Palaeosol development in Quaternary marine sediments and palaeoclimatic interpretations, Spencer Gulf, Australia

Marine Geology, 61 (1984) 315--343

315

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

PALAEOSOL DEVELOPMENT IN QUATERNARY MARINE SEDIMENTS AND PALAEOCLIMATIC INTERPRETATIONS, SPENCER GULF, AUSTRALIA

N.B. BILLING

CSIRO Division of Soils, Glen Osmond, S.A. 5064 (Australia) (Accepted for publication March 19, 1984)

ABSTRACT Billing, N.B., 1984. Palaeosol development in Quaternary marine sediments and palaeoclimatic interpretations, Spencer Gulf, Australia. In: J.R. Hails and V.A. Gostin (Editors), The Spencer Gulf Region. Mar. Geol., 61: 315--343. A series of palaeosols developed in the Quaternary marine sediments of northern Spencer Gulf when exposed during successive glacio-eustatic low sea levels over the last ca. 220,000 yrs. The palaeosols show different degrees of pedogenic development from which palaeoclimatic inferences are made. Those formed prior to the 125,000 yrs B.P. marine transgression are the most strongly developed and leached, exhibiting strong, weUstructured, clay-rich B horizons, a feature not seen in later palaeosols. The younger palaeosols, formed after the late Pleistocene high sea-level phase, are not as strongly developed. Their most prominent features are carbonate accumulation horizons, even though they were, in places, exposed for as long as the pre-120,000 yrs B.P. palaeosols. Palaeoclimates inferred from the palaeosols suggest more humid conditions existed prior to ca. 125,000 yrs B.P. than have occurred since. Aeolian reworking of later palaeosols suggests arid phases occurred after ca. 125,000 yrs B.P. INTRODUCTION

The study of palaeosol development allows inferences to be made about palaeoclimates and soft environments. This is especially so if parent materials from which the palaeosols developed, are known. Many palaeosols from a variety of different environments and climatic zones have been described in the literature (Ruellan, 1974). Mostly they formed from terrigenous parent material such as alluvial, aeolian, volcanic or loessial deposits. However, studies of palaeosols developed in marine sediments are quite rare. The present study is a pedologic* and petrographic** analysis of palaeosols and the marine sediments from which they formed, as seen in vibrocores collected from the northern Spencer Gulf region of South Australia. Successive *Pedology is the study of the origin and classification of soils including the factors and processes of soil formation. **Petrography is the description and classification of rocks (soils in this case) usually based on microscopic study. 0025-3227/84/$03.00

O 1984 Elsevier Science Publishers B.V.

316 Quaternary transgressions and regressions of the sea into Spencer Gulf have left a sequence of marine strata which have undergone successive and differential pedogenesis. A preliminary study of palaeosols from cores in one part of this area has already been reported (Billing, 1981). The study of Quaternary soils developed over Australia's large inland areas, and the stratigraphy of lake-fills and associated deposits in geographically widespread areas, have traditionally been used to infer climatic histories (e.g. Dodson, 1975; Walker, 1978). This study of soil development in Quaternary marine strata, now submerged by the Holocene transgression, provides additional information on climatic history and provides a unique opportunity to examine pedogenic processes over distinct time intervals. STUDY AREA AND GEOLOGICAL SETTING Northern Spencer Gulf (Fig.l) lies within a seismically active region of South Australia bounded in the west by the ancient and stable Gawler shield and in the east by the folded and uplifted Flinders Ranges (Stewart and Mount, 1972). The climate of the northern Gulf grades from subtropical mediterranean in the south (Whyalla) to mediterranean desert in the north {Port Augusta) (Papadakis, 1975). Rainfall is winter dominant and ranges from 342 mm in Port Pirie to 244 mm in Port Augusta, with Whyalla receiving 271 mm annually. Mean daffy temperatures at Port Augusta are between 7°C minimum and 32°C maximum. Surface runoff is low because of the low rainfall and highly permeable soils of the region (Chittleborough et al., 1974), except after occasional high intensity, short duration rain storms. Five Quaternary marine units have been outlined by Hails et al. (1984a, this volume) in the subsurface of northern Spencer Gulf; the deposits are attributed to successive marine transgressions. During each regression, the marine deposits were exposed to subaerial weathering processes. The period of weathering which affected a particular sediment depended on its elevation relative to all subsequent high sea level stands. This is shown schematically in Fig. 2. The maximum levels reached by the various marine transgressions into Spencer Gulf have varied considerably. Deposits of the Older Pleistocene Beds and of the Mambray Formation are found at levels slightly higher than the present low water datum. Deposits of the False Bay Formation are limited to areas of the Gulf deeper than 8 m below low water datum, whilst sediments of the Lowly Point Formation are only found in areas deeper than 14 m below datum (Hails et al., 1984a, this volume). Germein Bay Formation deposits are found at heights up to 1 m above low water datum. These sedimentary deposits have ages estimated at ca. 220,000, 125,000, 105,000, 82,000 and 7000 yrs B.P., respectively (Hails et al., 1984b, this volume). These ages are used in this paper in an approximate sense only. Thus, deposits of the Older Pleistocene Beds were exposed for about 95,000 yrs prior to deposition of the Mambray Formation. The Mambray Formation sediments were exposed for either 20,000 yrs or 118,000 yrs before being covered by sediments of the False Bay Formation or the Germein Bay

317

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Yrx-0 0 o o AGE x 103yrsB.P INTERVALBETWEEN Germein Bay Formation 7 ~ TRANSGRESSIONSx 10:5yrs. (Holocene marine) t75 ] "Ll,l> Lowly Point Formation (L) 82 ~,23 ~'118 J 98 False Bay Formation (F) 105 Mambray Formation (M) 125 ~,20 J Older Pleistocene (0) 220 .95 marine beds Fig.2. Schematic diagram illustrating core penetration of Quaternary marine strata in the subsurface of northern Spencer Gulf, and the time available for soil formation at different

levels in the Gulf.

