Deltas & Estuaries Warm-Up

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Essay Question

Explain why most deltaic sequences have a coarsening upward facies succession. Don't just cite the vertical succession of environments in which these facies form, but be more critical in your analysis, and include a discussion of processes in your essay.

Multiple Choice Question

Under which of the following conditions are deltas unlikely to occur?

deposition along a convergent margin, where rivers are draining directly into the open ocean adjacent to the trench

along passive continental margins where large rivers are carrying large loads of sand and mud to the sea

in foreland basins at the margin of an uplifted fold and thrust belt

along a continental margin where rapid eustatic rise in sea level is occurring

in cratonic basins where major river systems are carrying sediment to inland seas

along the margins of a rapidly rising source area adjacent to a rapidly subsiding basin

Which of the following statements show faulty geologic reasoning?

Estuaries do not form when tidal currents or wave activity are significant agents of sediment transport.

Estuaries form when there is a balance between rate of sea level rise and deposition at the mouths of rivers (i.e., sea level is neither rising or falling)

Deltas and estuaries coexist along many passive continental margins, such as the Atlantic margin of the US

When river processes dominate greatly over wave and tide processes along a coastline, estuaries will be the dominant depositional environment.

the finest-grained facies of estuarine deposition tends to be in the central part of the estuary, where mixed-energy environments dominate (i.e. river-dominated processes and marine-dominated processes are equal in energy flux).

at the seaward margins of both wave-dominated estuaries and tide-dominated estuaries, facies may be similar to facies in wave-dominated deltas and tide-dominated deltas respectively. However, a major difference is lateral extent of the deposits parallel to depositional strike (i.e., parallel to the shoreline).