Knowledge and Geological techniques Comments understanding and skills Sedimentary rocks Investigation of the concept of Candidates should be aware exhibit differences in of the range of texture in ‘sediment maturity’. Immature texture which sedimentary rocks descriptive terms (as used on influences porosity and characterised by a wide range a grain size comparator): permeability: grain of mineral compositions and/or angularity very – angularity, sphericity, lithic clasts; mature angular to well size, sorting, which sedimentary rocks with rounded reflects: restricted mineralogies sphericity high to – dominated by mineral species the nature of rocks low sphericity resistant to weathering and from which they size reference to – erosional processes. were derived the Wentworth scale conditions of sorting very well to – Understanding that y = mx + c climate, poorly sorted represents a linear weathering, erosion relationship. and deposition For exemplification of operating during mathematical skills see their formation Mathematical Guidance for AS Geology. post-depositional factors as The mathematical skills sediments are identified are not exclusive to formed into this section of the sedimentary rocks: specification. diagenesis and lithification (compaction, recrystallisation, cementation, pressure solution).
Knowledge and understanding Geological techniques and skills Comments Sedimentary rocks exhibit differences in texture which influences porosity and permeability: grain angularity, sphericity, size, sorting, which reflects: the nature of rocks from which they were derived conditions of climate, weathering, erosion and deposition operating during their formation post-depositional factors as sediments are formed into sedimentary rocks: diagenesis and lithification (compaction, recrystallisation, cementation, pressure solution). Investigation of the concept of ‘sediment maturity’. Immature sedimentary rocks characterised by a wide range of mineral compositions and/or lithic clasts; mature sedimentary rocks with restricted mineralogies dominated by mineral species resistant to weathering and erosional processes. Understanding that y = mx + c represents a linear relationship. Candidates should be aware of the range of texture in descriptive terms (as used on a grain size comparator): angularity – very angular to well rounded sphericity – high to low sphericity size – reference to the Wentworth scale sorting – very well to poorly sorted For exemplification of mathematical skills see Mathematical Guidance for AS Geology. The mathematical skills identified are not exclusive to this section of the specification.
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