USGS Science⌕ Search

Geology topics

Raymond L. Ethington

Publications and source records attributed to Raymond L. Ethington.

5 recordsLinked to original sources
USGS2016

Proposed Auxiliary Boundary Stratigraphic Section and Point (ASSP) for the base of the Ordovician System at Lawson Cove, Utah, USA

T he 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 13C 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.

Utah↗
USGS2012

Ordovician of the Sauk megasequence in the Ozark region of northern Arkansas and parts of Missouri and adjacent states

Exposures of Ordovician rocks of the Sauk megasequence in Missouri and northern Arkansas comprise Ibexian and lower Whiterockian carbonates with interspersed sandstones. Subjacent Cambrian strata are exposed in Missouri but confined to the subsurface in Arkansas. The Sauk-Tippecanoe boundary in this region is at the base of the St. Peter Sandstone. Ulrich and associates divided the Arkansas section into formations early in the 20th century, principally based on sparse collections of fossil invertebrates. In contrast, the distribution of invertebrate faunas and modern studies of conodonts will be emphasized throughout this chapter. Early workers considered many of the stratigraphic units to be separated by unconformities, but modern analysis calls into question the unconformable nature of some of their boundaries. The physical similarity of the several dolomites and sandstones, complex facies relations, and lack of continuous exposures make identification of individual formations difficult in isolated outcrops. The oldest formation that crops out in the region is the Jefferson City Dolomite, which may be present in outcrops along incised river valleys near the Missouri-Arkansas border. Rare fossil gastropods, bivalves, brachiopods, conodonts, and trilobites permit correlation of the Cotter through Powell Dolomites with Ibexian strata elsewhere in Laurentia. Conodonts in the Black Rock Limestone Member of the Smithville Formation and the upper part of the Powell Dolomite confirm regional relationships that have been suggested for these units; those of the Black Rock Limestone Member are consistent with deposition under more open marine conditions than existed when older and younger units were forming. Brachiopods and conodonts from the overlying Everton Formation assist in interpreting complex facies within that formation and its correlation to equivalent rocks elsewhere. The youngest conodonts in the Everton Formation provide an age limit for the Sauk-Tippecanoe unconformity near the southern extremity of the great American carbonate bank. The correlation to coeval strata in the Ouachita Mountains of central Arkansas and in the Arbuckle Mountains of Oklahoma and to rocks penetrated in wells drilled in the Reelfoot rift basin has been improved greatly in recent years by integration of biostratigraphic data with lithologic information.

Arkansas, Missouri↗
USGS1999

Iapetonudus (N. gen.) and Iapetognathus Landing, unusual Earliest Ordovician multielement conodont taxa and their utility for biostratigraphy

The Early Ordovician (Tremadocian) multielement conodont genus Iapetognathus is one of the oldest denticulate euconodont genera known. The ramiform-ramiform apparatus structure of Iapetognathus is not similar morphologically to other Late Cambrian to Earliest Ordovician denticulate multielement taxa, such as Eodentatus or Cordyloduts, because the major denticulate process has a lateral rather than a posterior orientation as it is in the other two examples. For this reason the genus is believed to have developed from the coniform-coniform apparatus Iapetonudus ibexensis (N.gen., n.sp.) through the development of the denticulate lateral processes. The two genera have a number of morphologic features in common and appear in stratigraphic succession. Iapetognathus aengensis (Lindstro??m) is redefined as a multielement taxon using topotype material and Ig. preaengensis Landing is placed in synonymy with it. Iapetognathus sprakersi, recently described by Landing in Landing and others (1996), is recognized as a multielement species and the new multielement species, Ig. fluctivagus, Ig. jilinensis and Ig. landingi n. spp. are described herein, based on type specimens from Utah (U.S.A.), Jilin (China) and Colorado (U.S.A.) respectively. Iapetonudus and Iapetognathus are important genera in defining the level of the Cambrian-Ordovician boundary. Iapetonudus is currently recognized only from Utah, Texas and Oklahoma, but Iapetognathus is cosmopolitan in its distribution.

Brigham Young University Geology Studies↗