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 wherein thick Jurassic salts and evaporites could be deposited. These evaporites overlay a thick transitional crust, the local basement rock prior to rifting, and deposition of salts continued over the forming oceanic crust as rifting spread the sea floor throughout the Jurassic. It was during the Jurassic, approximately 140–160 million years ago, that the shape of the Gulf of Mexico as we know it was formed. The unique shape of the Gulf of Mexico, surrounded on all sides by continental crust, is the result of two different tectonic boundaries: an ocean-continent transform boundary, and a magmatic plume fueled seafloor spreading