PaleoAmerica
A journal of early human migration and dispersal
ISSN: 2055-5563 (Print) 2055-5571 (Online) Journal homepage: http://www.tandfonline.com/loi/ypal20
On the Dating of the Folsom Complex and its
Correlation with the Younger Dryas, the End of
Clovis, and Megafaunal Extinction
Todd A. Surovell, Joshua R. Boyd, C. Vance Haynes Jr & Gregory W. L. Hodgins
To cite this article: Todd A. Surovell, Joshua R. Boyd, C. Vance Haynes Jr & Gregory W.
L. Hodgins (2016) On the Dating of the Folsom Complex and its Correlation with the
Younger Dryas, the End of Clovis, and Megafaunal Extinction, PaleoAmerica, 2:2, 81-89, DOI:
10.1080/20555563.2016.1174559
To link to this article: http://dx.doi.org/10.1080/20555563.2016.1174559
Published online: 22 Apr 2016.
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Date: 18 June 2016, At: 16:37
RESEARCH REPORT
On the Dating of the Folsom Complex and its
Correlation with the Younger Dryas, the End of
Clovis, and Megafaunal Extinction
Todd A. Surovell
and Joshua R. Boyd
University of Wyoming, Laramie, WY
C. Vance Haynes Jr and Gregory W. L. Hodgins
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University of Arizona, Tucson, AZ
Using a set of high-quality radiocarbon dates, including three new dates from the Hanson site and one from
the Folsom component of Hell Gap, we provide a revised estimate of the duration of the Folsom period.
Limiting our sample to bone collagen samples pretreated using the XAD resin chromatographic or
ultrafiltration techniques, calcined bone, and charcoal from hearth features, we show that Folsom sites fall
within a limited range from 12,610 to 12,170 BP, or 440 years. This duration is considerably shorter than
previous estimates. Additionally, we show that there is little correlation between the onset and termination
of the Younger Dryas and the start and end of the Folsom complex. Finally, the youngest Clovis sites and
the last of the Pleistocene megafauna correlate well in time, but are followed by a 100-year gap until the
earliest Folsom sites, most likely a result of small sample size.
Keywords Folsom, Clovis, radiocarbon, Younger Dryas, Hanson site, Hell Gap site
1. Introduction
Because a large number of additional high-quality
dates have been produced from Folsom contexts in
recent years, we felt that a review of the chronology
of the Folsom complex was overdue. The age range
for Folsom provided by Haynes et al. (1992) of
10,950–10,250 14C yr BP (12,780–12,000 cal yr BP)
is now more than 20 years old. Holliday’s (1997,
2000a) more recent works suggest a similar but slightly
constricted range of 10,800–10,200 14C yr BP
(12,710–11,910 cal yr BP) for the northern Plains
and 10,800–10,100 14C yr BP (12,710–11,710 cal yr
BP) for the southern Plains, but do not include any
dates produced this millennium (see also Stanford
1999; Taylor et al. 1996). Moreover, it has been
noted that the span represented by Folsom correlates
to some degree in time with the Younger Dryas
stadial (12,850–11,650 cal yr BP) (e.g., Holliday
2000b; Jodry 1999; LaBelle 2012; Meltzer and
Holliday 2010; Stanford 1999; Surovell 2009). Using
a refined set of high-quality dates from 12 Folsom
components, we provide a revised age range for the
Correspondence to: Todd A. Surovell. Email: [email protected]
© 2016 Center for the Study of the First Americans
DOI 10.1080/20555563.2016.1174559
Folsom complex and examine its correlation with the
Younger Dryas, the end of Clovis, and megafaunal
extinction.
This paper was also inspired by four new radiocarbon dates first reported herein from Folsom contexts,
three on calcined bone from the Hanson Folsom site
and one on ultrafiltered collagen from the Folsom
component of the Hell Gap site. The Hanson and
Hell Gap site Folsom components are important in
Folsom dating because they have effectively served as
chronological bookends for the complex (Collard
et al. 2010; Haynes et al. 1992).
Dates from Hanson have long been problematic.
