University of North Dakota UND Scholarly Commons
Theses and Dissertations Theses, Dissertations, and Senior Projects
1970 Authigenic analcite in the Golden Valley Formation southwestern North Dakota Marvin J. Furman University of North Dakota
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Recommended Citation Furman, Marvin J., "Authigenic analcite in the Golden Valley Formation southwestern North Dakota" (1970). Theses and Dissertations. 103. https://commons.und.edu/theses/103
This Thesis is brought to you for free and open access by the Theses, Dissertations, and Senior Projects at UND Scholarly Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of UND Scholarly Commons. For more information, please contact [email protected]. Authentic Analcite in the Golden Valley Formation (?),
SouthWestern North Dakota
by
Marvin J. Furman
Bachelor of Science, St. Lawrence University 1965
A Thesis
Submitted to the Faculty
of the
University of North Dakota
in partial fulfillment of the requirements
for the degree of
Master of Science
Grand Forks, North Dakota
July 1970 /~ \
..,;,, .. ..:. .. _.
.,·
,,,,:;, /
I I t ·-----·- t ,-~~·__: ...... ;.... "":."' b ..:;.:::.:,o~ I•, -·.- .. ~ ... ,., ' . -.JV·-'"'.••-
I:.Ao.m. t!"'.. e ·u:;::vcrsity v:: gree that the Libr-.'.l.ry of this University shall m::::.:{o it f1~00:y available i'"ol,... ir:.spoct,ion. I further agreo th~t permission for 0xtensiv8 cor,yi~g
in r-.is ~bso:-.. ce )' by tho of the Dcp::..rtmcnt
or othc:..,, Ol~ tt.a.s or
It is c2..lso . ·
given to rri.e the University of :.:.:r.y schol~~ly uze which m.ay c~ of a.,y material The field
Tho writer is ir.debted to his fellow g:i.~aduatc st"..l.d0r:.ts whc acted. as a
sounding board for many of the ideas eh-pressed hero .. Spccia.1 th~:1.}:s
are extended to W. J. ·stone for the use of his samples and to H. C.
Ziebarth for his inv.11.uable assistance and suggestions on photogr~phic
. :rep;r-od:uct ion ..
.:, I l
iv 1 ·~ .i~:..DL~~ c_~ '""' -·~·~~·~.~~~"\ s
?::..;:/3
.li.CKl\O~·~·LWGl·:Z\J?S . . • . .. • ...... :;_ ',/
LIST 01~ TABL:SS 0 . .. .. • ...... " . . vii
7" -ell" ;..;..LvJ. OF ILLUSTRP.TI Ol'JS . • • ...... • . • . .. . • • • . viii :_r-~~ ..'.BS '.:'.R.ACT . • • .. .. • . • • • . 0 • . • . . • . . . ..
~ INTRODUCTION • . • • . .. . " ...... • . • . .!.
Modes of Cccurrcnce of P.,:,-.alcits • .. . • .. . • • l Scope ar.d Pc.r-_pose of Study • • • • • • • • . . . 2 Previous Investigations • . • . • . • .. . . • . . J Description o.f Study Area • . .. . • . .. . . • • • . 3
METHODS Ob, INVESTIGATIONS • • • ...... • . . • .. . • . 7
Sarnplir,3 .. .. " • . .. • • " ...... • .. . . • • ? .Analyti::::::.l Procedures .. • .. • .. " . • .. .. • .. . • • • 7 G;:;::.G :.'\?.l ~ 0 Q .. • " ...... • ...... 7 ?ct:..... ~;~:.*"r.. :~hic PrGpara. tio:c. . • • .. • . • • . 8 ..... ::-·o g:...'\s.:Jhic a:.11d C·;,tic~l ~:c:.::.suramen ts • . . 8
Q 8 X-?..~}" Diff~'\action )11talysis .. " . . . • . . P-t'occdures for X-R2.y Diff:i.'"'actio:'1 }_YJ.a.lysis . • .. g ...... • ...... 8 Precision and Accuracy of "SGrni- Q.1antit.ative X-Ray Diffraction ll .c:.r-.tlysis .. • .. • • .. .. • . • .. " • • . .. D::;·:,,:;~... rninatio~ of Ana.lcite Corrrposition .. .. • • 13 Clu)'" l"line~tl Analysis • • • . . . • .. • .. • .. • 15 j c:. G~~i:1. Size ,Analysis ...... • • ...... • . -.-1
STPJ~'I:IGl'::ii.J;...-;;~.i 0 0 l? • .. • " . • .. " • • .. • . .. • .. •
G0nartl Discussion .. .. ~ " • ...... • .. .. l? fuscz-i i:;~~i.:>i'lS oi' Formatic~s E:;cposed :L."l the A;:0;;.. o:f .A.nalcite-ba~~ing Sedimenta:.:-y Rock::, .. • .. . l'? 'I·c:... ~"::..G Rivel"' :£i'ormatio11 .. • ...... • .. .. • • . .. f $ S.:/.~.-::i:-1el. Fo:c-m.:ition 0 Butte . .. . • • . . • • 19 ~ " ...-,r- C,.::;~::.,:;n Valley F o~rr.. c. ti en ...... ~v l.t . . " • " ~' .:;-__ .. d:."'on Formation .. • ...... • . .. 2.2. 3:.~ulo 2-::· Fom.ation ...... " ...... \: .. il{aree Formation . .. . • • . . • 22 Stl.~c;.tic~:r~~phic and Litholc;c;ic Distrioutic.n o:f .An:.:..lcito .. • .. . • • . .. • • . • . • . V c,,.,,.....,,..... ~ ...... , ?.) ...... ,i..;...... Dizctt!i~ion . iL~n.lc:i.tc ~~ ·c.ho Sontinol B:~:.to Itc:c-:r:.::.:tion . . ?.h I !.J.1alcitc in +·...,ne Golden V::..lloy Forr.-1~t:l.on . . . . . 2L;.. I ,.'i; ? BT!\OGR.J\.P h"'Y o·'.t' ANA:CITE-BEJ._q=:; G RCCKS • ...... 29 j:
!1inern.ls .. .. . • ...... • • • "' ...... 29 Quar-;;.z . .. • ...... • 29 Feldspar ...... g ...... • .. • . . 2.9 Chert . • ...... • .. . . • • " . 32 1~1~lcitc .. • .. • . . . • . . . . • • • • . • • 32 ,:,f,:.., Cl.:1~r l"1inoral~ ...... • • . . .,, j • l!. ', j~ Rock TIJr,os • . . • • . • . • . . • ,J ( • • • ~ .Arkoso . . • • . • • ...... 43 ][ lmalcimolite • . . • • . • . . . • • • • 53
DISCUSSION . • • . • . . • • • . . • • • . . . . . • • 64
J:,Iineral Associations • • .. • . • . . . . • • . • . • . 6l~ ll Analcite-Pyroclastic Association • • • • . • • . 64 I .Analcite-Quarlz Association ...... • • . . 66 lu~alcite-Feldsp~~ Association • . . • • . • 66 Analcite-Sericitc Association .. . . . • . 79 . I 80 Fok~mn.tion of Sphcrulites • • ...... • • • .;'ii Ii Relationship of L-rialcite Occurrences i·r... t!"'.. e . A11' Arkose and Analcimolite • • . • • • • .. . 82 ~1nr1 Relation snip of .balcita Pistributiori to the 85 Post-Eocene Unco:nf ormity • . .. • " • .. . • • • • r ! l SC/.:Y.i".:"li.Y OF CONCLUSIONS ...... 86 j .. • • • • • • . • • . • • • \
.li.l~P~"\JDIX . • ...... • .. .. • . . • . • • • • • • • • • • 88
B?ERE:i.'JCES 0 103 . • .. " • • . • .. .. • • • • • • • • • • • . • Ii, 1,t1i
: ,:ti:1 ·1111 'ii ,1
'.,r•·I 1·:1:J:1 ·.1U:I
'f;li'li' (111111 1111!1 ,1111111 _1 1m11
vi LIST OF T.A3LEs
Table Page 1 Vru.uos Used for the Calcula-::.ion o:f N"cd.'.?.l Compositions • • • • • • • • • • • • • • • • . . • • • • • 11 2 Standard Deviations of the Weight Fractions of: Minor.:ils Obtained by Direct Scrd.-Quar.ti tati ve X-Ray tiffraction .!L"l.:i.lysis • • • • • ...... lJ J I'linimum level o:f Detoct. ...1.bili ty of' Y1inor.:1ls by Semi-Quantitative X-Ray Diff~action .Analysis • • • • • • • • • • • • • • • • • • • • . . . . 14 4 Goneral.izcd Section of Formations Exposeq in the Arca ot· A:.-'lalcite-boa:ring Sedimentary Rocks in Southwestern North Dakota ••••• • • • • • • 18 5 Minerals Identified in Samples Taken in Reconnaissance Study ••••••••••
/' • • • • • • • • 25. ·O X-Ray Dii'.fraction Powder: Data for ..A.na.lcite • • • • • • • 41 7 Cox.position of J.na.lci te • ·• • • • • • • • • • • • • • . . 42 8 Grc.in-Size Data for Analcite-bearing .!h~kcse •• '>•••••9•o••••• " ...... 9 l'icda.l Comyosi tion of L"la.lci te-beari..ng .Rocks on S(mtinel Butte • • • • • • • • ...... 59 .. 10 lfod.al Co:npcsition of .l\..i-:talcite-bearing Rocks en Flat Top Butte.·· ••••••••••• • •• 61 11 Modal Composition of 1:...'1alcita-bea:i:-ing Rocks on Bullion Butte .. • · • • • • .. • • • • • • • • • •
12 :Kodal Corc:oosi tion of }:n.alcite-be~ring Rocks c::i Slide and Cru:i.JJ~J Buttes • • • • • • • • • • •.• 63 13 Confider.ca Levels at which the Hypothesis 'x;,::::0 :.! X,.;::;.,can be Accepted. a.s Significant • • • • 0 • • • 71 J.::-eal. Locations :...'1d Stratig-~aphic Positions of Specimens Cited i."1 'i'axt • • • • • 0 • .. • ...... 89
vii ,. C, :tcfcror.. cu }X..::i • z cr~:i..:...... , . . . .
4 .A.il~lcit0 Si)i'.to:'"""~litc wi~h ;5 R.:.::.di.:µ. St~~ct~~0 • • . . .
Analcitc Sphorulite with .:.. lVia.ssive )5 5 Center .::ind Peripheral Radial Sti:"Uc~ure ••••
6 Distorted, Coalesced, ~~~alcite • .. .. • • • • • " • • • • Coarso-Grained IJ.litic Katrix 7 • • • • • 37 (Sericite) .... • • .. • .. • • •
8 SG~icite L~clusions in J.nalcite .40 .. .. • .. • .. Sphe!"Ulite • • • • • ... " .. • •
C;; }fodtl Co.:nposi tion of A."l.alci te- 45 bearing 1.rkose ••• o. v o ••••• • • •
~ ,... Y.d.ne~alogic Classification of .J.U .. • .. • • 48 }.nalcite-bearing Arkose • ~ • • " • • • • G~ain-Size Distribution of .P..nalcite-beari.."lg Al."'kose " ...... • • 52
Coa1.,se Sc~icite Fl~kes Or·i.ented Ta:.~gantial to the Periphe~"Y o~ 55 Sphe!'Ulites. • .. • • • It • • o • .. • • • • • • • • • a • .. 55 Texture of Analcimolite • • • • • • • • .. . • .. • 58 Modal Composition of :..nalcimolite • • • • • ,.. _ l5 Classification of Analcite Based O) 0 • .. .. • on Composition ...... C •••• • ... • • • - ., ...LO Sc.s.tt'er- Dia.gra."ll of Analcite 68 Dat:.~it.ll Plagicclase .. • • • • • • • • • • • • • •
Scat.tar Diagram of J... "1.alcite 70 Datrital. Potassium Feldspar • • • • • • • • viii -· ,.., •' ...... _..., .... _._...,, ..
r- .• ~. 19 VA 77
20 Cc:rr:::,a:.."'":~o~r: of .: ¥--~:1 rs:: o:: ...:..:.1tlci~::.o i:: ~·...:.:~:_ci:.:c:...::..!..:.~ ,., ,.,..r,.., ,., ·,.- ,- w,,-,,,.. ~,,.,,. ~ t-..Jv,....,.v .J' .,,.. ..__ ' ... ,,,,
.-... ,.,_., ...J,.-.vv1/'..,.,
...... ," .,..,_n,,.-,y,"- Tb.e ~~lei "~o ., ...... v
' . r,:--,·,..._ .,-:\ occ.:...... cc~~rs
as spherulitos i:r: the interstic0s cf ..~: .. 0 ~:.~!{osG ~:':.Q £.:.S lJ. cc:r.:cn.t :'.L.:"i the
c-r,.. ~-..- Three types of sptcr~litos a~e recog~iz0~: (:.) - J,.. .. 1!,,; _ _ uli~es with an internal radial str-~cture; (2) sptc~~lite~ with a ~.as-
si.ve center a.-rid a peripheral radial st::c-u.cture; c:,.;r.d (3) spherulites
an i:.ternal ht:vi:-.g
OCC'i.1::.-' ir.d:. v:..c:c...::..:.iy
K-feldspa~, and i:.lite~
arkose ur.it
,.#0 ...:.:t.::~io~-.:. feldspa~... s. It ·oronos.ad that &nalcite ;. ...
b }.:'1~lci te ::.~ cl.:1ssified
chemistry~ .:::.nd tics ,;.iith the foldspathoids (Deer, 1963).
.'..J"a~:cite is gene~ally expressed as varLJ.tions in composition, in which potassium substitutes for sodiu...'11, and sodium and aluminum substituta for silicon (Wilkinsor., 1963).
