Horizontal lamination and the sequence of bed phases and stratification under upper‐flow‐regime conditions

Abstract

Two forms of horizontal laminae have been produced under upper‐flow‐regime conditions in a flume by deposition on a plane bed and on low in‐phase waves. Upper plane bed laminae consist of approximately equal numbers of fining‐upward (FU) and coarsening‐upward (CU) textural laminae; heavy minerals, when present, are typically within or form CU laminae. In horizontal laminae formed under low in‐phase waves, FU laminae may predominate and are significantly thicker than CU laminae; heavy minerals are associated with the tops of some FU laminae and are absent from CU laminae. Deposits aggraded on plane beds and low in‐phase waves both display low‐angle (13–14°) upstream grain imbrication. Upper plane‐bed horizontal laminae are attributed to the effects of the burst/sweep cycle on local bedload transport (bursts form FU laminae and sweeps form CU laminae). Some FU laminae in in‐phase wave deposits are thought to form with downstream migration of bed waves on which sand size decreases from trough to crest. Heavy minerals are concentrated in the tops of these FU laminae due to their enrichment on the crests of the migrating bed waves. Other FU and CU laminae in in‐phase wave deposits probably formed by the action of bursts and sweeps, as on Upper plane beds. A sequence of bed phases and stratification formed under upper‐flow‐regime conditions is described based on the observations here combined with descriptions from the literature. With increasing flow strength the gradual sequence of bed phases is: (1) plane bed, (2) low relief, downstream‐migrating inphase waves increasing in amplitude and wavelength with increasing flow strength, (3) stationary in‐phase waves, (4) upstream‐migrating (including breaking wave) antidunes. The sequence of stratification formed under these bed phases is: (1) upper plane bed horizontal lamination, (2) in‐phase wave horizontal lamination to in‐phase wave foreset cross‐laminae, (3) in‐phase wave drape laminae, (4) antidune backset cross‐laminae.

Upper flow regime sheets, lenses and scour fills: Extending the range of architectural elements for fluvial sediment bodies

“…These structures are considered distinct from the "symmetrical dunes" formed experimentally by Saunderson and Lockett (1983) and from the very small-scale bed waves found by Bridge and Best (1988), among others. They may, however, be analogous to the "in-phase wave horizontal lamination with in-phase wave foreset cross-laminae" noted in flume experiments by Cheel (1990) at flow strengths transitional into the antidune bedform stability field. Associations of structures such as this have also been produced experimentally at a small scale by Alexander et al (2001) under upper flow regime conditions.…”

“…This is particularly so for structures that preserve an associated parting lineation or "primary current lineation" (Figure 2), thought to be the result of microvortices acting under high stream powers to sort and deposit sand grains (Allen, 1982). More recently, experimental data have allowed Bridge and Best (1988), Paola et al (1989), Cheel (1990), and Best and Bridge (1992) to propose that plane bedding is formed by the migration of low-amplitude bed waves across a flat surface. Evidence for such a process is typically preserved only at the lamina scale as small-scale textural variations and low-angle discordant surfaces.…”

Sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications: an example from Anglesey, north Wales, UK

“…Development and preservation of large-scale sinusoidal bedforms Large-scale sinusoidal bedforms with stoss-and lee-side preservation, including those described here, have been produced experimentally (Cheel, 1990) and recognised only rarely within the geological record (Fielding, 2006;Ito & Saito, 2006;Ito, 2010). Within a glacigenic context this includes subglacial drainage channels (Fisher et al, 2003) and outburst floods (jökulhlaups) debouching either subaerially (Duller et al, 2008) or onto subaqueous ice-contact fans (Lang & Winsemann, 2013).…”

“…Within a glacigenic context this includes subglacial drainage channels (Fisher et al, 2003) and outburst floods (jökulhlaups) debouching either subaerially (Duller et al, 2008) or onto subaqueous ice-contact fans (Lang & Winsemann, 2013). They have commonly been attributed to rapidly-aggrading stationary antidunes (Lang & Winsemann, 2010) that are supercritically climbing due to massive rates of sediment deposition under transitional dune to upper flow regimes (Cheel, 1990;Fielding, 2006).…”

“…This is because of the critical role subglacial meltwater plays in regulating the dynamics of ice masses, ice-marginal behaviour and associated hydrogeological systems within subglacial, marginal and proglacial areas (Boulton & Hindmarsh, 1987;Piotrowski et al, 2004Piotrowski et al, , 2006Evans & Hiemstra, 2005;Evans et al, 2006;Robinson et al, 2007;Boulton et al, 2009;Bartholomew et al, 2010). Put simply, subglacial meltwater deposits are the product of a hydrological regime that is not unique to subglacial environments, with similar regimes documented from a range of other sedimentary environments including intertidal (Cheel & Middleton, 1986), fluvial (Cheel, 1990, Røe, 1987Alexander et al, 2001) and channelised turbidity currents (Ito & Saito, 2006). Upper plane bed flow regimes have also been recognised within glacial meltwater systems including subglacial (this study ;Brennand, 1994;Fisher et al, 2003), englacial (Delaney, 2001(Delaney, , 2002 proglacial (Duller et al, 2008) and subaqueous ice-contact environments (Russell & Arnott, 2003;Hornung et al, 2007;Lang & Winsemann, 2013).…”