Redefining the Tonto Group of Grand Canyon and recalibrating the Cambrian time scale

Geology ◽  
2020 ◽  
Vol 48 (5) ◽  
pp. 425-430 ◽  
Author(s):  
K.E. Karlstrom ◽  
M.T. Mohr ◽  
M.D. Schmitz ◽  
F.A. Sundberg ◽  
S.M. Rowland ◽  
...  
Keyword(s):  
Isotope Dilution ◽  
Time Scale ◽  
Detrital Zircon ◽  
Grand Canyon ◽  
Earth Systems ◽  
Extinction Event ◽  
Central Arizona

Abstract We applied tandem U-Pb dating of detrital zircon (DZ) to redefine the Tonto Group in the Grand Canyon region (Arizona, USA) and to modify the Cambrian time scale. Maximum depositional ages (MDAs) based upon youngest isotope-dilution DZ ages for the Tapeats Sandstone are ≤508.19 ± 0.39 Ma in eastern Grand Canyon, ≤507.68 ± 0.36 Ma in Nevada, and ≤506.64 ± 0.32 Ma in central Arizona. The Sixtymile Formation, locally conformable below the Tapeats Sandstone, has a similar MDA (≤508.6 ± 0.8 Ma) and is here added to the Tonto Group. We combined these precise MDAs with biostratigraphy of trilobite biozones in the Tonto Group. The Tapeats Sandstone is ca. 508–507 Ma; the Bright Angel Formation contains Olenellus, Glossopleura, and Ehmaniella biozones and is ca. 507–502 Ma; and the Muav Formation contains Bolaspidella and Cedaria biozones and is ca. 502–499 Ma. The Frenchman Mountain Dolostone is conformable above the Muav Formation and part of the same transgression; it replaces McKee’s Undifferentiated Dolomite as part of the Tonto Group; it contains the Crepicephalus Biozone and is 498–497 Ma. The Tonto Group thickens east to west, from 250 m to 830 m, due to ∼300 m of westward thickening of carbonates plus ∼300 m of eastward beveling beneath the sub-Devonian disconformity. The trilobite genus Olenellus occurs in western but not eastern Grand Canyon; it has its last appearance datum (LAD) in the Bright Angel Formation ∼45 m above the ≤507.68 Ma horizon. This extinction event is estimated to be ca. 506.5 Ma and is two biozones below the Series 2–Miaolingian Epoch boundary, which we estimate to be ca. 506 Ma. Continued tandem dating of detrital grains in stratigraphic context, combined with trilobite biostratigraphy, offers rich potential to recalibrate the tempo and dynamics of Cambrian Earth systems.

scholarly journals Grand Canyon provenance for orthoquartzite clasts in the lower Miocene of coastal southern California

Geosphere ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1973-1998 ◽  
Author(s):  
Leah Sabbeth ◽  
Brian P. Wernicke ◽  
Timothy D. Raub ◽  
Jeffrey A. Grover ◽  
E. Bruce Lander ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Mojave Desert ◽  
Drainage System ◽  
Grand Canyon ◽  
Death Valley ◽  
Source Population ◽  
Source Regions ◽  
Detrital Zircon Ages ◽  
Central Arizona ◽  
Rule Out