Frison and Bradley (1980, 10) initially reported two
dates on “small” charcoal samples. The sample from
Area 1 of the site produced a date of 10,700 ± 670
14
C yr BP (RL-374), and a sample from Area 2
yielded an age of 10,080 ± 330 14C yr BP (RL-558).
These samples were not clearly associated with
hearth features, and as such their relationship to the
age of the Folsom occupation is unclear. They are
also imprecise with large standard deviations. Three
additional dates were produced, apparently in conjunction with Ingbar’s reinvestigation of the site in
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the late 1980s (Frison 1991, 25; Haynes et al. 1992;
Ingbar 1992, 1994). Ingbar (1992, 175) reported two
new dates from Area 2, presumably on charcoal, of
10,300 ± 150 14C yr BP (Beta-22514, ETH-3329) and
9970 ± 340 14C yr BP (Beta-22513). A third date of
uncertain material and provenience (most likely also
charcoal from Area 2) was reported by Frison (1991)
and Haynes et al. (1992); that date is 10,225 ± 125
14
C yr BP (Beta-31072). In sum, dates from Hanson,
all of which appear to be on charcoal stratigraphically
associated with the Folsom occupation, are highly
variable and span almost 1000 radiocarbon years.
Most subsequent studies of Folsom chronology have
relied on an average of the two older Beta dates to
provide an age estimate for the site of 10,260 ± 90
14
C yr BP or 12,022 ± 200 cal yr BP after calibration
(Collard et al. 2010; Haynes et al. 1992; Holliday
2000a). If correct, this would make Hanson one of
the youngest Folsom sites known to date.
Although there are numerous radiocarbon dates
associated with the Folsom component at Hell Gap
(Haynes 2009), all are somewhat problematic as they
are charcoal or soil organic matter dates with only
stratigraphic association. In other words, they may
not directly date the Folsom occupation. Based on
an average of three charcoal dates, Collard et al.
(2010) estimated the age of the Folsom component
to be 10,820 ± 170 14C yr BP or 12,740 ± 179 cal yr
BP after calibration. Those samples, however, were
derived from the Midland component at Locality 2,
which occurs stratigraphically in the same level as
the Folsom component at Locality I (Haynes et al.
1992, 96). If the Collard et al. (2010) Folsom date is
accurate, it would make the Hell Gap site the oldest
known occurrence of the Folsom complex, and
Collard et al. (2010, 2514) used this date to argue
that the Folsom complex originated in the vicinity of
Hell Gap and spread to the north and south from
there. Our new dates from Hanson and Hell Gap
suggest significantly different ages for both sites and
refine the chronology of Folsom considerably.
2. Methods and materials
2.1 Date selection criteria
There is a huge number of radiocarbon dates available
from Folsom contexts, and those dates are highly variable ranging in age from modern (SMU-153) in the
case of a date on bone apatite carbonate from the
Folsom site (Haynes et al. 1992) to 13,340 ± 170 14C
yr BP (NZA-1091) on a piece of charcoal recovered
from gully fill at the Lipscomb site (Hofman 1995).
The key to refining the age of the Folsom complex is
to whittle down the entire set of available radiocarbon
dates to isolate those that are most likely to accurately
date Folsom occupations. In evaluating the quality of
radiocarbon dates, we are most concerned with issues
82
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of pretreatment/contamination and context, by which
we mean the relationship between the age of the
sample and the age of the phenomenon it is intended
to date.
If pretreatment could always successfully remove all
contamination from a sample, bone should be a preferred material to date over charcoal. Dates on wood
charcoal can suffer from the old wood problem,
which adds unsystematic and potentially large errors
to the measured age of samples (Schiffer 1986).
Although an analogous “old bone” problem is theoretically possible, animal bone often retains cut
marks, impact fractures, and/or other contextual
clues that leave little doubt that its presence is due to
human action and that the death of an animal was
contemporaneous with the occupation of a site.
