ML17275A462
| ML17275A462 | |
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|---|---|
| Site: | Columbia  |
| Issue date: | 07/31/1978 |
| From: | WOODWARD-CLYDE CONSULTANTS, INC. |
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Text
PalsortIIsgnstlsM afhd Age 98'klrlQ 0872 Ral'Chquake Studies MPPSS Iwlcselesm'loject Nos.
0 8 4 Prepared for United Engineers 8c Constructors, inc.
July 1978 800vs50"~~
Woodvrard.ctyde Consuita~ts ~y c~
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1872 EARTHQUAKE STUDIES WASHINGTON PUBLIC POWER SUPPLY SYSTEM NUCLEAR PROJECT NOS.
1 AND 4 PALEOMAGNETIC MEASUREMENTS OF THE RINGOLD FORMATION AND LOESS UNITS NEAR HANFORD, WASHINGTON AND EVALUATION OF AGE DATING POTENTIAL OF QUATERNARY DEPOS ITS NEAR HANFORD g WASHINGTON TEXT AND APPENDIX A
& B prepared for UNITED ENGINEERS AND CONSTRUCTORS, INC.
Contract No. H.O.
52028 July 1978 WOODWARD-CLYDE CONSULTANTS Consulting Engineers, Geologists and Environmental Scientists San Francisco, California
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Three Embarcadero Center, Suite 700 San Francisco, California 94111 415-956-7070 Woodmai d Clyde Consultants July 27, 1978 13891A-6500-080 UNITED ENGINEERS
& CONSTRUCTORSr INC.
30 South 17th Street P.O.
Box 8223 Philadelphia, Pennsylvania 19101 Attention:
Mr. J.
R. Schmieder Assistant Project Manager Contract No. H.O.
52028 Gentlemen:
1872 EARTHQUAKE STUDIES WPPSS NUCLEAR PROJECTr NUMBERS 1 AND 4 WCC 6 PALEOMAGNEIT MEASUREMENTS AND EVALUATION OF AGE DATING POTENTIAL OF ATERNARY DEPOSITS NEAR HANFORD It is our pleasure to forward to you three (3) copies of the final report for the Task
- WCC6, entitled "Paleomagnetic Measurements of the Ringold Formation and Loess Units near
- Hanford, Washington and Evaluation of Age Dating Potential of Quaternary Deposits Near Hanford, Washington".
The final report contains two appendices, A and B.
A separate
- volume, Appendix C, is not intended for general distribution
- and, has only been assembled in a
limited quantity for accessability to the basic data.
please note that copies of the final report, including one '(1) copy of the Appendix C, have been forwarded to Mr.
David Tillson of WPPSS, as he has requested.
Should you have any questions, or require further information, please feel free to contact us.
ncerely;
~/
/
c~~y z Thomas Turcotte Project Manager TT/pam
Enclosures:
Final Report (3 copies),
Appendix C (2 copies) cc:
D. Tillson (5 copies, Appendix C (1 copy)
D. Tocher (1 copy)
Project File (1 copy), Appendix C (1 copy)
Consulting Engineers, Geologists and Environmental Scientists Offices in Other Principal Cities
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Woodward Clyde Consultants
SUMMARY
A preliminary study of the paleomagnetic polarity of the Ringold Formation in the Hanford
- area, and of two loess deposits in the Ellensburg and
- Yakima, Washington areas indicates that paleomagnetism could be a useful tool in dating and correlating these deposits.
The Ringold Formation exposed in White-Bluff has been shown to be magnetically stable and to contain a
polarity sequence suitable for correlation and possible age dating.
The stratigraphically
- thick, magnetically reversed section confirms that the age of the Ringold Formation is older than 700,000 years.
The loess deposits overlying the Naneum conglomerate on Craigs Hill in Ellensburg, Washington have good magnetic stability.
The lowest loess unit, approximately 3 meters thick, was deposited in a
reversed magnetic field.
On the basis of this magnetically reversed
- section, the deposits in the lower portion of the section are older than 700,000 years.
The magnetic stability of loess deposits from the section near Wymer Station is good.
The loess deposits have a
normal magnetic polarity and although not definitive
- evidence, suggests that these deposits are younger than 700,000 years.
An evaluation, of other possible dating or correlation techniques that might be used in the southeast Washington area indicates that uranium series, carbon 14, tephrochronology, and correlation of river terraces and Quaternary deposits are among the most useful dating techniques in the southeast Washington area.
Uranium series dates from the caliche
- deposits, which are widespread throughout the
- area, show a
large span in ages.
The oldest date of 55,000 years should be considered a minimum age for the onset of the formation of the caliche deposits.
TABLE OF CONTENTS LETTER OF TRANSMITTAL
SUMMARY
LIST OF FIGURES AND TABLE INTRODUCTION PART I PALEOMAGNETISM SAMPLE COLLECTION AND ANALYSIS RESULTS Ringold Formation Craigs Hill Loess Deposits Wymer Station Loess Deposits CONCLUSIONS Ringold Formation Craigs Hill Loess Deposits Wymer Station Loess Deposits Pa<ac 3.
