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Mineralogyandmorphologicalpropertiesofburiedpolygeneticpaleosolsformedinlatequaternarysedimentsonuplandlandscapesofthecentralplains,USA

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Geoderma 154 (2010) 508–517

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Mineralogy and morphological properties of buried polygenetic paleosols formed inlate quaternary sediments on upland landscapes of the central plains, USA

DeAnn Ricks Presley ⁎, Paul E. Hartley, M.D. RansomKansas State University, Department of Agronomy, United States

⁎ Corresponding author. Fax: +1 785 532 6315.E-mail address: deann@ksu.edu (D.R. Presley).

0016-7061/$ – see front matter. Published by Elsevier Bdoi:10.1016/j.geoderma.2009.03.015

a b s t r a c t

a r t i c l e i n f o

Article history:Received 14 August 2008Received in revised form 12 February 2009Accepted 20 March 2009Available online 22 April 2009

Keywords:PaleosolsMineralogyLandscapesLoessQuaternaryGreat PlainsCentral Plains

East central Kansas is largely comprised of alternating, level beds of Permian shale and limestone of theCentral Plains, USA. Polygenetic upland soils of east central Kansas have been formed though multiple andlikely different sets of soil forming factors. Upland soils in this region have a complex genesis, often containone or more paleosols, and form in multiple parent materials including loess, locally reworked loess orcolluvium, and residuum. The depth to bedrock rarely exceeds 2 m. Upland hillslope soils commonly containone or more paleosols, and can be observed on a variety of hillslope positions on the landscape. Generally, thelower paleosols are recognized by strongly expressed structure, thick continuous clay coatings on all faces ofpeds, and strong reddish color with either 7.5YR or 5YR hues. Soil textures of the paleosols often feel lessclayey than the overlying horizons in field determinations. At first, this was attributed to a decrease in claycontent, stickiness, and plasticity. However, subsequent laboratory characterization revealed that the claycontent was usually highest in the lower paleosol horizons, and that the clay mineralogy of the modern soilwas dominated by smectite, while the paleosols contained a mixed suite of minerals. Therefore, the perceiveddecrease in clay content was caused by a change in clay mineralogy, a feature that can be exploited in futurefield descriptions in order to more accurately distinguish between stratigraphic units in these thin, weldedpolygenetic soils. The age of the paleosols sampled in this study were typical for the late Quaternary-agedSeverance formation, clustering in two age ranges, which were ≈19,000 to 20,000 and ≈22,500 to 27,700uncalibrated 14C yr BP. The results from this study illustrate that although they might be thin, truncated, andwelded, late Quaternary-aged loess-derived soils and paleosols occur in regular, predictable patterns onmany upland hillslopes in the Bluestem Hills Major Land Resource Area, and this region should be included infuture regional investigations of the Central Plains.

Published by Elsevier B.V.

1. Introduction

The Bluestem Hills (Fig. 1) are underlain by alternating, level bedsof Permian shale and limestone, some of which are quite cherty.Differential weathering of the shale and limestone features hascreated a repeating bench-and-slope topography, and as such,relatively stable landforms exist up and down the larger, steephillslopes. Upland soils in the BluestemHills Major Land Resource Area(MLRA 76) are thought to have a long and complex genesis, to containmultiple parent materials, and to have formed under tallgrass prairiein an area that is transitional between udic and ustic moistureregimes. Parent materials were historically described as clayeysediments, such as residuum, although recent investigations havedescribed a more complicated and polygenetic suite of parentmaterials for the modern soil and underlying paleosols (Wehmueller,1996; Glaze, 1998). Thick loess deposits (N2 m) are not recognized inthis portion of Kansas, although thicker loess units are recognized in

.V.

other adjacent areas of the Central Plains. Although loess was likelydeposited in this region, it is generally held that most of the loess haseroded from the upland hillslopes.

Loess–paleosol sequences of the Quaternary Period are presentthroughout much of the plains. Loess units widely recognized in theCentral Plains include the Loveland (deposited approximately500,000 to 100,00 yr BP), Gilman Canyon Formation (depositedapproximately 41,000 to 20,000 yr BP), and Peoria Loess (depositedapproximately 25,000 to 11,000 yr BP). Frye and Leonard (1952)estimated that one-third of Kansas has Peoria loess at the surface.Later, Welch and Hale (1987) used a combination of sources includinggeologic maps and county soil surveys to estimate that approximately65% of the state was covered with Pleistocene loess. According toWelch and Hale (1987), widespread loess deposits are not recognizedin east-central and southeastern Kansas, which includes the southerntwo-thirds of the Bluestem Hills MLRA.

On upland landscapes in east central Kansas, including the studyarea, buried paleosols with preserved A horizons are rare. It is muchmore common to find the modern soil superimposed (e.g.,welded)almost seamlessly onto the Bt horizon of one (or more than one)

Fig. 1. Location of Bluestem Hills Major Land Resource Area in Kansas, and example of the landscape and vegetation of the study area.

509D.R. Presley et al. / Geoderma 154 (2010) 508–517

paleosol. Also, it is common to see a dark red soil that is located abovebedrock, and beneath the upper material (loess). This red paleosolsharply contacts interbedded Permian limestones and shales, and iscommonly regarded by soil scientists as being derived mostly fromresiduum from these bedrock members. The soil matrix is often darkred in color with hues of 5YR or 7.5YR (or redder) and values andchromas of 4 or less. This material is very clayey and dense, withstrongly expressed structure, thick clay films, and rock fragments thatmay or may not be similar to the underlying bedrock. Many soilscientists agree that this is a paleosol, but differ in opinions as to theparent material and age of the paleosol and/or sediments.

