Brent V. Alloway,* Vincent E. Neall and Colin G. Vucetich. Department of Soil Science, Massey University, Palrnerston North, Private Bag, New Zealand.
Quaternary International, Vol, 13/14, pp. 167-174, 1992. Printed in Great Britain. All rights reserved.
1040-6182/92$15.00 © 1992 INQUA/Pergamon Press Ltd
PARTICLE SIZE ANALYSES OF LATE QUATERNARY ALLOPHANE-DOMINATED A N D E S I T I C DEPOSITS FROM N E W Z E A L A N D
Brent V. Alloway,* Vincent E. Neall and Colin G. Vucetich Department of Soil Science, Massey University, Palrnerston North, Private Bag, New Zealand
On the western North Island, New Zealand, a Late Quaternary sequence of allophane-dominated cover-bed (Andisol) deposits have accumulated from intermittent accretion and rapid, subsequent weathering of aerially transported detritus of dominantly andesitic provenance. Particle size analyses of Andisol samples were attempted for textural classification and provenance studies. The hydrometer and sedigraph techniques were unsuccessful due to difficulties arising from the flocculation of shortrange order clay and organic constituents (SROCO), which prevented complete particle dispersion. Neither acidic (HCI) nor alkaline (NH4OH or NaOH) solutions were effective in completely dispersing samples, so an alternative chemical procedure was devised. This alternative pretreatment involves the selective dissolution of Andisol SROCO constituents by 0.2 mol acid-oxalate reagent (pH 3.0-3.5), and has considerable potential in the determination of particle size, soil textural classification and provenance of allophane-dominated andesitic deposits.
INTRODUCTION The central Taranaki landscape of western North Island, New Zealand, is dominated by the 2518 m andesitic Egmont Volcano. On depositional surfaces that surround this Late Quaternary stratovolcano, a thick (> 30 m) sequence of allophane-dominated cover-beds have formed from intermittent accretion and subsequent weathering of aerially transported finegrained andesitic detritus. The upper ca. 10 m of this sequence comprise~6 reddish beds with moderate to well developed soil structure, that alternate with 5 contrasting loess-like yellowish beds with poorly developed to massive soil structure. This sequence in north Taranaki, overlies marine sands and gravels on top of the NT2 wave cut surface indirectly dated ca. 125 ka BP (Alloway, 1989). The uppermost portion of this sequence constitutes the present-day soil at ground surface which was previously classed in the New Zealand genetic soil classification as a yellow-brown loam developed in andesitic tephra (Taylor, 1948). This soil was later given the name Andosol (FAO/ UNESCO, 1974), but has been recently classified in the U.S. Soil Taxonomy as an Andisol (Soil Survey Staff, 1990). The entire Late Quaternary sequence of reddish and yellowish beds is regarded as an Andisol succession since all beds are characterized by distinctive soil properties of high 15-bar water retention, high porosity and low bulk density, and dominated by short-range order clays with ferric and organic complexes. The Andisol succession is intercalated by numerous thick and/or coarse grained Egmont-sourced tephra interbeds that, where dated, permit chronocorrelation to diverse depositional environments in Taranaki. *Present Address - - Geology Department, University of Toronto, Scarborough Campus, 1265 Military Trail, Scarborough, Ontario M1C 1A4, Canada.
