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Richard Hereford – One of the best experts on this subject based on the ideXlab platform.

  • reevaluation of the crooked ridge river early pleistocene ca 2 ma age and origin of the white mesa Alluvium northeastern arizona
    Geosphere, 2016
    Co-Authors: Richard Hereford, Sue L Beard, William R Dickinson, Karl E Karlstrom, Matthew T Heizler, Laura J Crossey, Lee Amoroso, Kyle P House, Mark Pecha
    Abstract:

    Essential features of the previously named and described Miocene Crooked Ridge River in northeastern Arizona (USA) are reexamined using new geologic and geochronologic data. Previously it was proposed that Cenozoic Alluvium at Crooked Ridge and southern White Mesa was pre–early Miocene, the product of a large, vigorous late Paleogene river draining the 35–23 Ma San Juan Mountains volcanic field of southwestern Colorado. The paleoriver probably breeched the Kaibab uplift and was considered important in the early evolution of the Colorado River and Grand Canyon. In this paper, we reexamine the character and age of these Cenozoic deposits. The alluvial record originally used to propose the hypothetical paleoriver is best exposed on White Mesa, providing the informal name White Mesa Alluvium. The Alluvium is 20–50 m thick and is in the bedrock-bound White Mesa paleovalley system, which comprises 5 tributary paleochannels. Gravel composition, detrital zircon data, and paleochannel orientation indicate that sediment originated mainly from local Cretaceous bedrock north, northeast, and south of White Mesa. Sedimentologic and fossil evidence imply alluviation in a low-energy suspended sediment fluvial system with abundant fine-grained overbank deposits, indicating a local channel system rather than a vigorous braided river with distant headwaters. The Alluvium contains exotic gravel clasts of Proterozoic basement and rare Oligocene volcanic clasts as well as Oligocene–Miocene detrital sanidine related to multiple caldera eruptions of the San Juan Mountains and elsewhere. These exotic clasts and sanidine likely came from ancient rivers draining the San Juan Mountains. However, in this paper we show that the White Mesa Alluvium is early Pleistocene (ca. 2 Ma) rather than pre–early Miocene. Combined 40 Ar/ 39 Ar dating of an interbedded tuff and detrital sanidine ages show that the basal White Mesa Alluvium was deposited at 1.993 ± 0.002 Ma, consistent with a detrital sanidine maximum depositional age of 2.02 ± 0.02 Ma. Geomorphic relations show that the White Mesa Alluvium is older than inset gravels that are interbedded with 1.2–0.8 Ma Bishop–Glass Mountain tuff. The new ca. 2 Ma age for the White Mesa Alluvium refutes the hypothesis of a large regional Miocene(?) Crooked Ridge paleoriver that predated carving of the Grand Canyon. Instead, White Mesa paleodrainage was the northernmost extension of the ancestral Little Colorado River drainage basin. This finding is important for understanding Colorado River evolution because it provides a datum for quantifying rapid post–2 Ma regional denudation of the Grand Canyon region.

  • Valley-fill alluviation during the Little Ice Age (ca. A.D. 1400–1880), Paria River basin and southern Colorado Plateau, United States
    Geological Society of America Bulletin, 2002
    Co-Authors: Richard Hereford
    Abstract:

    Valley-fill Alluvium deposited from ca. A.D. 1400 to 1880 is widespread in tributaries of the Paria River and is largely coincident with the Little Ice Age epoch of global climate variability. Previous work showed that Alluvium of this age is a mappable stratigraphic unit in many of the larger alluvial valleys of the southern Colorado Plateau. The Alluvium is bounded by two disconformities resulting from prehistoric and historic arroyo cutting at ca. A.D. 1200–1400 and 1860–1910, respectively. The fill forms a terrace in the axial valleys of major through-flowing streams. This terrace and underlying deposits are continuous and interfinger with sediment in numerous small tributary valleys that head at the base of hillslopes of sparsely vegetated, weakly consolidated bedrock, suggesting that eroded bedrock was an important source of Alluvium along with in-channel and other sources. Paleoclimatic and high-resolution paleoflood studies indicate that valley-fill alluviation occurred during a long-term decrease in the frequency of large, destructive floods. Aggradation of the valleys ended about A.D. 1880, if not two decades earlier, with the beginning of historic arroyo cutting. This shift from deposition to valley entrenchment near the close of the Little Ice Age generally coincided with the beginning of an episode of the largest floods in the preceding 400–500 yr, which was probably caused by an increased recurrence and intensity of flood-producing El Nino events beginning at ca. A.D. 1870.

