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