Formation respectively. The False Bay Formation was in turn exposed for either 23,000 or 98,000 yrs before it was covered by Lowly Point Formation or Holocene sediments respectively. Lowly Point Formation sediments have all undergone about 75,000 yrs of exposure until submerged by the Holocene transgression at around 7000 yrs B.P. The time available for pedogenesis has thus varied and several weathering phases may have affected any sediment not covered by subsequent marine inundations. Palaeosols which formed during single subaerial exposures are those which are contained between successive marine sediments. The extent of pedogenesis in these single-phase palaeosols can be used for palaeoenvironmental interpretations, since multiple weathering effects are not superimposed on them. STUDY METHODS Palaeosols developed in Pleistocene marine sediments were examined in m a n y of the 330 submarine vibrocores collected from northern Spencer Gulf (Hails et al., 1984a, this volume}. They were recognized within the sedimentary sequences by having "weathering profiles characterized by zonation into horizons" (Morrison, 1967). The host marine sediments and palaeosols were examined both macroscopically and microscopically. Five representative

319

cores (Fig.l), with well-developed palaeosols formed in marine sediment of different ages, were selected for detailed thin section studies. Sedimentary strata and palaeosols encountered in these cores are shown schematically in Fig.2. The m e t h o d o l o g y and terminology used follows that of Dunham (1962}, Brewer (1964), Braithwaite (1975) and Parfenova and Yarilova (1977}. These five cores are shown in Fig.3 and their location in Fig.1. The stratigraphic c o n t e x t of each core is seen in the local geophysical profiles (Gostin et al., 1984, this volume). The stratigraphy, formation names and age interpretations follow Hafts et al. (1984a, this volume). RESULTS

The palaeosols are discussed according to the relative ages of the sedimentary strata in which they occur.

Palaeosols on Older Pleistocene marine beds (ca. 220,000 yrs B.P.) Representative core 1 70 (Figs.3 and 4) Macroscopic features. Features of the soil profile for this time interval include a structured clay B horizon and a calcareous horizon of soft and nodular calcium carbonate below the clay horizon (see Table I). The profile is approximately 1 m thick and grades into the underlying weathered shelly marine sediment. In a previous report by Billing (1981) this palaeosol was considered to have formed in alluvial fan sediment because of the absence of marine features and intensely red soil colours. Micromorphology. Micromorphological examination of palaesols from this formation confirms the marine origin of the parent materials (see Fig.5 and Table I). The presence of undifferentiated glaebules* suggests in-situ formation produced during drying phases (Parfenova and Yarilova, 1977, p.32). Palaeosols on Mambray Formation (125,000 yrs B.P.) Representative cores 170 (Fig.4); 79 (Fig.6) Macroscopic features. The soil material formed over the Mambray Formation marine sediments contained dispersed, weathered shell fragments, throughout (see Table I). In the two examples shown (Figs.4 and 6) it appears that the upper horizons are truncated or reworked as only 20--30 cm of the profile is preserved. In core 79 hard, rounded calcrete pisolites are contained within a fine carbonate mud matrix. The pisolites range from * G l a e b u l e s a r e 3 - D n o d u l e s o r concretions having a g r e a t e r c o n c e n t r a t i o n o f some constituent a n d / o r a difference in fabric compared with the enclosing soil m a t e r i a l o r a distinct b o u n d a r y w i t h the soil m a t e r i a l .

1

See Fig. 8

No. 109 2 3 4

1

?ig.3. R e p r e s e n t a t i v e cores f r o m n o r t h e r n S p e n c e r Gulf.

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P a l a e o s o l on o l d e r p l e i s t o c e n e marine beds• Brown A h o r i z o n over a reddish-brown strongly C t . cm. s tarluccatrueroeuds ct hl ar oy u gath o u265 Carbonate i n c r e a s e s to 285 cm.

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Fig.4. Lithostratigraphy and palaeosols of core 170 and the local sub-bottom profile (for symbols, see Fig.2). Depths below low water datum•

COLOUR

HORIZON DEVELOPHENT

OTHER FEArURES

1

II

IIl

-

1. Strong structural development Cpedality) 2. Harine fossil s h e l Is are not seen macroscopically (Fig.4) /Bi/ling, 1981)

1. A clay-rich (45-55% clay) B-horizon has developed, 2. A calcareous h o r i z o n of s o f t and h a r d nodules is present in the lower B horizon, 3. Carbonate is not completely l e a c h e d from the upper horizons, 4. Th e A-B h o r i z o n transition is distinct.

A

horizon br own ( 7 . 5 Y R 5 / 4 ) B - horizon r e d d i s h brown (5YR4/6)

Older Pleistocene Beds (c.220,O00 yr B.P.)

Features observed in the palaeosols

TABLE I

1. No s t r u c t u r a l development 2. Weathered shell fragments are visible in t h e p a l a e o s o l s and parent material, 3. Upper horizons are truncated on r e w o r k e d tommonly,

1. Hoderate clay illuviation has resulted in a weakly clay enriched horizon, 2. A calcareous horizon w i t h r o u n d e d and h a r d calcrete pistolites 2-20ram s i z e . 3. weakly leached,

whole soil brown ( 1 0 Y R 5 / 3 ) Parent material has red and yellow mottling in upper position.

MACROtlORPHOLOGY

Mambray F o r m a t i o n (c.125,000 yr B.P.)

soil (10YR5/3)

1. S h e l l s a r e common i n b o t h the. s e d i m e n t a n d t h e palaeosols. They are more w e a t h e r e d and friable in the upper palaeosols than in tile parent material. 2. Palaeosol thickness ranges from 40-170cm.