  • valley fill alluviation during the little ice age ca a d 1400 1880 paria river basin and southern colorado plateau united states
    Geological Society of America Bulletin, 2002
    Co-Authors: Richard Hereford
    Abstract:

    Valley-fill Alluvium deposited from ca. A.D. 1400 to 1880 is widespread in tributaries of the Paria River and is largely coincident with the Little Ice Age epoch of global climate variability. Previous work showed that Alluvium of this age is a mappable stratigraphic unit in many of the larger alluvial valleys of the southern Colorado Plateau. The Alluvium is bounded by two disconformities resulting from prehistoric and historic arroyo cutting at ca. A.D. 1200–1400 and 1860–1910, respectively. The fill forms a terrace in the axial valleys of major through-flowing streams. This terrace and underlying deposits are continuous and interfinger with sediment in numerous small tributary valleys that head at the base of hillslopes of sparsely vegetated, weakly consolidated bedrock, suggesting that eroded bedrock was an important source of Alluvium along with in-channel and other sources. Paleoclimatic and high-resolution paleoflood studies indicate that valley-fill alluviation occurred during a long-term decrease in the frequency of large, destructive floods. Aggradation of the valleys ended about A.D. 1880, if not two decades earlier, with the beginning of historic arroyo cutting. This shift from deposition to valley entrenchment near the close of the Little Ice Age generally coincided with the beginning of an episode of the largest floods in the preceding 400–500 yr, which was probably caused by an increased recurrence and intensity of flood-producing El Nino events beginning at ca. A.D. 1870.

Cynthia D. Scism – One of the best experts on this subject based on the ideXlab platform.

  • Sorption Characteristics of Radionuclides on Clays in Yucca Mountain Alluvium
    , 2006
    Co-Authors: M. Ding, P. W. Reimus, S.j. Chipera, W. Lukens, Cynthia D. Scism
    Abstract:

    Sorption of {sup 237}Np(V) and {sup 233}U(VI) was measured on clays separated from Yucca Mountain Alluvium as a function of solution pH and aqueous actinide concentrations. The results indicate that sorption of U and Np on the separated clay fraction depends strongly on solution pH. Np sorption on clays increases slowly with increasing pH from 3 to 7. Above pH 7, Np sorption on clays increases rapidly up to a pH of about 10. On the other hand, U sorption on clays reaches it maximum at a pH of about 6, with sorption decreasing as pH increases from 6 to 8 and then increasing again as pH increases further from 8 to about 10. The results suggest that a Freundlich isotherm can be used to describe U and Np sorption on clays at pH above 5.5. The results of this study indicate that clay minerals play a very important role in the sorption of U and Np on Yucca Mountain Alluvium. Indeed, the clay content of the Alluvium is probably considerably more important than water chemistry in predicting the ability of the Alluvium to attenuate the transport of these radionuclides.

  • Uranium and Neptunium Desorption from Yucca Mountain Alluvium
    , 2006
    Co-Authors: Cynthia D. Scism, P. W. Reimus, M. Ding, S.j. Chipera
    Abstract:

    Uranium and neptunium were used as reactive tracers in long-term laboratory desorption studies using saturated Alluvium collected from south of Yucca Mountain, Nevada. The objective of these long-term experiments is to make detailed observations of the desorption behavior of uranium and neptunium to provide Yucca Mountain with technical bases for a more realistic and potentially less conservative approach to predicting the transport of adsorbing radionuclides in the saturated Alluvium. This paper describes several long-term desorption experiments using a flow-through experimental method and groundwater and Alluvium obtained from boreholes along a potential groundwater flow path from the proposed repository site. In the long term desorption experiments, the percentages of uranium and neptunium sorbed as a function of time after different durations of sorption was determined. In addition, the desorbed activity as a function of time was fit using a multi-site, multi-rate model to demonstrate that different desorption rate constants ranging over several orders of magnitude exist for the desorption of uranium from Yucca Mountain saturated Alluvium. This information will be used to support the development of a conceptual model that ultimately results in effective K{sub d} values much larger than those currently in use for predicting radionuclide transport at Yucca Mountain.

