15 k.y. paleoclimatic and glacial record from northern

Jake Armour  Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico Peter J. Fawcett  87131, USA John W. Geissman 

ABSTRACT temporally equivalent to North Atlantic sea- The southern Sangre de Cristo Mountains, New Mexico, contain evidence of glacial ice drift events (cf. Bond et al., 1997, 1999) activity from the late Pleistocene to late Holocene. Sediment cores recovered from an and other cold events in the Northern Hemi- alpine bog (3100 m) trapped behind a Pinedale age moraine, ϳ2 km downvalley from a sphere (Denton and KarleÂn, 1973; Meyer et high-elevation cirque, reached glacial-age debris and recovered ϳ6 m of lake clays over- al., 1995). lain by gyttja. Accelerator mass spectrometry dating, sedimentology, variations in mag- netic properties, and organic carbon data reveal six distinct periods of glacial and/or Winsor Creek Drainage Basin periglacial activity. These include a late Pleistocene Pinedale glacial termination just be- The Winsor Creek drainage basin is located fore 12 120 14C yr B.P., a Younger Dryas chron cirque glaciation, an early Neoglacial ϳ60 km northeast of Santa Fe, New Mexico, periglacial event (ca. 4900 14C yr B.P.), a late Holocene cirque glaciation (3700 14Cyr on the eastern ¯ank of the Santa Fe Range B.P.), as well as late Holocene periglacial events at 2800 14C yr B.P. and the Little Ice (Fig. 1). The bedrock in the upper part of the Age (ca. 120 14C yr B.P.). Cold events in the middle to late Holocene correlate with subtle basin is Precambrian granite (Miller et al., ice-rafting events in the North Atlantic and records of cold events in North America and 1963). The uppermost part of the basin con- Europe and were probably hemispheric in extent. tains four cirques, the principal one containing Lake Katherine. These cirques are oriented Keywords: climate change, glacial geology, Holocene, New Mexico, Younger Dryas. east to northeast with steep slopes on their southern and southwestern sides. Downvalley, INTRODUCTION To better understand the timing of late Qua- a secondary bench marks the farthest extent The southern Sangre de Cristo Mountains, ternary changes in this region, we recovered of Quaternary glaciation and contains small New Mexico, are one of the southernmost six sediment cores from an alpine bog down- lakes and bogs, including Stewart Lake and high ranges along the Rocky Mountain chain. basin from a principal cirque in the Winsor bog B1 (ϳ3100 m elevation), all formed in This range preserves many glacial features; Creek basin, which preserves sedimentary re- depressions behind Pinedale moraines (Fig. however, the Quaternary geomorphic history cords of upbasin changes in hydrology (cf. 1). is not as well known as in the central Rockies. Anderson and Smith, 1994; Leonard, 1986; Wesling (1988) established the glacial chro- Wesling (1988) established a glacial chronol- Leonard and Reasoner, 1999). Paleoenviron- nology for this basin using moraine relative- ogy for the Winsor Creek drainage based on mental reconstructions for this site are based age data, including soil-pro®le development relative-age data of glacial deposits, and rec- on sediment grain size, magnetic properties, and degree of clast weathering and landform ognized six separate glacial advances. These total organic carbon, and carbon isotopic data. preservation. He assigned a Pinedale age to a include two Bull Lake advances (not shown We compare a well-dated paleoenvironmental moraine suite at 3100 m in the middle drain- in Fig.1), two Pinedale advances, a late Pleis- record from the bog core with an established age (P1 in Fig. 1) and a late Pinedale age (P2) tocene to early Holocene advance, and a late relative glacial chronology and demonstrate to moraines farther upvalley (Fig. 1). A mo- Holocene advance (Fig. 1). Wesling also iden- that limited alpine glacial advances occurred raine currently damming Lake Katherine at ti®ed two separate talus-¯ow events that post- during the Younger Dryas interval and the late 3580 m was assigned a late Pleistocene to ear- dated the Neoglacial advance and represent Holocene. We also show that middle to late ly Holocene age (Y) based on a more juvenile late Holocene periglacial episodes. Holocene periglacial events in the region are soil pro®le and steeper slopes than the classic

Figure 1. Map of Winsor Creek drainage basin, Sangre de Cristo Moun- tains, New Mexico. Po- sitions of late Pleisto- cene and Holocene moraines and principal cirques, lakes, and bogs in region are shown (adapted from Wesling, 1988). Insets show study area loca- tion and bog B1 detail with core locations.