Rarely can the same thing be said about charcoal,
except for charcoal recovered from features like
hearths, but even then, old wood should be a
concern, except perhaps in the case of dating annual
macrobotanical remains like seeds. Isolated flecks of
charcoal from sedimentary contexts have the
additional complication of having potentially been
redeposited. For these reasons, when dating a bison
kill, for example, if given the option to directly date
bone or a fleck of charcoal recovered from the
matrix within the bonebed, dating the bone should
be an obvious choice. That choice, however, has not
always been obvious because pretreatment cannot
always remove contamination.
Comparing bone and charcoal with respect to pretreatment and contamination, charcoal has traditionally been a much more reliable material. Removing
exogenous carbon from charcoal samples is usually
fairly straightforward because common contaminants
of charcoal (i.e., humic and fulvic acids and secondary
carbonates) have chemical properties that differ sufficiently from the carbon native to the sample that
they are easily separated. Separating contaminant
from endogenous carbon from bone samples, by comparison, is considerably more complicated, whether
dealing with its organic or inorganic components
(Taylor 1994), and reliable dating of bone was not
really possible until relatively recently. The development of XAD resin chromatographic (Stafford et al.
1988, 1991) and ultrafiltration (Brown et al. 1988)
methods for removing contamination from bone collagen appears to have dramatically improved the accuracy of bone dates when collagen is well preserved.
More recently, several studies have shown that
although macroscopically friable, highly crystalline
calcined bone can also produce reliable dates (Hüls
et al. 2010; Lanting et al. 2001; Snoeck et al. 2014;
Zazzo and Saliège 2011). When bone is calcined,
atmospheric and/or combustion gas CO2 is incorporated into the apatite matrix, which becomes
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Surovell et al.
impervious to the problems of ionic exchange that
have plagued attempts to date bone apatite carbonate
for decades. These improvements in pretreatment in
combination with the development of AMS dating,
in our opinion, have transformed bone from being
one of the least reliable materials for dating, to one
of the preferred materials. That said, in evaluating
the quality of bone dates, pretreatment methods
must be taken into account. We suggest that only
bone collagen samples pretreated using the XAD
and ultrafiltration methods should be considered
reliable, although some samples still produce anomalously young results (e.g., Byers 2002). We also consider dates on apatite carbonate from calcined bone
to be reliable, although more work testing the accuracy
of this method is needed.
Given these considerations, to isolate the highest
quality dates available from Folsom contexts, we
limit our sample to bone collagen dates wherein the
sample was pretreated using the XAD resin chromatographic and ultrafiltration techniques, bone apatite
dates from calcined bone, and charcoal samples recovered from hearth features. By limiting our sample this
way, we isolate those samples that are most likely to
have directly resulted from human occupation of a
site and minimize the effects of contamination. If
there are systematic errors in these dates, we expect
the bone collagen dates to be too young due to the
presence of small amounts of young carbon contamination, and we expect hearth charcoal dates to be
too old due to the possibility of old wood. It is
unclear if systematically directional errors are expected
for calcined bone dates, but experimental work has
shown that a partial old wood effect might be expected
if old wood was used and combustion gases contributed significant amounts of CO2 to apatite carbonate
(Hüls et al. 2010; Snoeck et al. 2014). We exclude
from our analysis all charcoal dates unassociated
with hearths, including samples with strong stratigraphic association. We also omit all dates on soil
organic matter because they do not directly date
archaeological occupations.
2.2
Sample
The total sample of Folsom radiocarbon dates meeting
our selection criteria includes 37 dates from 12 components and 10 sites (Table 1). Of these, 29 dates are
on bone collagen, three are on calcined bone, and
five are on charcoal from hearth features. Sites with
reliable dates are Agate Basin, Carter/Kerr-McGee,
Hell Gap, and Hanson in Wyoming; Waugh, Badger
Hole and all three components of Cooper in
Oklahoma; Barger Gulch Locality B and
Mountaineer in Colorado; and Folsom in New
Mexico. Our process for date selection notably eliminates a number of sites from which additional dates are
The Dating of the Folsom Complex
available including Black Mountain, Blackwater
Draw, MacHaffie, the Lake Ilo sites, and
Lindenmeier. At present, none of these sites has
high-quality bone or hearth charcoal dates.
