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Non-biostratigraphical methods of dating and correlation: an introduction

R. E. DUNAY 1 & E. A. HAILWOOD 2 1Mobil Ltd, 3 Clements Inn, London, WC2A 2EB, UK 2Core Magnetics, Sedbergh, Cumbria, LAIO 5JS, UK and Department of Oceanography, University of Southampton, S09 5NH, UK

Since the foundation of the science of geology, together many of these diverse techniques and the description and comparison of preserved disciplines and to explore their potential to solve organic remains has been the fundamental problems in stratigraphy. It is also the intention means to determine the relative ages of sedi- to introduce these techniques, each of which is mentary rock sequences and for correlating familiar to specialist researchers, to a wider these sequences in different areas. Significant audience of petroleum geologists who may find problems have arisen in dating and correlating them useful in the resolution of specific correla- those stratigraphic sequences which are impo- tion problems. verished in, or barren of, fossil remains. As a The techniques represented by the 11 papers result, when compared to the plethora of in this volume can be broadly grouped into five stratigraphic data available for Phanerozoic categories of analysis - mineral, chemical, marine sequences, stratigraphic information isotopic, luminescence and cyclicity. Of the available for terrestrial sequences is sparse papers presenting mineralogical techniques, indeed. It is no surprise, therefore, that major Morton & Hurst (Correlation of questions in stratigraphy still remain for such using heavy minerals: an example from the periods as the Lower , uppermost Statfjord Formation of the Snorre Field, north- Carboniferous and , which are domi- ern North Sea) employ analysis of heavy mineral nated by non-marine formations. suites to correlate sequences of the These problems are exacerbated in correlating basal Jurassic-uppermost Triassic Statt]ord For- and dating barren sequences encountered in mation in the Snorre Field area. Eleven heavy offshore exploration and appraisal drilling, as mineral zones have been recognized, which the the geoscientist has available normally only drill authors conclude reflect changes in sand prove- cuttings and occasional core samples to augment nance, and which can be correlated between log interpretation. With this sparse dataset, the wells. Mange-Rajetzky (Subdivision and corre- geoscientist must often make technical judge- lation of monotonous sandstone sequences using ments on the correlation and continuity of high-resolution heavy mineral analysis, a case potential hydrocarbon reservoir sections in study: the Triassic of the Central ) different wells which may affect exploration utilizes heavy mineral techniques in the correla- and field development decisions. Correlation of tion of normally unfossiliferous Triassic se- biostratigraphically impoverished sequences quences in the central North Sea. Jeans (Clay therefore can be of great significance, as mineral stratigraphy in Palaeozoic and Mesozoic Permian, Triassic and uppermost Carboniferous red-bed facies, onshore and offshore UK) hydrocarbon reservoirs are economically extre- indicates caveats to the use of clay mineralogy mely important, with about 11 000 million in stratigraphic studies, and presents two case barrels of oil equivalent being thus far discov- studies in this field, the first on the Devonian Old ered in these sequences on the UK Continental Red Sandstone of Scotland and adjacent off- Shelf alone. shore areas, and the second on the Triassic of Improvements in analytical techniques during the Southern and Central North Sea and the the past few decades have led to the development New Red Sandstone of the south Devon coastal of geological subdisciplines, some of which, in region. Carter et al. (The application of fission turn, have potential in providing alternative track analysis to the dating of barren sequences: means for dating and correlating sedimentary examples from red beds in Scotland and Thai- sequences. These techniques may prove particu- land) report on the use of fission track analysis larly useful in the dating and correlation of those of detrital zircon in determining maximum strata devoid of chronostratigraphically useful geological age. In examples from Scotland and fossil remains. Thailand, biostratigraphically barren strata of The purpose of this volume is to bring hitherto equivocal age have been dated as

From Dunay, R. E. & Hailwood, E. A. (eds), 1995, Non-biostratigraphical Methods of Dating and Correlation Geological Society Special Publication No. 89, pp. 1~ Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021

