Rocks and minerals: Sedimentary rocks 2.1.3
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|(a)||weathering and erosion, the mechanical chemical and biological processes that produce the sediment that form sedimentary rocks
||To include the formation of:
|(b)||the effect of the process of erosion on the characteristics composition of modern sediments
||To include transport processes, Hjulström curve, length of transport and the concept of maturity
|(c)||the diagnostic properties of rocks to recognise and measure grain sizes in samples, photographs and thin section diagrams
To include the phi scale (at AS, qualitative only).
Recall of Folk and Ward formulae is not required.
|(d)||(i) the classification of siliclastic rocks on the basis of their diagnostic properties (colour, composition, grain
size and grain shape, sorting)
(ii) the classification of carbonate rocks on the basis of their diagnostic properties (grain size, cement, mineral composition and fossil content, and sorting)
(iii) the diagnostic properties of rocks to identify siliclastic and carbonate rocks in samples, photographs and thin section diagrams
To include orthoquartzite, arkose, greywacke
To include the Dunham scheme (mudstone, wackestone, packstone, grainstone)
|(e)||the processes of diagenesis and lithification:
(i) mechanical compaction
(ii) chemical compaction by pressure dissolution and recrystalisation
(iii) growth of cements
(iv) how these changes in texture modify the porosity and permeability of rocks
To include the effects of diagenisis on siliclastic and carbonate grains, organic material and mud
To include silica, calcite, hematite and clay minerals
A selection of sedimentary rocks are presented one at a time in a ‘circus’. The students have each sample for two minutes in which time they record details of the specimen and give it a name.
Once familiar with the speed dating with rocks concept it can be used as a fun starter exercise whenever familiarity with rocks is important to the delivery of a topic or as revision.
University of Oxford’s Earth Science Department image store. Allows students to examine photographs of a variety of granular (and crystalline) rocks: as hand specimens, thin sections, field exposures and a virtual fieldtrip (to northwest Scotland).
‘Rocks in hand specimen’ takes you to a set of sedimentary, igneous and metamorphic rock pictures. An enlarged view comes with a short description of the rock.'Rocks of NW Scotland’ then ‘rock index’ opens and rocks can be viewed by outcrop, hand specimen and thin sections.
This topic considers the story of the sedimentary rock, learners will begin by looking at how the sediment is made, looking at the range of weathering processes and how the erosion of sediment will determine the grains produced. Learners will then think about how observations can be made of sedimentary rocks and how they can be recorded, the link between the energy in the setting and the grain size of the rock is important. Learners are introduced to the range of siliciclastic and carbonate rocks that can form and the frameworks that exist to classify them. Finally, learners think about the steps between sediment being deposited and then going on to be lithified.
Common misconceptions or difficulties students may have:
Areas here which learners are likely to find most challenging include the range of examples of sedimentary rocks which they need to recall the key characteristics of, this may be daunting to begin with, to build familiarity learners should have experience of hand specimens and photographs and thin sections and experience recording their own observations. The section on lithification and diagenesis may also be challenging as learners may struggle to visualise some of the processes, here the use of modelling activities and video clips is likely to support.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course:
The basic understanding of sedimentary processes is a theme that is revisited throughout the course some areas with it as a particular focus are sedimentary environments in time 4.1, applied sedimentology 5.1 and fluids and geological processes 5.2.
The topic could begin with a detailed look at the products and processes involved in each type of weathering looking in particular into how each type of sediment comes about. Learners could consider a range of videos here or model weathering processes in the lab. Following this learners could carry out a scientific investigation into sediment, they could sieve sediment and carry out statistical analysis on their data, during the analysis of results learners could use the hjulstrom curve to infer past energy levels.
A wide range of hand specimens of sedimentary rocks could be provided for learners to investigate similarities and differences with an attempt to infer environment of deposition from their observations. Once learners have some experience of the range that exists they could start to build up the classification system of siliciclastic and carbonate rocks and link these to the hand specimens, photographs and thin sections they have seen.
Lithification and diagenesis could be introduced using a range of video clips and scientific modelling to help learners visualise each stage, learners may consider how diagenesis would look in different sedimentary environments.
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