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Geological structures and deformation

4 dot points across 4 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do dip and strike describe the orientation of a tilted bed?

Dip is the angle a bed makes with the horizontal, measured in the direction of steepest slope; strike is the compass direction of a horizontal line on the bed, at right angles to the dip; dip and strike are measured with a compass-clinometer and recorded with the dip and strike symbol on geological maps, and the apparent dip seen in a cross-section can differ from the true dip.
A focused answer to the Eduqas GCSE Geology statement on dip and strike. Covers the definitions of dip (angle of steepest slope from horizontal) and strike (horizontal direction at right angles to dip), how they are measured and shown by the map symbol, the link to outcrop width, and how apparent dip differs from true dip.
13 min answer →

How do compression and tension produce folds and faults in rocks?

Rocks deform when stressed: compression produces folds (anticlines arch upwards, synclines sag downwards) and reverse faults, while tension produces normal faults; the type and orientation of folds and faults are evidence of the direction of past Earth movements and are shown on geological maps and cross-sections.
A focused answer to the Eduqas GCSE Geology statement on folds and faults. Covers how compression produces folds (anticlines and synclines) and reverse faults, how tension produces normal faults, the parts of a fold and fault, and how these structures record the direction of past Earth movements.
13 min answer →

What gap in time does an unconformity record?

Joints are fractures with no movement, formed by cooling, drying or pressure release; an unconformity is a buried erosion surface separating older rocks below from younger rocks above, recording a gap in time during which deposition stopped and erosion occurred; unconformities and joints are interpreted from cross-sections to reconstruct geological history.
A focused answer to the Eduqas GCSE Geology statement on joints and unconformities. Covers how joints form (cooling, drying, pressure release) with no movement, what an unconformity is and the sequence of events it records (deposition, uplift, erosion, renewed deposition), and how to read these from cross-sections.
13 min answer →

How do you work out the order of geological events from a cross-section?

Geological history is reconstructed from a cross-section using the principles of superposition (younger beds lie above older), original horizontality, cross-cutting relationships (a fault or intrusion is younger than the rocks it cuts) and included fragments; the order of deposition, deformation, intrusion, erosion (unconformities) and faulting is deduced to give a relative sequence of events.
A focused answer to the Eduqas GCSE Geology statement on reading cross-sections. Covers the principles of superposition, original horizontality, cross-cutting relationships and included fragments, and how to combine them to deduce the relative order of deposition, intrusion, deformation, erosion and faulting in an area.
13 min answer →