Radiocarbon analyses from Cincinnati, Ohio, and their implications for glacial stratigraphic interpretations

QUATERNARY

RESEARCH

34, l-11 (I!%%)

Radiocarbon Analyses from Cincinnati, Ohio, and Their Implications for Glacial Stratigraphic Interpretations THOMAS V. LOWELL AND KEVINM.SAVAGE Department of Geology, University of Cincinnati, Cincinnati,

Ohio 45221

C.SCOTTBROCKMAN Ohio Department

of

Natural Resources, Division of Geological

Survey, Columbus, Ohio 43224

AND

Radiocarbon

Laboratory,

Universiv of Pittsburgh, Pittsburgh, Pennsylvania Received May 16, 1989

15238

Detailed analysis of a site near Cincinnati, Ohio, shows that 14C ages of samples in a single geologic unit can have a range of several thousand years and ages from different stratigraphic units can overlap. At the Sharonville site, four “+C samples from organic silt below glaciogenic deposits have an inverted chronologic sequence, suggesting contamination, but nevertheless they indicate the silt was deposited before 27,000 yr B.P. A stump cluster in growth position, wood fragments, and moss from the upper surface of the silt may differ by as much as 2300 r4C yr. Five ages from the stump cluster constrain the timing of a glacier advance of the Laurentide ice sheet to its southern limit in the Cincinnati area at 19,670 k 68 yr B .P. Overlying glaciogenic sediments contain transported wood that may be as much as 3200 yr older than the advance. This range of ages points out that, for a given site, several age measurements are required to determine when a glacier advance occurred. Because the measured ages in this study span the entire interval suggested for a twofold sequence of advance, retreat, and readvance of the margin of the Miami sublobe, we suggest a single advance to its terminal position in the Cincinnati area as an alternate hypothesis for testing. 6 1990 University of Washington.

sites be used to assess the chronology of glacier fluctuations. The chronology of late Wisconsin ice margin advances and retreats has long been of interest for investigations such as paleoclimatic reconstruction and ice sheet modeling. Recently, the timing of these fluctuations has become important in helping to decipher problems of climatic and chemical cycles (Broecker and Denton, 1989). Mickelson et al. (1983) and Richmond and Fullerton (1986) provide recent reviews of the radiocarbon chronology for the southern margin of the Laurentide ice sheet. These summaries emphasized that the Great Lakes region contains some of the most detailed stratigraphic and chronologic information in North America, but nonetheless

INTRODUCTION

Radiocarbon analysis has provided valuable insights into the timing of late Quaternary geologic events. However, detailed studies from different geologic settings have shown that care must be exercised when evaluating a single measured age from a single geologic setting (e.g., Blong and Gillespie, 1978; Gilet-Blein ef al., 1980; King, 1985; Schiffer, 1986; MacDonald et al., 1987). As an additional example of potential problems, we present a series of radiocarbon ages from one glaciated site. These ages span a period longer than the suggested time interval for two major fluctuations of the Laurentide ice sheet. We urge that multiple age estimates from single 1

0033-5894190 $3.00 Copyright 0 1!390by the University of Washington. AU rights of reproduction in any form reserved.

LOWELL

2

enough problems remain that correlations of deposits in different lobes require an assumption of synchroneity of glacier fluctuations. This assumption makes it difficult to assess objectively the interaction of the ice sheet margins and climatic changes. To help assess the reliability of available radiocarbon ages, we analyzed organic materials in three different stratigraphic positions at our study site: (1) organic silt below a diamicton, (2) plant remains and stumps in growth position at the top of the silt, and (3) wood transported and deposited by glaciogenic activity. We chose these settings because the literature suggests that although similar units and stratigraphic associations are present elsewhere, commonly only one position has age estimates at a given site. DESCRIPTION OF THE SHARONVILLE SITE

