15 K.Y. Paleoclimatic and Glacial Record from Northern New Mexico

15 K.Y. Paleoclimatic and Glacial Record from Northern New Mexico

15 k.y. paleoclimatic and glacial record from northern New Mexico 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, ;2 km downvalley from a sphere (Denton and KarleÂn, 1973; Meyer et high-elevation cirque, reached glacial-age debris and recovered ;6 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 ;60 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 (;3100 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. 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 ®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. 6 1s) pro®le was assigned a late Holocene age (N). Beta-153457 B1-5 325 9 890 6 60 Bulk sediment A radiocarbon date of 3570 6 145 14C yr B.P. Beta-153454 B1-5 347 10 070 6 60 Charred wood Beta-153456 B1-5 347 10 190 6 60 Bulk sediment from charcoal underlying till at the base of Beta-153455 B1-5 362 10 180 6 50 Charred wood this moraine shows a late Holocene glacial ad- AA-35802 B1-6 21 120 6 40 Bulk peat vance. Equivalents for both the Y and N mo- AA-35801 B1-6 63 990 6 35 Bulk peat AA-35800 B1-6 95 2 770 6 45 Charcoal raines are found in all cirques in the area (Fig. AA-35799 B1-6 153 2 950 6 45 Bulk peat 1). AA-35795 B1-6 171 3 495 6 50 Wood AA-35794 B1-6 206 4 550 6 50 Charcoal AA-35798 B1-6 245 5 010 6 50 Grassy sediment METHODS AA-35797 B1-6 310 8 100 6 75 Bulk sediment Six sediment cores were obtained from bog AA-35793 B1-6 381 9 765 6 55 Wood B1 using a Livingston square-rod piston corer. AA-35796 B1-6 444 12 120 6 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 d13C excursion of 23½ 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 6 60 14C yr B.P.) DISCUSSION ratory) using standard AMS techniques. Dates and a charred wood date (10 070 6 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 ;120 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 6 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 ;2 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 6 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 6 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.

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