BY D.M. LESLIE SOIL BUREAU, LOWER HUTT
N,Z, SOIL BUREAU SCIENTIFIC REPORT 34
Department of Scientific and Industrial Research, New Zealand 1978 Bib 1i ographi c Reference:
LESLIE, D.M. 1978: An interpretation of a section through Quaternary deposits and paleosols at Taiaroa Head, Otago Peninsula, New Zealand. N.Z. Soii BUl'eau Saientifia Report 34 Zlp.
ISSN 0304-1735
E.C.KEATING, GOVERNMENT PRINTER, WELLINGTON, NEW ZEALAND - 1978 CONTENTS Page Abstract 4 Introduction 5 Stratigraphic units 5 Geochronology 11
Analyses 15
Acknowledgments 15 References 17
Appendix Section description 18
FIGURES Figure 1 Stratigraphic units 6-7 Figure 2 Aerial view of location 8
TABLES
Table 1 Taiaroa Head Section, soil stratigraphic units 9
Table 2 Sand mineralogy 10 Table 3 Geochronology and correlation 12 Table 4 Phosphorus fractions 16 .4
ABSTRACT
Twenty-four stratigraphic units are described, including 10 Quaternary units which are the main concern of this report. For a type section at Taiaroa Head, seven paleosols, a number of lithological discontinuities, cyclic regolith layering features and the weathering status are interpreted in terms of stratigraphic position. In the absence of absolute dates, by the law of superposition, stratigraphy provides a relative chronology of the cyclic phenomena viz. deposition on slopes, soil formation, pedosphere stripping. It is assumed that the sequence is complete in that no strati graphic units have been totally removed. The units are correlated by assigning each the youngest possible age consistent with the complete sequence. Thus the oldest paleosol is correlated with the Waiwheran Inter glacial and the stratigraphic unit (10) in which it developed forms the basal member of this Quaternary sequence. · 5
INTRODUCTION
Relict periglacial features are characteristic of the Quaternary in the Dunedin District. Solifluction and loessial deposits, stone stripes and modified landforms have been well described by Brockie (1964), Raeside (1964) and Leslie (1973a,b,c,d). In the inland environment of Central Otago, relict periglacial and cold climate features, contemporary with and at a latitude comparable to those of Dunedin, have been well documented (Mccraw 1959, 1965; Wood 1969; Mark and Bliss 1970; Leamy and Burke 1973). During a soil survey of Otago Peninsula (Leslie 1978), a complex regolith stratigraphy was examined, which has been interpreted as a pattern of sequential erosional and depositional Quaternary events (Leslie 1973b).
Although no marker beds based on absolute dates have been identified, several sections have been described (Leslie 1973b) which show that the pattern of relict surfaces and deposits mapped as late Oturian (Leslie 1973c) also occurred in a similar cyclic sequence much earlier in the Quaternary. Correlation of these soil sections, based on degree of weathering, lithology, paleosol characteristics and erosion intervals, has suggested a possible reconstruction of upper Quaternary environments on Otago Peninsula.
Those features recognised and described for Otago Peninsula as a whole are best seen in the "type" section at Taiaroa Head (Fig.1). This site is 100 m above sea-level (Fig.2), on a northerly aspect at Grid Ref. NZMS1 S164/2 3435:8325. It is marked on N.Z. Soil Bureau Map 136 (Leslie 1973c).
