15 k.y. paleoclimatic and glacial record from northern
New Mexico
Jake Armour

Peter J. Fawcett

John W. Geissman 
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico
87131, USA
ABSTRACT
The southern Sangre de Cristo Mountains, New Mexico, contain evidence of glacial
activity from the late Pleistocene to late Holocene. Sediment cores recovered from an
alpine bog (3100 m) trapped behind a Pinedale age moraine, ;2 km downvalley from a
high-elevation cirque, reached glacial-age debris and recovered ;6 m of lake clays overlain by gyttja. Accelerator mass spectrometry dating, sedimentology, variations in magnetic properties, and organic carbon data reveal six distinct periods of glacial and/or
periglacial activity. These include a late Pleistocene Pinedale glacial termination just before 12 120 14C yr B.P., a Younger Dryas chron cirque glaciation, an early Neoglacial
periglacial event (ca. 4900 14C yr B.P.), a late Holocene cirque glaciation (3700 14C yr
B.P.), as well as late Holocene periglacial events at 2800 14C yr B.P. and the Little Ice
Age (ca. 120 14C yr B.P.). Cold events in the middle to late Holocene correlate with subtle
ice-rafting events in the North Atlantic and records of cold events in North America and
Europe and were probably hemispheric in extent.
Keywords: climate change, glacial geology, Holocene, New Mexico, Younger Dryas.
INTRODUCTION
The southern Sangre de Cristo Mountains,
New Mexico, are one of the southernmost
high ranges along the Rocky Mountain chain.
This range preserves many glacial features;
however, the Quaternary geomorphic history
is not as well known as in the central Rockies.
Wesling (1988) established a glacial chronology for the Winsor Creek drainage based on
relative-age data of glacial deposits, and recognized six separate glacial advances. These
include two Bull Lake advances (not shown
in Fig.1), two Pinedale advances, a late Pleistocene to early Holocene advance, and a late
Holocene advance (Fig. 1). Wesling also identified two separate talus-flow events that postdated the Neoglacial advance and represent
late Holocene periglacial episodes.
To better understand the timing of late Quaternary changes in this region, we recovered
six sediment cores from an alpine bog downbasin from a principal cirque in the Winsor
Creek basin, which preserves sedimentary records of upbasin changes in hydrology (cf.
Anderson and Smith, 1994; Leonard, 1986;
Leonard and Reasoner, 1999). Paleoenvironmental reconstructions for this site are based
on sediment grain size, magnetic properties,
total organic carbon, and carbon isotopic data.
We compare a well-dated paleoenvironmental
record from the bog core with an established
relative glacial chronology and demonstrate
that limited alpine glacial advances occurred
during the Younger Dryas interval and the late
Holocene. We also show that middle to late
Holocene periglacial events in the region are
temporally equivalent to North Atlantic seaice drift events (cf. Bond et al., 1997, 1999)
and other cold events in the Northern Hemisphere (Denton and Karlén, 1973; Meyer et
al., 1995).
Winsor Creek Drainage Basin
The Winsor Creek drainage basin is located
;60 km northeast of Santa Fe, New Mexico,
on the eastern flank of the Santa Fe Range
(Fig. 1). The bedrock in the upper part of the
basin is Precambrian granite (Miller et al.,
1963). The uppermost part of the basin contains four cirques, the principal one containing
Lake Katherine. These cirques are oriented
east to northeast with steep slopes on their
southern and southwestern sides. Downvalley,
a secondary bench marks the farthest extent
of Quaternary glaciation and contains small
lakes and bogs, including Stewart Lake and
bog B1 (;3100 m elevation), all formed in
depressions behind Pinedale moraines (Fig.
1).