The strongly contrasting morphological characteristics of reddish (Sr-units) and yellowish (Sy-units) beds indicates that the intensity of surficial weathering has not remained constant with time, and variations appear to reflect climatic oscillations. This has been verified from variations in the palynological and mineralogical records obtained from peat and Andisol sections in Taranaki, respectively. These records suggest that reddish beds accumulated during warm climatic episodes, and yellowish units accumulated during cool or cold episodes (Alloway, 1989; Alloway et al., 1991). Field studies indicate that thickness variations of Stand Sy-units also appear to reflect climatic oscillations. The thinning pattern of these units is similar to that for Egmont-sourced coarse ash and lapilli marker interbeds. All units thin with increasing distance from Egmont Volcano, and their distribution pattern is consistent with prevailing wind patterns. However, the general thinning pattern of yellowish beds is in places, interrupted by localized thickening, and in the uppermost yellowish bed (Syl), by erosional unconformities and wedging eolian sands. Such features are consistent with higher rates of erosion and transferral of detritus during Sy- depositional episodes, when climatic conditions were either cooler or colder compared to those of the present. Early laboratory studies on Andisol samples in western North Island were usually conducted within 1.5 m of the present-day ground surface, and were concerned with the unusually high allophane content and its associated physical and chemical properties (Birrell, 1951; Birrell and Fieldes, 1952; Saunders, 1956; New Zealand Soil Bureau, 1968). More recently, Stewart et al. (1977) emphasized grain size and mineralogical variations within a representative Andisol profile as an accurate means of differentiating postglacial tephra (here correlated to Srl) from late last glacial 'tephric loess' (here correlated to upper Syl).
167
168
B.V. Alloway et
This study therefore attempts to use grain size variations to further distinguish between various beds of the Sr-/Sy-Andisol succession. SAMPLE SITES
Andisol profiles (Entic Dystrandepts) at two well drained sites were selected for detailed particle size studies. The first site, Waitui, was located on the elevated dissected remnants of the ca. 500 ka Eltham laharic surface (Neall, 1979) that borders the Egmont ring plain (ca. 24 km from the present-day Egmont Volcano summit). This site (now destroyed) comprised a ca. 5.5 m high embankment in which the stratigraphic relationships of Srl to uppermost Sy3 were clearly displayed. The second site is a prominent road cut through the NT2 terrace at the north Taranaki coast (ca. 42 km from the Egmont summit), ttere, Srl to Sy5 are displayed in a 9.5 m thick cover-bed sequence that overlies near-shore andesitic sands and gravels above the wave cut surface. Channel samples were collected from 0.2 m below ground surface (above this level being disturbed by cultivation). PARTICLE SIZE ANALYSES
It has been generally accepted that particle size distributions of allophane-dominated samples cannot be accurately measured because of allophane flocculation, preventing complete particle dispersion (Soil Survey Staff, 1965). Dispersion treatments such as using deflocculants, followed by mechanical agitation have proved ineffective. Japanese studies on the dispersion of Andisols have been summarized by Kobo (1964), and an extensive series of tests on the dispersion of similar soils in the Antilles and Latin America have been reported by Colmet-Daage et al. (1972). From these results it appears that there is no single method which applies to all Andisols or even different horizons within the same Andisol profile, since allophanes with different AI/Si ratios react differently to various dispersion treatments. The most promising dispersion method currently available involves treatment at pH 10 (NH4OH or NaOH) or pH 4 (HC1) after peroxidation and washing in water (Wada and Harward, 1974). Wada (1977) suggested that an alkaline medium be used for soils containing allophane with a SiO2/A]20 3 ratio of 2 or higher, whereas an acidic medium is best for those soils containing imogolite or allophane with a SIO2/A1203 ratio lower than 2. Particle size analyses of Andisol samples from Taranaki sites proved difficult, with considerable time spent identifying the most satisfactory dispersion treatment. Neither an acidic nor an alkaline pretreatment proved effective, so an entirely new procedure was devised. This pretreatment involved the chemical dissolution of the short range order clays and organic complexes (hereafter referred to as SROCO), after which particle size analyses of the residues were determined. This selective chemical dissolution can not
al.
only be used for the determination of non-crystalline SROCO constituents, but also has considerable potential for the quantitative determination of the residual sand, silt and crystalline clay constituents following pretreatment. In this study, the acid-oxalate extraction method (Tamm, 1932) was used as a pretreatment procedure. This particular extraction method selectively dissolves short range order materials that are composed of allophane and ferrihydrite materials (Schwertmann, 1964; Higashi and Ikeda, 1974; Wada and Wada, 1977). If conducted in the dark, dissolution of crystalline oxides and layer silicates is very limited (Tamm, 1932; Higashi and Ikeda, 1974; Fey and Le Roux, 1975, 1977; Wada, 1977; Wada and Wada, 1977).
