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Extractable Fe and Al in late Pleistocene and Holocene paleosols on Niwot Ridge, Colorado Front Range
CATENA
vol. 15, p.17-26
Braunschweig 1988
EXTRACTABLE FE AND AL IN LATE PLEISTOCENE AND HOLOCENE PALEOSOLS ON NIWOT RIDGE, COLORADO FRONT RANGE W.C. M a h a n e y , N o r t h Y o r k O n t a r i o B.D. F a h e y , C h r i s t c h u r c h
SUMMARY Surface and buried paleosols on Niwot Ridge in the Front Range of Colorado were analyzed for extractable Fe and AI to determine if their distributions would assist in the interpretation of past and present soil-forming environments. Extractable Fe and AI distributions in surface and buried paleosols suggest that leaching is more pronounced in the older paleosols with a considerable difference in soil-forming environment between Pleistocene interstadial, later Pleistocene, and postglacial paleosols. Using radiocarbon dated buried A horizons it appears that little pyrophosphate-extractable Fe and A1 have been translocated downward into these middle-latitude alpine buried paleosols. There is no evidence that the Na-pyrophosphate extractable Fe and AI were affected by degradation of organic matter following burial; however, the data suggest that some amorphous Fe and AI ISSN 0341-8162 (~1988 by CATENAVERLAG, D-3302 Cremlingen-Destedt,W. Germany 0341-8162/88/5011851/US$ 2.00 + 0.25 CATENA
might have been affected by soil water movement over permafrost and by redistribution of preweathered sediments.
1
INTRODUCTION
As pointed out by DORMAAR & LUTWICK (1983), VALENTINE & DALRYMPLE (1976), and PAWLUK (1978), buried soils undergo transformations that cause changes in taxonomic parameters and make taxonomic placement difficult. Buried A and B horizons generally experience color changes, increases in bulk density, and degradation (often complete loss) of soil structure. Since extractable Fe and AI have been used to separate surface soils and place them taxonomically (BLUME & SCHWERTMANN 1969, LUTWlCK & DORMAAR 1973), we set out to determine whether a knowledge of extractable Fe and AI would prove useful in interpreting the genesis of surface and buried horizons in three generations of paleosols on Niwot Ridge in the Colorado Front Range (phot.1). Specifically, we sought to establish firstly, whether the three paleosol groups could be differentiated on
An Interdisciplinary Journal of SOIL SCIENCE H Y D R O L O G Y ~ E O M O R P H O L O G Y
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Mahaney & Fahey
the basis of extractable Fe and AI parameters; secondly, whether extractable Fe and AI data might be used to determine the amount of downward movement from surface horizons to buried units; and finally whether buried paleosols had been contaminated by leaching effects.
2
(middle to late Holocene) ( M A H A N E Y et al. 1984). The paleosols in this study are divided into three groups: Group 1 (buried paleosol in NR7), presumably formed during Pinedale (Wisconsinan, Wtirm) interstadial paleoclimate that may have been cool and moist relative to the present;
F I E L D AREA
N i w o t Ridge lies east of the Continental Divide, trending west to east between 3900 and 3400 m elevation. The alpine climate is cold and dry. Data from D1 station on Niwot Ridge (3750 m) in the study area (phot.1), gives a mean annual air temperature ofo3.3°C and an average annual precipitation of 648 mm (MARR 1967). The continental location is expressed by the low available moisture, cool summer, and high annual temperature range. Windy conditions are common; winds on Niwot Ridge average 8.5 m/sec, and gusts of greater than 50 m/sec are reached in winter months (BENEDICT 1968). The topography of the field site owes its character to the movement of valley glaciers that deepened the South Saint Vrain Drainage and the Green Lakes Valley which lie north and south of the field sites, respectively (phot.1). The origin of transported regolith (outlined in black on phot.1) in which turf- and stonebanked lobes and terraces formed, is attributed either to pre-Pleniglacial glacial activity or to mass wasting (personal communication, R.E MADOLE, 1975). The microrelief on the Ridge is the product of episodic gelifluction that appears to have occurred during a Pinedale interstadial period, near the end of the Pinedale Glaciation ( M A H A N E Y & FAHEY 1980), and during the Neoglacial
(AIkNA
Group 2 (NR2 through NR5 and NR7 ground paleosol) formed during the later Pleistocene near the end of the Pinedale Glaciation (first under a colder, drier paleoclimate and later a warmer and w e t t e r (variable) paleoclimate, e.g. BENEDICT, 1968; MADOLE, 1976; MAHANEY, 1974); Group 3 (NR6 and 8) formed during first a middle Holocene climate that may have been warmer and wetter (BENEDICT, 1968), and later under Neoglacial paleoclimates that are considered to have been highly variable but generally cold and dry.
3
METHODS
Soil descriptions follow the SOIL SURVEY STAFF (1951, 1975) and BIRKEL A N D (1984). Sites were selected on representative turf- and stone-banked terraces and lobes previously described by B E N E D I C T (1968). Our use of the term paleosol follows that of R U H E (1965) and includes both surface and buried profiles that formed under more than one paleoclimate. To prevent the dissolution of Fe and AI no acid pretreatment was used in this study. As pointed out by DORMAAR & L U T W I C K (1983) it is im-
An Interdisciplinary Journal ol SOIL SCIENCE
IIYDROLOQY (IEOMORPHOLOGY
Extractable Fe and AI, Pleistocene and Holocene Paleosols, Colorado
19
P h o t o 1 : Niwot Ridge in the Central Colorado Front Range, Western U.S.A. The view
is from the east towards D-I station where meteorological observations were made at 3750 m. Sites N R 2 - 8 are located at or near the crest o f the Ridge.
