Rocky Mountain Geology最新文献

{"title":"Morphology and taphonomy of an exceptional trackway from the Flathead Sandstone (Middle Cambrian) of Wyoming","authors":"D. W. Boyd","doi":"10.2113/GSROCKY.45.1.23","DOIUrl":"https://doi.org/10.2113/GSROCKY.45.1.23","url":null,"abstract":"Two sandstone slabs from the Cambrian Flathead Sandstone of Wyoming exhibit different preservational modes of an exceptionally large and unusual trackway. On the smaller slab, the trackway is a depression on the top of the bed (concave epirelief). A greater length of the trackway is preserved on the larger slab, where it is a raised feature on the bottom of the bed (convex hyporelief). The latter trace is a cast of the original trackway made on a now-missing mud layer, whereas the epirelief trace likely represents an undertrack. The original trackway consisted of two parallel pockmarked furrows separated by a broad ridge. Individual depressions in furrows cannot be matched across the ridge and do not contain discrete scratch marks. At one place the linear succession of imprints comprising one furrow changes to a scattering of discrete pits. Although taxonomic identity of the trackway’s maker is uncertain, the animal was bilaterally symmetrical and had paired appendages like an arthropod or an onychophoran. The sole of the large slab exhibits several unilobate traces that intersect the major trackway as well as one another. Their smooth surfaces, lack of marginal ridges, and discontinuous nature suggest that they were made by burrowers or furrowers following the sand/mud interface subsequent to casting of the major trackway. Their origin remains problematic.","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"45 1","pages":"23-34"},"PeriodicalIF":0.0,"publicationDate":"2010-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSROCKY.45.1.23","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68309715","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Revisiting the life and scientific reputation of Ferdinand Vandeveer Hayden","authors":"M. Picard","doi":"10.2113/GSROCKY.45.1.73","DOIUrl":"https://doi.org/10.2113/GSROCKY.45.1.73","url":null,"abstract":"Profiles of Rocky Mountain Geologists – a continuing series Hayden annoyed almost everyone he knew at one time or another; he thrived on spiteful controversy. —Mike Foster, 1994, p. 351 At the period of his greatest success Hayden was always the same unpretentious and enthusiastic seeker for knowledge. —Edward Drinker Cope, 1888\u0000\u0000Had Congress created the United States Geological Survey (USGS) in 1877, rather than a year later, Ferdinand Vandeveer Hayden (Fig. 1) would likely have become the first director. He was the favorite. If this had happened, Hayden's reputation and prominence today would be completely different. Figure 1. \u0000F. V. Hayden, about the time of his directorship of the U.S. Geological Survey of the Territories, 1870. Courtesy of U.S. Geological Survey Photographic Library.\u0000\u0000\u0000\u0000By many accounts, Hayden was the most qualified of the principal candidates for the USGS directorship, a group that included Clarence King, John Wesley Powell, and George Montague Wheeler. Congressional support for Hayden's U.S. Geological and Geographical Survey of the Territories, and for Hayden as its leader, was greater than that for the Geological Exploration of the Fortieth Parallel (the King Survey), the Geographical Survey West of the 100th Meridian (under Wheeler, of the U.S. Army's Corps of Engineers), or the Geographical and Geological Survey of the Rocky Mountain Region (the Powell Survey).\u0000\u0000At the time, from his published studies and newspaper stories, Hayden was well known and respected both in the U.S. and in Europe. He managed many people and projects, and he raised the money to keep people in the field and in offices writing their reports, the publication for which he also arranged. During the 25 years or so of his exploration in the American West—up to about 1878—Hayden's publications exceeded in number and were frequently equal to or superior in quality to those …","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"45 1","pages":"73-81"},"PeriodicalIF":0.0,"publicationDate":"2010-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSROCKY.45.1.73","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68309870","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"John Strong Newberry: Pre-Civil War geologic exploration of the Cascade arc and Colorado Plateau","authors":"K. Aalto","doi":"10.2113/GSROCKY.45.1.59","DOIUrl":"https://doi.org/10.2113/GSROCKY.45.1.59","url":null,"abstract":"John Strong