STRATIGRAPHIC UNITS
Within the Taiaroa Head section, 24 stratigraphic units have been recognised, overlying basaltic agglomerate of the first eruptive phase in the Dunedin district (Benson 1968). All units are described in the Appendix and are listed in stratigraphic order in Table 1. -
This report is primarily concerned with the upper inferred Quaternary units (1-12) within the Taiaroa Head section. Lower units (13-24), however, comprise a sequence of bedded tephra rarely exposed in Dunedin district. This may provide valuable information about stratigraphic relationships and allow more precise dating of volcanic events in the area. Some minor work has been done in an attempt to determine the composition of the tephra, its source and its approximate age. Results of mineralogical determinations for the sand fractions of three of the tephra units are listed in Table 2. The beds are probably derived from an andesitic volcanic source post-dating Dunedin district's first eruptive phase which has a suggested age of Waiauan to Opoitian (Coombs et al. 1960). The sequence is earlier than stratigraphic unit 10 which is correlated with the Waiwheran Interglacial in
9
TABLE 1 Taiaroa Head Section, stratigraphic units Stratigraphic unit Thickness (cm) 1. Quartzofeldspathic sand drift 50 2. Loess (paleosol I) 200 3. Basic volcanic derived coluviwn (paleosol II) so 4. Bouldery solifluction deposit 150 5. Loess/volcanic derived colluviwn (paleosol III) 70 6. Loess (paleosol IV) 120 7. Bouldery solifluction deposit 75 8. Lbess/volcanic derived colluviwn (paleosol V) 140 9. Loess (paleosol VI) 150 10. Basic volcanic derived colluviwn (paleosol VII) 45 11. Tuffaceous derived colluviwn (strongly weathered) 65 12. Tuffaceous derived colluviwn 65 13. Laminated dark yellowish brown and very pale brown water-laid tephra 18 14. Laminated strong brown, light yellowish brown and pale yellow water-laid tephra 20 15. Laminated pale yellow and white water-laid tephra with Fe layerings 4 16. Pale yellow and light yellow-brown tephra 14 17. White tephra with lapilli and Fe nodules 18 18. Pale yellow tephra with lapilli and clay lenses 13 19. Laminated pale brown water-laid tephra with leaf impressions 20 20. Laminated light brownish grey and dark brown water- laid tephra with lapilli 10 21. Laminated dark brown tephra 26 22. Yellow and brownish yellow tephra with lapilli 18 23. Dark brown tephra 53 24. In situ weakly weathered basaltic agglomerate > 300 10
TABLE 2 Sand mineralogy Stratigraphic unit 17 18 19 Minerals detected fine sand coarse sand
relative amounts t
Clay aggregates a A a A Acid feldspar c c R a Felsitic aggregates c c Andesine R tr R R Glass (vesicular) tr Muscovite tr tr Biotite tr Quartz R Magnetite tr Zeolite c a R*
t A = > 50%, a = 30-50%, C = 10-29%, c = 5-9%, S = 1-4%, R = < 1%, Tr = trace, - = not detected (Analyst : A.V.Weatherhead)
* X-ray determination (Mr N. Wells, pers.comm.) indicates the zeolite is near chabazite and gmelinite
this report. Benson (op. ait.) mapped this area as "older flood plain conglomerate" which included "bedded tuffs': so the tephra units described here were probably those included by Benson in his "older flood plain conglomerate". Unit 24 of the sequence is considered the equivalent of Benson's "basal tic agglomerate"· A study of the paleobotany, mineralogy and paleogeography of the tephra units could prove scientifically rewarding.
While no absolute dates have been obtained for the Taiaroa Head stratigraphic units and the correlations made are problematical, yet some assessment of relative time can be made, based on warm climate (paleosols) and cold climate features. When these features are compared with the New Zealand Quaternary column a chronology of events is possible. In attempting this correlation two assumptions are made. First, that the sequence is complete, i.e. no stratigraphic units have been totally removed, and second, that the ages of the individual units are the youngest possible consistent with the complete sequence. 11
GEOCHRONOLOGY
Table 3 summarises diagrannnatically the following interpretations of events and time correlations.
Units 11 and 12 are the oldest Quaternary deposits in this sequence. Their physical properties indicate that they could have been derived by erosion of older tuffaceous units (13 and 14) exposed upslope from the section. Large, disorientated, incohesive blocks of tuffaceous material within unit 12, probably derived from unit 14, indicate that the colluvium moved only a short distance from its source. Although units 11 and 12 are both sandy, unit 11 is appreciably more weathered and is separated for that reason. Clay and manganese coatings on clasts and fragments, characteristic of unit 11, indicate by their nature and their arrangement that weathering took place before deposition. Both units are tentatively correlated with the Waiwheran Interglacial.