1. Little o r no i l l u v i a l clay-rich horizons 2. Weak d i t [ n s e calcareous horizons with mostly soft carbonate

whole brown

F a l s e Bay F o r m a t i o n (c.lO5,000 yr B.P.)

soil b ro w n ( 1Y5/2 )

l. No s t r u c t u r a l dew, lopmenL 2. Shelly material is obvious throughout

1. Little o r no t l l u v i a l clay-rich horizons carbonate enriched horizon.~ w i t h s o f t and h a r d c a r b o n a t e ' 2. Weakly developed 3. Sharp boundaries beLu, e e n u p p e r a n d l o ~ ' e r horizons suggests trunc a t i o n a n d r e w o r k i n g o[ the upper prolile

whole 1ight

L o w ly P o i n t f ' o r m a t i o n (c.82,000 yr B.P.)

SURFACEHORIZONS

ILLUVIAL HORIZONS

I

II

1. Improved s i z e s o r t i n g and rounding compared to the lower palaeosol, suggesting aeolian reworking of upper palaeosol. (Fig. 7c, d)

1. Clay glaebules with 1. D a r k c l a y g l a e b u l e s desiccation cracks often often with desiccation present. Glaebules have cracks, undifferentiated fabric 2. Brown micritic Calcareous glaebules were patches occur in the not present (Brewer,1964) lower profile. 2. Hicritic calcite 3. Glaebules have coatings occur around shelly cores, sand grains and as void 4. Calcite infilled infilling. (Fig. 5b) vughs and cavities are 3. Increased proportions present, of plasma and improved 5. Carbonate coatings sorting and rounding in are seen around grains the palaeosol compared in the calcareous horizon. to the parent material (Fig. 5a, c) 4. Small shell fragments and forams are commonly observed in both the underlying sediment and the palaeosol and are more weathered near the surface. 5. Clay coatings and carbonate coatings are present around voids 6. Clay lamellae were not observed.

1. Sand g r a i n s s u p p o r t e d in fine matrix, 2. Sand grains not well sorted or well rounded No evidence for aeolian activity 3. Carbonate has been partly leached out (Fig. 5a)

MICROMORPHOLOGY

1. S o f t d i f f u s e c a r b o n a t e 1. C a l c i t e l i n e d vughy and discrete calcareous cavities and grain haloes glaebules are present in imply porosity reduction some palaeosols of original sediment by (Fig. 10e,c) leaching. 2. Calcite crystal 2. Brown micritic overgrowth of vughy carbonate plasma matrix cavities (Fig. lOb,e) supports poorly sorted 3. Brown micritic calcite angular and rounded quartz: entirely forms the matrix sand (Fig. 12b) of the palaeosols in 3. Shell material is core 223, but shell is weathered and micritized. also present in core 120 4. Very few elastic sand grains are present in the calcareous horizons of cores 223 and 120 which may indicate restricted circulation marine or evaporitic type of sediment source.

1. Good s i z e s o r t i n g , 1. Well r o u n d e d and s i z e rounding -aeolian reworked sorted sand - aeolian reworked reworked. 2. Very little fine grained matrix. 3. Reduced maximum grain size (sorting) compared to the carbonate horizon. (Fig. 12a, b) 4. Rounded calcilutite and limestone sand grains are present amongst the largely quartzose grainstone. (Dunham, 1962) ( F i g . 12a)

Oo to &o

tO

325

Fig.5. A. Core 170, 236--242 cm, crossed polarisers; Sediment (above)A-Horizon boundary (diagonally across top right-hand corner) of palaeosol on Older Pleistocene marine beds, showing depletion of carbonate in palaeosol (leached) and greater proportion of clayey matrix compared with the Mambray Formation marine sediment above the boundary. Scale = 1 ram. B. Core 170, 276--280 cm, plain light. Calcareous horizon of palaeosol on Older Pleistocene marine beds. Calcitic cutans mantle some sand grains and voids (1). Forams and weathered shell fragments are present (2). Scale = 1 mm. C. Core 170, 378--380 cm, crossed polarisers. Older Pleistocene marine beds below palaeosol. Echinoid (1) and shell fragments (2) are common. Scale = 1 mm.

a b o u t 2 to 20 mm in diameter and often contain marine fossils. The colours of these palaeosols (Munsell Soil Colour, 1 0 Y R 5 / 3 ) are lighter than the underlying older palaeosols and have a much more abundant shelly fauna. The underlying parent sediment is mottled red and yellow (see Table I).

Micromorphology. Thin section studies of the Mambray Formation palaeosols illustrate that there has been some clay enrichment as well as calcareous horizon development and subsequent induration (see Fig. 3 and Table I). In core 170 the upper part of the palaeosol contains dark clay glaebules which often have cracks. Thisis underlain by a calcareous horizon in which carbonate coatings on grains are common. Brown micritic patches are the main signs of pedogenesis in the lower part of the profile (e.g. Braithwaite, 1975) even though the Mambray Formation sediment in this case has been exposed from ca. 125,000 to ca. 7000 yrs B.P.

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becoming less calcareous below 350. Some carbonate nodules 3 0 0 - 3 6 0 cm. Some red mottles a r o u n d 3 0 5 cm.

------ ' -- __,

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orange, brown and white, m a r i n e s e d i m e n t a t 3 5 0 cm.

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The palaeosol on Mambray Formation sediment in core 79 (Fig.6) is truncated down to a layer of hard calcrete rubble. In thin section these micritic calcite, laminar coated glaebules contain agglomeratic shelly cores (Figs.7A, B) often with vughs displaying calcite crystal growth around the walls. In the lower profile (Fig.7B) clay-rich dark brown micritic laminar-coated glaebules are contained in a pale buff micritic matrix. The parent marine sediment shows some clay-rich, red mottles and other diagenetic changes as shown by diffuse, irregular, brown micritic patches similar to those reported by Braithwaite (1975) in Aldabra and by James (1972) and Harrison (1977} in the Caribbean. Improved sorting and rounding of sandgrains in the upper part of the palaeosol, when compared with the underlying sediment suggests that there may have been some aeolian reworking (Fig.7C, D}.