Newberry (1822–1892) was trained in medicine but left a successful practice to join three major exploratory expeditions in the American West from 1857–1859, after which he abandoned medicine for paleontology and geology. He was among the first naturalists to study the Cascade Range in California and Oregon and to visit the Grand Canyon region of the Colorado Plateau. His expedition reports provided the stratigraphic and geomorphic foundations for later investigations, including the famous Powell, Hayden, King, and Wheeler surveys of the 1860–1880s, and the pioneering work in the Cascades in the 1880–1890s by Joseph Silas Diller and Israel Cook Russell. Although Newberry’s later career focused on paleobotany, paleontology, and the geology of Ohio, he stands as a pioneer in western geology of the pre-Civil War era.","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"45 1","pages":"59-71"},"PeriodicalIF":0.0,"publicationDate":"2010-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSROCKY.45.1.59","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68309794","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Age and Uranium Content of Detrital Zircon in the Cretaceous to Eocene Strata of the Powder River Basin, Buffalo, Wyoming","authors":"Joseph Speas Wold","doi":"10.2113/35.1.31","DOIUrl":"https://doi.org/10.2113/35.1.31","url":null,"abstract":"Abstract Age and uranium content of detrital zircon in the Cretaceous to Eocene strata of the Powder River basin, Buffalo, Wyoming. Department of Geology, Union College, Schenectady, New York, June 2010. This study addresses changes in sedimentary provenance revealed through the characteristics of detrital zircon during the unroofing of the Bighorn Mountains and the synchronous formation of the Powder River Basin (PRB) in northeastern Wyoming. Detrital zircons from three Mesozoic-Cenozoic sedimentary formations in the PRB and the Cambrian Flathead Sandstone from Alcova Reservoir were evaluated for U/Pb age, uranium content, and grain roundedness. Basement unroofing and uplift of the Bighorns resulted from the Laramide Orogeny that caused differential uplift of Precambrian basement rocks and their overlying strata to form the backbone of the Bighorn Mountains. Detrital zircon from the Cambrian Flathead Formation, Maastrichtian Lance Formation, Paleocene Fort Union Formation, and Eocene Wasatch Formation show up-section changes in U/Pb ages, uranium content, and roundedness. Zircons from the Lance and Fort Union formations are dominated by Cretaceous grains and a wide range of Precambrian grains with ages centered around 1000, 1400, and 1800 Ma. Zircons in the Eocene Wasatch Formation have a very different pattern: approximately 93% are Precambrian with nearly 60% in a cluster around 1800 Ma. Uranium content from the three formations show a decrease up section from the Lance Formation containing the highest mean U concentration (385 ppm), to the Fort Union Formation with (359 ppm), and the Wasatch Formation (267 ppm). These data suggest uplift and erosion of a source rock with abundant Precambrian grains. The high degree of rounding suggests these detrital zircons in the Wasatch Formation are predominantly recycled and not first cycle from the Archean basement. Furthermore, the rounded and recycled Wasatch grains may have significance in the formation of uranium in the PRB due to their susceptibility of dissolution causing roll-front deposits.","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"1 1","pages":"101-120"},"PeriodicalIF":0.0,"publicationDate":"2010-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/35.1.31","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68133136","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The long-term burial and exhumation history of basement blocks in the footwall of the Wasatch fault, Utah","authors":"S. Nelson, R. Harris, B. Kowallis, M. Dorais, K. Constenius, M. Heizler, Daniel E. Barnett","doi":"10.2113/GSROCKY.44.2.103","DOIUrl":"https://doi.org/10.2113/GSROCKY.44.2.103","url":null,"abstract":"Thermochronologic studies of the Santaquin and Farmington Canyon crystalline basement complexes, exposed in the footwall of the Wasatch fault in Utah, provide rare opportunities to investigate the long-term tectonic, burial, and exhumation history of this region. Both complexes underwent amphibolite-facies metamorphism at ∼1700 Ma, followed by a complex pressure-temperature-time history. By 740–770 Ma, exhumation had brought both complexes to the surface from a depth of ∼9–10 km (3–3.5 kbar), followed by reburial by passive margin, Oquirrh Basin, and foreland basin sedimentation from Neoproterozoic through early Cretaceous time.