  • The Sorption/Desorption Behavior of Uranium in Transport Studies Using Yucca Mountain Alluvium
    , 2005
    Co-Authors: Cynthia D. Scism
    Abstract:

    Yucca Mountain, Nevada is the proposed site of a geologic repository for the disposal of spent nuclear fuel and high-level radioactive waste in the United States. In the event repository engineered barriers fail, the saturated Alluvium located south of Yucca Mountain is expected to serve as a natural barrier to the migration of radionuclides to the accessible environment. The purpose of this study is to improve the characterization of uranium retardation in the saturated zone at Yucca Mountain to support refinement of an assessment model. The distribution of uranium desorption rates from Alluvium obtained from Nye County bore holes EWDP-19IM1, EWDP-10SA, EWDP-22SA were studied to address inconsistencies between results from batch sorption and column transport experiments. The Alluvium and groundwater were characterized to better understand the underlying mechanisms of the observed behavior. Desorption rate constants were obtained using an activity based mass balance equation and column desorption experiments were analyzed using a mathematical model utilizing multiple sorption sites with different first-order forward and reverse reaction rates. The uranium desorption rate constants decreased over time, suggesting that the Alluvium has multiple types of active sorption sites with different affinities for uranium. While a significant fraction of the initially sorbed uranium desorbedmore » from the Alluvium quite rapidly, a roughly equivalent amount remained sorbed after several months of testing. The information obtained through this research suggests that uranium may experience greater effective retardation in the Alluvium than simple batch sorption experiments would suggest. Electron Probe Microanalysis shows that uranium is associated with both clay minerals and iron oxides after sorption to alluvial material. These results provide further evidence that the Alluvium contains multiple sorption sites for uranium.« less

Wenbing Guo – One of the best experts on this subject based on the ideXlab platform.

  • Mechanical Properties of Mega-Thick Alluvium and Their Influence on the Surface Subsidence
    Geotechnical and Geological Engineering, 2019
    Co-Authors: Gaobo Zhao, Wenbing Guo
    Abstract:

    Surface subsidence caused by mining is closely related to the nature and structure of overburden and soil layer. Characteristics of mining subsidence under the condition of mega-thick Alluvium are special. Through analyzing the mechanism of mining subsidence with mega-thick Alluvium, surface subsidence was divided into three parts, i.e., bedrock surface subsidence with non-Alluvium, bedrock surface subsidence with mega-thick Alluvium and consolidation subsidence. Mechanical Properties of Mega-thick Alluvium and their Influence on the Surface Subsidence were studied by means of geotechnical test and numerical simulation. The shear strength of clayey soil in Jiaozuo mining area were researched through unconsolidated undrained triaxial test. The ranges of internal friction angle and cohesion force of clayey soil in this area were presented. Taking a panel covered by mega-thick Alluvium as an example, based on the test results, the influences of thickness, friction angle and cohesive force of Alluvium on surface subsidence were analyzed. Results of numerical simulation were compared with field data. Results show that the maximum surface subsidence value increases with the increase of the thickness of Alluvium, decreases with the increase of the friction angle and cohesive force. This paper combines geotechnical tests of Alluvium mechanical properties with surface subsidence, which has a certain guiding significance for the study of mining subsidence.

P. W. Reimus – One of the best experts on this subject based on the ideXlab platform.

  • Mineralogical Charecteristics of Yucca Mountain Alluvium and Effects on Neptunium (V) Sorption
    , 2006
    Co-Authors: M. Ding, S.j. Chipera, P. W. Reimus
    Abstract:

    Saturated Alluvium is expected to serve as an important natural barrier to radionuclide transport at Yucca Mountain, the proposed geological repository for disposal of high-level nuclear wastes. {sup 237}Np(V) (half-life = 2.4 x 10{sup 5} years) has been identified as one of the radionuclides that could potentially contribute the greatest dose to humans because of its relatively high solubility and weak adsorption to volcanic tuffs under oxidizing conditions. The previous studies suggested that the mineralogical characteristics of the Alluvium play an important role in the interaction between Np(V) and the Alluvium. The purpose of this study is to further evaluate the mineralogical basis for Neptunium (V) sorption by saturated Alluvium located down-gradient of Yucca Mountain.