C H E M I C A L P R E T R E A T M E N T AND PARTICLE SIZE P R O C E D U R E
Andisol samples were air dried and gently disaggregated so as to pass through a 2 mm sieve. Sub-samples of ca. 10 g were weighed, then added to 1 1 of 0.2 mol acid-oxalate (pH 3.0-3.5) and shaken end on end in the dark at ca. 20°C overnight. The sub-sample was then centrifuged at 5000 rpm for 5 min. The clear supernatant was then carefully, but completely decanted off. A further 1 I of 0.2 mol acid-oxalate was added to the sub-sample, which was shaken in the dark for a further 24 hr. Following selective dissolution, the sub-sample was then wet sieved through a 30 ~m mesh. The > 30/~m fraction was oven dried, sieved into respective size fractions and weighed. The material passing through the 30 ~m mesh was retained and centrifuged at 2500 rpm. The clear supernatant liquid was decanted off, while the < 30 /~m fraction was retained, oven dried and weighed. Grain size was then calculated for the residuum on a short range order clay and organicfree (SROCO-free) basis. Visual inspection of residuum fractions following chemical pretreatment indicated the negligible effects of dissolution upon the crystalline constituents.
RESULTS
Grain size data expressed as percentage of total sample (air dry basis; < 2 mm) is plotted with respect to profile depth (Fig. 2), and on modified USDA textural ternary diagrams (Fig. 3) for soil textural classification. At Waitui, most samples with the exception of coarse ash and lapilli inter-beds, plot within the clay and clay loam textural fields. The most uniquely distinguishing feature at Waitui is the high (16-35%) silt and crystalline clay content in upper Syl. Other units (Srl, lower Syl, Sr2, Sy2 and Sr3) contain notably less (1127%) silt and crystalline clay. Srl, Sr2 and Sr3 plot within a narrow field on the ternary diagram and are distinguished by high (44-56%) SROCO and low (2534%) sand content. Lower Syl and Sy2 are coarser
169
Particle Size Analyses of Andesitic Deposits
TAR KI
\
REGION NEW
\ WAITARA
PLYMOUTH
ONAER~ WAITUI
)KATO
INGLE~/OODdQ
682m
140A0m
/ EGMONT VOLCANO* .,"2si 8mi
STRATFORD
)UNAKE
10 km
HAWERA
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NORTH ISLAND ,~ NEW
ZEALAND
LOCATIONtt~
174OE 178OE 36os
~tral N o r t h Island
• dormant and active volcanoes r-
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FIG. 1. Location map of the Waitui and Onaero sample sites in Taranaki, western North Island, New Zealand.
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172
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• upper Syl • lower Syl x Sy2 [ ] Sy3
et al.
SROCO
SROCO
aa ~k.
/
o Srl • Sr2 ÷ Sr3
clay
%
cb ÷o °+00oO silty clay loam
clay loam sandy o clay loam
silt loam
loam
Sand sandy loam
Silt and crystalline clay
Sand (a)
A • x o • •
upper Syl lower Syl Sy2 Sy3 Sy4 Sy5
SROCO
o • + • •
SROCO
? P
Srl Sr2 Sr3 Sr4 Sr5
clay
Y
O
÷ clay loam ~
sandy clay loam loam
Sand
/
silty ' clay loam silt loam
sandy loam
Sand
Silt and crystalline d a y
(b) FIG. 3. Modified U.S.D.A. soil textural ternary diagram (a) Waitui and (b) Onaero. Ticks on the triangular diagram are at 10% intervals.