A distinct lithological discontinuity separates unit 10 from unit 11. Unit 10, showing pronounced pedological alteration, is the oldest buried soil (paleosol VII) in this sequence. It consists of strongly weathered clayey colluvium derived from basic volcanic lava, with well developed nut and blocky structures, clay illuvial features and prominent manganese coatings to fissures and ped faces. Although this strong weathering is primarily pedological, the colluvial parent material was probably pre argillised to some degree, in view of the weathering status of the units above and below. Pre-argillisation on this type of rock can be explained by the following hypothesis. Jointed lavas with deep spheroidal weathering (i.e. weathering associated with interglacial periods) are connnonly found on Otago Peninsula on sites protected from erosion, especially on the flatter, high altitude, sunnnit and interfluve areas (Leslie 1973a). When these areas are subjected to cryoplanation the zones of deep weathering are differentially denuded. Smaller boulders and the clayey matrix combine to form either a solifluction or a colluvial slope deposit, depending on the severity of the climate. Larger boulders remain in situ to form felsenmeer and thus do not occur in the colluvium; ,they are not found in unit 10.
At the top of unit 10, surface pedological horizons are missing. They could have been lost during the intense and widespread periglaciation of the Waimaungan Glaciation. During this period colder temperatures and resultant vegetation changes induced hillslope instability. Shallow surface processes such as soil creep and solifluction partially stripped the pedosphere.* Sea level dropped, exposing a broad expanse of marine sediments in Otago Harbour and along the Otago coast. Strong winds preferentially carried coarse fractions onto lower slopes by saltation and spread loessial silts over much of the mid-altitude area.
* Pedosphere stripping (Bruce 1973) is here expanded to include removal of soil horizons, either total or in part, by any eroding process such as. wind or mass movement, on hilly as well as flat landscapes. 12 1
TABLE 3 - Geochronology and correlation'
Ewints Psdolo11ical comlation with NZ chronology Soil Stratigraphic Soll horizon Degree of soil Depth (m) lnterglacials I Unit (number) designation weathuing Ptdological * Gealogical Glacials I St:adials lntenladials ConteinpararY c:illma:te:_:.: sand accumulation Sand drift (1) A weak sOr1·creveiciPm~n1· . .. _:.: ··· by saltation ARANUIAN ·. ~w:d'rm cJim.ate ··: • ; 0 _ _ ~ ~Aa_ -l--'-mc':':'c":"....:_-1,.'·~·~~·~ii~':':":";J. p~m~';";i.:.,: :~.~-.-.!------_, T 1 - ·· ..... -.. co!d climate - rapid I KUMARA 3·2 !// .//// luBx weak loess accumul.ation STADIAL loess (2) R (////// KUMARA 3·2/3·1 -- I- lNTERSTAOIAL luBC moderate to strong KUMARA3·1 r,,/ / //// STADIAL ,/'/_~// G KUMARA 312 Volcanic colluvium (Sl V//// ,· very strong L I/ // / /·_/ INTERSTADJAL A KUMARA 2-2 V _. / . '/,/-' c Bouldery STADL 8 In situ loess (9) 9 - 10 * Stipple indicates probable depth of soil formation 13 Unit 9 represents a slow loessial accumulation under. gradually warming temperatures, with time for biological activity (worm casts, root tunnels and pores) to develop throughout the 1.5 m deposit. Moderate weathering in the VIuC horizon probably took place on pre-argillised silts and clays from volcanic material, which were incorporated in slope deposits during the early stages of loess deposition. As temperatures warmed (possibly during the onset of the Terangian Interglacial), sea level gradually rose again and the source of loess became more and more restricted. Accumulation slowed and soil formation became more intense. Paleosol VI (unit 9) developed during this period with the following features: .B, Bz(x)•C horizon