We hypothesize that although the upland soils of east central Kansaslack buriedAhorizons that are preserved, they are polygenetic and often

contain two paleosols. In addition, these upland soils occur on hillslopelocations across the landscape and can be recognized by subtledifferences in morphology as well as differences in mineralogicalcomposition. Therefore, the objective of this study was to usemorphology aswell as laboratory characterization includingmineralogyto identify the stratigraphy and features of soil development withinpolygenetic soil profiles that are mapped on hillslopes. The secondaryobjectives were to confirm field observations of paleosols and subtledifferences noticed between paleosols, which are often difficult todistinguish in thin loess-derived soils due toweldingof the thin units viapedogenesis (Jacobs and Mason, 2007; Johnson et al., 2007), and torelate these thin, predominately loess-derived soils to the current bodyof knowledge on Great Plains loess and paleosol sequences.

510 D.R. Presley et al. / Geoderma 154 (2010) 508–517

2. Site and methods

2.1. Geographic setting and site location

The study area is located in the lower Cottonwood River watershedin the Bluestem Hills Major Land Resource Area in eastern ChaseCounty, Kansas (Fig. 1). Land use for all sampled pedons is eithernative range or land that is in hay pastures. In this physiographicregion, the shallow nature of the soil profiles makes it unsuitable forcultivation. However, some land was cultivated for a brief periodduring the mid twentieth century and then planted to grass for hayproduction. Sampling locations A, B, and C were in native rangepastures, and D was in a formerly cultivated hay pasture. Predominantvegetation types are listed in Table 1. Annual precipitation is 785 to965 mm (USDA-NRCS, 2006).

2.2. Field description and sampling

Nineteen soil pedons were sampled from four hillslope positions.All pedons were described using the Field Book for Describing andSampling Soils (Schoeneberger et al., 2002). Five representativepedons (i.e., representative of the soils mapped on these hillslopepositions) were selected for laboratory characterization, isotopicanalysis, and numerical dating. Bulk samples were collected fromthe horizons of all selected pedons for laboratory characterization andthick horizons (N20 cm) were split and sub-sampled. Four of thesepedons were chosen for mineralogical analysis. From these fourpedons, three horizons (per pedon) were selected for clay miner-alogical analysis using X-ray diffraction spectrometry.

2.3. Laboratory characterization

Air-dry bulk samples were crushed with a wooden rolling pin andpassed through a No.10 sievewith 2mm square openings. Soil pHwasdetermined in a 1:1 soil/water suspension using method 8C1F of theSoil Survey Laboratory Staff (1996). Total carbon (TOC) wasdetermined using a high-frequency induction furnace (Leco ModelCNS-2000, St. Joseph, MI) following the procedure of Tabatabai andBremner (1970). Particle size distribution was determined using amodification of the pipet method of Kilmer and Alexander (1949) andmethod 3A1 from the Soil Survey Laboratory Method Manual (1996).Organic matter was removed from samples with 30% hydrogenperoxide. Cation exchange capacity (CEC) and base saturation % weredetermined by summing the NH4OAc extractable bases and the BaCl2-TEA extractable acidity (method 5A3a of the Soil Survey LaboratoryStaff (1996). Exchangeable sodium percentage (ESP) was determinedby dividing the exchangeable sodium by the sum of cations CEC.

2.4. Mineralogy

Total silt and clay mineralogy was analyzed following the methodsof Jackson (1975). Samples were pretreated with 1 M NaOAc and 30%H2O2 to remove carbonates and organic matter, respectively. Silt andclaywere fractioned through at least eight sedimentation periods. Fiveclay treatments were prepared: Mg 25 °C, Mg-ethylene glycolsolvation, K 25 °C, K 350 °C, and K 550 °C. Two milliliters of solution

Table 1Site characteristics of characterized pedons.

Pedon Elevation (m) Slope (%) Aspect Hillslope position Slope shapea Vegetation

A 382 2 225 Backslope LC AndropogonB 376 2 180 Backslope LL AndropogonC1 368 4 270 Backslope LL AndropogonC2 368 1 270 Shoulder LL AndropogonD 358 2 158 Footslope LC Bromus inerm

a LL — linear–linear, LC — linear–concave.

(containing 30 mg of clay) were pipetted onto a glass slide. A PhillipsXRG-3100 generator and an APD 3520 X-Ray diffractometer was usedto analyze all samples. The clay specimens were scanned from 2°2θ to34°2s for the Mg 25 °C treatment, and from 2°2θ to 15°2θ for the othertreatments. The silt samples were scanned from 18°2θ to 54°2θ usingpowder diffraction specimen holders. The d-spacing of each peak wasdetermined using the table on p. 224 of Jackson (1975), and the clayminerals were subsequently identified.

2.5. Numerical dating and stable isotope analysis

Five horizons (one per pedon) were selected for numerical datingof paleosols. Samples were analyzed by the Illinois Geological SurveyIsotope Geochemistry Laboratory. Samples were processed, purifiedand collected by cryogenic distillation for accelerator mass spectro-metry (AMS) 14C and δ13C analyses (Hong Wang, personal commu-nication). Stable carbon isotope values (‰) are reported relative to astandard reference material, the Peedee belemnite (PDB) standard(Faure, 1998).

3. Results and discussion

3.1. Soil characterization

Of the 19 pedons that were described, five were selected fordetailed investigation, one from each general sampling area (A, B, andD) and two pedons from site C (Fig. 1 and Table 1). A summary of fielddescriptions for the five characterized pedons is presented in Table 2.Physical and chemical characterization data are given in Table 3. Allpedons are arranged in order of the highest to the lowest elevation.

3.1.1. Morphology and stratigraphy: evidence for multiple stages ofpedogenesis

All pedons were sampled from upland landscape positionsdescribed as hillslopes primarily ranging from 1 to 2% slope, and upto 4% for pedon C1 (Table 1). Note that the hillslope designationreflects the microtopgraphy of the landscape, which is composed ofmany, complex slopes. Despite being located on upland hillslopes, thepedons exhibited morphological features indicative of stable land-forms. Table 2 contains information about the parent materialstratigraphy, horizonation, matrix color, and clay film morphology asdescribed in the field. At all of the sampling locations, a paleosol,which was welded to the modern soil, occurred at a depth ofapproximately 0.8 to 1 m. A second, more strongly expressed paleosolwas observed in all sampling locations deeper in the soil profile(Table 2), except for pedon D, where only one paleosol was recognizedin the field investigation.