C A T E N A - - A n Interdisciplinary Journal o f S O I L S C I E N C E
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Mahaney & Fahey
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portant to ensure that pretreatment is uniform for all extractions. Extractable Fe and A1 were obtained from 5 g samples comprising material less than 2 mm with dithionite-citrate-bicarbonate (Fed + Aid) using procedures established by M E H R A & JACKSON (1960). Extraction with sodium dithionite removes finely disseminated hematite + goethite + amorphous Fe and AI + organicallycomplexed Fe and A1. Acid ammonium oxalate removes only amorphous Fe + A1, + organically-complexed Fe and A1, and sodium pyrophosphate is used to extract only organically-complexed Fe and AI (McKEAGUE & DAY 1966). Extractable cations Ca and Mg were analyzed using NHaOA,: as documented by PEECH (1947) and SCHOLLENBERGER & SIMON (1945). All extracts were analyzed in duplicate using an atomic absorption spectrophotometer; pH determinations were made by electrode using a 1:1 soil water ratio.
compared with the youngest group of paleosols (NR6 and 8). The pH distributions in these older profiles yield only slight increases with depth, but do not indicate any downward movement of H ÷ ions. Because the ratio of extractable Ca to Mg is higher in the surface horizons we considered that some airfalt influx or base recycling by plants might have occurred. The uniform ratios of Ca/Mg below the A horizons yield a trend similar to that documented in other paleosols at nearby sites (MAHANEY & FAHEY 1976, 1980), and indicate little if any downward movement in this older group of paleosols. The youngest paleosols (NR6 and 8 in Group 3) are found forming in turfand stone-banked lobes and terraces. The younger mid to late-Holocene age of these deposits was demonstrated previously by BENEDICT (1968) on the basis of topographic position and radiocarbon dates. These paleosols tentatively classify as Cryochrepts and Cryopsamments, have variable ages ranging 4 RESULTS AND from mid to late Holocene, and variDISCUSSION able profile relationships (fig.I). Profile NR6 is a multistorey unit consisting of The older groups (1 and 2) of paleosols an Entisol overlying an Inceptisol; soil (NR7 and NR2 through NR5) formed organic matter extracted from the A l b in turf-banked terraces during and near horizon in the latter was dated by radiothe end of the Pinedale Glaciation ( carbon at 5050+ 170 yr BP (Gak-8359). 10,000 yrs BP) (MAHANEY & FAHEY Chemical analysis of the NR6 profile 1980). While these paleosols vary some- shows a rather uniform pH distribution what in thickness (81 152 cm; fig.l), they with depth, and only a slight increase in cover fresh, undifferentiated sediments extractable Ca in the overlying surface that are perennially frozen and difficult soil. This suggests that base recycling by to sample. The paleosols described in plants may require considerable time to fig.1 (NR2-5 and 7) are all Inceptisols, build up residual Ca in surface horizons; tentatively identified as Cryochrepts. the uniform Ca/Mg ratio at depth sugThe paleosols comprising Groups 1 gests that leaching from the surface has and 2 yield profiles with greater hori- been minimal, and that little, if any geozon complexity, substantially thicker B biochemical contamination has occurred horizons, but with a similar chemistry lower down in the profile. ('AI ~ N A
A n Interdisciplinary Journal o t S O I L S C I E N C E
HYI)ROI,OGY
(;IOMORPHOIOGY
Extractable Fe and AI, Pleistocene and Holocene Paleosols, Colorado
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CATENA
Aa lnterdiaciplinaty Journal of SOIL SCIENCE HYDROLOGY GEOMORPHOLOGY
Mahaney & Fahey
22
Profile NR8 comprises two Entisols. Soil organic matter in the Ab horizon radiocarbon dates at 450 + 80 yr BP (GaK8358). The pH profile shows little variation with depth, suggesting only minor movement of H ~ ions. Little leaching is supported further by data for extractable Ca and Mg (Ca/Mg ratio) which is uniform downward into the Ab horizon. Therefore, we believe the radiocarbon dates on the whole-soil organic material in the buried paleosol horizons (profiles NR6 and 8) approximate the time of burial. This is substantiated further by the relatively low standard deviations on both radiocarbon age determinations. As shown in tab.l, there are only a few age-dependent trends among the three groups of paleosols. Organicallycomplexed Fe tends towards lower amounts in the lower horizons of profiles NR-5, which may reflect somewhat higher translocation effects in Group 2. The increase in Fep in the B2b and Cb horizons of profile NR7 (Group 1) suggests that this truncated buried profile either formed in a paleoclimate sufficiently different from today or over a longer interstadial (Pinedale = Wisconsinan) time period. The distributions for Feo (amorphous Fe), with some exceptions, show somewhat higher amounts in surface and subsurface horizons of the older profiles (NR2-5 and 7). While there is some variation in Fea between the parent materials (Cu horizons) in paleosol groups 2 and 3, there are in general higher amounts of crystalline Fe in the surface and subsurface horizons of Groups 1 and 2. The most noticeable increase occurs in the buried paleosol (NR7) where Fea increases nearly fourfold from the ground paleosol (Group 2) to the buried paleosol (Group 1). These differences reflect changes in extractable Fe observed in AIENA