Abstract Orthoquartzite detrital source regions in the Cordilleran interior yield clast populations with distinct spectra of paleomagnetic inclinations and detrital zircon ages that can be used to trace the provenance of gravels deposited along the western margin of the Cordilleran orogen. An inventory of characteristic remnant magnetizations (CRMs) from >700 sample cores from orthoquartzite source regions defines a low-inclination population of Neoproterozoic–Paleozoic age in the Mojave Desert–Death Valley region (and in correlative strata in Sonora, Mexico) and a moderate- to high-inclination population in the 1.1 Ga Shinumo Formation in eastern Grand Canyon. Detrital zircon ages can be used to distinguish Paleoproterozoic to mid-Mesoproterozoic (1.84–1.20 Ga) clasts derived from the central Arizona highlands region from clasts derived from younger sources that contain late Mesoproterozoic zircons (1.20–1.00 Ga). Characteristic paleomagnetic magnetizations were measured in 44 densely cemented orthoquartzite clasts, sampled from lower Miocene portions of the Sespe Formation in the Santa Monica and Santa Ana mountains and from a middle Eocene section in Simi Valley. Miocene Sespe clast inclinations define a bimodal population with modes near 15° and 45°. Eight samples from the steeper Miocene mode for which detrital zircon spectra were obtained all have spectra with peaks at 1.2, 1.4, and 1.7 Ga. One contains Paleozoic and Mesozoic peaks and is probably Jurassic. The remaining seven define a population of clasts with the distinctive combination of moderate to high inclination and a cosmopolitan age spectrum with abundant grains younger than 1.2 Ga. The moderate to high inclinations rule out a Mojave Desert–Death Valley or Sonoran region source population, and the cosmopolitan detrital zircon spectra rule out a central Arizona highlands source population. The Shinumo Formation, presently exposed only within a few hundred meters elevation of the bottom of eastern Grand Canyon, thus remains the only plausible, known source for the moderate- to high-inclination clast population. If so, then the Upper Granite Gorge of the eastern Grand Canyon had been eroded to within a few hundred meters of its current depth by early Miocene time (ca. 20 Ma). Such an unroofing event in the eastern Grand Canyon region is independently confirmed by (U-Th)/He thermochronology. Inclusion of the eastern Grand Canyon region in the Sespe drainage system is also independently supported by detrital zircon age spectra of Sespe sandstones. Collectively, these data define a mid-Tertiary, SW-flowing “Arizona River” drainage system between the rapidly eroding eastern Grand Canyon region and coastal California.

scholarly journals Evaluating the Shinumo-Sespe drainage connection: Arguments against the “old” (70–17 Ma) Grand Canyon models for Colorado Plateau drainage evolution

Geosphere ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 1425-1456
Author(s):  
Karl E. Karlstrom ◽  
Carl E. Jacobson ◽  
Kurt E. Sundell ◽  
Athena Eyster ◽  
Ron Blakey ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Gulf Of California ◽  
Colorado Plateau ◽  
Grand Canyon ◽  
River System ◽  
Death Valley ◽  
Transverse Ranges ◽  
Drainage Connection ◽  
The Pacific ◽  
History Of

Abstract The provocative hypothesis that the Shinumo Sandstone in the depths of Grand Canyon was the source for clasts of orthoquartzite in conglomerate of the Sespe Formation of coastal California, if verified, would indicate that a major river system flowed southwest from the Colorado Plateau to the Pacific Ocean prior to opening of the Gulf of California, and would imply that Grand Canyon had been carved to within a few hundred meters of its modern depth at the time of this drainage connection. The proposed Eocene Shinumo-Sespe connection, however, is not supported by detrital zircon nor paleomagnetic-inclination data and is refuted by thermochronology that shows that the Shinumo Sandstone of eastern Grand Canyon was >60 °C (∼1.8 km deep) and hence not incised at this time. A proposed 20 Ma (Miocene) Shinumo-Sespe drainage connection based on clasts in the Sespe Formation is also refuted. We point out numerous caveats and non-unique interpretations of paleomagnetic data from clasts. Further, our detrital zircon analysis requires diverse sources for Sespe clasts, with better statistical matches for the four “most-Shinumo-like” Sespe clasts with quartzites of the Big Bear Group and Ontario Ridge metasedimentary succession of the Transverse Ranges, Horse Thief Springs Formation from Death Valley, and Troy Quartzite of central Arizona. Diverse thermochronologic and geologic data also refute a Miocene river pathway through western Grand Canyon and Grand Wash trough. Thus, Sespe clasts do not require a drainage connection from Grand Canyon or the Colorado Plateau and provide no constraints for the history of carving of Grand Canyon. Instead, abundant evidence refutes the “old” (70–17 Ma) Grand Canyon models and supports a <6 Ma Grand Canyon.

scholarly journals Supplemental Material: Evaluating the Shinumo-Sespe drainage connection: Arguments against the “old” (70–17 Ma) Grand Canyon models for Colorado Plateau drainage evolution

