a call for australian loess: discussion and commentary

A Call for Australian Loess: Discussion and CommentaryAuthor(s): Ian SmalleySource: Area, Vol. 40, No. 1 (Mar., 2008), pp. 131-134Published by: Wiley on behalf of The Royal Geographical Society (with the Institute of BritishGeographers)Stable URL: http://www.jstor.org/stable/40346098 .

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Area (2008) 40.1, 131-134

Commentary

A call for Australian loess: discussion and commentary

Ian Smalley Giotto Loess Research Group, Waverley Materials Project, Nottingham Trent University,

Nottingham NG1 4BU

Email: [email protected]

Revised manuscript received 8 November 2007

A study of loess in Australia brings the idea of 'desert' loess back into view. Production of particles in deserts still presents problems, but deserts do make adequate storage regions for loess particles - usually produced in adjacent mountains. Straightforward for Central Asia or China (a particle source in High Asia and convenient deserts en route to eventual deposition), but the Sahara and Australian deserts traditionally present problems. If loess material is allowed to be silt-sized clay agglomerate particles as well as the usual clastic primary minerals, then loess in Australia seems reasonable. Loess

acquires its remarkable loessic qualities via aeolian deposition - the nature of the

particles is perhaps of lesser importance. A more generalised approach to airborne sediments might be attempted, with two major types of suspension material recognised: large dust (maybe coarse and very coarse silt, say 20-60 fxm, or perhaps 4-6 phi) and small dust (fine and very fine silt, 2-8 fim, 7-9 phi). Loess is made from large dust.

Key words: Australian loess, glacial loess, desert loess, mountain loess, loess definitions, large dust, small dust

Introduction Haberlah (2007), in his recent Area contribution, makes a good case for loess in Australia, or rather he makes a good case for the concept of loess being detached from its entrenched glacial/periglacial environment, and re-examined in a desert setting, and perhaps given an arid dimension. Various

interesting requirements develop from the Haberlah

proposals: is the definition of loess adequate for 2007? Does the idea of glacial loess need to be re- examined and re-evaluated? Can the idea of 'desert' loess be reconciled with on-going loess scholarship? Will Australia join Serbia and New Zealand in the ranks of the great loess nations? The Area definition of loess (Smalley and Derbyshire 1990) is possibly too precise and over-prescriptive; the Smalley (1966)

protocols for the nature and formation of glacial loess certainly require revision, and that famous Australian statement by Butler (1956), which suggested the non-existence of desert loess, has certainly come up for reconsideration.

Glacial loess The crux of the reasoning was thus: to make the vast amounts of loess material that we see

comprising the loess deposits of the world, a very large amount of geo-energy was required. This material is largely silt-sized quartz and the grinding energies required to produce the cubic kilometres observed could only be supplied by glacial action, no other natural Quaternary agency being available. Thus the sort of reasoning which Charles Darwin so

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1 32 Commentary

It was a long, detailed and carefully argued paper, but it was written in Russian and published in a local journal in Tomsk. And yet it is moderately well known, and the origin of the 'desert loess' idea is firmly lodged with Obruchev. This is largely due to the efforts of Merzbacher (1913). Merzbacher relates to Obruchev much as Edward Fitzgerald relates to Omar Khayyam. One has the central idea, the other provides the exposure. Omar Khayyam wrote of 'Dust into dust, and under dust' (a classic desert situation) but those actual words were

Fitzgerald's [Quatrain 23]. Merzbacher's 1913 paper in Petermanns Geographisches Mitteilungen (in three

parts) showed Obruchev's loess idea to the wider world; the idea that loess is associated with desert

regions; that there is a desert+loess relationship. The idea was proposed in 1911, its validity was

questioned in 1956 by Bruce Butler. Butler, as a CSIRO pedologist, cast an eye over all of Australia. And saw no loess; no loess, as conventionally defined, was to be found in the desert regions of Australia - a notably desertic country. Butler (1956) offered the opinion that desert loess maybe did not exist. This opinion, published in an Australian journal, had an important effect on the desert loess debate. Butler was suggesting that there is NOT a significant desert+loess relationship, and this led to many years of subsequent discussions (see Smalley and Vita- Finzi 1968; Smalley and Krinsley 1978; Whalley et al. 1982; Smith et al. 1987; Wright 2001).