173
Particle Size Analyses of Andesitic Deposits
grained than Sr-units, with less (31--45%) SROCO and a greater (34--49%) sand content. At Onaero, all samples plot within the clay textural field. High silt and crystalline clay content distinguishes upper Syl (24-30%) and lower Sy3 (22-27%) from all other Sr- and Sy-units, which contain notably less (1624%) silt and crystalline clay. Lower Srl, upper Syl and lower Sy3 is characterized by low sand (18-25%) and high SROCO (49-58%) content, whereas other units (upper Srl, Sr2, Sy2, Sr3, upper Sy3, Sr4, Sy4, Sr5 and Sy5) contain greater sand and less SROCO. With the exception of upper Syl and lower Sy3, Syunits cannot be differentiated from Sr-units. DISCUSSION Particle size analyses of the Andisol profiles at Waitui and Onaero (Fig. 3) reveal that grain-size variation is greatest at Waitui closer to Egmont Volcano. Here, the texture of Srl, Sr2 and Sr3 is similar and can be clearly differentiated from lower Syl and Sy2 which contain lower SROCO and higher sand. However, at Onaero, there is less distinctive grain size variation, with the texture of Sr-units resembling that of lower Syl, Sy2, upper Sy3, Sy4 and Sy5. Sy-units at Onaero are finer grained than equivalent units at Waitui but Sr-units remain of similar fine texture, Upper Syl and lower Sy3 contain significantly higher silt than all other Sr- and Sy-units. The silt content of upper Syl at Onaero and Waitui is similar but slightly higher than the silt content of lower Sy3 at Onaero. These high silt values in upper Syl and lower Sy3 are found to closely correspond with major peaks of total quartz content (TQC) determined quantitatively by Xray diffraction (Alloway et al., in press; Fig. 2). Quartz grains within soils derived from basaltic and andesitic volcanic ash have been demonstrated to be of eolian origin (Campbell, 1971; Mokma et al., 1972; Stewart et al., 1977, 1986). Therefore, high silt values recorded in profiles at Waitui and Onaero reflect increased interregional eolian addition to the Andisol succession, and dramatic shifts in the provenance of accretionary sediment from dominantly andesitic to combined andesitic-quartzose source areas. The addition of silt-
sized quartzose particles to both Syl and Sy3 have been related to episodes of full glacial climate that correspond with Oxygen Isotope Stages 2 and 4, respectively (Alloway et al., in press). The concentration of SROCO (< 2 mm; air dry basis) of selected, stratigraphically equivalent samples from both Waitui and Onaero are compared (Table 1) to the concentration of allophane calculated for the same samples by the method of Parfitt and Wilson (1985). This method uses acid-oxalate extractable AI (Alo) and Si (Sio), and pyrophosphate extractable AI (Alp), which gives an estimation of AI in Al-humus complexes. The AI/Si ratio for allophane is determined from ( A l o - A l p ) / S i o and multiplied by 28/27 to give the atomic ratio. The allophane content of the soil is then calculated by multiplying Sio by a factor corresponding to the Ai/Si ratio. Ferrihydrite concentration was similarly estimated but using acid-oxalate extractable Fe (Feo) which is multiplied by 1.7% (Childs, 1985). The combined allophane and ferrihydrite content for the selected samples range between 25 and 38% of the total sample and are approximately 20% lower compared to SROCO values determined under the same laboratory conditions. This discrepancy between SROCO and combined allophane/ferrihydrite contents suggest that those values determined by the method of Parfitt and Wilson (1985) may be significantly underestimated. Grain-size variation with depth (Fig. 2) confirms the existence of coarse ash inter-beds recognized macroscopically within the Andisol profile. However, in correlating inter-beds of finer ash grade, difficulties in the field typically arise from (a) loss of identifying characteristics as individual tephras thin and/or merge from source to grade into Andisol beds, and (b) the masking effects of post-depositional mixing and weathering in the Andisol-forming environment. The selective dissolution procedure enables fine-grained tephra inter-beds which cannot be readily observed macroscopically within the Andisol profile, to be more identifiable. This will ultimately enable more widespread correlation of the finer grained tephra inter-beds between Andisol profiles and, depending on the sampling interval, an assessment of pedogenic mixing.