2.3
Calibration and averaging methods
We calibrated all dates using OxCal version 4.2 (Bronk
Ramsey 2009) and the IntCal13 calibration curve
(Reimer et al. 2013). We report calibrated dates as 1σ
ages with means and standard deviations as shown
in Table 1. We averaged all calibrated dates from
each site or component using the Long and
Rippeteau (1974) method. Site-averaged dates are presented in Table 2.
3. Results
3.1 New dates from the Hanson site
As part of a project to analyze previously unexamined
materials recovered during water screening in the
1970s excavations, we identified several lots of calcined bone of sufficient quantity for radiocarbon
dating. It should be noted that we do not know with
certainty if these samples are associated with hearth
features, but we assume that they were burned during
the Folsom occupation. We feel confident in that
assumption since the probability of bone becoming
calcined is much higher in a hearth than in a natural
fire (Buenger 2003). In all, we submitted three
samples to the University of Arizona AMS
Laboratory. We submitted two samples from the
central excavation block in Area 2; those samples produced dates of 10,626 ± 77 (AA-106384) and 10,600 ±
77 (AA-106385) 14C yr BP. A third sample taken from
two adjacent one-foot squares from the northwestern
excavation block of Area 2 dated to 10,688 ± 77 14C
yr BP (AA-106386). All three dates are statistically
indistinguishable and after calibration and averaging,
suggest an age for the Folsom occupation at Hanson
of 12,605 ± 45 cal yr BP. This is approximately 600
years older than the prior age estimate for the site,
and as we argue below, it makes Hanson one of
oldest, if not the oldest, known Folsom site. The variation seen in the entire set of dates from the Hanson
site serves nicely as a microcosm of the problems
inherent to dating the Folsom complex as a whole.
3.2
New date from Hell Gap
We submitted a bone sample from the Folsom component at Locality I of Hell Gap to the University of
Arizona AMS Laboratory where the collagen fraction
was isolated using the ultrafiltration method. This
sample, collected by Vance Haynes in June of 1964,
produced an age of 10,490 ± 62 14C yr BP (AA77592UF) or 12,412 ± 127 cal yr BP, which would
place the Folsom component at Locality I of Hell
Gap roughly in the middle of the Folsom age range,
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Table 1
High-quality radiocarbon dates from Folsom contexts
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Site
Sample number
C age
14
Cσ
Cal age
Cal σ
Agate Basin
Agate Basin
Agate Basin
Badger Hole
Badger Hole
Badger Hole
Barger Gulch, Loc. B
UCIAMS-122570
UCIAMS-122571
SI-3733
UCIAMS-98369
PSU-5144\UCIAMS-111184
PSU-5457/UCIAMS-122579
Beta-173385
Collagen
Collagen
Charcoal
Collagen
Collagen
Collagen
Charcoal
10,430
10,135
10,780
10,300
10,395
10,370
10,770
25
25
120
25
35
25
70
12,309
11,809
12,699
12,078
12,262
12,241
12,688
102
91
116
72
94
92
47
Barger Gulch, Loc. B
Beta-173381
Charcoal
10,470
40
12,406
110
Carter/Kerr-McGee
Carter/Kerr-McGee
Cooper Lower
UCIAMS-122572
UCIAMS-122573
CAMS-94850
Collagen
Collagen
Collagen
10,600
10,520
10,600
25
25
40
12,598
12,487
12,590
38
46
55
Cooper Lower
Cooper Lower
Cooper Lower
Cooper Middle
PSU-6077/UCIAMS-140849
PSU-6078/UCIAMS-140520
PSU-6079/UCIAMS-140581
CAMS-82407
Collagen
Collagen
Collagen
Collagen
10,560
10,570
10,630
10,530
30
30
30
45
12,534
12,552
12,619
12,494
59
59
36
73
Cooper Middle
Cooper Middle
Cooper Upper
PSU-6075/UCIAMS-140847
PSU-6076/UCIAMS-140848
CAMS-94849
Collagen
Collagen
Collagen