In fact, there is an obvious form of desert+loess

relationship - but not in Australia. And not really in the Sahara. And it is not as direct as Obruchev

appeared to suggest. Some deserts appear as sources of loess because they are also sinks and stores for loess material. Smalley and Krinsley (1978) suggested that this is the case in the Chinese loess+desert situation. But all this depends on the simple definition of loess; stretch the definition somewhat and a new

argument develops. The Chinese loess is 'mountain' loess; it has its origins in High Asia, it is transported to the desert regions, and it resides in the desert

regions, and eventually becomes loess. If it is to be classified in terms of origin, it is mountain loess.

Mountain loess

Mountain loess appears in a discussion of New Zealand loess (Smalley 1978) and again in the Area definition of loess (Smalley and Derbyshire 1990, so called because it appeared in Area in 1990). The mountains were the alternative regions for particle

specifically warned against was used to establish the case for glacial grinding (see Smalley 1966). But

having made this latter observation we might need to consider some comments by Muhs and Bettis:

we agree with Wright (2001) that regardless of the process of origin, much loess can be considered to be 'glacial' in the sense that the optimum climatic and geomorphic conditions for loess formation in many regions occurred during glacial periods. (2003, 67)

and note also the observation by Carl Troll (1944) 'Ohne Frost, Kein Loess'. In the Area discussion (Smalley and Derbyshire 1990) it was proposed that the term 'ice-sheet loess' should replace 'glacial loess' to show that the loess in question was associated with

large-scale continental glaciation, but this modifica- tion has not proved popular. There are only two large real deposits of ice-sheet loess in the world. These are the North American loess and the USWR loess -

the Ukraine South-West Russia loess associated with the rivers Dnepr, Don and Volga. Muhs and Bettis may be misleading us; loess formed in cold mountains might be better called mountain loess.

Modifications to the basic grinding hypothesis became necessary when it was realised that the quartz particles in nature which were to provide the raw material for the glacial grinding process were much weaker than had been assumed. Quartz had been seen as a very strong, resistant mineral, requir- ing huge energies to crush, but this is not the case. Quartz sand is full of defects (now called Moss defects after AJ Moss of CSIRO who promoted their investi- gation) and these defects mean that other natural processes need to be considered when quartz silt production is being studied. Intense weathering will produce silt; High Asia produces silt for the loess deposits of China and Central Asia, and for the alluvial deposits of north India and Bangladesh. High cold tectonic regions produce silt - this led to the naming of 'mountain' loess (see Assallay et al. 1998).

Smalley and Leach (1978) suggested a major role for glacial loess in the deposits of East and Central Europe, but they were almost certainly wrong. The Danube basin loess and the Polish loess are mountain loess. The assumption that the British loess is glacial (Jefferson et al. 2003) is probably wrong: as unlikely as it seems, this is probably Alpine loess brought by the old Rhine.

Desert loess

The original desert loess paper, by Obruchev (1911), was published in Siberia early in the twentieth century.

Area 40 No. 1,pp. 131-134,2008 ISSN 0004-0894 © The Author.

Journal compilation © Royal Geographical Society (with The Institute of British Geographers) 2008



Commentary 133

production; alternative, that is, to glaciated regions. Mountain loess is perhaps not an entirely suitable term, but it did recognise the enormous contribution to silt production made by High Asia (and by the

Alps and the Carpathians and the Southern Alps and the Andes). There is a major problem with mountain loess; there is no clear view of exactly how the silt is produced. It is possible to suggest that there are vast amounts of geo-energy available in what are often

very high, very cold, very tectonically active mountain

regions, but exactly how this is deployed into silt formation has not been described. Presumably mountain

glaciers can contribute some material, but mountain loess was definitely set to be an alternative to

glacial loess. New Zealand loess is mountain loess; the Southern Alps produce material, rivers like the Clutha move the material, and a final aeolian event

emplaces the loess deposit. There should be similar

deposits associated with the Great Dividing Range.

