Late Quaternary eolian and alluvial response to paleoclimate, Canyonlands, southeastern Utah Marith C. Reheis† Richard L. Reynolds Harland Goldstein U.S. Geological Survey, MS-980, Federal Center, Box 25046, Denver, Colorado 80225, USA Helen M. Roberts Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, Wales, UK James C. Yount U.S. Geological Survey, MS-980, Federal Center, Box 25046, Denver, Colorado 80225, USA Yarrow Axford Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA Linda Scott Cummings Paleo Research Institute, 2675 Youngfi eld Street, Golden, Colorado 80401, USA Nancy Shearin Bureau of Land Management, Monticello Field Offi ce, Monticello, Utah 84535, USA ABSTRACT began at ca. 6 ka and ended by ca. 3–2 ka, fol- sheets and dunes are common features of semi- lowed by a shift to drier modern conditions; arid regions, and their deposits and intercalated In upland areas of Canyonlands National localized mobilization of dune sand has per- paleosols potentially contain a long-term record Park, Utah, thin deposits and paleosols show sisted to the present. These interpretations of landscape response to climate fl uctuations. late Quaternary episodes of eolian sedimen- are similar to those of studies at the Chaco Mineral dust may strongly infl uence land- tation, pedogenesis, and climate change. dune fi eld, New Mexico, and the Tusayan scapes and ecosystems by adding materials to Interpretation of the stratigraphy and opti- dune fi eld, Arizona, and are consistent with soils that change their properties (e.g., Reheis cally stimulated luminescence ages of eolian paleoclimate interpretations of pollen and et al., 1995; Simonson, 1995; Herrmann et al., and nearby alluvial deposits, their pollen, packrat middens in the region. 1996). Dust incorporated into aridic soils affects and intercalated paleosols yields the follow- A period of rapid deposition and infi ltra- water-infi ltration rates, the evolution and stabil- ing history: (1) Eolian deposition at ca. 46 ka, tion of eolian dust derived from distant igne- ity of desert surfaces, the distribution of surface followed by several episodes of alluviation ous source terranes occurred between ca. 12 and subsurface water (McFadden et al., 1987, from some time before ca. 40 ka until after and 8 ka. Before ca. 17 ka, and apparently 1998; McDonald et al., 1996), and relations 16 ka (calibrated). (2) Eolian deposition from back to at least 45 ka, paleosols contain little among eolian dust, distribution of plants and ca. 17 ka to 12 ka, interrupted by periods of or no such infi ltrated dust. After ca. 8 ka, soil crust, rain-water runoff, and productivity pedogenesis, coinciding with late Pleistocene either the supply of dust was reduced or the (McFadden and McAuliffe, 1997; Shachak and alluviation as local climate became warmer more arid climate inhibited translocation of Lovett, 1998; Belnap et al., 2000; Reynolds et and wetter. (3) A wetter period from 12 to dust into the soils. al., 2001). 8.5 ka corresponding to the peak of summer The Canyonlands physiographic section of monsoon infl uence, during which soils formed Keywords: Colorado Plateau, dunes, eolian the Colorado Plateau (Fig. 1) is characterized by relatively quickly by infi ltration of eolian silt dust, paleoclimate, paleosols, soil nutrients. high-elevation (1500–2200 m) benches, mesas, and clay, and trees and grasses were more and slickrock buttes of resistant sandstone. These abundant. (4) A drier period between ca. 8.5 INTRODUCTION landforms, in many cases isolated from alluvial and 6 ka during which sheetwash deposits and colluvial sedimentation, are commonly accumulated and more desertlike vegetation Semiarid and arid regions of the world react mantled by a thin layer of fi ne-grained sandy was dominant; some dunes were reactivated sensitively to climate change. Indicators of sediment supporting upland grass and shrub at ca. 8 ka. (5) Episodic eolian and fl uvial environmental change commonly used in stud- steppe. Active wind transport of sand occurs deposition during a wetter, cooler period that ies of these areas include lacustrine deposits, in areas of abundant sand supply and where pollen from stratigraphic sequences, and plant vegetation has been disturbed by land use. Lay- †E-mail: [email protected]. macrofossils from packrat middens. Eolian sand ers of locally derived eolian sand separated by GSA Bulletin; July/August 2005; v. 117; no. 7/8; p. 1051–1069; doi: 10.1130/B25631.1; 10 fi gures; 4 tables; Data Repository item 2005106. For permission to copy, contact [email protected] © 2005 Geological Society of America 1051 REHEIS et al. paleosols in small relict dune fi elds indicate late Quaternary changes in land-surface stability. WA In this paper, we discuss the depositional MT OR history, age, and paleoclimate setting of eolian ID Arches and alluvial deposits and intercalated paleosols WY National at fi ve sites in the area of Canyonlands National NV UT CO Park Park, Utah. The relatively thin deposits of eolian CA sand preserve