PART II AGE DATING EVALUATIONS INTRODUCTION RESULTS CONCLUSIONS 7
7 8ll FIGURES APPENDIX A CHAPTER ON PALEOMAGNETISM FROM WOODWARD-CLYDE CONSULTANTS AGE DATING REPORT APPENDIX B URANIUM SERIES AGE-DATING RESULTS APPENDIX C PALEOMAGNETZC DATA (Separate Volume)
LIST OF FIGURES Number Title LOCATION MAP OF RZNGOLD FORMATION SECTION PHOTOGRAPH OF RINGOLD FORMATION SECTION LOCATION MAP OF CRAIGS HILL LOESS SECTXONg ELLENSBURGf WASHXNGTON LOCATION MAP OF WYMER STATION LOESS SECTION PHOTOGRAPH OF WYMER STATION LOESS SECTION LOCATION MAP OF WALLULA GAP TRENCH 1 DECLINATION AND INCLINATION VERSUS STRATIGRAPHIC HEXGHT AT RZNGOLD FORMATION SECTION STEREONET PLOTS OF MAGNETIZATION DIRECTIONS AT RINGOLD FORMATION SECTION INTENSITY VERSUS STRATIGRAPHIC HEIGHT AT RINGOLD FORMATION SECTION 10 VGP LATITUDE AND MAGNETIC POLARITY VERSUS STRATIGRAPHXC HEIGHT AT RINGOLD FORMATION SECTION 12 13 14 15 16 17 SCHEMATIC SECTION WITH MAGNETIC POLARITY AT RXNGOLD FORMATION SECTION DECLINATION AND INCLINATION VERSUS STRATIGRAPHIC HEIGHT AT CRAIGS HILL LOESS SECTION STEREONET PLOTS OF MAGNETIZATION DIRECTXONS AT CRAZGS HXLL LOESS SECTION XNTENSITY VERSUS STRATIGRAPHIC HEIGHT AT CRAIGS HILL LOESS SECTION VGP LATXTUDE AND MAGNETIC POLARITY VERSUS STRATIGRAPHIC HEIGHT AT CRAIGS HILL LOESS SECTION PHOTOGRAPH OF PART OF CRAIGS HILL LOESS SECTION STEREONET PLOTS OF MAGNETIZATION DIRECTIONS AT WYMER STATION LOESS SECTION
Number Title 18 19 VGP LATITUDE AND MAGNETIC POLARITY VERSUS STRATIGRAPHIC HEIGHT AT WYMER STATION LOESS SECTION PHOTOGRAPH OF CALICHE COATINGS WALLULA GAP TRENCH 1
TABLE URANIUM SERXES DATES ON CALICHE COATXNGS FROM THE WALLULA GAP TRENCH
Woodward Clyde Consultants INTRODUCTION Part,I of this report presents the results of the preliminary study of the paleomagnetic polarity of the Ringold Formation in the Hanford, Washington area and two loess deposits in the Ellensburg and Yakima, Washington areas.
Part II presents the results of an evaluation of age dating techniques which may apply to Quaternary deposits in the southeast Washington area.
The objectives of the preliminary study of the Ringold Formation were to evaluate its magnetic stability and whether or not'it contains a polarity sequence suitable for age dating and correlation.
Samples from approximately 120 meters of silts and sands were collected from a section extending from a basal contact with a
conglomerate up to a
caliche cap and overlying loess.
The section, the type section of the Ringold Formation, is exposed in the White Bluffs along the Columbia River in the west half of Section 25,
- TllN, R28E.
The approximate locations of the upper and lower parts of this section are shown on Figure 1, and a photograph with closeup of a portion of the cliff forming unit sampled is shown in Figure 2.
The section was laterally offset to obtain maximum exposures.
A preliminary study of the paleomagnetic polarity was made of loess deposits overlying the Naneum conglomerate at Craigs Hill in the southern portion of Section 36,
- T18N, R18E, at Ellensburg, Washington.
The objectives of this study were to evaluate if these deposits of loess are magnetically stable and were formed in a reversed magnetic field.
Approximately 16 meters of section (with samples from ll stratigraphic levels) were collected at this location.
The location of this section is shown on Figure 3.
Paleomagnetic samples were also collected from a loess section approximately 22 meters thick along the Yakima River in the
Woodward Clyde Consultants southwestern portion of Section 4,
- T15N, R19E, approximately 1
km south of Wymer Station (Figure 4).
Ten stratigrphic levels at this location were collected, including a number of ash
- units, one of which was approximately 3/4 of a
meter thick.
Photographs of this ash unit and section collected are shown in Figure 5.
The objective of the age dating study was to evaluate the feasibility of using various techniques for dating the Quaternary deposits in the Hanford area.
This study consisted of a
one day field reconnaissance and a brief review of the, geologic literature compiled by WPPSS.
Focus of the field reconnaissance was on dating techniques that would apply to a fault exposure near Wallula Gap (Figure 6) and immediate area.
Three samples of caliche for uranium series dating were collected and dated.
PART I PALEOMAGNETISM SAMPLE COLLECTION AND ANALYSIS Paleomagnetic samples for this study were collected by two techniques.
The most common technique for friable material was to hand carve a pedestal of the rock to fit into a 5
cm plastic cube.
The cube was oriented before removing the sample from the outcrop.
The samples were sealed inside the plastic cubes with non-magnetic fiberglass resin.
The remaining samples were collected in oriented blocks from the cemented or consolidated lenses.
These blocks were carefully re-oriented in the laboratory and sample cubes cut from them.
The approximate orientation errors for these samples is less than 5 degrees and randomally distributed, which for the purposes of this study does not affect the interpretation of the results.
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Woodward Clyde Consultants Two samples were usually collected at each stratigraphic level to compare magnetic signatures as a check on the consistency of magnetization and the magnetic stability of the rock units.
An attempt was made to sample at 5-7 meter stratigraphic intervals, although for the most
- part, samples were selectively collected from the more resistant and most unweathered units.
The samples were measured with a
superconducting rock magnetometer and were demagnetized in steps in a
400 hertz alternating field (AF) at four or more demagnetization levels.
The number of demagnetization levels varied depending on the magnetic coercivity ranges of the samples.
The AF demagnetization unit is magnetically shielded and rotates the samples about three axes during demagnetization.
The results of the AF demagnetization provides a
means to evaluate the magnetic stability of the section by comparing the relative direction and intensity changes during demagnetization.