other Rocky Mountain glacial sequences (MAHANEY 1974, MAHANEY & FAHEY 1976, 1980, MAHANEY et al. 1984). The data for extractable AI show fewer variations with only a slight tendency for AI to increase from the youngest to the oldest group of paleosols. The tendency for Alp, to increase in the buried A horizons, and in the surface A horizons, mirrors variations in Fe with depth, and reflects the complexing action of organic matter. The close similarity in values of Alo and Aid reflects the slow rate of conversion of Alo to Aid (relative to Fe where the differences are greater). The U.S. soil taxonomy (SOIL SURVEY STAFF 1975) uses extractable Fe and AI to identify certain B horizons in surface soils. In this study the distribution of both Fe and AI provide information on present and past soilforming environments. For example, in the lower solum of profile NR7 (Group 1) the higher values for Fep (the organically complexed and more mobile form of Fe) suggest greater movement downward relative to the B horizon in the Group 2 unit. In profile NR6, both surface and buried paleosols show little evidence for downward movement of Fe and AI, although overall amounts are sometimes higher than in the older profiles. The relative differences between the lower solum in NR7 (Group 1) and the Group 2 paleosols (NR2-7) plus Group 3 (NR6 and 8) possibly reflect the paleoclimatic differences during Pinedale interstadial time compared with later Pleistocene and postglacial time. Since these paleosols form largely over frozen substrates, fluctuating perched water tables might bring higher water levels and inundation of part of several,
An Interdisciplinary
Jourmd of SOIL S ( I E N ( ! [
HYDROLOGY
(JEOMORPHOLO(]Y
Extractable Fe and AI, Pleistocene and Holocene Paleosols, Colorado
Site
Horizon
Depth (cm)
Extractable Iron (%)
Fep
Fe o
Fe d
Alp
Alo
Aid
0.88 0.92 0.64 0.79
1.39 1.02 0.73 0.96
0.91 0.53 0.37 0.54
0.77 0.33 0.25 0.22
Extractable Aluminum (%)
23
Feo/Fea
Fee + A l e Fed + Aid
0.89 0.40 0.32 0.22
0.63 0.90 0.88 0.82
0.68 0.67 0.57 0.74
NR2
A1 Bt Clox C2ox
0-12 12-18 18-43 43-81
0.63 0.45 0.23 0.34
NR3
AI lIB1 IIB2t IICox
0-18 18-38 38~9 69-152
0.40 0.29 0.30 0.24
0.46 0.41 0.47 0.52
0.84 0.73 0.76 0.74
0.75 0.46 0.62 0.18
0.54 0.34 0.41 0.28
0.55 0.38 0.47 0.27
0,54 0,56 0,62 0.70
0.85 0.68 0.75 0.42
NR4
AI IIB21 IIB22 IIB23 IICox
0-14 14-22 22-34 34-53 53-104
0.52 0.42 0.33 0.22 0.15
0.71 0.54 0.52 0.58 0.72
1.44 0.99 0.86 0.89 0.87
0.98 0.77 0.73 0.67 0.49
1.01 0.70 0.55 0.50 0.48
1.11 0.57 0.58 0.55 0.54
0.49 0.54 0.60 0.67 0.83
0.56 0.76 0.74 0.62 0.45
NR5
AI B21 B22 Cox Cu
0-20 20--46 46-64 64-101 I01 +
0.77 0.33 0.19 0.18 0.13
0.73 0.44 0.29 0.50 0.54
1.23 0.99 0.83 0.84 0.61
1.02 0.76 0.60 0.55 0.36
0.86 0.41 0.42 0.38 0.29
0.94 0.47 0.42 0.47 0.38
0.59 0.44 0.34 0.59 0.88
0.82 0.75 0.61 0.56 0.37
NR6
AI Clox C2ox Alb A3b B2b Cbox Cub
0-10 10-30 30-40 40--51 51q55 65-90 90-135 135 +
0.63 0.51 0.41 0.80 0.97 0.67 0.27 0.17
0.87 0.94 0.92 0.98 0.87 0.85 0.48 0.28
1.05 1.05 1.13 1.02 0.98 0.98 0.84 0.72
0.66 0.86 0.77 1.10 1.22 0.98 0.86 0.66
0.53 0.51 0.41 0.80 0.97 0.69 0.27 0.17
0.47 0.70 0.77 0.98 1.27 0.71 0.83 0.60
0.82 0.89 0.81 0.96 0.88 0.87 0.57 0.39
0.84 0.78 0.62 0.95 0.97 0.98 0.68 0.63
NR7
AI B1 B2 C1 C2ox C3 B2b Cb
0-15 15-28 28-43 43-80 80-97 97-113 113-140 140 +
0.74 0.49 0.95 0.22 0.79 0.41 2.72 1.03
1.02 0.60 1.14 0.23 1.12 0.44 2.72 1.12
1.69 1.08 1.90 0.93 1.57 0.83 5.79 2.00
0.58 0.68 0.87 0.60 0.65 0.70 0.89 1.05
0.29 0.25 0.31 0.24 0.28 0.20 0.36 0.25
0.32 0.34 0.49 0.40 0.45 0.42 0.68 0.62
0.60 0.55 0.60 0.69 0.71 0.53 0.47 0.56
0.66 0.68 0.76 0.62 0.71 0.82 0.58 0.79
NR8
All A12 Clox C2ox Ab Cbox
0-10 10-20 20-43 43-89 89-114 114 +
0.55 0.37 0.41 0.34 0.63 0.59
0.71 0.55 0.70 0.50 0.75 0.56
0.99 0.83 0.97 0.90 1.13 0.96
0.62 0.57 0.68 0.73 0.96 0.89
0.57 0.37 0.41 0.34 0.63 0.52
0.32 0.32 0.38 0.45 0.53 0.53
0.72 0.66 0.72 0.56 0.66 0.65
0.90 0.82 0.81 0.79 0.96 0.99
1: Extractable Fe and AI in profiles NR2-8 in late Pleistocene turf-banked terraces on Niwot Ridge.
Tab.
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HYDROLOGY~EOMORPHOLOGY
Mahaney & Fahey
24
or even all profiles, from time-to-time. High Fe,, values are considered to be indicative of amorphous inorganic and organically-complexed Fe accumulating at a high water level (DORMAAR & L U T W I C K 1983). Within the older paleosols of Group 1 and Group 2, horizons B2b and B2 in profile NR7, and Bt in NR2, have higher Feo suggesting they might be subjected frequently to water saturation and reducing conditions. In the youngest group (3) of paleosols only the Clox in NR8 might have been subjected to water saturation for significant periods of time. The crystallization of Fe in paleosols is considered to provide important age criteria in soil genesis, and the activity ratio of Feo/Fej is often utilized to assess the degree of aging (BLUME & S C H W E R T M A N N 1969, M A H A N E Y 1974, D O R M A A R & L U T W I C K 1983, M A H A N E Y & S A N M U G A D A S 1986). Within the oldest paleosol (NR7-B2b, Cb) the Feo/Fea ratio suggests that more amorphous Fe has been converted to crystalline Fe. In the Nr2-5 and surface NR7 profiles of Group 2 the values are usually somewhat higher suggesting less conversion to crystalline Fe. In the youngest group (NR6 amd 8) the surface paleosols, overlap with buried units in relative amounts of Feo/Fea suggesting some preweathered minerals might have been incorporated into ground paleosols in some cases. Overall the data suggest that more amorphous Fe was converted to crystalline Fe in older paleosols making the Feo/Fea ratio an important age indicator. The U.S. Soil Taxonomy (SOIL SURVEY STAFF 1975) uses the ratio Fe r + Alp/Fea + Alu as a definition for spodic horizons and of evidence of movement downward of Fe and AI in the profile. ( A I ENA
The older groups (1 and 2) of paleosols NR4 and 7 show some evidence of downward movement within the sola, while the youngest group shows slight movement only in the NR6 profile. While these surface and buried B horizons appear to inherit some A1r and F%, none of them meets the chemical definition of a spodic horizon (secondary illuvial humus plus extractable Fep and Alp) . Examination of extractable Fe and A1 in buried profiles (NR6, 7 and 8) shows that they mirror distributions obtained in some surface paleosols, although the amounts are much greater in the buried NR7 profile. PAWLUK (1978) and D O R M A A R & L U T W I C K (1983) have pointed out that following burial, diagenetic changes might affect the humus reserve, that ultimately would affect the rate at which pyrophosphateextractable Fe and AI form. Alternatively, Fep and Alp might leach downward from the overlying paleosol. Since the soil chemistry for these sites does not suggest any appreciable leaching effects, we consider that these buried A horizons contain enough organic matter (4.23% in NR6-Alb; 8.46 in NR8-Ab) for organically complexed Fe to continue to form, although not at a fast rate. A study of the numbers of anaerobic microbes in the residual humus in these Ab horizons might yield data on their ability to remove organic matter which might otherwise be available for complexing of A1 and Fe (e.g., similar to what is known of the role of microflora in the Afroalpine soils of Mount Kenya; M A H A N E Y & BOYER 1986). 5