  • Sorption Characteristics of Radionuclides on Clays in Yucca Mountain Alluvium
    , 2006
    Co-Authors: M. Ding, P. W. Reimus, S.j. Chipera, W. Lukens, Cynthia D. Scism
    Abstract:

    Sorption of {sup 237}Np(V) and {sup 233}U(VI) was measured on clays separated from Yucca Mountain Alluvium as a function of solution pH and aqueous actinide concentrations. The results indicate that sorption of U and Np on the separated clay fraction depends strongly on solution pH. Np sorption on clays increases slowly with increasing pH from 3 to 7. Above pH 7, Np sorption on clays increases rapidly up to a pH of about 10. On the other hand, U sorption on clays reaches it maximum at a pH of about 6, with sorption decreasing as pH increases from 6 to 8 and then increasing again as pH increases further from 8 to about 10. The results suggest that a Freundlich isotherm can be used to describe U and Np sorption on clays at pH above 5.5. The results of this study indicate that clay minerals play a very important role in the sorption of U and Np on Yucca Mountain Alluvium. Indeed, the clay content of the Alluvium is probably considerably more important than water chemistry in predicting the ability of the Alluvium to attenuate the transport of these radionuclides.

  • Uranium and Neptunium Desorption from Yucca Mountain Alluvium
    , 2006
    Co-Authors: Cynthia D. Scism, P. W. Reimus, M. Ding, S.j. Chipera
    Abstract:

    Uranium and neptunium were used as reactive tracers in long-term laboratory desorption studies using saturated Alluvium collected from south of Yucca Mountain, Nevada. The objective of these long-term experiments is to make detailed observations of the desorption behavior of uranium and neptunium to provide Yucca Mountain with technical bases for a more realistic and potentially less conservative approach to predicting the transport of adsorbing radionuclides in the saturated Alluvium. This paper describes several long-term desorption experiments using a flow-through experimental method and groundwater and Alluvium obtained from boreholes along a potential groundwater flow path from the proposed repository site. In the long term desorption experiments, the percentages of uranium and neptunium sorbed as a function of time after different durations of sorption was determined. In addition, the desorbed activity as a function of time was fit using a multi-site, multi-rate model to demonstrate that different desorption rate constants ranging over several orders of magnitude exist for the desorption of uranium from Yucca Mountain saturated Alluvium. This information will be used to support the development of a conceptual model that ultimately results in effective K{sub d} values much larger than those currently in use for predicting radionuclide transport at Yucca Mountain.

Phillip A Pearthree – One of the best experts on this subject based on the ideXlab platform.

  • river evolution and tectonic implications of a major pliocene aggradation on the lower colorado river the bullhead Alluvium
    Geosphere, 2015
    Co-Authors: Keith A Howard, Kyle P House, Rebecca J Dorsey, Phillip A Pearthree
    Abstract:

    The ∼200-m-thick riverlaid Bullhead Alluvium along the lower Colorado River downstream of Grand Canyon records massive early Pliocene sediment aggradation following the integration of the upper and lower Colorado River basins. The distribution and extent of the aggraded sediments record (1) evolving longitudinal profiles of the river valley with implications for changing positions of the river’s mouth and delta; (2) a pulse of rapid early drainage-basin erosion and sediment supply; and (3) constraints on regional and local deformation. The Bullhead Alluvium is inset into the Hualapai and Bouse Formations along a basal erosional unconformity. Its base defines a longitudinal profile interpreted as the incised end result after the Colorado River integrated through lake basins. Subsequent Bullhead aggradation, at ca. 4.5–3.5 Ma, built up braid plains as wide as 50 km as it raised the Colorado River’s grade. We interpret the aggradation to record a spike in sediment supply when river integration and base-level fall destabilized and eroded relict landscapes and Tertiary bedrock in the Colorado River’s huge catchment. Longitudinal profiles of the Bullhead Alluvium suggest ≥200 m post-Bullhead relative fault uplifts in the upper Lake Mead area, >100 m local subsidence in the Blythe Basin, and deeper subsidence of correlative deltaic sequences in the Salton Trough along the Pacific–North American plate boundary. However, regionally, for >500 km along the river corridor from Yuma, Arizona, to Lake Mead, Arizona and Nevada, the top of the Bullhead Alluvium appears to be neither uplifted nor tilted, sloping 0.5–0.6 m/km downstream like the gradient of a smaller late Pleistocene aggradation sequence. Perched outcrops tentatively assigned to the Bullhead Alluvium near the San Andreas fault system project toward a Pliocene seashore or bayline twice as distant (300–450 km) as either the modern river’s mouth or a tectonically restored 4.25 Ma paleoshore. We conclude that Bullhead aggradation peaked after 4.25 Ma, having lengthened the delta plain seaward by outpacing both 2 mm/yr delta subsidence and 43–45 mm/yr transform-fault offset of the delta. Post-Bullhead degradation started before 3.3 Ma and implies that the river profile lowered and shortened because sediment supply declined, and progradation was unable to keep up with subsidence and plate motion in the delta.