Marine Sedimentary Cycles of Tertiary in Mississippi Embayment and Central Gulf Coast Area

The principles of marine cyclic deposition are discussed briefly and a classification of marine sedimentary cycles is presented. The principles are applied to the Tertiary section of the Mississippi embayment. Five major marine cycles are differentiated, each representing a major transgression of the sea into this embayment. Facies and thickness distribution of the older Tertiary cycles indicate the presence of a positive area (submarine plateau) in southeast Mississippi, which is bounded on the north and northwest by negative areas (synclines). Isopach studies also show a progressive expansion of this positive area north and northwest during Eocene time, with a corresponding north and northwestward shifting of the bordering synclinal areas. The theory is advanced that the southeast Mississippi plateau constitutes a part of the northern front of the Gulf of Mexico neutral plate, and that its progressive northward expansion is caused by a gradual rise and possible northwestward drift of this plate, in connection with the Tertiary orogenic movements in the Greater Antilles. Epeirogenic movements in the Miss ssippi embayment and its borderlands are considered to be responsible for the different marine transgressions during the Tertiary. These movements reached a climax at the end of Jackson and during early Oligocene time, after which the sea retreated from the Mississippi embayment. Marine deposition during Miocene time is restricted to the Gulf Coast areas with one minor transgression occurring during the deposition of the Heterostegina zone.