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The strangest 0.05% of the geological history
Earth-Science Reviews 50 Ž2000. 125–133 www.elsevier.comrlocaterearscirev
Earth reflections
The strangest 0.05% of the geological history A.J. van Loon ) Geocom, Benedendorpsweg 61, 6862 WC Oosterbeek, Netherlands Received 7 February 2000; accepted 7 February 2000
Abstract The historical geological perspective is the main cause that much more is known about young rocks than about older ones. Most is therefore, obviously, known about Quaternary rocks, but this does not imply that the Quaternary is understood much better than the older periods. On the contrary, facies distributions — particularly in glacigenic successions — seem often so much more chaotic than in successions from other periods that the Quaternary could be considered as the strangest 0.05% in the geological history. It is most unlikely, however, that the Quaternary differs so much from other periods. It must therefore be concluded that many of the apparent discrepancies between Quaternary and older rocks either are due to different approaches followed during investigations, or reflect a geologically still immature situation, because destructive agents have had insufficient time to remove material or to obscure specific characteristics. In spite of these probably fundamental differences between Quaternary and older sediments — that will disappear with time — it is likely that the application of Quaternary investigation methods to older rocks — and that of hard-rock research methods to Quaternary successions — may contribute substantially to a better understanding of both the remote geological past and the nearby geological history. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Quaternary; historical geological perspective; hard-rock analysis; soft-rock investigation
1. Introduction One of the fundamental differences between earth sciences and the other natural sciences is that the study object of the former, the earth itself, is continuously destroying its own history. The knowledge of rocks — and all related topics, ranging from fossil content to metamorphic events — therefore becomes
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Fax: q31-26-33-90783. E-mail address: [email protected] ŽA.J. van Loon..
more fragmented with increasing age Ževen though so much is known about, for instance, early fossils that the fossil record over the past 540 million years provides a good documentation of life in the past Gee, 1999; Benton et al., 2000.. This is the famous ‘historical geological perspective’ that urges researchers to develop ever more refined and sophisticated analytical methods to unravel the oldest rocks. One might approach the historical perspective also from the opposite side: the younger the rocks, the more of them are still present. This makes the Quaternary by far the most intensively studied period. It also makes the rock successions formed during this
0012-8252r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 1 2 - 8 2 5 2 Ž 0 0 . 0 0 0 1 5 - 5
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Fig. 1. Glacitectonic disturbances in the Hinderink quarry ŽGermany..
period the best known, with so numerous details that it is difficult — even for a specialist — to remain aware of all new data and their interpretations. The extremely detailed knowledge of the Quaternary history Žsee, among other things, the abundant data on the extreme climatic fluctuations at the end of the Weichselian, the resulting floral developments and the sudden sedimentary changes; Hoek, 1997; Bjorck ¨ et al., 1998; Bos, 1998; Huyzer and Vandenberghe, 1998; Vandenberghe et al, 1998; Isarin and Renssen, 1999; see also the international conference ‘Recognition of abrupt climate change in clastic sedimentary environments: methods, limitations, and potential’, held in Stockholm in June 1998, and the workshop ‘Rapid climatic warming at the end of the last glacial: palaeodata analysis and climate modelling’ held in Haarlem in February 2000. does not necessarily imply, however, that this period is also the best understood, that worldwide correlations between events and rocks are always possible, and that the data are stored — and retrievable — in the most practical way. One would rather be inclined to state that we do not understand at all what happened during the Quaternary, that correlations over long distances appear wrong much more frequently than correlations between remote rocks of much higher age, and that mapping of Quaternary areas results in much less understandable maps than mapping elsewhere. Such a statement would, obviously, be unjustified. There is, however, some truth in it, which does not always receive sufficient attention. This is partly due
to specific obstacles for interpretation Žsuch as glacitectonics and periglacial disturbations; Figs.1 and 2., but not less to the fact that Quaternary earth scientists appear to work commonly with objectives, tools and models that differ from those used by hard-rock geologists. A consequence is that Quaternary geology in many respects differs from the other earth-science disciplines, that results are presented in different ways, and that it is relatively difficult to apply knowledge of the Quaternary to hard-rock geology Žand reversed.. It may be interesting to analyse how and why the discrepancies between the Quaternary Žsoft-rock. geology and hard-rock geology could develop, but it is more important to find out whether Žand if so, how. the discrepancies could disappear, to the mutual benefit of all geologists.
2. The special status of Quaternary geology Earth scientists comprise geologists and geographers. From the very beginning, physical geographers dealt primarily with the actual earth and the exogenic agents that affect it Žwhich resulted in oceanography, atmospheric sciences, pedology, hydrology, etc., being commonly included in geographical education., whereas geologists directed their attention mainly to lithified rocks. From this perspective, it is not amazing that Quaternary geology was — and still is — most commonly taught in university by geographers, even though there is a —
Fig. 2. Cryoturbations in a small sand quarry at Funen ŽDenmark..