Criteria for recognition of a paleosol included differences instructure, color, clay coating morphology, and field textures (Wangand Arnold, 1973). Moderate, medium, prismatic structure wascommonly observed in themodern soil, andmoderate fine or mediumsubangular blocky dominated both paleosols. The modern soil wasdescribed with 10YR mollic colors in the epipedon, and commonly as10YR4/3 in the lower portion. Hues of 7.5YR or 5YR were observed inthe paleosols, and the color of the residuum varied depending on thebedrock (commonly gray or green colors for non-calcareous shale, and

Taxonomic classification

gerardii, Sorghastrum nutans, Panicum virgatum Fine, smectitic, mesic Pachic Argiustollgerardii, Sorghastrum nutans, Panicum virgatum Fine, smectitic, mesic Pachic Argiustollgerardii, Sorghastrum nutans, Panicum virgatum Fine, smectitic, mesic Pachic Paleustollgerardii, Sorghastrum nutans, Panicum virgatum Fine, smectitic, mesic Pachic Argiustollis Fine, smectitic, mesic Typic Argiustolls

Table 2Selected field morphological properties of characterized pedons.

Soil horizon Depth (cm) Matrix colora Structureb Stickinessc Plasticityd Ped surface featurese Concentrationsf % N2 mm

Pedon AA1 0–14 10YR2/1 1 f sbk ms mpA2 14–22 10YR2/2 2 f sbk vs vpBt1 22–55 10YR3/2 2 m pr vs vp 5 f dBt2 55–71 10YR3/3 2 m pr vs vp 5 f dBt3 71–89 10YR4/3 2 m pr vs vp 2 f d 1Btk1 89–116 7.5YR4/4 2 m pr vs vp 1 f d 2 m can 12Btk2 116–143 7.5YR3/3 2 f sbk vs vp 10 f d 1 f cam 13Bt1 143–169 5YR3/3 2 f sbk ms ms 25 f c 13Bt2 169–180 10YR5/4 1 f sbk ms mp 54Cr 180–200+ Weathered calcareous shale

Pedon BA 0–7 10YR2/1 1 f sbk ss spBA 7–14 10YR2/1 2 f sbk ms mpBt1 14–35 10YR3/2 2 m pr vs vp 5 f pBt2 35–51 10YR3/3 2 m pr vs vp 5 f pBtk 51–73 10YR4/3 2 m sbk vs vp 5 f p 20 f canBt1’ 73–83 10YR4/3 2 m sbk vs vp 5 f p2Bt2 83–99 7.5YR4/3 2 m sbk vs vp 25 f c 23Bt3 99–138 7.5YR3/3 2 m sbk ms mp 50 f c –

4Cr 138–143+ 10YR5/4 Weathered non-calcareous shale

Pedon C1A 0–20 10YR2/1 1 f sbk ss spBt1 20–33 10YR2/2 2 m pr vs vp 5 f dBt2 33–52 10YR3/2 2 m pr vs vp 5 f d 1Bt3 52–69 10YR3/4 2 m pr vs vp 5 f d 2Btky 69–108 10YR4/3 2 m pr vs vp 10 f d 2 f can 5

2 f gym2Bt 108–148 7.5YR3/3 2 m sbk vs vp 25 f c 23CB 148–167 2.5YR5/3 1 m sbk ms mp 80

7.5YR3/33C 167–189 5Y5/2 0 ma ms mp 804Cr 189–207+ 5Y5/2 Weathered non-calcareous shale

Pedon C2A 0–19 10YR2/1 1 f sbk ss sp 1Bt1 19–30 10YR2/1 2 f sbk vs vp 5 f d 1Bt2 30–57 10YR2/2 2 m pr vs vp 5 f d 1Bt3 57–72 10YR3/4 2 m pr vs vp 5 f d 1Btk 72–92 7.5YR4/3 2 m pr vs vp 5 f d 2 m can 12Btky 92–126 7.5YR3/3 2 m pr vs vp 10 f d 1 f can 5

1 f gym3Bt1 126–175 7.5YR3/2 2 f sbk ms mp 25 f c 53Bt2 175–222 7.5YR2.5/2 2 f sbk ms mp 50 f c 54C 222–237 5Y5/2 0 ma vs vp 505Cr 237–250+ 10YR5/6 Weathered limestone

Pedon DA 0–17 10YR2/1 2 f gr ss spBA 17–26 10YR2/2 2 f sbk ms mpBt1 26–41 10YR3/2 2 m sbk vs vp 20 f dBt2 41–55 10YR4/2 2 f pr vs vp 10 f dBt3 55–77 10YR4/3 2 m pr vs vp 8 f d 1Bt4 77–100 10YR4/3 2 f pr vs vp 2 f p 12Btg1 100–165 2.5Y5/2 2 m pr vs vp 10 f d 22Btg2 165–200 2.5Y5/2 2 m pr vs vp 5 f d 22Btg3 200–206+ 2.5Y6/2 2 m pr vs vp 5 f d 10

a Moist color of broken ped faces.b Grade — size-type.c ss — slightly sticky, ms — moderately sticky, vs — very sticky.d sp — slightly plastic, mp — moderately plastic, vp — very plastic.e Abundance (%), contrast, continuity.f Abundance (%), size, type, can — carbonate nodules, cam — carbonate masses, gym — gypsum masses.

511D.R. Presley et al. / Geoderma 154 (2010) 508–517

tan for limestone or calcareous shale). Clay coatings were lessabundant and either patchy or discontinuous in the modern soil,and more abundant and continuous, coating all faces of peds in thepaleosols.

