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The article discusses the development of step-pool bedforms through high flow rates and high sediment influx and transport rates in the U.S. It notes that step setting events are responsible in mobilizing and rearranging the large step-forming grain sizes. Laboratory experiments are conducted and result shows that step bedforms are created during the flow movement of large, step-forming clasts. During the experiment, several step formations are proposed including particle cluster, migrating hydraulic jump, cascade, antidune and scouring formation models.

Channel-scale sedimentary units associated with bedrock-controlled riffle-pool morphology are examined in detail along Sandy Creek gorge, an ephemeral stream in arid south-eastern central Australia. Pool-fills comprise cut-and-fill assemblages of poorly sorted sediments ranging in texture from muds to boulders. Five unit types are defined based on particle size, sedimentary structures, geometry and bounding surface character: (1) coarse-grained bar platform; (2) fine-grained bar supraplatform; (3) fine-grained pool-fill; (4) fine-grained bench; and (5) modern pool-fill. The last coarse-grained unit currently lining the pools suggests an altered sedimentation style over the post-settlement period (post-ad 1860s). Situated at bedrock valley constrictions, pool-fills are compared with other sedimentary units associated with recirculating currents: eddy bars and slackwater deposits. But only the fine-grained bench units reflect eddy recirculation; the pool-fills are principally forced-bars associated with bedrock-controlled or‘forced’ riffle-pool morphology. A late Holocene palaeoflood history is proposed based on radiocarbon ages from the pool-fills: multiple phases of cut-and-fill activity were preceded by a superflood 3400–1900 years ago that eroded the pool-fills to bedrock. The resilience of the pool-fills was illustrated by the passage of a 1-in-100-year flood in 1992, which caused only minor erosion. The presence of pool-fills may provide a window to past phases of river activity that cannot be extracted from either historical records/observations or palaeoflood slackwater sediment analyses. The formation and sedimentary preservation potential of these landforms reflect a combination of hydraulic and structural influences, but the occurrence of high-magnitude floods exerts the dominant control. [ABSTRACT FROM AUTHOR]

Fine sediment deposition in the ocean is complicated by the cohesive nature of muds and their tendency to flocculate. The result is disaggregated inorganic grain size (DIGS) distributions of bottom sediment that are influenced by single-grain and floc deposition. This study outlines a parametric model that characterizes bottom sediment DIGS distributions. Modelled parameters are then used to infer depositional conditions that account for the regional variation in the grain sizes deposited by turbidity currents on the Laurentian Fan–Sohm Abyssal Plain, offshore south-eastern Canada. Results indicate that, on the channellized Laurentian Fan, the mass fraction of floc-deposited mud increases only slightly downslope. The small evolution in this fraction arises because sediment concentration and turbulent energy are associated in turbidity currents. On the Sohm Abyssal Plain, however, the mass fraction of floc-deposited mud decreases, probably as a result of lower sediment concentration at this source-distal site. Estimates of the mass fraction of mud deposited as flocs suggest that floc deposition is the dominant mode by which sediment is lost from suspension, although single-grain deposition contributes more to the depositional flux in proximal areas where high energy breaks flocs and in distal areas where low sediment concentration limits floc formation. It is concluded that, throughout the dispersal system, changes in the fraction of flocculated mud deposited from turbidity currents reflect changes in sediment concentration and energy downslope. [ABSTRACT FROM AUTHOR]

The observed size in the thin-section is less than the true train sizes of the clastic rock as the thin-section plane does not necessarily pass through the centre of gravity of the grains. Correction factors based on probability theory give corrected arithmetic moments of the size distribution in the elastic rock from the observed arithmetic moments of the size distribution in the thin-section. The corrected arithmetic moments so obtained are transformed to their equivalent corrected phi moments which are useful to generate the unknown size distribution of the clastic rock by the help of Edgeworth's series. [ABSTRACT FROM AUTHOR]