᭧ 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 ®gures; 1 table. 723 Pinedale deposits. An inset lateral moraine TABLE 1. RADIOCARBON DATES FROM BOG CORES B1-5 AND B1-6 within the Lake Katherine cirque with little Lab number Core Depth Radiocarbon date Material dated soil development and a very sharp surface (cm) (14C yr B.P. Ϯ 1␴) pro®le was assigned a late Holocene age (N). Beta-153457 B1-5 325 9 890 Ϯ 60 Bulk sediment A radiocarbon date of 3570 Ϯ 145 14C yr B.P. Beta-153454 B1-5 347 10 070 Ϯ 60 Charred wood Beta-153456 B1-5 347 10 190 Ϯ 60 Bulk sediment from charcoal underlying till at the base of Beta-153455 B1-5 362 10 180 Ϯ 50 Charred wood this moraine shows a late Holocene glacial ad- AA-35802 B1-6 21 120 Ϯ 40 Bulk peat vance. Equivalents for both the Y and N mo- AA-35801 B1-6 63 990 Ϯ 35 Bulk peat AA-35800 B1-6 95 2 770 Ϯ 45 Charcoal raines are found in all cirques in the area (Fig. AA-35799 B1-6 153 2 950 Ϯ 45 Bulk peat 1). AA-35795 B1-6 171 3 495 Ϯ 50 Wood AA-35794 B1-6 206 4 550 Ϯ 50 Charcoal AA-35798 B1-6 245 5 010 Ϯ 50 Grassy sediment METHODS AA-35797 B1-6 310 8 100 Ϯ 75 Bulk sediment Six sediment cores were obtained from bog AA-35793 B1-6 381 9 765 Ϯ 55 Wood B1 using a Livingston square-rod piston corer. AA-35796 B1-6 444 12 120 Ϯ 95 Bulk sediment Minor compaction of 5%±10% was noted for each core segment. The entire sequence of late Pleistocene and Holocene sediment was re- 95 14C yr B.P.). A second light colored clay values are in the bioturbated clay. A sharp covered in three (B1-4, B1-5, and B1-6) of the at 400 cm depth is overlain by 30 cm of ␦13C excursion of Ϫ3½ occurs at 400 cm six cores, and sedimentologic and stratigraph- coarsely laminated, gray clay. A 4-mm-thick (Fig. 2). In the upper gyttja units, TOC is ic features were observed and noted for each. layer of ®ne-grained, subangular quartz sand high, except within sand layers where it drops The cores were sampled for radiocarbon dat- caps this unit. Several dates from within and to near 0%. ing (University of Arizona Accelerator Mass just above this unit are shown in Figure 3. A Spectrometer [AMS] and Beta-Analytic labo- bulk sediment date (10 190 Ϯ 60 14C yr B.P.) DISCUSSION ratory) using standard AMS techniques. Dates and a charred wood date (10 070 Ϯ 60 14Cyr Sediment cores from the Lake Stewart area were obtained on isolated wood fragments, B.P.) were taken at the same depth (348 cm) bogs record a typical life cycle of a small al- charcoal, and organic sediments, all from the in core B1-5 and showed an offset of ϳ120 pine with a lake to bog transition punctuated center of the core drives to minimize contam- 14C yr between the different materials. Above by discrete sedimentary events marking epi- ination. For organic sediments, the entire sam- the quartz sand layer, a 60 cm interval of sodes of climate change. These deposits re- ple was pretreated to remove rootlets and coarsely laminated clays is abruptly overlain cord events in the upper basin, and can be tied grass, and treated with acid and combusted. by 70 cm of bioturbated clays. to the post-Pinedale glacial chronology of the The cores were continuously sampled for At 180 cm depth in B1-6, a 20-cm-thick basin. Sedimentologic, MS, and ARM varia- magnetic susceptibility (MS), anhysteretic coarse-grained sand (3495 Ϯ 50 14C yr B.P.) tions distinguish episodes of glacial activity, remanent magnetization (ARM), and acquisi- marks the transition from clays to dark brown as well as periglacial activity (Benson et al., tion of isothermal remanent magnetization gyttja. The upper ϳ2 m of core is punctuated 1996; Bischoff et al., 1997). Rosenbaum et al. (IRM) data. Oriented samples were precut by two additional clastic horizons, a