Chapter 1 Paleopedology

Paleopedology is the study of ancient soils, and is the stratigraphic subdivision of glacial deposits derived from an ancient Greek word (πεδov, πεδoυ) (Chamberlain 1895). for ground. It has nothing to do with pedestrians Much older paleosols were discovered by the (Latin pes, pedis) or pediatricians (Greek παιs, Scottish physician James Hutton (1795), who παιδos). Soils of the past, either buried within sedi- regarded red rocks along angular unconformities mentary sequences or persisting under changed of Devonian age in the River Jed and at Siccar surface conditions, are the main subject matter of Point, southeast of Edinburgh, as comparable with paleopedology. In this book, it is seen as an histori- surface soils and sediments on the modern land- cal perspective on soil genesis and as a way of scape (Figure 1.2). “From this it will appear, that reconstructing the geological history of land sur- the schistus mountains or vertical strata of indu- faces on Earth. Soils, like organisms, sediments, rated bodies had been formed, and had been wasted and surface environments, have changed over the and worn in natural operations of the globe, before past 4567 million years of recorded Earth history. horizontal strata were begun to be deposited Some understanding of soil burial and erosion in these places...” (Hutton 1795, v. 1, p. 438). These can be inferred from classical Greek accounts by ideas were reiterated in John Playfair’s (1802) Plato in Athens, and by Herodotus in Egypt “Illustrations of the Huttonian Theory of the (Retallack 2013a), but the first demonstration of a Earth” which, because of its conciseness and clarity fossil soil was by Luigi Marsigli (1726), whose mili- of expression, was more influential than Hutton’s tary engineering report for Austro-Hungarian original two volumes. Emperor Leopold I showed soil buried by alluvium The oldest record of buried soils within a con­ near what is now Stari Slankamen, Serbia solidated sedimentary sequence were the “dirt beds” (Figure 1.1). Not much was made of this observa- (Figure 1.3) and fossil stumps reported in the latest tion at the time, but Marsigli’s buried Ustoll (cal- Jurassic limestones of the Dorset Coast by Webster careous Mollisol) is now known to be about 125 ka (1826) and popularized in William Buckland’s in age (Buggle et al. 2014). During the late nine- (1837) “Bridgewater Treatise.” Other fossil forests teenth century, many such buried soils were widely were discovered in the late nineteenth century, and recognized within Quaternary deposits of loess and their stumps and associated fossil plants described, till. These “weathered zones,” “forest zones,” and but little was made of their substrates as fossil soils. “soils,” as they were variously termed, were found Examples include the tourist attractions of Eocene in the Russian Plain by FeofilatkovCOPYRIGHTED (in the 1870s as Sequoia MATERIAL forests of Yellowstone National Park, USA, recounted by Polynov 1927), in the midcontinental and Carboniferous stumps of tree-lycopsids at United States by McGee (1878), and near Timaru, Clayton (Yorkshire) and in Victoria Park (Glasgow), New Zealand by Hardcastle (1889). By the turn of both in Britain (Seward 1898). While Seward the century such observations had been used for appreciated the significance of fossil soils and their

Soils of the Past: An Introduction to Paleopedology, Third Edition. Gregory J. Retallack. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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Figure 1.1 Danube river terrace, showing modern soil (A = Terra fructifera pinguis nigra et cretaceo), over buried black soil (B = Terra nigra fructifera pinguis) with a subsurface horizon of carbonate nodules (C = Terra lutosa, cinericio et in fragmento cretacea priabilis), and floodplain (D = Ripa arenosa, qualis plerumq, Septentrionalis existet). Source: From Marsigli 1726.

Figure 1.2 Angular unconformity between Early Silurian (430 Ma), Hawick Rocks and Late Devonian (360 Ma), Upper Old Red Sandstone along the river Jed in southeastern Scotland. Source: From Hutton (1795).

stumps as indicators of past worlds, study of the soil science (Tandarich and Sprecher 1993). Since paleosols themselves had to await the development classical times, soils have been studied from the point of soil science. of view of plant nutrition. It was not until 1862 that Despite these discoveries, the origin of paleope­ the Saxon scientist Fredrich A. Fallou first published dology as a discrete field of inquiry can be traced the term “pedologie” for the study of soil science, as back to the late nineteenth century develop­ment of opposed to what he termed “agrologie,” or practical

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Lower Calcareous state Purbeck of fresh water beds. formation.

Burrstone. Dirt bed, Temporary black mould, dry land. and pebbles.

Marine Portland

formation. stone.

Section of the Dirt-bed in the Isle of Portland shewing the subterranean remains of an ancient Forest. De la Beche. Figure 1.3 “Dirt beds” (paleosols) in a stratigraphic section through the latest Jurassic (Tithonian, 150 Ma), Purbeck formation on the Isle of Portland, Dorset, England. Source: From Buckland (1837).

