Downloaded from http://sp.lyellcollection.org/ by guest on September 30, 2021 High resolution stratigraphy in modern and ancient marine sequences: ocean sediment cores to Palaeozoic outcrop ROBERT B. KIDD 1 & ERNEST A. HAILWOOD 2 i Department of Geology, University College of Wales, PO Box 914, CardiffCF1 3YE, UK 2 Department of Oceanography, University of Southampton, Southampton S09 5NH, UK The Deep Sea Drilling Project (DSDP), over its cesses such as sea level and climate change. initial ten years of operations, relied almost Sedimentologists attempting to establish rates of entirely on a developing biostratigraphy based erosional, transportational and depositional on microfossil groups for its stratigraphic con- processes, and palaeontologists specializing in trol. During that same period, high resolution evolutionary studies require particularly fine stratigraphic methods were developed for Quat- definition of geological events. ernary marine cores through combination of The striking advances that have been achieved microfossil biostratigraphy and paleomagnetic in fine-scale stratigraphic studies of ocean sedi- reversal sequences. The introduction of the ment sequences have depended upon inte- hydraulic piston corer in 1982 provided the gration of information from a range of means to extend the surface core studies to stratigraphic techniques, in particular the com- depth and amajor impulse to paleoceanographic bination of microfossil biostratigraphy (gener- studies. By the end of the DSDP programme in ally using more than one fossil group) with 1984, an integrated high resolution stratigraphy magnetostratigraphy and/or oxygen isotope for the North Atlantic had emerged, based on stratigraphy (e.g. Kennett 1982). By 1989, microbiostratigraphy, magnetostratigraphy and stratigraphic resolution of better than a few isotope stratigraphy which had extended the thousand years was being quoted for the Pleisto- identification of Milankovitch cycles to the Plio- cene by marine stratigraphers (Ruddiman et al. cene. 1989) and successes were well established in Through the Ocean Drilling Program's oper- extending the integrated magneto-biostrati- ations since 1986, integrated Cenozoic stratigra- graphic approach to Cenozoic marine strato- phies have been extended to all the major oceans types on land (Zijderveld et al. 1986; Channell et and emphasis is now placed on extending these al. 1988; Premoli-Silva et al. 1988). to land sections. Resolution in pre-Cenozoic marine sequences has begun to benefit from the same integrated approach along with emerging Concept of a "multidisciplinary" conference techniques such as strontium isotope stratigra- phy and 'cyclostratigraphy'. on high resolution in stratigraphy The Geological Society Marine Studies Group Introduction and background has, for many years, been concerned with the dissemination of developments in marine geol- Stratigraphy: a rapidly developing field ogy to the wider land-based geological com- munity, through the promotion of national and The deciphering of geological events from the international conferences. The majority of the sedimentary record requires increasingly precise papers presented in this volume were originally stratigraphic resolution if we are to advance our given at a Geological Society conference in understanding of the Earth's system and its London, co-sponsored by the Marine Studies processes. An important development of the Group and the Stratigraphy Committee. The 1980s was the recognition that the record of principal aims of this meeting were (i) to focus orbitally-modulated late Cenozoic and Quatern- on recent advances in Quaternary and late ary climatic fluctuations might provide a key to Cenozoic stratigraphic resolution, with a par- improving resolution further back in the strati- ticular emphasis on developments in approaches graphic record (e.g. Imbrie 1985). It is important such as magnetic, isotopic, geochemical and to improve stratigraphic resolution on these molecular stratigraphy, (ii) to extend these longer timescales in order to explore the causal considerations to aspects of stratigraphic resol- relationships and driving mechanisms of pro- ution in the Mesozoic, Palaeozoic and beyond, From HAILWOOD,E. A. & KIDD, R. B. (eds), High Resolution Stratigraphy Geological Society Special Publication, No. 70, pp. 1-8. Downloaded from http://sp.lyellcollection.org/ by guest on September 30, 2021 2 R.B. KIDD & E. A. HAILWOOD and (iii) to address problems of intercorrelation Contributions to the Volume between different stratigraphic schemes and The present volume makes no attempt to rep- their chronometric calibration, together with resent all of the various presentations and dis- developments in sequence stratigraphy and cussions at the