These and other aspects of the paleomagnetic procedures are presented in.
Appendix A.
All data were recorded and computed during measurement by an on-line computer.
These data are shown in listing and plot form for each individual sample in Appendix C.
RESULTS Rin old Formation Magnetic stability of the Ringold Formation is generally good, based on the relative declination and intensity changes during demagnetization.
Of the approximately 37 stratigraphic
- levels, samples from a portion of the section (40 to 50 meters above the base) had large secondary magnetization overprints.
The resultant directions from this portion, although probably representing true
- polarity, may not represent the original
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Woodward Clyde Consultants magnetization direction.
The variation of declination and inclination with stratigraphic height above the base for both the natural remanent magnetization (NRM) and the selected demagnetization levels are shown on Figure 7.
These same results plotted on a
stereonet are shown on Figure 8.
The improved grouping for both normal and reverse direction after demagnetization further demonstrates magnetic stability.
The degree of magnetic stability of this'ection is also shown by the intensity of magnetization (Figure 9).
The magnetization of samples from 70 meters and above was more stable than most of the lower section.
This part of the of the section has a consistently higher intensity of magnetization (Figure 9).
The most unstable samples are from the part of the section between 40 and 50 meters and they have relatively low magnetic intensities.
The weakest NRM intensities were 2
to 3
x 10 emu/
cm for the ash unit at approximately 65 meters above the base of the section.
The magnetic polarity for this section of the Ringold Formation is shown on Figures-10 and ll.
Figure 10 is a plot of the VGP (Virtual Geomagnetic Pole) latitude versus stratigraphic height above the base with magnetic polarity and Figure ll presents the magnetic polarity with a
schematic section.
The section consists of a loess unit with normal magnetic polarity overlying a
reversed magnetic polarity
= section of
/he Ringold Formation, which extends from approximately 100 meters to 25 meters above the base.
A.
possible polarity transition occurs between 25 and 20 meters.
Below 15 meters above the base to a
sand lense in the conglomerate, approximately 3 meters below the
- base, the magnetic polarity is normal.
Only three stratigraphic sampling levels were collected between 30 and 60 meters, which is inadequate to fully assess
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Woodward Clyde Consultants the magnetic polarity of this section.
- However, on the basis of three samples between 40 and 50 meters, it is probable that the part of the section between 30 and 60 meters is also of reversed magnetic polarity.
Sample level 22 has apparently normal magnetic polarity.
This sample was collected at the top of the reversely polarized part of the Ringold Formation.
Samples of the Ringold Formation and caliche cap collected a
several hundred feet laterally of few feet stratigraphically above sample 22 have normal magnetic polarities.
Further samples from this and adjacent sections at closer spacings will be required to-resolve whether or not a
normal polarity exists at the very top of the exposed Ringold Formation in this section.
Crai s Hill Loess De osits previous paleomagnetic work has shown that the loess deposits that overlie the Naneum conglomerate on Craigs Hill have reversed magnetic polarity (R.
D.
- Bentley, personal communication).
Magnetic stability of samples from 11 stratigraphic levels from this site, based on direction and intensity change during AF demagnetization, was good.
One sample level, level '38, showed a large secondary magnetization component, and samples from level 40 had some secondary magnetization.
This secondary magnetization was removed at approximately 100- oersteds.
The inclination and declination of these samples versus approximate stratigraphic height above base are shown on Figure 12.
The directions of magnetization of these samples are shown also on a
stereonet plot in Figure 13.
A comparison of the grouping of directions at NRM and after AF demagnetization shows the good magnetic stability after removal of secondary magnetization components.
The NRM intensity of magnetization of these samples range from 2 x 10 to 1
x 10 emu/
cm after AF demagnetization g'igure 3.4l.
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Woodward Clyde Cansuttants The VGP latitude and polarity of samples from the Craigs Hill loess section is shown in Figure 15.
Approximately the lower 3 meters of the section has reversed magnetic polarity and the portion of the section above approximately 4 1/4 meters has normal magnetic polarity.
At this location, at least three loess depositional units have been mapped (R. A.
- Bentley, personal communication).
- However, on the basis of examination during collection, it was not possible to distinguish more than an upper and lower unit.
A photograph of the lower portion of the upper unit is shown in Figure 16.
The lower unit, which represents the lower 3 meters of the section, had reversed magnetic polarity.
W mer Station Loess De osits The magnetic stability of these
- samples, on the basis of direction and intensity change during AF demagnetization, is good~
The amount of direction change during AF demagnetization was
- small, as shown on Figure 17.
The NRM intensity of these samples ranged from 9 x 10 to 3 x 10 emu/cm All samples from this section have normal magnetic polarity and are shown with VGP latitude versus stratigraphic height above base on Figure 18.
A photo of the sampled part of the section at Wymer Station is shown in Figure 5.
These loess deposits exposed in the bluffs on the west side of the Yakima River are interbedded with conglomerates and contain several ash layers.
The ash layer near the base is approximately 3/4 meter thick with two 20 centimeter thick ash layers in the overlying section.
R.
D.
Bentley (personal communication) has tentatively identified the thickest ash unit as the Magama ash.
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Woodward Clyde Consultants CONCLUSIONS Rin old Formation On the basis of these preliminary
- studies, the Ringold Formation exposed in White Bluff has been shown to be magnetically stable and to contain a
polarity sequence suitable for correlation and possible age dating.
The stratigraphically
- thick, magnetically reversed secti'on confirms that the age of the Ringold Formation is older than 700,000 years (Appendix A).
Crai s Hill Loess De osits The loess deposits overlying the Naneum conglomerate on Craigs Hill have good magnetic stability.
The lowest loess
- unit, approximately 3 meters
- thick, was deposited in a
reversed magnetic field.
