STRATIFICATION AND BEDFORMS


General Information

 

Bedforms
Bedding

Plane Bed without Movement

Small Ripples

Megaripples

Plane Bed with Sediment Movement

Dunes

Antidunes

General Information

Planar Bedding

Cross-bedding

Graded Bedding

Evenly Laminated Sand and Horizontal Bedding

Coarsely Interlayered Bedding

Thinly Interlayered Bedding (Rhythmites)

Thinly Laminated Mud

Homogeneous Bedding

Convolute Bedding

Imbricate Bedding

 

Planar Bedding

Upper plane bed: Upper plane bed flow occurs in fine and very fine sand when the flow velocity is increased above that needed for ripple formation (very fine sand) or dune formation (fine sand). Upper plane bed flow occurs in the upper flow regime (Fd>1). Basically, upper plane bed flow is intense sediment transport over a flat bed.

The bed surface in upper plane bed flow is marked in detail by system of low linear ridges, a few grain diameters high, which align parallel to flow direction. These ridges are separated by low linear furrows; both form by disruption of the viscous sub-layer. Incoming sweeps push grains aside to form the small ridges and furrows.

Upper plane bed results in planar stratification. If lithified rock containing upper plane bed lamination is split parallel to bedding, parting lineation is commonly observed.

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A cartoon showing the development of upper plane bed stratification. Note the current lineations shown on the bed surface and the parting lineations shown on the parted surface (top of the second white layer). Parting lineation in a Jurassic sandstone from northwestern China. Lens cap (lower right) for scale. Flow was either top to bottom or bottom to top.

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A small tidal channel on the central California coast. You can see the edge of the channel in the upper left corner and a quarter for scale in the right-central part of the photograph. Flow is from the top of the photo to the bottom of the photo. Most of the lower and central part of this photo is in the upper plane bed field. There is a small standing wave train at the top of the photo, where antidunes are being produced. A close up shot of the upper plane bed portion of the tidal channel shown above, looking straight down. Flow is right to left. Note the quarter in the upper right part of the photograph. Note also the streaking of grains parallel to flow.

An example of upper plane bed stratification in a Cretaceous fluvial deposit in northwestern China. The black object in the upper central part of the photograph is a lens cap for scale.

Upper plane bed stratification in a modern beach deposit. Note that the 3-D nature of this cut demonstrates the horizontal and planar nature of this structure.

 

Cross-bedding

This figure shows flow along the bed across a set of sinuous-crested bedforms. Note that this bottom-hugging flow converges into a scour point (i.e., forms an attachment point). Note also the geometry of the cross beds along different cuts relative to the flow direction and that these sinuous-crested bedforms result in trough cross-beds in the cut perpendicular to flow. Tabular dune cross-beds in a Sinian sandstone from northwestern China. Flow was left to right.

  Multiple sets of dune foresets forming tabular cross-stratification. The outcrop is about 4 meters high. Flow was right to left. Note that all sets are subcritically-climbing as is typical for dunes, and that some of the dune foresets are overturned.

 

Small-ripple Bedding

Megaripple Bedding

Wave-ripple Bedding

Wind-ripple Bedding

Wind riples on dune Wind climbing ripple

 

Longitudinal Cross-bedding

Channel-fill Cross-bedding

Antidune Cross-bedding

Microdelta Cross-bedding

Beach and Longshore Bar Cross-bedding

 

Hummocky Cross-bedding

 

see also Beach/Coastal Environments

Sand Dune Cross-bedding (see also Aeolian Systems)

 

Sand-Drift Cross-bedding

Scour-and-Fill Cross-bedding

Climbing-ripple Lamination

   

 

Flaser and Lenticular Bedding

 

 

Ripple Bedding with Flasers

Flaser Bedding

Wavy Bedding

Lenticular Bedding

 

Graded Bedding

     

 

Evenly Laminated Sand and Horizontal Bedding

Coarsely Interlayered Bedding

Thinly Interlayered Bedding (Rhythmites)

Lacustine Varves Green River, USA

 

Thinly Laminated Mud

Homogeneous Bedding

Convolute Bedding

Convolute Bedding Multiple sets of dune foresets forming tabular cross-stratification. The outcrop is about 4 meters high. Flow was right to left. Note that all sets are subcritically-climbing as is typical for dunes, and that some of the dune foresets are overturned.

 

Imbricate Bedding

Imbricate Bedding (layer above pen)