Paleontology in Louisiana
In part, this is because Louisiana’s semi-humid climate results in the rapid weathering and erosion of any exposures and the growth of thick vegetation that conceal any fossil-bearing strata.
In addition, Holocene alluvial sediments left behind by rivers like the Mississippi, Red, and Ouachita, as well as marsh deposits, cover about 55% of Louisiana and deeply bury local fossiliferous strata.
While fossils of this age have been found within the region encompassed by the state's modern borders, they originated elsewhere and were incorporated as clasts in much younger rock and are therefore not informative about the wildlife of Paleozoic Louisiana.
[1] Louisiana remained completely underwater until the mid-Mississippian, when continental drift began to slowly reunite the northern and southern landmasses into Pangaea.
Pangaea itself began to break up early in the Mesozoic, separating North America from the other continents and forming the Gulf of Mexico.
Such remains and the Natives' mythological interpretations had already caught the attention of scientists like Georges Cuvier by the mid-1700s, which highlights Louisiana's long history of paleontology.
Much of the geology underlying the Louisiana area was detached from Laurentia in the process, and the Precordillaria terrane was shifted by plate tectonics until it collided with and attached to what is now Argentina.
The Iapetus continued to submerge Louisiana between Early Cambrian to Middle Mississippian times, eventually becoming a body of water known as the Rheic Ocean.
Oceanic crust, island arcs, and trenches that formed and sediments that accumulated during this period have largely been consumed by subduction.
During the collision between these continents, the remaining, small portion of oceanic crust and overlying sediment were shoved northward by Gondwana and incorporated into the Ouachita Mountains within Arkansas and Oklahoma during the Late Mississippian to the Early Pennsylvanian times.
During the Middle Pennsylvanian, Permian, and Triassic, the region of Louisiana consisted entirely of dry land underlain by Gondwana-derived crust as part of the newly formed supercontinent of Pangea.
By the end of the Early Cretaceous, the combination of deposition and subsidence had created the modern morphology of the Gulf of Mexico basin.
[7] Exposures of rocks older than Upper Cretaceous are lacking within the borders of Louisiana so that is when the local fossil record began.
[8] The rocks containing Cretaceous fossils are exposed only in small areas lying directly over the Protho and Rayburn salt domes in northwest Louisiana where they have been displaced from deep in the subsurface.
[8] Since the beginning of the Cenozoic, the shoreline of the Gulf of Mexico has shifted back and forth across Louisiana in response to sea level fluctuations, sediment accumulation, and tectonic subsidence.
Research by Judith Schiebout has recovered a rich fauna, including numerous taxa of fossil vertebrates, from caliche conglomerates from this unit.
[15] Terrestrial invertebrates included snails, who were preserved in the loess that blankets the uplands bordering either side of the Mississippi River Valley.
[19] The bones of Pleistocene megafauna, including mastodons, sometimes are found during the excavation of loess for fill or the construction of roads or buildings.
[21] The Cane River Site is a low road-side cut made doing the construction of Interstate Highway 49 near Natchitoches, Louisiana.
