The Ohio State University

1983-09

Provenance Dates and Feldspar Fractionation

in Late Wisconsin Till of the Cuba Moraine,

Ohio

Taylor, Karen S.; Faure, Gunter The Ohio Journal of Science. v83, n4 (September, 1983), 177-182http://hdl.handle.net/1811/22946

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Ohio Journal of Science (Ohio Academy of Science) Ohio Journal of Science: Volume 83, Issue 4 (September, 1983)

Copyright © 1983 Ohio Acad. Sci. 0030-0950/83/0004-0177 $2.00/0

PROVENANCE DATES AND FELDSPAR FRACTIONATION IN LATEWISCONSIN TILL OF THE CUBA MORAINE, OHIO1

KAREN S. TAYLOR and GUNTER FAURE, Department of Geology and. Mineralogy, The Ohio StateUniversity, Columbus, OH 43210

ABSTRACT. Late Wisconsin till of the Cuba Moraine in Ohio consists of sediment con-tributed by local Paleozoic bedrock and by the igneous and metamorphic rocks of theCanadian Precambrian Shield. Feldspar in this till is derived predominantly from theGrenville and Superior structural provinces of Canada which are 1.07 b.y. and 2.70 b.y.old, respectively. Rb-Sr provenance dates of feldspar in the — 18 +35 mesh fractions oftill range from 1.21 b.y. to 2.01 b.y. and confirm that the feldspar is a mixture of grainsfrom these 2 provinces. The K-feldspar/plagioclase ratio of the — 18 +35 mesh fraction isconsistently greater than that of the —120 +250 mesh fraction. This relationship alsowas seen in the till of the Powell Moraine of Ohio and in Cenozoic till of Antarctica andmay be caused by preferential grinding of plagioclase during transport at the base of theice. The feldspar in the — 18 +35 mesh fraction is enriched in K-feldspar by about 25%compared to feldspar in the — 120 +250 mesh fraction of till in the Cuba Moraine.

OHIOJ . SCI. 83 (4): 177-182, 1983

INTRODUCTION

The Cuba Moraine of Ohio is one ofmany glacial deposits in the midwesternUnited States and Canada that were de-posited during the Late WisconsinanGlaciation. The till of the Cuba Moraine iscomposed of detritus originating from thePaleozoic sedimentary rocks that form thebedrock of this region and from the igneousand metamorphic rocks of the CanadianPrecambrian Shield. Feldspar is a commonconstituent of Ohio till and is derived al-most entirely from the Precambrian Shieldof Canada (Gross and Moran 1972, Taylorand Faure 1979, 1981). This feldspar is amixture of grains derived from theGrenville and Superior structural provincesof the Canadian Shield that recrystallized1.07 b.y. and 2.70 b.y. ago, respectively.Rb-Sr dates of the feldspar, separated fromthe till of the Powell-Union City Moraine,range from about 1.2 to 1.9 b.y. and thusconfirm that the feldspar has a mixedprovenance (Taylor and Faure 1981).

'Manuscript received 16 December 1981 and inrevised form 21 May 1982 (#81-51).

Taylor and Faure (1981) analyzed feld-spar in 4 size fractions of 2 till samplesfrom the Powell Moraine and showed thatthe K-feldspar/plagioclase and Rb/Sr ra-tios increase with increasing grain size. Asimilar relationship also was observed inthe Cenozoic tills of the TransantarcticMountains by Faure and Taylor (1981a).The objectives of the present study are todetermine the Rb-Sr provenance dates offeldspar in till from the Cuba Moraine andto study the apparent mineralogical frac-tionation of feldspar first observed byTaylor and Faure (1981).

