Tide and Wave Dominated Coasts Warm-Up
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Essay Question
Macrotidal coasts (tidal range >4m) lack barrier island systems and are characterized only by peritidal depositional settings. However, along mesotidal coasts (tidal range 2-4m), tidal flats are developed along the margins of lagoons in a back-barrier setting. Write two paragraphs, the first describing the vertical facies succession for a mesotidal coast where progradation is occurring, and the second describing the vertical facies succession for a mesotidal coast where transgression is occurring. Be sure in each case to relate the facies succession to processes and the environments of the depositional system defined by these processes. (You may find box 9.2 helpful.)
Multiple Choice Question
Which of the following statements is true?
most barrier sequences in the ancient record are transgressive
progradational barrier sequences have grain-size trends similar to those of prograding deltas
deposits of tidal inlets are often significant in the assemblage of sediments formed in migrating barrier-island depositional systems
balance between rate of sediment supply and rate of change of sea level will determine whether a barrier sequence is transgressive or regressive, and also will determine whether transgressive sequences will be preserved
tidal indicators such as reactivation surfaces and flaser bedding are not present in sediments of barrier island depositional systems
wave activity is the dominant process in the shoreface of a barrier island. The lower shoreface has the highest energy levels, and as a consequence, lacks evidence of extensive bioturbation.
If you were trying to recognize barrier-island depositional systems in the stratigraphic record, which of the following would be dependable indicators?
features such as reactivation surfaces, tidal bedding (tidal bundles), and herringbone cross bedding
coarsening upward sequence of facies
bioturbated muds overlain by landward-dipping cross bedding in lobe-like deposits of coarse sand, overlain by seaward-dipping cross-bedded sands which fine upward
lens-shaped deposits of sand showing tidal features, interfingering with coarsening upward sands capped by aeolian deposits
fining upward sequence of facies
vertically repetitive, cyclic deposits