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 zone of uniformly thinned transitional crust, which is half the typical 40 kilometer thickness of normal continental crust. It was at this time that rifting first created a connection to the Pacific Ocean across central Mexico and later eastward to the Atlantic Ocean. This flooded the opening basin to create the Gulf of Mexico as an enclosed marginal sea. While the Gulf of Mexico was a restricted basin, the subsiding transitional crust was blanketed by the widespread deposition of Louann Salt and associated anhydrite evaporites. During the Late Jurassic, continued rifting widened the Gulf of Mexico and progressed to the