Fining Upward vs Coarsening Upward Sequence
Fining Upward
It is generally found in River point bars and Sand deposited by a turbidity flow, where there is less disturbance and more settling time. In basins, the larger (denser) grains settle first and gradually the smaller grains and finally sand, silt and clay settle to form the fining upwards sequence.
In a non-marine setting, fining upward is predominant within meandering or tidal channel deposits with an upward decrease in fluid velocity within a channel (coarser sediments at base of channel).
In a shallow-marine setting, this trend usually reflects an upward deepening and a decrease in depositional energy (shoreline retreat). In deep-marine settings, this trend reflects waning of submarine fans (reducing of sand contents).
Coarsening Upward
In coarsening upwards sequence, the grain size gradually increases towards the top (a gradual upward decrease in gamma response). This trend usually implies an increase in depositional energy.
In shallow marine settings, this trend reflects a change from shale-rich into sand-rich lithology and upward increase in depositional energy with shallowing-upward and coarsening.
In deep marine settings, this trend reflects an increase in the sand contents of turbidite bodies. This trend also may indicate gradual change from clastic to carbonate deposition.
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