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Sequence : a revolution without a cause?

R. C. L. WILSON Department of Sciences, The Open University, Milton Keynes MK7 6AA, UK

Abstract: The paper presents personal reflections on the origins and utility of sequence stratigraphic models. These focus on two questions: (1) does sequence stratigraphy represent a revolution in our understanding of the stratigraphic record, and (2) does it provide a new means of global correlation? The f-n-st question is answered in the affirmative, at least insofar as sequence stratigraphy enables us to integrate a wide range of data and interpretations across a huge range of spatial and temporal scales. The recognition of the importance of stratal surfaces has led to a greater understanding of the response by sedimentary to climatic, tectonic and eustatic changes. But it has yet to be shown that eustatic signals can be detected unequivocally in the stratigraphic record. Therefore this 'new global stratigraphy', based on the premise that sequence boundaries are primarily controlled by eustatic changes, is not yet a reality. Testing this hypothesis is beyond the resolution of current biostratigraphic and chronostratigraphic techniques.

When I was invited to contribute to the Lyell to the subject are given by Wilson (1992) and bicentenary meeting, I was asked to talk about Christie-Blick and Driscoll (1995). Textbooks by 'Sequence stratigraphy and sea-level change'. It Miall (1996) and Emery and Myers (1996) provide was hardly surprising that 'sea-level change' was in-depth coverage, with Miall's text offering much included in the title, because over 150 years after constructive criticism. The best introduction from Lyell addressed the sea-level controversy, we are the Exxon school is the colourful volume on still trying to unravel tectonic and eustatic signals siliciclastic stratigraphy (Van Wagoner et al. from the sedimentary record. But sequence strati- 1990). Reflective articles by Posamentier and graphy is not just about sea-level change. It Weimer (1993) and Walker (1990) are well worth identifies genetic packages of strata bounded by reading. time-related physical surfaces: and their correlative conformities, and surfaces caused by flooding events. Peter Vail and the 'Exxon Method, problems and doctrine school' claimed that eustatic sea-level changes are The beginnings the dominant control on stratal geometries and distributions within them. For readers not The roots of sequence stratigraphy lie in the recog- familiar with it, the sequence stratigraphic nition, some 40 years ago, of packages of strata approach is summarised in Fig. 1. It develops a bounded by continent-wide unconformities. Tech- simplified version of a frequently used diagram nological advances that enabled the petroleum which is often referred to as the 'Exxon slug'. exploration industry to move offshore played a key To some geologists, the sequence stratigraphic role in stimulating stratigraphers to take this 'big approach heralded the possibility of the 'new global view'. High-quality marine seismic data enabled stratigraphy' whereby stratigraphic surfaces caused stratigraphic architecture to be determined at the by globally synchronous eustatic sea-level changes basin and scales. Out of this could be used as a means of global correlation. grew the conceptual framework that enables the However, others regarded it as dressing up integration of a range of scales of stratigraphic regressions, transgressions etc. in unnecessary new information from a single laminae to a first order terminology. stratigraphic sequence. This paper presents personal reflections on the I first learnt about seismic and sequence sequence stratigraphic approach gained both as a stratigraphy through a workshop run by Esso UK teacher and researcher. It focuses on the questions soon after the 'old testament' was published explicitly and implicitly stated in the title, but does (Payton 1977). They ran another in the 1980s, not attempt to provide a thorough description or around the time of the appearance of the 'new comprehensive critical review. Brief introductions testament' (Wilgus et al. 1988). The first meeting

WILSON, R. C. L. 1998. Sequence stratigraphy: a revolution without a cause?. 303 In: BLUNDELL,D. J. & SCOTT, A. C. (eds) Lyell: the Past is the Key to the Present. Geological Society, London, Special Publications, 143, 303-314. Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

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was, of course, seismically oriented, and the second which I find more use with students is given in Fig. one focused more on the outcrop and well log 2 -but this is not proof of the proposition! scales. At the first meeting there was some robust How can eustatic signals be determined from discussion about a number of problems and coastal onlap charts ? contentious issues, which was hardly surprising Exxon charts have a characteristic saw-tooth shape with people such as Drummond Matthews and with abrupt initial falls followed by gradual rises. Tony Hallam present. A few of these problems are The early derivative sea-level curves reflected such discussed below. asymmetry. In the early 1980s revised smoother curves were published, as by then it had been recognised that the landward encroachment of Are seismic reflections really time lines? across older strata (onlap) along The examples given by the Exxon group at the Esso continental margins, as seen on seismic sections, workshop (e.g. Vail, Todd & Sangree 1977, figs involved marine and fluvial sediments. The latter 3-6) were not entirely convincing. A diagram for were deposited during periods when coastlines Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

