23. Sand patterns: sedimentary structures 2 hr
Concepts
Inorganic
sedimentary
structure
Organic
sedimentary
structure
Bed
Ripple mark
Burrow
Trail
Classification
Sias
Measuring
Recording
Observing
Attitudes
Appreciation of
natural
environments
Interest in
methods of
science
Aim
• To gain some understanding of the way structures in reef-top sediment
deposits are produced by moving water and air, and by living things.
You will need
• Reef-walking gear
• Snorkelling gear
• Clipboard and paper
• Plastic ruler
• Camera (optional)
• Transparent viewing box
This activity requires approximately 2 hours part of which should be at time of
low tide and part at higher tide level. It could be carried out over a number of
days.
In places where deposits of sand or other sediments are forming, air, water
and living things act on the sediment to produce distinctive features
known as sedimentary structures. These include various kinds of ripple
marks, grooves, burrows, tracks and trails.
What to do
1.
As the tide goes out, walk along the beach and also through the water on the
inner reef flat.
(a) Look for structures produced on the surface of the sand by moving water.
You might find grooves, or ripple marks, or other similar structures. How
many different kinds can you find? A transparent viewer will help you
look through shallow water to the sandy bottom.
(b) Try to make a pictorial catalogue of all the different kinds of sedimentary
structures produced here by water movement. Make labelled sketches
with a scale. Use a camera, too, if you have one.
In each case, try to work out which way the water currents or waves
moved to produce the structure. Show this on your sketches with arrows.
(c) If you see ripple marks, note their wavelength (i.e., distance between
crests) and amplitude (i.e., difference in height between trough and crest).
Are the crests, in plan view, straight or curved? Are the marks, in profile
view, symmetrical or asymmetrical? Draw sketches. Do you think they
were produced by currents (asymmetrical) or waves (symmetrical)?