October 1990 and January 1991 wire-line logging stratigraphy. sessions. All of the contributors were invited to The response to the call for papers was submit papers for peer-review and publication in outstanding and this necessitated extending the the volume. Many accepted, but others had originally-planned two-day conference to two presented review papers or contributions on separate, but closely-linked two-day meetings, developments in techniques that had been pub- one held in October 1990 and the other in lished or were planned to be published else- January 1991. This tremendous response is a where. Nevertheless, the volume brings clear indication of the extent of interest in together much of the proceedings of the sessions 'open-forum' discussions on developments in and, most importantly, provides under one stratigraphic resolution. The subjects addressed cover a representative cross section of the issues at the two meetings were broadly separated into discussed at this multidisciplinary gathering of two parts, the first focusing mainly on Quater- stratigraphers. nary and Tertiary topics, together with develop- The purposes of this editorial are (i) to ments in stratigraphic techniques, and the summarize some of the stratigraphic develop- second focusing largely on Mesozoic and Paleo- ments in marine geology that led up to the zoic topics. However, some mixing of topics conference, (ii) to highlight some particularly between the two parts was maintained and both significant topics addressed at the two meetings parts of the meeting were characterised by lively (especially where the corresponding conference discussions and debates. presentation did not result in a contribution to this volume), and (iii) to briefly consider some of What is high resolution in stratigraphy? the possible ways in which stratigraphic resol- ution may be improved in the future. One clear consensus on this question, arising from the four days of presentations and dis- cussions, was the predictable: 'it depends on The ocean record where you are in the geological timescale'. Just as the meaning of 'hi-fi' is, to a large extent, in At the present day, approximately 70% of the the ear of the beholder, so is the definition of Earth's surface lies beneath a cover of 4 km or 'high resolution' in stratigraphy dependant on more of seawater. Open ocean pelagic sequen- the particular application! ces deposited in this environment offer the An attempt at a statement of achievable greatest potential for stratigraphic completeness resolutions for different parts of the geological available in the geological record. Sampling of timescale is shown in Table 1. This represents this record has been largely by piston coring the authors' view of the state-of-the-art in early techniques (Kullenberg 1947; Weaver & 1991. Some of these figures are already being Schultheiss 1990) or by ocean drilling (Storms improved upon, especially for the late Quater- 1990). nary, where concerns about global climate Until the early 1980s, two distinct levels of change are driving rapid developments over the stratigraphic resolution had been established for shorter timescales. Figures for a decade earlier the ocean record, relating respectively to the are shown in brackets to emphasise the rapid deep sea drilling cores recovered through the improvements in stratigraphic resolution in oceanwide activities of the JOIDES drilling recent years. vessel 'Glomar Challenger' and conventional piston cores taken by other research vessels. The Table 1. Achievable resolution for integrated drilling programme depended almost entirely on stratigraphy in marine sediment sequences (circa 1991) microfossil biostratigraphy for its age control whilst major advances were being made by Quaternary <1 to 3 ka (1980:c.20 ka) combining stratigraphic techniques in the study Late Cenozoic 5 to 10 ka (1980:c. 100 ka) of piston cores. Early Cenozoic 10 ka to 1 Ma Late Cretaceous 100 ka to 1 Ma Early Cretaceous c. 10 Ma Development ofan integrated stratigraphy Jurassic 50 ka to 150 ka* Triassic 225 ka to 2 Ma* The limit of penetration of conventional piston corers in pelagic carbonate-rich sequences is * See Cope (this volume). around 20 m subbottom. A sediment sequence Downloaded from http://sp.lyellcollection.org/ by guest on September 30, 2021 INTRODUCTION 3 recovered by this method usually consists of a areas of the ocean basins, below the carbonate 6.5 cm diameter transparent plastic tube filled compensation depth (Berger & Vincent 1981), with the sediment, which has been cut into 1.5 m calcium carbonate is ubiquitous in the oceans. long sections. In the laboratory, these sections However, the proportion of carbonate present are split lengthwise, revealing a flat surface for in the sediment varies