An exception to these trends, namely the color criteria, occurred inpedon D. At a depth of 100 cm, a color transition from 10YR4/3 to2.5Y5/2 occurred quite abruptly in pedon D, along with an increase in

the clay content. This transition was interpreted as a change instratigraphy, with the gray color resulting from iron depletion. Manygray, non-calcareous shales occur in this area, but abundant reddish-colored redoximorphic concentrations were also observed. Therefore,the “g” subscript was added to the horizon nomenclature. Clay filmswere present on ped faces, so the horizons were designated with 2Btgnotation. Since no additional changes in stratigraphy were observed

Table 3Selected physical and chemical properties of characterized pedons.

Soilhorizonsa

Depth(cm)

Sand(%)

Silt(%)

Clay(%)

FC:TCb

pH TOC(%)c

BS(%)d

ESP(%)e

Pedon AA1 0–14 3.5 71.1 25.4 0.62 5.8 2.47 81.3 2.1A2 14–22 3.1 58.7 38.2 0.65 6.4 1.43 92.9 5.7Bt1 22–40 1.7 49.4 48.9 0.68 7.0 1.13 85.8 5.6Bt1 40–55 1.2 53.3 45.5 0.65 7.3 0.98 92.2 7.2Bt2 55–71 1.5 53.4 45.1 0.67 7.6 0.78 89.9 8.1Bt3 71–89 2.4 56.7 40.9 0.62 7.3 0.45 92.0 8.0Btk1 89–116 3.4 56.7 39.9 0.58 7.7 0.32 85.8 7.82Btk2 116–143 4.2 52.6 43.2 0.60 6.8 0.37 83.8 8.23Bt1 143–169 4.5 37.5 58.0 0.72 7.4 0.43 86.8 8.33Bt2 169–180 2.1 44.8 53.1 0.60 nd nd nd nd4Cr 180–200+ nd nd nd nd nd nd nd nd

Pedon BA 0–7 2.8 67.2 30.0 0.67 7.7 4.78 68.1 0.9BA 7–14 2.3 589 38.8 0.73 7.8 2.13 64.6 1.6Bt1 14–35 1.8 53.2 45.0 0.68 7.1 1.34 82.6 3.9Bt2 35–51 2.2 54.5 43.3 0.66 7.6 1.08 85.3 7.0Btk 51–73 3.3 53.3 43.4 0.67 7.8 0.86 81.0 7.6Bt1’ 73–83 2.8 51.7 45.5 0.69 nd 0.52 92.8 10.52Bt2 83–99 2.2 50.2 47.6 0.67 7.4 0.39 87.0 11.53Bt3 99–138 2.0 49.4 48.6 0.72 7.3 0.49 82.2 10.74Cr 138–143+ nd nd nd nd nd nd nd nd

Pedon C1A 0–20 3.0 73.6 23.4 0.56 6.4 2.05 59.2 2.5Bt1 20–33 3.1 53.7 43.2 0.66 6.7 1.35 67.2 4.2Bt2 33–52 2.8 52.1 45.1 0.62 7.2 1.15 82.8 5.9Bt3 52–69 2.7 53.0 44.3 0.61 nd 0.81 86.1 7.3Btky 69–90 3.8 54.0 42.2 0.63 nd 0.40 93.9 8.4Btky 90–108 3.5 50.2 46.3 0.66 7.7 0.28 75.5 7.02Bt 108–130 3.4 46.2 50.4 0.68 7.5 0.28 86.5 7.62Bt 130–148 2.6 47.0 50.4 0.65 7.4 0.18 78.4 6.73CB 148–167 0.9 58.7 40.4 0.55 7.9 0.10 71.2 6.03C 167–189 0.3 57.6 42.1 0.45 7.9 0.13 88.2 6.74Cr 189–207+ nd nd nd nd nd nd nd nd

Pedon C2A 0–19 4.0 65.4 30.6 nd 5.9 2.30 nd ndBt1 19–30 2.9 56.5 40.6 nd 6.2 1.32 nd ndBt2 30–46 2.8 55.4 41.8 nd 6.9 1.07 nd ndBt2 46–57 2.6 56.0 41.3 nd 7.5 0.88 nd ndBt3 57–72 nd nd nd nd nd nd nd ndBtk 72–92 3.2 56.8 40.0 nd 7.6 0.57 nd nd2Btky 92–126 2.5 56.9 40.6 nd 7.4 0.38 nd nd3Bt1 126–154 2.6 51.6 45.7 nd 7.6 0.45 nd nd3Bt1 154–175 nd nd nd nd nd nd nd nd3Bt2 175–222+ 2.0 51.3 46.7 nd 8.2 0.37 nd nd

Pedon DA 0–17 5.5 68.3 26.2 0.50 5.9 2.50 64.7 0.0BA 17–26 4.7 60.9 34.4 0.63 nd 1.61 62.2 0.5Bt1 26–41 3.6 55.2 41.9 0.69 5.7 1.10 73.2 1.5Bt2 41–55 4.8 55.7 39.5 0.71 5.7 0.77 77.9 2.4Bt3 55–77 5.3 58.4 36.3 0.71 6.8 0.54 82.8 4.1Bt4 77–100 5.7 54.9 39.4 0.72 7.4 0.28 90.3 7.22Btg1 100–130 3.5 39.4 57.1 0.82 7.6 0.22 93.0 9.72Btg1 130–165 4.6 45.4 50.0 0.80 7.8 0.10 94.2 11.22Btg2 165–200 6.4 50.0 43.6 0.76 7.7 0.06 95.6 11.82Btg3 200–206+ 7.8 52.3 39.9 0.75 nd 0.05 90.5 10.6

a Thick horizons (N≈40 cm) were split for chemical and physical analyses.b FC:TC — fine clay:total clay.c TOC — total organic carbon.d BS — base saturation.e ESP — exchangeable sodium percentage.