Palaeosols on False Bay Formation (ca. 105,000 yrs B.P.) Representative cores 109, 120, 223 (Figs.8, 9 and 11) Macroscopic features. Palaeosols developed in this marine sediment are mostly brown coloured (10YR5/3m), strongly calcareous and contain weathered shell fragments. Diffuse red mottlings are common at the transition to the underlying parent material which tends to have an olive and olive green colour. The most prominent feature of these palaeosols is the carbonate-enriched zone (calcareous horizon) consisting of diffuse soft carbonate with a few calcrete pisolites. Clay enrichment is minimal. Weathering of shells is more pronounced in the upper part of the palaeosol, decreasing gradually with depth. Thicknesses of sola preserved range from 40 to 170 cm. Note: In cores 109 (Fig.8} and 120 (Fig.9) False Bay Formation sediment has been exposed from ca. 105,000 yrs B.P. until the Holocene transgression. In core 223 the palaeosol in False Bay Formation sediment developed in the time interval 105,000--82,000 yrs B.P. (Fig.ll). Micromorphology. Palaeosols on the False Bay Formation have developed calcareous horizons to various degrees in the cores examined. Clay-enriched horizons were less evident, although the common occurrence of red-brown clay glaebules in the upper part of the palaeosol remnants suggests that clayey horizons may have been developed. However, truncation of the upper profile precludes further comment.

Fig. 7. C. Core 170, 130 cm, plain light. Upper horizon of Mambray Formation palaeosol with cracked clay glaebules (1) (clay sand?), rounded quartz sand (2) and rounded carbonate sand in a buff coloured micritic plasma matrix. Note improved sand grain-size sorting compared to Fig.6D. Scale = 1 mm. D. Core 170, 165--170 cm, plain light. Lower Mambray Formation palaeosol calcareous horizon. Diffuse micritic carbonate matrix (1) (no nodules or segregations)supporting rounded and angular quartz sand, forams and thin shell fragments (2). Scale = 1 mm.

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FALSE BAY FORMATION

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P--D~"~

I.'~_i.~ ~ ~5

Clear change to: Palaeosol. Brown

(I0 YR 5/3) sandy clay, massive, firm. Gradual chanse to: Pale brown (i0 YR 6/3) Light to medium clay (firm, sandy)• Slightly indurated massive carbonate common as above, more concretionary, shell fragments less weathered in appearance. Gradual chanse to: Grey-olive estuarine shelly wackestone, some pale carbonate mottlings. Pale-olive colour at base.

=

FALSE BAY FORMATION

Fig.9. Lithostratigraphy and palaeosols of core 120 and the local sub-bottom profile (for symbols see Fig.2). Depths below low water datum. R refers to reworked material.

332 Strong evidence of aeolian reworking is seen in the upper profiles of all the False Bay Formation palaeosols, in particular, sand grains are well rounded and well sorted (Fig.10A, D).

Palaeosols on the Lowly Point Formation (ca. 82,000 yrs B.P.) Representative core 223 (Fig. 11) Macroscopic features. Palaeosols formed on this unit exhibit weak calcareous horizons in which there is also slight clay enrichment, however, the brown, sandy upper horizons have been eroded and reworked (see Table I). The calcareous horizons are composed mainly of diffuse soft carbonate although nodular concretions also occur. Complete and fragmented shells are visible in this carbonate horizon although they are weathered and often friable. Micromorphology. Micromorphological studies also show that the weakly leached soil has had aeolian reworking in the upper part (see Fig.12 and Table I). DISCUSSION The present-day climate of northern Spencer Gulf is semi-arid and leaching processes in modern soils are not intense (as seen in Chittleborough et al., 1974, p.23). The small amount of fluvially transported sediments brought into the gulf are incorporated in the skeletal, carbonate-rich, subtidal marine sediment. There are no major deltaic or continental red bed sediments intercalating with the Holocene marine sediment or intertonguing within earlier Pleistocene marine strata, except in isolated localities (Hails et al., 1984a, this volume}. Climatic inferences may be derived from the nature of the palaeosols developed in the marine sediments. Aeolian contributions, horizonation, carbonate dissolution and deposition, accumulation of organic matter, textural changes caused by clay illuviation and also microscopic features can provide clues to palaeoclimatic conditions. Evidence for in-situ palaeosol formation in marine sediment comes from examination of the sharpness of boundaries to the underlying sediment, presence of clay nodules (papules of Brewer, 1972) and the presence of externally derived materials transported by aeolian or fluvial agencies. Semi-arid and arid soil environments result in the development of indurated carbonates (calcretes) which, once formed, persist for a long time, even under changed environmental conditions (Yaalon, 1971, p.36). Other pedogenic features are more transient, such as organic horizons, mottles and some chemical characteristics; persisting at most for only a few thousand years after burial (Yaalon, 1971; Table II). The palaeosols which formed on Pleistocene marine sediments of Spencer Gulf thus still display variously devel-

335

carbonates seen in the upper horizons of these palaeosols, closer affinity is suggested with the Desert Loams than with the Red-Brown Earths. Their generally thin sola (<1 m) accords with this suggestion. The aeolian reworking of the upper horizons of the palaeosols may post-date the formation of the illuvial horizons and thus cannot be used as climo-pedogenetic evidence. It is not suggested that softs elsewhere, similar to these palaeosols, are the same age, indeed younger counterparts or equivalents have been described from the region (Williams, 1973). As there is very little information in the literature about palaeoclimates from this epoch, interpretations must be rather more speculative than for later weathering episodes. On the basis of past oxygen isotope levels (Chappell, 1974, 1976; Bowler, 1980) the epoch was considered to be warm initially, with gradual cooling toward the glacial phase around 115,000 yrs B.P., although there were several fluctuations within that trend. Palaeosols on the Mambray Formation (ca. 125, O00--ca, 105,000 yrs B.P. -- R e c e n t weathering epochs) Only a moderate degree of pedogenesis is displayed in the palaeosols developed on the Mambray Formation, notwithstanding that in the representative cores cited (cores 79 and 120), the sediment has been continuously exposed until the Holocene transgression. The degree of pedogenesis of the Mambray Formation palaeosols is only slightly greater than that seen on younger sediments. Therefore, it can be inferred that subaerial weathering has not been intense in the Spencer Gulf region for the last ca. 125,000 yrs. There is some variation in the carbonate content of the parent materials and this is reflected in the degree of calcareous horizon development. Clay illuviation and carbonate leaching are moderately expressed macroscopically and the latter is easily observed in thin section as micritisation and carbonate coatings on sand grains (Fig.7A, B). Laminar coated calcrete nodules ob-

