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A field of sand dunes was discovered by the side-looking sonars of a deep-towed geophysical instrument package at a water depth of 2.65 km on the north flank of the Carnegie Ridge in the eastern equatorial Pacific. The dunes are moving down the flat floor of an erosional valley that has been excavated through calcareous ooze to a resistant, manganese-encrusted chalk stratum. Transverse dunes (mean wave length 20 m) anc barchans (length 6 to 80 m) are arranged in long, narrow belts. Stereo photographs (875 oriented pairs) of the dunes and of the current-swept rock floor show that average dune height is —0.6 m, the steep (25° to 30°), lee side is generally smooth, and the upstream slope is covered with short-crested current ripples. A core from a transverse dune recovered moderately sorted sand, composed of broken fragments (70 percent) and intact tests of Quaternary age Foraminifera. Photographs and side-looking sonar records both indicate a northwestward, down-valley sediment transport. The dunes are thought to be formed and propelled by fast (>30 cm/sec) currents of dense water, which spill episodically over the Carnegie Ridge into the Panama Basin.

Knik River of southern Alaska is a glacial river with a valley train which was, until recently, swept each summer by a brief large flood resulting from the sudden draining of an ice-dammed lake (Lake George). These flows were 10 to 20 times larger than the postflood summer discharge of approximately 20,000 cfs and were responsible for the morphological and alluvial characteristics of the valley train. Flooding stopped after the 1966 season. During its first 16 mi of travel, where alluvial contamination from side streams is unimportant, the coarse fraction of the valley train changes systematically in size and shape. Grain size decreases by 94 percent, although this figure pertains to two populations: oversized particles and coarse particles which are readily moved by Knik flood flows. If the latter population alone is considered, reduction is 87 percent. At the same time, specimens of quartz and graywacke become progressively more elongated, and foliated specimens show the same change initially, but then deviate to become progressively more platy. Downstream from mile 16, Knik River alluvium is contaminated by detritus from an old outwash fan of the nearby Matanuska River. Sixteen miles of travel in a Kuenen-type abrasion tank reduced the size of Knik River gravel by only 8 percent and failed to change its shape. We conclude that downvalley changes in size and shape of coarse gravel are caused chiefly by sorting processes, aided by frost action which splits foliated particles into platy fragments. During shape-sorting, platy specimens are the most transportable, elongated specimens are intermediate, and compact (equidimensional) specimens are the least transportable. Our data support Russell9s (1939) contention that sorting is favored by aggradation and extreme variations in discharge.

Time-series measurements of bottom currents on the northern Oregon continental shell reveal widely varying speeds with means near 10 cm per sec. Current direction is more constant but often is rotary. Frequency power spectra indicate that generation may be due to internal and surface tides. Measurements of turbidity along four transects and at two time-series stations indicate that suspended material concentrates principally at the seasonal thermocline, at the permanent pycnocline, and at the bottom. Thickness and intensity of the bottom layer vary with both current strength and the amount of fine material in the surface sediment, whereas the intensity of the midwater layer appears to be related to the distance from the sediment source. The midwater layer also increases in vertical extent away from the shore. Seaward transport at the upper two surfaces provides a mechanism by which terrigenous sediment and biogeneous material bypasses the outer continental shelf.

Short oversteepened reaches were molded in the beds of model channels formed in well-sorted, noncohesive sands 0.67 mm and 2 mm in diameter. In each run of the experiment a fall of 0.1 foot in a length of 1.0 foot was provided. The over-all slopes of the channels upstream and downstream from the oversteepened reach were made equivalent and ranged from 0.0012 to 0.0088. The abrupt break in the profile at the head of the over-steepened segment constituted a knickpoint. Progressive changes in the position of the knickpoint and in the slope of the oversteepened reach were measured during runs in which discharge, over-all slope, and particle size were varied independently. I n every run, the slope of the water surface and the slope of the bed below the knickpoint decreased with time. As the knickpoint moved upstream, the channel directly above the knickpoint first steepened and narrowed. Following the initial steepening, the slope became progressively less. At the lower end of the oversteepened reach, sediment eroded from above was deposited as a dune, which advanced downstream and caused the channel to widen and locally to steepen. Following the passage of the dune, the slope again flattened. For runs with identical initial (over-all) slopes, discharge, and widths, the slope below the knickpoint decreased faster in the channel of finer sand. The rate of change of slope in the oversteepened reach below the knickpoint depends upon the magnitude and the rate of change of erosion along this reach which, in turn, depends upon the magnitude and the rate of change of the sediment transport along the reach. If the rate of transport is great, the oversteepened slope below the knickpoint is reduced rapidly. Analysis of the data indicates that the higher the ratio of the oversteepened slope to the average slope the more rapid the rate of decrease of the oversteepened slope. These results are comparable to changes observed in natural stream channels following meander cutoffs. The laboratory experiment confirms the observation that upstream migration of knickpoints accompanied by undiminished slopes does not occur in noncohesive, homogeneous bed material. Several hypothetical cases are discussed in which it is assumed that resistant material is present in the channel profile.