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fortunate — tendency towards integration between both earth-science disciplines. Whereas hard-rock successions easily reach thicknesses of several kilometres, Quaternary successions do not. The result is that Quaternary geologists, used to relatively thin successions, adapted other criteria for distinguishing between lithological units than hard-rock geologists do. In the United States, formations commonly are many hundreds of metres thick; in Europe, this is commonly an order of magnitude less, but the rule remains that the fundamental unit of lithostratigraphy, the formation, must be a unit that is well mappable in the field on the basis of its lithological characteristics Žwhich may include macrofossils, etc... This is entirely different in Quaternary geology, where formations rarely reach such thicknesses, and where they may be distinguished on the basis of laboratory analyses Žheavy-mineral content, pollen assemblages, and even C-14 datings.. Another remarkable difference between hard-rock geology Žwhich is meant in the following to include all non-Quaternary geology, although Tertiary deposits are commonly unlithified, as even Precambrian rocks may be. and Quaternary geology is that the latter shows specialisation of many researchers depending on the age of the rocks studied: some Quaternary geologists deal with the Pleistocene epoch, others with the Holocene epoch; a combination is relatively rare. Such a kind of specialisation is fairly uncommon in hard-rock geology, although there are, obviously, specialists in Late Ordovician graptolites or Westphalian foraminifers. Such specialists have chosen their study object, however, for reasons other than the specific time-span. The — at first sight — fairly strange subdivision between Pleistocene and Holocene research is, obviously, related to the most characteristic phenomenon of the Quaternary, i.e. the occurrence of ice ages. The Holocene reflects the epoch after the last ice age, but it is not truly clear why Holocene geologists are rarely involved in research regarding the various Pleistocene interglacials, which should — according to our present-day insight — be geologically very well comparable with the Holocene Žsee, for instance, Van Kolfschoten and Gibbard, 2000.. The main arguments that Holocene researchers give for their limited field of interest are that Ž1. the Holocene has been preserved much better than any of the
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Pleistocene interglacials Žthe historical perspective!. so that investigation of the Holocene provides much more detail about the natural development, and Ž2. a most important tool for analysis of the Holocene, i.e. C-14 dating, is not possible for the Pleistocene interglacials. These arguments may sound reasonable, but they are not, as will be discussed further on. It is not very well understandable why Pleistocene geologists restrict their activities mainly to glacigenic sediments, and only rarely to the sediments formed during interglacials, particularly since these interglacials may provide so much interesting information about both natural sedimentary developments during such times and climatic fluctuations Žsee, e.g., Tzedakis, 1999; Kukla, 2000; Van Kolfschoten and Gibbard, 2000.. It is, from a scientific point of view, not truly clear either why they do — as a rule — not study hard-rock equivalents from previous glaciations, if for comparison only. The fact that Pleistocene researchers work commonly in a geographical environment Žwhere hard-rock geology is out of scope. must be considered as the prime reason; the historical perspective cannot really play a role because hard-rock geologists involved in glacigenic deposits switch among Permo-Carboniferous, Ordovician and Precambrian rocks ŽLink and Gostin, 1981; Eyles, Eyles and Gostin, 1998., and, moreover, they do often study Pleistocene glacigenic deposits for comparison. A third aspect that makes the Quaternary different from other periods is that it was defined as a separate unit, apart from the Tertiary, because of the occurrence of ice ages, and their large impact on the sedimentary development in those parts of the world that received most geological interest at the time. Such a basis for the distinction of a separate unit ŽVan Vliet-Lanoe, ¨ 1998. is remarkable, since environmental or climatic reasons did not play a similar role in the establishment of other epochs; nor have previous ice ages been a reason to distinguish the time of their occurrence as separate epochs, even though their deposits are often much thicker and have a much wider extent than those of the Pleistocene glaciations. It must thus be concluded that Quaternary geology has a special status, with a relatively isolated position outside a wider geological context. I want to emphasize here explicitly that this statement does not
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relate to the work of every individual Quaternary geologist, but rather represents a generalisation Žand generalisations are by definition not entirely true.. 3. Discrepancies in research methods The greater majority of people live in areas with a Quaternary cover; more specifically, the largest concentrations of people are to be found in Holocene areas, either in deltas or otherwise along coasts, or — to a lesser degree — in alluvial plains. This implies not only that constructional activities Žbuildings, roads, etc.. take place largely on or in a Quaternary subsoil, but also that these areas must provide huge amounts of raw materials, such as clay for bricks, sand for concrete, gravel for road pavements, and groundwater for drinking and for numerous industrial purposes. These conditions — and many more — imply that a sound knowledge of the regional Quaternary geology is of great economic importance. This explains why the relatively thin Quaternary cover receives much more attention than older deposits from both pure and applied geologists, not only in a relative sense, but even in absolute terms. One might expect that the need for understanding of the Quaternary would imply the use of all geological knowledge available. This is, however, not commonly the case. Where hard-rock geologists have learned to apply models for the prediction of a wide variety of phenomena such as mineral occurrences, facies distributions and joint directions, much of the research in Holocene areas is still based on hand borings ŽFig. 3.. And where hard-rock geologists are used to compare field data with those from rocks elsewhere in the world — often of a different age — this type of comparison is scarce for research in the Pleistocene. On the other hand, many hard-rock geologists analyse successions and interpret their depositional environments and paleoclimatological characteristics without ever going to a similar recent environment, let alone in a climatological zone with identical geological processes. Such a negligence of available data must result in suboptimum research results for both hard-rock and Quaternary geologists. It is amazing — and I feel that I can say so because I have been educated as a hard-rock geologist but I’ve worked for some decades as a Quater-
Fig. 3. Hand borings in a Holocene coastal swamp of Suriname.
nary geologist — that both ‘parties’ seem so little interested in each other’s knowledge. This is the more unfortunate because the fairly separated activities result in an ever growing gap between the methods used and the presentation forms chosen. This makes it increasingly difficult to bridge the gap that exists between the ‘hardliners’ and the ‘softies’. I do not use these words by incidence, because hard-rock geology is — if one more generalisation is allowed — much more based on hard science than Quaternary geology, which is still much more the field of physical geographers who pay more attention to ‘soft’ topics such as physical planning, the environmental impact of the exploitation of natural resources, and the relationship between landscape and the geological substratum. One of the most characteristic resulting discrepancies is the different behaviour as soon as stratigraphy becomes involved. This is obvious from both the procedures with respect to interpretation Žand application. of stratigraphic terminology and the choice of criteria for establishing formations and other lithostratigraphic units ŽHarland et al., 1972; Holland et al., 1978.. With respect to terminology, Quaternary geologist used to apply informal terms like ‘Nagele sands’ ŽWiggers, 1955. without any exact criteria for how
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to distinguish such an informal lithostratigraphic unit, let alone how it fits in a formal stratigraphic framework. Attempts to formalize such names in a more geological context Že.g., Van Loon and Wiggers, 1977. are commonly neglected. It is not uncommon either that Quaternary geologists use non-informative terms for the sediments under study, such as ‘units’, subdivided in Pleistocene units T8, T6 and T5; Holocene units T4 and T3; and modern wsic!x unit T2 ŽStraffin et al., 1999. — sometimes even in a misleading way such as ‘the first Upper Pleistocene unit’ ŽAntoine et al., 1999., geomorpholocal descriptions such as ‘slope deposit’ ŽGegnian et al., 1999., lithological descriptions such as ‘gyttja’ ŽBennike, 2000., or environmental interpretations such as ‘organic limnic sediments’ ŽTurney et al., 2000.. Even stranger are descriptions of sections consisting of sedimentary bodies that are described in different ways, such as ‘lower tillrlower lacustrine unitrdiamict unitrupper lacustrine unitrupper till’ ŽFowler, 1999.. It is also interesting that some researchers use formal formation names for the hard-rock substratum and informal, genetic names for the Quaternary; an example is the use of ‘Stanton Formation’ for the bedrock and of ‘loess’ as stratigraphic terms in one contribution ŽColgan, 1999.. It must also be noticed, however, that some Quaternary-oriented journals such as the Journal of Quaternary Science seem quite alert with respect to formal names for Quaternary sediments Žsee, among others, Oms et al., 2000.. In spite of such positive exceptions, there can be no doubt that the frequent use of informal names must commonly lead to misunderstandings and misinterpretations. What might be considered an even greater disadvantage is that correlations between informal units are commonly extremely difficult Žif possible at all., so that reliable paleogeographic reconstructions on the basis of previous literature become almost impossible. This problem is further increased because so many publications on the Quaternary are based on exposures in small sand or gravel pits that are being exploited and that will disappear completely after some time. With respect to the choice of formations Žand therefore of formation boundaries., it seems that Quaternary geologists are more inclined than hardrock geologists to distinguish formations on the basis of — accidental — present-day situations than on
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the basis of geological considerations. In hard-rock stratigraphy, just like in present-day situations, one is confronted with interfingering marine and continental deposits. Hard-rock geologists commonly take such — geologically important — boundaries as a basis for the distinction of separate formations. In Holocene areas, such an approach is not commonly followed — and proposals that are both practical and fulfill the stratigraphic requirements regarding nomenclature ŽRoeleveld, 1974; Griede, 1978. are commonly not adopted by Quaternary-oriented authorities such as the — then — Geological Survey of The Netherlands ŽZagwijn and Van Staalduinen, 1975. — possibly because it seems easier to attribute all sediments in a coastal area to one single formation. These different approaches make it even more complicated to compare hard-rock data with modern equivalents. Interpretation of hard-rock successions thus cannot profit optimally from the knowledge of present-day developments and situations, nor can Quaternary geologists profit optimally from the vast amount of data concerning natural developments in the geological past. The relatively isolated position of Quaternary geologists is also maintained because Quaternary research data are, for a large part, published in journals that are entirely devoted to the Quaternary Žsuch as Geographie Physique et Quater´ naire, Journal of Quaternary Research, Journal of Quaternary Science, Quaternaire, Quaternary Newsletter, Quaternary Research, Quaternary Science ReÕiews, and Quaternary Studies in Poland ., or that are strongly oriented on the Quaternary Žsuch as Boreas, Permafrost and Periglacial Processes, and Palaeogeography, Palaeoclimatology, Palaeoecology ..