.iL"lalcite occurs in igneous and sedimentary r-o;.;:c. It is a pri- rr.a:..":l n-.:.i:~e:..1 .:.l o::-..· la-ce forrac2tio:-1 in sorne inter:r..edi~tu .~r.G. basic igr:ecus
1T. c:.::..so fo:."l71S in
In sedimentary rocks ...... :: -·- occurs icositetra.-
1:..c~~::-.:::.::.. c:.j:::.tals, spnerulites, and most frequently as :.:-e::_:,l.:..ce:::er.ts of
?~c,csed·o?igins for analcite in sedime~tary rocks ~~e by: (1)
' .,..,Q'l -::,y CB·- ..-L: ~
,_ C,- '\).; :..·.~3..:-;tion and alte::c.ation of ot:;.er .c.lkali zeoli~~es ( C-ood\o·Tl:r_ a~~·:": uu....:.-
(4) reaction between saline wate~~ (Iel-
(5) reaction ~nd alteration of prirrw.ry tectosil~~~te
. - c~~tll1on authigenic sil.ic:::.te ::.::::.:.Y:Cl.._.J.-LS
.... ; . . . ~- c~~~ene~~c processes. generally~
-. '.)------c..~-:d ct:cmical .::..dju~trr:.cn.t o-:;.."" tb.o sediment aft or d.o:')cs::.. :.:..v ::.. ') -.,~, o::: ar..:ilcite by .:.lbite a:nd qua:...... tz (':'J.:::7::.er~ 19.58).
Pettijohn (1957) includas in ci~~genasis the precesses of cc~0nt~- tion~ authigenesis, diagenetic differentiation) intrastratal solu~ion,
~nd co:npactioi". Cementation is the precipitation of mineral matter in the voicis o~ a elastic sedimont, :esu~~ing i.~ i~d~~~tion or the sedi-
Luthigencsis :.s ·.:..10 :-.:-esult of reactio:i among the con-
on otb.ers ulready present.
fo:: the seldom.
::·;:~.:;:-~ cc:ap~otion ':Jecausa of the low torc.perature conditicr1s (:?ackr..:.rr. a...vid
l960). A typical
:::i:r.0:.:-:.ls ..
~:t~iS..s·tra:Cal solutio11 is a cherricul at.. trit.ion by so:ut:..c;c-.. s
-'-'-_:._::g en. ·.:.l:e e;c:1s·.:.i tuents of' a rock after deposition ..
SCC?E A?:.'D PU?.?OSE OF STUDY
...... ·::::. considered too~ :,:;ossible of p:-.y::;ic;:.l . . . in <.i:i.~;.::(.;{... ~ s ..... ~
studies. Net.a.Ole made ~y Coombs (1954) Coe:.::::;;:;, (:.959). Various
:11:..s study is another contri~ui:.ion to the ove:ra:l analysis.
A Dl~jor occu:rrenco of analcite in a single rock unit was sel;ected for
Occurrences of analcite v.rith respect to associated detrital and
u:d corr.position
PREVIOUS Il'ivE'SfIGA'I'IONS
r,-,\...... ~.i,. ... O
1·.o _iN_O -i,T., ·+ o _ v•·y ~·" ...i...Ong:.., _..., ua.e 48° N htitude. T'_,:.
.... - ... -... b:...-...:...::.11gs , Slope, '-,_,..,.,. ..,..,.,. ' ..!.~ )' .. ,.11..;.,'"""""""" .,,,
to 600 feet above tl:0 plain .. ra.ir... orosion. I ' •1-, ... • I The area is drained by the Little Y.d.ssouri Rive~ and its 1:.r:1.vu ... anos.
if Ill •.
Figure 1. .Reference Map ,-~l' 2S Kllldeor Mountain,
NOlllH OAll:OlA D I DUNN COUNTY
T lITTU -50UII RIVH l
OLDEN VALLEY COUNTY ___ I_ L BILLINGS COUNTY t
STARK COUNTY
_J
· SLOPE COUNTY . MEI'HODS OF INVESTIGATION
SAMPLING
Tertiary rocks in southwestern North Dakota have been sampled to determine the occurrence of authigenic analcite. A total of 252 spot
samples were taken. Analcite could not be distinguished in hand s~eci-.
men and was identified by x-ray diffraction analysis. This required sa.Illpling to be carried out in two stages. First, reconnaissance sam,..;. pling was undertaken to determine the distribution and major occurrences of analcite-bearing rocks. The.analcite-bearing rocks were then sampled in detail. Factors influencing the choice of sample localities included · the coourrence of complete sections, outcrops showing variations in lithology-, and sed.imentary structures. Sections more than ten feet thick were spot. sampled at five-foot intervals from the top of the unit. Sections less than ten feet thick were sampled ·at the base, middle and top. Selected oriented samples were ta.ken from sedimentary structures.
Areal locations and stratigraphic positions of samples cited in this ,. paper are given.in the appendix and Figure 1.
ANALYTICAL PROCEDURES
General
The analcite-bearing·rocks 'Were examined in thin section to de termine the characteristics, occurrence, and textural relationships
of the detrital and authigenic minerals •. X-ray diffraction methods were used :for qualitative and semi-quantitative mineral analysis. Grain ? 8 size distribution was determined by sieve and pipette analysis.
Petrographic PreEaration The majority ot analcite-bearing rocks used for thin sectioning were friable and required. special treatment. The samples were cut into slabs measuring approximately 1 X J/4 X 1/8 inches and impregnated us ing a technique.developed by Renton (1965).
Petrographic and Optical Measurements Thirty-one thin sections were examined.. An ocular micrometer was used for grain-size measurements. Grain shape was estimated. by visual comparison with a. roundness-spbericity chart (Krumbein and Sloss, 1963). Index of refraction was determined by the Becke line method. The com position of plagioclase in thin section w~s determined by Wahlstrom's procedure (1960). Extinction angles, measured with respect to aP propriate cleavage planes, were plotted on a determinative curve from which the molecular percent of anort.hite was read (Wahlstrom, 1960, PP• 120-125). Extinction angles were measured from the trace of {010} in fragments cut paralled to {001} , from the trace of {010}1n sections cut normal to { 001} and {01cj, and from the trace of the {010} plane in sections showing albite twinning or {010} cleavage.
X-Ray Di.ff raction Analysis
Procedures for .X...ray Diffraction Analysis--194 samples were se lected for routine qualitative and semi-quant~tative x-ray diffraction analysis. A sample me&1$Uring approximately 6 X 4 X 4 inches was crushed and a 20 gram sub-sample was taken. The sub-sample was ground 9 in a 8000 Spex Mixer/Mill in Spex vial 8001 for seven minutes. A secon:l sub-sample of 150 mg. was taken and ground in Spex vial 5004 for an additional seven minutes. One gram of the sample was then back-loaded in a cylindrical, rotating sample holder. The following machine conditions were used: X-Ra.y Generator (Phillips Constant Potential .50 KV-.50 ma).
X-Ra.y Tube. (Machlett Cu Tube-Short Anode) 37 KV-18 ma. Diffractometer (Phillips High Angle)
l degree 2 Q scan speed. l degree divergence and anti-scatter slit.
Ni filter. Detector (Phillips Scintillation-Transistorized) 1.0 KV. Circuit Panel (Phillips 12206/53), Bristol. Recorder.
PHA, width 3.5v, l.evel 6.ov. Linear scale •. l second time constant. 2 X l.03 counts per second. 30 inches per hour chart speed.
Minerals were identified by peak position and relative intensity on the diffractogram. Di:f'fractograms of reference minerals and the ASTM File wel"e used for reference.
Modal c~mpositions were semi-quantitatively determined by the meth f 11111 (,i [Ill:,,a od and developed by Alexander and Klug (1948) modified by !£1roux,. et al. ,1111 -- 11111' I pU (19.53) and Karner (1968). The weight fraction of a given mineral. com ponent was cal.cul.a.tad :from the expression& 10
= I •As* X1 (-) -• I .,A 1 where,
X = weight fraction of component 1. ~i:-= ma.ss absorption coefficient of component 1 • .;(,(':'=mass absorption coefficient of bulk sample. I= intensity diffracted at a definite Bragg angle 20 by crystal line component 1 in the bulk sample. (~) = intensity diffracted at a definite Bragg angle 20 by pure • crystalline component 1. The equation expresses the weight fraction o~ a mineral component in the bulk sample as a ratio of the peak intensity of the mineral compon ent to the peak intensity of a pure standard mineral, corrected for ab..; sorption. Leroux, --et al. (1963) further established the following re- lationship to experimentally determine the absorption correction:
where,
,r.:? = apparent density of a pure sample of component 1.
J°s = apparent density of a sample containing weight fraction X of component 1.
T0 = intensity of incident x-ray beam.
T5 = intensity transmitted by sample containing weight fraction X ~! component 1.
T1 = intensity transmitted by pure component 1.
Measurements were ma.de of the peak intensity of a given com ponent in the bulk sample and ~orresponding· intensity of the pure com.- ;1
u. ponent. The peak intensity of the component in the bulk sample was determined by the difference between the peak height and backgro.und intensity. Values for the mass absorption coefficients of the miner als were taken from Tatlock (1966) or calculated from the data of Klug and Alexander (1954). The values used for the calculation of the weight fractions are given in Table 1. The results of these analyses are given in Tables 9, 10, ll, and 12, and Figures 9 and 14.
Precision and Accuracy of Semi-Quantitative X-Ray Di.ffraction Mineral Analysis-... Ex:pressing the results of the analyses as semi- quantitative rather than quantitative implies a lesser degree of ac~ curacy. Error has been introduced by using standards for measurement of 100 percent peak intensity that are not from the sample (standards
.1 TABLE 1. VALUES USED FOR THE CALCULATION OF MODAL COMPOSITIONS UND Mineral Peak Posi- 100 percent Intensity Mass Absorption Specimen Standard tion 29 (counts per second) Coefficient .3.3 Quartz 20.9 1200 3S 825 Potassium 27.5 1640 49 Feldspar 43?4 Sodium Plagio- 28.0 2800 clase 2506 Analcita 15.9 1604 34 2.382 Muscovite 17.8 900 43 *Total Clay ·19.9 190 .36
Bul~le 40 ( ..
* Clay fraction standard separated from samples 12 taken from U. N. D. , Department of' Geology Ref'erence Collection). As the properties of' the mineral components of' the sample depart more f'rom the riorm of' the standards, the results become more semi-quanti tative. The range of' composition and crystallinity of' the minerals in the sample is narrow and does not vary systematically. The intro duced error, there.fore, is approx:i.mately constant. The data has beeri used only for comparison within itself', and in this respect is con sidered valid. . Niskanen (1964) investigated the accuracy and precision of' direct quantitative x,..ray diffraction analysis. The mean error of an analysis of a synthetic mineral mixture was within two percent. However, the accuracy of an actual rock analysis was considerably poorer, with a mean error of approximately ten percent. The variables af'fecting the reproducibility of data obtained by the previously described technique are: (1) inconsistencies in the measurement of peak intensities; (2) variations in packing the unori ented power and the degree of p~ferred orientation in the power; and (3) variations in the grain size of ·the powder due to inconsisten cies in grinding. To evaluate the affect of these variables on the reproducibility of the data eight samples were selected and scanned three times after unloading, remixing, and repacking. The standard deviations of the computed weight fractions of the individual minerals r 11 in the bulk s·ample &'I'S givan in Table 2.
· The minimwn limit of detectability of a mineral component·in the bulk sample is largely a function of the cry~tallinity of the substance (Klug and Alexander, 19.54 ) •. A poorly crystallized mineral may be a 13 TABLE 2. STANDARD DEVIATIONS OF THE WEIGHT FRACTIONS OF MINERAI.S OBTAINED BY DIRECT SEMI- UANTITATIVE X-RAY DIFFRACTION ANALYSIS Mineral. Standard Deviation er ten
Quartz 0.08 Potassium Feldspar 0.17 Na-plagioclase 0.34 A:nalcite 0.10 Muscovite 0.94 Total Clay 0.35
major component of a sample, but may not yie+d a significant peak. Generally, a peak was considered significant and the intensity was measured, if the peak was approximately three standard deviations of the height of the background peaks above the lower boundary of. the ·lrP' ·~· i 1j"l background trace. If a peak did not fulfill the above conditions, but ta 'I was still considered present, the minerals was reported as a trace a J1i ~ mount. The a.mount of a mineral tha.t was reported as a trace varies ... J :' . :: ~ with the substance. The amount of a mineral reported as undetected or trace, therefore, may range from colllplete absence to the maximum values in Table J.
Determination of Analcite Compgsition Fifteen samples were selected to determine a.nalcite composition. The samples represent the vertical and lateral extent of analcite bearing rocks in the Golden Valley Formation {?). The procedure used !or this analysis was developed by Sa.ha. (1959; 1961). It is based on variation of the {639) peak position of analcite with varying unit cell 14
TABLE 3. MINIMUM LEVEL OF DE.TECTABILITY OF MINERALS BY SEMI-QUANTI TATIVE X-RAY DIFFRACTION ANALYSIS Miheral Minimum Level of Detectability (parts per ten) Quartz 0.2 Potassium Feldspar 0.1 Na-plagioclase 0.1 Ana.lcite 0.1
Muscovite 0.2 Total Clay 1.2 composition. The composition is expressed as the silica ratio:
2 Si0 /Na o + .AJ. o • Silicon was added as an internal standard. The 2 2 2 3 sample was scanned through 78.5° to 76.0° 28 at 0.25 degrees per min ute, using a cha.rt speed of 1.5 inches per hour. The previously de scribed diffractometer was used. The angular difference between the (639) peak of analcite and the (JJl) peak position of silicon was plot ted· on Saba's (1959) determinative curve; from which the silica ratio was read. Each sample was seamed three times and an average value was used. The average of the standard deviations of the replicate analyses is 0.04.