On the basis of this magnetically reversed
- section, the deposits in the lower portion of the section are older than 700,000 years (Appendix A).
mer Station Loess De osits The magnetic stability of loess deposits from the section near Nymer station is good.
The loess deposits have a
normal magnetic polarity
- and, although not def initive
- evidence, suggests that these deposits are younger than 700,000 years.
PART II AGE DATING EVALUATIONS INTRODUCTION In addition to the paleomagnetic evaluation of the Ringold Formation and selected loess
- deposits, an evaluation was made
Noodward Clyde Consultants of other possible dating or correlation techniques that might be used in the southeast Washington area.
If additional dating techniques could be shown to be of use in this area, these techniques would aid in the evaluation of the age of geologic faults and structures in the area.
The focus of these studies was exposures of a fault in the Wallula Gap area (Figure 6).
RESULTS possible dating techniques that could be used in the geologic setting of the Wallula Gap trench area include uranium series, carbon 14, tephrochronology, degree of weathering, and correlation of river terraces and Quaternary deposits.
Uranium Series Datin Caliche is a widespread near surface deposit throughout the southeast Washington area.
Three samples of caliche were collected from the Kennewick fanglomerate, exposed in the west wall of the Wallula Gap trench (WNP-1/4
- PSAR, Amendment 23),
and submitted for uranium series dating.
In the area of the Wallula Gap
- trench, the Kennewick fanglomerate is 5
to 6 meters thick and the caliche coatings that occur in the upper portion are 30 to 60 cm thick.
The Kennewick fanglomerate is predominantly basalt gravels with boulders as large as 60 cm.in diameter.
Sample A-1 was collected from an area of caliche concentration in and on a
group of boulders lying above a
zone of fault gouge approximately 3-5 meters wide.
Sample A-2 was collected from a
location approximately 50 meters to the south of Sample A-1 and consisted of scrapings of caliche coating from a large boulder.
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The results of the uranium series dates for these samples are shown in Table 1; the full lab report is in Appendix B.
These dates are widely spread.
The spread may in part reflect the thickness of the caliche coatings as sample B
was from a
relatively thicker coating than A-1 or A-2.
The young date for sample A-2 also suggests that the caliche
- process, is continuing today.
Table 1
URANIUM SERIES DATES ON CALICHES COATINGS FROM THE WALLULA GAP TRENCH Sam le Identification Age
~(ears
)
A 1 A-2 16g000
+ 3i000 2 000
+
1 000 55 f 000
+
5 /000 Sample B is from a locality approximately'ne hundred meters to the south of Sample A-2, and consists of scrapings of caliche from a
large boulder.
photographs of this sample location are shown in Figure 19.
Although caliche material at this sample location is relatively thick for the Wallula Gap
- area, no layering in the caliche coating could be observed'.
Thus the radiochemical processes and therefore dates should be considered to represent a
composite of the ages of precipitation and resolution of this material'.
Abundant caliche coatings on the underside of pebbles exposed.
at the surface suggest that the caliche process is continuing today.
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Noodwai d Clyde Consultants The 55,000 year date for Sample B provides a minimum date for initiation of caliche formation.
In this reconnaisance the relationship of the faulting to the caliche horizon was not examined in detail.
However, if the faulting in this area pre-dates the initiation of the caliche process it is older than 55,000 years on the basis of these dates.
- 14. technique can date material younger than 40,000 to 70,000 years which may aid in dating some of the younger soil forming episodes.
No carbon 14 dating was found in the reconnaissance of the Wallula Gap trench area.
Fossil Remains A small fossil was found near location A in the Wallula Gap trench.
It was contained in a pocket in the caliche cobbles and was discovered as these.
cobbles were collected for analysis.
The fossil consisted of a
well preserved jaw structure and teeth of a small rodent.
No attempts have been made, to date this fossil, as it is probable that this location is a burrow from the present surface.
River Terraces Mapping and stratigraphic correlation of the sequence of Quaternary river terraces developed throughout the area appears to be a valuable tool for relative age of surficial structural features in the southeast Washin~gto area.
The development of terraces may represent a
span of time from recent to the age of the Ringold Formation.
From a review of mapped geologic structures in the area, it appears that most of the structures have a definable relationship to terrace surfaces.
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Woodward Clyde Consultants Te hra Dating and Correlation There are a
number of ash units in the loess sections and within the Ringold Formation, and a number of volcanic sources for this ash material.
It might be possible to correlate or date certain of these ash units on the basis of sources or volcanic eruptive episodes.
Although extensive work would be
- required, the possiblity of using fission track, trace element chemistry, magnetic susceptibility, hydration rinds, or other techniques, or combination of techniques exists in these ash units.
CONCLUSIONS Uranium series, carbon 14, tephrochronology, and correlation of river terraces and Quaternary deposits are among the most useful dating techniques in the southeast Washington area.
Uranium series dates from the caliche
- deposits, which are widespread throughout the area',
show a
large span in ages.
The oldest date of 55,000 years should be considered a minimum age for the onset of the formation of the caliche deposits.
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(a) View to east showing bluffs of the cliffforming unit of the Ringold Formation.
Box is area of closeup shown in (b).
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PHOTOGRAPH OF RINGOLD FORMATION SECTION PALEOMAGNETISM AND AGE DATING WPPSS HANFORD PROJECT Project No. 13891A Woodward Clyde Consultants Figure 2
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PHOTOGRAPH OF WYMER STATION LOESS SECTION PALEOMAGNETISM AND AGE DATING WPPSS HANFORD PROJECT PrOjeCt NO ~ 13891A Figure 5 Woodward Clyde Consultants
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DECLINATION INCLINATION 90 180o 270o Oo 90o 90 50 co 50o 90o DECLINATION INCLINATION 90 180o 270o 0o 90o 90o 80o Oo 80o 90o 110 PS'4 w II
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13891A Noodward Clyde Consultants Figure 7
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13891A Woodward.Clyde Consultants Figure ll
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13891A Woodward Clyde Consultants Figure 15
43 42 41 View to southwest of outcrop of loess deposits at Craigs Hill. Flagging, from base marks location of oriented blocks collected for samples 41 and 42, and at top collection of oriented cubes for sample 43.
