The Gulf of Mexico did not exist 250 million years ago when there was but one supercontinent, Pangea. As Pangea split apart, the Atlantic Ocean and Gulf of Mexico opened. Louisiana slowly developed, over millions of years, from water into land, and from north to south.[7] The oldest rocks are exposed in the north, in areas such as the Kisatchie National Forest. The oldest rocks date back to the early Tertiary Era, some 60 million years ago. The history of the formation of these rocks can be found in D. Spearing's Roadside Geology of Louisiana.[11]
Main article: Mississippi River Delta
The youngest parts of the state were formed during the last 7,500 years as successive deltas of the Mississippi River: the Maringouin, Teche, St. Bernard, Lafourche, the modern Mississippi, and now the Atchafalaya.[12] The sediments were carried from north to south by the Mississippi River.
In between the Tertiary rocks of the north, and the relatively new sediments along the coast, is a vast belt known as the Pleistocene Terraces. Their age and distribution can be largely related to the rise and fall of sea levels during past ice ages. In general, the northern terraces have had sufficient time for rivers to cut deep channels, while the newer terraces tend to be much flatter.[13]
Salt domes are also found in Louisiana. Their origin can be traced back to the early Gulf of Mexico, when the shallow ocean had high rates of evaporation. There are several hundred salt domes in the state; one of the most familiar is Avery Island.[14] Salt domes are important not only as a source of salt; they also serve as underground traps for oil and gas.[15]