Wesling (1988) established the glacial chronology for this basin using moraine relativeage data, including soil-profile development
and degree of clast weathering and landform
preservation. He assigned a Pinedale age to a
moraine suite at 3100 m in the middle drainage (P1 in Fig. 1) and a late Pinedale age (P2)
to moraines farther upvalley (Fig. 1). A moraine currently damming Lake Katherine at
3580 m was assigned a late Pleistocene to early Holocene age (Y) based on a more juvenile
soil profile and steeper slopes than the classic
Figure 1. Map of Winsor
Creek drainage basin,
Sangre de Cristo Mountains, New Mexico. Positions of late Pleistocene and Holocene
moraines and principal
cirques, lakes, and
bogs in region are
shown (adapted from
Wesling, 1988). Insets
show study area location and bog B1 detail
with core locations.
q 2002 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected].
Geology; August 2002; v. 30; no. 8; p. 723–726; 3 figures; 1 table.
723
Pinedale deposits. An inset lateral moraine
within the Lake Katherine cirque with little
soil development and a very sharp surface
profile was assigned a late Holocene age (N).
A radiocarbon date of 3570 6 145 14C yr B.P.
from charcoal underlying till at the base of
this moraine shows a late Holocene glacial advance. Equivalents for both the Y and N moraines are found in all cirques in the area (Fig.
1).
METHODS
Six sediment cores were obtained from bog
B1 using a Livingston square-rod piston corer.
Minor compaction of 5%–10% was noted for
each core segment. The entire sequence of late
Pleistocene and Holocene sediment was recovered in three (B1-4, B1-5, and B1-6) of the
six cores, and sedimentologic and stratigraphic features were observed and noted for each.
The cores were sampled for radiocarbon dating (University of Arizona Accelerator Mass
Spectrometer [AMS] and Beta-Analytic laboratory) using standard AMS techniques. Dates
were obtained on isolated wood fragments,
charcoal, and organic sediments, all from the
center of the core drives to minimize contamination. For organic sediments, the entire sample was pretreated to remove rootlets and
grass, and treated with acid and combusted.
The cores were continuously sampled for
magnetic susceptibility (MS), anhysteretic
remanent magnetization (ARM), and acquisition of isothermal remanent magnetization
(IRM) data. Oriented samples were precut
with Cu-Be (nonmagnetic) tools and then
placed in plastic cubes.
Total organic carbon (TOC) analysis was
completed using a standard continuous flow
elemental analyzer. The mass spectrometer
method uses small samples and provides isotopic carbon ratios and organic carbon concentrations. There is no contamination by inorganic carbon sources in the sediment cores
because the source bedrock is uniformly
granitic.
RESULTS
Three sediment cores reached coarse rubble,
supported by ground-penetrating radar data
(G. Gettemy, 1999, personal commun.). Consistent stratigraphy and MS profiles allow us
to directly correlate cores B1-4, B1-5, and B16. The 14 AMS radiocarbon dates from the 2
cores dated increase with depth (Table 1; Figs.
2 and 3) and support these correlations. The
stratigraphy and radiocarbon date control were
best displayed in core B1-6 (Fig. 2), and so
we describe this sequence in detail. The basal
debris in B1-6 is directly overlain by 7 cm of
light colored clay, which represents the initial
infilling of depressions behind Pinedale moraines. This unit is overlain by 60 cm of finely
laminated lake clay (basal date of 12 120 6
724
TABLE 1. RADIOCARBON DATES FROM BOG CORES B1-5 AND B1-6
Lab number
Core
Depth
(cm)
Beta-153457
Beta-153454
Beta-153456
Beta-153455
AA-35802
AA-35801
AA-35800
AA-35799
AA-35795
AA-35794
AA-35798
AA-35797
AA-35793
AA-35796
B1-5
B1-5
B1-5
B1-5
B1-6
B1-6
B1-6
B1-6
B1-6
B1-6
B1-6
B1-6
B1-6
B1-6
325
347
347
362
21
63
95
153
171
206
245
310
381
444
95 14C yr B.P.). A second light colored clay
at 400 cm depth is overlain by 30 cm of
coarsely laminated, gray clay. A 4-mm-thick
layer of fine-grained, subangular quartz sand
caps this unit. Several dates from within and
just above this unit are shown in Figure 3. A
bulk sediment date (10 190 6 60 14C yr B.P.)
and a charred wood date (10 070 6 60 14C yr
B.P.) were taken at the same depth (348 cm)
in core B1-5 and showed an offset of ;120
14C yr between the different materials. Above
the quartz sand layer, a 60 cm interval of
coarsely laminated clays is abruptly overlain
by 70 cm of bioturbated clays.
