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“Coarsening upward” successions typical of subtidal sand bars have been recognised in the NE-trending linear sandstone bodies which occur within marine shale in the Eze-Aku Formation (Upper Cretaceous) of southeastern Nigeria. The ideal succession, 15–20 m thick, consists of the following units from bottom to top: (1) bioturbated grey siltstone (offshore mud); (2) wave-ripple-laminated, fine-grained well-sorted sandstone (offshore sands); (3) trough and tabular, cross-bedded medium-grained sandstone with channelled base (subtidal channel complex); (4) trough cross-bedded, medium-grained sandstone with bimodal-bipolar paleocurrent pattern (subtidal bar); (5) coarse, pebbly trough cross-bedded sandstone with wave-rippled top, rare burrows and a bimodal-bipolar paleocurrent pattern (subtidal bar). A sixth facies, not a part of the normal sequence, consists of coarse, carbonate-cemented pebbly sandstone grading into pure shell-limestone (bar margin). The sand bars seem to have grown on a shallow mud-bottomed, wave-worked inland sea inhabited by burrowers. A model for the stages of the vertical growth of the bar is presented.

Ancient turbidites have mostly been described from flysch sequences. This paper deals with an occurrence of non-flysch turbidites from ancient glacial-lake sediments belonging to the Talchir formation (upper Carboniferous) of the Raniganj coalfield, India. The turbidites occur, punctuating a long sequence of glaciolacustrine shales and siltstones, as sandy inter-beds, usually 40-50 cm. thick, having a graded base (often sole-marked) and laminated top with slump structures and parallel, current-ripple, and convolute laminations. The glaciolacustrine sediments also contain varve-like rhythmites containing current-generated structures like current-ripple laminations and sole marks in the sand laminae. These are also believed to have been deposited by turbidity currents. A number of pebbly mudstones, interbedded with the turbidites and the rhythmites, have been interpreted as deposits made by high-density turbidity currents. Available evidence shows that the oversteepened and overloaded front of an outwash de...

Sediments and bed forms from three braided outwash plains and one steep non-braided mountain stream in the Rocky Mountains of Alberta are compared to sediments and structures exposed in a paleo-outwash sequence.Channel sediments are subdivided into (a) pool facies: ripple- and parallel-laminated silty sand, with current crescents around isolated stones; and (b) riffle facies: parallel-stratified gravel and silt or silty sand.'Transverse ribs' constitute a bed form typical of riffle portions of channels. This bed form occurs as a train of regularly spaced pebble, cobble, or boulder ridges oriented transversely to the flow. Locally, the pebbly ribs are separated by, and rest on, a stone-free silty substratum. It is suggested that transverse ribs constitute a common equilibrium bed form in higher gradient riffle portions of gravelly alluvium.Longitudinal bars dominate interchannel areas of the modern outwash plains. They consist of coarse, poorly sorted gravel, either massive or exhibiting crude horizontal stratification. The paleo-outwash, composed of finer-grained and better sorted gravel, is characterized by sets 5 to 30 cm thick of cross-stratified sand and by sets 75 to 82 cm thick of cross-bedded pebble gravel. These may be related to progradation of dunes and bars, respectively.Standard deviations of channel azimuths in modern outwash plains are appreciably less than that recorded by cross-stratification measurements in the time-transgressive sequence of paleo-outwash. This is partly due to the braided system of channels having swept from side to side across the plain through time.

Experiments have been carried out in a circular flume in which silt-sized sediments were allowed to be deposited from a decelerating suspension current of density between 1.044 to 1.013. The sediment was first thrown into complete suspension at a high flow speed. An instantaneous deceleration caused rapid deposition of a graded bed. Depending on the rate of subsequent deceleration, various kinds of incomplete Bouma-type sequences were produced. Slow deceleration produced the following sequence (bottom upwards): graded bed-parallel laminae-ripple laminae--sinusoidal ripple laminae-suspension blanket. Moderate deceleration produced a similar sequence but without sinusoidal ripple laminae. Rapid deceleration caused deposition of a graded bed followed by parallel lami ae and topped by a suspension blanket. Very rapid deceleration produced a single graded bed with a suspension blanket on top. When the speed was decreased gradually, no graded bed was formed. Instead, the sequence produced was either, (1) upstream-dipping laminae (antidune cross-stratification)--ripple laminae-suspension blanket or, (2) parallel laminae-ripple laminae-suspension blanket. It was noted that the celerity of ripple and the upward building rate of the deposited layer were functions of the rate of deceleration. Average grain size and sorting of the deposit were also found to be affected by varying deceleration.

Sedimentary differentiation is defined here as the process by which initially heterogeneous mixtures of sediments are split into diverse end products with different textural and mineralogical composition. The study of a suite of arkosic sandstones from the Barakar Formation (Lower Permian) of the South Karanpura coalfield, India reveals distinct linear trends of textural evolution when the grain-size-distributions of the sandstones are treated as three-component systems and plotted on triangular diagrams. Similar linear trends of mineralogical evolution are revealed when their compositions are plotted on a quartz-feldspar-clay triangle. The size triangle shows two converging linear trends, one ranging from a poorly-sorted gravel-sand-clay mixture to a well-sorted coarse sand and the other ranging from a poorly-sorted sand-silt mixture to the same coarse sand end member. The composition triangle again shows two clearly separated linear trends, one starting from a quartz-clay mixture and ending in the pure quartz end (orthoquartzite). The other starts from a quartz-feldspar-clay mixture and ends in a quartz-feldspar mixture (arkose). In both the cases the maturity of the sandstones increases from one end to the other by gradual elimination of clay. From the above data, and a few other observations the entire history of the sediments from the source rock to the final lithology of the sedimentary rock has been traced.