The Global boundary Stratotype Section and Point (GSSP) for the base of the Ordovician System is at the First Appearance Datum (FAD) of the conodont Iapetognathus fluctivagus at Green Point in Newfoundland, Canada. Strata there are typical graptolitic facies that were deposited near the base of the continental slope. We propose establishing an Auxiliary boundary Stratotype Section and Point (ASSP) at the FAD of I. fluctivagus at the Lawson Cove section in the Ibex area of Millard County, Utah, USA. There, strata consist of typical shelly facies limestones that were deposited on a tropical carbonate platform and contain abundant conodonts, trilobites, brachiopods, and other fossil groups. Cambrian and Ordovician strata in this area are ∼5300m thick, with the Lawson Cove section spanning 243m in three overlapping segments. Six other measured and studied sections in the area show stratigraphic relationships similar to those at Lawson Cove. Faunas have been used to divide these strata into 14 conodont and 7 trilobite zonal units. The widespread olenid trilobite Jujuyaspis occurs ∼90cm above the proposed boundary at Lawson Cove; this genus is generally regarded as earliest Ordovician. Rhynchonelliform and linguliform brachiopods are common to abundant and are useful for correlation. The FAD of Iapetognathus fluctivagus and occurrences of Jujuyaspis and the Lower Ordovician planktonic graptolite Anisograptus matanensis all occur within a 2.4m interval of strata at a nearby section. Non-biological correlation tools include a detailed sequence stratigraphic classification and a detailed carbon-isotope profile. Especially useful for correlation is a positive δ13C excursion peak ∼15cm below the proposed boundary horizon. All of these correlation tools form an integrated framework that makes the Lawson Cove section especially useful as an ASSP for global correlation of strata with faunas typical of shallow, warm-water, shelly facies.
|Number of pages||18|
|State||Published - 2015|
Bibliographical noteFunding Information:
J. F. Miller's research was funded by National Science Foundation Grants EAR 8108621, EAR 8407281, EAR 8804352, EAR 0642405 and by several Faculty Research Grants from Missouri State University. R. L. Freeman's research was supported partially by a College Research Activity Award from the University of Kentucky College of Arts and Sciences. J. F. Taylor acknowledges the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research. J. F. Taylor's research was also funded through grants from the National Science Foundation (EAR 9902812), Faculty Professional Development Committee of the Pennsylvania State System of Higher Education, and the Indiana University of Pennsylvania University Senate Research Committee. J. D. Loch acknowledges support from a University of Central Missouri University Research Grant. Jason Miller (Pixelate Photography) took the photos in text-figures 5 and 6. Damon Bassett discussed carbon-isotope stratigraphy with the senior author. John Cutler helped Miller and Evans with fieldwork in the Ibex area for many years. Robert Ganis, Robert Stamm, and Ian Percival reviewed the manuscript and made numerous useful suggestions.
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