arrangement; gammations associated with prismatic structures; compact, very firm fragipan; clay illuviation; and iron mottling and concretions. These features are characteristic of contemporary yellow-grey earths and suggest a comparable environment for the development of paleosol VI. · As with the other paleosols in this stratigraphic sequence, the solum of paleosol VI has been partially stripped. This type of landscape instability can mark the onset of an intense cold period. However, the material of unit 8 immediately above paleosol VI suggests that a climatic fluctuation took place. Such oscillations are characteristic of the onset of a more intense climatic change - in this case, the Terangian Interglacial. Minor hillslope instability during a short-term cooling period is often manifested as soil creep, which produces mixed surface materials through downslope transport. Unit 8, as an admixture of loess and volcanic-derived colluvium, could well have formed in this way. The strongly weathered soil (paleosol V) developed from unit 8 is tentatively correlated with the Terangian Interglacial. Again, as in unit 10, some pre-argillisation of the volcanic component of the colluvium is likely. Above unit 8, a sequence of bouldery solifluction material (unit 7) overlain by 1.2 m of loess (unit 6), suggests formation during the periglacial conditions of the Waimean Glaciation. A marked lithological discontinuity at the base of unit 7 suggests that paleosol V (unit 8) was partially stripped at its pedosphere by over-riding solifluction debris. This debris comprises large well-rounded volcanic boulders set in a strongly weathered silty clay matr.ix. The boulders are c·ore stones, relict from older deep weathering in jointed basalt as described earlier for unit 10. Embodied within clayey solifluction lobes, the stones would have slowly migrated downslope under a freeze-thaw regime. As the lobes moved., incohesive soil materials were stripped from the slope. Loessial materials forming unit 6 were probably deposited in a similar manner to those of unit 9. During the Waimean Glaciation, as with the Waimungan Glaciation, sea-levels dropped and exposed marine sediments to the wind. From their position relative to older stratigraphic units, units 7 and 6 are correlated with the Kumara 1 stage of the Waimean Glaciation. Morphological properties of paleosol IV developed on the loess of unit 6 show important characteristics of contemporary yellow-grey/yellow-brown earth intergrades. These are: colour, weak prismatic structure, and sub-gammate colour patterns. Strong pedological weathering in this unit indicates a significant period or greater intensity of soil formation than that for unit 9, which is correlated with the Oturian Interglacial. 14 The sequence of units 6 to 5 is similar to that for units 9 to 8, except that the erosion of surface horizons in unit 6 is more pronounced than for unit 9. This suggests that the erosion of unit 6 may have taken place under colder conditions than that of unit 9, although a longer period of erosion, a shallower soil or differing erosional intensity cannot be discounted. On the basis of soil morphological properties (Appendix), weathering status and the nature of the erosion intervals, the following correlations are made: paleosol IV - Oturian Interglacial; pedosphere stripping - Kumara 2.1 stadial; paleosol III - Kumara 2.2/2.l Interstadial. Further cold climate conditions are inferred from the sharp lithological discontinuity between units 5 (paleosol III) and 4. Unit 4 is a thick (1-2 m) bouldery deposit which shows little of the warm climate weathering and pedological alteration of the underlying unit 5 and the overlying unit 3. It could have been deposited under cold climate conditions as a result of processes described £or