2020 ◽  
Author(s):  
K.E. Karlstrom ◽  
et al.
Keyword(s):  
Detrital Zircon ◽  
Colorado Plateau ◽  
Grand Canyon ◽  
Quantitative Comparison ◽  
Cross Bedding ◽  
Drainage Connection ◽  
Comparison Results

Table S1: Rotations of measured paleomagnetic paleopoles to test the error introduced by measuring inclinations relative to cross bedding of different orientations instead of horizontal bedding. Table S2: Detrital zircon data used in this study. Table S3: Quantitative comparison results from DZstats.

scholarly journals Supplemental Material: Evaluating the Shinumo-Sespe drainage connection: Arguments against the “old” (70–17 Ma) Grand Canyon models for Colorado Plateau drainage evolution

2020 ◽  
Author(s):  
K.E. Karlstrom ◽  
et al.
Keyword(s):  
Detrital Zircon ◽  
Colorado Plateau ◽  
Grand Canyon ◽  
Quantitative Comparison ◽  
Cross Bedding ◽  
Drainage Connection ◽  
Comparison Results

Table S1: Rotations of measured paleomagnetic paleopoles to test the error introduced by measuring inclinations relative to cross bedding of different orientations instead of horizontal bedding. Table S2: Detrital zircon data used in this study. Table S3: Quantitative comparison results from DZstats.

The ages of stratified Precambrian rock sequences in central Arizona and northern Sonora

1968 ◽  
Vol 5 (3) ◽  
pp. 763-772 ◽  
Author(s):  
Donald E. Livingston ◽  
Paul E. Damon
Keyword(s):  
Sedimentary Rocks ◽  
Grand Canyon ◽  
Precambrian Rock ◽  
Isotopic Dating ◽  
Precambrian Rocks ◽  
Isotopic Evidence ◽  
The Third ◽  
Central Arizona ◽  
Second Period

Stratified sequences of Precambrian rocks from twelve localities in Arizona and Sonora yield geologic and isotopic evidence of multiple periods of rock accumulation and orogeny. Isotopic dating indicates that these rocks were formed from 1800 m.y. to 950 m.y. ago. The oldest rocks are metamorphosed sequences of volcanic and sedimentary origin. They are separated in time from a younger sequence of metamorphosed volcanic and sedimentary rocks by batholithic plutonism dated at approximately 1700 m.y. The second period of volcanism and sedimentation was terminated by batholithic plutonism about 1400 m.y. ago.Subsequent to the 1400 m.y. event, the "Younger Precambrian" rocks of Arizona, the Apache Group and probably the Grand Canyon Series, were deposited. These dominantly sedimentary rocks are characteristically only slightly and locally metamorphosed and deformed. Their age is greater than the 1150 m.y. old diabase sills and dikes that intrude them. Some areas that are not underlain by rocks of the Apache Group were metamorphosed and possibly intruded by silicic plutons about 1000 m.y. ago.From these data it appears that the stratified Precambrian rocks of Arizona can be assigned to three periods of accumulation. The first period occurred prior to about 1700 m.y., and the second occurred between 1700 and 1400 m.y. The third period, the deposition of the Apache Group, occurred between 1400 and 1150 m.y. ago.

The Anthropocene

2015 ◽  
Author(s):  
Jan Zalasiewicz ◽  
Colin Waters
Keyword(s):  
Time Scale ◽  
Natural Habitat ◽  
The Body ◽  
Geological Time ◽  
Nitrogen And Phosphorus ◽  
Geological Time Scale ◽  
Earth Systems ◽  
Species Invasions ◽  
The Earth ◽  
Sixth Mass Extinction

