Purpose:
In our study we shall examine slabs of Ordovician sediment and the orientation of the species on them. In our study we hope to determine the relative set and drift of the Ordovician currents and their role in shaping ocean floor life, specifically brachiopods. We feel that this study is important because it assists us in understanding the way the oceans behaved in the past. This allows us to make inferences about the ecosystems and weather during that time period. This information could help in the prediction and understanding of current and future oceanic processes.
Introduction:
During the Ordovician Ohio was covered by a shallow sea and was located near the equator, leaving behind fossiliferous limestone and shale rocks in Southwestern Ohio and surrounding areas. The sedimentary environment during this time was a shallow shelf occupied by diverse and abundant fauna, with associated terrigenous input from the Appalachian Mountains (Hay et al. 1981). Benthic communities at this time would have been affected by prehistoric currents and tides. According to research done by Ross (1975), currents had an affect on trilobite distribution. Krawinkel (1995) also found that, "fossil concentrations can be grouped into fossil concentrations produced by non-turbulent shelf currents…" The currents were also shaped by the benthic communities themselves. In denser communities were growth was abundant a wave-current baffle was produced (Harris and Martin, 1979). We hope to find a relationship between brachiopods and the Ordovician oceanic currents.
Procedure:
We will set a grid in the Liberty formation 120 meters long, selecting slabs at 30 meter intervals from the same bottom middle and top strata of the Brookville Lake Causeway roadcut. On each of the slabs we will record the orientation of the slabs by marking North on them. Then we will measure the size of the species with venire calipers, compass orientation in degrees, and angle of repose with a protractor. For each slab we will create the following spreadsheet from the data and run statistical analyses such as the T-test and P-test to compare the slabs from each strata. From these analyses we hope to determine patterns of the orientation and size distribution of the species on the slabs and draw conclusion from what we find.
Slab #
Slab location
Area of Slab
Species # Occurrence Length Width Orientation Valve Angle of From North Exposed Repose
Species 1
Species 2
Species 3
Species 4
Species 5
Species 6
Predictions:
-We expect to be able to determine the relative set and drift of the currents.
-We expect to find patterns in brachiopod size distribution.
-We expect slower currents to be revealed by smaller species with a concave orientation and with a greater abundance of species.
-We expect to see larger species with a convex orientation and a lower species density to show faster currents.
-We expect to see similarities from slabs taken from the same strata.
-Similarities between slabs of different strata would suggest that the current was constant throughout the Liberty formation where if discontinuity exists, the current was changing through the formation.
Tentative Calendar
We have already collected our slabs and plan to do the initial measurements by next week. The following week we will run our test and begin to draw conclusions from what we find. The week after that we plan to complete our final presentation of our results.
Works Cited
Harris, Frank W. and Martin, Wayne D., 1979 "Benthic Community Development in Limestone Beds of the Waynesville Formation of Southeastern Indiana." Journal of Sedimentary Petrology, Vol. 49, No. 4. P. 1295-1306
Hay, Helen B., Pope, John K., and Frey, Robert C., 1981. "Lithostratigraphy, Cyclic Sedimentation and Paleoecology of the Cincinnatian Series in Southwestern Ohio and Southeastern Indiana." GSA Cincinnati-Field Trip No. 1
Krawinkle, Hannelore, and Seyfried Hartmut. 1996 "Sedimentologic, palaeoecologic, taphonomic and ichnologic criteria for high-resolution sequence analysis: a practical guide for the identification and interpretation of discontinuities in shelf deposits." Sedimentary Geology, 102, 79-110.
Ross, Reuben James Jr. 1975 "Early Paleozoic Trilobites, Sedimentary Faceis, lithospheric plates and ocean currents." Fossils and Strata, n.4 307-329.
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