units 7 and 10. Deposition of the material is associated with pedosphere stripping. Warmer temperatures later induce further minor hillslope instability and deposition of volcanic-derived colluvium (unit 3). Warm climate weathering follows (paleosol II). Paleosol II probably formed during the Kumara 3/'2 Interstadial. The strong weathering of this soil is more likely to be the result of pre argillisation of the colluvium, probably during an earlier interstadial or the Oturian Interglacial, than of weathering under a hot humid or a longer duration temperature climate. A disconformity separating the loess deposit of unit 2 from paleosol II (unit 3) is interpreted as a phase of instability that probably marks the onset' of the Kumara 3 stage of the mid-Otiran Glaciation. The thickness, of the unit 2 loess could well be the result of an intensely cold period with considerable source areas and, by inference, very low sea-levels. Again, however, other possibilities such as longer time or stronger and more frequent winds cannot be discounted. The IuBC horizon of paleosol I is more weathered than the overlying horizons of the same paleosol (see Table 4). The following sequence of events is therefore postulated: following pedosphere stripping (paleosol II), loess accumulated rapidly in a cold climate, incorporating into the IuBC horizon small amounts of pre argillised volcanic-derived material; loess accumulation then slowed but did not stop and, during this period of quiescence, soil formation intensi fied; loess then began to accumulate more rapidly depositing another 1.5 m thickness before accumulation ceased. This sequence is correlated as follows: first phase of loess accumulation and soil development - Kumara 3.1 stadial; quiescent period of loess accumulation and soil development - Kumara 3.2/3.l Interstadial; final phase of loess accumulation - Kumara 3.2 Statial. The latter marked the end of the Otiran Glaciation. As temperatures continued to rise the formation of paleosol I continued. Sand drift (unit 1) now overlying paleosol I is correlated with a period of redistribution of sand from coastal dunes. The dunes were fed from prograding beaches, formed after sea-level reached a post-glacial peak and sand was' spread onto adjacent hillslopes by saltation, as seen at Taiaroa Head. Soil development on the sand drift has continued slowly since it was stabilised. 15 ANALYSES Field physical properties viz. texture, colour and structural development are valuable parameters to indicate the presence or absence of paleosols, but to support the physical descriptive data selected horizons were sampled for phosphorus fractionation to help confirm the geochronological interpretation. The presence of a paleosol is in general indicated by a decrease in primary P (apatite), and an increase in residual and occluded P when these are expressed as a percentage of total P, and when the P fraction percentages are compared with P levels in overlying and underlying horizons within the soil section. Table 4 lists the results of P determinations from 12 sampled horizons. Primary P levels show that the soils are all significantly weathered except for the beach sand horizon (SB Lab.No.8821A) and the first (SB Lab.No.8821 B-D) and third (SB Lab.No.8821 I-K) loess soils.. An anomaly is that the C horizons of these two loessial soils appear to be more weathered than the overlying B horizons. This may be explained by the possibility that at the onset of a loess depositional event weathered volcanic 'fines' representing interglacial soil formation were available and were incorporated with the loess as it accumulated. There is no field indication that the C and B horizons of these two loessial soils were deposited separately. The index of soil weathering indicated in Table 3 is based on the P fraction data with consideration of parent material differei.