SEQUENCE STRATIGRAPHY 305

Fig. 1. Sketch cross-sections illustrating the basic concepts and terminology of sequence stratigraphy. Sketches (a) to (g) illustrate the stages in the development of one depositional sequence during one cycle of relative sea-level change. Slightly modified from Skelton et al. (1997).

moved seaward, yet on seismic sections landward new testaments, and especially the famous - or onlap continued. infamous - Haq curve (Haq et al. 1988), heralded the start of a new era of stratigraphic studies. How can sea-level curves for individual locations Perhaps a means of global chronostratigraphic yield a means of global correlation ? correlation was within reach? This euphoria This was, and still is, a minefield. Different probably resulted from the fact that, to many approaches, and different authors, produce different people, traditional stratigraphy had slipped into the curves for the same period of time (Fig. 3). Twenty doldrums. Many with an historical bent years after the first global curves were published, had taken refuge in and found that all the evidence on which a series of Exxon school the sequence stratigraphic approach widened their curves are based have still not been published horizons - in space and time - as they attempted to although some is contained in the appendix of Haq analyse basin-wide data sets and interpretations. et al. (1988). Despite such shaky foundations (and The historical development of sequence strati- others which are discussed by Miall 1996) many graphy was significantly different from the way geologists felt that the contents of the old and Lyell's ideas were introduced to, and eventually Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

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Fig. 2. A cartoon to explain why seismic reflections are time lines, and do not follow lithostratigraphic boundaries. Changes in tone density depict facies changes; these are relatively abrupt across time lines, but gradual parallel to them.

accepted by, the scientific community, or for that that it provides a new means of global correlation matter the exposure to peer review of later based on the supposed eustatic signals. So method conceptual advances. Seismic stratigraphy came became tainted by doctrine. Lyell avoided this trap, out of the corporate closet in the late 1970s, about as discussed by Jim Secord during his Linnean ten years after it had been routinely applied during Society lecture at the Bicentenary Meeting (see also petroleum exploration activities. The birth and Secord 1997). early childhood of sequence stratigraphy were not Therefore it is important to distinguish the subjected to open debate as were Lyell's analytical framework of sequence stratigraphy from observations and interpretations. Perhaps there debates about eustatic signals and the 'new global were robust debates within Exxon, but they failed stratigraphy'. With this in mind, this paper addres- to ensure that the method was distanced from ses two questions contained within its title: (1) does eustatic explanations when the subject entered the sequence stratigraphy represent a revolution in our public domain in 1977. Unfortunately, this led to understanding of the stratigraphic record, and (2) judgements about the value of the sequence does it enhance our ability to determine the causes stratigraphic approach being clouded by the claim (i.e. the relative contributions made by eustasy,

rise lOOm 50 0 50m ,i it 4

-= Berriasian ,0) LUL)

o Volgian

~ Kimm.

.J Oxfordian

~,.2 Callovian

Fig. 3. Late Jurassic sea-level curves compared. (a) Haq et al. (1988) based on a compilation of coastal onlap and sequence stratigraphic studies. (b): Hallam (1988) based on 'stage by stage analysis of the areal spread of seas over the continents as inferred from palaeographic studies' with shorter-term cyclic changes inferred from facies analyses which enabled 'the recognition of extensive shallowing and deepening events in epicontinental marine sequences'. (c) Sahagian et al. (1996) based on the sedimentary record of repeated flooding and exposure of the very low gradient ramp of the Russian Platform. Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

SEQUENCE STRATIGRAPHY 307 tectonics and depositional processes) of relative revolution in historical geology, or a minor or sea-level change at single locations and across intermediate step forward? Consider this question basins? in the context of the following definitions:

The subdivision of basin fills into genetic A revolution? packages bounded by unconformities and their What are we looking for in a revolution? I have correlative conformities. (Emery & Myers neither the space nor the expertise to discuss at (1996). length ideas about scientific revolutions, so I will The predictable succession of physical quote just two views. Kuhn (1970) used the stratigraphic units including sequences, systems concepts of 'normal' and 'extraordinary' science to tracts and parasequences. These depositional explain what he considered to be the nature of units are defined on the basis of internal stratal scientific revolutions. Normal science is like puzzle 'geometries' and evolve in response to changes solving; it is research firmly based on one or more in shelfal accommodation space. (Vail, pers. past scientific achievements that a particular comm. 1992). discipline acknowledges for a time as supplying the foundation for its continued practice. Extraordinary Notice that the definition given by Peter Vail in a science is preceded by a period of uncertainty, short course avoids the dreaded word 'eustasy'. when investigators may divide into different 'Shelfal accommodation space' is used instead, schools of thought, so that there is no generally which is perhaps a tacit recognition of the difficulty accepted consensus. Extraordinary science begins (many geologists would say impossibility) of when a new paradigm takes over from a previously unravelling from the rock record the relative held one: a new consensus then prevails and the contributions of eustasy, tectonics and sedimentary 'revolution' has begun. New ideas suddenly enable processes in creating and filling the space available a whole range of previously puzzling phenomena to for sediments to fill (Fig. 4). Both the definitions be explained, and so a rigorous 'mopping-up' quoted above focus on method, but 'explanation' operation commences. The emergence of plate still figures in the Vail definition. So has sequence tectonics fits this definition of a scientific revo- stratigraphy enabled 'a whole range of previously lution very well. puzzling phenomena to be explained', or is it just Not all historians of science agree with Kuhn, another step forward in stratigraphic procedures maintaining that it is too simplistic to define just and understanding? We do not have a global model

two distinct kinds of scientific progress (normal - a cause - that integrates a variety of observations and extraordinary). Jevons (1973) wrote: and interpretations in a manner similar to that achieved by . The Vail definition Contributions form a continuous spectrum, quoted above clearly recognises this by leaving out within which really major changes are rare, and the link with eustasy. So have we witnessed a minor ones most frequent, but with intermediate revolutionary change in method and approach? I ones occurring with intermediate frequency. will consider this question first and then return to Did the advent of sequence stratigraphy represent a the issue of 'causes'.

Fig. 4. Sketch cross section across a basin margin showing the controls that determine the space available for to accumulate. The primary controls are eustatic, tectonic and climatic. They determine sediment supply, and the development of equilibrium profiles in erosional and depositional systems that are linked to base levels related to sea level, the water table and . Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

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Building on the shoulders of others A new paradigm or an effective catalyst? Table 1 is a chronological list of geologists, and the Sequence stratigraphy represents a new concepts they proposed, that are embraced by paradigm in geology. (Miall 1996) sequence stratigraphy. These are the foundations Sequence stratigraphy is often regarded as a that underpin sequence stratigraphy, starting with relatively new science, evolving in the 1970s Hutton and Lyell. The younger roots of sequence from seismic stratigraphy. In fact sequence stratigraphy lie in our fascination with cyclic stratigraphy has its roots in the centuries-old sequences, and the recognition by Larry Sloss of controversies over the origin of cyclic stratal assemblages bounded by continent wide sedimentation and eustatic versus tectonic unconformities (Sloss et al. 1949; Sloss 1963). controls on sea level. (Emery & Myers 1996) Sloss also contributed to the evolution of sequence stratigraphy through his supervisory role when These two views represent end members of a Peter Vail was a graduate student. We should not range of opinion about the significance of the forget other contributions, such as Rich's (1951) sequence stratigraphic approach. Miall's view is depositional topography (fondoform, clinoform, perhaps a little surprising, given that he has been undaform) which was the forerunner of the Exxon such a strong critic of the 'new global stratigraphy' 'slug', Wheeler's (1958) chronostratigraphic charts claims of the Exxon school. However his accolade that were (and still are) used to dissect the Exxon is for the method, not the doctrine of eustatic 'slug' in time, and Busch's (1971) genetic incre- control. ments of strata and genetic sequences of strata, the Few stratigraphers would deny that sequence definitions of which are similar to the para- stratigraphy has reinvigorated stratigraphic sequences and parasequence sets of the Exxon research over the past 25 years. At the very least, it school. has enabled us to look at old data with new eyes, The ability to take the 'big view', as was done by and take a basin scale (and larger) view when Sloss and Rich, was significantly enhanced by accumulating and interpreting new data. This has technological advances that enabled stratigraphic resulted in the publication of a multitude of papers architecture at the basin and continental margin and special volumes on the subject. The burgeoning scales to be determined using high quality marine sequence stratigraphic literature consists of a seismic data. Out of this has grown the conceptual spectrum of papers from those applying the new framework, albeit with a continental margin bias, nomenclature in a predominantly descriptive way, that enables the integration of a range of scales of to others who use the concept to come to a better stratigraphic information (see below). understanding of basin dynamics. For an example

