New U–Pb constraints identify the end-Guadalupian and possibly end-Lopingian extinction events conceivably preserved in the passive margin of North America: implication for regional tectonics

2016 ◽  
Vol 155 (1) ◽  
pp. 119-131 ◽  
Author(s):  
V. I. DAVYDOV ◽  
J. L. CROWLEY ◽  
M. D. SCHMITZ ◽  
W. S. SNYDER
Keyword(s):  
North America ◽  
Volcanic Ash ◽  
New Age ◽  
Passive Margin ◽  
Cool Water ◽  
Extinction Event ◽  
Stratigraphic Position ◽  
Extinction Events ◽  
Phosphoria Formation ◽  
Regional Tectonics

AbstractThe discovery and dating of a volcanic ash bed within the upper Phosphoria Formation in SE Idaho, USA, is reported. The ash occurs 11 m below the top of the phosphatic Meade Peak Member and yielded a 206Pb/238U date of 260.57 ± 0.07 / 0.14 / 0.31 Ma, i.e. latest Capitanian, Guadalupian. The stratigraphic position of this ash near the top of the Meade Peak phosphatic Member of Phosphoria Formation indicates plausible completeness of the sedimentation within the Guadalupian–Lopingian and probably at the Permo-Triassic (P-T) transitions. The new radiometric age reveals that the regional biostratigraphy and palaeontology of Phosphoria and Park City formations requires serious reconsideration, particularly in cool water conodonts, bryozoans and brachiopods. The new age proposes that the Guadalupian–Lopingian boundary (GLB) coincides with the Meade Peak – Rex contact and consequently with the end-Guadalupian extinction event. The lack of a major unconformity at the P-T transition suggests that the effects of the Sonoma orogeny were not as extensive as has been assumed.

New age constraints on the Late Cretaceous lower Williams Fork Formation, Coal Canyon, Colorado

2021 ◽  
Vol 58 (1) ◽  
pp. 5-26
Author(s):  
Jordan T. Walker ◽  
Andres Aslan ◽  
Rex D. Cole ◽  
Michael T. Heizler
Keyword(s):  
Late Cretaceous ◽  
Volcanic Ash ◽  
New Age ◽  
Piceance Basin ◽  
Weighted Mean ◽  
Analytical Uncertainty ◽  
Marine Strata ◽  
Williams Fork ◽  
Williams Fork Formation ◽  
Stratigraphic Position

The precise age of terrestrial sediments in the Late Cretaceous Williams Fork Formation of western Colorado is poorly constrained due to a paucity of radiometric data. Sanidine and zircon dating of a volcanic ash encased in coal (i.e., the Coal Canyon ash) within the Cameo-Wheeler coal zone of the lower Williams Fork Formation in Coal Canyon, Colorado provides an important new age constraint for the southwestern Piceance Basin. A 10-30 cm thick, light gray, clayey mudstone encased in coal was sampled for both zircon U-Pb and sanidine 40Ar/39Ar geochronology. The presence of numerous euhedral zircon crystals, a lenticular geometry, and a clayey texture suggest that the mudstone is a minimally reworked and slightly altered volcanic ash. Analysis of the euhedral zircon crystals (n=108) in the ash produced a statistically robust U-Pb date with 93 grains yielding a weighed mean age of 74.52 ±0.11 Ma (1σ analytical uncertainty). 40Ar/39Ar sanidine analyses yielded a younger weighted mean age of 73.10 ±0.12 Ma (1σ analytical uncertainty) based on 6 of the 36 grains analyzed. Our preferred age is given by the weighted mean age of the sanidine as it is based on higher precision analyses that can better discriminate older inherited grains that are likely included in the zircon mean-age calculation. Isotopic data for the Coal Canyon ash overlap in age with a K-Ar date of 72.5 ±5.1 Ma for a widespread Williams Fork Formation tonstein, known as the Yampa Bed, found in coal-bearing outcrops and mine workings throughout the northern Piceance and Sand Wash basins and Axial Basin Uplift. Based on the similarity in isotopic age, sedimentologic context and stratigraphic position, we suggest that the Coal Canyon ash and the regionally extensive Yampa Bed are coeval. Additionally, this correlation corroborates that the Cameo-Wheeler coal zone of the Williams Fork Formation in the southwestern Piceance Basin is correlative with the Middle coal zone of the Danforth Hills and Yampa regions. Lastly, this proposed correlation may suggest that the Coal Canyon ash, like the Yampa Bed, correlates with the Baculites reesidei ammonite zone, which is associated regionally with a bentonite dated to 72.94 ±0.45 Ma. Detrital sanidine geochronology of two lower Williams Fork sandstone units that overly the Coal Canyon ash did not produce grains younger than the ash and thus do not quantitatively improve the chronostratigraphy of these specific units. Lastly, the Coal Canyon ash date serves as a basis for future evaluations of the diachroneity of non-marine strata of the Williams Fork Formation.