~es between horizons plus the possibility of pre-argillisation. ACKNOWLEDGMENTS The assistance of Mr N.M.Kennedy in field description and sampling is gratefully acknowledged. TABLE 4 - Phosphorus fractions in pa1eoso1s at Taiaroa Head Soil Bureau Strati- Depth Horizon Total P Primary P Occluded P Residual P Laboratory graphic (m) Designation (ppm) (ppm) % total (ppm) % total (ppm) % total Number Unit 8821A 1 0.05-0.20 A 39 13 33 1 2.5 12 31 8821B 2 0.60-0.75 IuAB 44 11 25 3 7 13 30 8821C 2 1. 20-1.45 IuB 50 15 30 4 8 10 20 x 8821D 2 2.00-2.30 IuBC 40 6 15 5 13 12 30 8821E 3 2.60-2.80 IIuB 34 1 3 3 9 7 21 8821F 5 4.70-5.00 IIIuB 43 5 12 5 12 10 23 8821G 6 5.80-6.20 IVuB(x) 32 4 13 3 9 10 31 8821H 8 7.80-8.20 VuB 40 3 8 5 13 11 28 a->-"' 9 8.70-9.10 VIuB 45 20 44 3 7 10 22 88211 1 9.40-9.70 54 20 37 5 9 12 22 8821J 9 VIuB 2 (x) 8821K 9 9.80-10.00 VIuC 40 13 31 5· 13 8 20 88211 10 10.15-10.40 VIIuB 47 5 11 6 13 14 30 Analyst: A.S. Burke 17 REFERENCES Benson, W.N. 1968: DIIDedin District 1:50 OOO. N.Z. GeoZogicaZ SUI'Vey MisceZZaneous Series, Map 1 Brockie, W.J. 1964: Patterned grolIDd - some problems of stone stripe development in Otago. Proceedings of the 4th N.Z.Geography Conference: 91-104 Bruce, J,.G.I 1973: Loessial deposits of southern South Island 'with a definition of Stewarts Claim Formation. N.Z. JournaZ of GeoZogy and Geophysics 16: 533-48 Coombs, D.S.; White, A.J.R.; Hamilton, D. 1960: Age relations of the DIIDedin volcanic complex and some paleogeographic implications. Part, 1. N.Z. JournaZ of GeoZo(JY and'Geophysics 3: 325-36 Leamy, M.L. 1973: Subsoil claypans as Quaternary markers in semi-arid Central Otago. N.Z. JournaZ·of GeoZogy and Geophysics 16: 611-22 Leamy, M.L.; Burke, A.S. 1973: Identification and significance of paleosols in cover deposits in Central Otago. N.Z. JournaZ of GeoZogy and Geophysics 16: 623-35 Leslie, D.M. 1973a: Quaternary deposits and surfaces in a volcanic landscape on Otago Peninsula. N.Z. JournaZ of GeoZogy and Geophysics 16: 557-66 1973b: Relationship between soils and regolith in a volcanic landscape on Otago Peninsula. N.Z. Journal of Geology and Geophysics 16: 567-74 1973c: Map of Quaternary deposits and surfaces, Otago Peninsula, New Zealand, 1:31 680. N.Z. SoiZ Survey Report 3 1973d: Taiaroa Head Section • Pp.144-50 in'Guidebook for Excursion 6 (Central South Island) of New Zealand.' IX INQUA Congress, Christchurch, New Zealand. Leslie, D.M. 1978: Soils of Otago Peninsula, New Zealand. N.Z. Soil Survey Report 28 Mark, A.F.; Bliss, L.C. 1970: The high-alpine vegetation of Central Otago, New Zealand. N.Z. Journal of Botany 8: 381-451 McGraw, J.D. 1959: Periglacial and allied phenomena in western Otago. N.Z. Geographer 15: 61-8 1965: Landscapes of Central Otago. Pp.30-45 in Lister, R.G.; Hargreaves, R.P. (Ed.): "Central Otago". N.Z. Geographical Society MisceZZaneous Series 5 Raeside, J.D. 1964: Loess deposits of South Island, New Zealand and soils formed on them. N.Z. Journal of Geology and Geophysics 7: 811-35 Wood, B.L. 1969: Periglacial tor topography in southern New Zealand. N.Z. JournaZ of GeoZogy and Geophysics 12: . 361-75 18 APPENDIX: SECTION DESCRIPTION, TAIAROA HEAD, OTAGO PENINSULA Stratigraphic units, in order of increasing age Unit 1 Parent material: 50 cm quartzo-feldspathic sand drift Morphology: A horizon: dark greyish brown (lOYR 3/2) fine sand; loose; weakly developed fine and medium nut structure breaking to single grain; many roots; indistinct boundary, Unit 2 Parent material: 2 m schist-derived loess Morphology: IuAB horizon: yellowish brown (lOYR 5/4) fine sandy loam; firm; moderately developed coarse and medium nut (tending blocky) structure; porous;· abundant organic accumul ation in pores and inter-ped areas; a few Fe