sand lay- (1996) showed that in a granitic basin, fresh with Cu-Be (nonmagnetic) tools and then er at 100 cm depth (2770 Ϯ 45 14C yr B.P.), detritus contains a higher concentration of placed in plastic cubes. and a dark clay layer at 18 cm depth (120 Ϯ coarser magnetite than more heavily weath- Total organic carbon (TOC) analysis was 40 14C yr B.P.). ered detritus, and we assert that a similar phe- completed using a standard continuous ¯ow Sedimentologic changes correlate with rock nomenon is recorded in glacial activity in the elemental analyzer. The mass spectrometer magnetic, TOC, and carbon isotopic data (Fig. cirque above the Lake Stewart area. The method uses small samples and provides iso- 2). High MS intervals in the lower lake clays agreement of rock magnetic data among all topic carbon ratios and organic carbon con- correlate with the basal light clay (460 cm) cores (Fig. 3) is strong evidence for a consis- centrations. There is no contamination by in- and with clays at the quartz sand layer (365 tent response to changes in precipitation, driv- organic carbon sources in the sediment cores cm). In the upper half of B1-6, peaks in MS en by changes in climate. Other intervals of because the source bedrock is uniformly (180 cm, 110 cm, and 18 cm) correlate with coarse sand were deposited rapidly in pulsed granitic. periods of enhanced clastic deposition in the events and probably originated from freshly lake or bog, while a fourth (230 cm) shows exposed cirque slopes and from older Pinedale RESULTS no discernible change in sediment character. moraines upvalley from the bog (Fig. 1), be- Three sediment cores reached coarse rubble, This feature correlates across all deep cores cause the streams have bedrock channels. supported by ground-penetrating radar data (Fig. 3) and represents a period of enhanced The date of 12 120 Ϯ 60 14C yr B.P. from (G. Gettemy, 1999, personal commun.). Con- delivery of high-susceptibility phases. The above the basal light colored clay provides a sistent stratigraphy and MS pro®les allow us ARM data (Fig. 2) correlate with MS data, minimum age for Pinedale termination. This to directly correlate cores B1-4, B1-5, and B1- indicating that these trends are driven by date is consistent with other limiting estimates 6. The 14 AMS radiocarbon dates from the 2 changes in concentration of ferrimagnetic for Pinedale deglaciation in the central Rock- cores dated increase with depth (Table 1; Figs. phases, principally magnetite, as demonstrated ies (e.g., Elias et al., 1991; Madole, 1980; 2 and 3) and support these correlations. The by isothermal remanent magnetization (IRM) Menounos and Reasoner, 1997), as well as stratigraphy and radiocarbon date control were and back®eld demagnetization data (Fig. 2). with hydrologic changes in the best displayed in core B1-6 (Fig. 2), and so TOC data (Fig. 2) vary from the lower lake basin to the west (Dethier and Reneau, 1996). we describe this sequence in detail. The basal environment (5%±20% organic C) to the up- The large MS spike in the basal clay is con- debris in B1-6 is directly overlain by 7 cm of per bog environment (10%±50% organic C). sistent with a glacial origin, either rock ¯our light colored clay, which represents the initial The ␦13C data also show a trend with depth, or rill washing of unweathered glacial debris. in®lling of depressions behind Pinedale mo- becoming lighter in value higher in the core. Organic sedimentation quickly increased fol- raines. This unit is overlain by 60 cm of ®nely There is considerable variability in TOC be- lowing deglaciation, presumably in response laminated lake clay (basal date of 12 120 Ϯ tween 460 cm and 330 cm depth; the lowest to warmer climates.

