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WalesGeologyQuick questions
F2: Surface and Internal Processes
Quick questions on Sedimentary processes and environments - WJEC A-Level Geology
6short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What are the main sedimentary structures?Show answer
Bedding (stratification) is the layering produced by successive episodes of deposition, the most fundamental sedimentary structure, recording changes in supply or conditions over time.
What are using structures to reconstruct environments?Show answer
A geologist combines grain size, sorting, composition and structures to deduce the environment. Well-sorted, well-rounded, cross-bedded sandstone with no fossils suggests a desert dune field; fine, graded beds (turbidites) suggest a deep-sea fan; fossil-rich, symmetrically rippled limestone suggests a warm, shallow shelf sea.
What is devonian Old Red Sandstone?Show answer
Cross-bedded, red, desiccation-cracked sandstones across Wales and the Welsh Borders record ancient rivers and floodplains under an arid climate, an environment read straight from the structures. Turbidite sequences. Repeated graded beds in deep-water successions record turbidity currents sweeping sediment down the continental slope, each bed a single flow event. Tidal flat mudcracks. Polygonal mudcracks preserved in shales record repeated exposure and drying on a tidal flat, fixing both the environment and the way-up of the sequence.
What is q1?Show answer
State how cross-bedding indicates the direction of the depositing current. [1 mark]
What is q2?Show answer
A bed fines upwards from pebbles at the base to mud at the top. Name the structure and state the way-up. [2 marks]
What is q3?Show answer
What environment is suggested by desiccation cracks in a mudstone, and why? [2 marks]
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