Table 1. The foundations of sequence stratigraphy

Year Author(s) Concepts

1788 Hutton Unconformities separating cycles of uplift, and deposition 1835 Lyell Sea-level change and uplift of land 1839 Sedgwick & Murchison Unconformities as physical boundaries of geological Periods 1840 Agassiz Glacial theory 1842 Maclaren Glacioeustasy 1894 Walther Law of succession of facies 1898/1909 Chamberlin Diastrophic control of stratigraphy by sea-level changes 1906 Suess Onlap and offiap attributed to eustasy 1913 Grabau Recognised interrelationship of subsidence and sediment supply 1924 Stille Global unconformities caused by tectonism and resulting eustatic effects 1935 Wanless & Shephard Carboniferous cyclothems and glacioeustacy 1940 Grabau -30 Ma 'rhythm of the ages': heat flow and transgressions/regressions 1949 Sloss et al. First proposal of concept of stratigraphic sequences 1951 Rich Depositional topography: genetically related associations of sediment types. 1958 Teichert Facies sequence 1958 Wheeler Chronostratigraphic charts 1963 Sloss Major continent-wide -boundsequences related to orogenies 1965 De Raaf et al. Vertical profiles (facies successions) 1971 Busch Genetic increments (GIS) and sequences of strata (GSS) Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

SEQUENCE STRATIGRAPHY 309 of the utility of the method one has only to look at similar patterns may be produced by several the extent to which papers presented at successive different combinations of controlling factors. meetings on the petroleum geology of NW Europe Modelling aids our understanding of what rates of (Woodland 1975: Illing & Hobson 1981; Brooks & processes are unrealistic or impossible, and what Glennie 1987; Parker 1993) show the degree to combination of rates are plausible (Fig. 5(c)). which geologists and managements of companies Models can also be used to predict facies distri- have progressively espoused the new approach. butions ahead of drilling in partially explored However, a mountain of paper does not signal a basins (e.g. Lawrence et al. 1990). revolution in stratigraphy. Modelling studies demonstrate the likelihood Sequence stratigraphy does not provide an all that the combination of eustatic changes and embracing global causal model. It is a catalyst, or differential subsidence across rift basins can perhaps an up-to-date toolkit, designed to utilize produce sequence boundaries and depositional and integrate a wide range of data sets and explore systems tracts differing in age across a relatively more deeply spatial and temporal stratal relation- small area (e.g. Gawthorpe et al. 1994). Christie- ships. Integration and interrelationships are the Blick and Driscoll (1995) highlighted the difficulty essence of sequence stratigraphy, based on the well of predicting the timing of the sedimentary established traditions of biostratigraphy, facies response to external 'drivers'. They stated: analysis and chemostratigraphy. It provides a if the phase relation between the eustatic signal framework with which to integrate observations and the resulting stratigraphic record varies from and interpretations derived from different data sets, one place to another, then the synchrony or lack from outcrops through basins to crustal plates, and thereof of observed stratigraphic events may through time (Figs 4 & 5). It has forced us to think prove to be less useful then previously thought as more deeply about how space for sediments to a criterion for distinguishing eustasy from other accumulate is created, about the significance of controls on sedimentation. stratal surfaces and units, and about the hierarchical structure of sedimentary successions and the factors that shape their architecture. The difficulty of manipulating so much data, and The new global stratigraphy the complexity of considering possible controls, Mission impossible? inevitably led to the development and application of modelling studies. Not surprisingly, there are The identification of facies and their environmental optimistic and pessimistic views about their value, interpretation is crucial to the application of as the following quotations from the same volume sequence stratigraphic concepts. As this approach (Dott 1992) show: is, to say the least, not entirely objective, it is not surprising that different workers may arrive at Mathematical modelling in the late 1970s ... different interpretations, as demonstrated by the allowed us to relate sea level, subsidence, and examples from the Upper Jurassic shown in Fig. 6. sediment supply to produce the curves on our So can sequence boundaries and other stratal global cycle chart, which implies a major role for surfaces offer a means of global correlation because eustasy throughout Panerozoic time. (Vail 1992) they are generated by eustatic changes of sea level? As already discussed, the hypothesis that A wide range of geological characteristics places sequence boundaries and flooding-related surfaces limits on the tectonism and eustasy. This allows signal global changes in sea level is fundamentally the application of a family of reasonable tectonic flawed because we are unable to isolate the eustatic and eustatic models to explain basin history ... signals from those caused by tectonic and models can generate complex basinal sequences sedimentary processes. This is not the only with high fidelity using plausible inputs. Thus difficulty. Notwithstanding the problem that assumptions heaped on assumptions work. different workers may not be able to agree on (Kendall et al. 1992) sequence stratigraphic interpretations of the same Using modelling studies, can we really unravel succession, proving that stratal surfaces are the effect of a multitude of controls on the archi- globally synchronous is an almost impossible task tecture of a given basin fill? They help us under- within the resolution of the current geological stand a multitude of possibilities and rule out timescale. This is particularly difficult in unlikely combinations of possible controls, but they successions deposited before the current icehouse cannot separate and quantify the effects of different period began, and there is still a long way to go controls on real stratigraphic patterns which we even within this interval of time. observe. This does not mean that stratigraphic Miall (1994) pointed out the problems of modelling is worthless: it makes us aware that correlating stratal surfaces between basins: the Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

