The geology of Mississippi includes some deep igneous and metamorphic crystalline basement rocks from the Precambrian known only from boreholes in the north, as well as sedimentary sequences from the Paleozoic. The region long experienced shallow marine conditions during the tectonic evolutions of the Mesozoic and Cenozoic, as coastal plain sediments accumulated up to 45,000 feet thick, including limestone, dolomite, marl, anhydrite and sandstone layers, with some oil and gas occurrences and the remnants of Cretaceous volcanic activity in some locations. Geologic History, Stratigraphy & Tectonics The Black Warrior Basin was the southern margin of the proto-North American continent Laurentia. Precambrian rocks have only been found in a few boreholes in the north of the state, including microperthite granite and a syenite sample dated to 785 million years ago in the Proterozoic. The oldest documented basement granites are 790 million years old and researches Thomas and Osborne, in 1987 found gneiss up to 1.12 billion years old. Paleozoic (539-251 million years ago) During the Ordovician, the 650 foot thick Knox Dolomite, Stones River Group and Nashville Group sediments formed in the shallow marine platform environment of the Black Warrior Basin. Shale, limestone and undifferentiated sediments comprise the Wayne Group and Brownsport Formation from the Silurian, overlain by Devonian chert and the Chattanooga shale. Some Devonian rocks contain trilobite fossils. A number of different formations took shape during the Carboniferous, including the Floyd Shale, intermixed with several different sandstone layers and overlain by the Pottsville Formation. Shallow seas dropped between the Mississippian and Pennsylvanian around 330 million years ago. During the formation of the supercontinent Pangea, sediments in the Black Warrior Basin were uplifted and faulted as the region experienced dry, continental conditions. Mesozoic (251-66 million years ago) The Mississippi Interior Salt Basin underlies southern and west-central Mississippi with up to 3000 feet of Late Jurassic salt and 50 shallow salt domes. It formed during the beginnings of the Gulf of Mexico during the breakup of Pangea. Triassic igneous sills injected into shales in the Black Warrior Basin during the rifting process. Salt deposition ended by 150 million years ago. Mantle upwelling thinned the crust in the Jurassic. In Mississippi, the Smackover Limestone covered over earlier evaporite deposits. A complex stratigraphic sequence formed during the Cretaceous, with the reef limestones, anhydrite and sandstones of the Rodessa Formation, Mooringsport Formation, Paluxy Formation, Gordo Formation and Coker Formation, overlain by the Eutaw Group,