The Cumberland Marshes in east‐central Saskatchewan, Canada, occupy over 5000 km2 and contain a variety of active and abandoned fluvial features, including straight to sinuous isolated channels, anastomosed channel systems, levees, and crevasse splays in addition to marshes, lakes and bogs. In 1873, an avulsion of the Saskatchewan River diverted most of its flow into a portion of the Cumberland Marshes (locally termed the breakout area), and altered the alluvial terrain as the invaded wetlands adjusted to the influx of sediment and water. These adjustments continue today, and so far over 500 km2 of wetlands have been affected by the avulsion. Avulsion‐controlled modification of the wetlands involves the initiation and evolution of crevasse splays and splay complexes. Three intergradational forms are recognized, each associated with characteristic sand‐body geometries. Stage I splays are small, lobate in plan, crossed by unstable distributary channels, and form wedge‐shaped sheets which depositionally overlie fine‐grained, organic‐rich wetland sediments. Stage II splays and splay complexes evolve both spatially and temporally from Stage I splays. They are larger, contain dense networks of anastomosed channels, and form disconnected tabular sand bodies or continuous sand sheets, some of which incise underlying wetland sediments. Stage III splays develop from either Stage I or II splays and contain few but stable anastomosed channels that deposit isolated stringer sands encased in fine‐grained floodplain sediments. Although sand bodies deposited by splays comprise important components of the evolving floodplain, various fine‐grained facies occurring in levees, shallow lakes, abandoned splay channels, and interchannel floodplains dominate the avulsion deposits. The post‐1873 record of deposition and terrain modification in the breakout area suggests four stages of floodplain evolution following avulsion. In the initial avulsion stage, new channels and splay complexes increase in numbers rapidly as diverted discharge of water and sediment overwhelm the adjacent floodbasin. The anastomosed stage is characterized by an approximate balance between rates of new channel and splay development, and abandonment of old ones. This stage continues for as long as new floodplain areas are invaded. The rate of new splay development eventually decreases as accessible floodplain becomes aggraded, forcing a higher rate of channel abandonment and concentration of remaining flow into fewer but larger channels (reversion stage). The result of reversion is eventual return to a single channel stage, completing the avulsive sequence and initiating a new alluvial ridge. For the Saskatchewan River, this final‐stage single channel will likely produce a meander belt which occupies only a portion of the more extensive avulsion belt which preceded it.

Isotopic labeling of Bombyx mori silk fibroin was achieved biosynthetically using two approaches. First, labeled fibroin was achieved by feeding silk worms [13C1]Gly and [13C1]Ala along with an artificial diet. Second, in vitro production of [15N]Gly and [15N]Ala labeled B. mori silk fibroin was accomplished by culturing the posterior silk glands isolated from five-day-old silkworm larvae in the fifth instar stage. Orientation-dependent 15N and 13C solid-state NMR spectra of these isotope-labeled silk fibroin fibers were observed when the fiber axis was arranged at various angles between 0° and 90° to the magnetic field direction. Such data from the silk II structure was simulated on the basis of the chemical shift anisotropy to determine the Euler angles that relate the principal axis system (PAS) to the fiber axis coordinate system. The dipolar modulated 15N and 13C chemical shift powder pattern spectra of 13C−15N double-labeled silk fibroin model peptides were observed and simulated to determine the Euler angles for transforming the PAS to molecular symmetry axis (MSA) system. The specific orientations of NH, NC1, C1O, and C1N bonds for Ala and Gly residues in the oriented silk fibroin fiber were determined with a combination of these Euler angles. The conformational space for the Ala and Gly residues of the silk fibroin fibers was substantially reduced with these bond orientations and the known Cα ( i - 1)−Cα ( i +1) vector orientation from fiber diffraction studies. The best fit torsion angles (φ,ψ) within the reduced conformational space were determined as (−140°, 142°) and (−139°, 135°), respectively within experimental error (±5°). The distance of the unit cell length determined here results in excellent agreement with the fiber diffraction data.

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