310 l~. c. L. WILSON Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

SEQUENCE STRATIGRAPHY 311

Fittoni Rotunda NOT Pallasioides STUDIED NOT Pectinatus STUDIED Hudlestoni Wheatleyensis Scitulus Elegans IAutissiodorensis Eudoxus Mutabilis NOT Cymodoce STUDIED Baylei

Wignall 1991 Hantzpergue Haq. etaL Proust etal. 1985 1989 1995 Fig. 6. The difficulty of reaching agreement on the location of sequence boundaries: alternative interpretations of the Kimmeridgian sensu anglico of northwestern Europe (from Proust et al. 1995). Sequence boundaries are shown as thick lines.

inability to map them directly from place to place The future means that they must be correlated using biostratigraphy or exceptionally chemostratigraphy Despite all the difficulties of global correlation, or magnetostratigraphy. He showed how the there can be little doubt that our profession will limitations of time resolution involved in the pursue cycles in the geological record for a long various steps necessary to date and correlate time to come -just as it has done in the past. A stratigraphic events ranges between a few hundred promising line of investigation is to determine the thousand and several millions years. Thus error extent to which global geochemical signatures may be heaped on error so that the error range in correlate with flooding events identified using biostratigraphic resolution is often greater than the stratigraphic and sedimentological features. Studies duration of stratigraphic sequences. of pelagic limestones suggest that The existence of cycles occurring at different 'within certain limits, the correlation of the ~13C frequencies and amplitudes adds to the problems of profile with published sea-level curves may be recognising global signals (Fig. 7), because differ- extremely close' and that 'such a relationship could ent depositional settings may record different well relate to shelf-sea area governing the global frequency events. So there is a danger that a lower burial rate of organic carbon' (Jenkyns 1996). order event in one place may be correlated with a During the present icehouse period, 0180 variations higher order one in another, and so on. are a proxy for glacioeustatic sea-level changes, Optimists argue that if key events as indicated by and in some areas these have been shown to be sequence boundaries and transgressive/flooding correlated with sequence boundaries (e.g. Carter et surfaces do turn up in the same zonal positions in al. 1991; Naish & Kemp 1997). Notably, the many places around the world, then there is a oxygen isotope studies of Browning et al. (1996) possibility that the global signal is strong enough to showed that -volume changes occurred across overcome regional variability in tectonic sub- sequence boundaries beneath the New Jersey sidence and uplift. coastal plain after 42 Ma (when Antarctic ice sheets