\u0000\u0000The final structural pathway to present-day surface exposure of both complexes began in early Cretaceous time, with crustal contraction along the Sevier belt and resultant structural stacking. Structural breaching of the thrust culminations and final cooling of the crystalline complexes occurred as a result of Tertiary through Holocene extension and accompanying normal faulting.\u0000\u0000Inferred exhumation rates for the last 10–15 my are on the order of 0.3–0.6 mm/yr, although recent slip rates across the Wasatch fault appear to be several times higher. This suggests that: (1) periods of enhanced slip on the Wasatch fault from Miocene to present time may have been punctuated by periods of quiescence; and (2) the fault now may be experiencing an episode of rapid slip. Alternatively, strain may have been partitioned into multiple fault strands at a boundary between the Provo and Nephi segments.","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"44 1","pages":"103-119"},"PeriodicalIF":0.0,"publicationDate":"2009-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSROCKY.44.2.103","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68310068","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural development of high-temperature mylonites in the Archean Wyoming province, northwestern Madison Range, Montana","authors":"K. Kellogg, D. Mogk","doi":"10.2113/GSROCKY.44.2.85","DOIUrl":"https://doi.org/10.2113/GSROCKY.44.2.85","url":null,"abstract":"The Crooked Creek mylonite, in the northwestern Madison Range, southwestern Montana, is defined by several curved lenses of high non-coaxial strain exposed over a 7-km-wide, northeast-trending strip. The country rocks, part of the Archean Wyoming province, are dominantly trondhjemitic to granitic orthogneiss with subordinate amphibolite, quartzite, aluminous gneiss, and sills of metabasite (mafic granulite). Data presented here support an interpretation that the mylonite formed during a period of rapid, heterogeneous strain at near-peak metamorphic conditions during an early deformational event (D1) caused by northwest–southeast-directed transpression. The mylonite has a well-developed L-S tectonite fabric and a fine-grained, recrystallized (granoblastic) texture. The strong linear fabric, interpreted as the stretching direction, is defined by elongate compositional “fish,” fold axes, aligned elongate minerals, and mullion axes. The margins of the mylonitic zones are concordant with and grade into regions of unmylonitized gneiss. A second deformational event (D2) has folded the mylonite surface to produce meter- to kilometer-scale, tight-to-isoclinal, gently plunging folds in both the mylonite and country rock, and represents a northwest–southeast shortening event. Planar or linear fabrics associated with D2 are remarkably absent. A third regional deformational event (D3) produced open, kilometer-scale folds generally with gently north-plunging fold axes.\u0000\u0000Thermobarometric measurements presented here indicate that metamorphic conditions during D1 were the same in both the mylonite and the country gneiss, reaching upper amphibolite- to lower granulite-facies conditions: 700 ± 50° C and 8.5 ± 0.5 kb. Previous geochronological studies of mylonitic and cross-cutting rocks in the Jerome Rock Lake area, east of the Crooked Creek mylonite, bracket the timing of this high-grade metamorphism and mylonitization between 2.78 and 2.56 Ga, nearly a billion years before the 1.78-Ga Big Sky orogeny, which overprinted the basement rocks exposed in adjacent ranges of the Wyoming province.","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"44 1","pages":"85-102"},"PeriodicalIF":0.0,"publicationDate":"2009-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSROCKY.44.2.85","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68309981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural and tectonic evolution of the Douglas Creek arch, the Douglas Creek fault zone, and environs, northwestern Colorado and northeastern Utah Implications for petroleum accumulation in the Piceance and Uinta basins","authors":"J. Bader","doi":"10.2113/GSROCKY.44.2.121","DOIUrl":"https://doi.org/10.2113/GSROCKY.44.2.121","url":null,"abstract":"The Douglas Creek arch is a north–south-trending faulted anticline that separates the Uinta basin of northeastern Utah from the Piceance basin of northwestern Colorado. Previous work indicates that the arch initially formed during the Laramide orogeny as part of a broad, north–south-trending uplift that extended from northwest Colorado into southern Wyoming and included the Rock Springs uplift. The axis of this structure was offset sinistrally and truncated by the late-Laramide uplift of the Uinta Mountains. This study examines available geologic, structure, Bouguer gravity, aeromagnetic, seismic, and paleomagnetic data to investigate this late-Laramide history, as well as indications of younger, post-Laramide tectonic events that have shaped the Douglas Creek arch and environs. This study also uses the existing data to evaluate the genetic relationships between Precambrian basement structures and shallower structures formed in the sedimentary cover.