CONCLUSIONS
Paleosol profiles often provide useful information regarding present and
An Inlerdisciplinarv Journal of SOIL SCIENCE
HYDROLOGY
GEOMORPHOLO(.;Y
Extractable Fe and AI, Pleistocene and Holocene Paleosol~ Colorado
25
past soil-forming environments. In the REFERENCES present study Fep, Alp, Fee and Ale BENEDICT, J.B. (1968): Recent glacial history possess some mobility, while Fed and of an alpine area in the Colorado Front Range, U.S.A. II. Dating the glacial deposits. J. Glac., Aid vary between groups providing age4, 77-87. dependent data. In all, extractable forms BIRKELAND, P.W. (1984): Soils and Geomorof A1 and Fe yield some data on differphology. Oxford, N.Y., 372 p. ences in soil-forming environments beBLUME, H.P. & SCHWERTMANN, U. (1969): tween Pleistocene interstadial environGenetic evaluation of profile distribution of aluments and the later Pleistocene/Holocene minium, iron and manganese oxides. Soil Sci. Soc. Amer. Prec., 33,438 444. time periods. Overall considerably less DORMAAR, J.F. & LUTWICK, L.E. (1983): downward movement appears to have Extractable Fe and A1 as an indicator for buried occurred in the younger paleosols relasoil horizons. CATENA, 10, 167-173. tive to the oldest profile (NR7, Group 1). LUTWICK, LE. & DORMAAR, J.F, (1973): Fe The Fee/Fed ratio, while providing useful status of Brunisolic and related soil profiles. age-related data, also appears to provide Can. J. of Soil Sci., 53, 185-197. proxy data for former perched soil water MADOLE, R.F. (1976): Glacial geology of the Front Range, Colo. In: W.C. Mahaney (ed.), fluctuations. In cold environments where Quaternary Stratigraphy of North America. permafrost occurs beneath the surface Dowden, Hutchinson and Ross, Stroudsburg, this information may prove important in Pa., 297-318. analyzing soil water fluctuations within MAHANEY, W.C. (1974): Soil stratigraphy and the active permafrost layer. We suggest genesis of Neoglacial deposits in the Arapaho and Henderson cirques, central Colorado Front that additional research with extractable Range. In: W.C. Mahaney (ed.), Quaternary forms of AI and Fe might provide a sigEnvironments: Proceedings of a Symposium, nificant body of data on age, soil waGeographical Monographs, 5, 197-240. ter fluctuations, and diagenesis in buried MAHANEY, W.C. & FAHEY, B.D. (1976): Quahorizons. ternary Soil Stratigraphy of the Front Range ACKNOWLEDGEMENT We thank R.E Madole for access to sites NR2-4 at a time when they were opened for fabric investigations by INSTAAR (U. of Colorado) staff and faculty. We also thank J. D. Ives former Director of INSTAAR for logistical and financial support and for permission to use phot. 1. Rolf Kihl (INSTAAR) provided meticulous particle size determinations for some of the soil and sediment samples. We thank Leon Follmer (Illinois Geological Survey) and an anonymous reviewer for their thought-provoking criticisms. We gratefully acknowledge financial support from the universities of Guelph and York. Mrs. J. Allin prepared the figures.
Colo. In: W.C. Mahaney (ed.), Quaternary Stratigraphy of North America. Dowden, Hutchinson and Ross, Stroudsburg, Pa., 319352. MAHANEY, W.C. & FAHEY, B.D. (1980): Morphology, composition and age of a buried paleosol on Niwot Ridge, Front Range, Colorado, U.S.A. Geoderma, 23, 209-218. MAHANEY, W.C. & SANMUGADAS, K. (1986): Notes on the use of extractable iron and clay minerals for determination of soil age. Gee. Tid., 85, 14-19. MAHANEY, W.C. & BOYER, M.G. (1986): Microbiology of surface and buried soils: some examples from Mount Kenya. CATENA, 13(2), 155-167. MAHANEY, W.C., HALVORSON, D., PIEGAT, J. & SANMUGADAS, K. (1984): Evaluation of dating methods used to assign ages to Quaternary deposits in the Wind River and Teton Ranges, western Wyoming. In: W.C. Mahaney (ed.), Quaternary Dating Methods. Elsevier, Amsterdam, 355-374.
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MARR, J.W. (1967): Ecosystems of the east slope of the Front Range in Colorado. Univ. of Col. Stud. Ser. Biol., 8. I- 134. MCKEAGUE, A. & DAY, J. (1966): Dithioniteand oxalate extractable Fe and AI as aids in differentiating various classes of soils. Can. J. Soil Sci., 46, 13 22. MEHRA, O.P. & JACKSON, M.L. (1960): Iron oxide removal from soils and clays by a dithionite citrate system buffered with sodium bicarbonate. In: A. Swineford (ed.), Natl. Conf. on Clays and Clay Minerals, 1958, Pergamon, London, 317-327.
PAWLUK, S. (1978): The pedogenic profile in the stratigraphic section. In: W.C. Mahaney (ed.), Quaternary Soils. Geo-Abstracts, Norwich, U.K., 61-75.
PEECH, M.L, ALEXANDER, T., DEAN, L.A. & REED, J,F. (1947): Methods of soil analyses for soil fertility investigations. Washington. D.C., USDA Circ. 757, 25 p. RUHE, R.F. (1965): Quaternary paleopedology. In: H.E. Wright, Jr. and D.G. Frey (eds.), The Quaternary of the U.S., Princeton Univ. Press, Princeton, 755-764. SCHOLLENBERGER, C.J. & SIMON, R.H. (1945): Determination of exchange capacity and exchangeable bases in soils - - ammonium acetate method. Soil Science, 59, 13-24. SOIL SURVEY STAFF (1951): Soil Survey Manual, U.S.G.S,, Washington. SOIL SURVEY STAFF (1975): Soil Taxonomy, Ag. Handbook 436, U.S.D.A., Washington. VALENTINE, K.W.G, & DALRYMPLE, J.B. (1976): Quaternary buried paleosols: a critical review. Quat. Res., 6, 209-222.