At 180 cm depth in B1-6, a 20-cm-thick
coarse-grained sand (3495 6 50 14C yr B.P.)
marks the transition from clays to dark brown
gyttja. The upper ;2 m of core is punctuated
by two additional clastic horizons, a sand layer at 100 cm depth (2770 6 45 14C yr B.P.),
and a dark clay layer at 18 cm depth (120 6
40 14C yr B.P.).
Sedimentologic changes correlate with rock
magnetic, TOC, and carbon isotopic data (Fig.
2). High MS intervals in the lower lake clays
correlate with the basal light clay (460 cm)
and with clays at the quartz sand layer (365
cm). In the upper half of B1-6, peaks in MS
(180 cm, 110 cm, and 18 cm) correlate with
periods of enhanced clastic deposition in the
lake or bog, while a fourth (230 cm) shows
no discernible change in sediment character.
This feature correlates across all deep cores
(Fig. 3) and represents a period of enhanced
delivery of high-susceptibility phases. The
ARM data (Fig. 2) correlate with MS data,
indicating that these trends are driven by
changes in concentration of ferrimagnetic
phases, principally magnetite, as demonstrated
by isothermal remanent magnetization (IRM)
and backfield demagnetization data (Fig. 2).
TOC data (Fig. 2) vary from the lower lake
environment (5%–20% organic C) to the upper bog environment (10%–50% organic C).
The d13C data also show a trend with depth,
becoming lighter in value higher in the core.
There is considerable variability in TOC between 460 cm and 330 cm depth; the lowest
Radiocarbon date
(14C yr B.P. 6 1s)
9 890
10 070
10 190
10 180
120
990
2 770
2 950
3 495
4 550
5 010
8 100
9 765
12 120
6
6
6
6
6
6
6
6
6
6
6
6
6
6
60
60
60
50
40
35
45
45
50
50
50
75
55
95
Material dated
Bulk sediment
Charred wood
Bulk sediment
Charred wood
Bulk peat
Bulk peat
Charcoal
Bulk peat
Wood
Charcoal
Grassy sediment
Bulk sediment
Wood
Bulk sediment
values are in the bioturbated clay. A sharp
d13C excursion of 23‰ occurs at 400 cm
(Fig. 2). In the upper gyttja units, TOC is
high, except within sand layers where it drops
to near 0%.
DISCUSSION
Sediment cores from the Lake Stewart area
bogs record a typical life cycle of a small alpine with a lake to bog transition punctuated
by discrete sedimentary events marking episodes of climate change. These deposits record events in the upper basin, and can be tied
to the post-Pinedale glacial chronology of the
basin. Sedimentologic, MS, and ARM variations distinguish episodes of glacial activity,
as well as periglacial activity (Benson et al.,
1996; Bischoff et al., 1997). Rosenbaum et al.
(1996) showed that in a granitic basin, fresh
detritus contains a higher concentration of
coarser magnetite than more heavily weathered detritus, and we assert that a similar phenomenon is recorded in glacial activity in the
cirque above the Lake Stewart area. The
agreement of rock magnetic data among all
cores (Fig. 3) is strong evidence for a consistent response to changes in precipitation, driven by changes in climate. Other intervals of
coarse sand were deposited rapidly in pulsed
events and probably originated from freshly
exposed cirque slopes and from older Pinedale
moraines upvalley from the bog (Fig. 1), because the streams have bedrock channels.