4. Consequences for understanding the Quaternary It is often heard that Quaternary geology deserves a place of its own because it is much more complex than the geology of any other period. The rapid facies changes, particularly in glaciated areas, the complex interfingering of marine and continental deposits, and the commonly very thin — and therefore relatively difficult to trace and recognise —
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Fig. 4. Huge Quaternary exposures in the overburden of an opencast browncoal mine near Jaroszow ´ ŽSudetic foreland, Poland..
units are taken as a proof. According to many Quaternary geologists, this makes the Quaternary an exceptional part of the geological history. There is no doubt that the Quaternary is highly interesting, if only because the sediments allow easy 3-D inspection. Even more interesting is, however, that huge quarries exist Žfor exploitation of Quaternary sediments or with a Quaternary overburden that must be removed. that provide huge outcrops that gradually ‘step back’ as long as the exploitation continues ŽFig. 4.. The result is a much larger wealth of detailed information about 3-D facies changes than can ever be obtained in hard-rock deposits. Particularly such huge outcrops have yielded so much information about even the slightest facies changes that an extremely detailed knowledge about numerous sub-recent depositional environments has been obtained. The knowledge about complex and complicated depositional environments, with the continental glacial environment as probably the best example, has grown so much that it sometimes becomes difficult to see the trees through the wood. This has certainly contributed to the idea that the Quaternary deserves a special status because of its highly complex nature.
would be — if it had developed in the same way as Quaternary geology. The answer must be that we would have now a much more detailed insight in the genesis and the interrelationships of older rocks that may now still be enigmatic ŽFig. 5.. On the other hand, considering the efforts and manpower required to unravel the relatively thin Quaternary, one must also conclude that a Quaternary approach to older rocks would have resulted in few rocks having been investigated thus far. If the research of older rocks — on the basis of the methods applied by Quaternary geologists — would have started from the top of the Tertiary downwards, we would certainly not have reached the Mesozoic by now, let alone the Palaeozoic and the Precambrian. We would now be confronted with tens of thousands of formation names — possibly even many more — resulting in an almost inextricable jungle of units many of which would change names every now and then, would not be well defined, would not have stratotypes, and would be largely applicable on a local basis only. We would be confronted with literature that would be published overwhelmingly not according to the type of research Žsedimentological, geophysical, etc.., but in Žnow imaginary. journals such as Early Pliocene Geology, Journal of Hemphillian Mammals and Walachian Orogenesis. Such journals would provide us with numerous interesting details, but it would be extremely difficult to get an overview of the geological developments with time.
5. Imaginary hard-rock research by Quaternary methods One may wonder how hard-rock geology would have developed — and what our geological insights
Fig. 5. The still somewhat enigmatic Precambrian ŽLate Brioverian. diamicts near Donville ŽFrance., possibly representing tills that underwent mass transport in still unlithified state.
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On the other hand, we would have such a detailed insight in specific evolutionary stages of flora and fauna, including the role played by shifting habitats during periods of changing climate or other environmental parameters, that we would be much more aware of evolutionary developments during longer time intervals. This could certainly contribute to a better understanding of natural changes, and thus to environmental policies that would be based on a much more sound basis than is commonly the case nowadays. We would certainly also have a much better insight in the amounts and distribution of natural resources in the stratigraphic units that would have been investigated, so that exploitation could be implemented in a more structured way, and with considerably less waste than happens to occur nowadays. This leads to the fairly surprising conclusion that a Quaternary-geology approach to hard-rock units might result in a more sustainable economy as far as geology is concerned. This would apply only to the relatively small percentage of rocks that could have been studied, however. Another consequence is that the detailed knowledge that we have about Quaternary glaciations would not have been applied to glacigenic rocks of pre-Quaternary glaciations, as these rocks would not yet have been investigated.
6. Imaginary Quaternary research with a ‘hardrock’ approach It is equally attractive to hypothesize about how our knowledge about the Quaternary would have developed if it would, from the very beginning, have been approached in the same way as older rocks. There would certainly not have been so many formations and other lithostratigraphic units Žmany of them with an informal status., and the genetic interpretation of successions would have given more attention to overall developments and less to small, relatively unimportant phenomena. One could very well imagine, for instance, that the entire Quaternary in glaciated areas would have been considered as one formation, in the same way that rocks representing a series of glaciations and interglaciations of preQuaternary age are included in one single formation.
