AS91189 Earth and Space Science 2.3 - Geological Processes in a New Zealand Locality
What this standard tests
AS91189 assesses an investigation of geological processes in a New Zealand locality. You interpret evidence such as rock type, structure, landform and sequence, and link it to processes operating at a particular place and scale.
Core rules and concepts
- New Zealand sits on the Pacific–Australian plate boundary. Relevant processes include subduction (Hikurangi margin), transform faulting (Alpine Fault), volcanism (Taupō Volcanic Zone), uplift, erosion, transport and deposition.
- A landform is evidence, not the process itself. Name the process and explain how it produced the feature.
- Use geological sequence rules: superposition (older below younger), cross-cutting relationships (a fault or intrusion is younger than what it cuts), and unconformities (a gap in time).
- Scale and rate matter: a fault scarp may form in seconds, a river terrace over thousands of years, and greywacke uplift over millions.
Worked example
A locality shows greywacke basement, a fault scarp, and river gravels above the scarp. Greywacke is a hardened Mesozoic marine sedimentary rock, so it records deposition, burial and deformation. The scarp indicates recent displacement on an active fault. The gravels suggest river deposition after faulting, unless the gravels themselves are offset - in which case the fault moved after deposition. A defensible sequence is: greywacke deposition → uplift and faulting → erosion → gravel deposition. The reasoning uses rock type, cross-cutting relationships and superposition, and it states what evidence would test the alternative order.
Traps that cost marks
- Naming a landform without naming the process that formed it.
- Confusing erosion with deposition, or transport with both.
- Ignoring geological time and comparing processes at incompatible scales.
- Assuming every NZ fault is the plate boundary itself.
- Presenting an interpretation as fact without citing the evidence.