Some 75% of the rocks at the Earth’s surface are sedimentary in origin, and these include the familiar sandstones, limestones and shales, and the less common but equally well-known salt deposits, ironstones, coal and chert. Sedimentary rocks of the geological record were deposited in the whole range of natural environments that exist today. The study of these modern environments and their sediments and processes contributes much to the understanding of their ancient equivalents. There are some sedimentary rock types; however, for which there are no known modern analogues, or their inferred depositional environments are only poorly represented at the present time.

formations or indeed on any other process in which time played an integral and fundamental role. The advent of radionuclide dating, with the attendant absolute measure of age, changed the views of geology and processes that can occur in ways that have been of major significance. In addition, the radionuclides allow a direct comparison of absolute age to the prior proxies. Accordingly, not only had one available a true age dating but also a proxy scale that could be tie <...>

The intensive studies in the I 960's and I 970's of modern hallow marine carbonate environments in the Persian Gulf (e.g., Shearman, 1963, 1966; Kinsman, 1966; Butler, I 970; Kendall and Skipwith, 1969; Purser, 1973), Florida and the Bahamas (e.g., Shinn and others, 1969; Hardie, 1977a; Enos and Perkins, 1979), and Western Australia (e.g., Logan and others, 1970, 1974b), led to spectacular advances in our understanding of the deposition and early diagenesis of carbonate rocks. These stud1es were part of a major revolution in edimentology that saw a radical change from an approach based heavily on grain textures to one based on sedimentary structures and early diagenetic features. In this new approach, paleo-environments of serumentary deposits are ruagnosed from the vertical and lateral rustribution of elemental rock uruts (subfacies and faCJes), characterized principally by their assemblages of sedimentary structures and early diagenetic features in combinallon With other properties such as sedimentary textures and biota, using analogs established from observations of processes and their sedimentary records 10 modem depositional environments (the "comparative sedimentology" method of Ginsburg, I 974) <...>

As the General Preface accompanying Volume I contains an introduction to the work as a whole, it is only necessary for me here to outline the scope of the second volume.
Volume I1 is about sedimentary structures found in relatively complex physical settings, where groupings or hierarchies of features are often of most interest, and more emphasis is placed than in the first volume on cohesive as opposed to cohesionless beds. Secondary currents can exist for a number of reasons in boundary-layer flows, giving rise to flow-parallel sedimentary structures on both kinds of bed.