Fig. 2. Image of Pedon B, sampled using a hydraulic soil probe. All pedons were sampledfrom native, grazed pastures. A radiocarbon date of 24,490±120 14C yr BP, and a δ13Cvalue of −16.9‰ was obtained for the 3Bt3 horizon (99–143 cm).

512 D.R. Presley et al. / Geoderma 154 (2010) 508–517

within the sampling depth (206 cm), the presence of only onepaleosol was recognized in pedon D. It was debated whether this sitewas an upland footslope of the Bluestem Hills, or a paleoterrace of thepresent-day Cottonwood River.

Due to the silty textures and lack of coarse (N2mm) fragments, theupper portion of all pedons was called loess (Table 1). A few coarsefragments ranging from 2 to 10 mm-diameter were present in the

paleosol horizons. However, the field textures were described as siltyclay loam or clay, so the parentmaterial was termed reworked loess. Inpedons A, B, and C2 the stratigraphy was interpreted as follows: loessover reworked loess (upper paleosol), over reworked loess (lowerpaleosol), over residuum weathered from limestone and shale(example shown in Fig. 2). Pedon C1 was thought to contain loessover reworked loess (upper paleosol), over two units of residuum.Pedon D was described with loess over reworked loess (paleosol) to adepth of over two meters. Between 83 cm (pedon B) and 116 cm(pedon D) of loess was described on the upland positions, and 142 cmof loess was described on the lowest hillslope position examined inthis study (pedon D).

3.1.2. Physical and chemical properties

3.1.2.1. Particle size analysis. Despite having differences in thicknessof the solum, and individual parent materials, all of the pedons have asimilar distribution of the clay content with depth (Table 3). All of thepedons had two clay maxima, one at a depth of approximately 25–50 cm, and onemuch deeper in the profile (N1m). Pedons A, B, C1, andC2 contained less than 5% sand in the profile, and the sand content ofpedon D was not greater than 8%. The particle size distribution of allhorizons sampledwas bi-modal (Fig. 3) with large quantities of coarsesilt (50 to 20 µm), to medium silt (20 to 5 µm) and clay (b2 µm).Mason et al. (2003) found problems with using mean particle size forwind strength when they observed sedimentary aggregates in Chorizons of Peoria loess in Nebraska. In thin section, non-pedogenicclay coatings were present on silt and sand grains. Aggregates werealso visible in thin section. Muhs et al. (1999) observed bi-modaldistributions in studies of clayey loess in eastern Colorado, with peaksin the 20–30 µm range, and in the b4 µm clay-size fraction, andattributed this to either a local, clayey source such as the Pierre shale,or silt-sized clay aggregates (Muhs et al., 1999).

In pedon A, the particle size distribution of the Bt1 (40–55 cm,modern soil) was very similar to the distribution of the 2Btk2 horizon(116–143 cm, upper paleosol). The 3Bt2 horizon (169–180 cm, lowerpaleosol) had a lower coarse silt % and higher coarse and fine clay %, aswell as a higher fine clay to total clay ratio, FC:TC (Table 3). Due to thepreviously mentioned differences in morphology, and particle sizedistribution, two paleosols were described in pedon A.

Fig. 3. Stratigraphy, 14C dating, and δ13C values.

513D.R. Presley et al. / Geoderma 154 (2010) 508–517

In pedon B, the particle size distribution of the Bt2 horizon of themodern soil (35–51 cm) was different than the distribution of the twopaleosol horizons (2Bt2 and 3Bt3), which were similar to each other(83–99 and 99–138 cm, respectively). Despite having differences inthe abundance of clay films (25% in the 2Bt2 horizon, and 50% in the3Bt3 horizon), the particle size distribution does not support theconcept of two paleosols in pedon B. The abundance of clay films, aswell as the FC:TC is greater for the 3Bt3 horizon. Therefore, it ispossible that the two horizons may actually be different horizons ofthe same paleosol, and thus this shallow pedon (138 cm to residuum)might only contain one paleosol.

Both pedons C1 and D have particle size distributions that appearto be unique for each of the three horizons analyzed. In pedon C1, themodern soil (Bt2, 33–52 cm) and upper paleosol (2Bt, 108–130 cm)contain large quantities of coarse silt and fine clay, while the 3CBhorizon (148–167 cm) contains an abundance of fine silt and arelatively lower quantity of fine clay. However, these data support thehorizon nomenclature of all three horizons sampled from the C1pedon. The FC:TC for the argillic horizons were 0.62 and 0.68 for theBt2 and 2Bt horizons, respectively (Table 3), and they were bothdescribed in the field as containing 5% and 25% clay coatings (Table 2).The 3CB horizon lacked clay coatings and had a FC:TC of 0.55. Pedon Dhas the most differences between the three selected horizons. The Bt2horizon of the modern soil (41–55 cm) contains the most coarse siltand the least fine clay, the upper part of the paleosol (upper portion of2Btg1, 100–130 cm) is intermediate, and the lower part of the paleosol(2Btg2, 165–200) contains the least coarse silt and a great deal morefine clay than the other horizons. Therefore, despite the similarity infield described properties, particle size data differs for the twopaleosol horizons.

3.1.2.2. Chemical properties. Selected characterization data forchemical properties are shown in Table 3. Surface horizons of pedonsA, C1, C2 and D were similar with pH values ranging from 5.8 to 6.4and total carbon (TC) values between 2 to 2.5%. Pedon B had a highersurface horizon pH (7.7), which might be attributed to its shallowerdepth, both overall (138 cm to residuum) and for the modern soil inparticular (83 cm). Pedon B also contained greater TC (4.78%).However, this value is extremely high for eastern Kansas, so oneexplanation might be that some surface litter was mixed with thepedon B surface sample prior to TC analysis, or another possibility isthat this pedon was actually less eroded than the other pedons in thestudy. Total C values decrease regularly with depth in all pedons,

increasing slightly in the lower paleosols of pedons A, B, and C1. Aspreviously mentioned, no distinct, former surface horizons arepreserved in these soils. Rather, it is thought that the paleosols weretruncated and later became welded to the modern soil profile. Inprevious studies, Wehmueller (1996), Glaze (1998), and Gunal andRansom (2006) observed clay coatings that superimposed carbonatefeatures in thin sections as well as higher FC:TC in paleosols, indicativeof clay illuviation from the modern soil into the paleosol horizons.