agricultural science. The foundations of modern soil Polynov included the study of four kinds of materials science were laid by Vasily Dokuchaev with a detailed within paleopedology. “Secondary soils” encompass account of the dark, grassland soils of the Russian those formed by two successive weathering regimes Plain (1883). This monograph demonstrated that such as grassland soils degraded by the advance of soils could be described, mapped, and classified in a forests after the retreat of glacial ice. “Two-stage scientific fashion. Furthermore, their various features soils” were recognized to have an upper horizon of could be related to environmental constraints, of recent origin, but deeper horizons of more ancient which climate and vegetation were considered espe­ vintage. “Fossil soils” were defined as soil profiles cially important. By the early part of the twentieth developed on a surface and subsequently buried. century there was an established scientific tradition Polynov’s final category of “ancient weathering of research on soil geography, classification, and products” included redeposited remnants of soils genesis in Russia, as summarized in the influential such as laterites and china clays. general works of K.D. Glinka (1927). Modern soil science in North America can be In the course of these early Russian investigations, traced back to Eugene W. Hilgard’s (1892) certain soils were found to be anomalous in that monograph on the relationship of soil and climate. their various features did not fit the general This, and the first large scale mapping and relationship between soil type and their climate and classification of North American soils by Milton vegetation. It had long been suspected that these Whitney (1909), were largely independent of were very old soils, perhaps products of past comparable research done by Russian soil scientists. environments. In 1927, Boris Polynov summarized Soviet influence first appeared in the work of Soviet observations of this kind. His short paper, Curtis Marbut, particularly his monumental soil which introduced the term paleopedology, can be survey of the United States (Marbut 1935). considered the foundation of this branch of science. Paleopedology also was introduced into North

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America through a Soviet connection. Constantin paleoclimatology (Driese and Nordt 2013), and Nikiforoff completed doctoral studies at the paleoanthropology (Henke and Tattersall 2007). Novalexandrovsk Institute of St. Petersburg in pre- Wider applications of paleopedology can be revolutionary Russia, but by 1943 was a scientist anticipated for the future. with the U.S.D.A. Soil Conservation Service when Paleopedology has proven especially useful for he published a short essay outlining the role and understanding the general rules of soil forma- scope of paleopedology. A supporting study of tion, or nomopedology (Retallack 2013a). Such paleosols in the same journal of 1943 by Kirk information is required to interpret paleoen­ Bryan and Claude Albritton made clear the vironments from paleosols, thus stimulating a practical application of such studies. compilation of a variety of transfer functions to Ideas on the classification and origin of soils infer paleoclimate, atmospheric composition, have been especially useful for studies of Quaternary ecological productivity, and soil age (Sheldon and stratigraphy and geomorphology. Such studies are Tabor 2009). Fossil soils also provide historical now conducted in most parts of the world, coordi- validation for theories about how soils form. The nated by a Commission on Paleopedology estab- geological history of soils can be viewed as a long- lished in 1965 at the 7th Congress of the term natural experiment in which many International Association for Quaternary Research fundamental conditions of soil formation, such as in Denver, USA. An early result of the commis- vegetation and atmospheric composition, have sion’s activities was the publication of recommen- changed (Retallack 1996a, 2007a). Information dations for recognizing and classifying paleosols in from fossil soils can strengthen ideas about how a volume of research papers edited by Dan H. soils form and how they should be classified. Yaalon (1971). Mapping units for Quaternary pale- Paleopedology is also finding application in the osols have been incorporated into official strati- study of Earth’s earliest landscapes and ancient graphic codes (e.g. North American Commission surfaces of other planetary bodies. Such studies on Stratigraphic Nomenclature 1982). Modern can be called astropedology (Retallack 2013a). As research on Quaternary paleosols can be found in for astrobiology (Rothery et al. 2018), the big books and journals on soil science, geography, questions of astropedology are the origin of life, archeology, and Quaternary research (Holliday life beyond Earth, and life on the early Earth 1992, 1994; Follmer et al. 1998). (Retallack 2016a). Weathering of soils by microbes Studies of pre-Quaternary paleosols were slow is the ultimate source of nutrient elements for life to gain momentum, but there have been three inter- such as calcium, magnesium, potassium, sodium, national meetings devoted to them since 1987 and phosphorus, and terrestrial microbiomes are (Retallack 2013a). For many years little was made now known to be very ancient (Retallack 2018a; of those few cases where paleosols were explicitly Retallack et al. 2016a). Paleosols on Mars have recognized (Barrell 1913; Collins 1925; Sharp 1940; vesicular structure and a degree of chemical Allen 1947; Thorp and Reed 1949; Sidorenko weathering compatible with microbial metabolism 1963). Later they were found useful for reconstruct- (Retallack 2014a). Martian paleosols are thus ing paleoenvironments (Allen 1974; Retallack promising for further investigation of life on the red 1975, 1976, 1977), and even deep sea cores (Ford planet. 1987; Holmes 1992), Information on paleosols is Finally, long sequences of paleosols recording now included in recent books on the evolution of global climate and vegetation change in deep time surface environments (Stevenson 2007), weathering are informing studies of global change, or mundo­ (Drever 2004), atmosphere (Shaw 2014), microbes pedology (from Latin for “world” mundus). The (Noffke and Chafetz 2012), wetlands (Greb and link between atmospheric carbon dioxide and a DiMichele 2006), dinosaurs (Currie et al. 2004), warmer–­wetter climate can be explored using

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transfer functions from paleosols for these past as a guide to the future, Oregon’s western Alfisols variables (Sheldon and Tabor 2009), applied to will develop into Oxisols and its eastern Aridisols long sequences of paleosols in which various into Mollisols, with profound consequences for forcings have acted to different degrees, in order to agriculture and society (Retallack et al. 2016b). gain understanding of sensitivity of climate to Patterns of changes in soil and terrestrial greenhouse forcing (Retallack 2009a). If middle productivity with greenhouse forcings are now Miocene greenhouse soils of Oregon can be taken coming into focus from studies of paleosols.

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