The date of 12 120 6 60 14C yr B.P. from
above the basal light colored clay provides a
minimum age for Pinedale termination. This
date is consistent with other limiting estimates
for Pinedale deglaciation in the central Rockies (e.g., Elias et al., 1991; Madole, 1980;
Menounos and Reasoner, 1997), as well as
with hydrologic changes in the Rio Grande
basin to the west (Dethier and Reneau, 1996).
The large MS spike in the basal clay is consistent with a glacial origin, either rock flour
or rill washing of unweathered glacial debris.
Organic sedimentation quickly increased following deglaciation, presumably in response
to warmer climates.
GEOLOGY, August 2002
Figure 2. Stratigraphic profile of
sediment core B1-6 showing lithostratigraphic units, 14C dates, magnetic susceptibility profile (SI v),
anhysteretic remanent magnetization (ARM) intensity (mA/m), total
organic carbon (TOC, weight percent) and d13C of organic matter.
Four insets in ARM intensity column show curves of acquisition of
isothermal remanent magnetization (IRM) and backfield demagnetization of saturation IRM for selected samples. Values above each
curve are specific depths for each
sample selected. Values of coercivity of remanence, as defined by xintercept on backfield demagnetization curve: 110 cm 0.0070 T; 162
cm 0.0075 T; 373 cm 0.095 T; 421
cm 0.060 T.
Glacial advance in the upbasin cirques
probably caused dramatic changes in sediment
properties at 400 cm in core B1-6, including
a second light colored clay, an abrupt increase
in MS, a sharp decrease in TOC, and a large
negative d13C shift (Fig. 2). Changes in sediment texture and MS are consistent with
cirque glacial activity and enhanced runoff delivering more clastic sediment with a higher
concentration of magnetite downbasin. These
changes are subtle because the cirque glacier
would have been ;2 km upvalley. The decrease in TOC is attributable to a colder cli-
mate with less vegetation in the basin and less
organic material in the catchment. The 23‰
carbon isotopic shift (synchronous with the
TOC decrease) is also consistent with a dramatic decrease in vegetation around and upbasin from the lake. The dominant arboreal
species at this elevation is Engelman spruce,
which has an isotopic composition of
;225‰. Lake algae, however, has an isotopic composition ranging from 228‰ to
231‰ (Meyers and Lallier-Vergies, 1999).
The isotopic shift can be explained by a relative decrease in terrestrial organic matter in-
Figure 3. Correlation of magnetic susceptibility (MS) profiles of deep sediment cores B1-4, B1-5, and B1-6, including radiocarbon dates for B1-5 and
B1-6. Key climatic episodes are noted; see text for details. LIA is Little Ice
Age.
GEOLOGY, August 2002
put into the lake and a concomitant relative
increase in algal contribution.
We correlate this interval of sedimentary
change with an event that produced a large
terminal moraine in the Lake Katherine
cirque, assigned a late Pleistocene to early Holocene age by Wesling (1988). Radiocarbon
dates from this interval (10 190 6 60, 10 180
6 50, 10 070 6 60, and 9765 6 55 14C yr
B.P.; Fig. 3) show that it is clearly within the
Younger Dryas chron. The quartz sand layer
and the large MS spike in clays that cap this
unit represent the end of glacial advance and
possibly reflect a breach in the Lake Katherine
moraine that produced a large flood that
washed glacial debris downbasin and into the
lake. Such events are common for small
cirque moraines (Costa and Schuster, 1988).
The date from just above the MS spike and
sand layer (9890 6 60 14C yr B.P., Fig. 3) is
also consistent with this unit being a Younger
Dryas termination. Several examples of Younger Dryas glacial advances have been recognized in the central Rocky Mountains (e.g.,
Gosse et al., 1995; Menounos and Reasoner,
1997; Reasoner et al., 1994), and a cooling
event in the San Juan Mountains of Colorado
occurred during the Younger Dryas (Reasoner
and Jodry, 2000).