A predominantly monominera.lic specimen (4775) allowed easy con centration of analcite for indexing. The sample was crushed and en riched by notation. The decanted fraction, dried, was ground with a mortar and ..Pestle by hand for ten minutes. Quartz was added as an internal standard to detect peak shift due to misalignment or instru ment.response. The sample was scanned through 80° to 2° 20 at 0.25 degrees per minute, using a cha.rt speed o:t 1.5 inches per hour. 15
Clay Mineral Analysis Four samples of analcite-bearing arkose were selected for a de- tailed identification of clay minerals by x-ray diffraction. The sam ples were disaggregated by· crushing and')' 41/J fraction was separated by sieving. Smaller fractions were separated by settling in an aqueous suspension. Oriented and random mountings were prepared. Oriented mountings of 4.)i, 2,,1,(, and Grain Size Analysis Twenty-seven samples representing the l4teral and vertical extent of. the analcite-bearing arkose were selected for grain size analysis. 16 The samples were disaggregated by crushing as recommended by Folk (1964). Sand-sized and smaller grains were separated by sieve analy sis. The sand-sized grains were divided into the basic divisions of sand-sized material 0£ the Wentworth Scale. The silt-clay fraction was di£ferentiat4;Ki using North Dakota Geologica1 Survey Procedure A-65 (Clayton, 1965 ). The results 0£ -,these analyses are given in Table 8 and Figure 11. .1w1 J •f I t '11 ' -~ ill i: I ir1t1 1if l· [ii I ; !'i!' .:, 111 ·1. : ; 111• ~ ill i •• lllill ':r·:,,~·.· .-, ? :{:.-:-, ,. .:~·:?tt~1t':?'.::??'' ··r:.·~?-ft:?:f?:'c-::t?;~\~,-f~~:~~~~1/r:~trtr2"~~{f'~fl~~-r~~'f'~~f~~t1J~l.. :: ~ 'N ... ~· . TABLE 4 . GENERALIZED SECTION OF FORMATIONS EXPOSED IN THE AREA OF ANALCITE-BEARING SEDIMENTARY ROCKS IN SOUTHWESTERN NORTH DAKOTA SYSTEM SERIES GROUP, FOffi1ATION, MAXIMUM LITHOLOGIC CHARACTERISTICS MEMBER THICKNESS ; ARIKAREE 260 feet Greenish-white to light gray cross-bedded MIOCENE FORMATION (? ) (Denson sandstone and siltstone interstratified with and Gill, limestone. Light gray friable sandstones. 1965) Pyroclastics. (Denson and Gill, 1965). . i- UNCONFORMITY BRULE 250 feet FORMATION (Denson and Predominantly tuffaceous silts. r.-ni. lG6t;) !~µ'.I~- OLIGOCENE E-4 C, 190 feet Sandy claystones, coarse-grained locally con- CHADRON glomeratic sandstone, bentonitic claystone, f....l j FORMATION (Denson anc co Gill, 1965 fresh water limestone interbedded with silt- -UNCONFORMITY stone. (Denson and Gill, 1965) TERTIARY f4 11DICKINSON 11 150 feet MOlBER (Hickey, Yellow to gray J Massive sandstone up to ~6 1966) micaeous sands 70 feet exposed. Tan to ::,.I;:! EOCENE and sandstones. white, medium- to coarse- ~! grained. Locally cross- sogr:,:. Light colored bedded. Questionable "HEBRON" 45 feet kaolinitic clays western facies of the MEMBER (Hickey, and shales ? Golden Valley Formation. 1966) · i- UNCONFORMITY (Hickev. 1CJ66) i 620 feet Dark gray bentonitic claystone and shale. z SEN'rINEL BUTTE (Royse, Buff to brown sandstone. Beds of lignite. 0 FORMATION 1967a) ~~ PALEOCENE 0 ~ ffi 520 + feet Gray to tan sandstone, siltstone and shale. 0 TONGUE RIVER µ:, (Royse, Beds of lignite. FORMATION 1967a) ~~'"!"I'-·~~=--.-· t _,,-,:~:c"o·.~'iiii: ~,i,...... ,.... . ,.~. ------±¢'.T"77 mm:· ==="'="==--~- --= = =- ==-- . - •ijj.' !!!! lf!'Jftll flrff<:::~.'-,_ -:"' ..::.._.,. i,,4 ..;.. ,,... i,,.... .;:;;._ ~_...... r.T~ . ~;::--;;._ -~ 19 described and named by Leonard (1908; 1911). Leonard and Smith (1909) differentiated the Fort Union "Formation" into the Tongue River and Sentinel Butte Members. Royse (1967a) ha.s redefined the Tongue River and Sentinel Butte as formations. The Tongue River Formation,generally, rests conformably on the Ludlow and Cannonball Formations of the lower Fort· Union Group (Denson and Gill, 1965). A. local hiatus, however, is recogni·zed at the Tongue River-Cannonball contact (A. Cvancara, Department of Geology, University of North Dakota., personal communication, 1970). The Tongue River For mation is composed of fine- to medium-grained, cross-bedded sandstones,· shales, clays, claystones, and lignites. Published measurements of the "'r. thickness o:t the Tongue River Formation vary widely. The author con \ ' ( ! 1' 1,,11 siders Royse•s figure for thickness (1967a), of approximately JOO feet i ill ' 1 ';1r1 11111 in southern Golden Valley County, the most accurate. The Tongue River 11'1] ; ~, I' :I Formation is exposed in Golden Valley, Billings,-Slope, Stark, Dunn, I ' "\ J McKenzie, Williams, and Morton Counties, North Dakota (Royse, 1967b) • Sentinel Butte Formation The Sentinel Butte Formation rests co~ormably on the Tongue River Formation. It consists of clays, shales, lignites, and sandstones inter bedded with sands, siltstones, claystones, and marls. Reports on the thickness o:t the Sentinel Butte Formation, like the Tongue River F~rma tion, vary ~~ely. The Sentinel Butte Formation is exposed on major buttes in Golden Valley, Billings, and Slope Counties, North Dakota and along the Missouri Escarpment· (Royse, 1967b). TABLE 5 MINER:ALS IDENTIFIED IN SAMPLES TAKEN IN RECONNAISSANCE STUDY Plagioclase Potassium Volcanic Specimen* Quartz Felds:Qar Feldspar Analcite Calcite Ihlomite ClaI Glass Muscovite Sentinel Butte Formation 5957 X X X X 4749 X X X X X 5983 X X X X X N· 5997 X X X X X X .X \J\ 5974 X X X X X X 5998 I X X X X X X .5971 X X X X X. X 5999 X X X X X X X 6000 X X X X X X 6001 X X X X X X X .59e4 X X X 6002 X X X X X X X .598.5 X X X X *Refer to Appendix and Figure 1 for areal and stratigraphic positions of cited specimens. -----·~------~_':;,,.:=__ wa-.1w a UI ,~Fil ~!'!""-""- - ---,.,.,,.,.. n,.,.. - f!! ._,I!! IIIT#'I/Fl!f!fll lu *# ,~ .,, {II . .. ~{ fl1I ..- LqiZ I... It~. L.&, TABLE J (continued) Plagioclase Potassium Volcanic SEecimen Quartz FeldsEar Felds12ar Analcite Calcite Dolomite Cla;[ Glass Muscovite 6003 X: X X X(?) X X 6004 X X X X X X X 5980 X X X 5978 x· X X X 5986 X X. ~ Golden Vallex Formation 4736 X X X X X 6005 X X X X X X 4724 X X X 4735 X X X 5973 X X X 4739 X X 4730 X X X 5989 X X ·a rhf-_.,, ------::;:-= = ".;\'':''~~;'r,< :_f'."~-{':~\f~ TABLE 3 (continued) Plagioclase Potassium Volcanic SE(!<:imen Quartz Feldspar Feldspar Analcite Calcite Dolomite Cl~ Glass Muscovite . 5981 X X X X X X 5982 X X X X X X 5975 X X X X X .5970 X X X X X X 5972 X X X X X X ~ 5796 X X X X X Chadron Formation 5977 X X X lJ.694 .x X X X X Arikaree Form~tion .{]_) 4742 X X X X X X 47i10 X X X X 47li·l X X X X 5988 X X X X X X ---·-· ------~,,,,,,./1111.,...... !~!'!'.~ "'~""·"' ··~-- ~ ... , ... -11 P'llrf';/ii!i! ... . ' Ti !ii'il . ,-iii' - ii, ~ TABLE 3 (continued) Plagioclase Potassium Volcanic S:eecimen 9£artz Felds:ear FeldsEar Analcite Calclte Dolomite Clal Glass MUS.£.(?.Yite 5987 X X X X X 4745 X X X X X 4744 X X X X X ~ I I, - ==~---···:::: _:.. - -- ... ":.--~ - '"!'_· • :::~ ---~ ------~ ------·------·------>"·-,99"·~ l'_;;Vf··~ 1~~-J · "lf-lJf1!P;" ..,.., - - ---n~-. Jrlf.. A ~s-- ---·------·- .. --·1--= 'li;l'!' II! .....·. ti·-."',:.,,II -· ""'- ·r_ ~------~ . .; ilt. · a PETROGRAPHY OF ANALCITE-BEARING ROCKS MINERALS QUARTZ Quartz is a constituent of all the analcite-bearing rocks exam I ined. It occurs as anhedra.l, detrital grains. The grains occur both Y! individually and a.s composites of individual grains. The individual grains range in sphericity .from 0.3 to 0.5 and average 0.4. The roundness ranges from 0.1 to 0.9 and averages 0.2. The grains have moderate to strong undulatory extinction. They range in diameter from 0.1 mm to 0.3 mm and average 0.2 mm. The composite quartz grains consist of aggregates of individual grains joined at sutured contacts. The composite grains range in di ameter from 0.2 mm to 1.7 mm and average 0.5 mm. The individual grains comprising the aggregates have slight to moderate undulatory extinction, and have approximately the same dimensions as the individual quartz grains described above. The grains occur in the sediment embedded in the cement or matrix. The grains are commonly embayed (Fig. 2). FELDSPAR Detrital plagioclase and potassium are both present in the ana.1- cite-bearing arkose. The plagioclase ranges in composition from AhsoA,n20 to Ab55An45 ~ However, due to possible ambiguity in determin ing the sign of extinction angles, the plagioclase maybe as albitic as Ar\o• The grains a.re anhedral and range in diameter from 6.1 :mm F.igure 2. Detrita.l quartz grain. Arrows point out embayed edge. The quartz grain is embedded in a.rgilla.ceous matrix. X JOO Crossed Nic9ls Specimen 4670 F.igure J. Detrita.l aJ.bite grain. Arrow points out pitted edge. The albite grain is embedded in a.rgillaceous ~trix. X JOO Crossed Nicols Specimen 4670 't )2 f~ to 1.0 nun and average 0.4 mm. The sphericity ranges from 0.3 to 0.9 t t~ and averages 0.6. The roundness ranges from 0.1 to 0.9 and averages 0.3. The potassium feldspar occurs as microcline and possible ortho clase. The microcline bas been identified by the characteristic cross hatched twinning. The grains identified as orthoclase, however, may I be untwinned microcline. The grains range in diameter from 0.1 mm to L: 1.6 mm and average 0.8 mm. Grain roundness ranges from O.l to 0 •.5 and , "' I i: averages 0.3. The sphericity ranges from 0 •.5 to 0.9 and averages 0.7. 1'1 The detrital feldspars, like the quartz, are commonly embayed (Fig. 3 ). CHERT Detrital chert occurs as anhedral grains ranging in diameter from 0.2 mm to 0.4 mm. There are also isolated and very minor occurrences of spherically shaped, possibly authigenic, cher:t, grains. ANALCITE Analcite occurs as spherical and sub-spherical grains ranging in diameter. from 0.1 mm to 0 •.5 mm and averaging 0.2 mm. Three types of grains are recognized: (1) grains with a radial internal structure (Fig. 4); .(2) concentrically-structured grains with a massive center and a peripheral radial structure (Fig • .5); and (3) grains without an internal structure or a poorly-defined internal. structure (Fig. 6). Thia mode of occurrence of analcite fits the definition of the term "spherulite" as used by Pettijohn (19.57, p. 96). Spherulites are defined as minute, sub-spherical, radial bodies which ha11e formed in, 33 ~, and which coalesce to form packed polyhedra. The spherulites with poorly-defined or absent internal structure are the most abundant. Spherulites with radial structure are the next most abundant, followed by the concentrically-structured spherulites. Analcite is generally thought to be isometric. However, the M.a.l tese cross interference figure on the radial spherulites and the slight birefringence indicates that the analcite is anisotropic. The optical I, behavior of the spherulites is dependent on the optical properties of ! •1 '1 Ii the analcite, the state of elastic strain of the individual crystal I' lites, and the relative crystallite orientation. The slight birefrin gence has been variously attributed to loss of water, strain, or to ordering of the Si, Al atoms in the structure (Deer,~&·, 1963). Coombs (19.5.5) has recognized a modification of analcite that is bire fringent and biaxial. Departures from the isometric lattice dimensions are not detectable, a1though weak anomalous reflections may appear. 