10,565
10,575
10,505
30
30
45
12,543
12,561
12,462
59
57
87
Cooper Upper
Cooper Upper
Folsom
Folsom
Folsom
Folsom
Folsom
Folsom
Hanson
Hanson
Hanson
Hell Gap
Mountaineer
Mountaineer
Mountaineer
Mountaineer
Mountaineer
Waugh
Waugh
PSU-6073/UCIAMS-140845
PSU-6074/UCIAMS-140846
CAMS-74656
CAMS-74658
CAMS-96034
CAMS-74657
CAMS-74659
CAMS-74655
AA-106384
AA-106385
AA-106386
AA-77592UF
CAMS-105764
CAMS-105765
UCIAMS-11240
UCIAMS-11241
AA-98753
NZA-3602
NZA-3603
Collagen
Collagen
Collagen
Collagen
Collagen
Collagen
Collagen
Collagen
Calcined bone
Calcined bone
Calcined bone
Collagen
Collagen
Collagen
Collagen
Collagen
Collagen
Charcoal
Charcoal
10,565
10,575
10,450
10,450
10,475
10,500
10,520
10,520
10,626
10,600
10,688
10,490
10,440
10,295
10,380
10,445
10,328
10,379
10,404
30
30
50
50
30
40
50
50
77
77
77
62
50
50
30
25
100
85
87
12,543
12,561
12,348
12,348
12,439
12,462
12,478
12,478
12,584
12,558
12,631
12,412
12,329
12,100
12,250
12,356
12,157
12,243
12,275
59
57
124
124
86
79
88
88
85
98
63
127
123
131
91
111
196
155
154
though it is important to note that this is a single date
and has a fairly large standard deviation. Based on this
date it would be difficult to argue that Hell Gap is
positioned spatio-temporally near to the origin of the
Table 2
Site-averaged and calibrated radiocarbon dates from Folsom
contexts
Site
Agate Basin
Badger Hole
Barger Gulch
Carter/Kerr-McGee
Cooper Lower
Cooper Middle
Cooper Upper
Folsom
Hanson
Hell Gap
Mountaineer
Waugh
84
14
Material
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n dates
Cal age ± σ
3
3
2
2
4
3
3
6
3
1
5
2
12,187 ± 59
12,169 ± 49
12,644 ± 43
12,552 ± 29
12,588 ± 24
12,538 ± 36
12,536 ± 37
12,442 ± 38
12,605 ± 45
12,412 ± 127
12,259 ± 53
12,259 ± 109
NO.
2
Reference
Carlson (2015)
Carlson (2015)
Frison (1982)
Bement et al. (2012)
Carlson (2015)
Carlson (2015)
Surovell and
Waguespack (2007)
Surovell and
Waguespack (2007)
Carlson (2015)
Carlson (2015)
Johnson and Bement
(2009)
Carlson (2015)
Carlson (2015)
Carlson (2015)
Johnson and Bement
(2009)
Carlson (2015)
Carlson (2015)
Johnson and Bement
(2009)
Carlson (2015)
Carlson (2015)
Meltzer (2006)
Meltzer (2006)
Meltzer (2006)
Meltzer (2006)
Meltzer (2006)
Meltzer (2006)
This paper
This paper
This paper
This paper
Stiger (2006)
Stiger (2006)
Stiger (2006)
Stiger (2006)
Morgan (2015)
Hofman (1995)
Hofman (1995)
Folsom complex, although one might be able to
make that argument for Hanson.
3.3
Folsom in time
For the entirety of our sample, Folsom dates range in
age from 10,135 ± 45 to 10,780 ± 120 14C yr BP, or
11,809 ± 91 to 12,699 ± 116 cal yr BP after calibration
(Table 1 and Figure 1). That range, however, is
expanded greatly by the two oldest dates and the
youngest date in the sample. If those ages are excluded,
the great majority of Folsom dates (91.9 per cent of
our sample) falls within a much narrower range of
10,295 ± 50–10,688 ± 77 14C yr BP, or 12,078 ±
72–12,631 ± 63 cal yr BP. Notably, the two oldest
dates in the sample are charcoal dates from hearth features at Barger Gulch (10,770 ± 70 14C yr BP, Beta173385) and Agate Basin (10,780 ± 120 14C yr BP,
SI-3733) and may be affected by the old wood
problem. In other words, Folsom peoples were likely
burning Clovis-aged wood. This is almost certainly
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The Dating of the Folsom Complex
Figure 1 All high-quality calibrated radiocarbon dates from Folsom contexts plotted in rank order. Boxes indicate one sigma
age ranges, and whiskers show two sigma age ranges. Gray boxes are bone dates and black boxes are charcoal dates.