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Such a formation would have been defined as the entire succession on top of, and including, the first glacigenic deposit within the Neogene, and a stratotype would have been chosen, sampled, analysed, described and — as much as possible — preserved Žmany Quaternary formations now have stratotypes in borings and are defined on the basis of, for instance, heavy minerals; see, for instance, Zagwijn and Van Staalduinen, 1975.. It might have been described as ‘an alternation of glacialrglacigenic, periglacial and interglacial deposits, formed both subaerially and subaqueously under, inside or on top of a land-ice mass, as well as the ice-affected fluvial and eolian sediments in front of the ice, and including the intercalated deposits that were formed during warmer intervals’. Such a description may look noninformative, particularly through the eyes of Quaternary geologists. Yet, it is exactly the way in which most hard-rock formations are described and interpreted, without any undesired loss of information: the various ice-deposited diamicts Žtills. would probably have been defined as members, and the interglacial deposits, the loesses, and the proglacial fluvial deposits would probably have, too. This would have resulted in a handsome stratigraphy, with members that show local differences. Each member could be described for specific localities, and there would be no reason to relate a genesis directly to a formation name, such as is commonly done now in NW Europe ŽEhlers, 1983.. A similar approach would have been followed for the Holocene Žif not included in the overall formation. and there would certainly not be separate formations for brooks, river dunes, etc... There would rather be, for instance, one marine and one continental formation, however intricate their interfingering contacts in a coastal area might be ŽFig. 6.. The marine one might include full-marine, tidal-flat, estuarine, lagoonal, and — possibly — beach and dune deposits. The continental formation would include fluvial, eolian and — possibly — mass-flow deposits. Both formations would be described as comprising a number of facies, which might — but need not necessarily — represent members. There would certainly be no Holocene formations or members defined on the basis of their C-14 age, although such datings would doubtlessly be used to help unravel the paleogeographic development in detail.
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Fig. 6. Alternation of peat and marine clay in a core drilled in a Holocene section in NW France.
A more standardized stratigraphic framework for Quaternary deposits might help comparing these deposits with older equivalents. As hard-rock successions contain many mature sequences and cycles, and because so many detailed facies analyses have been carried out for them, such a comparison might greatly contribute to the understanding of Quaternary successions and facies distributions.
7. Conclusions The Quaternary has an extremely detailed lithostratigraphic subdivision, which suggests a most refined logging and mapping. Indeed, logs and maps are extremely detailed, but the data are not always Žprobably even only for a small part. presented in a way consistent with international stratigraphic standards ŽHedberg, 1976; NACSN, 1983.; the sedimentological presentation differs from the usage in hard-rock geology because different sedimentary facies are commonly described not as facies, but in the framework of a separate formation Žor other stratigraphic unit.. A most remarkable approach in this context is the use of lithofacies codes Žaccording to, or adapted from, Miall, 1977., which are handled in
a divergent way: where the codes were meant to indicate the lithological Žprimarily grain-size. differences between various units, Quaternary geologists tend to distinguish units on the basis of different codes. This goes so far that, in marine dropstones, each single stone is considered by some Quaternary geologists as a separate facies, within a number of facies of, for instance, laminated and massive muds. The large number of units distinguished in Quaternary geology is therefore misleading as far as they suggest that the sedimentological andror stratigraphic analysis of the sediments involved are fundamentally more detailed than similar analyses carried out in older sediments. Still, one must realise that the Quaternary is different from other periods in its sedimentary record. One can compare it with a water surface: according to the law of gravity it should be plane Žapart from the slight curve due to the form of the earth.. If the water surface is rough due to external forces, it will gradually come to rest if sufficient time is allowed after the forces have stopped. The Quaternary sedimentary record may be compared with a wave Žrepresenting a temporary phase of instability., whereas the older rocks — like the deeper water masses — have largely come to rest. Future erosion, orogenesis and numerous other process will affect the Quaternary deposits that have been formed, as well as those that still have to be formed. Their preservation potential is also much smaller than that of older deposits because of their near-surface position. If we wait long enough — in fact, a geological time — we will find back a strongly reduced and altered Quaternary record that looks very similar to that of older ones. But for the time being, it forms a strange chaos of facies; this makes, at least for some time, the Quaternary the strangest 0.05% of the geological history.
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A.J. Õan Loon r Earth-Science ReÕiews 50 (2000) 125–133 Bos, J.A.A., 1998. Aspects of the Lateglacial-Early Holocene vegetation development in Western Europe. Ph.D. thesis. Utrecht Univ., 240 pp. Colgan, M.P., 1999. Early middle Pleistocene glacial sediments Ž780 000–620 000 BP. near Kansas City, northeastern Kansas and northwestern Missouri USA. Boreas 28, 477–489. Ehlers, J. ŽEd.., 1983. Glacial Deposits in NW Europe. Balkema, Rotterdam, 470 pp. Eyles, C.H., Eyles, N., Gostin, V.A., 1998. Facies and allostratigraphy of high-latitude, glacially-influenced marine strata of the Early Permian southern Sydney Basin Australia. Sedimentology 45, 121–161. Fowler, B.K., 1999. Geogr. Phys. Quat. 53, 109–116. ´ Gee, H., 1999. The Search of Deep Time: Beyond the Fossil Record to a New History of Life. Free Press, 304 pp. Gegnian, L., Zhijiu, C., Daokai, G., Yongqiu, W., 1999. Permafrost Periglacial Proc. 10, 369–375. Griede, J.W., 1978. Het ontstaan van Frieslands noordhoek wThe genesis of the N part of Frieslandx. Ph.D. thesis. Free University of Amsterdam, 186 pp. Harland, W.B., Ager, D.V., Ball, H.W., Bishop, W.W., Blow, W.H., Curry, D., Deer, W.A., George, T.N., Holland, C.H., Holmes, S.C.A., Hughes, N.F., Kent, P.E., Pitcher, W.S., Ramsbottom, W.H.C., Stubblefield, C.J., Wallace, P., Woodland, A.W., 1972. A concise guide to stratigraphic procedure. J. Geol. Soc. ŽLondon. 128, 295–305. Hedberg, H.D. ŽEd.., International Stratigraphic Guide. Wiley-Interscience, New York, 200 pp. Hoek, W.Z., 1997. Late-glacial and early Holocene climatic events and chronology of vegetation development in the Netherlands. Veg. Hist. Archaeo-Botany 6, 197–213. Holland, C.H., Audley-Charles, M.G., Bassett, M.G., Cowie, J.W., Currey, D., Fitch, F.J., Hancock, J.M., House, M.R., Ingham, J.K., Kent, P.E., Morton, N., Ramsbottom, W.H.C., Rawson, P.F., Smith, D.B., Stubblefield, C.J., Torrens, H.S., Wallace, P., Woodland, A.W., 1978. A guide to stratigraphical procedures. Geol. Soc. London Spec. Rept. 10, 18. Huyzer, B., Vandenberghe, J., 1998. Climatic reconstruction of the Weichselian Pleniglacial in northwestern and central Europe. J. Quat Sci. 13, 391–417. INTIMATE Members, Bjorck, S., Walker, M.J.C., Cwynar, L.C., ¨ Johnsen, S., Knudsen, K.-L., Lowe, J.J., Wohlfarth, B., 1998. An event stratigraphy for the Lat Termination in the North Atlantic region based on the Greenland ice-core record: a proposal by the INTIMATE group. J. Quat. Sci. 13, 283–292. Isarin, R.F.B., Renssen, H., 1999. Reconstructing and modelling Late Weichselian climates: the Younger Dryas in Europe as a case study. Earth-Sci. Rev. 48, 1–38.