1'-ray diffraction powder data for the Golden Valley(?) analcite (specimen 477.5) are given in Table 6. In contrast to the reference data for analcite (ASTM File--7-363, 7-340, and 19-1180) there are a number of minor reflections absent. Most of the absent reflections are in the high angle region (28)40°). In the low angle region (29<40°) three reflections are absent: . (4111 3:30), (420), and (.530, 43:,). This is similar to Crook's (1967) observations, in which the (411, JJO), (600, 442), ~ (200') refiections were noted to be weak or absent. In addition, (721), (8J..l), and (!Q.51) reflections were recognized, but do not correspond to a:ny reflection in the re£erence data. The signif icance of these reflections is·not immediately apparent. The possibil- Figure 4. Analcite spherulite with internaJ. radial structure. The internal structure is identified by the Maltese cross inter!erence figure. The partially included · detrital grain is quartz. The birefringent rim is sericite. X 600 Crossed Nicols Specimen 4672 Figure S. .Analcite spherulite with a massive center and a peripheral radial structure. Dotted line outlines the massive center. The spherulite is embedded in ~. sericitic matrix. X 600 Crossed Nicols Specimen 4672 Figure 6. Distorted, coalesced, analcite spherulites. These spherulites do not show any internal structure. Argillaceous matrix (illite ?) outlines the spherulite shapes. X JOO Crossed Nicols Specimen 4q72 'I Figure 7 • Coarse-grained illitic matrix (sericite ). Black areas are analcite.· · X 600 Crossed.Nicols Specimen 4672 !i ~1d1 ' 1;11• i',i,.. I llii i l· i iii i I iii r I I Ill I II I l i I I• 38 ity ofan unrecognized mineral impurity in the sample, however, must be considered. The composition of analcite is given in Table 7. The extremely fine-grained, polycrystalline nature o:f the analcite spherulltes pre cluded an accurate determination o:f the index o:f refraction. CLAY MINERALS lllite, and possibly kaolinite, are the only clay minerals that have been identified in the analcite-beari.ng rocks. Two textural mod ifications o:f the clay minerals have been recognized in thin section. A fine-grained variety occurs in the interstices o:f the arkose. A '\ coarse-grained variety also occurs in the interstices o:f the arkose (Fig. 7), and replaces detrital quartz and :feldspar. It also occurs as inclusions in the analcite sp~erulites (Fig. 8). The coarse grained variety consists o:f interlocking, platy flakes. This :fits the ' description of authigenic illite outlined by Carrigy and Mellon (1964 ). .l The coarse-grained illite replacing quartz also :fits the description Ill 11 11 ,•1 C o:f authigenic muscovite given by Rex (1966). Coarse-grained illite • Iii ; 1•im.: is generally referred to .as sari.cite (Pettijohn, 1957). Seri.cite, . •I 11•1. however, is intermediate in composition between the "ideal" composition , 1Jll;l; 1 11 i 1~ 1 11 I I '1 I and I o:f illite muscovite (Grim, 1968; Reesman ~d Keller, 1967). . t and ! 151 r Val.de Hower (1963) have proposed distinguishing between illite : 1,,, i polym.orphs ~ sediments as a method for identifying a.uthigenic illite. '.1;·:; I I Attempts :to identity the illite polymorphs in various size :fractions ::.I . I 11•1 o:f the analcita-bearing arkose ~re not conclusive. The critical peaks 'I,.! :for identification o:f individual polymorphs are very closely spaced (Grim, 1968). · The peaks obtained from the samples were broad and di.:f- '.39 fused, and individual peak positions could not be positively identi.f'ied. ' Figure 8. Sericite inclusions in an analcite spherulite. Birefringent rim around spherulite is also sericite. Spherulite is adjacent to detrital quartz grain and embedded in argillaceous matrix. X 600 Crossed icols Specimen 4672 41 TABLE 6. :X...RAY DIFFRACTION POWDER DATk FOR ANALCITE (SPECIMEN 4775) i,, I· (hkl) :· I (obs.) d (obs.) :: 200 l 6.811 6.860 80 5.6ll 5.600 2ll 220 27 4.822 4.852. 17 3.678 3.667 321 400 100 3.427 3.430 63 2.925 . 332 422 15 2.849 2.801 510, 431 28 2.683 2.691 27 2.508 2.505 5~ 440 15 2.430 2.425 10 2.287 2.287 600, 442 16 2.222 2.256 6ll, .532 640 19 1.903 1.903 15 1.866 1.867 721 10 1.811 1.802 730 21 1.740 1.748 · 732, 651 15 1.716 1.715 800 15 1.687 1.689 811 13 1.595. 1.595 831 13 1.416 1.400 932, 763 15 1.358 1.294 lOll 13 1;.287 1.2.88 774 10 1.264 1.265 12.33 13 1.223 1.220 1251 . l •.. .•;! E 'al 42 TABLE 7. COMPOSITION OF Ai.'W..CITE Specimen · 28 Anal. (639)-29 Si (331) 2Si02/ ( Ma2o + Al2o3) 4670 i.ao0 4.28 4775 1.80° 4.28 4684 1.82° 4.35 4686 1.80° .· 4.28 4678 1.86° 4.52 4727 1.83° 4.43 6994 1.76° 4.00 699.5 1.a:3° 4.43 6996 1.73° 3.91 70ll 1.91° 4.8.5 4778 1.83° 4.43 7014. 1.86° 4 •.52 4674 1.82° 4.35 4773 1.80° 4.28 7008 1.87° 4.66 ROCK TYPES ARKOSE The minerals composing the arkose are quartz, chert, Na-plagio clase, K-feldspar, analcite, and illite. Chert is a minor constituent and is included a.s part of the quartz content. Fine-grained illitic matrix and sericite occupy the interstices of the arkose. The modal composition of the arkose is given in Figure 7. Quartz is generally the most abundant mineral component. Analcite is usually the next most abundant mineral. The average analcite content is ap proximately 30 percent. The analcite ranges from complete absence to a maximum of approximately 70 percent. The feldspars are relatively minor constituents. The sum of the plagioclase and potassium feldspar contents, on the average, does not exceed more than 20 percent of the composition of the rock. Potassium feldspar is the more abundant variety. Seric:ite occurs sporadically and is generally a minor com ponent. However, it may comprise as much as 30 percent of the rock. The classification of the rock as an arkose is based on the amount of feldspar, total clay, and rock fragments present. Metamorphic quartz grains are the rock fragments. These components, re-computed to 100 percent, have been plotted on Folk's (1964) classification diagram (Fig• 10) • The majority of the ~ints are in the arkose and subarkose categories. ·· The arkose is texturally immature and poorly sorted. Grain sized data of the arkose are presented in Table 8. The a.rkose is character ized by a relatively high standard deviation. Th e grain-size mode is ' ,, . -. ~·.' itt 'fi'' ~ '"'' Figure 9. Modal Composition of Anal.cite-Bearing Arkose Data from samples oited in Tables 9, 10, 11, and 12. ,.' SERICITE I I I 4.li Ii.& 5.6' ·u TOTAL CLAY ~ .. t<- FELDSPAR t ;., 46 at the very fine sand-coarse silt boundary of tho Wentworth size clas sification. All samples analyzed show positive skewness toward the fin er grain sizes. In a plot of the sand-silt-clay content of the arkose, the majority of the points fall in the sarid corner (Fig. ll). The grain-size distribution has a narrow range. ,,' '. Detrital quartz and feldspar make up the framework of the a.rkose. The grains are unoriented in the matrix. A small percentage of the quartz and feldspar grains are in contact. The interstices of the arkose are occupied by analcite and illite. f'r Analcite occurs as individual spherulites in the matrix or as aggregates of spherulites. In the aggregates the original spherical shape is dis torted to a polyhedral shape (Fig. 6). The spherulites range widely in diameter. Fine-grained illite and coarser sericite frequently out line the individual spherulites in the aggregates (Fig. 6). The spher ulites range from undistorted individuals in the matrix, to where the matrix between the spherulites in the aggregates has been reduced to a veinlet remnant. Matrix may not always be present at the boundaries of the distorted spherulites. Analcite and sericite frequently occur together in the arkose. Sericite oi'ten occurs as unoriented inclusions in the spherulites. Spherulites in the sericite matrix may have indistinct boundaries. Coarse sericite grains, where in contact with spherulites, are oriented with their long axes·tangential to the spherulites (Fig.'12). Spherulites occasionally occur in contact with detrital quartz , I a.".ld feldspar grains and are distorted. The spherulites may partially or wholly include the detrital grains. ;# Figure 10. Mineralogic Classification of Analcite-Bearing Arkose (After Folk, 1964 ). · Plotted points represent analyzed samples. 'I ! Q F~~-----~----~--'t.M Q--Orthoquartzite_ SG-Subgraywacke G-Graywacke SA-Subarkose A-Arkose FSG-Feld5pathic Subgraywacke · IA-Impure Arkose FG-Feldspathic Graywacka .•. ':':' 'i"'.V"~'HM%!(119M$1$1! tG))LQIJ44i . . TABLE 8 GRAIN SIZE DATA OF ANALCITE-BEARING ARKOSE Gra.In Size Grain Size Mean Skewness Specimen* . Median ( Q ) Standard Deviation 50 Mz=(¢16+t50+¢8'+) Skr=~l~-t~~-,2t50 + ~+185-2¢50 ()r= peJ..!'f/16 + ~ 4708 3.6 ¢ 4.3 ¢ + 0.56 1.3 ¢ 4691 3.J ¢ 3.9 ¢ + 0.65 1.8 ¢ 4783 3.1 ¢ 3.3 ¢ + 0.57 1.3 ¢ 4788 3.5 ¢ 3.9 ¢ + 0.63 1.2 ¢ 4748 3.1 ¢ 3.5 ¢ + 1.43 1.3 ¢ $ 4774 · 3.5 ¢ 4.o ¢ + 0.82 1.7 ¢ 4747 3.5 ¢ 3.9 ¢ + 0.45 1.4 ¢ 4785 3.3 ¢ 3.9 ¢ +·0.64 1.6 ¢ 4680 3.2 ¢ 3.7 (J + 0.61 1.3 ¢ 4675 3.0 ¢ 3.5 ¢ + 0.71 1.5 ¢. 4776 3.1 ¢ 3.5 ¢ + o.64 1.3 ¢ 4686 3.1 ¢ 4.6 ¢. + 1.33 1.5 ¢ 4672 3.6 ¢ 4.2 ¢ + 0.53 1.8 ¢ 4783 3.3 ¢ 3.7 ¢ + 0.46 1.5 ¢ *Refer to Appendix and Figure l for stratigraphic and areal locations of cited specimens ··-=""""="''"";,,=~. ""•'~"-·':,,C-. TABLE 8 (continued) Grain Size Grain Size Mean Skewness Standard Deviation Specimen Median ( Q_so) Mz=(¢16+P2o+¢84) sk1=~:9~~;~@i,o + ~;~~-~~~o (J1=¢84~¢16 + ~ 4670 J.4 ¢ 4.o ¢ + 0,57 \ 1.6 ¢ 4671 3.5 ¢ 4.1 ¢ + 0.55 - 1.5 ¢ 4679 . J.2 ¢ 4.o ¢ + 1.21 1.0 ¢ 4687 J.1 ¢ . J.6 ¢ + o.66 1.3 ¢ \J\ 467:, 3.1 ¢ 3.6 ¢ + o.66 1.8 ¢ 0 4674 3.2 ¢ 3.5 ¢ + 0.50 1.3 ¢ 4689 J.1 ¢ J.4 ¢ + 0.51 1.1 ¢ 4688 J.O ¢ . 3.3 ¢ + 0.71 1.1 ¢ 4707 J.4 ¢ 4.0 ¢ + 0.58 1.6 ¢ 4787 3.4 ¢ . 4.1 ¢ + 0.62 1.8 ¢ ia,:,.4111..•..•. _...... -~?~ ,r,_ b .... .-- '; ·- ---·-~---~- • ~ 18-"'I ;_;,- Si~-,-, !'i1I' 1:·~ ::. ... ' ~,~.,.;' ··- -.... ii.,'"·.. t·~~ Figure 11. Grain-Size Distribution of .Analcite-Bearing Arkose Plotted points represent analyzed samples. 1 11 .-~ I .!1111 II Ill 11 II 11 llii; I~, ~ l!i;q ..., ' fll1-- ' , ..!'. ! ' ·11ii. I •• sand silt · (I.Ot-4.. 01) (4.0fJ-8~08) .53 There are some differences in analcite content of the arkose in its lateral ro.."tent. The modal compositions of the arkose from the different buttes are given in Tables 9, 10, ll, and 12. Arkoses from Slide and Chalky Buttes have the lowest average analcite content, ap proximately 1.5 percent. Arkoses from Sentinel and Flat Top Buttes have approximately the same average analcite contents, 30 percent. Arkose from Bullion Butte has the highest average analcite content, approxi mately 40 percent. The analcite-bearing arkose, compared to the modal compositions of "typical" arkoses (Pettijohn, 1957 ), is notably dei'icient in potas sium and plagioclase feldspars. AN.ALCIMOLITE. The minerals composing the analcimolite are analcite, quartz, and illite. Analcite is consistently the predominant mineral component. The term analcimolite is applied to a rock type in which analcite is the principle miner~ constituent. Th~ anal.cite content ranges from approximately 40 percent to 80 percent and averages approximately 60 ' ! \ - percent. The modal composition of the analcimolite is given in Figure l I Ii ~ 1 Ir ! I 11• 14. 1' f I Ill Quartz grains form the framework of the analcimolite. The grains .· I t * I have high sphericity and low roundness, and have an average diameter • I f I of 0.17 mm •. ~cite does not occur as spherulites as it does in the 't I : I arkose, but occupies the interstices of the a.nalcimolite as the ce .' t I menting material. Analcite in the analcimolite appears to be massive, but a red stain outlines what might be individual grains (Fig. 13). ! I ! f 1. I. l4'~ \ l; '. I. 1 · :1 '. ''. f l l i j Figure 14. . Modal. Composition of" Analcimolite. Data from samples cited in Tables 11 and 12. I. ~-.. N=8 ANALCITE 100 Lu 0 z 50 Lu a: a: 0 7.5 ::> 0.5 1.5 2.5 3.5 4.5 5.5 . 