Fig. 5. Sequence stratigraphy: its role in promoting the integration of different data sets, and as a framework for exploring the interrelationships in space and time of the controls on the creation of sediment accommodation and the resultant stratal units. (a) Sequence stratigraphy provides a framework for the integration of data sets collected across a range of scales, shown on a log-log plot. (b) The hierarchy of scale of stratal units in thickness and time, shown on a log-log plot. (c) Estimates of the ranges of sediment accommodation space versus the time periods over which various processes operate to produce such space, shown on a log-log plot (Dickinson et al. 1994). Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

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Fig. 7. Changing frequencies and amplitudes of eustatic change. (A) The 'first order' curves of Hallam (1977) and Vail et al. (1977) show sea-level peaks in the Early Palaeozoic and Cretaceous, separated by a low in the Permo~ Triassic. The smaller scale fluctuations on the Hallam curve represent second order changes. Left side of (B) and (C) (from Tucker 1993): cartoons showing the possible changes in the amplitude of third-fifth-order sea-level changes during icehouse and greenhouse periods. During icehouse periods, higher frequency and amplitude Milankovich- related changes dominate over lower frequency and amplitude third order changes. During greenhouse times, the third-order changes probably had higher amplitudes than Milankovich-related changes, and so are more likely to generate sequences. Right side of (B) and (C): cartoons (not to scale) showing differences in mean elevation and amplitudes of sea levels during icehouse and greenhouse periods. Lower mean sea level during icehouse times are accompanied by high amplitude short-term changes so that the upper parts of continental slopes, continental shelves and coastal plains are subjected to frequent flooding and exposure. In contrast, high mean sea level during greenhouse periods result in extensive epeiric seas covering platforms and low angle ramps, so that relatively small changes in sea level cause extensive flooding or emergence over large areas.

began to form), but no link was revealed between Conclusion ~180 variations and sequence boundaries before this time. Few geologists would deny that sequence strati- There are limitations to the application of studies graphy has reinvigorated stratigraphic research of recent sedimentary systems and basin over the past 25 years. At the very least, it has architecture in order to understand the controls on enabled us to look at old data with new eyes, and sequence development during greenhouse periods. take a basin scale (and larger) view when acquiring This is because during icehouse periods deposi- and interpreting new data. This has resulted in the tional systems may not reach equilibrium during publication of a plethora of papers and special the relatively short time spanned by a single higher volumes on the subject. But does this signal a order cycle of sea-level change (Fig. 7B). They revolution in stratigraphy? were more likely to have done so during Judgements about the value of the sequence greenhouse periods. Would storm processes be stratigraphic approach are often clouded by argu- more or less significant than they are today in ments concerning whether it provides a new controlling architecture during greenhouse times? method for global correlation because sequences During greenhouse times, the amplitudes of global were largely the result of eustatic sea-level changes. sea-level changes were probably much smaller than Therefore it is important to distinguish the those of icehouse times, and they occurred over analytical framework and predictive capability of longer periods of time: this must have had a sequence stratigraphy from debates about eustatic significant effect on rates of sediment supply. So signals and the 'new global stratigraphy'. does sequence architecture change between It is probably unlikely that high resolution greenhouse and icehouse times as suggested by sequence stratigraphic studies will ever, on their Read et al. (1991)? These and many other questions own, succeed in proving that sequence boundaries remain to be explored. can be used as globally synchronous stratigraphic Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021