Loess defined Muhs and Bettis touched on an interesting point about the nature of loess:

the question of whether loess should be considered as a distinct sediment body or whether it is essentially a fine-grained facies of eolian sand with a common source. (2003, 64)

They were considering classic clastic particle loess, but similar considerations might apply in the Australian environment. Is loess a truly distinctive sediment? Is loess material specifically defined by some natural variables or is it just a subset of particulates from a whole range of detrital granular materials - the

range from gravel to clay? In the case of loess which is dominated by quartz silt there appears to be evidence accumulating that there is some sort of 'loess mode' in nature. In fact, studies of loess in Kazakhstan and Voyvodina, where very careful

grain size analysis has been carried out, suggest that

quartz delivers two distinct modes at about 20 fim and 40 Jim (see Smalley and O'Hara-Dhand 2007; O'Hara-Dhand et al. 2007). But if the particles are

clay agglomerates rather than monomineralic fragments, perhaps there is a more fuzzy particle range. It has been shown that many particles lifted from old Lake Chad region in North Africa to form Saharan dust are constrained in size by the mode of formation of the original lake sediments (see Evans et al. 2004; Smalley et al. 2005) - this gives rise to what has been called 'small dust', high travel material with a

size range around 2-8 \irr\. Similar material can be raised from Australian lake beds.

The problem of defining loess is still being dis- cussed (Smalley and Jary 2004), but the discussions tend to be backward looking because the great definition controversy concerned the Russian/Soviet approach to loess. Rozycki (1990, 30) has described the events related to the 'In-situ or pedological' theory of loess formation, all the amazing claims for loess 'as a product of weathering and soil formation.' He mentions the Soviet geographers who were producing maps of world loess in the late 1930s and early 1940s with hardly any loess on at all. Nothing met the criteria. I. P. Gerasimov (Director of the Geographical Institute in Moscow) famously visited the widespread loess deposits in the South Island of New Zealand on a field trip with the 1973 INQUA Congress: he denied that there was any loess present: they were peculiar times. But now there is some reaction to this and Russian scholars show widespread loess. The recent Trofimov (2001, 11) map shows well- marked loess in Australia (and in New Zealand; this map reproduced in Smalley and Jary 2005). Haberlah (2007) has pointed to aridity as a significant loess factor. Kriger (1965) made this a key point of his approach to loess; his 'aridity index' controlled loess formation, and deserves to be looked at again. Kriger was probably the leading Russian loess scholar of recent times, but he published exclusively in Russian and is not as well known as he should be.

Large dust and small dust Loess is an aeolian deposit. Loess is composed of material which has been transported in suspension in the atmosphere (sometimes called dust). Material which is transported by saltation forms dunes. Aeolian loess transportation is low and short; large dust is not carried very far. Small dust can be carried very high and over vast distances. Large dust and small dust form distinct sedimentological entities, and can perhaps be demarcated. Large dust is essentially coarse or very coarse silt size; in most major loess deposits it consists largely of quartz particles, but with modest

feldspar and other minerals. It may be possible for

significant amounts of large dust to exist where the

particles consist of clay-mineral agglomerates; these could have a desert origin and form 'loess' deposits.

Small dust provides the materials for far-travel dust clouds. It is largely produced in arid desert situations, from ancient lake beds (see Evans et al. 2004; Smalley et al. 2005). The proposed size constraints are: large

Area 40 No. 1 , pp. 1 3 1 -1 34, 2008 ISSN 0004-0894 © The Author. Journal compilation © Royal Geographical Society (with The Institute of British Geographers) 2008



1 34 Commentary

dust, coarse and very coarse silt, say 20-60 |im, maybe 4-6 phi; small dust, fine and very fine silt, 2-8 jxm, 7-9 phi. In a generalised mineralogy most

large dust consists of quartz silt, and most small dust is composed of clay mineral agglomerates.

Commentary What do we need? It would be useful to have a moderately detailed map of loess distribution in Australia. Huge detail is not required; the map of European loess in Trofimov (2001) is very simple; something similar for Australia would be useful. Much has been learned about loess in the Danube basin from maps showing high ground, major rivers and loess deposits. It would be useful to have

particle size analyses, and some mineralogical details and perhaps some particle images. If non- clastic loess is to make a significant contribution to the Australian landscape, it should be established whether there is a particle-making mechanism that delivers large dust particles, and what the particle size constraints are. The simple Monte Carlo model of sedimentation in lakes points to a particle production mode of around 2-8 Jim; one can see Australian dry lakes producing small dust; is there a mechanism for large dust production? Does the Great Dividing Range act like the Carpathians and produce conventional mountain loess? The Haberlah plea for Australian loess can (will) be supported, but he is opening the gate on to a long road.