STUDY SITE

The samples for this study were col-lected along the strike of the Cuba Morainebetween Xenia and Chillicothe in south-central Ohio (fig. 1). This moraine, stud-ied in some detail by Foster (1950) andRosengreen (1970), is shown on the glacialmap of Ohio (Goldthwait et al. 1961), andis discussed by Dreimanis and Goldthwait(1973) in a general history of the Wis-consinan Glaciation in the Huron, Erie,and Ontario lobes. Two l4C age determi-nations from Todd Creek valley west of

177

178 K. S. TAYLOR AND G. FAURE Vol. 83

FIGURE 1. Map showing Cuba Moraine, Powell Moraine and the Gahanna till location in central Ohio. Thecollecting sites along the Cuba Moraine are identified by number in table 1.

Sligo, Ohio, are 21,137 ± 1,435 yearsB.P. (OWU-159) and 22,255 ± 1,652years B.P. (OWU-160). Wood from theCuba Moraine 1.6 km northwest of NewPetersburg gave a 14C date of 20,460 ±700 years B.P. (W2459). Rosengreen(1970) concluded from these dates that theScioto sublobe of the Erie lobe reachedits maximum southward advance about21,350 years B.P.

FELDSPAR PROVENANCE DATESIn an earlier study, Taylor and Faure

(1981) extracted feldspar from the— 60 +120 U.S. standard mesh fractionbecause it contains about 32% of the feld-spar in Late Wisconsin till in Ohio (Taylorand Faure 1979). For the current study, the— 18 + 35 mesh fraction was analyzedbecause it has a higher Rb/Sr ratio and is

therefore a more sensitive geochronometer.Feldspar in this fraction also tends to beless weathered than the — 60 +120 meshfraction because it has less surface area perunit weight. Carbonate grains were dis-solved by leaching with 2N HNO 3 and themagnetically susceptible mineral grainswere removed by means of a Frantz Iso-dynamic Magnetic Separator. The sampleswere further refined by ultrasonic treat-ment. Rb/Sr ratios were determined byX-ray fluorescence and 87Sr/86Sr ratioswere measured on a mass spectrometer(Nuclide Corp., Model 6-60-S) as de-scribed by Taylor and Faure (1979). TheEimer and Amend SrCO3 interlaboratoryisotope standard was analyzed 2 times inthe course of this study and has an average87Sr/86Sr ratio of 0.70811 ± 0.00015

OhioJ. Sci. FELDSPAR DATES AND FRACTIONATION 179

(1(7). This result is in agreement withvalues reported from other laboratories.Rb-Sr provenance dates were calculatedusing a value of 0.7040 for the initial87Sr/86Sr ratio and 1.42 X 10" " y " 1

for the decay constant of 87Rb.The resulting dates (table 1) range from

1.21 to 2.01 b.y. and have an average of1.61 ± 0.07 b.y. (la). The date for thesample collected at Kingman (table 1) wasomitted from the average because it con-tained residual grains of dolomite as dis-cussed later in this report. All of the prove-nance dates are between the ages of theGrenville Province (1.07 b.y.) and the Su-perior Province (2.70 b.y.) of Canada andtherefore indicate the feldspar grains aremixtures from these 2 source areas. Thisresult compares favorably to dates fromthat part of the Powell Moraine which wasalso deposited by the Scioto sublobe of theErie lobe (fig. 1). The dates from this sec-tion of the Powell Moraine range from1.2 b.y. to 1.8 b.y. with a mean of1.54 ± 0.06 b.y. (Taylor and Faure 1981).The similarity of provenance dates for these2 segments of the recessional morainessuggests the feldspar was derived from thesame sources and was mixed approximatelyin the same proportions. These results con-firm the conclusion of Dreimanis andGoldthwait (1973) that the till of the CubaMoraine, like that of the Powell Morainebetween Crestline and Rushsylvania,

Ohio, was deposited by the Scioto sublobeduring Late Wisconsin time.