Fig.10. A. Core 120, 160--165 cm, plain light. Aeolian reworked upper False Bay Formation palaeosol showing well-rounded and sorted sand grains. B. Core 120, 300--315 cm, plain light. False Bay Formation palaeosol fine-grained nodular calcrete with vughy calcite lining voids (1). Very little detritus, occasional gastropod shell (2). Scale = 1 ram. C. Core 109, 145 cm, plain light. Pseudo-ooliths in upper reworked False Bay Formation palaeosol (1). Laminar coated, rounded sand-size grains are loosely supported in a micritic calcite matrix (2). Scale = 1 ram. D. Core 223, 260 cm, crossed polarisers. Medium sand from upper False Bay Formation palaeosol. Rounded clay glaebules (1) also occur. Very little carbonate remains, only as thin grain coatings (2). Scale = 1 ram. E. Core 223, 410 cm. Soft carbonate at base of False Bay Formation palaeosol with very little quartz sand in a micritic carbonate plasma matrix. Faint pseudo-ooliths are strongly micritised (1). Vughy coatings line voids (2). Scale = 1 mm.

336 Meters to

LINE 30

223 ....

.

I

15

500m

I

M M \ ,-~,-~M

223 Ocm ,,.,,.

~.,,, ..~ ..-..,

Grey

•

.

• •.

.

.

L ~ 'r

shel

Psktlat-ine

wackestotle.

.

". . .

.

FORMAT ION

t :¢ ~ T . :

.'.'.,.'. : !".," • ".'" • .2 .... ".'.'.'.i

130 - -

C::::::: _'~'.L'._~

o o ~ 0o

2:30

:" . ' . ' . '

,

.,

.

.

.

.

.

LOWLY POIN'I --FORHATION

abruptly

•

ca

loamy

sand

to

overlying

sandy pink,

Ioanl soft

rbonate.

•

.

..-

.'. ". ' ' . ' •"' ' ..... .-

/

Clear chan~e tg: P a l a e o s o i on FAI,SE BAh' Fro.

""

. • •, ...

G r a d u a l chan~e to: Pale grey shelly estuarine marine, includes rubbly calcareous horizon of palaeosol.

Brown

i.~"-"

HOLOCENE PLEISTOCENE

a,,d lo~,,,y ~and. t70

¢'o~ ~ 0e'~Q o ,o •

----". " . ' . -

Cle_~y..ehan~e to: P a l a e o s o l on LOWLY POINT Fm. Upper soil horizon - aeolian r e w o r k e d brown s a n d y loam

FAI.SE BAY FORMATION

• .

. .

• . -.. • ..

-"

• -"

..

..... . . "... ......

410 s o f t ,

massive,

pink

calcreke.

F i g . l l . Lithostratigraphy and palaeosols o f eore 223 and the loeal s u b - b o t t o m profile (for symbols

see Fig.2).

Depths

below

low water

datum.

337 T A B L E II Summary of sediment--palaeosol--climate relationships

HAR lNE D E P O S [TS (yea rs •. P. × I0 ~ a p p r o x ) 7-

G E R H E [ N BAY F()RHAT ItiN

P A L A F; O S O L S C L A S S I F I CAT ION

FEATURES

DEPOSITION

OF G E R H E I N

CL IH A T I C INFERENCE

BAY F O R M A T I O N

P A L A E O C L I H A T lC EVIDENCE FROH L IT E R A T U R E

Warm Cool, very arid (Dunefields, W.A. ) 17,000 B.P.

cooler.

wetter,

A l l u v i a l de pos i t s , Burra Creek. Arid. Fossil Pt. Augusta,

dune

36,000 B.P.

Weakly developed palaeusols with diffuse sott, liue earth carbonate horizons 1ormed over c.75,000 years Aeol Jan reworked Ul)l)er Ilorizolls. 82-

I.OW[.'l P O I N T I't)RHAT [ tin

DEPOSITION

f A L S E I~A~ I ORHAI'I ON

HAHBRAY H)RHAI']ON

Arid. from

DEPOSITION

Warll/ 6 0 1 8

Calcareous Sands I,oams a nd So[ollised Bruwn Soils.

Semi-arid becoln i ng arid last.

Arid. PaJaeosols I r o m ] a Re f I o o r s , Warm 6 0 1 8 c u r v e

Calcareous Red Earths and Grey[)rOWIl C a l c a r t , o t l s Soils (Aridisols)

F]uttuating moist/dry arid last.

Cool

6 0 I~* c u r v e

Warm 6 0 1 8

curve

Cold 6 0 1 8

curve

Red Duple× Soils e.g. Red-brown Earths or Desert Loams (Alfisols or Aridisols)

Wet-dry climates) either season= ally humid or semi-arid

mihl

O[.DER I'I,E 1 S'['OCENE HARI NE BEDS

turv(.

OF ~IAHBRAY F O R H A T I O N

Strongly developed palaeosols with red-hrown clay B subsoil and difluse soit ca l c i iiiii ca r b o n , l t e horizons.

220-

Palaeosols lake floors

BEPOSI'I'I(}N OF" FALSE BAy EORNATION Weakly developed i,alaeosols with {drhollat(, ilodul(,s in t h e c a l t a r e o u s Jl o t- i z o [ l , Sum{, clay i [luviation

125-

Flu(tuating Semi-arid to arid becoming very arid last.