\u0000\u0000Results of this study suggest that a major east–west-oriented structure, the Douglas Creek fault, likely has a Precambrian ancestry and was reactivated during the Phanerozoic. Structures in the study area are consistent with periodic sinistral slip, dominantly along the Douglas Creek fault, most recently during late-Laramide tectonic events. Northwest-striking fractures flanking the Douglas Creek arch and extending into the surrounding basins are likely synthetic strike-slip faults related to a subsequent period of dextral slip on the Douglas Creek fault. This deformation could be the result of the northwest translation of the Colorado Plateau and opening of the Rio Grande rift during post-Laramide Tertiary extension.\u0000\u0000Wrench faulting has created enhanced permeability and numerous structural traps for petroleum accumulation across the Douglas Creek arch and in the surrounding basins. Wrench structures are identified by their distinct geometries, and the origins of their individual features can be discerned using supporting subsurface data. Knowledge of the genesis of the wrench system allows for better understanding of wrench structures and thus a better potential for success in the search for oil and gas.","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"44 1","pages":"121-145"},"PeriodicalIF":0.0,"publicationDate":"2009-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSROCKY.44.2.121","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68309704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Heart Mountain and South Fork fault systems Architecture and evolution of the collapse of an Eocene volcanic system, northwest Wyoming","authors":"E. C. Beutner, T. Hauge","doi":"10.2113/GSROCKY.44.2.147","DOIUrl":"https://doi.org/10.2113/GSROCKY.44.2.147","url":null,"abstract":"Thanks to Anders et al. (this volume) for their attention to the legacy of the late Ed Beutner, and to his and my recent Rocky Mountain Geology paper (Beutner and Hauge, 2009). I make no claim of being able to reply to their comment as aptly as Ed would have, but here I'll try to represent my own perspective (and Ed's, as I recall it) on their remarks.\u0000\u0000Beutner and Hauge (2009) made a case for an early, noncatastrophic phase of displacement along the Heart Mountain (HM) detachment, followed by final catastrophic emplacement of the allochthon. Anders et al. (this volume) argue that this noncatastrophic phase is not supported by the evidence, and they cite both data (calcite twinning; radiometric ages) and models (Aharonov and Anders, 2006) in support of this claim. The models of Aharonov and Anders (2006) and Beutner and Hauge (2009) are fundamentally incompatible because the Aharonov and Anders model requires that the Paleozoic strata of the future allochthon were intact and able to confine pressure that triggered catastrophic failure. In the Beutner and Hauge model, significant extension of the HM allochthon had already taken place when catastrophic failure was triggered. Both models have weaknesses. To varying degrees they require initial conditions that are improbable, explain away conflicting data, inadequately confront alternative models, and make predictions that are not borne out by available data. The resolution of the problems of the initiation, maintenance, and rate of displacement of the HM allochthon has been hampered by the vast scale, rugged terrain, and concealment by younger strata that have made observations difficult. As it has for over a century, the problem remains unresolved.\u0000\u0000### Issues Surrounding Beutner and Hauge's (2009) Comments on Aharonov and Anders (2006)\u0000\u0000The following paragraphs respond directly to the comments of Anders et al. (this volume) in the context of the two competing models.