6.5 0 0 0 LL QUARTZ 0 100 >- 0z 50 L1J ::> 0 0 1.5 2.5 3.5 4.5 5.5 6.5 7.5 LLl 0::: u...... z 100 TOTAL CLAY LLl 0 a:: 50 LL.I a.. ilfl 11 ~! 0 ii !Ill 0.5 ,.. 5 2.5 3.5 4.5 5.5 6.5 7.5 ii •. PARTS PER TEN : I ll II Ir II 'I II r II I II : tr , I• The average diameter of these possible grains is 0.08 mm. Analcite composing the analcimo~ite has approximately the same composition.as analcite in the arkose. lllite is present as irreguJ.a.r masses in the analcite. There is some variation in the analcite content of the analcimo lite in its lateral extent. Analcimolite i'rom Slide Butte has the high"'! est average analcite content, approximately 70 percent. Analcimolite from Chalky Buttes has the lowest average anal.cite content, approximate- . ly 50 percent. Analcimolite :from. Bullion .Butte has an average analcite content of approximately 60 percent. The modal compositions of the analcimolite from the different buttes are given in Tables lJ. and 12. .i••'':J I I: i111ia1I I 1 I , 1 !it· 11.llt:·, l I . ~1,,-.~r .. t::;·i, .. n:''!l!I'1,;I! ,,i ·;111, '\: Jll: 11111:: 1111:~·· c!:lll!I~' D1: 111~1: • ! 11::. I •· , I I I II r I ~ 11 I! ! I I ., I f I Ii Figure 12 •. Coo.rse soricite flakes oriented tangential to "t.h,:i periphery of spherulitcs. Black area are~ analcit~ spherulites. X 600 C:.~cssed Nicols Specime:r. 4670 ... l. -~&.:!:"a....:._Lt3..!.,.... -- Specimen L~775 TABLE 9 MODAL COMPOSITION OF ANALCITE-BEARING ROCKS ON SENTINEL BUTTE T. 139 N., R. 104W., GOLDEN VALLEY COUNTY S~ecimen* Quartz ·. Plagioclase K-Feldsea:r .Anal.cite Muscovite tsericite) Total Cla~E Total 7008 4.6** - 0.7 5.9 -*** T**** 11.2 7009 3.8 o.6 o.4 1.2 - 3.0 9.0 7010 4.8 - o.4 3.7 - T 8.9 ?Oil 3.4 1.5 0.7 1.8 2.0 9.4 - '-" 7012 5.6 1.0 0.7 0.7 2.0 1 •.5 n.s '° 4708 4.2 - 1.3 5.3 T' 2• .5 13.3 4705 4.4 1.5 o.6 3.9 1.3 T 11.7 4681 4.6 T 0.9 J.4 - T 8.9 4690 3.8 o.4 o.6 2.0 - 3.0 9.8 4680 l.4 o.4 0.9 3.2 T 2.5 8.4 5970 4.2 T o.B 3.3 1.6 T 9.9 4675 4.6 0.9 . 2.1 2.6 2.7 T 12.9 2.Q!.2 • l.•4 , . - 0.6 . 5.6 - · T 9.6 *Refer to Appendix and Fieure 1 for stratigraphic and areal locations of cited specimens. **Mineral contents expressed as parts per ten ***Mineral not detected ****Mineral detected only in 'trace amount . .. ,--~··-.~--~"-Br-- ··-,-";:~1\1~· ~· '!!!,i, 111.". ''•Jlllll! TABLE 9 (con't~) ~fm~~=~~;_· J>~Tu.it~se~ •PK.:::.t)ld.s_i9.r·:' ~i~ill~~Ji::I~e~~I J~?t~' ~r~ 5981 3.2 0.8 0.7 1.7 3.1 T 9,5 4689 2.7 1.3 1.2 2.0 - 2.5 9.7 4693 4.lf. 1.0 1.0 1.3 T 2.0 9.7 4682 4.7 T 1.2 4.7 T T 10.6 4686 3.4 T 0.9 3.9 T 2.0 10.2 T O, 4707 3.4 o.4 0.9 1.7 2.5 8.9 0 4679 3.8 6.. 4 1.7 3.7 - T 9.6 L}688 4.9 1.0 0.9 2.1 T 2.0 10.9 7014 5.3 T 0.7 4.2 1.3 T 11.3 7015 3.9 o.4 0.5 1.9 2.6 2.0 11.3 _J TABLE 10 MODAL COMPOSITION OF ANALCITE..BEARING ROCKS ON FL!\T TOP BUTTE T. 139 N., R. 104 W., GOLDEN VALLEY COUNTY ------§J?ecJ;/llen~-- 3:(!.1artz.. ~·t Pfaito.tllli=K-%).1-~r-~lclte MtiS£2Ji:£i. Giericite r "Jota.'.C]].~~ ~ 4785 2.6. 2."6 0.5 1.6 - 4.0 9.3 l~672 5.9 T o.4 4.0 1.3 T 11.6 4669 4 •.3 1.0 1.6 - - 2.5 9.4 4674 5.1 T .. 6.2 1.5 T 12.8 °'t-' 4787 4.2 - 1.5 - - 4.0 10.0 4670 3• .3 T 0.7 3.9 - 2.0 0.9 4788 .3.1 - 0.5 4.3 - 2.0 9.9 4673 5.7 T .. 3.7 T 1.5 10.9 4671 4.1.j. T 0.9 3.6 T 2.0 10.9 4748 4.6 o.a 0.9 - 1.6 2.0 9.9 4747 3.8 T 0.5 . 3 •.3 3.1 2.0 9.7 s;i:, ~ TABLE 11 MODAL COMPOSITION OF ANALCITE-BEARING ROCKS ON BULLION BUTTE T. 137 N., R. 102 W., BILLINGS COUNTY ~-~gilir,t'z--P.~·~ -·~J',tltjpp~:~~~~1~·ic~'[~J=:~:)'ot~1,,~9l~L-T"c;'E:iI 4779 a.a - - 5.9 - 3.1 9.8 4770 10.6 2.7 !"' - 5.9 T 2.0 4783 2.5 1.2 1.4 l.4 - 2.5 9.0 4775 1.0 6.2 2.0 9.2 - - - o, N 7007 1.9 - - 6.6 - 1.0 9.5 4771 5.1 1.0 0.5 0.5 - 2.0 9.1 l.J,774 5.9 T 0.9 3.3 2.2 1.0 13.3 !~782 4.4 T .. . 4.2 1.3 T 9.9 7016 5.0 T T 5.0 T T 10.0 4773 0.9 - - 5.3 - 3.0 8.2 468/+ 5.0 T - 5.IJ 1.3 - 11.7 l.J,785 4.2 ... - 6.0 - - 10.2 l.J,?77 7.0 -- 2.0 2.6 - 11.6 4772 2.4 o.6 1.7 3.2 - 2.0 9.9 =- ~ ~~ TABLE 12 MODAL COMPOSITION OF ANALCITE-BE.ARING ROCKS ON SLIDE AND CHALKY ~UTTES T. 139 N. , R. 101 W. , SLOPE COUNTY §Eicim~~9-r.<2:.~:_f~~~. -- y:9~cb?l'ii.~it;c}~s~·Ti~iplTI:-fo_t~;l~' Clay~-- t~I~I : 6994 2.2 - - 6.3 - T 8.5 6998 B.o o.4 0.7 3.9 - - 11.0 6999 7.6 o.4 0.3 1.4 T T· 9.7 6997 4.4 1.3 0.5 1.6 T 2.0 9.8 T 9.0 7000 7.2 o.4 0.3 l.l - \.,J°" 7001 3.6 T 1.0 2.0 T 4.0 10.6 7002 2.5 - - 7.3 - T 9.8 9.8 6995 1.9 - - 4.9 - 3;0 7003 2.. 1 - - 4.7 - 3.0 9.9 7001-J. 7.2 1.3 0.9 0.7 1.3 1.5 12.8 7005 1.7 1.3 o.s 1.1 - 4.0 8.9 /+729 7.7 - 0.5 l.1 - 2.0 11.3 4727 2.0 - - 6.0 1.3 1.5 9.0 6996 1.5 - - 7.7 - T 9.2 7006 2.1 - - 4.6 - 2o0 8. '? DISCUSSION MINERAL ASSOCIATIONS The association and significance of the following materials, with respect to the occurrence of analcite, 1ri.ll be dealt 'With in turn: volcanic glass, quartz, plagioclase, potassium feldspar, and sericite. Analcite-Pyroclastic Association Pyroclastic materials containing volcanic glass a::.."'e in close' proximity to the analcite-bearing rocks of the Golden Valley Formation (? ). Ash beds are present above and below the analcite-bearing rocks , on Sentinel, Flat Top, and Chalky Buttes. The recognized genetic relationship between analcite and volcanic glass warrants consideration of the tuffaceous material as precursor to the analcite. A survey of the occurrences of analcite believed to have originated from pyroclastic materials _shows that the vitroclastic texture is commonly preserved (Bradley, 1928; 1929; Bramlette and Posn jak, 1933; Ross, 1941; Coombs, 1954; Deffeyes, 1959; Gulbrandsen and 1in Cressman, 1960; Brown and Thayer, 1963; Terrugi, 1964; Loughnan, 1966; Ijima. and Utada, 1966; Robinson, 1966; Wilkinson and Whetten, 1967 ). This texture is not present in the a.rkose of analcimolite, sug~esting that the analcite in these occurrences has not been derived from vol canic glass. Whetten and Coombs (1967) have proposed a genetic classification of sedimentary analcites based on composition. Annlcites originating from siliceous volcanic glasses a.re silica-rich. The Si/Al ratio of 64 2i Inforrcd Group Gl"oup Grvup Arlill.(6J9)-Si(331) Comoosition A B C ( anhvdrous ) 2.13 .12 2.10 .09 .08 .07 .06 .05 .CLI· .03 .02 .01 2.00 .99 .98 .97 .96 .95 .94 .93 .92 .91 Ar 1.90 .89 .88 .87 kr .86 Ar, Ar .85 I .24 .83 Ar, Ar, An .82 Ar, Ar .81 1.80 Ar, Ar, Ar, An :n .79 .78 .77 .76 An .75 .74 .73 An .72 .71 1. 0 E::rolanation Group A--Sil~ca-rich analcites formed from siliceous volcanic gla.ss by inferred reaction with saline waters. Group B--Analcites occurring in a burial metamorphic enviro~.ment. Group C--Silica-poor analcites inferred to be formed by di1"ect p:::-ecipi tation or by reaction of highly alkaline water with sediment. Ar--Composition of ana.1.oite in arkose; A.~--Composition of ana.lcite in a....'1.alcimoli te. Figure 15. Classification of Analcite Based on Composition (After Whetten and .Coombs, 1967) 66 the Golden Valley(?) analcite is low, 2.0 to 2.4. Analcite of this low Si/Al. composition is.generally considered to have originated by direct precipitation from highly alkaline waters, or by reaction of such waters with clay minerals or other sedimentary materials (Fig. 15). A..~alcite-Quartz Association · Detrital quartz is present in all of the analcite-bearing rocks exainined. There is no apparent relationship in the distribution of quartz and analcite in the analcite-bearing rocks. The detrital quartz in the analcite-bearing rocks is e.mbayed. The embayments are interpreted as the effects of dissolution by reaction with interstitial water. There is no textural indication of analcite replacing the quartz. The majority of natural, fresh, surface waters are undersaturated with respect to amorphous silica, but supersaturated with respect to quartz. However, the corroded condition of the quartz suggests that a s.olutionin contact with the sediment, at some time in the history of the sedi!l!ent, was undersaturated with respect to quartz. P.nalcite-Feldspar Assoc;ation There is a well-defined relationship in the distribution of anal cite and the.. detrital .feldspars. A plot of analcite versus plagioolase contents of the ana1cite-bearing arkose shows a decrease i.~ plagioclase with an increase in analcite (Fig.16). Curves have been calcul.:i.ted by the method of least squares for the point distributions in Figures Ii ' • I Figure 16. Scatter Diagram of Analcite-Detrital Plagioclase Data taken from specimens cited in Tables 9, 10, 11, an.d 12. , r I . ,t,':. :/ 0 f ,....: I I Po 0 IC',.) U> b C°",I e c:.:, .~ 0 ...... • Id C c::> left) (!) II .... 1-, le • 0 I CD • g I eo • e r:/ • e o • d • o/e q • /· - () / o,,,, _.,,. / ---·- ...... - - - o e 0 q 0 N (U8J .&ad SJJDd) 3S'113019'11d Figure 17. Scatter Diagram of .Ana.lcite-Detrital Potassium Feldspar Data taken from speoimens cited in Tables 9, 10, ll, and 12. I • I 0 J r,.: I I I • f •• I I I I I I o e, C c 9 lo 0 ·~ [,!: pI ';,,lilfV: 1~ 0 I ' •=eV) o I' e . e e o e,~ ~= p Q 0/ Go 'xc:::o • 0 / = I i ;~ (!I; ,,. ,,. q q 0 C\I (UaJ J9d SJJD.d) 0,'o'dS013.::J...;..>I 71 16, 17, and 18. The curves are the best possible fits for the trends of the point distributions and give the highest correlation coeffi cients. The calculated curve in Figure 18 defines the point distri bution as curvilinear. The curve is used only to define qualitatively point distribution. There is a similar curvilinear relationship 71. 16, 17, and 18. The curves are the best possible fits for the trends of the point distributions and give the highest correlation coeffi cients. The calculated curve in Figure 18 defines the point distri bution as curvilinear. The curve is used only to define qualitatively the point distribution. There· is a similar curvilinear relationship between analcite and potassium feldspar (Fig. 17). The curvilinear distribution of the previously described rela tionship can be explained by the vertical distribution of analcite, plagioclase, and potassium feldspar in the section (Fig. 21). The analcite content increases upward in the section. Correspondingly, the. feldspar content decreases upward in the section. The significance of the vertical distribution of these minerals has been statistically tested. The unit has been divided into a lower 30 foot section and an upper 30 foot section. The statistical significance of the differ ences between the mean mineral contents of the upper and lower halves of the section have been computed. Table. 13 gives the confidence levels at which differences in the mean mineral contents in the upper TABLE 13.--Confidence Levels at which the Hypothesis 'I,30 f:. x(30: can be ac_cepted as Significant .Mineral x.,. 30 -x< 30 Confidence Level .Analcite 4.3 ppt • 2.3 ppt. 99.5 Plagioclase 0.2 ppt. 0.5 ppt. 99 •.5 It is concluded, from the distribution relationships, that anal:, cite has been derived from the detrital feldspars. This .conclusion is supported by the results of m:i.