724 GEOLOGY, August 2002 Figure 2. Stratigraphic pro®le of sediment core B1-6 showing litho- stratigraphic units, 14C dates, mag- netic susceptibility pro®le (SI v), anhysteretic remanent magnetiza- tion (ARM) intensity (mA/m), total organic carbon (TOC, weight per- cent) and ␦13C of organic matter. Four insets in ARM intensity col- umn show curves of acquisition of isothermal remanent magnetiza- tion (IRM) and back®eld demagne- tization of saturation IRM for se- lected samples. Values above each curve are speci®c depths for each sample selected. Values of coerciv- ity of remanence, as de®ned by x- intercept on back®eld demagneti- zation 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 mate with less vegetation in the basin and less put into the lake and a concomitant relative probably caused dramatic changes in sediment organic material in the catchment. The Ϫ3½ increase in algal contribution. properties at 400 cm in core B1-6, including carbon isotopic shift (synchronous with the We correlate this interval of sedimentary a second light colored clay, an abrupt increase TOC decrease) is also consistent with a dra- change with an event that produced a large in MS, a sharp decrease in TOC, and a large matic decrease in vegetation around and up- terminal moraine in the Lake Katherine negative ␦13C shift (Fig. 2). Changes in sedi- basin from the lake. The dominant arboreal cirque, assigned a late Pleistocene to early Ho- ment texture and MS are consistent with species at this elevation is Engelman spruce, locene age by Wesling (1988). Radiocarbon cirque glacial activity and enhanced runoff de- which has an isotopic composition of dates from this interval (10 190 Ϯ 60, 10 180 livering more clastic sediment with a higher ϳϪ25½. Lake algae, however, has an isoto- Ϯ 50, 10 070 Ϯ 60, and 9765 Ϯ 55 14Cyr concentration of magnetite downbasin. These pic composition ranging from Ϫ28½ to B.P.; Fig. 3) show that it is clearly within the changes are subtle because the cirque glacier Ϫ31½ (Meyers and Lallier-Vergies, 1999). Younger Dryas chron. The quartz sand layer would have been ϳ2 km upvalley. The de- The isotopic shift can be explained by a rel- and the large MS spike in clays that cap this crease in TOC is attributable to a colder cli- ative decrease in terrestrial organic matter in- unit represent the end of glacial advance and possibly re¯ect a breach in the Lake Katherine moraine that produced a large ¯ood 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 Ϯ 60 14C yr B.P., Fig. 3) is also consistent with this unit being a Younger Dryas termination. Several examples of Youn- ger Dryas glacial advances have been recog- nized in the central (e.g., Gosse et al., 1995; Menounos and Reasoner, 1997; Reasoner et al., 1994), and a cooling event in the San Juan Mountains of 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 sedimen- tation rates, and negative MS values that show little immature detritus (e.g., Fe-Ti oxides, fer- romagnetic silicates) in the sediment. We in- terpret no periglacial activity in the cirques Figure 3. Correlation of magnetic susceptibility (MS) pro®les of deep sedi- during this interval. ment 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 The lake to bog transition dominates the Age. middle Holocene to modern segment of the

GEOLOGY, August 2002 725 sediment cores, which includes four episodes 14C yr B.P., a second glaciation during the macrofossil analyses: Quaternary Research, of increased clastic sediment deposition that Younger Dryas chron in the high-elevation v. 36, p. 307±321. Gosse, J.C., Evenson, E.B., Klein, J., Lawn, B., and correlate with MS spikes. The coarsest sand cirques, an early to middle Holocene warmer Middleton, R., 1995, Precise cosmogenic 10Be layer at 180 cm depth has a date of 3495 Ϯ interval, a cirque glacier advance at 3600 14C measurements in western North America: 50 14C yr B.P., coeval with the late Holocene yr B.P., and a series of middle to late Holocene Support for a global Younger Dryas cooling lateral moraine in the Lake Katherine cirque periglacial episodes, including a Little Ice Age event: Geology, v. 23, p. 877±880. 