Sequence Stratigraphy of the Middle and Upper Ordovician of the Eastern United States
Steven Holland (UGA Stratigraphy Lab) and Mark Patzkowsky (Penn State University) have been reconstructing the sequence stratigraphy and biofacies of the Middle and Upper Ordovician for parts of the eastern United States. The results of these studies are summarized in a correlation chart, available as a pdf. This chart represents a work in progress, and should be viewed as a hypothesis to be tested. The original correlation charts were published in Holland and Patzkowsky (1996), with the Nashville Dome correlations added in Holland and Patzkowsky (1997, 1998). If you have any comments or questions on these charts, send them to Steven Holland at firstname.lastname@example.org.
We have numbered the third-order sequences sequentially, and prefix the numbers by the series in which the sequence starts. So, sequences that begin in the Whiterockian start with W, those that begin in the Mowhawkian begin with M, and those that begin in the Cincinnatian start with C.
The main problem with the numbering scheme is that when new sequence boundaries are found, it may force the renumbering of sequences. For example, originally only five third order sequences were recognized in the type Cincinnatian. An additional third-order sequence boundary was later recognized near the base of the Fairview Formation, within the middle of what was the C1 sequence. As a result, the C1 was split into the C1 and C2 sequences, the former C2 sequence became the C3 sequence, and so on. Such renumberings should not be a problem as long as one always cites the version of a particular chart being used.
If depositional sequences become formalized as part of the North American Stratigraphic Code, we will assign these sequences names, following NASCN procedures.
Our time scale was built in three steps. First, we related our sequence boundaries to Walt Sweet's graphic correlation. The locations of stage boundaries have been identified within the graphic correlation, and many of our sequence boundaries correspond to stage boundaries, so they could be placed within the graphic correlation. Other sequence boundaries were located more approximately within the graphic correlation. Sloan (1987) showed how the graphic correlation scale could be calibrated to the time scale with the radiometric date for the Deicke k-bentonite and by using the age of the Ordovician/Silurian boundary. These dates allow the interpolation of all ages between these two horizons and the extrapolation of ages for horizons below the Deicke. We used a date of 454.2 Ma for the Deicke K-bentonite (Kunk and Sutter, 1984), and an interpolated date of 443.5 Ma for the Ordovician/Silurian boundary (Tucker et al., 1990; Fordham, 1992).
Fordham, B. G. 1992. Chronometric calibration of mid-Ordovician to Tournaisian conodont zones: a compilation from recent graphic-correlation and isotope studies. Geological Magazine 129:709-721.
Holland, S. M., and M. E. Patzkowsky. 1996. Sequence stratigraphy and long-term paleoceanographic change in the Middle and Upper Ordovician of the eastern United States. Pp. 117-130 in B. J. Witzke, G. A. Ludvigsen and J. E. Day, ed. Paleozoic sequence stratigraphy: views from the North American craton. Geological Society of America Special Paper 306, Boulder.
Holland, S. M., and M. E. Patzkowsky. 1997. Distal orogenic effects on peripheral bulge sedimentation: Middle and Upper Ordovician of the Nashville Dome. Journal of Sedimentary Research 67:250-263.
Holland, S. M., and M. E. Patzkowsky. 1998. Sequence stratigraphy and relative sea-level history of the Middle and Upper Ordovician of the Nashville Dome, Tennessee. Journal of Sedimentary Research 68:684-699.
Kunk, M. J., and J. F. Sutter. 1984. 40Ar/39Ar age spectrum dating of biotite from middle Ordovician bentonites, eastern North America. Pp. 11-22 in D. L. Bruton, ed. Aspects of the Ordovician System (Palaeontological Contributions from the University of Oslo 295). Universitetsforlaget, Oslo.
Sloan, R. E. 1987. Black River / Trenton extinction, paleooceanography and chronology of the Middle and Late Ordovician of the Upper Mississippi Valley. Geological Society of America Abstracts with Program 19:246.
Tucker, R. D., T. E. Krogh, R. J. Ross, Jr., and S. H. Williams. 1990. Time-scale calibration by high-precision U-Pb zircon dating of interstratified volcanic ashes in the Ordovician and Lower Silurian stratotypes of Britain. Earth and Planetary Science Letters 100:51-58.