Addresses of aathors: William C. Mahaney Geography Department, Atkinson College, York University 4700 Keele Street North York Ontario Canada M3J 1P3
B.D. Fahey Forest Research Institute P.O. Box 31-011 Christchurch, New Zealand
CAFENA
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vol. 15, p.17-26
Braunschweig 1988
EXTRACTABLE FE AND AL IN LATE PLEISTOCENE AND HOLOCENE PALEOSOLS ON NIWOT RIDGE, COLORADO FRONT RANGE W.C. M a h a n e y , N o r t h Y o r k O n t a r i o B.D. F a h e y , C h r i s t c h u r c h
SUMMARY Surface and buried paleosols on Niwot Ridge in the Front Range of Colorado were analyzed for extractable Fe and AI to determine if their distributions would assist in the interpretation of past and present soil-forming environments. Extractable Fe and AI distributions in surface and buried paleosols suggest that leaching is more pronounced in the older paleosols with a considerable difference in soil-forming environment between Pleistocene interstadial, later Pleistocene, and postglacial paleosols. Using radiocarbon dated buried A horizons it appears that little pyrophosphate-extractable Fe and A1 have been translocated downward into these middle-latitude alpine buried paleosols. There is no evidence that the Na-pyrophosphate extractable Fe and AI were affected by degradation of organic matter following burial; however, the data suggest that some amorphous Fe and AI ISSN 0341-8162 (~1988 by CATENAVERLAG, D-3302 Cremlingen-Destedt,W. Germany 0341-8162/88/5011851/US$ 2.00 + 0.25 CATENA
might have been affected by soil water movement over permafrost and by redistribution of preweathered sediments.
1
INTRODUCTION
As pointed out by DORMAAR & LUTWICK (1983), VALENTINE & DALRYMPLE (1976), and PAWLUK (1978), buried soils undergo transformations that cause changes in taxonomic parameters and make taxonomic placement difficult. Buried A and B horizons generally experience color changes, increases in bulk density, and degradation (often complete loss) of soil structure. Since extractable Fe and AI have been used to separate surface soils and place them taxonomically (BLUME & SCHWERTMANN 1969, LUTWlCK & DORMAAR 1973), we set out to determine whether a knowledge of extractable Fe and AI would prove useful in interpreting the genesis of surface and buried horizons in three generations of paleosols on Niwot Ridge in the Colorado Front Range (phot.1). Specifically, we sought to establish firstly, whether the three paleosol groups could be differentiated on
An Interdisciplinary Journal of SOIL SCIENCE H Y D R O L O G Y ~ E O M O R P H O L O G Y
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Mahaney & Fahey
the basis of extractable Fe and AI parameters; secondly, whether extractable Fe and AI data might be used to determine the amount of downward movement from surface horizons to buried units; and finally whether buried paleosols had been contaminated by leaching effects.
2
(middle to late Holocene) ( M A H A N E Y et al. 1984). The paleosols in this study are divided into three groups: Group 1 (buried paleosol in NR7), presumably formed during Pinedale (Wisconsinan, Wtirm) interstadial paleoclimate that may have been cool and moist relative to the present;
F I E L D AREA
N i w o t Ridge lies east of the Continental Divide, trending west to east between 3900 and 3400 m elevation. The alpine climate is cold and dry. Data from D1 station on Niwot Ridge (3750 m) in the study area (phot.1), gives a mean annual air temperature ofo3.3°C and an average annual precipitation of 648 mm (MARR 1967). The continental location is expressed by the low available moisture, cool summer, and high annual temperature range. Windy conditions are common; winds on Niwot Ridge average 8.5 m/sec, and gusts of greater than 50 m/sec are reached in winter months (BENEDICT 1968). The topography of the field site owes its character to the movement of valley glaciers that deepened the South Saint Vrain Drainage and the Green Lakes Valley which lie north and south of the field sites, respectively (phot.1). The origin of transported regolith (outlined in black on phot.1) in which turf- and stonebanked lobes and terraces formed, is attributed either to pre-Pleniglacial glacial activity or to mass wasting (personal communication, R.E MADOLE, 1975). The microrelief on the Ridge is the product of episodic gelifluction that appears to have occurred during a Pinedale interstadial period, near the end of the Pinedale Glaciation ( M A H A N E Y & FAHEY 1980), and during the Neoglacial
(AIkNA
Group 2 (NR2 through NR5 and NR7 ground paleosol) formed during the later Pleistocene near the end of the Pinedale Glaciation (first under a colder, drier paleoclimate and later a warmer and w e t t e r (variable) paleoclimate, e.g. BENEDICT, 1968; MADOLE, 1976; MAHANEY, 1974); Group 3 (NR6 and 8) formed during first a middle Holocene climate that may have been warmer and wetter (BENEDICT, 1968), and later under Neoglacial paleoclimates that are considered to have been highly variable but generally cold and dry.
3
METHODS
Soil descriptions follow the SOIL SURVEY STAFF (1951, 1975) and BIRKEL A N D (1984). Sites were selected on representative turf- and stone-banked terraces and lobes previously described by B E N E D I C T (1968). Our use of the term paleosol follows that of R U H E (1965) and includes both surface and buried profiles that formed under more than one paleoclimate. To prevent the dissolution of Fe and AI no acid pretreatment was used in this study. As pointed out by DORMAAR & L U T W I C K (1983) it is im-
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IIYDROLOQY (IEOMORPHOLOGY
Extractable Fe and AI, Pleistocene and Holocene Paleosols, Colorado
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P h o t o 1 : Niwot Ridge in the Central Colorado Front Range, Western U.S.A. The view
is from the east towards D-I station where meteorological observations were made at 3750 m. Sites N R 2 - 8 are located at or near the crest o f the Ridge.