mottles (7.SYR 4/4 and 5/6); cutans (SYR 3/4); indistinct boundary, IuBx horizon: light olive brown (2.SY 5/4) fine sandy loam; very firm; brittle; very compact; moderately developed prismatic primary structure with a moderately developed coarse blocky secondary structure; porous; clay and organic lining to root channels; weak net gammate with SY 2/2 gleying; cutans(lOYR 4/3) along dominant vertical gammate fissures; many very fine Fe concretions; indistinct boundary, IuBC horizon: brown (lOYR 5/3) and light olive brown (2.SY 5/4) fine sandy loam - sandy loam; firm - very firm; compact; weakly developed prismatic structure; porous; abundant relict root channels; diffuse cutans; a few very fine Fe concretions and a few medium Fe mottles (lOYR 4/3); distinct boundary, Unit 3 Parent material: 50 cm colluvium derived from basic volcanic rock Morphology: liuB horizon: dark yellowish brown (lOYR 3/4) silty clay; very firm in situ ; strongly developed medium coarse blocky structure; abundant cutans; many strongly weathered volcanic granules and small stones throughout; sandy material of loessial origin and derived from overlying IuC horizon fills inter-ped areas; indistinct boundary, Unit 4 Parent material: 1. 5 m soliflual slope deposit Morphology: Coarse, rounded, weakly weathered core stones set in silty clay matrix, distinct boundary, Unit 5 Parent material: 70 cm colluvium derived from loess and basic volcanic rock Morphology: IIIuB horizon: light yellowish brown (2.SY 6/4) clayey fine sandy loam; friable; moderately developed medium and coarse blocky structure; abundant cutans (lOYR 4/3); a few strongly weathered basic volcanic rock fragments; many weakly weathered stones in top 15 cm; distinct boundary, 19 . Unit 6 Pa:rent material: 1.2 m loess Morphology: IVuB(x) and IVuCll horizons: yellowish brown (lOYR S/4) fine sandy loam; firm to very ·firm; compact; weakly developed prismatic structure with a weakly developed very coarse blocky secondary structure; subgammate; porous; diffuse cutans; gleying along vertical fissures (SY 6/4) and as diffuse patches within peds; Mn coatings along fissures; indistinct boundary, Unit 7 Pa:rent materiaZ: SO cm - 1 m soliflual slope deposit MorphoZogy: IVuC12 horizon: coarse, rounded, weakly weathered boulders (core stones) set in silty clay matrix, Unit 8 Pa:rent materiaZ: 80 cm - 2 m colluvium derived from loess and basic volcanic rock MorphoZogy: VuB horizon: yellowish brown (lOYR S/4 - 5/6) with diffuse areas of brownish yellow (lOYR 6/6) clayey fine sandy loam; . very firm; weak to moderately developed coarse blocky structure; many very fine strongly weathered basic volcanic stones; cutans (lOYR 4/4) with Mn coatings to fissures, relict root channels and ped faces; very sharp boundary (litho logical discontinuity), Unit 9 Pa:rent materiaZ: 1.S m loess MorphoZogy: VIuB1 horizon: light yellowish brown (2.SY 6/4) fine sandy loam; firm to very firm; moderately developed prismatic primary structure with a weakly developed coarse blocky secondary structure; many diffuse Fe mottled zones (7.SYR S/6) with associated Mn mottles; primary peds gley coated (SY 6/2); many cutans (7.SYR 4/4); indistinct boundary, VIuB2(x) horizon: light yellowish brown (2.SY 6/4) fine sandy loam to sandy loam; very firm; compact; moderately developed coarse prismatic structure; gammate; S-cm thick Fe (lOYR S/6) selvedge to prism faces; gley (SY S/2) coatings to prisms; Mn fissure coatings on gley surfaces; indistinct boundary, VIuC yellowish brown (lOYR S/4) and olive (SY S/3) fine sandy loam; firm; massive to single grain; many fine diffuse Fe mottles (SYR S/6); distinct boundary, Unit 10 Pa:rent materiaZ: 4S cm colluvium derived from basic volcanic ·rock MorphoZogy: VIIuB horizon: brown (lOYR 4/3) silty clay loam; firm to very firm; weak to