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Neutron Activation Analysis for Correlating Volcanic Ash Soils

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Neutron Activation Analysis for Correlating Volcanic Ash Soils AN ABSTRACT OF THE THESIS OF GLENN ARNOLD BORCHARDT for the Ph. D. (Name) (Degree) in SOILS presented on August 15, 1969 (Major) (Date) Title: NEUTRON ACTIVATION ANALYSIS FOR CORRELATING VOLCANIC ASH SOILS Redacted for Privacy Abstract approved: E, Harward The objectives of this study were:1)To determine the trace element differences between sample sites and between deposits of Mazama, Newberry, Glacier Peak, and St. Helens volcanic ash in the Pacific Northwest,2)To correlate volcanic ash in peat bogs with volcanic ash from upland sites,3)To verify Mazama ash as parent material of soils occurring along a 450 km transect inOregon, and 4)To determine the trace element composition of clays derived from volcanic ash. Samples were irradiated in a TRIGA Reactor, followed by detection of elements with a high resolution 30cc Ge(Li) semi- conductor detector and a 4096 multichannel analyzer. Gamma- ray spectra were analyzed with a computer program to determine the following average composition in Mazama volcanic glass: Ele- Ele- Ele- ment ppm s mentppm ±5 mentppm ±S Na 3.44% .16% Sm5.0 .4 Hf 6.4 .4 Rb 50, 8. Eu0.89 .08 Ta 0.23 .08 Cs 3.9 .7 Tb 0.83 .14 Co 2,6 .3 Ba 660. 70. Yb 3,5 .7 Fe1.48%.09% La 22. 2, Lu 0.56 .07 Sc 6.4 .4 Ce 44. 3, Th 6,5 .3 Cr 1.6 .6 Field variability of Mazama and Newberry ash deposits in Oregon was about 5%, whereas the variability of the crystal-rich Glacier Peak and St. Helens ash of Washington was greater.Low coefficients of variation of mean ratios (variation analysis) and dis- criminant function analysis of the concentrations of 19 elements classified unidentified volcanic ash samples with ash from known sources.The activation analysis data support previous identification of Mazama ash in the Pacific Ocean, and at Steptoe Canyon, Washington and Edmonton, Alberta. At least 18 cm of Mazama ash (dated at 6500- 7420 radio- carbon years) occurred in peat bogs up to 450 km from the source at Crater Lake, Oregon. An older ash layer from Glacier Peak (> 9650 years) occurs in northeastern Oregon.Soils in northeastern Oregon may contain about 5 cm of St. Helens Y, a 3000 year old ash, mixed into upper horizons. The trace element compositions of volcanic glass from C horizons of soils along a 450 km transect in Oregon correlate with ejecta from Mt. Mazama. Enrichment and leaching effects in weathered horizons interfere with correlations that use variation analysis.However, the discriminant function classified Al and AC as well as C horizon samples with the Mazama group.Enrichment of transition metals in upper horizons occurred in the following order: Cr> Co> Fe Sc,Na/Fe and Na/Co ratios were measures of weathering intensity.The abundances of Hf, Th, and the rare earth elements remained relatively unchanged throughout 6600 years of weathering.Sc/Fe, Th/Hf, La/Sm, and Th/Sm ratios were not changed appreciably by weathering.These stable ratios were used with discriminant function analysis to aid in correlation of weathered soil horizons. Weathering in soils developed on volcanic ash resulted in enrichment of trace elements in sand- size volcanic glass.This led to a study of the <Zp. weathering products.The clay fractions of soils developed from Mazama ash contained phases other than glass. Rare earth element abundances were about three times the amounts found for unweathered volcanic glass.Sodium in the <Zi. fraction was only 10% of the amount in glass while the transition metals were as much as nn' tinis higher in cLay than in glass.Such in cr'-'aseS were remarkably similar for clays from five soils along the 450 km transect of Mazama volcanic ash derived soils.The abun- dances of Cr and Go, as well as Fe and Sc in clay fractions increased with watherinntensitv in the flay Creek soil.The Sc/Fe ratio both c a y and the Mazarna volcanic glass from which it was derived.Chemical treatments revealed the solubilities of rare earth elements in Day Creek clay to be greater than those in the more intensely weathered Parkdale clay.High Sc/Fe ratios indicated a possible detrital origin for the crystalline clay minerals comprising 20% of the clay fractions in both soils.Clays from non- ashy soils of western Oregon also contained high concentrations of transition metals and rare earth elements. An attempt to correlate clays from different volcanic ash layers revealed chemical similari- ties between soil clays from Glacier Peak and Mazama ash and lapilli, but the chemical composition was different for soil clays formed on Newberry lapilli. Neutron Activation Analysis For Correlating Volcanic Ash Soils by Glenn Arnold Borchardt A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the Doctor of Philosophy June 1970 APPROVED: Redacted for Privacy Profesor of soils in charge of major Redacted for Privacy Head ofeparment of Soils