Early to middle Holocene sections of the
cores are characterized by low TOC (probably
due to extensive bioturbation), low sedimentation rates, and negative MS values that show
little immature detritus (e.g., Fe-Ti oxides, ferromagnetic silicates) in the sediment. We interpret no periglacial activity in the cirques
during this interval.
The lake to bog transition dominates the
middle Holocene to modern segment of the
725
sediment cores, which includes four episodes
of increased clastic sediment deposition that
correlate with MS spikes. The coarsest sand
layer at 180 cm depth has a date of 3495 6
50 14C yr B.P., coeval with the late Holocene
lateral moraine in the Lake Katherine cirque
(3570 6 145 14C yr B.P.). Cold climate episodes in the basin are characterized by greater sediment delivery and must be the result
of enhanced precipitation and/or glacial runoff. Three other clastic events (ca. 4900,
2770 6 45, and 120 6 40 14C yr B.P.) are
characterized by MS spikes and sharp decreases in TOC. The youngest is a Little Ice
Age equivalent. There are no equivalent moraines for these three events in the high
cirques; however, there are imprecisely dated
talus-accumulation events. We interpret each
of these events to reflect periglacial processes,
including enhanced snowmelt-runoff floods,
and thus cold climate periods. The late Holocene glacial advance is younger than expected for these southerly latitudes, but it is
consistent with glacial advances of similar
ages in the Colorado Front Range (e.g., Benedict, 1973; Miller, 1973; Richmond, 1986).
The dates of each of these four middle to
late Holocene cold climate events correlate
within 100–200 14C yr with episodes of enhanced sea-ice drift in the North Atlantic
Ocean (Bond et al., 1997, 1999) and with glacial advances in other ranges in the Northern
Hemisphere (e.g., the Alps, the St. Elias
Range of the Yukon Territory and Alaska), although these are not as precisely dated (Denton and Karlén, 1973). We also note a strong
correlation with cooler and effectively wetter
events in Yellowstone National Park fire and
alluvial records (Meyer et al., 1995). These
Holocene cold climate periods may actually
be hemispheric in extent, but because they are
smaller in amplitude than climate changes in
the Pleistocene, they are only recognized in
environments primed to record the signal. For
much of the past 15 k.y. the climatic evolution
of northern New Mexico has been similar to
that of the North Atlantic basin.
CONCLUSIONS
The Winsor Creek drainage basin, southern
Sangre de Cristo Mountains, contains a detailed and complete late Pleistocene–Holocene
record of environmental change. Sedimentary
cores from bogs downbasin from the highest
cirque reveal clear stratigraphic and sedimentologic changes that we correlate with the glacial chronology of the basin. Analyses of paleoclimatic proxy information, including rock
magnetic properties and organic carbon data,
also strongly support these correlations.
The basic chronology of latest Pleistocene
to Holocene climatic events includes Pinedale
equivalent valley glaciation just before 12 120
726
14C
yr B.P., a second glaciation during the
Younger Dryas chron in the high-elevation
cirques, an early to middle Holocene warmer
interval, a cirque glacier advance at 3600 14C
yr B.P., and a series of middle to late Holocene
periglacial episodes, including a Little Ice Age
equivalent.
Both the Younger Dryas glaciation and Holocene cold climate phases correlate in time
with cold climate episodes in the North Atlantic basin and elsewhere in North America and
Europe, showing that north-central New Mexico responded to the same large-scale climatic
forcing as other parts of the Northern
Hemisphere.
ACKNOWLEDGMENTS
Financial support was provided by grants from
the National Science Foundation (OPP-9614907 to
Fawcett) and from the New Mexico Geological Society and Colorado Scientific Society (to Armour).
We thank the Pecos District Forest Service for access to the site, Viorel Atudorei for help with the
carbon analyses, Grant Meyer for discussions, and
Frank Pazzaglia for introducing us to this area. We
also thank D. Dethier, W. Anderson, and an anonymous reader for constructive reviews.
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Manuscript received January 4, 2002
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Manuscript accepted April 29, 2002
Printed in USA
GEOLOGY, August 2002