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portant to ensure that pretreatment is uniform for all extractions. Extractable Fe and A1 were obtained from 5 g samples comprising material less than 2 mm with dithionite-citrate-bicarbonate (Fed + Aid) using procedures established by M E H R A & JACKSON (1960). Extraction with sodium dithionite removes finely disseminated hematite + goethite + amorphous Fe and AI + organicallycomplexed Fe and A1. Acid ammonium oxalate removes only amorphous Fe + A1, + organically-complexed Fe and A1, and sodium pyrophosphate is used to extract only organically-complexed Fe and AI (McKEAGUE & DAY 1966). Extractable cations Ca and Mg were analyzed using NHaOA,: as documented by PEECH (1947) and SCHOLLENBERGER & SIMON (1945). All extracts were analyzed in duplicate using an atomic absorption spectrophotometer; pH determinations were made by electrode using a 1:1 soil water ratio.
compared with the youngest group of paleosols (NR6 and 8). The pH distributions in these older profiles yield only slight increases with depth, but do not indicate any downward movement of H ÷ ions. Because the ratio of extractable Ca to Mg is higher in the surface horizons we considered that some airfalt influx or base recycling by plants might have occurred. The uniform ratios of Ca/Mg below the A horizons yield a trend similar to that documented in other paleosols at nearby sites (MAHANEY & FAHEY 1976, 1980), and indicate little if any downward movement in this older group of paleosols. The youngest paleosols (NR6 and 8 in Group 3) are found forming in turfand stone-banked lobes and terraces. The younger mid to late-Holocene age of these deposits was demonstrated previously by BENEDICT (1968) on the basis of topographic position and radiocarbon dates. These paleosols tentatively classify as Cryochrepts and Cryopsamments, have variable ages ranging 4 RESULTS AND from mid to late Holocene, and variDISCUSSION able profile relationships (fig.I). Profile NR6 is a multistorey unit consisting of The older groups (1 and 2) of paleosols an Entisol overlying an Inceptisol; soil (NR7 and NR2 through NR5) formed organic matter extracted from the A l b in turf-banked terraces during and near horizon in the latter was dated by radiothe end of the Pinedale Glaciation ( carbon at 5050+ 170 yr BP (Gak-8359). 10,000 yrs BP) (MAHANEY & FAHEY Chemical analysis of the NR6 profile 1980). While these paleosols vary some- shows a rather uniform pH distribution what in thickness (81 152 cm; fig.l), they with depth, and only a slight increase in cover fresh, undifferentiated sediments extractable Ca in the overlying surface that are perennially frozen and difficult soil. This suggests that base recycling by to sample. The paleosols described in plants may require considerable time to fig.1 (NR2-5 and 7) are all Inceptisols, build up residual Ca in surface horizons; tentatively identified as Cryochrepts. the uniform Ca/Mg ratio at depth sugThe paleosols comprising Groups 1 gests that leaching from the surface has and 2 yield profiles with greater hori- been minimal, and that little, if any geozon complexity, substantially thicker B biochemical contamination has occurred horizons, but with a similar chemistry lower down in the profile. ('AI ~ N A
A n Interdisciplinary Journal o t S O I L S C I E N C E
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(;IOMORPHOIOGY
Extractable Fe and AI, Pleistocene and Holocene Paleosols, Colorado
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CATENA
Aa lnterdiaciplinaty Journal of SOIL SCIENCE HYDROLOGY GEOMORPHOLOGY
Mahaney & Fahey
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Profile NR8 comprises two Entisols. Soil organic matter in the Ab horizon radiocarbon dates at 450 + 80 yr BP (GaK8358). The pH profile shows little variation with depth, suggesting only minor movement of H ~ ions. Little leaching is supported further by data for extractable Ca and Mg (Ca/Mg ratio) which is uniform downward into the Ab horizon. Therefore, we believe the radiocarbon dates on the whole-soil organic material in the buried paleosol horizons (profiles NR6 and 8) approximate the time of burial. This is substantiated further by the relatively low standard deviations on both radiocarbon age determinations. As shown in tab.l, there are only a few age-dependent trends among the three groups of paleosols. Organicallycomplexed Fe tends towards lower amounts in the lower horizons of profiles NR-5, which may reflect somewhat higher translocation effects in Group 2. The increase in Fep in the B2b and Cb horizons of profile NR7 (Group 1) suggests that this truncated buried profile either formed in a paleoclimate sufficiently different from today or over a longer interstadial (Pinedale = Wisconsinan) time period. The distributions for Feo (amorphous Fe), with some exceptions, show somewhat higher amounts in surface and subsurface horizons of the older profiles (NR2-5 and 7). While there is some variation in Fea between the parent materials (Cu horizons) in paleosol groups 2 and 3, there are in general higher amounts of crystalline Fe in the surface and subsurface horizons of Groups 1 and 2. The most noticeable increase occurs in the buried paleosol (NR7) where Fea increases nearly fourfold from the ground paleosol (Group 2) to the buried paleosol (Group 1). These differences reflect changes in extractable Fe observed in AIENA
