Encyclopedia of Geoarchaeology

2017 Edition
| Editors: Allan S. Gilbert

Climatostratigraphy

  • Philip L. Gibbard
Reference work entry
DOI: https://doi.org/10.1007/978-1-4020-4409-0_6

Definition and introduction

That part of geological time most germane in archaeology, the Quaternary Period, has long been subdivided on the basis of represented climatic changes. The overriding influence of climatic change on geological processes in the Quaternary has meant that climate-based classification (referred to as climatostratigraphy or climostratigraphy) has remained central to the subdivision of the succession. This entry discusses the role of climatostratigraphy (geologic-climate classification) and its relation to chronostratigraphy for the division of the Quaternary sequence.

Climatostratigraphy (“climostratigraphy”)

Since the middle of the nineteenth century, Quaternary sediment sequences, and therefore the chronology of human activity and evolution, have traditionally been divided on the basis of the climatic changes they represent, particularly sequences based on glacial deposits in central Europe and mid-latitude North America. This approach was adopted by early workers for terrestrial sequences because it seemed logical to divide glacial diamicton (unconsolidated, poorly sorted sediments) and non-glacial deposits found in stratigraphic sequences into glacial (glaciation) and interglacial periods, respectively (cf. West, 1968, 1977; Bowen, 1978). In other words, the divisions were fundamentally lithological (Figure 1). The overriding influence of climatic change on sedimentation and erosion during the Quaternary has meant that, despite the enormous advances in knowledge during the last 150 years, climate-based classification has remained central to the subdivision of the succession. Indeed, the subdivision of the modern isotope (e.g., Railsback et al., 2015) stage sequence of ocean sediments is itself based on the same basic concept (e.g., Railsback et al. 2015). It is this approach which has brought Quaternary geology so far, but at the same time, it causes considerable confusion to workers attempting to correlate sequences from enormously differing geographical, and thus environmental, settings. This is because of the great complexity of climatic change and the very variable effects these changes impose upon natural systems, including humans.
Climatostratigraphy (climostratigraphy), Figure 1

Fossiliferous sand deposits (shown by diagonal cross hatching) between tills (shown by angular symbols) exposed in the Cowden Burn railway cutting at Neilston in Renfrewshire, Scotland, reproduced from Geikie (1874, Figure 27).

The recognition of past climatic events based on environmental indicators within sediments is an inferential method and by no means straightforward. Sediments are not unambiguous indicators of contemporaneous climate, so that other evidence – such as fossil assemblages, characteristic sedimentary structures (including periglacial structures) or textures, soil development, etc. – must be relied upon wherever possible to determine the origin and climatic affinities of a particular unit. Local and regional variability of climate complicates this approach because particular sequences are always the result of local climatic and environmental conditions, yet there remains the need and desire to equate them to a global scale. For at least the first half of the twentieth century, the preferred scale was that developed for the Alps at the turn of the twentieth century by Penck and Brückner (1909) (Table 1).
Climatostratigraphy (climostratigraphy), Table 1

The Alpine sequence in increasing age, as proposed by Penck and Brückner (1909), with later additions from Doppler et al. (2011). Transition dates provided where they are known

Postglacial (Holocene)

← ca. 11.7 ka

Würm glacial (Würmian)

← ca. 117 ka

Riss/Würm interglacial

← ca. 128 ka

Riss glacial (Rissian)

← ca. 350 ka

Mindel/Riss interglacial

 

Mindel glacial (Mindelian)

 

Günz/Mindel interglacial

 

Günz glacial

 

Donau/Günz interglacial

 

Donau glacial

 

?Biber glacial

← ca. 2,600 ka

Since the mid-twentieth century, a comparable scheme developed in northern Europe has been dominant, at least in Europe, but similar schemes have also been established elsewhere, such as in North America or the former USSR. More recently, these schemes have tended to be replaced by the marine- or ice-core oxygen isotope records. Today, the burden of correlation lies in equating local, highly fragmentary, yet high-resolution terrestrial and shallow marine sediment records on the one hand, with the potentially continuous, yet comparatively lower resolution isotope sequence from oceanic sediments on the other (cf. Gibbard and van Kolfschoten, 2005).