Our detailed investigation was conducted at a site near the late Wisconsin limit north of Cincinnati, Ohio (Fig. 1). The Sharonville site is in a north-trending stream gully in the upland east of the Mill Creek Valley (Fig. 2). Urbanization of this drainage basin and subsequent increased stream erosion has produced fresh exposures of unconsolidated sediments overlying bedrock. The lower units are well exposed; however, the upper units are slumped. Although previous mapping (Gray et al., 1972) indicated that late Wisconsin drift is restricted to the major valley west of our site, our age analysis shows that the drift is present at Sharonville. At least in this area, the late Wisconsin drift limit is south of the position mapped previously. The most important exposure, 2 m high and 15 m long, near the junction of two tributaries, is known informally as the “stump site” (Figs. 2 and 3) This site has limited FIG. 1. of the late Wisconsin the valley.

ET AL.

vertical extent because the upper surface is an erosional stream terrace. Lithostratigraphic units exposed at the stump site include: Unit 6. Coarse terrace gravel lag, present only along the downstream end of the terrace. Unit 5. Compact silt-rich diamicton (till) up to 1.7 m thick. The upper surface is an unconformity marking the base of an eroded stream terrace. This unit contains inclusions of Units 3 and 4 and scattered sand lenses but is massive otherwise. Small wood fragments are present locally in the diamicton at the base of the unit. Unit 4. Massive calcareous clay O-40 cm thick. The upper part of this unit grades into Unit 5 over a distance of 2-3 cm. The clay protected the stumps in Unit 3 during subsequent deposition of the diamicton of Unit 5. Unit 3. Organic-rich silt that grades upward from Unit 2 and reaches 50 cm in thickness. The unit is massive and leached; grain size averages 65% silt. The upper part of the unit contains disseminated plant remains. The uppermost zone is bryophyte mat 2-3 cm thick (Ao paleosol horizon). At least eight stumps are present in the upper surface of the silt. They are in growth position but they extend upward only IO-25 cm above the organic mat and are covered and encased by Unit 4. Unit 2. Clay-rich diamicton (till) with intense alteration at the upper surface. The alteration extends through the 50-cm-thick unit in the trench. Unit 1. Ordovician shale and limestone exposed in a trench dug at the base of the section. Bedrock crops out in the stream bed upstream from the stump site. Logs suitable for age determinations were not observed in Unit 5 at the stump site; however, logs were obtained at four nearby sections in diamicton that are litho-

Map showing location of the Sharonville site at the southern margin of the Miami sublobe Wisconsin Laurentide ice sheet. A portion of the Hartwell moraine (previously mapped late limit) crosses the Mill Creek Valley. The Sharonville site is on the dissected upland east of Late Wisconsin ice limits after Dyke and Prest (1987) and Gray et al. (1972).

INTERPRETATION

OF

3

14C AGES

9z” 4.9’

dW 98’ G’ -.___..

BC

40-N

SO”

Y

SHARONVILLE

SITE

4

LOWELL

ET

AL.

N

[PITT - 03531 \\

0.624

11

---_ ::.‘:.‘.‘.I ... . . .. .. .... - -

-

-

293,22

25

“STUMP

SITE”

0.730 274, 26 25

0.702

A

Wood

encased

IPITT-

in scdlments

02261

1OOm

’

~+I03 Limestone

C.I. = 5m Dolomite

Other

FIG. 2. Plan view of the Sharonville site. Location of the stump site and other dated sections are shown. Circles represent pebble orientations projected on the lower hemisphere of an equal-area projection. Numbers beside circles represent a measure of fabric strength Sl (0 = random, 1 = uniform), azimuth and plunge of the mean vector VI, and number of pebbles. Contours represent 2 standard deviations from random with the black areas representing the maximum deviation. Measures after Lawson (1979). Bar graphs show grain size and clast lithology.