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Kukla, G.J., 2000. The last interglacial. Science 287, 987–988. Link, P.K., Gostin, V.A., 1981. Facies and palaeogeography of Sturtian glacial strata ŽLate Precambrian. South Australia. Am. J. Sci. 281, 353–374. Miall, A.D., 1977. A review of braided river depositional environment. Earth-Sci. Rev. 13, 1–62. NACSN ŽNorth American Commission on Stratigraphic Nomenclature., 1983. North American stratigraphic code. Am. Ass. Petrol. Geol. Bull. 67, 841–875. Oms, O., Agudtı, ´ J., Gabas, ` M., Anadon, ´ P., 2000. Lithostratigraphical correlation of micromammal sites and biostratigraphy of the Upper Pliocene to Lower Pleistocene in the Northwest Guadix-Basa Basin Žsouthern Spain.. J. Quat. Sci. 15, 43–50. Roeleveld, W., 1974. The Groningen coastal area. A study in Holocene geology and lowland physical geography, Ph.D. thesis. Free University of Amsterdam, 252 pp. Straffin, E.C., Blum, M.D., Colls, A., Stokes, S., 1999. Alluvial stratigraphy of the Loire and Arroux rivers ŽBurgundy France.. Quaternaire 10, 271–282. Turney, C.S.M., Coope, G.R., Harkness, D.D., Lowe, J.J., Walker, M.J.C., 2000. Implications for the dating of Wisconsinan ŽWeichselian. Late-Glacial events of systematic radiocarbon age differences between terrestrial plant macrofossils from a site in SW Ireland. Quat. Res. 53, 114–121. Tzedakis, P.C., 1999. The last climatic cycle at Kopais, central Greece. J. Geol. Soc. ŽLondon. 156, 425–434. Vandenberghe, J., Coope, R., Kasse, K., 1998. Quantitative reconstructions of paleodimates during the last interglacial - glacial in western and central Europe: an introduction. J. Quat. Sci. 13, 361–366. Van Kolfschoten, Th., Gibbard, P.L. ŽEds.., 2000. The Eemian — Local Sequences, Global Perspectives. Geol. MijnbouwrNeth. J. Geosci. 79, 129 pp. Van Loon, A.J., Wiggers, A.J., 1977. The Nagele Member of the Groningen Formation ŽHolocene, The Netherlands.. Meded. Werkgroep Tertiaire Kwart. Geol. 14 Ž4., 103–123. Van Vliet-Lanoe, ¨ B., 1998. Frost and soils: implications for paleosols, paleoclimates and stratigraphy. Catena 34, 157–183. Wiggers, A.J., 1955. De wording van het Noordoostpoldergebied. wThe genesis of the Noordoostpolder areax Van Zee tot Land 14, 216 pp. Zagwijn, W.H., Van Staalduinen, C.J., 1975. Toelichting bij geologische overzichtskaarten van Nederland. wExplanation of Geological Survey Maps of The Netherlandsx Meded. Rijks Geol. Dienst, Haarlem, 134 pp.
Earth reflections
The strangest 0.05% of the geological history A.J. van Loon ) Geocom, Benedendorpsweg 61, 6862 WC Oosterbeek, Netherlands Received 7 February 2000; accepted 7 February 2000
Abstract The historical geological perspective is the main cause that much more is known about young rocks than about older ones. Most is therefore, obviously, known about Quaternary rocks, but this does not imply that the Quaternary is understood much better than the older periods. On the contrary, facies distributions — particularly in glacigenic successions — seem often so much more chaotic than in successions from other periods that the Quaternary could be considered as the strangest 0.05% in the geological history. It is most unlikely, however, that the Quaternary differs so much from other periods. It must therefore be concluded that many of the apparent discrepancies between Quaternary and older rocks either are due to different approaches followed during investigations, or reflect a geologically still immature situation, because destructive agents have had insufficient time to remove material or to obscure specific characteristics. In spite of these probably fundamental differences between Quaternary and older sediments — that will disappear with time — it is likely that the application of Quaternary investigation methods to older rocks — and that of hard-rock research methods to Quaternary successions — may contribute substantially to a better understanding of both the remote geological past and the nearby geological history. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Quaternary; historical geological perspective; hard-rock analysis; soft-rock investigation
1. Introduction One of the fundamental differences between earth sciences and the other natural sciences is that the study object of the former, the earth itself, is continuously destroying its own history. The knowledge of rocks — and all related topics, ranging from fossil content to metamorphic events — therefore becomes
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Fax: q31-26-33-90783. E-mail address: [email protected] ŽA.J. van Loon..
more fragmented with increasing age Ževen though so much is known about, for instance, early fossils that the fossil record over the past 540 million years provides a good documentation of life in the past Gee, 1999; Benton et al., 2000.. This is the famous ‘historical geological perspective’ that urges researchers to develop ever more refined and sophisticated analytical methods to unravel the oldest rocks. One might approach the historical perspective also from the opposite side: the younger the rocks, the more of them are still present. This makes the Quaternary by far the most intensively studied period. It also makes the rock successions formed during this
0012-8252r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 1 2 - 8 2 5 2 Ž 0 0 . 0 0 0 1 5 - 5
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Fig. 1. Glacitectonic disturbances in the Hinderink quarry ŽGermany..
period the best known, with so numerous details that it is difficult — even for a specialist — to remain aware of all new data and their interpretations. The extremely detailed knowledge of the Quaternary history Žsee, among other things, the abundant data on the extreme climatic fluctuations at the end of the Weichselian, the resulting floral developments and the sudden sedimentary changes; Hoek, 1997; Bjorck ¨ et al., 1998; Bos, 1998; Huyzer and Vandenberghe, 1998; Vandenberghe et al, 1998; Isarin and Renssen, 1999; see also the international conference ‘Recognition of abrupt climate change in clastic sedimentary environments: methods, limitations, and potential’, held in Stockholm in June 1998, and the workshop ‘Rapid climatic warming at the end of the last glacial: palaeodata analysis and climate modelling’ held in Haarlem in February 2000. does not necessarily imply, however, that this period is also the best understood, that worldwide correlations between events and rocks are always possible, and that the data are stored — and retrievable — in the most practical way. One would rather be inclined to state that we do not understand at all what happened during the Quaternary, that correlations over long distances appear wrong much more frequently than correlations between remote rocks of much higher age, and that mapping of Quaternary areas results in much less understandable maps than mapping elsewhere. Such a statement would, obviously, be unjustified. There is, however, some truth in it, which does not always receive sufficient attention. This is partly due
to specific obstacles for interpretation Žsuch as glacitectonics and periglacial disturbations; Figs.1 and 2., but not less to the fact that Quaternary earth scientists appear to work commonly with objectives, tools and models that differ from those used by hard-rock geologists. A consequence is that Quaternary geology in many respects differs from the other earth-science disciplines, that results are presented in different ways, and that it is relatively difficult to apply knowledge of the Quaternary to hard-rock geology Žand reversed.. It may be interesting to analyse how and why the discrepancies between the Quaternary Žsoft-rock. geology and hard-rock geology could develop, but it is more important to find out whether Žand if so, how. the discrepancies could disappear, to the mutual benefit of all geologists.