the case for the Barger Gulch date because another
charcoal sample from the same feature yielded a date
almost 300 calendar years younger (10,470 ± 40 14C
yr BP, Beta-173381). On the opposite end of the
spectrum, a recent bone date from Agate Basin
(10,135 ± 25 14C yr BP, UCIAMS-122571) reported
by Carlson (2015) stands as a clear outlier in the
sample (Figure 1). This date might be affected by contamination or could be intrusive from the overlying
Agate Basin component at the site.
By averaging multiple dates from sites or components, measurement error in mean age estimates
and standard deviations are reduced. The averages
we report include all of the dates, even those that
appear to be outliers. After averaging, the age range
represented by Folsom is shortened even more
(Table 2 and Figure 2). The youngest Folsom component in the sample is from the Badger Hole site in
Oklahoma at 12,169 ± 49 cal yr BP, and the oldest is
Barger Gulch Locality B in Colorado at 12,644 ± 43
cal yr BP. If the older date from Barger Gulch is
omitted, Hanson is the oldest site in the sample,
dating to 12,605 ± 45 cal yr BP. Using the dates
from Badger Hole and Hanson, therefore, the
Folsom complex was at least ∼440 years in length
and spanned the time period from approximately
12,610 to 12,170 cal yr BP. This is considerably
shorter than the estimates provided by Haynes et al.
(1992) and Holliday (2000a). Haynes et al. (1992),
for example, estimated the Folsom period to have
lasted ∼780 years from 12,780 to 12,000 cal yr BP.
Of course, a sample of dates from only 12 sites is unlikely to represent the entirety of the age range encompassed by the Folsom complex (Prasciunas and
Surovell 2015). To refine the 436-year time span represented by the mean age difference between Hanson
and Badger Hole, we performed a simple Monte
Carlo experiment to allow an error estimate to be
placed on our estimate of the Folsom time span. We
drew 12 random ages from uniform distributions of
hypothetical age ranges spanning 440–1000 years in
Figure 2 Site-averaged calibrated radiocarbon dates from
Folsom contexts. Boxes indicate the one sigma calibrated
age ranges, and whiskers show the two sigma calibrated age
ranges.
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10-year increments and examined the dated ranges of
dates that resulted. Each experiment was repeated
10,000 times. We calculated probability as the percentage of randomized date ranges for which the difference
between the oldest and youngest randomized dates was
less than or equal to 436 years. In other words, we are
examining the likelihood of observing an age range of
436 years or less in a sample of 12 sites from a phenomenon that actually lasted anywhere between 440 and
1000 years. We found that the Folsom complex might
have lasted as long as 660 years (Supplementary
Figure 1), but longer time spans are unlikely (P <
0.05). Furthermore, an observed age range of 436
years for this sample size is typical of a phenomenon
that persisted for approximately 510 years
(Supplementary Figure 2). In other words, with larger
samples the time span represented by Folsom will
undoubtedly increase but not significantly. At most, it
will be expanded by around 200 years.
3.4 Correlation with the Younger Dryas, the
end of Clovis, and megafaunal extinction
It is well known that the Folsom complex correlates in
time with the Younger Dryas climatic event. That said,
based on high resolution analysis of the Greenland
NGRIP ice core, Younger Dryas cooling in the
North Atlantic lasted approximately 1200 years from
12,850 to 11,650 cal yr BP (Steffensen et al. 2008),
so it would be difficult to argue at this point in time
that changes in material culture seen in Folsom compared to Clovis (e.g., changes in projectile point manufacture) are related to Younger Dryas climate change,
as the oldest Folsom sites in our sample date to
roughly 240 years after the onset of the Younger
Dryas. Additionally, the Folsom period appears to
have ended some 500 years before climatic warming
at the end of the Younger Dryas. In other words,
while Folsom hunter–gatherers had to cope with the
climates of the Younger Dryas, there is no clear correlation between climate change and changes in material
culture as reflected by the start or end of the Folsom
complex (see Eren 2012; Meltzer and Holliday 2010).