Redacted for Privacy Dean of Graduate School Dt thesis is presented August 15, 1969 Trned bMuriel Davis for Glenn Arnold Borchardt ACKNOWLEDGMENTS The author wises to express his appreciation to Dr. M. E. Harward for his guidance and stimulating discussions.The sugges- tions and instructions in the technical aspects of activation analysis given by Dr. R. A. Schmitt were invaluable.Special thanks are extended to Drs. E. C. Knox, E. M. Taylor, and C. T. Youngberg for their interest in this study.The author is indebted to those indi- viduals who contributed samples for analysis and to those members of the Department of Soils who helped collect samples.The assis.. tance of J. A. Norgren in obtaining ash from peat bogs was extremely helpful.Special thanks go to Dr. A. A. Theisen who suggested this approach to the identification of volcanic ash deposits.I wish to thank my wife, Marilyn, for her encouragement and helpfulness during the investigation and throughout the preparation of this disser- tation. Partial support of the Atomic Energy Commission, contract AT(45- i)-.2062, is gratefully ac:knouJedge!. TABLE OF CONTENTS Page INTRODUCTION 1 Statement of the Problem 2 Objectives 3 I TRACE ELEMENT CHARACTERIZATION AND CORRELATION OF CASCADE RANGE PYROCLASTICS 5 Introduction 5 Materials and Methods 9 Standard Solutions 9 Standard Rocks 9 Standard Volcanic Ash Samples 9 Unidentified Volcanic Ash 13 Isolation of Volcanic Glass 15 Analytical Methods 16 Results and Discussion 18 Standard Rocks 18 Whole Samples Compared to Glassy Fractions 19 Variability Within Deposits 21 Differences Between Volcanic Ash Deposits 26 Elemental Abundances 26 Rare Earth Element Distributions 27 Correlation of Samples 29 Statistical Methods 29 Correlation of Unidentified Samples 40 Conclusions 49 I I CORRELATION OF VOLCANIC ASH LAYERS OF PEAT BOGS 51 Introduction 51 Materials and Methods 53 Results and Discussion 57 Radio- Carbon Dates 57 INAAC 58 Mazama Ash 62 Glacier Peak Ash 67 St. Helens Y Ash 67 Elemental Ratios 70 Conclusions 76 Page III CORRELATION OF VOLCANIC ASH SOILS 77 Introduction 77 Materials 79 Methods 79 Results and Discussion 83 Vertical Homogeneity of Mazama Pumice 84 Correlation of Soil Parent Materials with Mazama Volcanic Ash 86 Weathering Effects 93 Elemental Ratios for Correlating Soils 97 Removal of Iron Oxide Coatings 106 Conclusions 110 IV TRACE ELEMENT CONCENTRATION IN AMORPHOUS CLAYS OF VOLCANIC ASH SOILS 111 Introduction 111 Materials 113 Methods 116 Results and Discussion 116 Less than Two Micron Glass 116 Trace Element Concentration as a Function of Depth 120 Chemical Pretreatments 127 Origin of 2:1 Layer Silicates 134 Comparisons of Mazama Soil Clays to Weathering Products of Other Materials 135 Clays from Other Volcanic Ash Deposits 138 Comparison to Mazama Volcanic Glass 139 Variation Analysis 141 REE Distribution Patterns 143 Conclusions 145 BIBLICGfAPLi' I 47 I\PPENDICES 152 LIST OF FIGURES Figure Page I.TRACE ELEMENT CHARACTERIZATION AND CORRELATION OF CASCADE RANGE PYRO- CLASTICS 1 Locations of volcanic ash sampling sites in the Pacific Northwest 6 2 Example of gamma-ray spectrum obtained with a Ge(Li) detector and a 4096 multichannel analyzer 17 3 Rare earth element (REE) distribution patterns for standard ash samples 28 II.CORRELATION OF VOLCANIC ASH LAYERS OF PEAT BOGS 1 Locations of peat bogs from which volcanic ash samples were obtained for activation analysis 52 III.CORRELATION OF VOLCANIC ASH SOILS 1 Locations of the five transect soils derived from Mazama ash, including Parlcdale loam sampled near Mt. Hood 80 2 Elemental enrichment in Mazama volcanic glass in relation to soil depth 94 IV.TRACE ELEMENT CONCENTRATION IN AMORPHOUS CLAYS OF VOLCANIC ASH SOILS Locations of soils and volcanic ash deposits from which clays were obtained fcr activation analysis 114 High angle X-ray diffraction patterns of residues from clays treated for removal of amorphous material 121 Low angle X-ray diffraction patterns of residues from clays treated for removal of amorphous material 122 Figure Page 4 Effect of soil weathering on elemental enrichment in soil clays derived from Mazama ash 124 S Scandium in clay and very fine sand- size glass of Day Creek soil horizons 126 6 La and Ce in relation to Sm for clays and glass from Mazama, Newberry, and Glacier Peak volcanic ash 144 LIST OF TABLES Table Page I.TIACE ELEMENT CHARACTERIZATION AND CORRELATION OF CASCADE RANGE PYROCLASTICS 1 Analyses of USGS rock standards and comparisons to INAA results of Gordon etal. (1968) 10 2 Volcanic ash samples used as standards 12 3 Unidentified volcanic ash samples 3 4 Comparison of whole samples of volcanic ash to glassy fractions 20 S Analyses of volcanic glass isolated from standard ash layers 22 6 Ratios to Mazama volcanic glass composition (average of eight samples) for regional samples 31 7 Coefficients of variation (%) for standard ash samples normalized to average elemental abundances for Mazama; Newberry; Glacier Peak; St.
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