@

NUMBER

-

OR0 MAT ON TOP OF UNIT3

I FOR VERTICAL

-7

.---b \ \ \ ay

kbl

20,200

19,200 19,690

/ \

AREA IN DETAIL

_.-_._

A

PITT-0507,stump

5

2 1,120&l organic

units. Circled numbers refer to units

30,PITT-0225, mat

1,945*180,PITT-0224,roots

+ 140,

5 140,PITT-0508,stump * 150, PITT-0509,root

@CLAY

ages in the various stratigraphic

%

0

$&r-2

I-

Wood/roots

/ ,,,i~iTii” / 1 Organic silt

of organic mat

L

extent

MODERNt/EC&T/

of the “stump site” and location of radiocarbon

21,570f 180, PITT-0226,roots

19,310 k 170, PITT-050_6, stump

19,960 + 170, PITT-0227,stump

m

“NlT

I

Ttds-87-09 “ SHARONDALE RD Face Orientation =34O Elevation at Base = 219 m 0 1 EQUAL SCALE

FIG. 3. Stratigraphy described in text.

I

South

c\I,,

6

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stratigraphically equivalent to Unit 5. Primary field data to support this interpretation are the nearly continuous exposure of the diamicton throughout the valley; gaps between sections are less than 15 m, and the maximum distance to the logs is less than 290 m. Additional field support includes (1) similarity of structures in the diamicton at all sections (deformed and undeformed sand and silt bodies, clay clasts), (2) wood incorporated in the diamicton throughout the valley, and (3) consistent northwest-plunging pebble fabrics (Fig. 2). Supporting laboratory data includes similarities in (1) grain-size distributions (Fig. 2) of the diamicton matrix, (2) pebble lithology (Fig. 2), and (3) clay mineralogy of the matrix (Fig. 4). The field evidence and laboratory data support our interpretation that the massive diamicton at the stump site (Unit 5) is lithostratigraphically equivalent to the diamicton that encloses the other analyzed log samples. DESCRIPTION OF RADIOCARBON ANALYSES

The purpose of multiple radiocarbon analyses was to determine the variation of measured ages between and within geologic

11.o Two-Theta

17.0

23 0

290

(Degrees)

FIG. 4. X-ray diffraction pattern of glycolated <2 pm fraction from diamicton matrix adjacent to logs collected for radiocarbon age analysis. Locations of samples are shown on Figure 2.

ET AL.

units. To this end three sets of samples were collected and analyzed. Each sample set consisted of wood or organic-rich silt that was frozen after collection. The samples were analyzed at the Radiocarbon Laboratory, University of Pittsburgh; all samples were boiled in NaOH to remove humic contaminants before hydrochloric acid treatment and eventual combustion. Each sample was counted at least twice in two different counting systems for periods of not less than 4000 min each to avoid intercounter bias in this age range. All ages were calculated on the basis of the Libby half-life value and are reported with la counting errors. The first set consists of four ages (Table 1, Figs. 3 and 5) in stratigraphic succession through the organic silt (Unit 3). These ages, from disseminated organic matter in the silt, ranged from 24,510k 260 (PITT0350) to 26,490 + 300 yr B.P. (PITT-0348); except for PITT-035 1, these measured ages are in reverse stratigraphic order. The second set of ages (Table 1, Figs. 3 and 5) was expected to provide the age of the uppermost organic layer (Ao paleosol horizon) just prior to overriding by glacier ice. Wood in the organic silt (PITT-0224, -0225, -0226), yielded ages from 21,120k 1301 to 21,945 k 180 yr B.P. The most important ages of this set are from in situ stumps. These ages ranged from 19,200 + 140 to 20,200 + 140 yr B.P. (Table 1, Figs. 3 and 5). The third set of ages (Table 1, Fig. 2) is from logs encased in diamicton in exposures within 290 m of the stump cluster. The ages were expected to indicate the variation of ages of logs that were transported by ice. This set had a measured age range of nearly 3000 14C yr, from 22,550 rt 275 (PITT-0228) to 19,610 k 120 (PITT-352) yr B.P. STRATIGRAPHIC SIGNIFICANCE RADIOCARBON ANALYSIS

OF

Set 1, Organic Silt Initial interpretation of these ages suggests that the organic silt accumulated from

INTERPRETATION

1. RADIOCARBONAGESFROMTHE

TABLE

Lab number

OF

4s (yr B.P.)

