Three major rivers supply most of the clay-mineral detritus that the northeastern Gulf of Mexico receives. The mineralogy of the clay supplied by each river is a product of the weathering versus parent-rock interplay in the drainage basins. In the western drainage basins, erosion and transportation of essentially unaltered montmorillonitic sediments prevails. Eastward, weathering becomes more effective, and kaolinite gradually becomes more abundant in the soils and river clays. Consequently, the Mississippi River is contributing a montmorillonitic clay-mineral suite, and the Apalachicola River is contributing a kaolinitic suite. The Mobile River, between these two rivers, is contributing an intermediate clay-mineral suite. The river sediments pass through the various bays and estuaries with only minor alterations in their clay-mineral suite which are of too small a magnitude to affect significantly the gross regional distribution pattern.
Within the Gulf of Mexico, that portion of the clay not flocculated by saline water at the river mouths is distributed first by the wind-driven shallow water currents and then by the semi-permanent oceanic currents. A gradational facies pattern is developed in which the sources of supply, their magnitudes, and the distributional directions are clearly evident.
Clay-mineral distributional patterns in the modern Apalachicola River area are similar to those in the Texas lower Eocene (Wilcox) sediments. Similar weathering and current factors may have produced the analogous clay-mineral facies patterns.