TABLE 1. Dissolution analyses of selected samples (Air dry; < 2 mm) from Andisol profiles at Waitui and Onaero, western North Island, New Zealand Acid-oxalate
Pyrophosphate Alo-AI p
(m)
Alo %
Sio %
Feo %
Alp %
Fep %
Sio %
Fhest * %
Allophanet
SROCO
7.80 7.55
3.70 4.65
1.65 1.65
0.32 0.42
0.03 0.03
2.02 1.53
2.80 2.80
29.6 27.9
53.06 51.49
8.95 6.75
4.25 3.90
2.20 0.86
0.31 0.28
0.02 0.02
2.03 1.65
3.74 1.46
34.0 23.4
57.16 46.00
Waitui
0.90-1.00 2.70-2.80 Onaero
0.60-0.70 1.70-1.80
*Ferrihydrite concentration estimated from method described by Childs (1985). tAllophane concentration estimated from method described by Parfitt and Wilson (1985).
174
B.V. AUoway et al.
This pretreatment procedure involving selective dissolution of SROCO constituents has considerable potential in its application to Andisol sequences of the circum-Pacific, not only in the determination of particle size, soil textural classification and provenance of allophane-dominated beds, but for tephra inter-beds as well. Presently, a limitation of this technique is that a large volume (2 1) of acid-oxalate is required to treat relatively small quantities of sample (ca. 10 g). The quantity of treated < 30/zm sediment residue is often too small (< 3 g) for accurate hydrometer, pipette or sedigraph grain size determinations to be undertaken. ACKNOWLEDGEMENTS This research is part of Alloway's Ph.D Thesis. We thank DSIR Land Resources, Wellington, New Zealand for financial assistance, and K. M. Giddens of DSIR Land Resources who conducted the pyrophosphate and acid-oxalate extractable A1, Si and Fe determinations.
REFERENCES Alloway, B.V. (1989). Late Quaternary cover bed stratigraphy and tephrochronology of north-eastern and central Taranaki, New Zealand. Unpublished Ph.D Dissertation, Massey University, New Zealand. Alloway, B.V., McGlone, M.S., Neall, V.E. and Vucetich, C.G. (1992). The role of Egmont-sourced tephra in evaluating the paleoclimatic correspondence between the bio- and soilstratigraphic records of central Taranaki, New Zealand. Quaternary International, 13114, 187-194. AUoway, B.V., Stewart, R.B,, Neall,. V.E. and Vucetich, C.G. (in press). A record of last glacial climate determined from aerosolic quartz influx in a terrestrial andesitic environment, New Zealand. Quaternary Research. Birrell, K.S. (1951). Some physical properties of New Zealand ash soils. Proceedings of the 7th Congress of the Royal Society of New Zealand, pp. 208--216. Birrell, K.S. and Fieldes, M. (1952). Allophane in volcanic ash soils. Journal of Soil Science, 3, 156-166. Campbell, I.B. (1971). A weathering sequence of basaltic soils near Dunedin, New Zealand. Journal of Science, 14, 907-924. Childs, C.W. (1985). Towards understanding soil mineralogy II. Notes on ferrihydrite. Soil Bureau Laboratory Report CM7. NZ Soil Bureau Department of Scientific and Industrial Research, Lower Hutt, New Zealand. 16 p. Colmet-Daage, F., Gautheyrou, J., Gautheyrou, M., de Kimpe, C. and'Fusil, G. (1972). Dispersion et etude des fractions fines de sol a allophane des Antilles et d'Amerique latin. Part 1 Dispersion, CAH., ORSTOM Serie Pedologie (France), 10, 169-191.