Haynes has also noted that black mats and other contemporaneous sediments and soils with which Folsom
components are often associated correlate in time with
the Younger Dryas (Haynes 2008; c.f. Holliday et al.
2011; Taylor et al. 1996). If these deposits, as
Haynes (2008) has argued, began accumulating at
ca. 10,800 14C yr BP, this is equivalent to a calendar
age of approximately 12,700 cal yr BP (Figure 3). In
other words, black mats may have begun accumulating
roughly 150 years after the onset of the Younger
Dryas. In fairness, much of this difference in interpretation results from improvements in the radiocarbon
calibration curve for the terminal Pleistocene. Over
the last 17 years, from the IntCal98 to the IntCal13
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calibration curves, a radiocarbon age of 10,800 14C
yr BP has decreased in calendar age from ca. 12,850
cal yr BP, at the start of the Younger Dryas, to
12,710 cal yr BP, almost 140 years after it.
Of similar age to the onset of black mat deposition
are the youngest Clovis sites (Haynes 2008; Waters and
Stafford 2007). The youngest well-dated Clovis site is
Jake Bluff, from which five high-quality bone collagen
dates are available (Bement and Carter 2010). Using
our calibration and averaging methods, the age of
Jake Bluff is 12,714 ± 11 cal yr BP, or approximately
100 years older than the Hanson site. Based on our
reanalysis of Folsom radiocarbon dates, there is an
apparent 100-year gap between Clovis and Folsom.
Given our error analysis above, the simplest explanation for this gap is sample size in the statistical
sense (Prasciunas and Surovell 2015). With increased
numbers of dated sites, this gap will shrink and theoretically disappear entirely. For example, eliminating
this gap could be accomplished by adding only 50
years to each of the Clovis and Folsom time ranges,
and it is likely that this will happen as more Clovis
and Folsom components are dated, possibly even
with the sample of sites that have already been excavated. Nonetheless, from a statistical point of view,
the apparent lack of chronological overlap between
these two cultural complexes at current sample sizes
would suggest that the transition between the two
was likely rapid and abrupt (Taylor et al. 1996). It is
also interesting to note the youngest dates on extinct
Pleistocene megafauna correlate well in time with the
youngest Clovis sites (Waters et al. 2015). In
Figure 3, we plot our revised age range for Folsom
relative to Clovis, the Younger Dryas, and the youngest dates on Pleistocene megafauna. It is now apparent
that the Clovis-Folsom transition occurred at least a
century after the onset of the Younger Dryas, as did
Pleistocene extinction. In other words, strong climatic
forcing of either of the Clovis-Folsom transition or
megafaunal extinction seems unlikely, unless a lag
effect was at play. The observed lag between the start
of the Younger Dryas as recorded in Greenland ice
cores, and the accumulation of black mats (Haynes
2008) might suggest that such a lag was in effect,
also supported by the idea that the cooling at the
onset of the YD was gradual, lasting some 200 years
(Steffensen et al. 2008).
4.
Discussion and conclusions
Several years ago, Waters and Stafford (2007) published a revised chronology for the Clovis complex
based on a series of high-quality and site-averaged
radiocarbon dates. Their primary conclusion was
that dates on Clovis appeared to be highly clustered
in time, and that the duration of the Clovis complex
was considerably shorter than what was previously
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Surovell et al.
The Dating of the Folsom Complex
Figure 3 Our revised age range for Folsom and the end of Clovis (hatched polygons) plotted on the IntCal13 calibration curve
(Reimer et al. 2013) relative to the Younger Dryas stadial (gray polygon) and youngest dates on Pleistocene megafauna (thick
black line).
believed. In this paper, we have undertaken a similar
exercise and come to similar conclusions. Our
methods for culling high from low quality radiocarbon
dates are different from those of Waters and Stafford
(2007), but our results are similar. In particular, we
have excluded all radiocarbon dates on charcoal,
except for those associated with hearth features.
