ABSTRACT

The most likely fault pattern (north of 36°) is northeast-trending faults about 8 miles apart with some northwest and north-trending faults. Completely concealed faults may be much more abundant (about 3 miles apart). The hypothesis that the Mississippi Embayment "syncline" is a tensional structure is supported by the fact that the cumulative heave on faults appears to be much greater than the stretching necessary to account for the syncline. The rock on either side of the embayment has spread apart a minimum of 195 to 325 feet (60-100 meters) while the center subsided by normal faulting at least 600 feet (185 meters). There may be 75 or more faults across the embayment. Although the rift model can be only partly the explanation for the total embayment depression depth (1800 feet=550 meters) in northwest Tennessee, it is still valid enough to assert that spreading has occurred between the embayment sides (Ozarks and the Highland Rim). The calculated rate of spreading is small, a minimum of 2 and a miximum of 12 feet (0.6 to 3.7 meters) per million years, a rate less than a hundredth of a millimeter per year.