Sedimentary Structures

Porosity Shale Compaction Outline

Clastic sediments display a wide variety of bed structures that help in determining such factors as "way-up" and depositional environment.

Planar bedding has little diagnostic importance but animal burrows or bed form irregularities my give an indication of way-up and environment.

Current cross bedding gives clear way-up indication as bed are truncated by the next influx of sediment. The orientation of the cross beds can also indicate the direction of water or wind currents.

Ripple-marked bedding indicates waves action and the ripple cusps point in the younging direction. Wave action usually indicate shallow marine conditions but ripples can be found in freshwater sediments also.

Imbricate bedding is the overlapping of fossil shells or platey pebbles and can be used as an indicator of current direction.

Graded bedding usually fines upwards to give an indication of way-up. Graded units represent individual pulses of sediment which may be seasonal or indicative of some other cyclic process.

Cut-and-fill bedding involves the reworking of sedimentary layers by new water channels. They provide both way-up and current direction indicators and are common in stream fluvial deposits.

Porosity Shale Compaction Outline
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