2. The special status of Quaternary geology Earth scientists comprise geologists and geographers. From the very beginning, physical geographers dealt primarily with the actual earth and the exogenic agents that affect it Žwhich resulted in oceanography, atmospheric sciences, pedology, hydrology, etc., being commonly included in geographical education., whereas geologists directed their attention mainly to lithified rocks. From this perspective, it is not amazing that Quaternary geology was — and still is — most commonly taught in university by geographers, even though there is a —
Fig. 2. Cryoturbations in a small sand quarry at Funen ŽDenmark..
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fortunate — tendency towards integration between both earth-science disciplines. Whereas hard-rock successions easily reach thicknesses of several kilometres, Quaternary successions do not. The result is that Quaternary geologists, used to relatively thin successions, adapted other criteria for distinguishing between lithological units than hard-rock geologists do. In the United States, formations commonly are many hundreds of metres thick; in Europe, this is commonly an order of magnitude less, but the rule remains that the fundamental unit of lithostratigraphy, the formation, must be a unit that is well mappable in the field on the basis of its lithological characteristics Žwhich may include macrofossils, etc... This is entirely different in Quaternary geology, where formations rarely reach such thicknesses, and where they may be distinguished on the basis of laboratory analyses Žheavy-mineral content, pollen assemblages, and even C-14 datings.. Another remarkable difference between hard-rock geology Žwhich is meant in the following to include all non-Quaternary geology, although Tertiary deposits are commonly unlithified, as even Precambrian rocks may be. and Quaternary geology is that the latter shows specialisation of many researchers depending on the age of the rocks studied: some Quaternary geologists deal with the Pleistocene epoch, others with the Holocene epoch; a combination is relatively rare. Such a kind of specialisation is fairly uncommon in hard-rock geology, although there are, obviously, specialists in Late Ordovician graptolites or Westphalian foraminifers. Such specialists have chosen their study object, however, for reasons other than the specific time-span. The — at first sight — fairly strange subdivision between Pleistocene and Holocene research is, obviously, related to the most characteristic phenomenon of the Quaternary, i.e. the occurrence of ice ages. The Holocene reflects the epoch after the last ice age, but it is not truly clear why Holocene geologists are rarely involved in research regarding the various Pleistocene interglacials, which should — according to our present-day insight — be geologically very well comparable with the Holocene Žsee, for instance, Van Kolfschoten and Gibbard, 2000.. The main arguments that Holocene researchers give for their limited field of interest are that Ž1. the Holocene has been preserved much better than any of the
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Pleistocene interglacials Žthe historical perspective!. so that investigation of the Holocene provides much more detail about the natural development, and Ž2. a most important tool for analysis of the Holocene, i.e. C-14 dating, is not possible for the Pleistocene interglacials. These arguments may sound reasonable, but they are not, as will be discussed further on. It is not very well understandable why Pleistocene geologists restrict their activities mainly to glacigenic sediments, and only rarely to the sediments formed during interglacials, particularly since these interglacials may provide so much interesting information about both natural sedimentary developments during such times and climatic fluctuations Žsee, e.g., Tzedakis, 1999; Kukla, 2000; Van Kolfschoten and Gibbard, 2000.. It is, from a scientific point of view, not truly clear either why they do — as a rule — not study hard-rock equivalents from previous glaciations, if for comparison only. The fact that Pleistocene researchers work commonly in a geographical environment Žwhere hard-rock geology is out of scope. must be considered as the prime reason; the historical perspective cannot really play a role because hard-rock geologists involved in glacigenic deposits switch among Permo-Carboniferous, Ordovician and Precambrian rocks ŽLink and Gostin, 1981; Eyles, Eyles and Gostin, 1998., and, moreover, they do often study Pleistocene glacigenic deposits for comparison. A third aspect that makes the Quaternary different from other periods is that it was defined as a separate unit, apart from the Tertiary, because of the occurrence of ice ages, and their large impact on the sedimentary development in those parts of the world that received most geological interest at the time. Such a basis for the distinction of a separate unit ŽVan Vliet-Lanoe, ¨ 1998. is remarkable, since environmental or climatic reasons did not play a similar role in the establishment of other epochs; nor have previous ice ages been a reason to distinguish the time of their occurrence as separate epochs, even though their deposits are often much thicker and have a much wider extent than those of the Pleistocene glaciations. It must thus be concluded that Quaternary geology has a special status, with a relatively isolated position outside a wider geological context. I want to emphasize here explicitly that this statement does not
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relate to the work of every individual Quaternary geologist, but rather represents a generalisation Žand generalisations are by definition not entirely true.. 3. Discrepancies in research methods The greater majority of people live in areas with a Quaternary cover; more specifically, the largest concentrations of people are to be found in Holocene areas, either in deltas or otherwise along coasts, or — to a lesser degree — in alluvial plains. This implies not only that constructional activities Žbuildings, roads, etc.. take place largely on or in a Quaternary subsoil, but also that these areas must provide huge amounts of raw materials, such as clay for bricks, sand for concrete, gravel for road pavements, and groundwater for drinking and for numerous industrial purposes. These conditions — and many more — imply that a sound knowledge of the regional Quaternary geology is of great economic importance. This explains why the relatively thin Quaternary cover receives much more attention than older deposits from both pure and applied geologists, not only in a relative sense, but even in absolute terms. One might expect that the need for understanding of the Quaternary would imply the use of all geological knowledge available. This is, however, not commonly the case. Where hard-rock geologists have learned to apply models for the prediction of a wide variety of phenomena such as mineral occurrences, facies distributions and joint directions, much of the research in Holocene areas is still based on hand borings ŽFig. 3.. And where hard-rock geologists are used to compare field data with those from rocks elsewhere in the world — often of a different age — this type of comparison is scarce for research in the Pleistocene. On the other hand, many hard-rock geologists analyse successions and interpret their depositional environments and paleoclimatological characteristics without ever going to a similar recent environment, let alone in a climatological zone with identical geological processes. Such a negligence of available data must result in suboptimum research results for both hard-rock and Quaternary geologists. It is amazing — and I feel that I can say so because I have been educated as a hard-rock geologist but I’ve worked for some decades as a Quater-
Fig. 3. Hand borings in a Holocene coastal swamp of Suriname.