~eral synthesis experiments, in which analcite has been produced in reactions between albite and water (Friedman, 1951; Fredrickson and Cox, 19.54; Morey and Chen, 1955; Sand, Roy, and Osborn, 1957; Morey and Fournier, 1961). Textural relation ships in the arkose indicate that a.nalcite is not directly replacing the feldspars. The analcite occurs as distinct spherulites. There is no penetration or embayment of the feldspars by analcite •. The equilibrium conditions for the reaction between analcite and albite have been experimentally investigated. Campbell and Fyfe ·(1965) determined the temperature and pressure of equilibrium for the reaction: At conditions of low PHzO the reaction is at equilibrium. at approrl mately 190° c. At temperatures less than 190° C. analcite is stable relative to albite. Silica activity can displace tpe equilibrium temperature (Ca.rnp bell and Fyfe, 1965). The corroded condition of the detrital quartz and feldspar suggests that the silica activity of the solution may be ~ significant factor i."1 controlling the analcite-feldspar relation ship. If a solution is saturated with respect to amorphous silica, the dissolution of albite will be depressed (Fyfe and McKay, 1962). Under such conditions albite·would be stable relative to analcite at temperatures less· than 190° C. The corroded quartz, however, suggests Figure 18. Vertical Distribution of Analcite, Plagiocl.ase, and Potassium Feldspar. Data taken from specimens cited in Tables 9, 10, ll, and 12. ANALCIN'.OLI TE 1-- ~ 70-1------~- ooe_ -~- 70-lf------7Q ------ r=0.61 e 60 • 60il y._ 9.2 x-0.3385 : Y=2.SX-1.1566 r=0.82 J: ANALCITE I 50 r=0.61 • .50 50 I • I 40 ; 40 / le •\ o BEARING ,~ Oo / LIJ •••- 0 I •e:, LL / I I 30 • • / 30 I / r I • • • • ~ ,A ••• 20~• / 20 \ ARKOSE 1. • • /Y=3.6Xl.1SlO • • • \0 \ • ,,e/ • •• \ • • ,,. \ IO~G 10 0 ,...... __ • • • '•\ e '•.... 0 ---- 0 II".". ~"'"2,WY ne lll""""{'','f\T .... -o... -- o I rn«>o • I I I I 11. I 0 I I I • o.o 1.0 2.0 3.o 4.o 5.0 s.o ~o a.o 0.0 1.0 2.0 3.0 0.0 ,:o 2.0 3:0 PARTS PER.. TEN PARTS F£R TEN PARTS PER TEN ANALCITE PLAGIOCLASE K-FELDSPAR '.i:c~ -:~ij 75 that the solution was undersaturated with respect to quartz~ Conse quently, the albite was probably easily dissolved in the solution. Hess (1966 ) has approximated the fields of stability of minerals in the system Na20-K2o-AJ.2o3-Si02-H2o at 25° c., on the basis of the composition of the solution in equilibrium with the minerals (Fig. 19). The single hachured area in Figure .19 represents the composi tion of natural lake and river waters (data from Livingstone, 1963). The surface water compositions are outside the stability field of analcite. The double hachured area is the composition of a solution in contact with analcite (Hay and Moiola, 1963). This solution is assumed to be in equilibrium with analcite, and representative of a solution from which analcite would crystallize. The arrow is a crude, . !f hypothetical, approximation of the change in composition of fresh sur l1~ifWi;:.U~ face water to produce a solution from which analcite would crystallize. The origin of the arrow has been purposely placed to the left of the Log [s102); 4 isopleth, the solubility of quartz. The corroded condition of the detrital quartz, as previously discussed, suggests tha:t, the original solution was undersaturated with respect to quartz. The proposeq solution from which analcite would crystallize, as in ferred from Hess's (1967) diagram, was undersaturated with respect to silica, alkaline, and had a high Na+ concentration. It has been pointed out that solutions of this composition usually do not exist at the surface of the earth. However, after burial the reaction of inter stitial water with the mineral components of the sediment, in the relatively closed system that would be produced ·by burial, could easily establish solutions of the :required concentration. As the quartz and Figure 19. Isoplethic sectio°n at lo~,· K+ = 4 of phase diagram for ~H~, the system .Na.2o-K2o-AJ.2o,=SiO 2.:if;~ (a.ft.en..~ss, 1966). J ':" %,1, ' Single hachured symbol represent~ of lake and river waters. Double hachured symbol represents the composition of a solution in equi~ib- h, !l \ rium with analcite. See text for discussion. 11 ..... l SOlU Bl LITY OF , QUARTZ:.- - - ANA LC I TE 10 ALBITE 9 I .I -SOLUBILITY 8 OF A MOR- ' I PHOUS I I SILICA LOG~· H .. I l \ 7 I I l PHILLIPSITE . GIBBS I TE I ' 6 'I 'l I RdOLI NITE I · 1 :t-FE LD- SPAR 5 2 78 feldspars dissolved, the solution composition moved to the right with increasing silica concentration. The compositipn would also move up ward, as indicated by the arrow, since the dissolved feldspars would add to the cation concentration and increase the pH of the solution. The pH, however, would be maintained at moderate alkalinity. As the silica concentration of the solution increased due to dissolution of the quartz and feldspars, the solubility of the feldspars wouJ..d be de pressed. Thus, the silica acts as a buffer. The potassiu.~ feldspar. probably reacted similarly, except that it is less soluble than sodium plagioclase (Keller,~ al., 1963). According to Hess's (1967) scheme, therefore, when the solution reaches a critical concentration of . [Na+} , H+ and [ SiO ] , analcite would crysta.lli ze. k J, 2 ' / This. reasoning is supported by data presented by Harris (1967), in which it has been shown that pore waters in a contemporary fluv.i..al sediment have a higher silica concentration than the overlying surface water. This approximation of an environment that would crystallize anal cite has been inferred from the relative distributions of the mine~a.ls, and the condition of the coexisting minerals. There are undoubtedly other governing factors. However, their influence is not immediately apparent or they cannot be evaluated by only a study of the natural mineral occurrences •.Some of these proba~le factors are the influence of the groundwater recharge system, the biological activity, and the interdependence among the various dissolution-precipitation reactions. It is therefore proposed that analcite crystallized from inter stitial solutions in the ·rock, from constituents derived from the dis- 79 solving feldspars. The dissolution and precipitation reactions probably took place at a relatively shallow depth of burial. The texture of the arkose suggests that it did not undergo extensive com paction. A very small percentage of the coarse elastic grains forming the framework of the arkose are in contact. Most of the compaction probably took place in the argillaceous matrix. The vertical distribution of analcite and feldspar in the unit is attributed to the removal of the interstitial water, the reaction media, with increasing depth of burial. Thus, the dissolution of the feldspars was impeded,.halting the l:"eaction sequence. Analcite-Sericite Association Sericite occurs in the arkose as a matrix surrounding the analcite and as unoriented inclusions in the analcite spherulites. The textural relationship suggests that the sericite formed prior to the a.nalcite, or at least prior to the formation of the spherulites. The oriented, coarse sericite grains at the periphery of the spherulites suggest that they have been pushed aside as the spherulites grew. Some of the sericitic matrix was probably included by the spherulites as they formed. The possible significance of the analcite-sericite association in the arkose, is that sericite has been produced, along with analcite, in minerals synthesis reactions between albite and water (Morey and Chen, 1955; Morey and Fournier, 1961). Sericite, like analcite, crys tallizes from alkaline solutions (Hemley, 1959). Thus, sericite and analcite may be products of the same environment and an interdopendent 80 reaction. FORMATION OF SPHERULITES Spherulitic crystalliza~ion has been recognized in igneous, meta morphic, and sedimentary rocks. Three ori~...ns for spheruJ..itic struc tures are proposed: (1) crystall.ization from a colloid; (2) segrega tion of disseminated mineral matter; and (3) crystall.ization from supersaturated, high polymer solutions. The applicability of these origins to the analcite spheruJ..ites are considered. Spherically-shaped bodies are generall.y thought to have crystal lized from a colloid (Rust, 1935). However, the textural criteria that has been generall.y interpreted as characteristic of colloidal c~"'Ystal- .1 lization has been critically reviewed (Roedder, 1968). It has been demonstrated that the textural features, colloform shape, syneresis cracks, ·concentric banding, and radial str.uctures, do not necessarily result from colloidal crystallization • . The textural relationships among the individual spheru1ites also suggest that_ they did not crystallize from a colloid. Colloids have high water contents and crystallization involves dessication and con traction. The mutual interference and distortion of the spherulites suggests expansion and coalescence. The orientation of the coarse sericite grains to the periphery of.the spheruJ..ites also suggests an increase in volume. As the spherulites grew they pushed the sericite grains aside, orienting them. It is concluded, on the basis of these considerations, that the spheruJ.ites did not crystallize directly from 81 a colloid. A colloidal phase, however, may possibly have been an inter mediate stage. Experimental studies (Fredrickson and Cox, 19.54) on the solubility of albite produced a gel from which a.nalcite crystal lized. The analcite, however, crystallized as a single crystal and not as a spherulite. Pettijohn (19.57) and Ramberg (19.58) attribute the development of accretionary forms, such as spherulites, to differentiation. It is proposed that mineral assemblages are most stable when segregated. This is based on the assumption that the rock mass will have a lower free energy, and will therefore be more stable, if the mineral is segregated.rather than disseminated. This explanation adequately ac~ counts for the occurrence of the spherulites. It has not, however, been experimentally verified. I Spherulitic crystallization from a supersaturated, high-polymer I I solution has been theoretically considered (Sears, 1963) and experi I mentally investigated (Bassett,~!!•, 1963; Ma.gill, 196.5). Spher J ulites are recognized to be the usual. w.ode of crystallization of high I I polymers (S~ars, 1961). l The formation of a spherulite, rather than a single crystal, is l a function of the critical. radius 0£ nucleation (Sears, 1961). There I I has been little investigation of the nucleation and polymerization of I silicates in"solution. Consequently, there is little basis for evalu I ation of the conditions which might crystallize spherulites or single crystals. The type of spherulitic structu?a that develops from a spher ulitic nucleus is determined by the conditions under which growth, as 82 distinct from nucleation, occurs (Sears, 1961; Magill, 1965 ) • The observed differences in the analcite spherulite structures, therefore, may be due to changes in conditions during growth (eg. solution con centration, temperature). Microscopic examination has revealed only limited information that could be used to infer the origin of the spherulites. Modifica tions in the spherulite structures suggests that there may have been some differences in the conditions governing spherulite growth, or that the spherulites may have undergone varying degrees of recrystallization after formation. Observed textural. relationships indicate that direct crystallization of the spherulites from a colloid is unlikely. How l:, ever, there is little basis to distinguish between differentiation or crystallization from a supersaturated, high-polymer solution as possible origins for the spherulites. RELATIONSHIP OF ANALCITE OC_CURRENCES IN THE ARKOSE AND ANALCIMOLITE The compositions of nalacite in the arkose and analcimolite vary within a naz:row range (Fig. 20). Analcite in the arkose is slightly more siliceous than anal.cite in the analcimolite. The average compo sition of analcite in the arkose is 4.39. The average composition of anal.cite in the analcimolite is 4~08. The composition·of anal.cite in sedimentary rocks is a function of the parent material from which it has been derived,. and the compo sition of the solution from which it crystallized (Whetten and Coombs, 1967; Ijima and Hay,. 