Department of the Gulf north. On November 3, 1863, the northern boundary was extended to latitude 33° north. On July 25, 1863, the department/district was transferred to the Department of Mississippi and Eastern Louisiana. It remained in that department only until January 28, 1864, when it was transferred to the Department of Alabama and Eastern Mississippi. Upon being transferred, the department/district boundaries were redefined as beginning at the mouth of the Pearl River, running north to latitude 32° north, east to the Georgia State line and south to the Gulf of Mexico. On May 8, 1864, the boundary was again modified to define the
Gulf of Mexico basin 20 kilometers. Beneath the sediments of the Gulf of Mexico basin, most of the pre-Triassic basement rocks are believed to be allochthonous thrust sheets sutured during the formation of Pangaea. However, it was during the break-up of the supercontinent that the foundation for the Gulf of Mexico sediments would be lain. Prior to the rifting which formed the Gulf of Mexico basin, extensional deformation in the Late-Triassic caused by the breakup up of Pangaea, and more specifically the rifting of the Atlantic Ocean, created basement graben formations which filled with terrestrial red bed sediments, and volcanic sediments from the eruption