other Rocky Mountain glacial sequences (MAHANEY 1974, MAHANEY & FAHEY 1976, 1980, MAHANEY et al. 1984). The data for extractable AI show fewer variations with only a slight tendency for AI to increase from the youngest to the oldest group of paleosols. The tendency for Alp, to increase in the buried A horizons, and in the surface A horizons, mirrors variations in Fe with depth, and reflects the complexing action of organic matter. The close similarity in values of Alo and Aid reflects the slow rate of conversion of Alo to Aid (relative to Fe where the differences are greater). The U.S. soil taxonomy (SOIL SURVEY STAFF 1975) uses extractable Fe and AI to identify certain B horizons in surface soils. In this study the distribution of both Fe and AI provide information on present and past soilforming environments. For example, in the lower solum of profile NR7 (Group 1) the higher values for Fep (the organically complexed and more mobile form of Fe) suggest greater movement downward relative to the B horizon in the Group 2 unit. In profile NR6, both surface and buried paleosols show little evidence for downward movement of Fe and AI, although overall amounts are sometimes higher than in the older profiles. The relative differences between the lower solum in NR7 (Group 1) and the Group 2 paleosols (NR2-7) plus Group 3 (NR6 and 8) possibly reflect the paleoclimatic differences during Pinedale interstadial time compared with later Pleistocene and postglacial time. Since these paleosols form largely over frozen substrates, fluctuating perched water tables might bring higher water levels and inundation of part of several,
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Jourmd of SOIL S ( I E N ( ! [
HYDROLOGY
(JEOMORPHOLO(]Y
Extractable Fe and AI, Pleistocene and Holocene Paleosols, Colorado
Site
Horizon
Depth (cm)
Extractable Iron (%)
Fep
Fe o
Fe d
Alp
Alo
Aid
0.88 0.92 0.64 0.79
1.39 1.02 0.73 0.96
0.91 0.53 0.37 0.54
0.77 0.33 0.25 0.22
Extractable Aluminum (%)
23
Feo/Fea
Fee + A l e Fed + Aid
0.89 0.40 0.32 0.22
0.63 0.90 0.88 0.82
0.68 0.67 0.57 0.74
NR2
A1 Bt Clox C2ox
0-12 12-18 18-43 43-81
0.63 0.45 0.23 0.34
NR3
AI lIB1 IIB2t IICox
0-18 18-38 38~9 69-152
0.40 0.29 0.30 0.24
0.46 0.41 0.47 0.52
0.84 0.73 0.76 0.74
0.75 0.46 0.62 0.18
0.54 0.34 0.41 0.28
0.55 0.38 0.47 0.27
0,54 0,56 0,62 0.70
0.85 0.68 0.75 0.42
NR4
AI IIB21 IIB22 IIB23 IICox
0-14 14-22 22-34 34-53 53-104
0.52 0.42 0.33 0.22 0.15
0.71 0.54 0.52 0.58 0.72
1.44 0.99 0.86 0.89 0.87
0.98 0.77 0.73 0.67 0.49
1.01 0.70 0.55 0.50 0.48
1.11 0.57 0.58 0.55 0.54
0.49 0.54 0.60 0.67 0.83
0.56 0.76 0.74 0.62 0.45
NR5
AI B21 B22 Cox Cu
0-20 20--46 46-64 64-101 I01 +
0.77 0.33 0.19 0.18 0.13
0.73 0.44 0.29 0.50 0.54
1.23 0.99 0.83 0.84 0.61
1.02 0.76 0.60 0.55 0.36
0.86 0.41 0.42 0.38 0.29
0.94 0.47 0.42 0.47 0.38
0.59 0.44 0.34 0.59 0.88
0.82 0.75 0.61 0.56 0.37
NR6
AI Clox C2ox Alb A3b B2b Cbox Cub
0-10 10-30 30-40 40--51 51q55 65-90 90-135 135 +
0.63 0.51 0.41 0.80 0.97 0.67 0.27 0.17
0.87 0.94 0.92 0.98 0.87 0.85 0.48 0.28
1.05 1.05 1.13 1.02 0.98 0.98 0.84 0.72
0.66 0.86 0.77 1.10 1.22 0.98 0.86 0.66
0.53 0.51 0.41 0.80 0.97 0.69 0.27 0.17
0.47 0.70 0.77 0.98 1.27 0.71 0.83 0.60
0.82 0.89 0.81 0.96 0.88 0.87 0.57 0.39
0.84 0.78 0.62 0.95 0.97 0.98 0.68 0.63
NR7
AI B1 B2 C1 C2ox C3 B2b Cb
0-15 15-28 28-43 43-80 80-97 97-113 113-140 140 +
0.74 0.49 0.95 0.22 0.79 0.41 2.72 1.03
1.02 0.60 1.14 0.23 1.12 0.44 2.72 1.12
1.69 1.08 1.90 0.93 1.57 0.83 5.79 2.00
0.58 0.68 0.87 0.60 0.65 0.70 0.89 1.05
0.29 0.25 0.31 0.24 0.28 0.20 0.36 0.25
0.32 0.34 0.49 0.40 0.45 0.42 0.68 0.62
0.60 0.55 0.60 0.69 0.71 0.53 0.47 0.56
0.66 0.68 0.76 0.62 0.71 0.82 0.58 0.79
NR8
All A12 Clox C2ox Ab Cbox
0-10 10-20 20-43 43-89 89-114 114 +
0.55 0.37 0.41 0.34 0.63 0.59
0.71 0.55 0.70 0.50 0.75 0.56
0.99 0.83 0.97 0.90 1.13 0.96
0.62 0.57 0.68 0.73 0.96 0.89
0.57 0.37 0.41 0.34 0.63 0.52
0.32 0.32 0.38 0.45 0.53 0.53
0.72 0.66 0.72 0.56 0.66 0.65
0.90 0.82 0.81 0.79 0.96 0.99
1: Extractable Fe and AI in profiles NR2-8 in late Pleistocene turf-banked terraces on Niwot Ridge.
Tab.
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or even all profiles, from time-to-time. High Fe,, values are considered to be indicative of amorphous inorganic and organically-complexed Fe accumulating at a high water level (DORMAAR & L U T W I C K 1983). Within the older paleosols of Group 1 and Group 2, horizons B2b and B2 in profile NR7, and Bt in NR2, have higher Feo suggesting they might be subjected frequently to water saturation and reducing conditions. In the youngest group (3) of paleosols only the Clox in NR8 might have been subjected to water saturation for significant periods of time. The crystallization of Fe in paleosols is considered to provide important age criteria in soil genesis, and the activity ratio of Feo/Fej is often utilized to assess the degree of aging (BLUME & S C H W E R T M A N N 1969, M A H A N E Y 1974, D O R M A A R & L U T W I C K 1983, M A H A N E Y & S A N M U G A D A S 1986). Within the oldest paleosol (NR7-B2b, Cb) the Feo/Fea ratio suggests that more amorphous Fe has been converted to crystalline Fe. In the Nr2-5 and surface NR7 profiles of Group 2 the values are usually somewhat higher suggesting less conversion to crystalline Fe. In the youngest group (NR6 amd 8) the surface paleosols, overlap with buried units in relative amounts of Feo/Fea suggesting some preweathered minerals might have been incorporated into ground paleosols in some cases. Overall the data suggest that more amorphous Fe was converted to crystalline Fe in older paleosols making the Feo/Fea ratio an important age indicator. The U.S. Soil Taxonomy (SOIL SURVEY STAFF 1975) uses the ratio Fe r + Alp/Fea + Alu as a definition for spodic horizons and of evidence of movement downward of Fe and AI in the profile. ( A I ENA
The older groups (1 and 2) of paleosols NR4 and 7 show some evidence of downward movement within the sola, while the youngest group shows slight movement only in the NR6 profile. While these surface and buried B horizons appear to inherit some A1r and F%, none of them meets the chemical definition of a spodic horizon (secondary illuvial humus plus extractable Fep and Alp) . Examination of extractable Fe and A1 in buried profiles (NR6, 7 and 8) shows that they mirror distributions obtained in some surface paleosols, although the amounts are much greater in the buried NR7 profile. PAWLUK (1978) and D O R M A A R & L U T W I C K (1983) have pointed out that following burial, diagenetic changes might affect the humus reserve, that ultimately would affect the rate at which pyrophosphateextractable Fe and AI form. Alternatively, Fep and Alp might leach downward from the overlying paleosol. Since the soil chemistry for these sites does not suggest any appreciable leaching effects, we consider that these buried A horizons contain enough organic matter (4.23% in NR6-Alb; 8.46 in NR8-Ab) for organically complexed Fe to continue to form, although not at a fast rate. A study of the numbers of anaerobic microbes in the residual humus in these Ab horizons might yield data on their ability to remove organic matter which might otherwise be available for complexing of A1 and Fe (e.g., similar to what is known of the role of microflora in the Afroalpine soils of Mount Kenya; M A H A N E Y & BOYER 1986). 5