The exchangeable sodium % (ESP) values of all five pedons rangedfrom 0 to 2.5% in the surface horizons, and increase with depth. Quiteoften, values are greater for shallower pedons, such as pedon B. Glaze(1998) concluded that Permian sedimentary bedrock was the likelysource for the elevated Na+, and Presley (2007) hypothesized thatparticles of local dust weathered from these Permian rocks may havebeen incorporated during deposition of the loess and/or withcolluviation in the late Quaternary period.

3.2. Mineralogy

3.2.1. Identification and distribution of silt and clay mineralsThe total silt fractions of all horizons were dominated by quartz,

and contained lesser amounts of plagioclase and K-feldspars (Table 4).Calcitewas observed in the silt fraction of three samples, though not inany horizons described in the field as containing carbonate nodules ormasses. Gypsum was not observed in any silt or clay despite beingobserved in the field at a depth of 92–126 cm in Pedon C2.

Total clay mineralogy is displayed in Fig. 4 for the Mg-25 and Mg-EG treatments. Additional treatments including K-25, K-350, K-550,and Mg-glycerol solvated were analyzed. These data are not shown,but the results are available in Presley (2007).

One of the greatest and most consistent within-profile differencesis that in pedons A, B, and C2, the modern soil contains greaterquantities of smectite and only trace amounts of vermiculite, whilethe upper and lower paleosol horizons analyzed contained approxi-mately equal abundances of smectite and vermiculite (Fig. 4). Incontrast, pedon D is the opposite as the modern soil containsconsiderably less smectite when compared with the paleosolhorizons. Clay mica or illite content varies both within pedons, andbetween all pedons. In pedon A, illite is most abundant in the paleosolhorizons, constituting approximately 30% of the total clay fraction. Theillite content is generally greater for pedon A than B for all horizons.Pedon C2, however, contains a large quantity of illite in all horizons,but like pedon A, the illite content increases with depth, and in nearly

Table 4Semi-quantitative mineralogy for total silt fraction (2000–50 µm).

Horizon Depth(cm)

Quartz Plagioclasefeldspars

Potassiumfeldspars

Calcite

Pedon ABt1 40–55 XXXa X X nd2Btk2 116–143 XXX X X nd3Bt2 169–180 XXX X nd XX

Pedon BBt2 35–51 XXX X X nd2Bt2 83–99 XXX X X X3Bt3 99–138 XXX X X nd

Pedon C2Bt2 46–57 XXX X X X2Btky 92–126 XXX X X nd3Bt2 175–222 XXX X nd

Pedon DBt2 41–55 XXX X X nd2Btg1 (upper) 100–130 XXX X X nd2Btg2 165–200 XXX XX nd nd

a Rating systemused is nd=none detected, X= trace, XX=5–10%, and XXX=N75%.

514 D.R. Presley et al. / Geoderma 154 (2010) 508–517

identical quantities for both paleosols. Like pedon B, pedon D containsa relatively low abundance of illite for all samples (Fig. 5).

In pedons A, B, and D, the kaolinite content appears constant withdepth in the horizons analyzed, and the total abundance is estimatedto be approximately 10% in all horizons of these pedons. The kaolinitecontent of pedon C2 appears to vary slightly with depth, with largerquantities present in the modern soil (Bt2, 30–57 cm) and upperpaleosol (2Btky, 92–126 cm) horizons, and slightly lower abundance

Fig. 4. Particle size distribut

in the lower paleosol (3Bt2, 175–222 cm). The kaolinite content of the3Bt2 horizon of pedon C2 is similar to that of the other horizonsanalyzed from pedons A, B, and D.

In field descriptions, the clay content of the paleosols of pedons A,B, and C2 was estimated to decrease by 8 to 10% relative to theoverlying modern soil, and to decrease in stickiness and plasticity.However, particle size determination indicated that the clay contentwas greater for the paleosols. The likely explanation for these threepedons, sampled in this study area, is the change in mineralogy class.The modern soil of pedons A, B, and C2 is dominated by smectite, andthe paleosols exhibit a more mixed mineralogy. Therefore, in additionto changes in color, clay filmmorphology, and structure, stickiness andplasticity differences may potentially be utilized to differentiatepaleosols from modern soils in field investigations. However, thesedifferences must be evaluated with subsequent laboratory analyses toverify the field observations.

3.2.2. Possible origin of clay minerals and explanations for differencesbetween modern soil, paleosols, and across hillslope positions

Possible explanations for differences in clay mineralogy, bothwithin and between profiles, include neo-formation of clay minerals(Allen and Hajek, 1989), additions from dust fall, sequential weath-ering of clay minerals, or inheritance from parent materials. The neo-formation hypothesis is rejected due to the high pH, abundant bases,andwell-drained conditions present in themodern soils and paleosolsalike of pedon A, B, and C2. High Si, Al, Mg, and restricted drainage arerequired for neo-formation (Borchardt, 1989), therefore, this is apotential explanation for the increased smectite content of bothpaleosols of pedonD (Fig. 4), sampled at the lowest elevation (Table 1),in a topographically lower landscape position, and containing gleyedmatrix horizons (Table 2). However, the pHof the paleosols exceeds 7.6

ion of selected pedons.

Fig. 5. X-ray diffractograms of the clay (b2 µm) fraction from 2° to 34° 2Θ for Mg saturated samples (lower set of spectra) and 2° to 15° 2Θ for Mg saturated and ethylene glycolsolvated samples (upper set of spectra).

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(Table 3), so the neo-formation hypothesis does not adequatelyexplain the high smectite content in the paleosols of pedon D.

