the ∼15 youngest grains identified in round 1, acquiring two additional dates per zircon; and (3) CA-TIMS of the ∼5 youngest grains identified by LA-ICP-MS. The youngest single-grain LA-ICP-MS dates are all younger than—and rarely overlap at 2σ uncertainty with—the CA-TIMS MDAs. The youngest kernel density estimation modes are typically several million years older than the CA-TIMS MDAs. Weighted means of round 1 dates that define the youngest statistical populations yield the best coincidence with CA-TIMS MDAs. CA-TIMS dating of the youngest zircon identified by LA-ICP-MS is indispensable for critical MDA applications, eliminating laser-induced matrix effects, mitigating and evaluating Pb loss, and resolving complexities of interpreting lower-precision, normally distributed LA-ICP-MS dates. Finally, numerous CA-TIMS MDAs in this study are younger than Bathonian(?)–Callovian and Oxfordian faunal correlations suggest, highlighting the need for additional radioisotopic constraints—including CA-TIMS MDAs—for the Middle–Late Jurassic geologic time scale

Family unity objectives of parents who teach their children: Ideological and pedagogical orientations to home schooling

This article examines parents who teach their children at home. Using the results from two qualitative studies the article suggests, while families have complex motives for teaching their children at home, an important commonality underlies their decision. Regardless of their orientation to home schooling the parents in these two studies felt that establishing a home school would allow them to maintain or further develop unity within the family. The article suggests a family's decision to home school is often made in an attempt to resist the effects on the family unit of urbanization and modernization. The policy implications of this finding are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43875/1/11256_2005_Article_BF01112403.pd

Use of the visual range of detection to estimate effective sweep width for land search and rescue based on 10 detection experiments in North America.

Although additional experiments are required for the medium- and low-visibility search objects and in the dry-domain ecoregion, we suggest search planners use the following correction factors to convert field-measured Rd to an estimate of the effective sweep width (W): high-visibility W = 1.8 × Rd; medium-visibility W = 1.6 × Rd; and low-visibility W = 1.1 × Rd