CONCLUSIONS
Paleosol profiles often provide useful information regarding present and
An Inlerdisciplinarv Journal of SOIL SCIENCE
HYDROLOGY
GEOMORPHOLO(.;Y
Extractable Fe and AI, Pleistocene and Holocene Paleosol~ Colorado
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past soil-forming environments. In the REFERENCES present study Fep, Alp, Fee and Ale BENEDICT, J.B. (1968): Recent glacial history possess some mobility, while Fed and of an alpine area in the Colorado Front Range, U.S.A. II. Dating the glacial deposits. J. Glac., Aid vary between groups providing age4, 77-87. dependent data. In all, extractable forms BIRKELAND, P.W. (1984): Soils and Geomorof A1 and Fe yield some data on differphology. Oxford, N.Y., 372 p. ences in soil-forming environments beBLUME, H.P. & SCHWERTMANN, U. (1969): tween Pleistocene interstadial environGenetic evaluation of profile distribution of aluments and the later Pleistocene/Holocene minium, iron and manganese oxides. Soil Sci. Soc. Amer. Prec., 33,438 444. time periods. Overall considerably less DORMAAR, J.F. & LUTWICK, L.E. (1983): downward movement appears to have Extractable Fe and A1 as an indicator for buried occurred in the younger paleosols relasoil horizons. CATENA, 10, 167-173. tive to the oldest profile (NR7, Group 1). LUTWICK, LE. & DORMAAR, J.F, (1973): Fe The Fee/Fed ratio, while providing useful status of Brunisolic and related soil profiles. age-related data, also appears to provide Can. J. of Soil Sci., 53, 185-197. proxy data for former perched soil water MADOLE, R.F. (1976): Glacial geology of the Front Range, Colo. In: W.C. Mahaney (ed.), fluctuations. In cold environments where Quaternary Stratigraphy of North America. permafrost occurs beneath the surface Dowden, Hutchinson and Ross, Stroudsburg, this information may prove important in Pa., 297-318. analyzing soil water fluctuations within MAHANEY, W.C. (1974): Soil stratigraphy and the active permafrost layer. We suggest genesis of Neoglacial deposits in the Arapaho and Henderson cirques, central Colorado Front that additional research with extractable Range. In: W.C. Mahaney (ed.), Quaternary forms of AI and Fe might provide a sigEnvironments: Proceedings of a Symposium, nificant body of data on age, soil waGeographical Monographs, 5, 197-240. ter fluctuations, and diagenesis in buried MAHANEY, W.C. & FAHEY, B.D. (1976): Quahorizons. ternary Soil Stratigraphy of the Front Range ACKNOWLEDGEMENT We thank R.E Madole for access to sites NR2-4 at a time when they were opened for fabric investigations by INSTAAR (U. of Colorado) staff and faculty. We also thank J. D. Ives former Director of INSTAAR for logistical and financial support and for permission to use phot. 1. Rolf Kihl (INSTAAR) provided meticulous particle size determinations for some of the soil and sediment samples. We thank Leon Follmer (Illinois Geological Survey) and an anonymous reviewer for their thought-provoking criticisms. We gratefully acknowledge financial support from the universities of Guelph and York. Mrs. J. Allin prepared the figures.
Colo. In: W.C. Mahaney (ed.), Quaternary Stratigraphy of North America. Dowden, Hutchinson and Ross, Stroudsburg, Pa., 319352. MAHANEY, W.C. & FAHEY, B.D. (1980): Morphology, composition and age of a buried paleosol on Niwot Ridge, Front Range, Colorado, U.S.A. Geoderma, 23, 209-218. MAHANEY, W.C. & SANMUGADAS, K. (1986): Notes on the use of extractable iron and clay minerals for determination of soil age. Gee. Tid., 85, 14-19. MAHANEY, W.C. & BOYER, M.G. (1986): Microbiology of surface and buried soils: some examples from Mount Kenya. CATENA, 13(2), 155-167. MAHANEY, W.C., HALVORSON, D., PIEGAT, J. & SANMUGADAS, K. (1984): Evaluation of dating methods used to assign ages to Quaternary deposits in the Wind River and Teton Ranges, western Wyoming. In: W.C. Mahaney (ed.), Quaternary Dating Methods. Elsevier, Amsterdam, 355-374.
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MARR, J.W. (1967): Ecosystems of the east slope of the Front Range in Colorado. Univ. of Col. Stud. Ser. Biol., 8. I- 134. MCKEAGUE, A. & DAY, J. (1966): Dithioniteand oxalate extractable Fe and AI as aids in differentiating various classes of soils. Can. J. Soil Sci., 46, 13 22. MEHRA, O.P. & JACKSON, M.L. (1960): Iron oxide removal from soils and clays by a dithionite citrate system buffered with sodium bicarbonate. In: A. Swineford (ed.), Natl. Conf. on Clays and Clay Minerals, 1958, Pergamon, London, 317-327.
PAWLUK, S. (1978): The pedogenic profile in the stratigraphic section. In: W.C. Mahaney (ed.), Quaternary Soils. Geo-Abstracts, Norwich, U.K., 61-75.
PEECH, M.L, ALEXANDER, T., DEAN, L.A. & REED, J,F. (1947): Methods of soil analyses for soil fertility investigations. Washington. D.C., USDA Circ. 757, 25 p. RUHE, R.F. (1965): Quaternary paleopedology. In: H.E. Wright, Jr. and D.G. Frey (eds.), The Quaternary of the U.S., Princeton Univ. Press, Princeton, 755-764. SCHOLLENBERGER, C.J. & SIMON, R.H. (1945): Determination of exchange capacity and exchangeable bases in soils - - ammonium acetate method. Soil Science, 59, 13-24. SOIL SURVEY STAFF (1951): Soil Survey Manual, U.S.G.S,, Washington. SOIL SURVEY STAFF (1975): Soil Taxonomy, Ag. Handbook 436, U.S.D.A., Washington. VALENTINE, K.W.G, & DALRYMPLE, J.B. (1976): Quaternary buried paleosols: a critical review. Quat. Res., 6, 209-222.
Addresses of aathors: William C. Mahaney Geography Department, Atkinson College, York University 4700 Keele Street North York Ontario Canada M3J 1P3
B.D. Fahey Forest Research Institute P.O. Box 31-011 Christchurch, New Zealand
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