Late Ordovician Paleontology, Sedimentology
and Stratigraphy in Ohio, Indiana and Kentucky
A Keck Geology Consortium Project
June 19 - July 16, 1999
Holocene earthquakes of magnitude >5 sometimes cause deformation in unlithified sediments, creating water escape structures, neptunian dikes, sedimentary breccias, recumbent folds, sand blows, ball and pillows, and convolute bedding (Tuttle and Seeber, 1991; Pope et al., 1997). These syndepositional and early postdepositional, seismically-induced liquefaction features are known as "primary seismites." Primary seismites are sediments deformed in situ by a seismic event; secondary seismites are reworkings of older seismite deposits (Pope et al., 1997). Many of the same features diagnostic of primary seismites are, however, also produced by "soft sediment" deformation which is caused by slumping or loading of unlithified sediments (Mills, 1983).
Deformed beds are obvious in the upper Fairview Formation (Upper Ordovician) near Maysville, Kentucky, and have been described by others (Pope et al., 1997). However, new exposures are now found in recent road cuts which have not yet been described. My paper will describe these beds and compare them to descriptions of seismites of different ages, locations, and lithologies outlined in earlier papers on the subject. These include locally common features, such as ball and pillow beds, resedimented breccias, and convolute bedding, as well as rarer features including tilted bedding, intrabed thrust faulting, and flame structures. I will investigate relationships between lithologies and structures, relative frequencies and the possibility that these features are not seismites, but are instead soft sediment deformation structures.
I hypothesize that the structures I have observed in the field are, in
fact, seismites. I also hypothesize that lithology, early cementation, and
stratigraphic relationships are instrumental in the formation of these
structures. These variables dictate not only whether or not deformational
structures form, but also which particular structures form, their resultant
horizontal and vertical extent, the scale of the features, and the
deformation of surrounding beds.