Terminology

Before the impact of the ocean-core isotope sequences, an attempt was made to formalize the climate-based stratigraphic terminology in the American Code of Stratigraphic Nomenclature (American Commission on Stratigraphic Nomenclature, 1961), where the so-called geologic-climate units were proposed. Here, a geologic-climate unit was based on an inferred widespread climatic episode defined from a subdivision of Quaternary rocks. Several synonyms for this category of unit have been suggested, the most recent being climatostratigraphical units (Mangerud et al., 1974) in which an hierarchy of terms is proposed. In subsequent stratigraphic codes, however (see Hedberg, 1976; North American Commission on Stratigraphic Nomenclature, 1983; Salvador, 1994), the climatostratigraphic approach has been discontinued since it was considered that for most of the geological column, “inferences regarding climate are subjective and too tenuous a basis for the definition of formal geologic units” (North American Commission on Stratigraphic Nomenclature, 1983, 849). This view has not found favor with Quaternary scientists, however, since it is difficult to envisage a scheme of stratigraphic subdivision for recent earth history that does not specifically acknowledge the climate change factor (Lowe and Walker, 1997). Accordingly, Quaternary stratigraphic sequences continue to be divided into geologic-climatic units based on proxy climatic indicators, and hence, following this approach, the Pleistocene-Holocene boundary (the base of the Holocene series/epoch), for example, is defined on the basis of the inferred climatic record (cf. below). Boundaries between geologic-climate units were placed at the transitions between those the stratigraphic units on which they were based.

The American Code (1961) defines the fundamental units of the geologic-climate classification as follows:
  • A glaciation is a climatic episode during which extensive glaciers developed, attained a maximum extent, and receded. A stadial (“stade”) is a climatic episode, representing a subdivision of a glaciation, during which a secondary advance of glaciers took place. An interstadial (“interstade”) is a climatic episode within a glaciation during which a secondary recession or standstill of glaciers took place.

  • An interglacial (“interglaciation”) is an episode during which the climate was incompatible with the wide extent of glaciers that characterize a glaciation.

In Europe, following the work of Jessen and Milthers (1928), it is customary to use the terms interglacial and interstadial to define characteristic types of non-glacial climatic conditions indicated by vegetational changes. Interglacial describes a temperate period with a climatic optimum at least as warm as the present interglacial (Holocene, Flandrian: see below) in the same region, and interstadial describes a period that was either too short or too cold to allow the development of temperate deciduous forest or the equivalent of interglacial type in the same region (West, 1977, 1984).

In North America, mainly in the USA, the term interglaciation is occasionally used for interglacial (cf. American Code, 1961). Likewise, the terms stade and interstade may be used instead of stadial and interstadial, respectively (cf. American Code, 1961). The origin of these terms is not certain, but the latter almost certainly derive from the French language word stade (m), which is unfortunate since in French, stade means (chronostratigraphical) stage (cf. Michel et al., 1997), e.g., stade isotopique marin = marine isotope stage.

It will be readily apparent that, although in longstanding usage, the glacially based terms are very difficult to apply outside glaciated regions. Moreover, as Suggate and West (1969) recognized, the term glaciation or glacial is particularly inappropriate since modern knowledge indicates that cold rather than glacial climates have tended to characterize the periods intervening between interglacial events over most of the earth. They therefore proposed that the term “cold” stage (chronostratigraphy) be adopted for “glacial” or “glaciation.” Likewise, they proposed the use of the term “warm” or “temperate” stage for interglacial, both being based on regional stratotypes. Lüttig (1965) also recognized this problem and attempted to avoid the glacial connotations by proposing the terms cryomer and thermomer for cold and warm periods, respectively. These terms have found little acceptance, however. The local nature of these definitions indicates that they cannot necessarily be used inclusively over great distances or between different climatic provinces (Suggate and West, 1969; Suggate, 1974; West, 1977, 1984) or indeed across the terrestrial/marine facies boundary (see below). In addition, it is worth noting that the subdivision into glacial and interglacial is mainly applied to the Middle and Late Pleistocene (i.e., the last 0.78 Ma).

Boundaries

Perhaps the biggest problem with climate-based nomenclature is where the boundaries should be drawn. Ideally, they should be placed at the climate change, but since the events are recognized only through the responses they initiate in depositional or biological systems, a compromise must be agreed upon. As Bowen (1978) emphasizes, there are many places at which boundaries could be drawn, but in principle, they are generally placed at midpoints between temperature maxima and minima, e.g., in ocean-sediment sequences. This positioning is arbitrary but is necessary because of the complexity of climatic changes. Problems may arise, however, when attempts are made to determine the chronological relationship of boundaries drawn in sequences that possess differing temporal resolution, show different sediment facies, or originate through the use of differing proxies. By contrast, in temperate northwest Europe, the base of an interglacial or interstadial is very precisely defined. It is placed at the point where herb-dominated (cold climate) vegetation is replaced by forest. The top (i.e., the base of the subsequent glaciation or cold stage) is drawn where the reversal occurs (Jessen and Milthers, 1928; Turner and West, 1968). It is unclear, however, how this relates to the timing of the actual climate change recorded, or how this is recorded by other proxies.