moderately developed coarse nut with blocky structure; a few subangular basic volcanic stones; abundant cutans (lOYR 3/3); Mn coatings along fissures and ped faces; distinct boundary, Unit 11 Parent materiaZ: 6S cm colluvium derived from tuffaceous beds MorphoZogy: strong brown (7.SYR S/6) medium and coarse sand; cutans (7 .SYR 4/4); Mn coatings; has similar properties to, but more weathered than Unit 12; indistinct boundary, 20 Unit 12 Pa:t>ent material: 6S cm colluvium derived from tuffaceous beds Morphology: variegated colour mosaic_ of fine, medium and coarse sands; many weathered basic volcanic granules and fine stones; matrix similar to material described for unit 22 with blocks of unit 14; indistinct boundary, Unit 13 Pa:t>ent material: 18 cm water-deposited tephra Morphology: laminations of dark yellowish brown (lOYR 4/4) silty clay and very pale brown (lOYR 7/4) fine sand; indistinct boundary, unit 14 Parent material: 20 cm water-deposited tephra Morphology: laminated; clay coatings (7.SYR 4/4) along vertical fractures; alternating layers of strong brown (7.SYR S/8) fine sand (with areas of secondary Fe ac'cumulation), light yellowish brown (lOYR 6/4) very fine sand, and pale yellow (2.SYR 7/4) silt; distinct boundary, Unit lS Pa:t>ent material: 4 cm water-deposited tephra Morphology: pale yellow (SY 7/3) fine and medium sand matrix with lenses of well laminated white (lOYR 8/2) silts; small zones of Fe accumulation (lOYR S/8); sharp boundary, Unit 16 Pa:t>ent material: 14 cm tephra Morphology: alternating layers of pale yellow (2.SY 7/4) silt and light yellowish brown (lOYR 6/4) silty clay, Unit 17 Pa:t>ent material: 18 cm tephra Morphology: white (SY 8/2) medium and coarse sand; well sorted; firm; bottom 5 cm strongly weathered lapilli fragments; - Fe nodules in top 2 cm; grades to fine sand matrix at base; sharp boundary, Unit 18 Pa:t>ent material: 13 cm water-deposited lapilli and coarse tephra Morphology: pale yellow (2.SY 8/4) medium and coarse sandy matrix with dark coloured lapilli fragments and very coarse sand; well sorted coarse fraction much of which is vesicular; grades - to coarser fraction at base (note reverse grading with layer 17); prominent lamination with thin light brownish grey (2.SY 6/2) silt and clay lenses; distinct boundary, Unit 19 Pa:t>ent material: 20 cm water-deposited tephra Morphology: pale brown (lOYR 6/3) silty clay; firm; well laminated with leaf imprints on laminae surfaces; coarse cobbles impressed along upper contact; sharp boundary, Unit 20 Pa:t>ent material: 10 cm water-deposited tephra Morphology: alternating layers of light brownish grey (2.SY 6/2) fine sand with lapilli and dark brown (7.SYR 3/2) silty clay; pronounced lamination; Fe (7.SYR 6/6) accumulation along bedding contacts; sharp boundary, Unit 21 Pa,rent material: 26 cm water-deposited tephra Morphology: morphologically similar to layer 23 but with pronounced lamination'; sharp boundary, 21 Unit 22 Pa:l'ent material: 18 cm tephra Morphology: yellow (2.5Y 7/6) and brownish yellow (lOYR 6/6) medium and coarse sand; many soft black (lOYR 2/1) dev1trified fragments; a few pyroxene minerals; pseudo bedding of coarse and fine fractions; much of coarse material is vesicular; well sorted apart from lapilli; soft, weathered palagonite inclusions; sharp boundary, Unit 23 Pa:l'ent material: 53 cm tephra Morphology: dark brown (7.5YR 3/2) silty clay; firm; conchoidal fracture; dark yellowish brown (lOYR 4/4) clay skins; fracture or pedological structure? (questionable paleosol), Unit 24 Pa:l'ent material: 150 cm+ in situ weakly weathered pyroclastic rock Morphology: well sorted tuff and ash-sized material with lapilli fragments; some vesicular clasts; yellow palagonite throughout (mapped Benson, 1968 as basaltic agglomerate of the First Eruptive Phase).