File:Fluvial deposits (Holocene; Roaring Run, Warren County, Ohio, USA) 1 (43690687410).jpg

Fluvial deposits are sedimentary layers laid down in fluvial systems - rivers and streams. In the channel facies, deposits are usually poorly sorted and cross-bedded. In the ancient rock record, channel deposits are typically sandstones and conglomerates. In the floodplain facies, deposits are usually fine-grained - in other words, mud. With burial and lithification, floodplain deposits become horizontally layered shales, maybe with mudcracks and occasional plant fossils, representing growth between flood events.

Seen here is a Holocene fluvial deposit alongside a modern stream channel in southwestern Ohio. The local bedrock is the famous Cincinnatian Series of the tristate area of Ohio-Kentucky-Indiana. Rocks in the Cincinnatian were deposited in relatively shallow marine facies during the Late Ordovician. The Cincinnatian succession is mostly interbedded fossiliferous limestones and shales. Most of the limestones are event beds (= tempestites), deposited during ancient storms.

This fluvial deposit is dominated by platy limestone slabs. Notice that many slabs are tilted slightly downward to the right (= upstream direction of the creek). Platy rocks in fluvial gravel deposits often attain this orientation - it's called "imbrication". Imbricated clasts in modern and ancient deposits are excellent indicators of flow direction.