Recent distributary channel-fill deposits (of various sizes) were studied in three mud-rich deltas of the Gulf Coast: the Mississippi, the Colorado-Matagorda, and the Trinity. Although the deltas differ markedly in size, they show similar geomorphology, depositional processes, and patterns of sand accumulation. Data were obtained from 2 major sources: (1) continuously cored borings with electric logs to study the depositional sequence of filled channels, and (2) fathometer surveys to study bed forms in modern channels.

Deposition within distributary channels reflects major depositional stages during the development of the channel. A complete depositional sequence consists, from the base upward, of an active-channel fill (deposited when the channel carried its full flow), a partial-abandonment fill (flow through the channel was reduced), and an abandoned-channel fill (deposited in essentially a still-standing body of water when channel was abandoned).

There is good agreement between cross bedding direction and sand-body elongation, i.e., crossbedding foresets dip downstream parallel with the channel axis. The dip azimuths for accretion beds in the upper part of the channel are too variable in their orientation to be useful trend indicators. The shoestring channel-fill deposits generally trend subnormal to the regional depositional strike, but can show a wide directional scatter.

Because delta channels scour 20-200 ft below sea level, channel-fill sands are commonly positioned stratigraphically lower than their contemporaneous delta-front sands. Although distributary channel-fill and point-bar sands show a similar sedimentary sequence, some sedimentologic and stratigraphic features are helpful in distinguishing the 2 sand types.

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