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Key Idea 2Key Idea 2 SEDIMENTARY ROCKS SEDIMENTARY ROCKS The mineralogy and texture of The mineralogy and texture of

sedimentary rocks are controlled by sedimentary rocks are controlled by processes of weathering, erosion and processes of weathering, erosion and depositiondeposition

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Immature sedimentary rocks are Immature sedimentary rocks are characterised by a wide range of characterised by a wide range of mineral compositions and/or lithic mineral compositions and/or lithic clasts; clasts;

Mature sedimentary rocks have Mature sedimentary rocks have restricted mineralogies dominated by restricted mineralogies dominated by mineral species resistant to mineral species resistant to weathering and erosional processesweathering and erosional processes

BrecciaBreccia

Sedimentary Sedimentary (fragmental)(fragmental)

Immature (wide Immature (wide range of fragments)range of fragments)

Angular fragments Angular fragments (little transport)(little transport)

Fragments range in Fragments range in size consider energy size consider energy current (landslide?)current (landslide?)

Credit: British Geological Society

Immature/MatureImmature/Mature Immature rocks - contain easily weathered Immature rocks - contain easily weathered

minerals (eg. first formed minerals from minerals (eg. first formed minerals from Bowen’s Reaction Series)Bowen’s Reaction Series)

Immature rocks – normally very little Immature rocks – normally very little transport (hence angular fragments), poorly transport (hence angular fragments), poorly sortedsorted

Mature rocks – mainly quartz (low Mature rocks – mainly quartz (low temperature minerals from Bowen’s temperature minerals from Bowen’s Reaction Series)Reaction Series)

Mature rocks - fragments often rounded due Mature rocks - fragments often rounded due to long history of weathering and erosion to to long history of weathering and erosion to remove majority of minerals, well sortedremove majority of minerals, well sorted

Fragment size/shapeFragment size/shape

Longer transport will reduce Longer transport will reduce fragment size and will round fragment size and will round fragment shapefragment shape

Geoscience page 88 figure 5.21 (b) Geoscience page 88 figure 5.21 (b) and (c) COPYand (c) COPY

We need to look more closely We need to look more closely at Mature sedimentary rocksat Mature sedimentary rocks

Why?Why?

In order to think of the processes In order to think of the processes which destroy minerals!which destroy minerals!