7

14C AGES

SHARONVILLE

SITE

Stratigraphic position

Material Age estimates from organic silts (Unit 3)

PITT-0348 PITT-0349 PITT-0350 PITT-035 1

26,490 25,490 24,510 25,340

+ k * *

300 160 270 295

PIl-I-0224 PITT-0225 PITT-0226

21,945 r 180 21,120 * 130 21,570 k 180

Organic Organic Organic Organic

silt silt silt silt

8 cm 20 cm 35 cm 47 cm

below below below below

Unit Unit Unit Unit

4 4 4 4

9.3% 5.3% 4.8% 3.9%

wt. wt. wt. wt.

loss” loss loss loss

Age estimates on organic layer at top of organic silt Lark root Moss, organic mat Larix

In organic silt Top of organic silt In organic silt

Age estimates from stump cluster PITT-0227 PITT-0506 PITT-0507 PITT-0508 PITT-0509

19,960 19,310 20,208 19,208 19,690

PITT-0228 PITT-0352 PITT-0353 PITT-0354

22,550 19,610 21,450 21,480

* t + k *

170 170 140 140 150

Larix Lark Larix Larix Larix

stump stump stump stump root

On organic On organic On organic On organic In organic

silt silt silt silt silt (same tree as PITT-0508)

Age estimates on transported wood (Fig. 2 for sample locations) 2 k f k

275 120 170 145

Log Log Log Log

Picea Picea Picea Picea

encased encased encased encased

in in in in

diamicton diamicton diamicton diamicton

L1wt. loss refers to the weight loss by combustion at 6OWC.

26,000 to 24,000 yr ago. The inverted stratigraphy of the ages, however, indicates the presence of contamination. Although “old” carbon contamination of samples in the upper stratigraphic horizons is possible, contamination by “young” carbon seems more plausible. Several studies (Kigoshi et al., 1980; Gilet-Blein et al., 1980; Geyh and Roeschmann, 1983) suggested that soil ages may be too young because of downward migration of surface organic compounds into lower soil horizons. Geyh and Roeschmann (1983) studied a fossil podzol that yielded conventional radiocarbon ages from 19,000 to 41,000 yr B.P. In that set of ages there was no correlation between measured age and depth and the authors suggested that the true age of the soil may be older than 41,000 yr B.P. Gilet-Blein et al. (1980) tested different extraction techniques and reported ages ranging from 28,900 to 24,300 yr B.P. for an interstadial soil in France. Different ages were obtained with different extraction techniques. On the

basis of the three profiles analyzed, they concluded that “young” material was incorporated in the soil, and that existing techniques cannot separate these contaminants from the older soil material. They also suggested that all soil ages should be treated as minimal ages only. Considering the Sharonville data in light of these studies and other factors mentioned above, we suggest that initial deposition of organic material in Unit 3 began prior to 27,000 yr B.P. during an interstade or interglaciation prior to the deposition of the diamicton (Unit 5). Set 2, Top of the Organic Silt The stump cluster ages provide the best stratigraphic control on glacier advance. These analyses are from wood, so contamination problems are minimal. Also, the upright positions with roots intact probably indicates that the trees were killed by overriding glacier ice. Several other stumps at the site support this interpretation: all were

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27Middle Unit

of 3

~ TOP unit

c.+ 3

I S,“mp cluster

Transported (Unit

wood 5)

FIG. 5. Radiocarbon ages and stratigraphic relationships. Ages in Table 1 are plotted in their relative stratigraphic positions to show age overlaps. The relative stratigraphic ages of samples from specific units increase toward the right on the horizontal axis. The ages from the middle of Unit 3 are in stratigraphic order, but ages from other groupings have no stratigraphic significance within the grouping.