OF I,O~41,Y P O I N T FONHATION

Weakly dev('loped pa I aeo so [ s w i t h di[ltlse solt ( a rboii;ite h~)rizons ~ontgli[H[) g a l('~ ( e ~ l e l l t e d llo,lu [ e s .

105-

Calcareous Sands and Sulonised Brm,'n SoiLs. (Aridisols)

601~* c u r v e

DEPOSI'IION OF OLDER P L E I S T O C E N E PIARINE BEDS

N a r m 6018

(Bo~'l e r ,

curve 1980)

~0

339

served throughout the profile of the palaeosols suggest fluctuating moist and dry soil conditions (Braithwaite, 1975). Aeolian reworking of the upper horizons, also a common feature, is most likely to be associated with cool, arid and windy (low sea level?) phases. Inland, near Whyalla, there are Calcareous Red Earths (Stace et al., 1968, Profile 24C) similar to the Mambray Formation palaeosol of core 170, whereas in core 79, the Mambray Formation palaeosol is similar to the GreyBrown Calcareous Softs group (Stace et al., 1968, Profile 7B). Both may be termed Aridisols (Soil Survey Staff, 1975). In Australia the Calcareous Red Earths are widespread in the semi-arid to arid regions on undulating plains and pediments (Stace et al., 1968, p.248) whereas the more highly calcareous Grey-Brown Calcareous Soils are "associated with limestone and highly calcareous sedimentary rocks wherever they are exposed in semi-arid to arid regions. They occur extensively in South Australia, on the Nullabor Plain and adjacent a r e a s . . . " (Stace et al., 1968, p.55). According to Chappell (1974) and Bowler (1980), the 125,000--105,000 epoch began with a warm phase, slightly warmer than present, then cooled toward ca. 110,000 yrs B.P. before sea level rose again at ca. 105,000 yrs B.P. The features seen in the palaeosols suggest development under relatively arid conditions and that the region did not experience extended humid climates. Palaeosols on the False Bay Formation (ca. 105,000--ca. 82,000 yrs B.P. -- R e c e n t weathering epochs) The development of weak, diffuse calcareous horizons and the lack of definite iUuvial clay horizons suggests a climate where precipitation has been sufficiently effective to leach some carbonates but not seasonal enough for the development of clayey B horizons (Chittleborough, 1981). Where the False Bay Formation has been continuously exposed until the Holocene, as in core 109, palaeosols are not strongly developed, implying that weathering conditions were not intense for this entire period. Furthermore, aeolian reworking of the upper part of palaeosols underlying the Lowly Point Formation, as in core 223, points to an arid, windy phase prior to the 82,000 yrs B.P. transgression. These palaeosols broadly equate with the Calcareous Sands (Stace et al., 1968, Profile 4A), Solonized Brown Soils (Stace et al., 1968, Profiles 19D, 19F) or Calcareous Loams (Northcote et al., 1975, p.24) depending on

Fig.12. A. Core 223, 140 cm, crossed polarisers. Aeolian reworked upper palaeosol. Roun d ed sand grains of quartz (1), and clayey carbonate (2) are common. Very little matrix is present. Note composite carbonate and quartz sand grain (3). Scale = 1 mm. B. Core 223, 200 cm, crossed polarisers. Calcareous, clay-rich horizon in lower paleosol on Lowly Point F o r m a t io n showing poorly sorted angular and rounded sand in brown micritic carbonate/clay matrix (1). Vughy calcite lines pores (2). Scale = 1 ram.

340 solum thickness and texture of parent materials. They are Aridisots in the U.S. Soil T a x o n o m y {Soil Survey Staff, 1975). Bowler (1980) suggests a long, dry interval from ca. 100,000 to ca. 50,000 yrs B.P. in the Mallee regions of New South Wales and Victoria on the basis of degree of pedogenesis in palaeosols beneath lake sediments. The South Australian data presented here agree with this hypothesis. Palaeotemperature curves (Chappell, 1974) show the ca. 105,000--ca. 82,000 yrs B.P. epoch to contain several minor fluctuations within a generally warm period. Palaeosols on the Lowly Point Formation (ca. 82,000--7000 yrs B.P. weathering epoch) The generally weak development within the palaeosols suggests arid to semi-arid climates for this interval (see Table II}. Clay horizons developed in the lower parts of the profiles are pedogenic responses to pluvial phases of climate viz. illuviation, leaching, ground-water effects (Fig.12B). Wind action during drier periods has, however, reworked the palaeosols down to the calcareous horizons and thus clay horizons were n o t observed intact (Fig.12A). Banding of carbonate within calcareous horizons indicates variations, either in leaching, suggesting fluctuating climates, or in level of water tables. Present classifications of similar terrestrial soils are Calcareous Sands or Solonized Brown Soils (Stace et al., 1968}, Aridisols (Soil Survey Staff, 1975). Recent work on lake levels and palynological evidence in Victoria, New South Wales and South Australia {Dodson, 1975; Walker, 1978; Bowler, 1980) suggests that there was a long dry interval until ca. 50,000 yrs B.P., followed by a wetter or cooler climate similar to the present until ca. 26,000 yrs B.P., then becoming drier until ca. 10,000 yrs B.P. Palynological evidence from the Nullarbor region in Western Australia and South Australia, also shows that the period ca. 20,000--10,000 yrs B.P. {encompassing the last glacial) was more arid than the present {Martin and Peterson, 1978). Similarly, palaeosols and aeolian sands in Western Australia indicate an intense aridity around 17,000 yrs B.P. during the last glacial maximum (Wyrwoll and Milton, 1976}. In the arid zone of South Australia, north of Spencer Gulf, palaeosols and alluvial fan sediments suggest broadly similar climatic sequences for this epoch (Williams, 1973). A fossil-bearing dune formed before 40,000 yrs B.P. was reactivated intermittently until 36,000 yrs B.P. (Williams, 1981). C-14 dates on charcoal and soil carbonates from alluvial fan deposits from Burra Creek, some 100 km east of Spencer Gulf indicate a return to a more pluvial climate (at least intermittently) after 36,000 yrs B.P. (D.L.G. Williams, pets. commun., 1982). Palaeotemperature curves show several fluctuations within an overall cooling trend for the ca. 82,000--17,000 yrs B.P. interval (Chappell, 1974; Bowler, 1980}. There is evidence {such as layered carbonate horizons} for climatic fluctuations within the palaeosols from this interval, however, truncation of the profiles during late arid, windy phases has made precise interpretations difficult.