A suite of 17 samples from the BrownTill at Gahanna, Ohio, (Goldthwait 1965,Taylor and Faure 1982) has a range of datesfrom 0.91 b.y. to 1.40 b.y. and a mean of1.20 ± 0.16 b.y. This till was presumablydeposited during an earlier advance of theScioto sublobe and may be older than thetill of the Powell Moraine. The provenancedates of the Brown Till are lower than thosefrom the Cuba and the Powell Moraines.One possible explanation for this result isthe presence of feldspar originating fromthe Berea sandstone (Mississippian) fromwhich more than 30% of the clasts in thistill were derived (Taylor and Faure 1982).The till of the Cuba Moraine does notcontain sandstone clasts in appreciableconcentrations which means the prove-nance dates of this till depend primarily onthe proportion of feldspar grains derivedfrom the Grenville and Superior Provincesof Canada.

FELDSPAR FRACTIONATION

Taylor and Faure (1981) reported thatthe Rb/Sr ratios of feldspar in 4 size frac-tions of till collected at Buck Run andGreenville, Ohio, along the Powell Mo-raine increase with increasing grain size.They found a similar correlation betweenK-feldspar/plagioclase ratios and grainsize. The reason for this relationship is that

TABLE 1

Rb/Sr, H7Rb/s6Sr, 87 / 86 ratios and dates for feldspar concentrates in till, Cuba Moraine, Ohio.

1.2.3.4.5.6.7.8.9.

10.11.

Sample

LattavilleS. SalemFruitdaleRainsboroSamanthaNew ViennaMartinvilleCowan LakeTodd Crk. UpperTodd Crk. LowerKingman

Rb/Sr

0.17610.22010.14800.27490.18010.21920.16060.18500.18670.21040.1642

87Rb/86Sr

0.51020.63790.42880.796680.52180.63510.46530.53600.54090.60970.4756

87/86

0.715460.718890.716390.718940.716830.715910.716170.716220.716550.717510.71223

Date, b. y.

1.56 ± 0.071.62 ± 0.082.01 ± 0.201.31 ± 0.041.71 ± 0.061.31 ± 0.051.82 ± 0.191.59 ± 0.031.62 ± 0.171.54 ± 0.081.21 ± 0.07

180 K. S. TAYLOR AND G. FAURE Vol. 83

Rb+ replaces K+ in K-feldspar and Sr+2

replaces Ca+ 2 in plagioclase. Therefore,the Rb/Sr ratio of any given sample ap-pears to be dependent on the feldspar min-eralogy which is dependent on grain size.Similar results were obtained by Faure andTaylor (1981a) for Cenozoic tills in theTransantarctic Mountains.

Enrichment of plagioclase in finegrained fractions of till was first noted byDreimanis and Vagners (1971). Suscepti-bility of plagioclase to preferential grind-ing was subsequently reported byHaldorsen (1977, 1978) during a study oftill in southeastern Norway. The apparentenrichment of the —18 + 35 mesh frac-tion in K-feldspar may be caused bymixing of fine grained plagioclase withcoarse grained K-feldspar. This may hap-pen because plagioclase tends to occur inthe groundmass of porphyritic igneousrocks, whereas K-feldspar tends to formphenocrysts and porphyroblasts. A secondpossible reason for the dependence of theK-feldspar/plagioclase ratio on grain sizemay be the preferential grinding of plagio-clase by glacial ice during transport.Chemical weathering of plagioclase doesnot account for the observed grain sizedistribution of this mineral becauseplagioclase weathers more rapidly thanK-feldspar (Krauskopf 1979) and shouldtherefore be depleted in the fine sandfraction.

The present study is part of a compre-hensive effort to test the hypothesis thatfeldspar fractionation is related to distanceof transport by the ice sheet (Faure andTaylor 198 lb). The feldspar-quartz concen-trates were ground to —200 mesh and werecompressed into 10-g pellets composed of3 g of powdered sample and 7 g ofboric acid as backing. The K-feldspar/plagioclase (K/P) ratios were estimated byX-ray diffraction (XRD) of these pelletsusing diffraction peaks at 27.5° 26 (micro-cline) and 28° 26 (plagioclase) for Cu X-radiation. The height above the baseline ofeach diffraction peak was determined bycounting for 100 sec. Eight replicate read-

ings were taken of each peak, and the pel-let was rotated 90° after each count. Theresulting measurements of the K/P ratioshave a reproducibility of about ± 10%, ex-pressed as one standard deviation of themean (table 2).