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PHOTOGRAPH OF PART OF CRAIGS HILL LOESS SECTION PALEOMAGNETISM AND AGE DATING WPPSS HANFORD PROJECT Project:
No 13891A Woodward Clyde Cons'ultants Figure 16
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13891A Woodward Clyde Consultants Figure 18
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PALEOMAGNETISM Introduction Paleomagnetism is a useful tool for dating sedimentary, volcanic,and and igneous rocks.
The application of paleomagnetism is based on the fact that rocks record the direction and intensity of the earth' magnetic field during their formation and retain this magnetic infor-mation for thousands to billions of years.
The age dating aspect of paleomagnetism takes advantage of the fact that the earth's field is dynamic and has undergone a number of distinctive changes in the geo-logic past.
The record of these changes can be used to date geologic materials.
The most easily recognized of all these changes is a rever-sal of the earth's magnetic field. The earth's field has reversed many times in the geologic. history of the earth, and the last major reversal occurred V00,000 years ago (Figure 4-1).
Theory The earth's magnetic field undergoes various changes in both intensity and direction over periods of time ranging from nanoseconds to millions of years.
Reversals of the polarity of the earthts field, on which magnetostratigraphy is based, appear to have occurred randomly in the geologic past and are recorded in rocks worldwide. Complete reversals having durations on the order of 10 years are called mag-netic polarity epochs. Complete reversals having durations on the order of 103 to 10" years are known as events.
Significant changes in magnetic pole position, but not a complete reversal, having durations on the order of 103 years are called magnetic excursions. Allof these magnetic phenomenahave potential for use in dating, but polarity epochs and some events arethe best dated and documented in geologic sections throughout the world. Other changes in declination and inclination (the magnetic azimuth and dip; respectively) called secular variations, which take place on a continental scale and have durations of 10 to 2
103
- years, also have applicationto dating in specific geographic areas WOODWARD-CLYDE CONSULTANTS 168
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AGE (Milbon Years)
AGE' (Mi((ion Years)
O a 0.013
~ 0.030+ 0.005 0.110+0.005 0.180+ 0.02 0.280+ 0.03 0.350+ 0.03 POLARITY EVENTS 8 EXCURS(ONS GOTHENBURG EXCURSION LASCHAMP "EVENT" BLAKE "EVENT" BIWA I "EVENT" 8)WA 11 "EVENT" BIWA IE "EVENT" EXPLANATION NORMAL POLARITY REVERSEO POLARITY 0.7w0.05 a 0.82+ 0.03 0.85+0.03
~ 0.90+0.05 I
1.00+ 0.05 WATKINS 8 EXCURSION JARAMILLO"EVENT" WATKINS A EXCURSION 1.60+0.05 1.7020.10 1.85' 10 2.00+ C(05 2.10e'0.05 "GILSA" EVENT OLOUVAI EVENT REUNION 2 EVENT REUNION 1 EVENT 230a0.10 I,
Ape K/Aror C (O ifovailable, some bossd safety on strotipraphic losition, sedimentation rote, foeno, varw onolot)y>> etc.
NOTKl 8tatte, Loschamp one 8hns 2 7(! swats were named ln orieinol references, bvt may represent escers iona insteod of short events which ore fell rewrsots of the earth's rnottnetM field, Corelation ot 'Oilso event with type locality is nol confirmed.
CATA FROM:
8onhommet ond 8obtLtne l19671 Cce l1969); OalrymPle l)972);
Oramme ond Hay (1971); Kowoi,sl al(1972); KetLIa and Koci (1972);
Morner, et ol(1971); Noel ond Torlinp (1976); Opdyl ~ (1972) i Smith ond Foster (1969); ttts tttins l(968); ond others.
Figure 4-1.
Magnetostratigraphy for the last 2.5 million years.
WOOOWAllO-CLYOE CONSULTANTS
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such as Europe, wheretheknown magnetic recordover the past several thousandyears includes secular variations. In other areas, the secular variation pattern could potentially be developed and applied to corre-lation problems.
Basically, paleomagnetism can be used to detect latitudinal movements relative to the earth's
- field, rotations about vertical and horizontal
- axes, and relative stratigraphic position in the magnetostratigraphic record.
The application of paleomagnetic studies that has-the greatest-potential in engineering geology is based largely on. magnetostrati-
- graphy, which can be used as a relative age dating and stratigraphic correlation tool in detecting and dating possible fault displacements in time-stratigraphic horizons.
Paleomagnetic polarity zones in them-selves do not have unique characteristics that allow identification of, for example, an older normalzonefrom a younger normalzone. There-fore, some'racketing age data (paleontologic or radiometric),
as well as a moderately continuous geologic section, are usually required as a basis for identifying the. general age of the paleomagnetic
.zones.
Paleomagnetism isbasedon the characteristic ability of magnetic min-erals to record and retain, in some cases on the order of billions of years, the magnetic field in which they were formed. This property is called natural remanent magnetization (NRM). One way in which NRM is acquired is by thermal remanent magnetization (TRM). A magnetic mineral acquires its magnetization as it cools through its Curie point, th e temperature at which the atomic and molecular thermal energy become sufficiently low that the spin directions and magnetic moments become locked along the ambient field direction. Natural remanent magnetization in rocks is also dependent on many other factors, including crystal structure and crystal size.