Climatostratigraphic units are not chronostratigraphic units

By the second half of the twentieth century, it was realized that Quaternary time should be subdivided as far as possible in keeping with the rest of the geological column – using time, or chronostratigraphy, as the basic criterion (e.g., van der Vlerk, 1959; Gibbard and West, 2000). Because stages are the fundamental working units in chronostratigraphy, they are considered appropriate in scope and rank for practical intraregional classification (Hedberg, 1976). However, the definition of chronostratigraphical units at the status of stage, with their time-parallel boundaries placed in continuous successions wherever possible, is a serious challenge especially in terrestrial Quaternary climate-dominated sequences. In these situations, boundaries in a region may be time parallel, but over greater distances, problems may arise as a result of diachroneity. It is probably correct to say that only in continuous sequences which span entire interglacial-glacial-interglacial climatic cycles can an unequivocal basis for the establishment of stage events using climatic criteria be truly successfully achieved. There are the additional problems which accompany such a definition of a stage, including the question of diachroneity of climate changes themselves and the detectable responses to those changes. For example, it is well known that there are various “lag” times of geological, biological, and human responses to climatic stimuli. Thus, in short, climate-based units cannot be the direct equivalents of chronostratigraphical units because of the time-transgressive nature of the former. This distinction of a stage in a terrestrial sequence from that in a marine sequence should be remembered when correlation is attempted.

In general practice today, these climatic subdivisions have been used interchangeably with chronostratigraphical stages by the majority of workers. While this approach, which gives rise to alternating “cold” and “warm” or “temperate” stages, has been advocated for 50 years, there remains considerable confusion about the precise distinction between the schemes, particularly among non-geologists. In Europe, many of the terms in current use, perhaps surprisingly, do not have defined boundary or unit stratotypes. This problem has been recognized, and steps are now being taken to define units formally through the work of the INQUA Subcommission on European Quaternary Stratigraphy (SEQS). Many fail to see the need for this, however, especially those who rely on geochronology, particularly radiocarbon, for correlation. For example, despite repeated attempts to propose a GSSP boundary stratotype for the base of the Holocene Series – i.e., the Pleistocene-Holocene (Weichselian-“Flandrian”) boundary (Olausson, 1982) – in the past, only recently has a universally acceptable boundary been defined (Walker et al., 2008).

Nomenclatural complexities

As already stated, the situation is more confused in languages other than English. For example, in German the terms glazial and interglazial are used as equivalents to the English stage. Such an approach, on the face of it, seems expedient until one considers certain stages that have been correctly, formally defined in the Middle and Early Pleistocene of the Netherlands, which are commonly used throughout Europe. Here the Bavelian Stage includes two interglacials and two glacials; likewise the Tiglian Stage comprises at least three interglacials and two glacials (de Jong, 1988; Zagwijn, 1992). Each of these interglacials is comparable in their characteristics to the last interglacial or Eemian, which is a discrete stage, which is also defined in the Netherlands. In these cases, workers have fallen back on the noncommittal term complex. One example is the Saalian of Germany, originally defined as a glaciation. This chronostratigraphical stage includes at least one interglacial and potentially a second, as currently defined (Litt and Turner, 1993). Attempts to circumvent the nomenclatural problem by defining a “Saalian Complex” are a fudge at best but one that is occasioned by linguistic and long-term historical precedent, as much as by geological needs.

Global correlation

The original intention was that “cold” or “warm” or “temperate” stages should represent the first-rank climate oscillations recognized in the geological record, although it has since been realized that some, if not all, are internally complex. Subdivision of these stages into substages or zones was to be based, in the case of temperate stages, on biostratigraphy, and in the case of cold stages principally on lithostratigraphy and or pedostratigraphy. Within the range of radiocarbon dating (ca. 30 ka), the most satisfactory form of subdivision is frequently that based on radiocarbon years (cf. Shotton and West, 1969); however, high-resolution investigations, such as the ice-core investigations, have allowed the recognition of ever more climatic oscillations of decreasing intensity or wavelength within the first-rank time divisions. These events are stretching the ability of the stratigraphical terminology to cope with the escalating numbers of names they generate. Terms such as “event,” “oscillation,” or “phase” are currently in use to refer to short or small-scale climatic events (often referred to as “sub-Milankovitch oscillations”). Clear hierarchical patterns are becoming blurred, but perhaps this should be seen as a positive development since the system must reflect the need to classify events that are recognized. Moreover, as our ability to resolve increasingly smaller-scale oscillations improves, a more detailed nomenclature will inevitably emerge. One possible approach is to avoid attempted chronostratigraphical classification in favor of an event scheme based on the recognition of “diachronic units” (e.g., Curry et al., 2011) or event stratigraphy, but in practice this differs little from that based on climate.

Therefore, for many geologists and archaeologists, chrono- and climatostratigraphical terminology are interchangeable. Although realistically, this situation is clearly unsatisfactory because of the imprecision that it may bring to interregional and ultimately to global correlation, it is likely to continue for the foreseeable future. The long-term goal should be to clarify the situation by continuing to develop a formally defined, chronostratigraphically based system that is fully compatible with the rest of the geological column, supported by reliable geochronology.

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Authors and Affiliations

  1. 1.Cambridge Quaternary, Department of GeographyUniversity of CambridgeCambridgeUK