nary geologist — that both ‘parties’ seem so little interested in each other’s knowledge. This is the more unfortunate because the fairly separated activities result in an ever growing gap between the methods used and the presentation forms chosen. This makes it increasingly difficult to bridge the gap that exists between the ‘hardliners’ and the ‘softies’. I do not use these words by incidence, because hard-rock geology is — if one more generalisation is allowed — much more based on hard science than Quaternary geology, which is still much more the field of physical geographers who pay more attention to ‘soft’ topics such as physical planning, the environmental impact of the exploitation of natural resources, and the relationship between landscape and the geological substratum. One of the most characteristic resulting discrepancies is the different behaviour as soon as stratigraphy becomes involved. This is obvious from both the procedures with respect to interpretation Žand application. of stratigraphic terminology and the choice of criteria for establishing formations and other lithostratigraphic units ŽHarland et al., 1972; Holland et al., 1978.. With respect to terminology, Quaternary geologist used to apply informal terms like ‘Nagele sands’ ŽWiggers, 1955. without any exact criteria for how
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to distinguish such an informal lithostratigraphic unit, let alone how it fits in a formal stratigraphic framework. Attempts to formalize such names in a more geological context Že.g., Van Loon and Wiggers, 1977. are commonly neglected. It is not uncommon either that Quaternary geologists use non-informative terms for the sediments under study, such as ‘units’, subdivided in Pleistocene units T8, T6 and T5; Holocene units T4 and T3; and modern wsic!x unit T2 ŽStraffin et al., 1999. — sometimes even in a misleading way such as ‘the first Upper Pleistocene unit’ ŽAntoine et al., 1999., geomorpholocal descriptions such as ‘slope deposit’ ŽGegnian et al., 1999., lithological descriptions such as ‘gyttja’ ŽBennike, 2000., or environmental interpretations such as ‘organic limnic sediments’ ŽTurney et al., 2000.. Even stranger are descriptions of sections consisting of sedimentary bodies that are described in different ways, such as ‘lower tillrlower lacustrine unitrdiamict unitrupper lacustrine unitrupper till’ ŽFowler, 1999.. It is also interesting that some researchers use formal formation names for the hard-rock substratum and informal, genetic names for the Quaternary; an example is the use of ‘Stanton Formation’ for the bedrock and of ‘loess’ as stratigraphic terms in one contribution ŽColgan, 1999.. It must also be noticed, however, that some Quaternary-oriented journals such as the Journal of Quaternary Science seem quite alert with respect to formal names for Quaternary sediments Žsee, among others, Oms et al., 2000.. In spite of such positive exceptions, there can be no doubt that the frequent use of informal names must commonly lead to misunderstandings and misinterpretations. What might be considered an even greater disadvantage is that correlations between informal units are commonly extremely difficult Žif possible at all., so that reliable paleogeographic reconstructions on the basis of previous literature become almost impossible. This problem is further increased because so many publications on the Quaternary are based on exposures in small sand or gravel pits that are being exploited and that will disappear completely after some time. With respect to the choice of formations Žand therefore of formation boundaries., it seems that Quaternary geologists are more inclined than hardrock geologists to distinguish formations on the basis of — accidental — present-day situations than on
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the basis of geological considerations. In hard-rock stratigraphy, just like in present-day situations, one is confronted with interfingering marine and continental deposits. Hard-rock geologists commonly take such — geologically important — boundaries as a basis for the distinction of separate formations. In Holocene areas, such an approach is not commonly followed — and proposals that are both practical and fulfill the stratigraphic requirements regarding nomenclature ŽRoeleveld, 1974; Griede, 1978. are commonly not adopted by Quaternary-oriented authorities such as the — then — Geological Survey of The Netherlands ŽZagwijn and Van Staalduinen, 1975. — possibly because it seems easier to attribute all sediments in a coastal area to one single formation. These different approaches make it even more complicated to compare hard-rock data with modern equivalents. Interpretation of hard-rock successions thus cannot profit optimally from the knowledge of present-day developments and situations, nor can Quaternary geologists profit optimally from the vast amount of data concerning natural developments in the geological past. The relatively isolated position of Quaternary geologists is also maintained because Quaternary research data are, for a large part, published in journals that are entirely devoted to the Quaternary Žsuch as Geographie Physique et Quater´ naire, Journal of Quaternary Research, Journal of Quaternary Science, Quaternaire, Quaternary Newsletter, Quaternary Research, Quaternary Science ReÕiews, and Quaternary Studies in Poland ., or that are strongly oriented on the Quaternary Žsuch as Boreas, Permafrost and Periglacial Processes, and Palaeogeography, Palaeoclimatology, Palaeoecology ..
4. Consequences for understanding the Quaternary It is often heard that Quaternary geology deserves a place of its own because it is much more complex than the geology of any other period. The rapid facies changes, particularly in glaciated areas, the complex interfingering of marine and continental deposits, and the commonly very thin — and therefore relatively difficult to trace and recognise —
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Fig. 4. Huge Quaternary exposures in the overburden of an opencast browncoal mine near Jaroszow ´ ŽSudetic foreland, Poland..
units are taken as a proof. According to many Quaternary geologists, this makes the Quaternary an exceptional part of the geological history. There is no doubt that the Quaternary is highly interesting, if only because the sediments allow easy 3-D inspection. Even more interesting is, however, that huge quarries exist Žfor exploitation of Quaternary sediments or with a Quaternary overburden that must be removed. that provide huge outcrops that gradually ‘step back’ as long as the exploitation continues ŽFig. 4.. The result is a much larger wealth of detailed information about 3-D facies changes than can ever be obtained in hard-rock deposits. Particularly such huge outcrops have yielded so much information about even the slightest facies changes that an extremely detailed knowledge about numerous sub-recent depositional environments has been obtained. The knowledge about complex and complicated depositional environments, with the continental glacial environment as probably the best example, has grown so much that it sometimes becomes difficult to see the trees through the wood. This has certainly contributed to the idea that the Quaternary deserves a special status because of its highly complex nature.
would be — if it had developed in the same way as Quaternary geology. The answer must be that we would have now a much more detailed insight in the genesis and the interrelationships of older rocks that may now still be enigmatic ŽFig. 5.. On the other hand, considering the efforts and manpower required to unravel the relatively thin Quaternary, one must also conclude that a Quaternary approach to older rocks would have resulted in few rocks having been investigated thus far. If the research of older rocks — on the basis of the methods applied by Quaternary geologists — would have started from the top of the Tertiary downwards, we would certainly not have reached the Mesozoic by now, let alone the Palaeozoic and the Precambrian. We would now be confronted with tens of thousands of formation names — possibly even many more — resulting in an almost inextricable jungle of units many of which would change names every now and then, would not be well defined, would not have stratotypes, and would be largely applicable on a local basis only. We would be confronted with literature that would be published overwhelmingly not according to the type of research Žsedimentological, geophysical, etc.., but in Žnow imaginary. journals such as Early Pliocene Geology, Journal of Hemphillian Mammals and Walachian Orogenesis. Such journals would provide us with numerous interesting details, but it would be extremely difficult to get an overview of the geological developments with time.
