Mike Tuke’s

INTERPRETING SEDIMENTARY ROCKS

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Interpreting sedimentary rocks History in a rock D Show how geologists can deduce the environment of deposition from the characteristics of the rock.  For example hold up a piece of black shale with fossil reeds: fine grain size = quiet water, dark colour = reducing, reeds = swamp. Deducing environment of deposition   A P 5 min per sample A variety of large pieces of sedimentary rocks representing different depositional environments are laid out. Students must look at each and state what can be deduced from each of the following characteristics if present: grain size, shape and sorting, colour, fossils, and sedimentary structures. They must then deduce the environment of deposition. Environmental interpretation of sand grains  A P F 40min Students are given labelled samples of modern sands from a variety of environments. The samples are either loose in a film canister or glued, using a solid glue such as Pritstick, to card.  They must describe the characteristics of each sand. They then examine a sandstone and say which sand it most closely resembles and thus determine the sandstones environment of deposition. Map of palaeo-environments A P F 15 min Students are given samples and a map showing the extensive outcrop of the strata from which the samples came. Students must work out the depositional environment of each sample and thus change the geological map into one showing the positions of the different palaeo-environments. Interpreting palaeo-environments Pa F 60 min Students are given the description of the rock types and rose diagrams showing the orientation of sedimentary structures. From this data they must deduce the environment of deposition, the direction wind or water flow and draw a very simple palaeo-map of the environment.