Much of the oil production in the United States takes place at offshore platforms along the coast of the Gulf of Mexico. Consider the geologic setting of the Gulf Coast, in the context of the theory of plate tectonics, and explain why an immensely thick sequence of sediment accumulated in this region and why so many salt-dome traps formed.

Plate tectonics is a theory explaining the large-scale motion of the Earth's lithosphere. The outer rigid layer of the Earth is divided into several plates that move on the fluid-like asthenosphere. The movement of these plates shapes the Earth's surface with the formation of basins, mountain ranges, volcanoes, earthquakes, and other geological features.

The Gulf of Mexico, located in the southeastern part of North America, is a passive margin that evolved as a result of the breakup of Pangea and the opening of the Atlantic Ocean. The area involves several tectonic plates, including the North American Plate, the Caribbean Plate, and the Cocos Plate.

The immense thickness of sediments in the Gulf Coast region is a result of three significant factors: 1. The existence of the large drainage basin of the Mississippi River system, which transports sediment from the central and eastern parts of North America and results in massive sedimentation in the Gulf of Mexico continental shelf. 2. Tectonic subsidence, due to the weight of the accumulated sediment and the stretching of the lithosphere during the formation of the Gulf of Mexico. 3. Sea-level changes throughout geologic time also contributed to the distribution and accumulation of sediments in the Gulf Coast region.

Salt domes are formed by the rise of buoyant salt through more dense overlying sediments, due to gravitational instability. In the Gulf of Mexico, these salt domes were formed during the Jurassic and Cretaceous periods due to the deposition of massive evaporite deposits, which took place in the restricted basin areas during the evaporation of seawater.

Salt domes play a crucial role in oil and gas production, as they create structural traps where hydrocarbons can accumulate. As salt migrates upward and pierces through overlying sediments, it creates pressure ridges, folds, and faults that can trap hydrocarbons. Furthermore, salt is impermeable, which helps in containing hydrocarbons that have migrated into the surrounding sedimentary layers. By understanding the geological setting of the Gulf Coast in the context of plate tectonics theory and the processes leading to sedimentation and salt dome formation, we can conclude that the Gulf of Mexico's oil-rich region is a result of the unique combination of tectonic activity, sedimentation, and the presence of numerous salt domes that aid in the trapping and accumulation of hydrocarbon deposits.