Human earth shapers/ETHS101/Resources/structures

Sedimentary Structures
Sedimentary structures are features of or in beds, formed by physical, chemical and biological processes at or shortly after the time the sediment was laid down (deposited). They are useful large scale features (centimetres to metres) that can help us to understand about where the sediment was laid down.They can help answer questions such as:


 * What was the agent carrying the sediment? Ice, water or wind?
 * Did the water or wind move rapidly?
 * Was the sediment dumped or did it lay down over longer periods of time?
 * Were the sediment laid down in deep water or in shallow seas or in streams and rivers?

Because we can see the processes that form sedimentary structures in action in various places today we can imagine the same processes happening in sediment laid down in the past.

{{IDevice Cross-bedding is formed by dune migration. Sand bounces up the long side of the dune and then cascades down and deposits on the down current side of the dune. Dunes are common in deserts, rivers and in the shallow seas.
 * theme=line
 * type=Web resources
 * title=Sedimentary structures: Cross bedding
 * body=
 * Cross-bedding image: Beds marked in dark solid line, cross-bed marked in dashed line.

overturned cross-bedding
A variant on cross-bedding is overturned cross-bedding. This happens when the sand is saturated and sloppy and is caught up in a strong current so that it slides down the down current slope.

}}
 * Overtuned cross bedding image: Thick Black line shows beds. Arrows point to over-tuned cross bed