Other ways in which rocks acquire NRM is by detrital remanent magnetization (DRM) and by chemical remanent magnetization (CRM).
DRM is acquired by sedimentary magnetic. particles aligning as small compass needles alongthe direction of the earth's magnetic field. CRM involves the oxidation or reduction ofiron minerals, forming secondary ItOODlNABO-CLYDE COMSVLTANTS 170
minerals such as
- hematite, magnetite, or tit'ano-magnatite; during their formation, these minerals record the direction of the earth's mag-netic field. It is by this CRM process that red beds acquire their magnetization
- and, although it is a secondar'y magnetization, it is usually assumed tohave occurredvery close tothe time of the formation of the rock and therefore, is a record of the field at that time.
Many other secondary factors, including viscous remanent magne-tization (VRM) and anhysteritic remanent, magnetization. (ARM), may have disturbed the original NRMin a rock, and a large part of a paleo-magnetic analysis isdirectedat discovering andremoving or correcting for disturbances to the original NRM direction.
Two techniques are commonly used for this process:
alternating field demagnetization and thermal demagnetization.
It is not always possible to correct for magnetic disturbances, and some samples may yield no useful infor-mation about their original NRM direction. However, the effect of such samples can be discounted because they are usually relatively few and can be detected and isolated during the analysis.
Procedure Samples collected for paleomagnetic analysis must be oriented at the time of sampling with respect to the earth's geographic coordinates.
The sample should be. collected, transported, and stored in a manner that does not disturb the sample physically, cause chemical alteration, oxidation, or. reduction of the sample, heat the sample significantly, or expose the sample to large magnetic or electrical fields.
Samples for paleomagnetic analysis are typically not large; usually they are one-inch-long sections of one-inch<<diameter core, or cubes approx-imately one inch on edge.
Consolidated material is either collected in blocks of a size appropriate for easy collection, or drilled with a small rock drill {typicallya chain saw motor adapted to water-cooled, one-inch-diameter, non-magnetic drillbits).
The rock drill facilitates the collection of well-oriented surface samples through the use of an orientation platform that can be slipped over the core before it is broken from the rock.
WOODWABD-CLYDE CONSULTANTS 171
For the sampling of unconsolidated material, the collecting techniques vary to fitthe nature of the material being collected.
They range from using small cookie-cutter-like devices, which work well in soft cohe-sive clays and
- sands, to the collection of large impregnated blocks that are trimmed on a rock or band saw to the proper size. Perhaps the most successful technique forthe collection of unconsolidated mate-rial involves carving a pedestal, placing a plastic cube over the ped-estal, orienting the cube, and removing the oriented sample encased in the plastic cube.
Subsurface unoriented core having only the top and bottom marked can be used for determining magnetic polarity on the basis of magnetic inclination alone.
This technique has been used successfully for both consolidated and unconsolidated rocks.
For this procedure to be applicable, the magnetic latitude of the site must be greater than approximately 20',
because at low magnetic latitudes the inclination is nearly horizontal and relative rotations of various sections of core would appear as reversals.
The most common, magnetometer in use today for paleomagnetic measurements is a spinner magnetometer, which spins the sample to produce a phase-and frequency-dependent signal that can be read with sensitivity above the magnetic noise created by the earth' magnetic field.
Many sedimentary samples are weakly magnetized and either cannot be adequately measured using a spinner magneto-meter, or the time required to measure the sample is long. A new type of magnetometer, a superconducting magnetometer, makes the measurement of very weakly magnetized samples rapid.
This mag-netometer takes advantage of the superconducting properties of many metals to create a;very stable magnetic-field-free space.
Paleomagnetic samples are usually successively demagnetized by one of two techniques:
alternating field demagnetization or thermal de<<
magnetization.
Single measurements using a superconducting mag-netometer take approximately 1 to 2 minutes to complete.
Several demagnetization steps are normally needed, but the total time required per sample is usually less than 30 minutes.
WOODWARD-CLYDE CONSULTANTS 172
Materials Any material that can acquire a magnetic field aligned along the field in which it formed (in the case of geologic material, the earth's field) may be used for paleomagnetic analysis if the original direction of magnetization can be determined, any possible secondary magnetization can be removed, and the orientation of the sample at the time of its formation can be determined.
Nearly.all igneous rock acquires a
magnetization upon cooling and can be used for paleomagnetic analysis.
Lava flows and dikes record the magnetic field during their cooling,.
which essentially represents an instant of geologic time.
Batholithic bodies cool over much longer pexiods of time; however, samples collected from separated sites can provide an average of the magnetic
-field of the batholith. Magnetic directions from batholithic material are often difficult to interpret because the original orientation is not recorded by an ancient horizontal reference mark such as a bedding plane.
Sedimentary rock ranging in grain size from medium-grained. sand-stone to finer-grained clay and silt usually provides a good record of the magnetic field.
Limestone, which contains very little ferri-magnetic material, has also been shown to retain good records of the earth's magnetic field.
Coarse-grained sandstone,and conglo-merate cannot be used for direct paleomagnetic analysis because a
large proportion of magnetic minerals are contained in the cobbles, which are oriented mechanically.
Age Range and Accuracy The app]ication of paleomagnetism to dating is dependent upon the facts that the earth's magnetic field is dynamic and has in the geologic past undergone distinctive changes.
The most major of these changes, reversal epochs and some
- events, are dated with good accuracy for the last 4.5 million years and are known with reasonable accuracy for Cenozoic and Mesozoic times.
The magnetostratigraphic column r
for the last 2. 3 million years is shown in Figure 4-1.
ItOODNARD-CL'YDE CONSULTANTS 173
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One polarity zone, reversed or normal, cannot be distinguished from another zone of the same polarity.
For this reason paleomagnetism requires other dates to provide a bracketing time so that the magnetic reversal sequence observed at a particular locality can be related to the known magnetostratigraphy.
