Sedimentary environments in time: Surface processes and products 4.1.2
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|(a)||(i) how the characteristics of the facies in a sedimentary environment are related to the methods of sediment transport
(ii) the diagnostic sedimentary structures produced by the sediment transport processes
(iii) the recognition, application and sketching of the diagnostic properties of sedimentary structures to interpret way-up and sedimentary environments, in the field and on photographs
|To include the characteristics of sediments transported by wind, glaciers, rivers and in shallow marine environments.
To include: cross-bedding, ripple marks, graded bedding, desiccation cracks, salt pseudomorphs and imbricate structure.
||the construction and interpretation of graphic logs of modern sediment sequences and ancient sedimentary rock
||To include fossil assemblages, sedimentary structures and directional data.
||deposition in fluvial environments which produces a characteristic three-dimensional architecture due to lateral migration
||To include: meandering rivers, braided rivers and alluvial fans (channel sandstones, flood plain clays and silts, breccias, and conglomerates).
||deposition in hot desert environments which are controlled by gradual aeolian processes and episodic high energy events
||To include wadis, dunes and playa lakes (aeolian sandstones, evaporites).
||deposition in shallow siliciclastic seas which produces characteristic offshore transitions from beach deposits, current reworked sand sheets to muds, below the wave base|
||deposition in shallow carbonate seas which produces characteristic limestones within, on and outside the reef (reef limestone, bioclastic limestone and oolitic limestones)
||deposition in deep water carbonate seas above the carbonate compensation depth.
||To include chalk, micritic limestones and a qualitative understanding of chert/flint formation in siliciclastic starved seas and continental slopes.|
Unit 4.1.2 contains a large amount of terminology which is used to identify and describe sedimentary structures and different environments, to support understanding here a wide range of visual aids could be used, lots of rock samples, modelling environments, field work, photographs. Learners will find that graphing skills from GCSE can be put to good use when constructing and interpreting sedimentary logs. Learners can investigate modern settings where sedimentary structures form for example desiccation cracks on lake beds or graded bedding and compare how these features appear when preserved.
Common misconceptions or difficulties students may have:
Challenges may include learners finding it difficult to move on from simplistic descriptions of environments which they may have used before and being able to add the sophisticated terms required for this level, perhaps a comparison between what they originally knew about shallow carbonate seas or reefs compared to what they know after will highlight this. Towards the end of the topic learners can be challenged with being provided with some pieces of evidence from a sedimentary environment which they must use to reconstruct the setting.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course:
A key link to later in the specification is to topic 7.1.1 the changing Earth where learners use their knowledge of paleoenvironments and can suggest the long-term changes that have occurred and how they are recorded in palaeontological and lithological evidence. Learners also consider how the pace of changes they observe in the rock record relates to changes happening due to the global impact of human activity.
Techniques for describing sedimentary compositions and how grains fit together could be introduced using some of the many practical activities suggested by ‘Mike Tuke’ in the link below. The computer programme to aid the drawing of graphic logs could give learners experience of how geologists working in this field may record and present their observations.
Surface processes and products could be introduced in a fairly general way to focus on appropriate use of terminology, this could be followed by case studies of each type of depositional environment when the terminology can be reinforced, learning could be supported by access to a range of evidence, rock samples, photographs, videos, maps, cross-sections. The virtual fieldtrips and reconstructions may help learners to understand the variety of rock types that can form in carbonate settings and how to link this variety to the processes in which they formed. The field trip to the Osmington oolite contains excellent photographs of the rock samples and clearly shows the variety that exists, a training opportunity for drawing and interpreting these rock types could be available here.
Learners can download the sed log programme, this allows graphic log data collected in the field to be converted into a computer file. There is a you tube tutorial link provided.
A selection of example logs of glacial, sabkah, river, littoral, dessert that can be used with SedLog to support teaching is attached.
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