truncated about lo-25 cm above their bases. The stump cluster provides a tight chronologic control for the age of the growing trees at the time of their death, and thus the timing of the glacier advance at the site. Five analyses were obtained from the stumps: one determination from each tree of the cluster, and a replicate analysis from one tree. All samples come from slices through the tree. The measured ages have a span of 1300 14C yr (Table 1, Fig. 5). The replicate analysis differed by almost 700 yr (PITT-0508, PITT-0509). What then is the age of the stump cluster? The range of ages indicates some type of contamination, counting, and (or) fractionation error. Present information is inadequate to determine the source of the variance so we simply averaged the ages using the procedure of Long and Rippeteau (1974). We assign a provisional age of 19,670 + 68 yr B.P. to the cluster and hence to the age of overriding by the ice sheet margin. Ages from around the stump cluster are also informative. If tree growth stopped approximately 19,670 + 68 yr B.P., then other material around

ET

AL.

the stumps has measured ages up to 2500 14C yr older than the stumps (including the la standard deviations; Table 1). One explanation is that there is a residence time of at least 2300 yr for organic matter on or near the paleosurface. A second explanation is that organic matter encased in silt has undergone fractionation to change its radiometric age. Presently we cannot differentiate between these two or other possibilities. Analysis of isolated wood pieces from organic silt below glaciogenic deposits may yield radiometric ages 2300 14C yr older than ages obtained from trees at the same site killed by glacial overriding. Set 3, Transported

Logs

If the averaged stump age (19,670 + 68 yr B.P.) documents the age of the glacier advance, what is the significance of the ages from the glacially transported logs? First, we note the similarity in ages of the transported logs and ages of wood taken from Unit 3. One age of transported wood (19,610 + 120 yr B.P., PITT-0352) is within the statistical overlap of the stump cluster. On the other hand, the remaining three samples (22,550 + 275, PITT-0228; 21,450+ 170, PITT-0353; and 21,480 t 145 yr B.P., PITT-0354) yielded ages similar to the average age of wood from the organic silts (21,439 5 91 yr B.P.). One possible explanation is that the transported wood contains two populations; wood that was growing on the former land surface and wood that was encased within silt prior to the glacier advance. An alternate explanation is that some of the wood was incorporated locally and some was transported to the Sharonville site. Three of the transported logs still retained their bark, suggesting that the trees were alive when the logs were incorporated. It is difficult to test directly these hypotheses until more is known about glacial entrainment and transportation processes and until more is known about possible contamination or fractionation processes.

INTERPRETATION

If only transported wood samples are available from a single stratigraphic unit at a site, it still may be possible to obtain a close age estimate for a glacier advance. Assuming that the measured age of each sample represents the true age of the tree at its death, the youngest age or ages obtained from transported wood would most closely indicate the age of the advance at that site. For example, the age of 19,610 + 120 yr B.P. (PITT-0352) from transported wood at our site is similar to the average age estimate of 19,670 + 68 yr B.P. from the stump cluster. Given the range of measured ages obtained at one site, what can be said about glacial correlations and chronologies based on single measurements from several sites? We suspect that internal variations in the geologic, biologic, and pedogenic systems produce the variation described above, and this noise renders intersite correlations largely speculative unless a number of ages are obtained from each site, preferably from two or more stratigraphic levels. IMPLICATIONS FOR EXISTING STRATIGRAPHIC FRAMEWORK

In this section we consider how age variations, as reported above, may allow alternative interpretations of existing glacialstratigraphic models. We examine one model in this context. Gooding (1963, 1975), from analysis of radiocarbon ages and stratigraphic sections, established the currently accepted stratigraphic framework for glacial deposits in the Miami and Scioto sublobe areas (Fig. 1). His data base included nearly 60 radiocarbon age estimates from 44 sites in southern Ohio and Indiana. Although only one or two ages were available from most of these sites, subsequent investigations have increased the number of ages. On the basis of his data set, Gooding (1975) suggested that the earliest late Wisconsin ice margin advanced southward into southeastern Indiana and westcentral Ohio about 22,000 yr B.P. and that it reached its