Concerning dust deposition as a possible explanation, Twiss (1983)observedmodern dust deposition in Kansas. Roberts et al. (2003) usedoptically stimulated luminescence (OSL) dating and found that massaccumulation rates of dust (loess) were extremely high at certaintimes in the late Pleistocene in Nebraska. It seems likely that much ofthe same material was probably available as a source to the BluestemHills of Kansas. However, if dust deposition was the explanation, themodern soils would be expected to be relatively enriched in primaryminerals such as feldspars and illite as compared with the paleosols,since the modern soils are constantly receiving inputs yet today. Thus,dust accumulation does not adequately explain differences withinpedons.

If sequential weathering was the explanation, according to thestability sequence of Jackson et al. (1952), horizons of soils withrelatively high illite content would be relatively less weathered thansoils that contain large quantities of smectite. In addition, the kaolinitecontent is nearly uniformwith depth and between profiles, and mightbe expected to increase in the more weathered, mature soil horizons.Therefore, the sequential weathering hypothesis is not supported forthe soils of this study since there is no evidence for the weathering ofillite to vermiculite or smectite and because the kaolinite content isrelatively uniform with depth.

Therefore, the simplest andmost likely explanation is that many ofthe features of pedons sampled across hillslope positions in eastcentral Kansasmay be attributed to inheritance from parent materials,namely late Quaternary loess and reworked loess. In a study of loess

deposits of Kansas, Gunal and Ransom (2006) observed smectite in Chorizons, and it was similar in abundance to the overlying soil andpaleosol. Therefore, the authors reasoned that the smectite was likelyinherited from the parent material (Peoria loess).

The horizons in this study that contain large quantities of illite (thepaleosols) contain more evidence of pedogenesis (stronger illuvialclay film morphology and larger FC:TC) than those with lower illiteand higher smectite content (the modern soils). Although it seemscontradictory to have the most evidence of illuviation in the horizons(paleosols) that contained the least weathered suite of minerals, thatis what our data shows. Therefore, the hypothesis of inheritance fromthe parent materials was selected for the well-drained Pedons A, B,and C2. These trends were not applicable for pedon D, which occurredat the lowest elevation, and contained a gleyed paleosol that wasenriched in smectite and fine clay relative to themodern soil. The neo-formation hypothesis is also rejected due the pH values in excess of7.6, so the most likely explanation selected to account for differencesbetween the modern soil and paleosols of pedon D is also inheritancefrom parent materials.

3.3. Paleosols, radiocarbon dates, and δ13C values

Due to the sampling locations, complexity of the landscape, andthus, potential mixing of parent materials, the use of either radio-carbon dating or luminescence methods might not seem appropriatefor two reasons. First, well-preserved A horizons do not exist in thesewelded soils, and because they are welded, overprinting with organicmatter, roots, etc. is highly probable. Second, luminescence methods,

516 D.R. Presley et al. / Geoderma 154 (2010) 508–517

commonly used in loess stratigraphy projects, are probably inap-propriate because of potential colluviation and pedoturbation. Inaddition, welding may have translocated clay and silt betweenstratigraphic units, further making luminescence methods inap-propriate in this study of polygenetic soils. Nonetheless, in a studyof paleosols, the question is often raised, what are the ages of thesesoils? When were they formed, and when was the new, overlyingmaterial deposited? Hence, radiocarbon dating of a selected set ofsamples (five) was done to satisfy curiosity, and is presented here asevidence in support of our hypothesis and other morphological andmineralogical data, i.e., that these soils formed during multiple phasesof pedogenesis. One sample was sent from each of the five pedonsdiscussed in the preceding sections.

3.3.1. 14C values for paleosolsIn pedon A, soil organic matter from a portion of the 3Bt1 horizon

(143 to 152 cm only) of the older and deeper paleosol was radiocarbondated (Fig. 3). From pedon B, the older paleosol (3Bt3) was also dated,from a depth of 99 to 138 cm. A portion of the older paleosol was alsodated from pedon C2 (3Bt2, 154–175 cm only). The dates obtainedwere as follows: 27,700±240 uncalibrated 14C yr BP for pedon C2; 24,490±120 for pedon B; and 22,490±90 for pedon A.

The upper paleosol was dated from pedons C1 and D. From pedonC1, the material dated was from the 2Bt horizon (108 to 148 cm).From pedon D, the material dated was from a portion of the 2Btg1horizon (from 100–130 cm only). The age of the younger paleosol was20,140±70 14C yr BP in pedon C1, and 19,030±60 14C yr BP in pedonD. Although the upper and lower paleosol horizons were not datedfrom the same pedons, it is encouraging that the upper paleosolconsistently returned younger dates than the lower paleosol. There-fore, it appears that both the morphology and radiocarbon ages ofpaleosols are reasonably consistent across the range of selectedhillslope landscape positions in the study area. Published age-rangesfor the Gilman Canyon Formation, based on radiocarbon and OSLdating, are as follows: 40,000 to 24,000 yr B.P. (Bettis et al., 2003),50,000 to 30,000 yr BP (Busacca et al., 2004), 36,000 to 22,000 (Muhset al., 1999), and 36,000 to 30,000 (Maat and Johnson, 1996).Karlstrom et al. (2008) recently published AMS radiocarbon dates of30,300 to 22,400 for soils developed in the Gilman Canyon Formation(loess) sampled in Kansas, from a complete late Quaternary loess-paleosol section approximately 100 km to the northwest of the studyarea. Mandel and Bettis (2001, 2003) observed a deposit that wassimilar in age and properties to the Gilman Canyon Formation loess invalleys and older footslopes in northeast Kansas and named thesecolluvial and alluvial facies the Severance Formation. Radiocarbonages of the Severance Formation range from 25,000 to 15,000 (Mandeland Bettis, 2003). Note that in the studies by Mandel and Bettis, theirprofiles contained well-preserved A horizons, making the use ofradiocarbon dating much more feasible and appropriate.