a nearly 50 k.y. record of alternat- Colorado River Tusayan Chaco ing periods of deposition and stability. In com- dunes ISKY dunes NM bination with pollen contained in these deposits, AZ dune Moab La Sal Colorado ' these records provide new insights on the late Plateau Mountains 30 N Quaternary landscape stability and paleoclimate 8 of the Colorado Plateau. In addition, textural 3 Green River and magnetic data record episodic additions of far-traveled infi ltrated dust in surface and buried Canyonlands, soils, with ecologic implications for modern National ecosystem dynamics in this area. Park STUDY SITES AND METHODS Hamburger Rock The Canyonlands area of the Colorado Pla- Indian Creek Salt Creek teau is cool and semiarid. At the Needles visitor center (Fig. 1), intermediate in location and alti- Needles tude (1523 m) between four of our sites, mean area annual precipitation is 21 cm (38 yr record), and 00'N mean January and July temperatures are –1.9 °C Colorado River Abajo 38 and 25.8 °C, respectively (National Climatic Mtns. Data Center, http://www.wrcc.sage.dri.edu/ 0 20 km Monticello climsum.html). The Neck station in the Island in the Sky district is 14 km from the northern 110 00 'W 109 30 'W study site (ISKY dune) and at the same altitude (1807 m). Precipitation and temperature ranges Figure 1. Maps of Canyonlands area and locations of study sites (“Needles area” includes are similar to The Needles despite the difference Virginia Park and graben-fi ll sites). Inset, location of Canyonlands area (black box) within in altitude. In both areas, ~40% of precipitation the Colorado Plateau and nearby dune fi elds. Mtns.—Mountains. falls during late July to October, the remainder being about equally distributed through the year; prevailing winds are from the west. area of sandy sheetwash alluvium in search of the Abajo Mountains (Fig. 1). The modern Study Sites subsurface archaeological features. As part of sediment transported by Salt Creek includes this study, Shearin et al. (2000) described and fi ne to medium volcanic gravel from the Abajo Virginia Park, the focus of most of our work sampled surface and buried soils and analyzed Mountains and sand derived locally from the (Fig. 1), is a sheltered basin of vegetated, sta- pollen samples from the sediment. Cedar Mesa Sandstone. We studied fi ve terrace bilized sand dunes bordered on three sides by The ISKY site is a quarry in a partially active surfaces fl anking Salt Creek (Fig. 4). vertical sandstone cliffs, and on the fourth by clifftop dune containing paleosols on the east- a canyon (Fig. 2, Table 1). Dune ridges rise as ern edge of the plateau between the Green and Sampling and Description much as 5 m above intervening swales. Auger Colorado Rivers (Figs. 1 and 3A; Table 1). The holes indicate the sand is at least 4 m thick, Quaternary dune sand is probably derived from Within Canyonlands National Park, strati- thinning to zero at the margins. Modern vegeta- erosion of the nearby Navajo Sandstone (Hunt- graphic descriptions and samples were primar- tion includes abundant grasses and shrubs and oon et al., 1982). The graben-fi ll site (Figs. 2 ily obtained with a soil auger, supplemented by scattered trees in bedrock and cliff-marginal and 3B; Table 1) east of Virginia Park contains natural exposures of dune sand and alluvium locations (Table 1; M. Miller, U.S. Geological deposits within a closed depression formed by in arroyo cuts and by two shallow hand-dug Survey, personal commun., 1998). Small drain- faulting due to fl ow of underlying salt beds soil pits (VP-1, VP-2; Fig. 2) in a dune crest ages dissect the Quaternary sediment within westward toward the Colorado River (Fig. 1; and a dune swale. Outside the boundary of the the basin and locally provide exposures of the Hunt, 1969; Walsh and Schultz-Ela, 2003). park, samples were collected from backhoe stratigraphy. Later incision by Chesler Canyon has created pits at Hamburger Rock (Fig. 1; Shearin et al., The Hamburger Rock site (Fig. 1, Table 1) has a near-vertical cut exposing more than 6 m of 2000) and from a 9-m-thick section of dune a thin sheet of Quaternary eolian sand, including slightly gravelly, poorly sorted, silty sand with sands and paleosols exposed by the quarry active coppice dunes overlying shale. The Bureau interbedded paleosols (Fig. 3B). at ISKY dune. Most of the outcrops and soil of Land Management excavated trenches in the Salt Creek is an intermittently fl owing pits were described (Table 2) following Birke- sand and underlying bedrock and in an adjacent tributary of the Colorado River that heads in land (1999). The soil-auger sequences were 1052 Geological Society of America Bulletin, July/August 2005 EOLIAN AND ALLUVIAL RESPONSE TO PALEOCLIMATE 601500 602000 9U-22 8U-13 8U-14 8U-11 00U-27 8U-10 9U-23 VP-2 0 VP-1 8U-12 421670 109 o 52'W 109 o 51' 109 o 50' 38 07'N o Graben fill (9U-21) THE 38 06' o Topographic contour, 1730 10-m interval NEEDLES Supplemental 2.5-m topographic contour Sample site 100 m 4216200 Figure 2.