The Anthropocene hypothesis—that humans have impacted “the environment” but also changed the Earth’s geology—has spread widely through the sciences and humanities. This hypothesis is being currently tested to see whether the Anthropocene may become part of the Geological Time Scale. An Anthropocene Working Group has been established to assemble the evidence. The decision regarding formalization is likely to be taken in the next few years, by the International Commission on Stratigraphy, the body that oversees the Geological Time Scale. Whichever way the decision goes, there will remain the reality of the phenomenon and the utility of the concept. The evidence, as outlined here, rests upon a broad range of signatures reflecting humanity’s significant and increasing modification of Earth systems. These may be visible as markers in physical deposits in the form of the greatest expansion of novel minerals in the last 2.4 billion years of Earth history and development of ubiquitous materials, such as plastics, unique to the Anthropocene. The artefacts we produce to live as modern humans will form the technofossils of the future. Human-generated deposits now extend from our natural habitat on land into our oceans, transported at rates exceeding the sediment carried by rivers by an order of magnitude. That influence now extends increasingly underground in our quest for minerals, fuel, living space, and to develop transport and communication networks. These human trace fossils may be preserved over geological durations and the evolution of technology has created a new technosphere, yet to evolve into balance with other Earth systems. The expression of the Anthropocene can be seen in sediments and glaciers in chemical markers. Carbon dioxide in the atmosphere has risen by ~45 percent above pre–Industrial Revolution levels, mainly through combustion, over a few decades, of a geological carbon-store that took many millions of years to accumulate. Although this may ultimately drive climate change, average global temperature increases and resultant sea-level rises remain comparatively small, as yet. But the shift to isotopically lighter carbon locked into limestones and calcareous fossils will form a permanent record. Nitrogen and phosphorus contents in surface soils have approximately doubled through increased use of fertilizers to increase agricultural yields as the human population has also doubled in the last 50 years. Industrial metals, radioactive fallout from atomic weapons testing, and complex organic compounds have been widely dispersed through the environment and become preserved in sediment and ice layers. Despite radical changes to flora and fauna across the planet, the Earth still has most of its complement of biological species. However, current trends of habitat loss and predation may push the Earth into the sixth mass extinction event in the next few centuries. At present the dramatic changes relate to trans-global species invasions and population modification through agricultural development on land and contamination of coastal zones. Considering the entire range of environmental signatures, it is clear that the global, large and rapid scale of change related to the mid-20th century is the most obvious level to consider as the start of the Anthropocene Epoch.

scholarly journals Detrital zircon U-Pb geochronology of Paleozoic strata in the Grand Canyon, Arizona

Lithosphere ◽  
2011 ◽  
Vol 3 (3) ◽  
pp. 183-200 ◽  
Author(s):  
George E. Gehrels ◽  
Ron Blakey ◽  
Karl E. Karlstrom ◽  
J. Michael Timmons ◽  
Bill Dickinson ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Grand Canyon

scholarly journals A constraint on post–6 Ma timing of western Grand Canyon (Arizona, USA) incision removed: Local derivation indicated by ca. 5.4 Ma fluvial deposits below Shivwits Plateau basalts north of Grand Canyon

Geosphere ◽  
2021 ◽  
Author(s):  
A.T. Steelquist ◽  
G.E. Hilley ◽  
I. Lucchitta ◽  
R.A. Young
Keyword(s):  
United States ◽  
Detrital Zircon ◽  
Colorado River ◽  
Landscape Evolution ◽  
Colorado Plateau ◽  
Grand Canyon ◽  
River System ◽  
Fluvial Deposits ◽  
Western Colorado ◽  
Rule Out

The timing of integration of the Colorado River system is central to understanding the landscape evolution of much of the southwestern United States. However, the time at which the Colorado River started incising the westernmost Grand Canyon (Arizona) is still an unsettled question, with conflicting interpretations of both geologic and thermochronologic data from western Grand Canyon. Fluvial gravels on the Shivwits Plateau, north of the canyon, have been reported to contain clasts derived from south of the modern canyon, suggesting the absence of western Grand Canyon at the time of their deposition. In this study, we reassess these deposits using modern geochronologic measurements to determine the age of the deposits and the presence or absence of clasts from south of the Grand Canyon. We could not identify southerly derived clasts, so cannot rule out the existence of a major topographic barrier such as Grand Canyon prior to the age of deposition of the gravels. 40Ar/39Ar analysis of a basalt clast entrained in the upper deposit (in combination with prior data) supports a maximum age of deposition of ca. 5.4 Ma, limiting deposition to post-Miocene, a period from which very few diagnostic and dated fluvial deposits remain in the western Colorado Plateau. Analysis of detrital zircon composition of the sand matrix supports interpretation of the deposit as being locally derived and not part of a major throughgoing river. We suggest that the published constraint of <6 Ma timing of Grand Canyon incision may be removed, given that no clasts that must be sourced from south of Grand Canyon were found in the only known outcrop of gravels under the Shivwits Plateau basalts at Grassy Mountain north of Grand Canyon.