1968). The analcite in the arkosa and analcimo- 83 lite are silica-poor (see Fig. 15). Analcite in the arkose and analcimolite have different textural appearances. Analcita in the arkose occurs as spheruJ.ites and in the analcimolite it occurs as a matrix devoid o:f structure. The analcirrLo lite has a smaller detrital mineral :fraction t~ the arkose. The analcimolite rests on the analcite-bearing arkose. The analcite content 0£ the arkose increases upward in the section. The analcimolite appears to be a culmination 0£ the increasing analcite content of the unit (see Fig. 14). It has been demonstrated that analcite in the arkose has been derived from the detrital feldspars. However, there is no evidence to warrant extending this relationship· to the analcimolite. The contact between the arkose and the ana.lcirrio lite is sharp. There is no indication of interaction between the two rock types. On the basis 0£ compositional similarities between analcite in the arkose and the analcimolita, it is concluded that they came :from similar parent materials (see Fig. 15; Explanation; Group C). Pro posed origins for analcimolite-like rocks that appear applicable to the Golden ~alley(?) a.nalcimolita are by direct precipitation from solution (Van Houten, 1962) and by crystallization of gels from alka li.'le springs (Eugster and Jones, 1968). There is no evidence to indi cate that the formation of analcite in the a.rkose and analcimolite was either dependent or independent. ------· ...... · I I \ \ I \ \ I \ \ l 85 RELATIONSHIP OF ANALCITE DISTRIBUTION TO THE POST-EOCENE m~CONI?ORM.ITY Denson (written communication to W.J. Stone, 1970) has defined the regionaJ. distribution of analcite: "In our experience, the oc currence of a.nalcite is restricted largely to the rocks directly under lying the regional unconformity at the base of the Oligocene and Mio cene. In the Williston Basin analcite can and does occur in all for mations transected by this unconformity." The tentativeness of this observatior is stressed, since the mineralogy of the rocks in the Tertiary sequence has not been completely examined in detail. The Tertiary rocks in which analcite does appear are the arkose and ana.1- cimolite assigned to the Golden Valley Formation and the sands of the Sentinal Butte and Tongue River Formations. ,ii! The significance of the restriction of analcite to rocks below the post-Eocene unconformity is not immediately apparent. The absence of analcite in these rocks may reflect climatic changes or differences in the mineral composition and physical properties (eg. porosity, per meability) of the sediment. These possibilities, however, are specu lative, and should be considered as largely tentative until there has been a more·detailed examination of the mineralogy of the rocks above the post-Eocene unconformity, to·determine the validity of Denson•s observation. l SUMMARY OF CONCLUSIONS 1. Analcite occurs in two distinct rock typos, arkose and analciroo lite. Analcite constitutes up to about 60 percent of tho arkose and up to 80 percent of the analcimolite •. I 2. The. a.nalcite-bearing rocks are possibly late Eocene in age, and I have been tentatively included in the Golden Valley Formation. I :,. The analcite occurs in the arkose as spherulites. Three types I of spherulites are recognized: (1) spherulites with a radial in I ternal structure; (2) spherulites with a massive center and a J peripheral radial structure; and(:,) spherulites with no internal 1 structure, or a poorly-defined internal structure. Proposed origins I for the spherulites are by diagenetic differentiation or by crystal I lization from a supersaturated, high polymer solution. The anal. l l cite is least abundant at the base of the arkose unit, and increas J es upward. The abundances oi' the analcite and the detrital feld I spars are inversely related. It is proposed that analcite in the I j arkose crystallized from alkaline, interstitial solutions, under saturated with respect to silica and with high Na+ concentration. I The required constituents were derived from feldspars dissolving 1 j in the interstitial solutions. Sericite o~curs with the analcite J in the arkose as a possible associated alteration product. l I 4. Anal.cite .. occurs 'in the analcimolite as a cement. Proposed origins. j I for the analcimolite are by precipitation from surface waters, or I by crysta11ization of gels from alka.line springs. I L 86 87 5• Anal-cite in the arkose and anal.ci"'lite is silica-poor• Ana1-- cite in the a.rkose, however, is more siliceous than anal.cite in the a,naleimOlite. I .. I I \ I '\ i I \ I I I I I I \ - I I I I i APPENDIX l f t l I l . I l 1 I l . i . I . 1 l I ...... ,-, ...... - ·~---· ~·--~. •••.• ~ ··- ·-·-- --·-- -·--···----~~---·-----. I I= &1ill!?l! ARE.AL LOCATIONS AND STRATIGRAPHIC POSITIONS OF SPECIMENS CITED IN TEXT (Numbered Localities Refer to Figure 1) Specimen ·Areal location strati_g;ral?.lJ?..c Po,sition . L:itholog;y_ SENTINEL BUTTE FORMATION 5971 T. 139 N,, R, 10'-I, W,, sec. 6, Southwest side of Sentinel Butte; Clayey sand se, 1/4, sw, 1/4, Golden Valley Base of white bed, 40 feet below County. Sentinel Butte-Golden Valley con tact; local~ty 5, 59?9 T. 139 N., R. 104 W., sec. 6, Southwest side of Sentinel But\e; Sandy clay $ . se, 1/4, sw. 1/4, Golden Valley base of white bed, 40 feet below County. Sentinel Butte-Golden Valley contact; locality 5. 59&.1, T. 139 N., R. 10'-I, W., sec. 6, Southwest side of Sentinel Butte; 9 Clay and se. 1/4, sw. 1/4, Golden Valley feet above base of White Bed, approx- claystone County. imately 40 feet below Sentinel Butte- Golden Valley contact; locality 5, 5985 T. 139 N., R. 10'-I, W., sec. 6, Southwest side of Sentinel Butte; Clay se. 1/4, sw 1/4, Golden Valley top of White Bed, approximately 40 County. feet below Sentinel Butte-Golden Valley contact; locality 5, 6004 T. 139 N., R. 104 W., sec. 6, Southwest side of Sentinel Butte; Lignite se. 1/4, sw. 1/4, Golden Valley 40 feet below Golden Valley-Sentinel County, Butte contact; locality 5, . '''''!1'l'IJIIIII . _...... ,. §pecimen ,a, ~£lw_tjpr;-- -·- ·- Stratig_a..Eitlcf:?S.!~ .::--)~.1lb212iY 597l} T. 139 N., R. 104 W., sac. 6, Southwest side of Sentinel Butte; Sandstone ne. 1/4, nw. 1/4, Golden Valley 30 feet below Golden Valley-Sentinel County. . contact; locality 5 • 6005 T. 139 N., R. 104 W., sec. 6, Southwest side of Sentinel Butte; Unconsolidated sw. 1/4, se. 1/4, Golden Valley 10 feet below Golden Valley-Sentinel sand County. Butte contact; locality 5. 5986 T. 139 N., R. 104 W., sec. 6, Southwest side of Sentinel Butte; Silty clay sw. 1/4, se. 1/4, se. 1/4, 6 feet below Golden Valley-Sentinel Golden Valley County. Butte contact; locality 5. 5998 T. 139 N., R. 104 W., sec. 8, Northwest side of Flat Top Butte; Clay ne. 1/4, sw. 1/4, Golden Valley 45 feet below Sentinel Butte-Golden '°0 County. · Valley contaat; base of white bed; locality 10. · 5999 T. 139 N., R. 103 W., sec 3, Northeast side of Sentinel Butte; Sandstone nw. 1/4, nw. 1/4, Golden Valley 100 feet below summit of butte; County. locality J.· 6001 T. 139 N., R. 104 W., sec. 8, Northwest side of Flat Top Butte; Unconsoli ne. 1/4, sw. 1/4, Golden Valley 40 feet above top of white bed; dated sand County. locality 10. 5978 T. 139 N., R. 104 W., sec. 6, North of Sentinel Butte; 100 feet Mudstone se. 1/4, nw. 1/4, Golden Valley below Golden Valley-Sentinel Butte County. contact; locality 23. 5980 T. 139 N., R. lOJ W., sec.·;, Approximately one-half mile east of Mudstone nw. 1/4, ne. 1/4, Golden Valley Sentinel Butte; exact stratigraphic County. position not determinable; locality 9. ~ ~. ~-- ,....:..------· .__...... ,.,...... ,,_~ --.-· -----·-·"-"-'-··---,...,. .• _ .... __ ... ~,-...,.._,_._.., -.-. ..c.:..-~ ...-..-- ••• ,--,·- ,·_:11111 §Ee~im~r•. .'~ - ...... : :::=4.;;tTo~atio1L-:-: ~- ~ strati'g.r.:'lriliic·p;~s}.!,ign:: --··--:1.r;;hoi~ 6003 T. 139 N., R. lOJ W., sec. 17, Southwest side of Flat Top Butte; Clay ne. 1/4, sw. 1/4, Golden Valley exact stratigraphic position not County. determinable; locality lJ. 5983 T. 1J9 N., R. lO!J. W., sec. 8, Northwest side of Flat Top Butte; Unconsoli .. ne •. 1/4, sw. 1/4, Golden Valley 60 feet above top of white bed; dated sand County. locality 10. GOLDEN VALLEY FORMATION(?) 5997 T. 1J9 N., R. 96 W., sec. 1, East side of Dobs~n's Butte; 5 Sandstone I-' nw. 1/4, sw. 1/4, Stark feet below summit of butte; '° County. locality 21. 4735 T. 138 N., R. 96 W., sec. 1, South side of small butte; 16 Silica- ne. 1/4, sw. 1/4, Stark feet below summit of butte; cemented County. locality 22. sandstone 4736 T. 138 N., R. 96 W., sec. 20, F.ast side of small butte; San~stone sw. 1/4, ne. 1/4, Stark summit of butte; locality County. 20. 4730 T. 138 N., R. 96 W., sec. 20, Northwest side of minor butte; Silica- sw. 1/4, ne. 1/4, Stark summit of butte; locality 22. cemented County. sandstone 5989 T. 138 N., R. 96 W., sec. 20, Northwest side of minor butte: Silica- sw. 1/4, ne. 1/4, Stark 2 feet below smnmit of butt~; cemented County. locality 22. sandstone pt:c ,..-_.,...,_,,.,,.,.._,._._...~_...... _~ . .--....·.--,,~.,..··~-~ .. -.i..._,,.,-~""""""'"''~-•..--,~,.--~...... :.,:.,.;. ..~·~:.,*'1'>'ftif ,-~ .,_.., r__..,.~..,. 'filil ~ir~2n- _4r'tal Location St.r.~~E.hic Positjorl- 'I1f2olo,gy 4724 T. 138 N., R. 96 W., sec. 20, South side of minor butte; base Silica- ne. 1/4, sw. 1/4, Stark of butte; locality 22. cemented County. sandstone 5973 T. 138 N., R. 96 W., sec. 7, Fast side of minor butte; Silica- ne. 1/4, sw. 1/4, Stark summit of butte; locality 19. cemented County. sandstone 4735 T. 138 N., R. 96 W., sec. 7, East side of minor butte; Silica- ne. 1/4, sw. l/4, Stark 3 feet below summit of butte; cemet;ited County. locality 19. sandstone 4729 T. 134 N., R. 101 W., sec. 28, Northeast side of Slide Butte; arkose nw. _1/4, sw. 1/4, Slope County. summit of butte; location 17. '°N 4734 T. 134 N., R.101 W., sec. 28, Northeast side of Slide Butte; arkose nw. 1/4, sw. 1/4, Slope County. summit of butte; location 17. 7002 T. 134 N., R. 101 W., sec. 28, South side of Slide Butte; analcimolite nw. 1/4, sw. 1/4, Slope County. summit of butte; locality 26. · 6994 T. 134 N., R. 101 W., sec. 28, South side of Slide Butte; analcimoli:t,e nw. 1/4, sw. 1/4, Slope County. summit of butte; locality 26. 4727 T. 135 N., R. 101 W., sec. 28, Northeast side of Slide Butte; arkose nw. 1/4, sw. 1/4, Slope County •. 7 feet below summit of butte; locality 17. 7004 T. 1)4 N., R. 101 W., sec. 15, North end of Challcy Buttes; arkose ne. 1/li., ne. 1/4, Slope County. 40 feet below Golden Valley- Chadron contact; locality 18. ~~;;-:::- __ --~ Ar:;tl Lo.cation Stratigr~,Iilii.~. Position . ___ µ thol_0;;r 6998 T. lY+ N., R, 101 W., sec. 15, · North end of Chalky Buttes; arkose ne, 1/4, ne. 1/4, Slope County. 35 feet below Golden Valley Chadron contact; locality 18. 6997 · T. 1;4 N., R. 101 W., sec. 1.5, North end of Chalky Buttes; Arkose ne. 1/4, ne. 1/4, Slope County. 30 feet below Golden Valley Chadron contact; locality 18. 6999 T. 1;4 N., R. 101 W., sec. 1.5, North end of Chalky Buttes; Arkose ne. 1/4, ne. 1/4, Slope County. 30 feet below Golden Valley Chadron contact; locality 18. 7000 T. 1;4 N., R. 101 W., sec, 1.5, North end of Chalky Buttes; Arkose ne, 1/4, ne, 1/4, Slope County. 30 feet below Golden Valley- ~ Chadron contact; locality 18. ?001 T. 1:,4 N., R. 101 W., sec. 1.5, North end of Chalky Buttes; Silty ne. 1/4, ne, 1/4, Slope County. 25 feet below Golden Valley- claystone Chadron contact; locality 18. 