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terminal position about 21,000 yr. B.P. (during the Fayette stade). Glacier recession ensued during the Connersville interstade from about 21,000 to about 20,000 yr B.P. The areal distribution of radiocarbon ages suggested to him that the ice margin receded some 55-80 km at this time (Gooding, 1975, Fig. 4). A second advance about 19,800 yr. B.P. (depositing the Shelbyville till) extended beyond the limits of the Fayette ice to the late Wisconsin maximum limit (Gray et al., 1972). Subsequent investigations have relied heavily on this stratigraphic and chronologic framework (Goldthwait ef al., 1981, and references therein), and to a large extent have supported it with some refinements, including the identification of two superposed units of Shelbyville till. Because our study site is south of the postulated limit of the Fayette advance, our observations and data cannot directly test Gooding’s (1975) stratigraphic model. However, our results refine the timing for the Shelbyville maximum, shifting it from 19,800 yr B.P. to approximately 19,670 + 68 yr B.P. In addition, these results also raise questions about the age assignments of Gooding (1975). If we had analyzed only the wood in the organic silt (Unit 3) at the Sharonville site, which yielded ages between 21,000 and 22,000 yr B.P., we would have assigned a Fayette age to the overlying diamicton. This interpretation is supported because three of the four ages from the overlying diamicton also produced similar radiocarbon ages. Conversely, if we had obtained only one sample from the diamicton (and by chance it was PITT0352, 19,610 + 120 yr B.P.), we would have assigned a Shelbyville age to the diamicton. The stump cluster (19,670 + 68 yr B.P.) supports this latter assignment. At the Sharonville site six 14C samples suggest ice advance of Fayette age, and six 14C samples suggest ice advance of Shelbyville age. We feel our age assignment of 19,670 + 68 yr B.P. for the glacial overriding is reasonable only because multiple age esti-

10

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mates from three different stratigraphic levels point to it. The range of our age estimates coincides with the ranges of previously published ages supporting a twofold glacier advance (Gooding, 1975). However, the stratigraphy of our site permits only one ice marginal advance; is it not possible that the published radiocarbon ages may represent only one, rather than two ice marginal advances in the eastern Indiana-western Ohio area? Further detailed lithostratigraphic analyses and correlation and radiocarbon studies are required to test existing stratigraphic models for the Miami sublobe, and that may also be true for glacial stratigraphies developed elsewhere. The range of ages obtained from isolated samples at different sites could result in development of a “radiocarbon stratigraphy” that is more complex than the actual ice margin history. This possibility is complicated further when the statistical errors of all of the measured ages are considered. As Mickelson et al. (1983) noted, the error ranges of many radiocarbon ages from Ohio and Indiana are greater than the durations of either the glacier advance or the interstade they are inferred to “date.” If the wide range of ages we report from a single site is typical, then possibly some of the complex, overlapping age assignments reported in the literature result from intrasite variation of radiocarbon ages rather than from a complex glacier behavior. A corollary is that with only a few age estimates at a glacialstratigraphic site, an age assignment is problematic, even if the ages appear to be in stratigraphic order. CONCLUSIONS

From our study of the Sharonville site we draw the following site-specific and general conclusions: (1) The stratigraphic significance of published radiocarbon ages from sites near the southern limit of late Wisconsin Laurentide glaciation should be critically reexamined, given the possible range of ages obtained

ET

AL.

from a single lithostratigraphic unit. Multiple ages from several units are necessary for an accurate age assignment of glacial events. (2) Age estimates of disseminated organic materials in silt probably should be treated as minimum ages and they should be assessed carefully on a site-by-site basis. (3) Glacially transported wood may be much older than the enclosing glacial sediment. The youngest cluster of multiple radiocarbon ages from a single unit at a site may provide the best estimate of the age of a glacier advance at that site. (4) Late Wisconsin ice in the Miami sublobe area in the vicinity of the Sharonville site extended south of the limit mapped by Gray et al. (1972). (5) A tentative hypothesis is advanced that the late Wisconsin ice margin of the Miami sublobe reached its southern limit approximately 19,670 + 68 yr B.P. (6) The measured age relationships reported here also permit an hypothesis in which the presently accepted age assignment of Fayette and Shelbyville ice advances results from sampling bias rather than from glacier variations. ACKNOWLEDGMENTS Ned Baker assisted in the sample collection, Steve Jackson identified the wood, and Norton Miller identified the bryophytes. George Denton and Greg McDonald provided thoughtful discussions on this topic. Hilt Johnson and Dave Mickelson provided comments on an early draft and David Fullerton and an anonymous reviewer greatly clarified later drafts. Lyla Messick assisted with the drafting. The University Research Council, the Dean’s Office of the College of Arts and Sciences, and the Department of Geology all supported the radiocarbon analyses.

