Sediments and past environments – sieve analysis, grain shape, cores and facies maps
GeographyEarth's Structure & LandformsAges 15–16Virtual lab
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Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Earth's Structure & Landforms
A virtual sediment lab. Shake 200 g of dune, beach, shallow-sea, river or glacial sand through a stack of sieves from 4 mm to 0.063 mm, weigh each fraction, plot the cumulative curve and read the median grain size and Trask's sorting coefficient So. Under the microscope, sort quartz grains into angular, rounded shiny and rounded matt to tell little transport, water or wind. Then use the present as the key to the past: grain size, structures such as cross-bedding, ripples and mud cracks, and fossils identify old river, beach, shallow-sea and desert layers in three cores, and eight boreholes build a facies map that locates the old coastline and the water depth.
Lesson: Sediments and sedimentary rocks: grain-size analysis, sorting, grain shape and reconstructing past environments
What it shows
Sediments record how they were carried and where they settled. Sieving gives the grain-size distribution: a steep cumulative curve and a small Trask coefficient So = √(d₂₅/d₇₅) mean a well-sorted sand, typical of wind or waves, while glacial deposits are poorly sorted. Grain shape tells the transport: angular after little transport, rounded and shiny in water, rounded and matt (frosted) after wind. By uniformitarianism, layers with the same grain size, structures and fossils as a modern river, beach, shallow sea or desert formed in such a place. Samples and sections are typical examples; sorting thresholds vary between textbooks.
How to use
In Sieving, choose a Sample, press Shake the sieves, then Weigh next sieve until the table is full; move Reading line to read the sizes at 25 %, 50 % and 75 %. In Grains, pick a shape under Mark as and tap each grain, then press Check marks. In Cores and Facies map, tap a layer or a site, read the clues and press the environment it shows.
Parameters you can change
- View Sieving, Grains, Cores, Facies map
- Sample Desert dune sand, Beach sand, Shallow-sea sand, River sand, Glacial deposit, Unknown sample
- Core Core 1, Core 2, Core 3
- Map Area 1, Area 2
- Show today's environments
Questions to explore
- Why are desert dune sands better sorted than glacial deposits?
- Which clues tell a beach sand from a river sand?
- What do sea layers lying on top of river layers tell us about the old coastline?
