6 research outputs found
The Effect of Storage on the Infectivity and Parasitic Development of Third-stage Haemonchus contortus Larvae in Sheep
Characterization of hardâtoâdifferentiate dune stratification types in the Permian Coconino Sandstone (Arizona, USA)
Dune stratification types, which include grainfall, grainflow and ripple lamination, provide a record of the fineâscale processes that deposited sediment on palaeoâdune foresets. While these facies are relatively easy to distinguish in some crossâbedded sandstones, for others â like the Permian Coconino Sandstone of northern and central Arizona â discrete stratification styles are hard to recognize at the bedding scale. Furthermore, few attempts have been made to classify fineâscale processes in this sandstone, despite its renown as a classic aeolian dune deposit and Grand Canyon formation. To interpret depositional processes in the Coconino Sandstone, crossâbed facies were characterized using a suite of sedimentary textures and structures. Bedding parameters were described at multiple scales via a combination of field and laboratory methods, including annotated outcrop photomosaics, strike and dip measurements, sandstone disaggregation and laserâdiffraction particle analysis, highâresolution scans of thin sections, and scanning electron microscopy. Crossâbeds were observed to be laterally extensive alongâstrike, with most dip angles ranging from the midâteens to midâtwenties. While some crossâbed sets are statistically coarser near their bases, others exhibit no significant vertical sorting trends. Both massive and laminated textures are visible in highâresolution scans of thin sections, but laminae contacts are commonly indistinct, making normal and reverse grading difficult to define. Diagenetic features, such as stylolite seams and large pores, are also present in some samples and might indicate alteration of original textures like detrital clay laminae and carbonate minerals. Observed textures and sedimentary structures suggest that the crossâbeds may consist of grainflow and grainfall deposits, but these remain difficult to differentiate at outcrop and thinâsection scales. This characterization of fineâscale processes will play a critical part in the development of depositional models for the Coconino Sandstone and elucidate interpretations for similar crossâbedded formations
Depositional history of a Mississippian crinoidal mound on the east flank of the Illinois basin
Potassium cycling and losses in grassland systems:a review
Cycling of potassium in grassland systems has received relatively little attention in research and practice in recent years. Balanced nutrient systems require consideration of nutrients other than nitrogen (N). Potassium (K) is needed in large amounts and is closely related to N nutrition. In intensive dairy farming, surpluses of K arise from the input of concentrates and fertilizer and are returned to the grassland and may lead to increasing K content in the soil. Organic farming, on the other hand, is characterized by limitations in input of nutrient sources and quantities. Leaching of K from grassland is usually low, but high levels of available soil K, high K input from fertilizer or at urine patches lead to increasing losses. High K inputs have a negative influence on Mg and Ca uptake by plants and can cause accelerated leaching of these cations. High levels of K have been associated with inducing nutrition-related dairy cow health problems such as milk fever (hypocalcaemia) and grass tetany (hypoinagnesaemia). This review gives an overview of the cycling of potassium and related cations in grassland systems especially with regard to leaching losses and identifies limitations to knowledge