Concentrations of Na and K were meas-ured by flame emission spectrometry andCa was determined by atomic absorptionspectrophotometry (to be referred to col-lectively as AA). The K/P ratios were cal-culated from the results.

In the calculation of the K /P ratiosfrom the chemical analyses, we assumed allof the Na was contributed by plagioclase.We believe the systematic error introducedby this assumption is insignificant whencompared with precision errors of ± 10%.Both sets of data are shown in table 2 andare plotted in fig. 2. A least-squares re-gression of the K/P ratios of both coarseand fine fractions, as measured by XRDand AA, indicates a slope of 1.053, an in-tercept of 0.0059, and a linear correlationof coefficient r2 = 0.7883. The goodnessof fit of the K/P ratios, determined byXRD and AA, to a line having a slope ofunity and passing through the origin indi-cates both analytical methods are yieldingidentical results on the average and no sys-tematic error exists. If the correlation lineis forced through the origin, the linear cor-relation coefficient increases to 0.9750.The improvement of the correlationachieved by this procedure confirms the ab-sence of systematic errors from the 2 datasets. We conclude, therefore, that theK/P values determined by X-ray diffrac-tion are a valid measure of the K-feldspar/plagioclase ratios of the samples.

An anomalously high concentration ofCa and Mg in the coarse fraction of thesample from Kingman (no. 11, table 2)was attributed to the presence of residualgrains of dolomite that had survived theacid treatment. This datum point thereforedeviated from the pattern formed by theother data sets. However, when the Ca con-tent was reduced by an appropriateamount, the data for this sample became

OhioJ. Sci. FELDSPAR DATES AND FRACTIONATION 181

TABLE 2

K-feldsparlplagioclase ratios for feldspar concentrates of till, Cuba Moraine, Obi

Samples

1. Lattaville

2. S. Salem

3. Fruitdale

4. Rainsboro

5. Samantha

6. New Vienna

7. Martinsville

8. Cowan Lake

9. Todd Crk. Upper

10. Todd Crk. Lower

11. Kingman

FractionMesh

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

- 1 8 + 35-120 + 250

X-ray DiffractionK/P

0.5420.3590.6610.5260.5960.4201.0720.8380.5010.5460.6390.4790.8660.6830.5170.3720.7120.3890.6370.6190.4340.323

Atomic AbsorptionK/P

0.5700.4510.6740.5100.4270.4180.9910.7820.5330.4940.6060.4870.5210.5030.4970.4260.6470.4650.5730.5130.5820.468

compatible with the others from the CubaMoraine. The presence of residual dolomitein the —18 + 35 mesh fraction of thesample from Kingman also caused a de-

0.8 1.0 1.2

K-fe ldspar/Plaqioclase by AA

FIGURE 2. Correlation of K-feldspar-plagioclaseratios of till from the Cuba Moraine determinedby X-ray diffraction (XRD) and atomic absorp-tion (AA).

crease of its 87Sr/86Sr ratio which re-sulted in a lowering of the provenance dateto 1.21 ± 0.07 b.y. (table 1). This datewas therefore omitted from the average ofthe provenance dates of the Cuba Moraineshown in fig. 3- This incident emphasizesthe importance of thorough acid treat-ment of the coarse fractions of till fromwestern Ohio where dolomite is present inthe bedrock.

The average of the K/P ratios of feldsparin the —18 +35 mesh fractions is signifi-cantly greater than that of the — 120 +250mesh fractions. Based on the XRD data,the K/P ratios are 0.652 ± 0.054 (la)for the' coarse fraction, whereas the finefraction has an average K /P value of0.521 ± 0.045 (lcr). A comparison basedon the AA data yields the same result.These measurements indicate that thefeldspar in the —18 +35 mesh fraction oftill in the Cuba Moraine contains approxi-mately 25% more K-feldspar than thefeldspar in the — 120 +250 mesh fraction.