FAO/UNESCO. (1974). Soil Map of the World, Vol. 1. Legend. UNESCO Press, Paris. Fey, M. and Le Roux, J. (1975). Quantitative determination of allophane in soil clays. Proceedings of the International Clay Conference, Mexico, pp. 451-463. Applied Publishing, Wilmette, Illinois. Fey, M. and Le Roux, J. (1977). Properties and Quantitative estimation of poorly crystalline components in sesquioxidic soil clays. Clays and Clay Mineralogy, 25, 285-294. Higashi, T. and Ikeda, H. (1974). Dissolution of allophane by acid-oxalate solution. Clay Science, 4, 205-212. Kobo, K. (1964). Properties of Volcanic ash soils. FAO/UNESCO. World Soil Resources Report, 14, 71-73. Mokma, D.L., Syers, J.K., Jackson, M.L., Clayton, R.N. and Rex, R.W. (1972). Eolian addition to soils and sediments in the south Pacific area. Journal of Soil Science, 23, 147-162. Neall, V.E. (1979). Sheets P19, P20 and P21 New Plymouth, Egmont and Manaia (lst Ed.). Geological Map of New Zealand 1 : 50,000. 3 maps and notes (36p.). DSIR, Wellington, New Zealand. New Zealand Soil Bureau (1968). Soils of New Zealand Part 2. New Zealand Soil Bureau Bulletin, 26, DSIR, Wellington, New Zealand. Parfitt, R.L. and Wilson, A.D. (1985). Estimation of allophane and halloysite in three sequences of volcanic soils, New Zealand. In: Caldas, E.F. and Yaalon, D.H. (eds), Volcanic Soils, Catena Supplement 7, Braunschweig. Saunders, W.M.H. (1956). Effective phosphate topdressing on the distribution of phosphorous in a soil formed from andesitic ash. Transactions of the 6th International Congress of Soil Science, B, 629-634. Schwertmann, U. (1964). Differenzierung der eisenoxide des bodens durch photochemische extraktion mit saurer ammonium oxalatelosung (in German), Zeitsehrift Pflanzenerndhrung, D~ngung und Bodenkunde, 105, 194-202. Soil Survey Staff (1965). USA Soil Classification. Soil Conservation Service, U.S. Department of Agriculture. U.S. Government, Washington, D.C. Soil Survey Staff (1990). Keys to Soil Taxonomy, fourth edition. SMSS technical monograph 6. Blacksburg, Virginia, USA. Stewart, R.B., Neall, V.E., Pollok, J.A. and Syers, J.K. (1977). Parent material stratigraphy of an Egmont loam profile, Taranaki, New Zealand. Australian Journal of Soil Research, 15, 177-190. Stewart, R.B., Neall, V.E., Syers, J.K. (1986). Origin of quartz in selected soils and sediments, North Island, New Zealand. New Zealand Journal of Geology and Geophysics, 29, 147-152. Tamm, O. (1932). Uber die oxalatmethode in der chemischen bodenanalyse. Meddelelser Skogsforsoksanst. Stockholm 27. Taylor, N.H. (1948). Soil map of New Zealand. Scale 1 : 2,027,520. NZ Soil Bureau. Wada, K. (1977). Ailophane and Imogolite. In: Dixon, J.B. and Weed, S.B. (eds), Minerals in Soil Environments, pp. 603-638. Soil Science Society of America, Madison, Wisconsin. Wada, K. (1978). Allophane and Imogolite. In: Mortland, M.M. and Farmer, V.C. (eds), International Clay Conference 1978, pp. 537545. Elsevier, Amsterdam. Wada, K. and Hayward, M.E. (1974). Amorphous clay constituents of soils. Advanced Agronomy, 26, 211-260. Wada, S.I. and Wada, K. (1977). Density and structure of Allophane. Clay Minerals, 12, 28%298.
