lagerföljden

Lagerföljden (literally "layer sequence") is a central concept in Swedish geology describing a chronological succession of sedimentary beds deposited over an interval of time. A lagerföljd is bounded at its base and top by surfaces such as unconformities, marked lithological changes, or shifts in fossil content; within it, formations, members and beds are recognized to reflect different lithologies or depositional environments. The term emphasizes the vertical stacking of materials and their temporal continuity, rather than a fixed absolute duration.

Its study provides information about past environments and sea-level changes, as well as depositional rates. By examining lithology, sedimentary structures and fossil assemblages, geologists correlate lagerföljder across regions and reconstruct paleoenvironments. The vertical and lateral variations within a lagerföljd help in understanding how sediment supply and accommodation space evolved through time.

Modern practice uses lithostratigraphy, biostratigraphy, and chemostratigraphy, and increasingly sequence stratigraphy, which focuses on sequence boundaries and systems tracts to interpret relative changes in accommodation and sediment supply. Where possible, radiometric dating yields absolute ages to constrain the timing of deposition.

Lagerföljden is the basis for bedrock mapping, regional geological history, and resource exploration, helping to relate rocks across distances and to understand basin development and tectonics. While the exact usage can vary regionally, the concept remains a foundational tool for describing and interpreting the sedimentary record in Sweden and the Nordic countries.