2 R.E. DUNAY & E. A. HAILWOOD

Permo-Triassic and Lower Cretaceous, respec- Rendell (Luminescence dating of Quaternary tively. sediments) outlines the use of luminescence Two papers detail chemostratigraphic studies. dating techniques, which date the last exposure Racey et al. (The use of chemical element to light of grains of sediment before burial, in analyses in the study of biostratigraphically dating Quaternary sediments. This technique is barren sequences: an example from the Triassic currently limited to Late Pleistocene sequences. of the central North Sea (UKCS)) present the However, the potential of extending lumines- results of their element analysis study to cence dating to older deposits certainly exists. correlate unfossiliferous Triassic Skagerrak For- In the final paper of the volume, Yang & mation sequences from central North Sea wells Kouwe (Wireline log-cyclicity analysis as a tool using ICP-AES (inductively coupled plasma- for dating and correlating barren strata: an atomic emission spectrophotometry). ICP-AES example from the Upper Rotliegendes of the techniques are employed also by Pearce & Jarvis Netherlands) report the results of a cyclicity (High-resolution chemostratigraphy of Quatern- analysis study in the usually unfossiliferous ary distal turbidites: a case study of new Upper Rotliegendes Group of offshore Nether- methods for analysis and correlation of barren lands. Five supersequences and 12 sequences sequences) in their correlation of barren late have been recognized, which are useful for Quaternary distal turbidites. The authors indi- regional correlation and field-scale correlation, cate that this technique has potential for respectively. correlating older biostratigraphically barren Whilst the papers presented in this special sequences. publication provide an excellent cross-section of Three contributions deal with the application non-biostratigraphical methods in current use, of isotope analyses to age dating and correla- there have been important developments in tion. Roberts et al. (SHRIMP zircon age control other relevant techniques, which are not repre- of Gondwanan sequences in Late Carboniferous sented in the volume, including magnetic polar- and Early Permian Australia) detail their age ity stratigraphy and high-resolution magnetic assignment of Late Carboniferous volcanic units susceptibility logging (e.g. Hauger et al. 1994; in Australia to the Euroj~ean Late Carbonifer- and various papers in Turner & Turner in press). ous Stages through 4~ ages and the newly It is to be expected that the continuing demand developed zircon U-Pb dating technique using for improvement in stratigraphic resolution in the sensitive high resolution microprobe biostratigraphically-barren strata will lead to (SHRIMP). Russell (Direct Pb/Pb dating of significant developments in many of the techni- Silurian macrofossils from Gotland, Sweden) ques presented in this volume, and to the presents his study on direct Pb/Pb dating of introduction of new techniques and approaches stromatoporoid carbonates. The resulting Pb/Pb in the future. Most importantly, we expect to see date is in good agreement with independent increasing emphasis on the integration of a chronometric determinations. This study was range of different techniques in the study of conducted on fossiliferous strata to provide individual formations, in order to exploit fully control, and the results indicate that the the strengths and to identify the weaknesses of technique has potential in dating non-fossilifer- the individual techniques. ous carbonates. Dalland et al. (The application of samarium-neodynmium (Sm-Nd) prove- References nance ages to correlation of biostratigraphically barren strata) detail the utility of Sm-Nd isotope HAUOER, E., LOVLIE, R. & VAN VEEN, P. 1994. analyses in determining provenance ages of Magnetostratigraphy of the Brent Statfjord Formation sediments in the Gullfaks Group in the Oseberg oil field, northern North Field, Norwegian North Sea. Provenance age Sea. Marine and Petroleum Geology, 11, 375-388. TURNER, P. d~ TURNER, A. in press. Palaeomagnetic profiles, integrated with other information, Applications in and facilitate correlation of discrete channel sands Production. Geological Society, London, Special with overbank mudstone deposits. Publication.