Fining‐upwards cycles in alluvial successions

Abstract

Fining-upwards cycles on a scale of thickness from a few metres to a few tens of metres, and consisting of a coarse grade member (erosive base) overlain by a fine grade member, are the hall-mark of a distinct non-marine sedimentary facies widely distributed in space and time. Using data on modern alluvial sediments, it is shown that the interpretation of the cycles in terms of an alluvial environment is probably correct. The cyclicity itself cannot yet be accounted for, although three principal factors are likely to have been involved.

Depositional evolution of a progradational to aggradational, mixed-influenced deltaic succession: Jurassic Tofte and Ile formations, southern Halten Terrace, offshore Norway

“…The erosional base, poor sorting, upward decreasing grain size trend, primary sedimentary structures and absence of bioturbation are all consistent with fluvial channel deposition (Allen, 1965;Leeder, 1973). In places, the repeated interbedding of facies F3a and F3b may record multi-storey stacking of bars, consistent with deposition on rapidly migrating bars, possibly in braided rivers M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT (Miall, 1996;Hartley et al, 2016).…”

An outcrop‐based study of the economically significant Late Cretaceous Rakopi Formation, northwest Nelson, Taranaki Basin, New Zealand

“…Most probably the rivers were sinuous fluvial systems, characterised by the fining-upward motif, comparable to the classic fining-upward "meandering" channel model of allen (1965). However, similar fining-upward cycles have also been observed in relatively low-sinuosity "braided" fluvial systems (Allen 1965;leeder 1973;Miall 1992;Browne & Plint 1994), so we do not wish to be too prescriptive about the meandering v's braided nature of the Cretaceous rivers. Thick stacked sandstone packages, as observed in the Rakopi Formation, King & Thrasher 1996).…”

Depositional environments of the Prince Creek Formation along the east side of the Toolik River, Sagavanirktok Quadrangle, North Slope, Alaska

“…The FUS is commonly capped by a carbonaceous shale or coal. These fining-upward successions are interpreted to be the deposits of meandering streams, point/scroll bars, and levees (in the sense of Allen, 1965Allen, , 1970Elliott, 1976;Nanson, 1980). Sand-dominated fining-upward successions of the Prince Creek Formation along the Toolik River appear to be laterally continuous for hundreds of meters; however their true width is obscured by tundra cover.…”