Slope=

K-f

eld

sp

ar/

Pla

gio

cla

se

by

XRD

182 K. S. TAYLOR AND G. FAURE Vol. 83

FIGURE 3. Histograms of Rb-Sr provenance datesof feldspar from the Cuba and Powell Moraines andfrom Gahanna.

The apparent enrichment of the coarse frac-tion in K-feldspar and the complementaryenrichment of plagioclase in the fine frac-tion confirms observations recorded pre-viously by Dreimanis and Vagners (1971),Haldorson (1977, 1978), Taylor and Faure(1981) and Faure and Taylor (1981a).

Additional studies of till from south-western Ontario and northern Ohio are inprogress and will be used to test thehypothesis that the observed mineralogicalfractionation of feldspar in till is related tothe distance of transport.

ACKNOWLEDGMENTS. The chemical analyses wereperformed by Karen Brady. The research was sup-

ported in part by NSF Grant DPP-7920407. This isContribution No. 63 of the Laboratory for IsotopeGeology and Geochemistry (Isotopia).

LITERATURE CITED

Dreimanis, A. and R. P. Goldthwait 1973Wisconsin glaciation in the Huron, Erie andOntario lobes. Geol. Soc. Amer., Mem. 136:71-105.

and U.J. Vagners 1971 Bimodal dis-tribution of rock and mineral fragments in basaltills. In: R. P. Goldthwait, (ed.), Till — a sympo-sium. Ohio State Univ. Press, 237—250.

Faure, G. and K. S. Taylor 1981a Provenance ofsome glacial deposits in the Transantarctic Moun-tains based on Rb—Sr dating of feldspar. Chem.Geol. 32: 271-290.

and 1981b Feldspar frac-tionation by glaciers. Abstr. Ohio J. Sci., Prog,and Abstr. Suppl. 81: 42.

Foster, J. W. 1950 Glaciations and ice lake ofPaint Creek Valley, Ohio. Unpubl. M. S. Thesis,Dept. Geol., Ohio State Univ., Columbus.

Goldthwait, R. P. 1965 Great Lakes-Ohio RiverValley. Guidebook for Field Conf. G, Int. Ass. forQuaternary Res., Vllth Congr., 71—78.

, G. W. White and J. L. Forsyth1961 Glacial map of Ohio. U.S. Geol. Surv.,Misc. Geol. Inv. Map 1—316.

Gross, D. L. and S. R. Moran 1972 Grain-sizeand mineral gradations within tills of theAllegheny Plateau. In: R. P. Goldthwait, (ed.),Till — a symp. Columbus, Ohio State Univ.Press, 251-274.

Haldorsen, S. 1977 The petrology of tills — astudy from Ringsaker, southeastern Norway. Nor.Geol. Unders. 366, 36 p.

1978 Glacial communition of min-eral grains. Nor. Geol. Tidsskrift. 58: 24-243.

Krauskopf, K. B. 1979 Introduction to geo-chemistry, 2nd ed. McGraw-Hill, NY. 617 p.

Rosengreen, T. E. 1970 Glacial geology ofHighland County, Ohio. Unpubl. Ph.D. Diss.,Dept. Geol., Ohio State Univ., Columbus.

Taylor, K. S. and G. Faure 1979 Mineral compo-sitions, 87Sr86Sr ratios, and concentrations ofstrontium and rubidium in late Wisconsin till ofOhio. OhioJ. Sci. 79: 320-324.

and 1981 Rb-Sr datingof detrital feldspar: A new method to study till. J.Geol. 89: 97-107.

and 1982 Feldspar prove-nance dates in a stratigraphic section of till inGahanna, Ohio. OhioJ. Sci. 82: 274-281.

Provenance Dates, b.y.

Brown T i l l , Gahanna

Powell Moraine