Radiocarbon dates on charcoal have been the bread
and butter of Paleoindian geochronology for more
than 60 years, but there is good reason to believe
that many charcoal dates in stratigraphic association
with archaeological occupations are in error. Instead
of directly dating Folsom occupations, many charcoal
dates are likely dating the litho—and pedostratigraphic units associated with those occupations.
With improvements in pretreatment methods coupled
with isotopic counting by accelerator mass spectrometry, bone dating is becoming the gold standard
for the field, whether in dating collagen or calcined
bone apatite. By limiting our sample to high-quality
bone dates and only charcoal samples associated
with hearth features, we suggest a limited age range
for Folsom of at least 440 years from 12,610 to
12,170 cal yr BP, but we expect that age range to
expand somewhat, likely on both margins.
There are a number of reasons why this new chronology is significant. It seems that the transition from
Clovis to Folsom in western North America post-
dated the onset of the Younger Dryas stadial significantly. The Younger Dryas also persisted well after
the last Folsom point was manufactured, perhaps for
as much as another 500 years. With our revised chronology, there is a gap between Clovis and Folsom of
approximately 100 years, although we are confident
that it will be eliminated as larger samples of both
kinds of sites are dated. Finally, the Clovis-Folsom
transition appears to correlate in time with the last
of the Pleistocene megafauna.
Given that this paper was inspired by several dozen
fragments of calcined bone found in vials containing
materials pulled from 1/16-in. screens at the Hanson
site in the 1970s and a bone sample collected at Hell
Gap in 1964, it would be prudent to emphasize that
there is considerable opportunity for additional
dating of Folsom and other collections already on
hand. Thousands of bone samples that could be
dated are sitting in laboratories and curation facilities
across the country. Thirty years ago, we could not regularly produce accurate radiocarbon dates from those
samples, but now we can. Carlson’s (2015) recent
efforts to date bone collagen from Folsom sites in combination with our new dates from Hanson and Hell
Gap in large part made this study possible, and we
hope to see similar efforts in the near future, which
will undoubtedly improve upon our contribution to
Folsom geochronology.
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Surovell et al.
The Dating of the Folsom Complex
Acknowledgements
The new radiocarbon dates from Hanson reported in
this paper were obtained thanks to the generous
support of the Cody Field Office of the Bureau of
Land Management, Wyoming. Kierson Crume in particular has been incredibly helpful in supporting our
work with the Hanson collection. We thank Brooke
Morgan and Brian Andrews for inviting us to participate in the Folsom SAA session in San Francisco from
which this volume evolved. We are also grateful to
three anonymous reviewers who provided valuable
feedback that improved this paper.
ORCID
Todd A. Surovell
8621
http://orcid.org/0000-0001-6587-
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Author Biographies
Todd A. Surovell is professor of anthropology at the University of Wyoming in Laramie. His research has focused
primarily on Paleoindian archaeology in the Great Plains of North America, and he has published extensively on
lithic technology, settlement organization, and Pleistocene extinctions, and currently he is conducting ethnoarchaeological research in Mongolia.
Joshua R. Boyd is an MA student in the Department of Anthropology at the University of Wyoming, Laramie.
His research interests include Paleoindian high-altitude adaptations, lithic technology, and communal hunting
strategies.
C. Vance Haynes Jr is emeritus professor of anthropology at the University of Arizona in Tucson. His primary
research interests relate to the archaeology and geoarchaeology of the American Southwest, as well as the peopling
of the Americas. In 1990 he was elected into the US National Academy of Sciences.
Gregory W. L. Hodgins is assistant professor of anthropology and assistant research scientist, Laboratory of
Tree Ring Research, at the University of Arizona in Tucson. His research interests include bone-dating in archaeology, compound-specific isotope analysis, and environmental-isotope analysis.
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