REFERENCES Broecker, W. S., and Denton, G. H. (1989). The role of ocean-atmosphere reorganization in glacial cycles, Geochimica et Cosmochimica Acta 53, 246% 2501. Blong, R. J., and Gillespie, R. (1978). Fluvially transported charcoal gives erroneous 14C ages for recent deposits. Nature (London) 271, 739-741. Dyke, A. S., and Prest, V. K. (1987). “Late Wisconsinan and Holocene Retreat of the Laurentide Ice

INTERPRETATION

Sheet,” Geological Survey of Canada Map 1702A, scale 1:5,000,000. Geyh, M. A., and Roeschmann, G. (1983). The unreliability of 14C dates obtained from buried sandy podzols. Radiocarbon 25, 409-tl6. Gilet-Blein, M. G., and Evin, J. (1980). Unreliability of 14C dates from organic matter of soils. Radiocarbon 22, 919929. Goldthwait, R. P., Stewart, D. P., Franzi, D. A., and Quinn, M. J. (1981). “Quaternary Deposits of Southwestern Ohio,” Cincinnati ‘81 Field Trip Guidebooks, Vol. III, pp. 405L432. American Geological Institute. Gooding, A. M. (1963). Illinoian and Wisconsin glaciations in the Whitewater basin, southeastern Indiana, and adjacent areas. Journal of Geology 71,665682. Gooding, A. M. (1975). The Sidney interstadial and late Wisconsin history in Indiana and Ohio. American Journal of Science 275, 993-1011. Gray, H. H., Forsyth, J. L., Schneider, A. F., and Gooding, A. M. (1972). “Geologic Map of the 1” x 2” Cincinnati Quadrangle, Indiana and Ohio, Showing Bedrock and Unconsolidated Deposits,” Regional Geologic Map No. 7, Part B, scale 1:250,000. Indiana Geological Survey. Kigoshi, K., Suzuki, N., and Shiraki, M. (1980). Soil dating by fractional extraction of humic acid. Radiocarbon

22, 853-857.

King, G. A. (1985). A standard method for evaluating

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radiocarbon dates of local deglaciation: Application to the deglaciation history of southern Labrador and adjacent Quebec. Gtographie Physique et Quaternaire 36, 163-182. Lawson, D. E. (1979). A comparison of pebble orientation in ice and deposits of the Matanuska Glacier, Alaska. Journal of Geology 87, 629-645. Long, A., and Rippeteau, B. (1974). Testing contemporaneity and averaging radiocarbon dates. American Antiquity 39, 205-215. MacDonald, G. M., Beukens, R. P., Kieser, W. E., and Vitt, D. H. (1987). Comparative radiocarbon dating of terrestrial plant macrofossils and aquatic moss from the “ice-free corridor” of western Canada. Geology 15, 837-840. Mickelson, D. M., Clayton, L., Fullerton, D. S., and Boms, H. W., Jr. (1983). The late Wisconsin glacial record of the Laurentide ice sheet in the United States. In “Late Quatemary Environments of the United States: Vol. 1” (S. C. Porter, Ed.), pp. 3-37. Univ. of Minnesota Press, Minneapolis. Richmond, G. M., and Fullerton, D. S. (1986). Summation of Quaternary glaciations in the United States of America. Quaternary Science Reviews 5, 183-196. Schiffer, M. B. (1986). Radiocarbon dating and the “old wood” problem: The case of the Hohokam chronology. Journal of Archaeological Science 13, 13-30.