Interpretation of SHRIMP and isotope dilution zircon ages for the Palaeozoic time-scale: II. Silurian to Devonian

2000 ◽  
Vol 64 (6) ◽  
pp. 1127-1146 ◽  
Author(s):  
W. Compston
Keyword(s):  
Isotope Dilution ◽  
Time Scale ◽  
Direct Determination ◽  
The Other ◽  
Magmatic Zircon ◽  
Age Group ◽  
Geological Time ◽  
Geological Time Scale ◽  
Ion Probe ◽  
Eruption Age

AbstractIon probe data are documented for zircons from tuffs within the early Llandovery, the mid-Caradoc and the Ludlow. 206Pb/238U ages for tuff magmatism have been interpreted using mixture-modelling to distinguish inheritance and Pb loss. Comparisons with the reference zircon SL13 have been improved through a direct determination of the component of secondary ion discrimination caused by changes in target potential.Interpretation of the SHRIMP data for the Birkhill ash (Scotland, Llandovery) is ambiguous. The more conservative possibility is that most zircons are 439 Ma, in close agreement with the previous isotope dilution ages for the same zircon concentrate. The other is that the 439 Ma group should be split into an inherited population at ˜447 Ma, with a minority at ˜434 Ma that corresponds with the ash volcanism. Although imprecise, the latter is detectably younger than the multi-grain MSID age, which itself might be a composite of the same two ages.Most zircon analyses from the mid Caradoc Pont-y-ceunant Ash, Wales, fit an age-group at 452.5 Ma, similar to its published 206Pb/238U age by MSID, with a definite older age group at ˜476 Ma but none showing Pb loss. By contrast, those from the Millbrig bentonite (Virginia) of the same age mainly fall in a well-defined post-eruption age group at 435 Ma, while the remainder give 456 Ma. Most zircon analyses from the Kinnekulle bentonite, Sweden, fall into an apparent 464 Ma group which exceeds other estimates for the mid-Caradoc magmatism. It is interpreted to be a composite age, caused by an inability to resolve it into a younger magmatic and older inherited group owing to the larger analytical errors of the Kinnekulle data. The best SHRIMP estimate for the mid-Caradoc volcanism is 452.6±1.7 Ma found by combining the ages for the three volcanic units. During unmixing of the combined ages, the Kinnekulle ages are redistributed and the 464 Ma ‘group’ vanishes. Precambrian grains are present in all the above volcanics.The original and new zircon analyses from the Laidlaw Volcanics (Canberra, Australia) of Ludlow age, are dominated by three groups of inherited zircons at ˜436 Ma, ˜450 Ma and ˜476 Ma, which makes it unfavourable for time-scale definition using zircons. The youngest zircon age group is 417.5 Ma (˜30%), but this is not associated with overgrowths on older grains or with wholly younger grains. Instead, it is composed of sporadic low ages within older grains suggestive of Pb loss rather than magmatic zircon growth. Nevertheless, the age for volcanism is 420.7±1.1 Ma based on published Rb-Sr and K-Ar dating, so that the youngest zircon group does appear to be associated with volcanism.One zircon U-Pb age for the Frasnian by MSID is much older than a precise age by other decay schemes, and another for the Lochkovian is significantly older than a recent SHRIMP age for the same Stage. By small changes in the common Pb composition, both MSID ages can be changed from single volcanic ages affected by Pb loss to an inherited and younger volcanic age, which removes the conflict with the other determinations.A zircon-based geological time-scale is constructed from the Ordovician to the Carboniferous using the time-points presented and discussed in Parts I and II of this paper.

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