A NEW TYPE OF CARBONATE SEISMITE AND ITS IMPLICATIONS FOR THE DEPOSITIONAL HISTORY OF THE MIDDLE MISSISSIPPIAN (MERAMECIAN) ST. LOUIS MEMBER OF THE SLADE FORMATION, EAST-CENTRAL KENTUCKY

The St. Louis Member of the Slade Formation in east-central Kentucky is a transgressive carbonate unit composed of three informal subunits, units A, B, and C, which represent progressively deepening-upward conditions, in what is interpreted to be a simple transgressive sequence. Across much of the outcrop belt, however, round to elliptical or elongate bodies of structureless dolosiltite, from a few inches to tens of feet in length, seem to be injected into unit B or between units B and C. The bodies crosscut, deform, and include fragments of the cut units, and some are associated with brittle deformation of overlying and underlying units, all of which suggest that the bodies are seismites related to post-depositional, pre-lithification seismicity. Flow rolls and other soft-sediment deformation abound in seismites, but this may be the first report of apparently foreign material injected into a unit during seismicity, a type of structure that we call injection rolls. The source of the injected muds remained a mystery until one St. Louis section revealed thin, in-place units of dolomitized, lagoonal and intertidal muds between units A and B and B and C, parts of which were in the process of deforming. This find suggests that the St. Louis is not a simple transgressive sequence, but rather a transgressive sequence interrupted by two regressive intervals and that subunit contacts are actually paraconformities, which served to isolated water-saturated muds and make then conducive for later deformation. Hence, injection rolls reflect an unusual synergy between depositional conditions and later seismicity.