14 Leonard, E.M., 1986, Use of lacustrine sedimentary (3570 Ϯ 145 C yr B.P.). Cold climate epi- equivalent. sequences as indicators of Holocene glacial sodes in the basin are characterized by great- Both the Younger Dryas glaciation and Ho- history, Banff National Park, Alberta, Canada: er sediment delivery and must be the result locene cold climate phases correlate in time Quaternary Research, v. 26, p. 218±231. of enhanced precipitation and/or glacial run- with cold climate episodes in the North Atlan- Leonard, E.M., and Reasoner, M.A., 1999, A con- off. Three other clastic events (ca. 4900, tic basin and elsewhere in North America and tinuous Holocene record inferred from pro- 14 glacial lake sediments in Banff National Park, 2770 Ϯ 45, and 120 Ϯ 40 C yr B.P.) are Europe, showing that north-central New Mex- Alberta, Canada: Quaternary Research, v. 51, characterized by MS spikes and sharp de- ico responded to the same large-scale climatic p. 1±13. creases in TOC. The youngest is a Little Ice forcing as other parts of the Northern Madole, R.F., 1980, Time of Pinedale deglaciation Age equivalent. There are no equivalent mo- Hemisphere. in north-central Colorado: Further consider- ations: Geology, v. 8, p. 118±122. raines for these three events in the high Menounos, B., and Reasoner, M.A., 1997, Evidence cirques; however, there are imprecisely dated ACKNOWLEDGMENTS for cirque glaciation in the Colorado Front talus-accumulation events. We interpret each Financial support was provided by grants from Range during the Younger Dryas chronozone: of these events to re¯ect periglacial processes, the National Science Foundation (OPP-9614907 to Quaternary Research, v. 48, p. 38±47. Fawcett) and from the New Mexico Geological So- including enhanced snowmelt-runoff ¯oods, Meyer, G.A., Wells, S.G., and Jull, A.J.T., 1995, ciety and Colorado Scienti®c Society (to Armour). Fire and alluvial chronology in Yellowstone and thus cold climate periods. The late Ho- We thank the Pecos District Forest Service for ac- National Park: Climatic and intrinsic controls locene glacial advance is younger than ex- cess to the site, Viorel Atudorei for help with the on Holocene geomorphic processes: Geologi- pected for these southerly latitudes, but it is carbon analyses, Grant Meyer for discussions, and cal Society of America Bulletin, v. 107, consistent with glacial advances of similar Frank Pazzaglia for introducing us to this area. We p. 1211±1230. also thank D. Dethier, W. Anderson, and an anon- Meyers, P.A., and Lallier-Verges, E., 1999, Lacus- ages in the Colorado Front Range (e.g., Ben- ymous reader for constructive reviews. trine sedimentary organic matter records of edict, 1973; Miller, 1973; Richmond, 1986). late Quaternary paleoclimates: Journal of Pa- The dates of each of these four middle to REFERENCES CITED leolimnology, v. 21, p. 345±372. late Holocene cold climate events correlate Anderson, R.S., and Smith, S.J., 1994, Paleoclimat- Miller, D.C., 1973, Chronology of Neoglacial de- within 100±200 14C yr with episodes of en- ic interpretations of meadow sediment and posits in the Northern Sawatch Range, Colo- pollen stratigraphies from California: Geolo- rado: Arctic and Alpine Research, v. 5, hanced sea-ice drift in the North Atlantic gy, v. 22, p. 723±726. p. 385±400. 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Bulletin, p. 1328±1341. cirque reveal clear stratigraphic and sedimen- Wesling, J.R., 1988, Glacial chronology and soil de- Denton, G.H., and KarleÂn, W., 1973, Holocene cli- tologic changes that we correlate with the gla- velopment in Winsor Creek drainage basin, matic variationsÐTheir pattern and possible southernmost Sangre de Cristo Mountains cial chronology of the basin. Analyses of pa- cause: Quaternary Research, v. 3, p. 155±205. [M.S. thesis]: Albuquerque, University of leoclimatic proxy information, including rock Dethier, D.P., and Reneau, S.L., 1996, Lacustrine New Mexico, 186 p. magnetic properties and organic carbon data, chronology links late Pleistocene climate and also strongly support these correlations. mass movements in northern New Mexico: Manuscript received January 4, 2002 Geology, v. 24, p. 539±542. The basic chronology of latest Pleistocene Revised manuscript received April 25, 2002 Elias, S.A., Carrara, P.E., Toolin, L.J., and Jull, Manuscript accepted April 29, 2002 to Holocene climatic events includes Pinedale A.J.T., 1991, Revised age of deglaciation of equivalent valley glaciation just before 12 120 Lake Emma based on new radiocarbon and Printed in USA

726 GEOLOGY, August 2002