Mississippi's Geology (Stewart 2003)

At various times in our geologic past, all of the coastal plain and indeed, the alluvial plain, has been under the sea on one or more occasions. The geological materials present on the surface reflect this history of intermittent advances and retreats of ancient seas. Some of these sediments were deposited under marine conditions during periods of inundation (especially notable in northeastern Mississippi). Thus, in some areas, we see outcrops of marl, limestone and even sandstone. Sediment in lower areas were deposited in swamps, along streams, and at the mouths of rivers (deltaic deposits). The so-called Delta region of northwestern Mississippi resulted from centuries of sediment depositions from the deltaic advances of the young Mississippi River into the prehistoric Mississippi Embayment, and from the flow and ebb of the Mississippi and Yazoo rivers as they have seasonally flooded into the lowlands of their floodplains and dropped their sediment loads.

The loess bluffs are believed due to wind transport and deposition of mildly alkaline silts from massive dust storms that occurred at the close of the Pleistocene. The brown loam bluffs form a mantle over the older coastal sediments that are continuous under the floodplains of the "Delta" region. As we travel eastward toward the bluffs from the "Delta", we begin a gentle ascent into rolling, silty foothills that transform in places, abruptly into the steep loess bluffs. The bluffs are thickest on the western edges (90-100 feet or more) and become gradually thinner as we continue to travel eastward away from the bluffs. Highly erodible, the loess region is characterized by a steep and deeply dissected topography that has given rise to highly diverse habitats.

The net result of mostly hydrogeologic processes on the state's landscape, is a complex but orderly arrangement of gravels, sands, silts, clays, and marls. Marine sediments form the bedrock underlying the surface features of Mississippi. For the most part, these sediments are unconsolidated (not cemented together) or poorly consolidated, with the result in Mississippi that there are few beds of hard sandstone and shale (shale is made of clay-sized particles bonded tightly together).

Geology & Geologic Resources
Mississippi has deposits of petroleum, salt, natural gas and low-grade lignite. The state also has deposits of clays (including bentonite), sand and gravel. Here and there, we find a bit of relatively pure limestone. The limestone bluffs under the deep loess along the Yazoo River at Vicksburg were once the site of a thriving portland cement industry, and in fact, cement products are still being produced from marl and limestone deposits in northeastern Mississippi.