finingupwards

Finingupwards, or a fining-upward sequence, is a sedimentary pattern in which grain size decreases from the bottom to the top of a bed or succession. The term describes the systematic shift from coarser sediments (such as gravel and sand) at the base to progressively finer sediments (such as silt and clay) higher in the sequence.

The feature forms whenever the energy of the transporting medium declines with time or distance. As currents slow, larger particles settle first, followed by progressively finer material carried in suspension. In some settings the fining-upward tendency can be produced by waning flow after a flood, by sediment gravity flows that lose energy, or by progradation of deposition away from a sediment source.

Fining-upward sequences occur in a variety of environments. In fluvial systems, channel-fill deposits often show upward-fining layers as energy decreases during waning flow. In marine settings, turbidity currents can produce graded, upward-fining beds. Deltaic and alluvial-fan deposits may also display fining-upward trends as sediment supply and flow conditions evolve. Lacustrine (lake) deposits and slope environments can exhibit similar patterns under changing transport conditions.

In stratigraphy, fining-upward sequences are usually identified by graded bedding, where grain size and sometimes percentage of fines increase upward within a bed. They serve as indicators of past energy regimes and help interpret depositional environments, paleocurrent directions, and time progression within a succession. The term is often contrasted with coarsening-upward sequences, which show the opposite grain-size trend.