5. Imaginary hard-rock research by Quaternary methods One may wonder how hard-rock geology would have developed — and what our geological insights
Fig. 5. The still somewhat enigmatic Precambrian ŽLate Brioverian. diamicts near Donville ŽFrance., possibly representing tills that underwent mass transport in still unlithified state.
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On the other hand, we would have such a detailed insight in specific evolutionary stages of flora and fauna, including the role played by shifting habitats during periods of changing climate or other environmental parameters, that we would be much more aware of evolutionary developments during longer time intervals. This could certainly contribute to a better understanding of natural changes, and thus to environmental policies that would be based on a much more sound basis than is commonly the case nowadays. We would certainly also have a much better insight in the amounts and distribution of natural resources in the stratigraphic units that would have been investigated, so that exploitation could be implemented in a more structured way, and with considerably less waste than happens to occur nowadays. This leads to the fairly surprising conclusion that a Quaternary-geology approach to hard-rock units might result in a more sustainable economy as far as geology is concerned. This would apply only to the relatively small percentage of rocks that could have been studied, however. Another consequence is that the detailed knowledge that we have about Quaternary glaciations would not have been applied to glacigenic rocks of pre-Quaternary glaciations, as these rocks would not yet have been investigated.
6. Imaginary Quaternary research with a ‘hardrock’ approach It is equally attractive to hypothesize about how our knowledge about the Quaternary would have developed if it would, from the very beginning, have been approached in the same way as older rocks. There would certainly not have been so many formations and other lithostratigraphic units Žmany of them with an informal status., and the genetic interpretation of successions would have given more attention to overall developments and less to small, relatively unimportant phenomena. One could very well imagine, for instance, that the entire Quaternary in glaciated areas would have been considered as one formation, in the same way that rocks representing a series of glaciations and interglaciations of preQuaternary age are included in one single formation.
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Such a formation would have been defined as the entire succession on top of, and including, the first glacigenic deposit within the Neogene, and a stratotype would have been chosen, sampled, analysed, described and — as much as possible — preserved Žmany Quaternary formations now have stratotypes in borings and are defined on the basis of, for instance, heavy minerals; see, for instance, Zagwijn and Van Staalduinen, 1975.. It might have been described as ‘an alternation of glacialrglacigenic, periglacial and interglacial deposits, formed both subaerially and subaqueously under, inside or on top of a land-ice mass, as well as the ice-affected fluvial and eolian sediments in front of the ice, and including the intercalated deposits that were formed during warmer intervals’. Such a description may look noninformative, particularly through the eyes of Quaternary geologists. Yet, it is exactly the way in which most hard-rock formations are described and interpreted, without any undesired loss of information: the various ice-deposited diamicts Žtills. would probably have been defined as members, and the interglacial deposits, the loesses, and the proglacial fluvial deposits would probably have, too. This would have resulted in a handsome stratigraphy, with members that show local differences. Each member could be described for specific localities, and there would be no reason to relate a genesis directly to a formation name, such as is commonly done now in NW Europe ŽEhlers, 1983.. A similar approach would have been followed for the Holocene Žif not included in the overall formation. and there would certainly not be separate formations for brooks, river dunes, etc... There would rather be, for instance, one marine and one continental formation, however intricate their interfingering contacts in a coastal area might be ŽFig. 6.. The marine one might include full-marine, tidal-flat, estuarine, lagoonal, and — possibly — beach and dune deposits. The continental formation would include fluvial, eolian and — possibly — mass-flow deposits. Both formations would be described as comprising a number of facies, which might — but need not necessarily — represent members. There would certainly be no Holocene formations or members defined on the basis of their C-14 age, although such datings would doubtlessly be used to help unravel the paleogeographic development in detail.
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Fig. 6. Alternation of peat and marine clay in a core drilled in a Holocene section in NW France.
A more standardized stratigraphic framework for Quaternary deposits might help comparing these deposits with older equivalents. As hard-rock successions contain many mature sequences and cycles, and because so many detailed facies analyses have been carried out for them, such a comparison might greatly contribute to the understanding of Quaternary successions and facies distributions.
7. Conclusions The Quaternary has an extremely detailed lithostratigraphic subdivision, which suggests a most refined logging and mapping. Indeed, logs and maps are extremely detailed, but the data are not always Žprobably even only for a small part. presented in a way consistent with international stratigraphic standards ŽHedberg, 1976; NACSN, 1983.; the sedimentological presentation differs from the usage in hard-rock geology because different sedimentary facies are commonly described not as facies, but in the framework of a separate formation Žor other stratigraphic unit.. A most remarkable approach in this context is the use of lithofacies codes Žaccording to, or adapted from, Miall, 1977., which are handled in
a divergent way: where the codes were meant to indicate the lithological Žprimarily grain-size. differences between various units, Quaternary geologists tend to distinguish units on the basis of different codes. This goes so far that, in marine dropstones, each single stone is considered by some Quaternary geologists as a separate facies, within a number of facies of, for instance, laminated and massive muds. The large number of units distinguished in Quaternary geology is therefore misleading as far as they suggest that the sedimentological andror stratigraphic analysis of the sediments involved are fundamentally more detailed than similar analyses carried out in older sediments. Still, one must realise that the Quaternary is different from other periods in its sedimentary record. One can compare it with a water surface: according to the law of gravity it should be plane Žapart from the slight curve due to the form of the earth.. If the water surface is rough due to external forces, it will gradually come to rest if sufficient time is allowed after the forces have stopped. The Quaternary sedimentary record may be compared with a wave Žrepresenting a temporary phase of instability., whereas the older rocks — like the deeper water masses — have largely come to rest. Future erosion, orogenesis and numerous other process will affect the Quaternary deposits that have been formed, as well as those that still have to be formed. Their preservation potential is also much smaller than that of older deposits because of their near-surface position. If we wait long enough — in fact, a geological time — we will find back a strongly reduced and altered Quaternary record that looks very similar to that of older ones. But for the time being, it forms a strange chaos of facies; this makes, at least for some time, the Quaternary the strangest 0.05% of the geological history.
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