The arrangement of sedimentary traits in the birdfoot delta of the Mississippi River is comparable to the structure of a leaf. Present-day facies can be correlated with delta platform deposits obtained from borings. The shape and distribution of sedimentary units, as disclosed from these borings, are shown on maps and sections. Factors controlling delta growth are the load of the river, number of main distributaries of the river, depth of water into which the delta front advances, and subsidence. The rate of lengthening of Southwest Pass, as determined from hydrographic surveys, provides a basis for establishing the rate of bird-foot delta growth and the date when the delta started to form, approaximately 1500 A.D. Since then, nearly 27 cubic miles of sediment have accumulated in the delta platform.

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