SEQUENCE STRATIGRAPHY 313 markers, especially during greenhouse periods. In CHRISTIE-BLICK, N. & DRISCOLL, N. W. 1995. Sequence the absence of a significant improvement in the stratigraphy. Annual Reviews of Earth and resolution of dating methods, the ultimate test will Planetary Science, 23, 451-478. be to show whether these surfaces are related to DICKINSON, W. R., SOREHEGAN, G. S. & GILES., K. A. geochemical signals of global change. 1994. Glacioeustatic origin of Permo-Carboniferous stratigraphic cycles; evidence from the southern The quotation below provides a strong reminder Cordilleran foreland region. In: DENNISON, J. M. & about the need to objectively record the nature of ETTENSOHN F. R. (eds) Tectonic and Eustatic the stratigraphic record, and then consider the Controls on Sedimentary Cycles. Concepts in processes that were responsible for what we Sedimentology and Palaeontology 4, Society of observe. Sedimentary Geology, 25-34. DoTr, R. H., Jr 1992. An bTtroduction to the Ups and Perhaps Lyell's greatest single contribution was Downs of Eustao'. Geological Society of America to separate study of the geological record - Memoir 180, 17-24. geology in its historical sense - from the study of EMERY, D. & MYERS, K. (eds) 1996. Sequence processes that produced this record. Sutton Stratigraphy. Blackwell Science, Oxford. (1975) GAWTHORPE. R. L.. FRASER, A. J. & COLLIER, R. E. LL. 1994. Sequence stratigraphy in active extensional We should not forget the pitfalls of using the basins: implications for the interpretation of ancient genetic stratigraphy route to interpreting the rock basin fills. Marine and Petroleum Geology, ll, record, for there is always the risk that method will 642-648. slip into doctrine. GRABAU, A. W. 1913. Principles of Stratigraphy. Seiler, New York. I am indebted to Peter Vail and his Exxon colleagues for -- 1940. The Rhythm of the Ages. Henri Vetch, Peking. stimulating my interest in sequence stratigraphy. An HAQ, B. V., HARDENBOL, J. 8,: VAIL, P. R. 1988. Mesozoic unpublished perspective on sequence stratigraphy by and Cenozoic and cycles of sea- Gerald Salisbury provided food for thought a year before level change. In: WILOL'S, C. K., POSAMENTIER. H., this paper was written. The comments of Angela Coe and VAN WAGONER, J., ROSS, C. & KENDALL, C. St. C. two anonymous reviewers are gratefully acknowledged. I (eds) Sea-Level Changes: an Integrated Approach. thank Angela Coe and the Open University for permission Society of Economic Palaeontologists and to reproduce Fig. 1. The contributions of Yvonne Mineralogists Special Publication 42, 71-108. Englefield and Denise Swann (word processing) and HALLAM, A. 1977. Secular changes in marine inundation Andrew Lloyd and John Taylor (figure drafting) are of USSR and through the gratefully acknowledged. . Nature, 269, 762-772. 1988. A re-evaluation of Jurassic eustasy in the light of new data and the revised Exxon curve, ln: References WILGUS, C. K., HASTINGS, B. S., KENDALL,C. G. ST. C., POSAMENTIER, H. W., Ross, C. A., VAN AGASSIZ, L. 1840. Etudes sur les . Privately WAGONER, J, C. (eds) Sea-Level Changes: an published, Neuchatel. Integrated Approach. Society of Economic BROOKS, J. & GLENNIE, K. W. (eds) 1987. Petroleum Palaeontologisls and Mineralogists Special geology of North-West Europe, Graham & Trotman. Publication 42, 261-273. London, vols 1-2. ILLING, L. V. & HOBSON, G. D. (eds) 1981. Petroleum BROWNING, J. V., MILLER, K. G. & PAK, D. K. 1996. Geology qf the of North-West Global implications of Lower to Middle Eocene Europe. Heyden & Son, Institute of Petroleum, sequence boundaries on the New Jersey coastal London. plain: the icehouse cometh. Geology, 24, 639-642. JENKYNS, H. C. 1996. Relative sea-level change and BUSCH, D. A. 1971. Genetic units in delta prospecting. carbon isotopes: data from the Upper Jurassic American Association of Petroleum Geologists (Oxfordian) of central and southern Europe. Terra Bulletin, 55, 1137-1154. Nova, 8, 75-85. CARTER, R. M., ABBOTT, S. T., FULTHORPE, C. S., JEVONS, E R. 1973. Science Observed. Allen & Unwin, HAYWICK, D. W, & HENDERSON, R. A. 1991. London. Applications of global sea-level and sequence KENDALL, C. G. ST. C., MOORE, E & WHIYrLE, G. 1992. stratigraphic models in southern hemisphere A challenge: is it possible to determine eustasy and Neogene strata from New Zealand. In: MACDONALD, does it matter? bT: DOTT, R. H., Jr (ed.) Eustasv: the D. I. M. (ed.) Sedimentation, Tectonics and Eustasv: Historical Ups and Downs of a Major Geological Sea-Level Changes at Active Margins. International Concept. Geological Society of America Memoir Association of Sedimentologists Special Publication 180, 93-107. 12, 41-65. KL'HN, T. S. 1970. The Structure of Scientific Revolutions. CHAMBERLAIN, T. C. 1898. The ulterior basis of time 2nd edn. University of Chicago Press, Chicago. divisions and the classification of geologic history. LAWRENCE, D. 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