341

Synopsis of palaeosols and palaeoclimatic inferences The oldest palaeosols, on the Older Pleistocene marine beds, are also the most strongly leached (see Tables I and II). This development occurred either during a long period of exposure or under more pluvial conditions than exist at present. The upper horizons are only slightly calcareous having been mostly leached of carbonate (Bathurst, 1975). Horizons of CaCO3 accumulation, containing soft nodular carbonate, were formed in the lower part of the strongly clay-enriched B horizons. All the younger palaeosols formed over the next three weathering intervals are less well developed, but have calcareous horizons in various stages of development (see Tables I and II). Most of the six stages of carbonate horizon development in relation to soil age (Brewer, 1972) (viz. fine earth carbonate; coatings and filaments; nodules; crystal sheets and cemented nodules; complete cementation; complete leaching), are observed. Palaeosols within Older Pleistocene beds have been exposed for up to ca. 75,000 yrs and contain only soft carbonate segregations in moderately well leached profiles. The Mambray Formation palaeosols at higher levels have undergone pedogenesis for ca. 118,000 yrs and contain soft and cemented nodules in the carbonate horizons. The False Bay Formation paiaeosols, exposed for ca, 23,000-98,000 yrs, have diffuse, soft {fine earth) carbonate horizons with a few cemented nodules. The Lowly Point Formation palaeosols contain only diffuse, soft (fine earth) carbonate horizons which formed over ca. 75,000 yrs of exposure. The oldest palaeosols may have had several phases of weathering and leaching. Illuvial clay-enriched B horizons may take only 5000 yrs to develop under certain conditions, according to Ballagh and Runge (1970), so these well-developed palaeosols may reflect a short period when optimal conditions existed during the pre-125,000 yrs B.P. weathering period. If so, it appears that these conditions were not subsequently repeated in the northern Spencer Gulf region because younger palaeosols are less well developed. Further studies of clay minerals a n d their transformations, resistant mineral ratios down profiles, X-ray diffraction studies of calcite to aragonite ratios and magnesium to calcium ratios in the carbonate of the palaeosols compared with "unaltered" marine sediments will further elucidate the understanding of soil forming conditions and palaeoclimatic sequences (Gavish and Friedman, 1969; Hutton and Dixon, 1981). CONCLUSIONS

The palaeosols described were formed as a result of pedogenic processes operating on marine sediments, periodically exposed, during the last 220,000 yrs. Varying degrees of soil development occurred. Differences between the palaeosols are related particularly to the duration of exposure and the prevailing climates operating on the parent materials. Other factors affecting the resultant palaeosols were their positions in the landscape, gains or losses of

342 s e d i m e n t a n d various localized c o n d i t i o n s , particularly organic influences. T h e palaeosols e x a m i n e d f r o m within the f o u r main w e a t h e r i n g e p o c h s have differing degrees o f pedogenesis. T h e y s h o w b r o a d c o n c u r r e n c e with palaeoclimatic evidence f r o m elsewhere in s o u t h e r n Australia. ACKNOWLEDGEMENTS T h e a u t h o r t h a n k s Drs. A.P. Belperio, V.A. G o s t i n a n d J.R. Hails for providing the stratigraphic f r a m e w o r k , seismic i n t e r p r e t a t i o n s , relative/absolute ages o f m a r i n e sediments, and the palaeoshoreline i n f o r m a t i o n on w h i c h this w o r k is based. V.A. Gostin, K.H. N o r t h c o t e , A.P. Belperio, G.M. B o w m a n a n d J.R. Hails reviewed and c o m m e n t e d o n the m a n u s c r i p t . J. T h o m p s o n assisted with p r e p a r a t i o n o f t h e thin sections. F. Gorostiaga, J. Coppi, and S. Proferes p r o v i d e d technical, p h o t o g r a p h i c and d r a u g h t i n g assistance. REFERENCES Ballagh, T.M. and Runge, E.C.A., 1970. Clay-rich horizons over limestone -- alluvial or residual? Soil Sci. Soc. A m . Proc., 34: 534--536. Bathurst, R.G.C., 1975. Carbonate Sediments and their Diagenesis (2nd ed.). (Developments in Sedimentology, 12) Elsevier, Amsterdam, 658 pp. Billing, N.B., 1981. Palaeosols and sediments of upper Spencer Gulf, South Australia. Descriptions and preliminary interpretations. C S I R O Aust. Div. Soils Divl. Rep.,

