Diagenesis Ii

Diagenesis is a highly developed, interdisciplinary field of study. It is reciprocal in that it borrows from numerous scientific or technological specialities and then, in turn, repays them with useful results. Too often, however, the information gained and concepts developed remain unintegrated instead of being utilized quickly by several related earth-science fraternities. This volume, the second of a multi-volume work, attempts to bring together such information, thereby assisting the individual and the research group in keeping up with the data explosion. There is no end in sight to diagenetic research because of its wide practical and intellectual appeals. Consequently, periodic reviews, such as presented in this volume, are greatly needed.

Diagenesis in Sediments and Sedimentary Rocks, Volume 2

Diagenesis is a highly developed, interdisciplinary field of study. It is reciprocal in that it borrows from numerous scientific or technological specialities and then, in turn, repays them with useful results. Too often, however, the information gained and concepts developed remain unintegrated instead of being utilized quickly by several related earth-science fraternities. This volume, the first of a multi-volume work, attempts to bring together such information, thereby assisting the individual and the research group in keeping up with the data explosion. There is no end in sight to diagenetic research because of its wide practical and intellectual appeals. Consequently, periodic reviews, such as presented in this volume, are greatly needed.

1 2 J. H. SCHROEDER and B. H. PURSER 1 Introduction A symposium convened during the Vth International Coral Reef Congress in Papeete, Tahiti, 1985, encouraged the editors to assemble this volume of case studies by participating and, especially, by nonparticipating scientists. An attempt was made to include case studies from various regions and geological periods, carried out on various scales from regional to ultrastructural. We hope to present an overall view of reef diagenesis. Although the volume focuses on reef diagenesis, fields also to be considered are biology, paleontology, and sedimentary facies distribution, as they provide the context and, to some extent, encompass the determinants of diagenetic processes. The scope has been limited to reef diagenesis because we feel that reefs have relatively clearly defined geometries, which facilitate the evaluation of diagenetic trends and the definition of diagenetic models. On the other hand, their many different components make reefs somewhat more complex than other deposits, and this creates difficulties in deciphering diagenetic histories; the study of reefs, therefore, is not the simplest manner of solving the many problems relating to carbonate diagenesis. An additional reason for evaluating reef diagenesis is the reservoir potential of these carbonate bodies. To illustrate the point, in the recent collection of 35 case studies of carbonate reservoirs (Roehl and Choquette 1985), reefs were involved in 15. The emphasis on porosity development in many studies of the present volume is therefore not of mere academic interest.

The first North Sea Oil and Gas Reservoirs Conference was held in Trondheim in 1985 as part of the Norwegian Institute of Technology's 75th anniversary celebrations. Favourable reactions from the delegates prompted the Committee to re-run the event some three and a half years later, and it is now intended that the Confe rence be held on a regular basis as long as there is a demand for this type of gathering. The objectives of the 1989 Conference, which were broadly similar to those of the previous one, were: (a) to bring together those engaged in various geoscientific and reservoir engineering aspects of North Sea Oil and gas reservoirs in one forum; (b) to demonstrate wherever poSsible the interdependence of the various disciplines and specializations; (c) to promote innovative, synergistic approaches to research and development programmes aimed at North Sea conditions; and (d) to reflect current trends in the reservoir sciences. Naturally there was no place for specialist parallel sessions in a Conference aimed at encouraging interdisciplinary integration and awareness.

Diagenesis of carbonates and clastic sediments encompasses the biochemical, mechanical, and chemical changes that occur in sediments subsequent to deposition and prior to low-grade metamorphism. These parameters which, to a large extent, control diagenesis in carbonates and clastic sediments include primary composition of the sediments, depositional facies, pore water chemistry, burial–thermal and tectonic evolution of the basin, and paleo-climatic conditions. Diagenetic processes involve widespread chemical, mineralogical, and isotopic modifications affected by the original mineralogy of carbonate and clastic sediments. These diagenetic alterations will impose a major control on porosity and permeability and hence on hydrocarbon reservoirs, water aquifers, and the presence of other important economic minerals. In this Special Issue, we have submissions focusing on understanding the interplay between the mineralogical and chemical changes in carbonates and clastic sediments and the diagenetic processes, fluid flow, tectonics, and mineral reactions at variable scales and environments from a verity of sedimentary basins. Quantitative analyses of diagenetic reactions in these sediments using a variety of techniques are essential for understanding the pathways of these reactions in different diagenetic environments.