Review article Journal of the Geological Society https://doi.org/10.1144/jgs2020-134 | Vol. 178 | 2021 | jgs2020-134 Terrestrial stratigraphical division in the Quaternary and its correlation P.L. Gibbard1* and P.D. Hughes2 1 Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER, UK 2 Department of Geography, School of Environment, Education and Development, University of Manchester, Manchester M13 9PL, UK PLG, 0000-0001-9757-7292; PDH, 0000-0002-8284-0219 * Correspondence: [email protected] Abstract: Initially, terrestrial evidence formed the foundation for the division of Quaternary time. However, since the 1970s there has been an abandonment of the terrestrial stage chronostratigraphy, which is based on locally dominated successions, in favour of the marine oxygen isotope stratigraphy which largely records global-scale changes in ice volume. However, it is now clear that glacial records around the world are asynchronous, even at the scale of the continental ice sheets which display marked contrasts in extent and timing in different glacial cycles. Consequently, the marine isotope record does not reflect global patterns of glaciation, or other terrestrial processes, on land. This has led to inappropriate correlation of terrestrial records with the marine isotopic record. The low resolution of the latter has led to a preferential shift towards high-resolution ice-core records for global correlation. However, even in the short term, most terrestrial records display spatial variation in response to global climate fluctuations, and changes recorded on land are often diachronous, asynchronous or both, leading to difficulties in global correlation. Thus, whilst the marine and the ice-core records are very useful in providing global frameworks through time, it must be recognized that there exist significant problems and challenges for terrestrial correlation. Received 12 July 2020; revised 30 September 2020; accepted 10 October 2020 From its earliest beginnings, the study of geology has been division of Quaternary time. Today the contrast could not be greater, fundamentally linked to the study of sedimentary strata and their with many abandoning the terrestrial chronostratigraphical classi- relationship to each other. This concept provides the very fabric of fication in favour of the ocean-floor isotope and ice-core the subject and its application in presenting and determining the stratigraphies. The driver of cyclic fluctuations in marine oxygen evolution of the Earth through time. This holds as true for the isotopes has long been attributed to orbital forcing (Hays et al. 1976; Quaternary as it does for any other part of the geological column. Imbrie and Imbrie 1980) and this has underpinned the timeframe to Therefore the division of the successions that record the passage of which both the marine isotope and ice-core records are tuned events and time provides the central pillar of palaeoenvironmental (Imbrie et al. 1984; Dansgaard et al. 1985; Ruddiman et al. 1989; and landscape reconstruction through the period. Bender et al. 1994; Lisiecki and Raymo 2005). Whilst undoubtedly Since the 19th century, when it was recognized that glaciers had the marine isotope and ice-core sequences offer a reliable been far more extensive than today, the basis of Quaternary history framework, it is essential to remember that these sequences, had been the distribution and spread of glacial materials in the especially those in ocean-bottom sediments, record both regional landscape (specifically tills, erratic rocks and associated meltwater and global-scale changes. This contrasts substantially with deposits). By late in the century the recognition that glacial ice had terrestrial or shallow marine sequences which preserve locally extended multiple times, their deposits being separated by fossil- dominated successions, reflecting local and regional events. Such bearing beds yielding evidence that temperate climate episodes events are not necessarily represented in the global patterns because intervened, led James Geikie (1894, 1895), among others, to coin the local responses to changes will inevitably lead to modifications the terms ‘glacial’ and ‘interglacial’ to classify these events. to any all-encompassing pattern. For this reason direct correlation of Subsequent development of the divisions and definition of terrestrial sediment sequences with those in the oceans and those in Quaternary time and events naturally followed. One of the most the ice cores should not be undertaken uncritically. Lessons from striking themes that recurs through the decades has been the desire the past have repeatedly shown that simplistic or mechanistic to equate events identified from local sequences with ‘global’ correlation, when examined in detail, is often inappropriate and records. This has happened against the background of repeated unsustainable. paradigm shifts, starting with the Alpine successions of Penck and The complexity of events shown by high-resolution palaeoenvir- Brückner (1911), then the sea-level chronology of Zeuner (1959) onmental investigations, such as those from the ice cores, have and Evans (1971) and most recently the marine oxygen isotope and allowed the recognition of ever more climatic oscillations of polar ice-core stratigraphies. Each of these paradigm shifts was seen decreasing scale. Consequently ‘event stratigraphy’ is now applied as a ‘revolutionary’ advance in understanding of what is to the subdivision of ice-core records and is widely applied and undoubtedly an extremely complex sequence of climatically indeed advocated for wider terrestrial correlations in some contexts driven changes at a range of scales. (e.g. Hughes and Gibbard 2015; Lowe et al. 2019; see below). The Until recognition of the implications of the marine isotope recognition of these events has substantial implications for our succession in the late 1960s and early 1970s (Shackleton 1967; understanding of the nature of landscape development and Broecker and van Donk 1970; Shackleton and Opdyke 1973; Hays terrestrial evolution. However, the unravelling of this evolution et al. 1976) terrestrial evidence formed the foundation for the requires a rigorous time-division foundation. The reconstruction of © 2020 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License (http://creativecommons.org/ licenses/by/4.0/). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/doi/10.1144/jgs2020-134/5227386/jgs2020-134.pdf by guest on 29 September 2021 2 P. L. Gibbard and P. D. Hughes events should use all available lines of evidence to ensure a rigorous finally it is deposited. Minor exceptions will be chemically local and regional chronostratigraphical scale. Over reliance on ice- precipitated deposits, biogenic deposits or volcanic dust products. core event stratigraphy, such as Greenland interstadials or stadials, Subsequent activity may result in modification of the deposited for global correlation could lead to the same erroneous correlations material by physical chemical processes, such as weathering, or soil that have arisen from attempted equation with marine isotope stages formation, and by plants or animals. (Hughes and Gibbard 2015). This point is reinforced by the fact that Whilst whole books have been written addressing the concepts of events resulting from the same causative agent are not necessarily sediment-process modelling, facies and architectural analysis and globally or even regionally isochronous (see below). taphonomic process investigations, it is not the purpose of this This review examines the bases for construction of terrestrial review to address a classification of sedimentary environments. sequences and their subdivision and, in turn, assesses the validity of Instead it is to consider the stratigraphical approaches to terrestrial their correlation with extra-regional and ‘global’ stratigraphies. and shallow marine stratigraphical sequences, both their correlation Finally, important recent and potential future developments are also and age determination. considered. Terrestrial environments and materials Terrestrial geological successions Terrestrial evidence is defined here as of rocks, sediments and It is natural that the first observations of sedimentary sequences and landforms found on or near land. Put in the simplest of terms, the landforms should begin with our observation of the landscape we nature of the terrestrial or continental environment is one of erosion inhabit. Therefore in the early development of geology, it was to be where, in general, natural processes break down pre-existing rocks expected that investigations primarily focused on the spread of and sediments (cf. Longwell and Flint 1962). These areas are by glacial sediments, with the realization that glaciers had in the recent their nature those above sea-level. However, the rapidity and scale of past been more extensive than today (see the review in Hansen changing sea-level in the Quaternary means that continental 1970). These studies necessarily began in mountain regions, environments also occur in fossil form below sea-level to depths especially the Alps where glaciers were already present, but later in excess of 100 m in coastal regions. Equally, in areas of isostatic extended to the plains of Europe and beyond when it was realized uplift shallow marine sediments may occur