Stratification and Sequence in Prograding Shoreline Deposits
Prograding shoreline deposits are used in this chapter to further illustrate the interpreta ion of primary structures and their sequence. Two main points are 1.Structures in environments with combinations of waves, tidal flows, and ephemeral currents can be interpreted in part from concepts presented in Chapter 2. Many of the primary structures are formed by complex or complexly varying hydrodynamic conditions and cannot be directly related to process on the basis of existing flume or wave tank experiments. However, the understanding of the general influence of varying conditions on bed configurations and stratification presented in Chapter 2 assists in placing reasonable constraints on interpretation.
2. Stratigraphic position and facies sequence provide some general environmental constraints which can be used to infer hydrodynamic conditions that produce these less well understood structures. For example, the vertical succession through a deposit formed by a prograding shoreline should be related to progressive depth and process changes observed along modern shoreline profiles. Carefully used, these inferences about environmental and hydrodynamic constraints can add to our understanding of primary sedimentary structures and their interpretation.
Shoreline and nearshore deposits are well represented in the geologic record. In keeping with the purpose and scope of this course, we shall discuss only a few examples that we believe to have common occurrence and broad application. We will consider only two examples of prograding sandy shoreline deposits, partly to examine the difference between these ancient sedimentary records
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Structures and Sequences in Clastic Rocks
These notes are for a course on the use of primary structures and stratification sequence as tools for interpretation of depositional environments. The emphasis is to provide a concise review of the factors that had led to the renaissance in clastic sedimentology during the decade leading up to 1975. The attempt is to provide an organized summary of both experimental studies and ideas on bed forms and primary sedimentary structures that was then relatively new and to show how this information could be applied to solving geologic problems. A second broad objective of the course is more philosophical, in that there is an attempt to outline some general approaches to interpretation and convey the goals of interpretation. The authors believe that there are a fairly small number of general depositional settings but that numerous environmental and process variables within each general setting lend considerable variation to the deposits themselves. The emphasis is at the scale of features and sequence that can commonly be observed in individual outcrops or cores. Interpretation begins with data collected at this level.