Palaeontology and Stratigraphy
What the exam tests
Palaeontology and Stratigraphy covers fossil preservation, index fossils, the geological time scale and the principles used to order and correlate rock sequences, including Kerala's Tertiary plant and invertebrate fossils.
Core rules
- Preservation modes: permineralisation, replacement, mould and cast, carbonisation, preservation in amber or tar, and trace fossils.
- Index fossils are short-ranging, wide-spread and abundant; graptolites, ammonoids and trilobites are classic examples.
- Principles: superposition, original horizontality, lateral continuity, cross-cutting relationships, inclusions and faunal succession.
- Eras: Palaeozoic, Mesozoic, Cenozoic. Glossopteris marks the Permian Gondwana flora; Deccan Trap volcanism and the K–Pg boundary lie near the end of the Cretaceous; Warkalli and Quilon beds are Tertiary.
Worked example
A sandstone contains Glossopteris leaves and rests on an eroded granite surface. Reasoning: Glossopteris is a Gondwana flora, so the bed is Permian. The granite must be older than the sandstone, and the erosion surface between sedimentary cover and igneous basement is a non-conformity.
Traps
Giving a period name without saying which era it belongs to. Treating a mould and a cast as the same thing. Invoking radiocarbon dating for Cretaceous or older material; radiocarbon is limited to a few tens of thousands of years. Forgetting that superposition applies only to undisturbed sequences.