For a minimum date only, the last major reversed epoch, which.occurs at the Brunhes-Matuyama boundary (Figure 4-1), proves an exception.
This paleomagnetic reversal is approximately 700,000 years old..
Therefore, in the majority of geologic situations dealing with the late Cenozoic Era, if a magnetically reversed section is present, it is at least 700,000 years old. Short, reversed paleomagnetic events ox excursions withinthe Brunhes Normal Magnetic Epoch, except possibly for the Blake Event, have not been well dated or documented by geologic
- research, and the likelihood of discovering these short events in most Quaternary geologic sections is small.
The accuracy with which a reversal can be dated depends on the parti-cular geologic situation., For example, in cases of continuous deposi-tion, the error in dating the sequence (given proper correlation of the magnetostratigraphy) would strictly be that error to which the date of the reversal is known, typically within 5 to 10 thousand years in the last 4. 5 millionyears.
However, in cases of discontinuous depo-sition, the reversal might occur at a time of non-deposition and the position of the reversal in the rock record may not represent the time at which the reversal occurred.
1
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Advantages and Disadvantages The advantages of paleomagnetic dating are that there is a wide range of materials that are amenable to paleomagnetic analysis and that the procedures required for the analysis are relatively inexpensive and quick.
However, several samples are generally required for reliable interpretations.
WOODWARD-CLYDE CONSULTANTS 174
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The disadvantage of paleomagnetic dating is that bracketing dates are usually required to define which reversal may be present in a particular rock sequence.
However, once these background data are established for a particular region, themagnetic stratigraphy essentially can serve as time lines that can be traced throughout the ax ea.
Facilities and Costs A commercial paleomagnetic facility was established by D. R. Packer for %'oodward-Clyde Consultants in 1974.
There are also several paleomagnetic laboratories available at universities and research institutions.
Because the use of paleomagnetic dating is very dependent upon the particular geologic problem, it is best to design a magnetic sampling pxogram geared to investigate a specific case.
An average geologic problem mayrequire only 10 samples or upto several hundred samples.
Each sample requires an average of 5 measurements costing approx-imately)10 per measurement,'r an avex'age of $ 50 per sample. Sample preparation and data interpretation, because they are very dependent on the difficulty of the problexn, are handled on a time-and-materials basis and average several hundred dollars in cost.
The time required for analysis is short.
An average project may take approximately two to four weeks, although in some circumstances arrangements can be made for acquiring results within one day's time.
References Bonhommet, N.,
and Babkino, J.,
- 1967, Magnetisme terrestre Sur la presence d'aimantations inversees dans la Chaine de Puys:
C.R.H. Aca. Sci., Ser. B, v. 264, p. 92-94.
Collinson, D. W., Creer, K. M.,
and Runcorn, S. K.,
1967, eds, Methods in Palaeomagnetism:
Elsevier, New York, 609 p.
- Cooke, H. B. S.,
- 1973, Pliestocene chronology: Long or short'?,
Quaternary Research,
- v. 3, p. 206-220.
Cox, A., 1969, Geomagnetic reversals:
Science, v. 163, p. 237-245.
WOODWARD-CLYDE CONSULTANTS 175
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Dalrymple, G. B.,
- 1972, Potassium-argon dating of geomagnetic reversals and North American glaciation, in Bishop, W.
W.,
and
- Miller, J. A., eds, Calibration of Hominoid Evolution, Scottish Academic Press, Edinburgh, Scotland,
- p. 107-34.
Eardley, A. J., Shuey, R. T., Gvosdetsky, V., Nash, W.P., Picard, M. D., Grey, D. C.,
and Kukla, G. J.,
- 1973, Lake cycles in the Bonneville Basin, Utah: Geol.
Soc.
America Bull., v. 84,
- p. 211-216.
- Gromme, C. S., and Hay, R. L., 1971, Geomagnetic polarity epochs:
Age and duration of the Olduvai normal polarity event: Nature,.
v.
10, p. 179-185.
Irving, E.,
- 1964, Paleomagnetism and its Application to Geological and Geophysical Problems: Wiley and Sons, New York, 399 p.
- Johnson, N. M., Opdyke, N. D., Lindsay, E. H.,
- 1975, Magnetic polarity stratigraphy of Pliocene-Pliestocene terrestial deposits and vertebrate
- forms, San Pedro Valley, Arizona: Geol.
Soc.
America Bull., v. 86, p. 5-12.
Kawai, N., Yaskawa, K., Nakajima, T., Torii, M., and Horie, S.,
- 19V2, Oscillating geomagnetic field with a recurring reversal discovered from Lake Biwa: Proceedings of Japan Academy, v.
48, p. 186-190.
Kukla, G. J.,
and Koci, A., 2972,. End. of the.last.interglacial in.
the loess record: Quaternary Research,
- v. 2, p. 3V4-383.
McElhinney, M. W.,
- 1973, Paleomagnetism and Plate Tectonics:
University Press, Cambridge, Massachusetts, 35V p.
- Moxner, N. A.,
- Lanser, J. P.,
and Hospers, J.,
- 1971, Late Weichselian paleomagnetic reversal: Nature, v. 234, p. 173-174.
Noel, M., and Tarling, D. H.,
- 1975, The Laschamp geomagnetic
'event'. Nature, v. 253, p. V05-V07.
- Opdyke, N. D.,
- 1972, Paleomagnetism of deep-sea cores: Review of Geophysics and Space Physics, v. 10, p. 213-249.
Smith, J.
D.,
and Foster; J.
H.,
- 1969, Geomagnetic reversal in Brunhes Normal Polarity Epoch: Science, v. 163, p. 565-56V.