Prograding clastic tidal coastlines in embayed areas, lagoons, and open coasts generate a graded, fining-upward sequence of sediments. This graded sequence is produced by a distinct zonation of sediment transport processes across a clastic intertidal flat. These transport zones are (1) tidal bedload transport (producing subtidal sand), (2) combination of tidal bedload transport and emergence runoff prior to exposure (producing low tidal flat sand), (3) alternation of bedload and suspension sedimentation (producing midflat interbedded sands and muds), and (4) suspension sedimentation (producing high tidal flat muds and clays). The distinction between subtidal and low intertidal flat sands is achieved by identifying sedimentary structures indicating late-stage emergence runoff prior to exposure in the low tidal flat sands. The contact between these two sands, one with and the other without emergence runoff sedimentary structures, coincides with the postion of mean low water. The top of the graded, fining-upward sequence consists of clay-sized sediment and coincides with the level of mean high tide. Such prograded fining-upward sequences contain within them a preserved record of tidal range. In Holocene sediments, the thickness of the interval representing low tidal flat, midflat and high tidal flat sediments coincides with mean tidal range . In fossil equivalents, the thickness of similar sequences gives a quantitative measurement of paleotidal range.

Measurement of more than 1200 cross-beds in lower Pennsylvanian sandstones of the southern Appalachian Mountains reveals a broad pattern of sediment transport to the southwest and west. Most of the sand appears to have been derived from the east and to have moved south-westward parallel to the axis of the Appalachian geosyncline. The pattern has a similar alignment to that in the Illinois basin, but it is at right angles to earlier Paleozoic dispersal directions in the Appalachian geosyncline. Little or no sand has been contributed from the Cincinnati arch. The cross-beds are in sheetlike sandstone formations; the sandstone is conglomeratic, contains plant impressions, and is composed of lenticular, channeling, quartzose sedimentation units. The variation in thickness and lateral persistence of sedimentation units is also reflected in a moderate variability of mean cross-bedding directions between adjacent formations, and even within the same formation. Cross-bedding variability between adjacent units is thought to be due to regional changes in the position and orientation of channel-way systems from deposition of one sandstone formation to the next. Changes of cross-bedding azimuths within the same formation may result from channel curvature of local meanderlike deposits or from channel migration as the sands coalesced into a blanket deposit.

An upland capping of gravel and overlying silt (Pliocene ?) covers approximately 600 square miles of the Coastal Plain of southern Maryland. This sheetlike deposit, which successively overlaps older formations to the northwest, has a fairly constant thickness of 25–30 feet, and dips southeastward at approximately 5 feet per mile. In the northern part of the upland, size and composition of the gravel show orderly changes eastward, which is also the direction of sediment transport as indicated by cross-bedding and gravel fabric. In the southern part of the area, facies changes are less orderly, and pronounced anomalies appear. These anomalies characterize both scalar and vector properties and therefore record a modification in conditions of deposition, probably induced by early Pleistocene climatic changes. The upland deposits are fluvial in origin. They were probably deposited by a graded ancestral eastward-flowing Potomac River which, in the process of lateral corrasion, spread a veneer of channel gravel and flood-plain silt. Later side- and down-cutting combined with a gradual southeastward migration of the river, resulted in the present large, thin gravel sheet.

During experiments on sediment transport and resistance to flow with a uniform 0.33-mm sand, data were recorded on the movement of individual rocks having intermediate diameters from about 0.1 to 0.5 foot. The experiments were conducted in a flume 2 feet wide by 60 feet long and for most runs, depth was held constant at 0.5 foot. The experiments showed that rocks on the sand bed moved downstream consistently only if the flow was in the upper regime—that is, only if the bed forms were plane bed, standing waves, or antidunes. The rocks moved at velocities that were approximately half the average velocity of the water. On all bed forms in the lower flow regime (ripples, ripples superimposed upon dunes, and dunes), the rocks moved upstream and down into the bed. That is, the rocks moved into a scour pocket that formed at the upstream side of the rock. The movement upstream and down into the bed is limited by and approximately equal to the distance below the original rock position of the minimum bed elevation plus approximately half the rock diameter. The data indicate that cross-bedded sand deposits formed by the ripple or dune phases of transport would contain few, if any, pebbles or cobbles. Because the flow, in at least the downstream reaches, of most rivers is in the lower regime, the upstream movement and scour into the bed demonstrated in these experiments is an important factor in the sorting process.

The Platte is a wide, shallow river which flows eastward from the Rocky Mountains across the Great Plains of Nebraska. Its lower reaches carry a dominantly sandy load and during intermediate and low discharges display a pronounced braided character accomplished primarily through dissection of tabular, flat-topped transverse bars. Transverse bars form by sediment aggrading to a profile of equilibrium (Jopling, 1966) and grow by downcurrent extensions of avalanche faces. Depth, velocity, and grain size tend to decrease on active bar surfaces from their upstream mouths to the downstream and lateral margins. Active surfaces are covered with small-scale bed forms whose distributions are controlled by the flow characteristics. A typical mouth-to-margin bed form progression is dunes to diminished dunes to ripples, reflecting downcurrent reduction of stream power. Water-surface slopes over active bars tend to be greater than those of the channel segments which feed them. Under ideal conditions, transverse bars are essentially lobate; however, most bars, especially during low discharges, assume irregular or asymmetrical patterns due to any of several factors that include bar-mouth cross-sectional geometry, proximity to exposed banks, adjacent currents, steadiness of flow, and basin depth distribution. Braiding (bar dissection) begins during decreasing discharges when the flow passing through the bar mouth becomes unable to sustain active sediment transport over the entire bar surface. A single bar, examined closely over a five-day period of gradually decreasing discharge, documents the evolution from wholly active to dissected states.