Atlas of sedimentary structures in estuarine and tidally-influenced river deposits of the Holocene Rhine-Meuse-Scheldt system: Their application to the interpretation of analogous outcrop and subsurafce depositional systems

Samenvatting

The first part of the atlas deals with the hydraulic and sedimentary origin of the characteristic structures, based on studies of the lower coalescing alluvial plains formed by the Pliocene to Recent Rhine-Meuse-Scheldt river system in The Netherlands and Germany. The material presented here is thus mainly - although not exclusively - applicable to other fluvial and estuarine systems considered to be close analogues. Before embarking on the origin of the sedimentary structures, the reader is familiarized with the processes that create sedimentary structures of tidal and fluvial origin (or combinations thereof). Relevant features related to tidal waves are discussed in Chapter 2, together with a synthesis of sediment dynamics and morphology and their resulting sedimentary assemblages and sequences. ... The sedimentary structures typical of each of the Rhine-Meuse- Scheldt sub-environments are detailed in Chapter 3, and their main characteristics are summarized using a series of diagnostic criteria. This involves a collation of characteristic sedimentary structures in the estuarine and fluvial-tidal transition zones to show how they change along a continuum, extending from pure tidal domains to the upstream limits of tidal signatures in fluvial sediments. The recent Rhine-Meuse-Scheldt examples have been studied in temporary excavations; and in most cases the environmental conditions at their time of deposition are known in remarkable detail from historical maps and/or hydrographic charts. The Pliocene deposits of the Rhine (Germany) are also suitable for reconstructing palaeo-environments because they have been examined over large areas revealed in open cast lignite mines. The second part of the atlas sees the Rhine-Meuse-Scheldt system used as a standard of reference and point of comparison with other worldwide ancient outcrop analogues believed to cover a similar range of natural variability (Ch. 4). Like the Pliocene to Recent examples, they too have supposedly originated in mesotidal settings (i.e., those experiencing 2 to 4 m tidal amplitudes at their marine boundaries). The information obtained from the recent exposures and - to the extent possible - the outcrop analogues, is then applied to the interpretation of subsurface core data from the Norwegian Continental Shelf, which illustrate a variety of analogous tidal facies and structures from prospective Late Triassic to Jurassic sedimentary systems (Ch. 5). The core photographs are supplemented by sedimentological core descriptions covering the various facies on display. In both cases - the outcrop examples and the cores - the illustrations are systematically ordered in a similar way to those of the Recent and Pliocene river data. In addition, several examples are presented which, to some degree, resemble inshore tidal deposits but in fact represent tidallyinfluenced nearshore environments. Additional background information on locations, general depositional settings, stratigraphy, and ages is given in the appendices (Appendix 1 - outcrop analogues; Appendix 2 - core analogues). Finally a selective synthesis and overview of all the characteristic sedimentary structures of inshore tidal environments and associated tidallyinfluenced fluvial channels for mediumsized rivers and micro-to mesotidal shorelines is presented in Chapter 6. Their diagnostic value is explained throughout. Although it is up to the reader to judge, the authors believe that the material contained herein will make a significant contribution to creating a \'library\' (as mentioned above) as well as aiding the interpretation of ancient outcrops and subsurface cores.