Lateral continuity and correlation
Matching layers across a valley, and where a layer ends.
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What you see
A river cuts a valley through a pile of layers. Dashed lines join the same layer on the two walls: the layers were once continuous sheets. On the right, one sandstone thins and disappears: the limit of a layer.
Key ideas
- Lateral continuity: layers extend sideways in all directions until they thin out or meet the edge of their basin.
- Correlation matches rock units between outcrops, wells or sections using rock type, fossils, sequence and logs.
- Layers end by pinching out or by changing gradually into another facies, for example sand passing into mud offshore.
Test yourself
1. The same limestone appears on both sides of a valley at the same height. What is the best explanation?
By lateral continuity, matching layers on both walls were one sheet before erosion removed the middle.
2. What is a pinch-out?
A layer that thins to nothing marks the edge of the area where that sediment was deposited.
3. Which tool helps correlate layers between wells that cannot be seen?
Gamma-ray, resistivity and other logs give each layer a signature that can be matched from well to well.
References
- Steno, N. (1669). De solido intra solidum naturaliter contento dissertationis prodromus. Florence.
- Boggs, S. (2012). Principles of Sedimentology and Stratigraphy, 5th ed. Pearson.
- Catuneanu, O. (2006). Principles of Sequence Stratigraphy. Elsevier.