References

Assallay A M, Rogers CDF, Smalley I J and Jefferson I F 1 998 Silt 2-62 urn, 9-4 phi Earth Science Reviews 45 61-88

Butler B E 1 956 Parna - an aeolian clay Australian Journal of Science 18 145-51

Evans R D, Jefferson I F, Kumar R, O'Hara-Dhand K and

Smalley I J 2004 The nature and early history of airborne dust from North Africa: in particular the Lake Chad basin Journal of African Earth Sciences 39 81-7

Haberlah D 2007 A call for Australian loess Area 39 224-9 Jefferson I F, Smalley I J and Northmore K 2003 Conse-

quences of a modest loess fall over southern and midland England Mercian Geologist 1 5 1 99-208

Kriger N I 1 965 Loess, its characteristics and relation to the

geographical environment Nauka, Moscow (in Russian) Merzbacher G 1913 Die Frage der Entstehung des Loesses

Petermanns Geographisches Mitteilungen 59 16-18, 69- 74, 1 26-30

Muhs D R and Bettis E A 2003 Quaternary loess-paleosol sequences as examples of climate-driven sedimentary

extremes in Chan M A and Archer A W eds Extreme

depositional environments: Mega end members in geo- logic time Geological Society of America Special Paper 370 53-74

Obruchev V A 191 1 The question of the origin of loess -

in defence of the aeolian hypothesis Izvestiya Tomskogo Tekhnologicheskogo Instituta 33 (in Russian)

O'Hara-Dhand K, Smalley I J and Machalett B 2007 Particle size analysis of loess from Ruma brickyard and Titel Plateau, Voyvodina, Serbia Sedimentary Geology submitted

Rozycki S Z 1 991 Loess and loess-like deposits Ossolineum, Polish Academy of Sciences, Warsaw (Polish original pub Warsaw 1 986)

Smalley I J 1 966 The properties of glacial loess and the formation of loess deposits Journal of Sedimentary Petrology 36 669-76

Smalley I J 1978 The New Zealand loess and the major categories of loess classification Search 9 281-2

Smalley I J and Derbyshire E 1990 The definition of ice- sheet and mountain loess Area 22 300-1 (reproduced in East Asia Tertiary-Quaternary Newsletter 12, 18-20, 1991)

Smalley I J and Jary Z 2004 A random walk towards a definition of loess New Zealand Soil News 52 142-6 (reprinted in Loess Letter 54)

Smalley I J and Jary Z 2005 Maps of worldwide loess distribution: from Keilhack to Kriger and beyond New Zealand Soil News 53 45-9 (reprinted in Loess Letter 55)

Smalley I J and Krinsley D H 1978 Loess deposits associated with deserts Catena 5 53-66

Smalley I J and Leach J A 1978 The origin and distribution of the loess in the Danube basin and associated regions of East-Central Europe - a review Sedimentary Geology 21 1-26

Smalley I J and O'Hara-Dhand K 2007 The Eden effect: or the

particle size analysis of loess material New Zealand Soil News 55 128-31

Smalley I J and Vita-Finzi C 1 968 The formation of fine particles in sandy deserts and the nature of 'desert' loess Journal of

Sedimentary Petrology 38 766-74

Smalley I J, Kumar R, O'Hara-Dhand K, Jefferson I F and Evans R D 2005 The formation of silt material for terrestrial sediments: particularly loess and dust Sedimentary Geology 179 321-8

Smith B J, McGreevy J P and Whalley W B 1 987 The experimental production of silt from sandstone under hot arid conditions Journal of Arid Environments 1 2 1 99-21 4

Trofimov V T ed 2001 Loess mantle of the Earth and its pro- oerties Moscow Universitv Press. Moscow (in Russian)

Troll C 1944 Struckturboden, solifluktion und frostklimate der erde Geologische Rundscham 34 545-694

Whalley W B, Marshall J R and Smith B J 1 982 The origin of desert loess: some experimental observations Nature 300 433-5

Wright J S 2001 'Desert' loess versus 'glacial' loess: quartz silt formation, source areas and sediment pathways in the formation of loess deposits Geomorphology 36 231-56

Area 40 No. 1 , pp. 1 31-1 34, 2008 ISSN 0004-0894 © The Author.

Journal compilation © Royal Geographical Society (with The Institute of British Geographers) 2008



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