- Stacey, F. D., and Banerjee, S. K.,
- 1974, The Physical Principles of Rock Magnetism:
Elsevier Scientific Publishing Company, Amsterdam, 195 p.
Strangway, D. W.,
- 1970, History of the Earth's Magnetic Field:
McGraw-Hill, New York, 168 p.
- Watkins, N. D.,
- 1968, Short-period geomagnetic polarity events in deep-sea sedimentary cores: Earth Planetary Sci. Letters, v. 4,
- p. 341-349.
WOOOWARO-CLYOE CONSULTANTS 176
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sourer ve DEPARTMENT OF GEOLOGICAL SCIENCES TELEPHoNE; (213) 746.27!7 Dr. Duane R. Packer Woodward-Clyde Consultants Three Embarcadero
- Center, Suite 700 San Francisco, CA 94111 Dec.
12, 1977 GEOCHEM W-4
- ,o fft RE: Uran'ium-series age dating results of.caliche samples from Washington
Dear Dr. Packer:
The radiometric dating on the three caliche samples you proviQeQ me (transmittal letter WPPSS 13891A-6500, dated 25 October, 1977) has been completed; We have attempted to make analyses on two splits of sample A-1 as adviseQ.
Unfortunately, on one of the splits, we encountered.
some.difficulties in the, radiochemical processing and were not be able to recover the results.
Hence only the data on the other split are reported here.
The sample size of A-2 was about 1.6 grams.
Although smaller than desired, it was still amenable to analyses because of the sample's higher-than-normal uranium content.
The analytical results and age estimates are presented in the table appended herewith (Attached Nl).
In the table, the
+
errors are one standard deviations derived from the counting statistics.
For a summary of the procedures in analysis and age cal-culation, please refer to Attached N2 of this letter.
A detailed discussion and evaluation of the dating method is given in a
'aper HTh-230/U-234 dating of allvial pedogenic carbonates in gravelly desert soils" by T.L. Ku, W.B. Dull, S.T.
Freeman and K.G. Knauss.
The paper has been presented at the 1977 Annual
'Meeting of Geological Society of America, and is submitted to the Bulletin of Geological Society of America for publication.
It is availble upon request.
Please note that inasmuch as caliche may form continuously over a period of time, the ages assigned in the table represent averacVes over such periods and thus are minima with respect to the onset of caiiche Eormation.
The relative ages of the three samples appear to be related to thickness of the caliche coat-ings; the youngest sample (A-2) has the thinnest coatings of
<1 mm. It seems likely that caliches are presently being formed in the area, at least for sample A-2.
cont...
UNIVI'.RSITYOFSOUTHFRNCAI.IFORNIA,I i.
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Dr. Duane R. Packer P.2 I understand that we are a little running behind the schedule.
Hope this will not cause any inconvenience to you. If you have questions regarding the results, I would be glad to respond.
Enclosed please also find an invoice for the work.
Sincerely, Richard Ku Professor
Enclosures:
- 1. Table summarizing radiometric and age data (Attached Nl).
2.
"Age determination of impure carbonates" by Teh-Lung Ku (Attached 52).
- 3. invoice.
RK/st
Radiiometric and Age Data on Caliches from Washington U234 (ppm)
U238 Th230 Th230 234 U
carb Th230 Sample*
No.
Age**
(103 yrs)
U Carbonate (ppm) 234 U
Th232 3.77+.15 0.25~.02 1.12+.04 8.25+1.69 0.16-.02 2.291.13 6.50+.42 1.01~.07 1.20~.08 l.ll+.09 62.8 0.14~.02 1613 (R) 2.01+-.07 (L)
A-2 (R) 2.08-+.10 1.05-.05 1.48-'.07 0.47-.02 0.02'.Ol 56.8 241 5.702.22 3.13+.28 1.124.05 1.31~.15 0.21-.02 2.00+.09 3.42+.21 0.995.06 1.30-".07 0.74-.05 3.32+.08 5.25~.24 1.06+.03 0.91~.04 0.45+.02 (L) 0.40'.03 55+ 5
- 57. 0 (R)
- (L) and (R) refer to the HCl-leachate fraction and residue (HCl-insoluble) fraction, respectively.
- Ages are calculated from the (Th
/U
)
data.
See Attached 52 for explanation.
230 234 carb
I I
I I
I I
I I
I I
I t
. racticn, during the leaching
" eat.".)ent are in order.
The correction is based on the assertions that the Tn found in the leachate comes rom the HCl-insolubles and th'at these insoluble phases should be old enough (e.g.
> 1 million years) so that their U
"/U and Th
/U
" ratios are equal to the equilibrium value of 1; 00.
This leads to an estimation of the activity ratio Th
/U
" of the carbonate, or
( h /U '")
from the following formula:
[(Th
) L(%CaC03) (Th
) L(%CaC03) (Th
'/Th '
R] :{(U
) L(%CaC03)
(Th '
(SCaCOq) (Th~/Th~'~)R+[).-(Th
/U~~") ] (1-aCaCOs)
(U
)>)
Zn this expression, concentrations of all the radionuclides are in acti'vity units, e.g.,
dpm (di'sinti'grations per minute) per gram of leachable material (subscript L) and dpm per gram of residue (subscript R).
The age of'he carbonate is then calculated from the 'equation:
(Th /U
")
=
(U
/U '"gl exp( )oa)]
cryrb
+[1 '-
(U
/U
") ] [Xo/(XQ-X4).j[1 exp(X4-X() ) tj Where Ao and X~ are respectively the decay constants of Th and U 3";
(U
/U
") L refers to the activity ratio of the two uranium isotopes in the leachate fraction; t is the age.
Reference Cited Ku, T. L.
(1965)
An evaluation of the U '"/U 'ethods as a tool for dating. pelagic sediments:
Jour.
Geophys.
Res.
70, 3457-3474.