Geographic variation in turnover and recovery from the Late Ordovician mass extinction

Paleobiology ◽  
2007 ◽  
Vol 33 (3) ◽  
pp. 435-454 ◽  
Author(s):  
Andrew Z. Krug ◽  
Mark E. Patzkowsky
Keyword(s):  
Mass Extinction ◽  
Late Ordovician ◽  
Mass Extinctions ◽  
Climatic Fluctuations ◽  
Extinction Rates ◽  
Large Size ◽  
Extinction Event ◽  
Global Extinction ◽  
Rate Of Recovery ◽  
Extinction Events

AbstractUnderstanding what drives global diversity requires knowledge of the processes that control diversity and turnover at a variety of geographic and temporal scales. This is of particular importance in the study of mass extinctions, which have disproportionate effects on the global ecosystem and have been shown to vary geographically in extinction magnitude and rate of recovery.Here, we analyze regional diversity and turnover patterns for the paleocontinents of Laurentia, Baltica, and Avalonia spanning the Late Ordovician mass extinction and Early Silurian recovery. Using a database of genus occurrences for inarticulate and articulate brachiopods, bivalves, anthozoans, and trilobites, we show that sampling-standardized diversity trends differ for the three regions. Diversity rebounded to pre-extinction levels within 5 Myr in the paleocontinent of Laurentia, compared with 15 Myr or longer for Baltica and Avalonia. This increased rate of recovery in Laurentia was due to both lower Late Ordovician extinction rates and higher Early Silurian origination rates relative to the other continents. Using brachiopod data, we dissected the Rhuddanian recovery into genus origination and invasion. This analysis revealed that standing diversity in the Rhuddanian consisted of a higher proportion of invading taxa in Laurentia than in either Baltica or Avalonia. Removing invading genera from diversity counts caused Rhuddanian diversity to fall in Laurentia. However, Laurentian diversity still rebounded to pre-extinction levels within 10 Myr of the extinction event, indicating that genus origination rates were also higher in Laurentia than in either Baltica or Avalonia. Though brachiopod diversity in Laurentia was lower than in the higher-latitude continents prior to the extinction, increased immigration and genus origination rates made it the most diverse continent following the extinction. Higher rates of origination in Laurentia may be explained by its large size, paleogeographic location, and vast epicontinental seas. It is possible that the tropical position of Laurentia buffered it somewhat from the intense climatic fluctuations associated with the extinction event, reducing extinction intensities and allowing for a more rapid rebound in this region. Hypotheses explaining the increased levels of invasion into Laurentia remain largely untested and require further scrutiny. Nevertheless, the Late Ordovician mass extinction joins the Late Permian and end-Cretaceous as global extinction events displaying an underlying spatial complexity.

Volcanoes of the passive margin: The youngest magmatic event in eastern North America

Geology ◽  
2014 ◽  
Vol 42 (6) ◽  
pp. 483-486 ◽  
Author(s):  
Sarah E. Mazza ◽  
Esteban Gazel ◽  
Elizabeth A. Johnson ◽  
Michael J. Kunk ◽  
Ryan McAleer ◽  
...  
Keyword(s):  
North America ◽  
Passive Margin ◽  
Eastern North America ◽  
Magmatic Event

Biogeographic shifts in a transgressive succession: the Cambrian (Furongian, Jiangshanian; Latest Steptoean–earliest Sunwaptan) agnostoid arthropodsKormagnostellaRomanenko andBiciragnostusErgaliev in North America

2013 ◽  
Vol 87 (5) ◽  
pp. 804-817 ◽  
Author(s):  
Stephen R. Westrop ◽  
Jonathan M. Adrain
Keyword(s):  
New Species ◽  
North America ◽  
Sea Level Rise ◽  
Sea Level ◽  
Local Extinction ◽  
Faunal Turnover ◽  
Upper Cambrian ◽  
Extinction Event ◽  
Stratigraphic Interval

The first records of the upper Cambrian agnostoid generaKormagnostella, E. Romanenko,inRomanenko and Romanenko, 1967, andBiciragnostusF. Ergaliev,inEraliev and Ergaliev, 2001, in Laurentian North America are from a narrow stratigraphic interval in the Steptoean–Sunwaptan boundary interval (Furongian, Jiangshanian) of Nevada and Utah. In Nevada, both genera occur in a condensed bioclastic lag below a major flooding surface, andKormagnostellaalso appears in a transgressive interval in Utah. Immigration of these genera is associated with sea level rise, and also with faunal turnover.Biciragnostusis confined to the latestElviniaZone, immediately below the onset of a trilobite and agnostoid extinction event at the base of theIrvingella majorZone (basal Sunwaptan).Kormagnostellais present in the latestElviniaZone, and has its highest occurrence in theI. majorZone. Stratigraphic data from the Karatau-Naryn Terrane, Kazakhstan indicate that both genera disappear near the local extinction ofIrvingella, suggesting that faunal turnover in that region may have been broadly correlative with the more profound extinction in Laurentia. New species areKormagnostella advena,K. insolitaandBiciragnostus viator.

scholarly journals Identifying the most surprising victims of mass extinction events: an example using Late Ordovician brachiopods

2017 ◽  
Vol 13 (9) ◽  
pp. 20170400 ◽  
Author(s):  
Seth Finnegan ◽  
Christian M. Ø. Rasmussen ◽  
David A. T. Harper
Keyword(s):  
Deep Water ◽  
Mass Extinction ◽  
Late Ordovician ◽  
Extinction Rate ◽  
Simple Method ◽  
Training Models ◽  
Extinction Event ◽  
Extinction Events ◽  
Mass Extinction Events

Mass extinction events are recognized by increases in extinction rate and magnitude and, often, by changes in the selectivity of extinction. When considering the selective fingerprint of a particular event, not all taxon extinctions are equally informative: some would be expected even under a ‘background’ selectivity regime, whereas others would not and thus require special explanation. When evaluating possible drivers for the extinction event, the latter group is of particular interest. Here, we introduce a simple method for identifying these most surprising victims of extinction events by training models on background extinction intervals and using these models to make per-taxon assessments of ‘expected’ risk during the extinction interval. As an example, we examine brachiopod genus extinctions during the Late Ordovician Mass Extinction and show that extinction of genera in the deep-water ‘ Foliomena fauna’ was particularly unexpected given preceding Late Ordovician extinction patterns.

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