7006 T. 1:,4 N., R. 101 W., sec. 15, North end of Chalky Buttes; Analcimolite ne·. 1/4, ne. 1/4, Slope County. 19 feet below Golden Valley Chadron contact; locality 18. 6996 T. 1:,4 N., R. 101 W., sec. 15, North end of Chalky Buttes; Analcimoli te ne. 1/4, ne. 1/4, Slope County. 19 feet below Golden Valley Chadron contact; locality 18. 700.5 T. 1;4 N., R. 101 W., sec. 1.5, North end of Chalky Buttes: Silty ne. 1/4, ne. 1/4, Slope County. 16 feet below Golden Valley- clay Chadron contact; locality 18. §'ri'eci·[ll~:~ ··:... :.~Jl.._ .. _ ~tigrapJlic. Posit_~~!l fithoJ.2.~. - 7003 T. 134 N., R. 101 W., sec. 15, North end of Chalky Buttes; Analcimolite ne. 1/4, ne. 1/4, Slope County. 15 feet below Golden Valley Chadron contact; locality 18. 6995 · T. 134 N., R. 101 W., sec. 15, North end of Chalky Buttes; Analcimolite ne. 1/4, ne. 1/4, Slope County. 15 feet below Golden Valley Chadron contact; locality 18. 4684 .. T. 137 N., R. 102 W., sec. 18, Northeast corner of Bullion Arkose ne. 1/4, sw. 1/4, Billings Co. Butte; 10 feet below summit of butte; locality 14. 7016 T. 137 N., R. 102 W., sec. 18, Northeast corner of Bullion Arkose ne. 1/4, svr. 1/4; Billings Co. Butte; base of section; locality 14. ~ 4772 T. 137 N., R. 102 W., sec. 7 Northeast corner of Bullion Arkose sw. 1/4, se. 1/4, Billings Co. Butte; base of sectio11; locality 14. 4776 T. 137 N., R. 102 W., sec. 18, West side of Bullion Butte; summit Arkose nw. 1/4, sw. 1/4, Golden Valley of butte; locality 15. Co. 4771 T. 137 N., R. 102 W., sec. 18, West side of Bullion Butte: 5 Arkose nw. 1/4, sw. 1/4, Golden Valley feet below sUITL'"lit of butte; Co. locality 15. 4781 T. 137 N., R. 102 W., sec. 18, West side of Bullion Butte; 10 Arkose nw. 1/4·, sw. 1/4, Golden Valley feet below surmni t of butte; Co. loc.ali ty 15. ---·------,------· l";~"i1=:12>"<;~.fion -· - h .. Stre,.tlgraphfc ~p9~Tion -~ 4783 T. 137 N., R. 102 w., sec. 18, West side of Bullion Butte; 12 Arkose ne. 1/4, sw. 1/4, Golden Valley feet below summit of butte; Co. locality 15. 7007 T. 137 N., R. 102 W., sec. 18, South end of Bullion Butte; Analcirnolite nw. 1/4, sw. 1/4, Billings Co. summit of butte; locality 16. 4775 T. 137 N., R. 102 W., sec. 18, South of Bullion Butte; 5 feet Analcimolite nw. 1/4, sw. 1/4, Billings Co. below summit of butte; locality 16. 4779 T. 137 N., R. 102 W., sec. 18, South end of Bullion Butte; Arkose nw 1/4, sw, 1/4, Billings Co. 10 feet below summit of butte; locality 16. ~ 4?77 T. 137 N., R. 102 W., sec. 18, South end of Bullion Butte; Arkose nw. 1/4, sw. 1/4, Billings Co. 15 feet below summit of butte; locality 16. 4770 T. 137 N., R. 102 W., sec. 18, South end of Bullion Butte; 20 Arkose -nw. 1/4, sw. 1/4, Billings Co. feet below summit of' butte; ~ctlily~. · 4782 T. 137 N,, R. 102 W., sec. 18, South end of Bullion Butte; 25 Arkose nw. 1/4, sw. 1/4, Billings Co. feet below summit of butte; locality 16. 4774 T. 137 N,, R. 102 W., sec, 18, South end of Bullion Butte; Arkose ne. 1/4, sw. 1/4, Billings Co. base of section; locality 16, 5972 T. 139 N., R. 104 W., sec. 8, Northeast corner of Flat Arkose ne. 1/4, sw. 1/4, Golden Valley Top Butte; summit of butte; Co. locality 11. ~BC¥~=:-:-: _Ar~~~ - ..., - ~-stx:~_t{g;:_E!phic ~sl_!:_:!.s.m --=---~:=--11i.Eoi2,gx 4670 T. 139 N., R. 104 W., sec. 8, Northeast corner of Flat Top Arkose ne. 1/4, sw. 1/4, Golden Valley Butte; 3 feet below summit of Co. butte; locality 11. 4674 T. 139 N., R. 104 W., sec. 8, Northeast corner.of Flat Top Arkose ne. 1/4, sw. 1/4, Golden Valley Butte; S feet below summit of Co. butte; locality 11. · 4788 T. 139 N., R. 104 W., sec. 8, Northeast corner of Flat Top Arkose ne. 1/4, sw. 1/4, Golden Valley Butte; 1S feet below summit of Co. butte; locality 11. 4782 T. 139 N., R. 104 W., sec. 8, Northeast comer of Flat Top Arkose ne. 1/4, sw. 1/4, Golden Valley Butte; 2S feet below summit of Co. butte; locality 11. '°°' 4787 T. 139 N., R, 104 W., sec. 8, Northeast corner of Flat Top Arkose ne. 1/4, sw. 1/4, Golden Valley Butte; 40 feet below summit of Co. butte; locality 11. · 4,669 T. 139 N., R. 104 W. ,· sec. 8, Northeast corner of Flat Top Arkose ne. 1/4, sw. 1/4, Golden Valley Butte; 4S feet below summit of Co. butte; locality 11. 4748 T. 139 N., R. 104 W., sec. 8, Northeast comer of Flat Top Arkose ne. 1/4, sw. 1/4, Golden Valley Butte; 55 feet below summit of Co. butte; locality 11. 4749 T. 139 N., R. 104 W., sec. 8, Northeast corner of Flat Top Arkosa ne. 1/4, sw. 1/4, Golden Valley Butte; base of section; locality Co. 11. ·~- -- ~i;en ·-_ --~ -~~~tion-- stratigra£hi£.~ition bi_th~ii Arkose 4685 T. 139 N., R. 104 W., sec. 16, South end of Flat Top Butte; ne. 1/4, sw. 1/4t Golden Valley summit of butte; locality 12. Co. Arkose 4785 T. 139 N., R. 104 W., sec. 16, South end of Flat Top Butte; nw. 1/4, ne. 1/4, Golden Valley summit of butte; locality 12. Co. Arkose 4673 T. 139 N., R. 104 W., sec.· 16, South end of Flat Top Butte; nw. 1/4, ne. 1/4, Golden Valley summit of butte; locality 12. Co. Arkose 4747 T. 139 N.t R. 10'4- W., sec. 16, Southwest side of Flat Top ne. 1/4, sw. 1/4, Golden Valley Butte; 25 feet below summit '°"...:) Co. of butte; locality 13. Arkose 4671 T. 139 N., R. 104 W., sec. 16, Southwest side of Flat Top nw. 1/4, ne. l/4t Golden Valley Butte; 60 feet below summit Co. of butte; locality 13. Northwest corner of Sentinel Arkose 4708 T. 139 N., R. 10'4- W., sec. 6, se. 1/4, sw. 1/4, Golden Valley Butte; summit of·butte; locality Co. 1. Northwest corner of Sentinel Arkose 4692 T. 139 N., R. 10'4- W., sec. 6, se. 1/4, sw. 1/4, Golden Valley Butte; summit of butte; locality Co. 1. Northwest corner of Sentinel Arkose 4707 T. 139 N., R. 104 W., sec. 6, se. 1/4, sw. 1/4, Golden Valley Butte; summit of butte; locality Co. 1 . . §m:ic~~~~--:~-=-~~··. ~-1.A:>catioi;"'- S~:rru1;;raphic Position Litholog_y 5882 T. 139 N., R, 104 W., sec. 8, Northwest side of Sentinel Arkose se. 1/4, sw, 1/4, Golden Valley Butte; 10 feet below summit Co. of butte; locality 1. 4680 T. 139 N., R. 104 W., sec. 8, Northwest side of Sentinel ·Arkose se, 1/4, sw, 1/4 1 Golden Valley Butte; 10 feet below summit Co. of butte; locality 1. 4705 T. 139 N., R. 104 W., sec. 8, Northwest side of Sentinel Arkose se. 1/4, sw. 1/4, Golden Valley Butte; 12 feet below summit Co. of butte; locality 1. 5975 T. 139 N., R. 104 W., sec. 8, Northwest side of Sentinel Arkose se. 1/4, sw. 1/4, Golden Valley Butte; 15 feet below summit '°0) Co. of butte; locality 1. 70($ T. 139 N., R. 104 W., sec. 8, Northwest side of Sentinel A:rkose se. 1/4, sw. 1/4, Golden Valley Butte; base section; locality Co. 1. 7014 T. 139 N., R. 104 W,, sec. 8, North side of Sentinel Butte; Arkose nw.~. 1/4, nw. 1/4, Gol~en Valley summit of butte; locality 2. 5970 T. 139 N., R. 104 W., sec. 8, North side of Sentinel Butte; Arkose nw. 1/4, nw. 1/4, Golden Valley summit of butte; locality 2. Co. 4690 T. 139 N., R. 104 W., sec. 8, North side of Sentinel Butte; A:rkose nw. 1/4, nw. 1/4, Golden Valley 15 feet below summit of butte; Co. locality 2. ~:np;;42,~PfHIIJ~*f.«'JA1#dl.JMA¥¥U:ffiilMh.4'M(i\'OHt;tbi~'l'-MitN'lf-.44if.il-hf\HAMJU ,irn:cr:FfT:'11''"'1!!~"'.:!-r.:n--;-;;.-.~,--";" .. ., . - t!t ~ ·-__!.~11,______-.-=:.:Strat.ig1~aphic.~t2-g~. -=:--:~~1£.Ez 4672 T. 139 N., R. 104 W., sec. 8, North side of Sentinel Butte; Arkose nw. 1/4, nw. 1/l,, Golden Valley 30 feet below summit of butte; Co. locality 2. 5981 T. 139 N., R. 104 W., sec. 8• North side of Sentinel Butte; Arkose nw. 1/4, nw. 1/4, Golden Valley 6S feet below summit of butte; Co. locality 2. 7011 T. 139 N., R. 104 W., sec. 8, North side of Sentinel Butte; Arkose nw. 1/4, nw. 1/4, Golden Valley 70 feet below summit of butte; Co. locality 2. 4688 T. 139 N., R. 104 W., sec. 8, North side of Sentinel Butte; Arkose nw. 1/4, nw. 1/4, Golden Valley base of section; locality 2. ~ Co. 4682 T. 139 N., R. 104 W., sec. 8, Southeast corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; sunimit of butte; locality Co. 3. 4681 T. 139 N., R. 104 W., sec. 8, Southeast corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; 5 feet below SUl11Illit of Co. butte; locality 3. 4693 T.1J9 N., R. 104W., sec. 8, Southeast corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; 35 feet below summit of Co. butte; locality 3. 5976 T. 139 N., R. 104 W., sec. 8, Southwest corner of Sentinel Arkose se. 1/4, nw. I/4, Golden Valley Butte; summit of butte; Co. locality 4. ·--~--- ...... --.. -- - ___ __gj:,ho1og_y _ §?!?Efil~~j_r.l!.~}u.. ~2.~.tL2!l._ .. -- §!:ratigraphic Position -7010 T. 139 N., R. 104 W., sec. 8, Southwest coFner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; summit of butte; Co. locality 4. l}686 T. 139 N., R. 104 W., sec. 8, Southwest corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; summit of butte; Co • locality 4. . 4691 T·. 139 N., R. 104 W., sec. 8, Southwest corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; summit of butte; Co. locality 4. 4679 T. 139 N., R. 104 W., sec. 8, Southwest corner of Sentinel Arkose ..... 0 se. 1/4, nw. 1/4, Golden Valley Butte; 15 feet below summit 0 . Co. of butte; locality 4 • 4687 T. 139 N., R. 104 W., sec. 8, Southwest corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; 20 feet below summit of Co. butte; locality 4. 4678 T. 139 N., R. 104 W., sec. 8, Southwest corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; 25 feet below summit of Co. butte; locality 4. 4689 T. 139 N., R. 104 W., sec. 8, Southwest corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; 25 feet below summit of Co. butte; locality 4. 4685 T. 139 N., R. 104 W.~ sec. 8, Southwest corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; 3o·reet below summit of Co. butte; locality 4. ~~------~~=·:::- g• • · c«.~r .• .. = st~~Tfioi:___ ..:-·-_r4~Io""g,y. 4675 T. 139 N., R. 104 W., sec. 8, Southwest corner of Sentinel Arkose se. 1/4, nw. 1/4, Golden Valley Butte; base of section; locality Co. 4. . 7008. T. 139 N., R. 104 W., sec. 6, West side of Sentinel Butte; Arkose se. 1/4, sw. 1/4, Golden Valley summit of butte; locality 6. Co. 7013 T. 139 N., R. 10'~ W., sec. 6, West side of Sentinel Butte; Arkose se. 1/4, sw. 1/4, Golden Valley summit of butte; locality·6. Co. t-1 CHADRON FORMATION f3 5977 T. 139 N., R. 104 W., sec. 16, Central part, west half of Siltstone nw. 1/4, ne. 1/4, Golden Valley Sentinel Butte; summit of Co. butte; locality 7. 4694 T. 139 N., R. 104 W., sec. 8, Central part, east half of Siltstone sw. 1/4, nw. 1/4, Golden Valley Sentinel Butte; sununit of Co. butte; locality 7. ARIKAREE FORMATION(?) 4745 T. 147 N., R. 96 W., sec. J4, Central part of South Kill Limestone se. 1/4, sw. 1/4, Dunn Co. deer Mountain; summit of butte; locality 24 • --=Tl"'r'V'-,.,·~~~.~-- ~-,..- ~-...... -~-.----~----~---~ .....,~,-- ~~-~~ §,ReCj_filen - = ___f..Ef?.al I..oce.t:i.on ., ___ , .. ·- St:ratigrfl.Rhic Posi_1ion ··-J~t'iwloJ3l: 5988 T. 147 N., R. 96 W., sec. 34, Central part of South Killdeer Limestone se. 1/4, sw. 1/4, Dunn Co. Mountain; summit of butte; lo.cality 24. ' 5987 T. 147 N., R. 96 W., sec. 34, Central part of South Killdeer Limestone ·se. 1/4, sw. 1/4, Dunn Co. Mountain; sum.mi t of butte; locality 24. 4744 T. 147 N., R. 96 W., sec. 34, Central part of South Killdeer Limestone se~ 1.4, sw. 1/4, Dunn Co. Mountain; summit of butte; locality 24. . 4745 T. 147 N., R. 96 W., sec. 34, East side of South Killdeer Sandstone I-' ' 0 se. 1/4, sw. 1/4, Dunn Co. Mountain; sununit of butte; N locality 25. 4741 T. 147 N., R. 96 W., sec. 34, East side of South Killdeer Sandstone se. 1/4, sw. 1/4, Dunn Co. 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