\u0000\u0000Beutner and Hauge (2009) …","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"29 1","pages":"147-164"},"PeriodicalIF":0.0,"publicationDate":"2009-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSROCKY.44.2.147","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68309848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"40Ar/39Ar dates for the Spanish Peaks intrusions in south-central Colorado","authors":"B. Penn, D. Lindsey","doi":"10.2113/GSROCKY.44.1.17","DOIUrl":"https://doi.org/10.2113/GSROCKY.44.1.17","url":null,"abstract":"A diverse suite of spatially and temporally juxtaposed igneous rocks ranging from alkaline lamprophyres to granites intruded south-central Colorado during late Oligocene and early Miocene time. In addition to the stocks of the East and West Spanish Peaks, there are three types of dikes exposed in the region, based on orientation: radial, subparallel (striking approximately east–west), and independent dikes. The most striking features of this area are the numerous dikes radiating out from West Spanish Peak, some rising several tens of meters above the surrounding terrain and discontinuously exposed for tens of kilometers. New results from 40Ar/39Ar dating indicate that magmatism in the Spanish Peaks region began about 26.6 Ma and continued until about 21.8 Ma. Field evidence suggests that the initial intrusions were subparallel alkaline lamprophyre dikes south of the Spanish Peaks. A subsequent period of sub-alkaline magmatism occurred, producing West Spanish Peak (24.6 ± 0.13 Ma), East Spanish Peak (23.9 ± 0.08 Ma), and the radial dikes focused on West Spanish Peak. The final phase of magmatism included subparallel sub-alkaline lamprophyre dikes northeast of the Spanish Peaks. The 40Ar/39Ar results of this study substantiate the intrusive history derived from field relationships and establish the order of intrusion as West Spanish Peak, East Spanish Peak, and radial dikes, respectively. This study has implications for both the timing and style of the initiation of the Rio Grande rift, as well as the petrogenetic relationship between alkaline and sub-alkaline rocks in relatively stable cratonic areas.","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"44 1","pages":"17-32"},"PeriodicalIF":0.0,"publicationDate":"2009-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSROCKY.44.1.17","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68309816","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Framework for stratigraphic analysis of Pliocene fossiliferous deposits at Hagerman Fossil Beds National Monument, Idaho","authors":"D. R. Ruez","doi":"10.2113/GSROCKY.44.1.33","DOIUrl":"https://doi.org/10.2113/GSROCKY.44.1.33","url":null,"abstract":"Hagerman Fossil Beds National Monument (HAFO), Idaho, is internationally significant for the vertebrate fossils from its hundreds of fossil localities spanning more than a million years of the Pliocene. This study establishes the background for comparisons among localities in the Glenns Ferry Formation within HAFO by describing the nature of the fossiliferous deposits, using published data to revise age estimates for HAFO localities, and relating the relative differences in elevation of the fossil-bearing localities to particular time horizons. Fossils from the anthills and blowout localities are considered to be essentially in situ stratigraphically. Species of modern harvester ants do gather fossils from more than the immediate area, but the maximum vertical movement is probably within the resolution of elevation possible at most HAFO localities. The microstratigraphy of blowout localities is described here for the first time, with vertebrate fossils derived exclusively from layers of about 12-cm thickness. Fossils recovered as surface float should be excluded from stratigraphic comparisons. Based on a combination of paleomagnetic and radioisotopic studies, the maximum age for the top of the Glenns Ferry Formation exposed at HAFO is estimated at 3.11 Ma, and the minimum age for the lowermost exposure is estimated at 4.18 Ma. It is improbable that strata of the Glenns Ferry Formation exist at HAFO that are younger than 3.04 or older than 4.29 Ma. Finally, using marker beds and published stratigraphic sections, the differences in elevation needed to compare localities in the Glenns Ferry Formation at HAFO against a generalized composite section are established. Fossil-bearing sites within this framework can be placed in proper stratigraphic context, and faunal change thereby can be evaluated more precisely.","PeriodicalId":34958,"journal":{"name":"Rocky Mountain Geology","volume":"44 1","pages":"33-70"},"PeriodicalIF":0.0,"publicationDate":"2009-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSROCKY.44.1.33","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68309948","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}