56/81, 23 pp. Blackburn, G., Bond, R.D. and Clarke, A.R.P., 1965. Soil development associated with stranded beach ridges in south-east South Australia. CSIRO Aust. Soil Publ., 22, 65 pp. Bowler, J.M., 1980. Quaternary chronology and palaeohydrology in the evolution of Mallee landscapes. In: R.R. Storrier (Editor), Aeolian Landscapes in the Semi-arid Zone of Southeastern Australia. Australian Society of Soil Science (Riverina Branch), Wagga Wagga, N.S.W., 17--36. Braithwaite, C.J.R., 1975. Petrology of palaeosols and other terrestrial sediments on Aldabra, Western Indian Ocean. Philos. Trans. R. Soc. London, Ser. B, 273: 1--32. Brewer, R., 1964. Fabric and Mineral Analysis of Soils. Wiley, New York, N.Y., 482 pp. Brewer, R., 1972. Microfabrics and soil history. In: R. Protz (Editor) Microfabrics of Soil and Sedimentary Deposits. Proceedings of a Symposium, Guelph, Ontario March 29-30, 1972. Univ. Guelph Dep. Land Resour. Sci., Centre Resour. Dev. Publ., 69: 161-196. Chappell, J., 1974. Relationships between sea levels, 180 variations and orbital perturbations, during the past 250,000 years. Nature, 252: 199--202. Chappell, J., 1976. Aspects of late Quaternary palaeogeography of the Australian--east Indonesian region. In: R.L. Kirk and A.G. Thorne (Editors), The Origin of the Australians. Australian Institute of Aboriginal Studies, Canberra, A.C.T., pp. 11--22. Chittleborough, D.J., 1981. Genesis. In: J.M. Oades, D.G. Lewis and K. Norrish (Editors), Red-Brown Earths of Australia. Waite Agric. Res. Inst., Univ. Adelaide and CSIRO Aust. Div. Soils, 168 pp. Chittleborough, D.J., Maschmedt, D. and Wood, R,Mc.R., 1974. Soils and Land Use of the Redcliff Point area, South Australia. South Aust. Dept. Agriculture, Specific Land Use Survey SS5, 26 pp. Dodson, J.R., 1975. Vegetation history and water fluctuations at Lake Leake, southeastern South Australia. II, 50,000 to 100,000 B.P. Aust. J. Bot., 23: 815--831. Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. In: W.E. Ham (Editor), Classification of Carbonate Rocks -- a Symposium. Am. Assoc. Pet. Geol., Tulsa, Okla., pp.108--121.

343 Gavish, E. and Friedman, G.M., 1969. Progressive diagenesis in Quaternary to Late Tertiary carbonate sediments: Sequence and time scale. J. Sediment. Petrol., 39: 980-1006. Gostin, V.A., Sargent, G.E.G. and Hails, J.R., 1984. Quaternary seismic stratigraphy of northern Spencer Gulf, South Australia. In: J.R. Hails and V.A. Gostin (Editors), The Spencer Gulf Region. Mar. Geol., 61:167--179 (this volume). Hails, J.R., Belperio, A.P., Gostin, V.A. and Sargent, G.E.G., 1984a. The submarine Quaternary stratigraphy of northern Spencer Gulf, South Australia. In: J.R. Hails and V.A. Gostin (Editors), The Spencer Gulf Region. Mar. Geol., 6 1 : 3 4 5 - - 3 7 2 (this volume). Hails, J.R., Belperio, A.P. and Gostin, V.A., 1984b. Quaternary sea levels, northern Spencer Gulf, Australia. In: J.R. Hails and V.A. Gostin (Editors), The Spencer Gulf Region. Mar. Geol., 61:373--389 (this volume). Harrison, R.S., 1977. Caliche profiles: indicators of near-surface subaerial diagenesis, Barbados, West Indies. Bull. Can. Pet. Geol., 25: 123--173. Hutton, J.T. and Dixon, J.C., 1981. The chemistry and mineralogy of some South Australian calcretes and associated soft carbonates and their dolomitisation. J. Geol. Soc. Aust., 28: 71--80. James, N.P., 1972. Holocene and Pleistocene calcareous crust (caliche) profiles: Criteria for subaerial exposure. J. Sediment. Petrol., 42: 817--836. Martin, H.A. and Peterson, J.A., 1978. Eustatic sea-level changes and environmental gradients. In: A.B. Pittock, L.A. Frakes, D. Jenssen, J.A. Peterson and J.W. Zellman (Editors), Climatic Change and Variability. Cambridge Univ. Press, Cambridge, pp.108--124. Morrison, R.B., 1967. Principles of Quaternary soil stratigraphy. In: R.B. Morrison and H.E. Wright (Editors), Quaternary Soils. Proe. Int. Assoc. Quaternary Research (INQUA), 8: 1--113. Northcote, K.H., Hubble, G.D., Isbell, R.F., Thompson, C.H. and Bettenay, E., 1975. A Description of Australian Soils. CSIRO, Glen Osmond, S.A., 170 pp. Papadakis, J., 1975. Climates of the World and Their Potentialities. The Author, Buenos Aires, 70 pp. Parfenova, E.I. and Yarilova, E.A., 1977. Handbook of Micromorphological Studies in Soil Science. Nauka, Moscow, 178 pp. (Translated from Russian by P. Aukland). Ruellan, A., 1974. Bibliography on Palaeopedology, 2nd list. International Union for Quaternary Research, Palaeopedology Commission, 439 pp. Soil Survey Staff, 1975. Soil Taxonomy. USDA Agric. Handbook No. 436,754 pp. Stace, H.C.T., Hubble, G.D., Brewer, R., Northcote, K.H., Sleeman, J.R., Mulcahy, M.J. and Hallsworth, E.G., 1968. A Handbook of Australian Soils. Rellim, Glenside, S.A., 435 pp. Stewart, I.C.F. and Mount, T.J., 1972. Earthquake mechanisms in South Australia in relation to plate tectonics. J. Geol. Soc. Aust., 19: 41--52. Walker, D., 1978. Quaternary climates of the Australian region. In: A.B. Pittock, L.A. Frakes, D. Jenssen, J.A. Peterson and J.W. Zeliman (Editors), Climatic Change and Variability. Cambridge Univ. Press, Cambridge, pp.82--97. Williams, D.L.G., 1981. Genyornis eggshell (Dromornithidae; ayes) from the late Pleistocene of South Australia. Alcheringa, 5: 133--140. Williams, G.E., 1973. Late Quaternary piedmont sedimentation, soil formation and palaeoclimates in arid South Australia. Z. Geomorphol., 17: 102--125. Wyrwoll, K. and Milton, D., 1976. Widespread late Quaternary aridity in Western Australia. Nature, 264: 429--430. Yaalon, D.H., 1971. Soil-forming processes in time and space. In: D.H. Yaalon (Editor), Palaeopedology: Origin, Nature and Dating of Palaeosols. Jerusalem, I.S.S.S. and Israel Universities Press, Jerusalem, 350 pp.