The uncalibrated 14C dates range from 27,700 to 22,490 yr BP forthe lower paleosol. These dates reflect a time when the paleosol waslikely buried by youngermaterial, i.e., the sediments that comprise theupper paleosol. (Thermoluminescence dating would be the besttechnique to estimate the time frame in which the sediments weredeposited). The upper paleosol, therefore, was likely buried byyounger sediments between approximately 20,140 to 19,030 (orpotentially younger). Due to the level of development and thenumerical ages, the lower paleosol could have either formed inLoveland loess and thus represent the Sangamon paleosol, or it couldhave formed in hillslope sediments of the Severance Formation, e.g.,reworked Gilman Canyon Formation loess. The upper, less developedpaleosol may have also formed in a younger unit of SeveranceFormation sediment, i.e., reworked Gilman Canyon Formation loess,and the modern soil profile is likely formed in Peoria loess, a unit thatis mapped on the surface across about 65% of Kansas (Welch and Hale,1987).

3.3.2. δ13C values for paleosolsThe δ13C values were−16.8‰,−16.9‰, and−17.0‰ for the lower

paleosol of pedons A, B, and C2 respectively (Fig. 3). The δ13C valueswere−17.5‰ and−19.2‰ (PDB) for the upper paleosol of the C1 andD pedons, respectively. During photosynthesis, green plants discrimi-nate in favor of the 12C isotope, and thus are depleted in 13C relative tothe atmosphere (Bender, 1970). Plants that follow the C3 pathway ofphotosynthesis (cool season grasses and trees) are more depleted in13C, and have values of δ13C that range from −23 and 34‰, with amean of −27‰ (PDB). Plants that follow the C4 photosyntheticpathway (warm season grasses) discriminate less against 13CO2 thanC3 plants, and thus are relatively less depleted than C3 plants, e.g., C4

plants have values of δ13C ranging from −6 to 23‰, with a meanof−13‰ (PDB) (O'Leary, 1981). Generally, C3 vegetation is associatedwith trees, forbs, and cool season-grasses common to cooler climates,while C4 vegetation is generally found in warm, semiarid environ-ments with high light intensity, such as grasslands and deserts.Studies have shown that both the proportion of C4 species and theproportion of C4 biomass in a given plant community are stronglyrelated to environmental temperature (Terri and Stowe, 1976; Tieszenet al., 1979; Boutton et al., 1980). Both paleosols have δ13C values thatare indicative of mixed C3–C4 vegetation, although the three values forthe lower, older paleosol are both very similar and closer to a moredominant C4 type vegetation. Relative to each other, these vegetationproxies suggest a slightly warmer and possibly drier climate waspresent between 27,700 and 22,000 yr BP (and thus similar to thepresent-day climate), and a relatively cooler and possibly more moistclimate was present 20,000 to 19,000 yr BP. Mandel (2006) reportedδ13C values of −15.5 and −15.9‰ for Severance Formation samplesdating to 22,620±340 and 24,560±350 14C yr BP at a location inChase County, Kansas (Mandel, 2006).

3.3.3. Relationships between mineralogy, paleosols, radiocarbon dates,and δ13C values

In the previous section, 14C values and δ13C values were differentfor the upper and lower paleosols sampled on different hillslopepositions. Therefore, although these soils were not sampled fromstable, summit landscape positions, they proved to contain a record ofpedogenesis from the late Quaternary geologic period in a geographicregion that is largely ignored by loess researchers (Fig. 1). Despitedifferences in ages and potential differences in climate, no majordifferences between the clay mineralogy of paleosols are apparent.Rather, the mineralogy of the paleosols and the younger, modern soilprofile contrastedmorewith the paleosols, and pedons A, B, C1, and C2contrasted with pedon D, the topographically lowest pedon sampledin this study.

4. Summary and conclusions

Field investigations of thin, loess- and reworked-loess-derivedsoils of east central Kansas revealed the potential presence of one ormore paleosols, characterized in the field as having lower claycontents than the overlying modern soil. Subsequent laboratorycharacterization revealed that the total clay content and FC:TC wereusually highest in the lowest paleosol horizons. The perceiveddecrease in clay content was actually caused by a change in claymineralogy. This trend can be exploited in future field descriptions inorder to more accurately distinguish between stratigraphic units inthese thin, welded polygenetic soils.

Polygenetic upland soils of east central Kansas have been formedthough multiple and likely different sets of soil forming factors. Thepresence of two buried paleosols that occur in regular, predictablelocations on the landscape is indicative of at least three periods ofparentmaterial deposition and soil formation. The age of the paleosolswas typical for the late Quaternary-aged Severance Formation,

517D.R. Presley et al. / Geoderma 154 (2010) 508–517

clustering in two age ranges, which were ≈19,000 to 20,000 and≈22,500 to 27,700 uncalibrated 14C yr BP.

Mineralogy of the modern upland soils tend to be dominated bysmectite, while paleosols had a more mixed mineralogy containingapproximately equal amounts of clay mica, vermiculite, smectite, andkaolinite. However, one pedon sampled on a long, linear-convexfootslope positionwas opposite in that themodern soil wasmixed andthe paleosols contained more than 50% smectite. Differences inmineralogy between the stratigraphic units were likely inherited fromthe parent materials. The high smectite content of the footslope pedonis likely from sequential weathering as the age is similar to the otherpedons. Although the stratigraphy appears similar, there could bedifferences in the source of the colluvium for the footslope pedon.

The results from this study illustrate that although they might bethin, truncated, and welded, late Quaternary-aged loess-derived soilsand paleosols occur in regular, predictable patterns on many uplandhillslopes in the Bluestem Hills Major Land Resource Area, and thisregion should be included in future regional investigations of GreatPlains loess.

Acknowledgements

Many thanks to the Kansas USDA-NRCS and three Chase County,Kansas landowners. Thank-you to Adam Sparks for the beautifulimage of the Bluestem Hills landscape.

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