TY - JOUR
T1 - Alluvial architecture of mid-channel fluvial–tidal barforms
T2 - The mesotidal Lower Columbia River, Oregon/Washington, USA
AU - Prokocki, Eric W.
AU - Best, James L.
AU - Ashworth, Philip J.
AU - Sambrook Smith, Gregory H.
AU - Nicholas, Andrew P.
AU - Parsons, Daniel R.
AU - Simpson, Christopher J.
N1 - Funding Information:
This research was funded primarily by ExxonMobil, but was also supported by UK Natural Environment Research Council (NERC) grant awards NE/H007954/1, NE/H006524/1, NE/H007261/1 and NE/H00582X/1. DRP also acknowledges funding received from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and innovation program (Grant Agreement 725955). We thank Mike Blum and Howard Feldman for their advice and insight during this research as well as the Clatsop Community College and Environmental Research and Training Station for providing space for field instrumentation, sediment core storage, and access to building equipment and tools. We also thank Kyungsik Choi, an anonymous reviewer, and Charlie Bristow, for their insightful remarks that strengthened the final version of this manuscript. A special thank you goes to Michael Wilkin, Katie Rathmell and António Baptista, for their invaluable advice and expertise regarding the Lower Columbia River. We also extend thanks to Steve Sandbach, Kyle Balling and Claire Keevil, for helping with data collection and, lastly, we thank Pat Killion (captain of the Tansey Point) whose many years of navigational experience along the Lower Columbia River made this research possible.
Funding Information:
This research was funded primarily by ExxonMobil, but was also supported by UK Natural Environment Research Council (NERC) grant awards NE/H007954/1, NE/H006524/1, NE/H007261/1 and NE/H00582X/1. DRP also acknowledges funding received from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and innovation program (Grant Agreement 725955). We thank Mike Blum and Howard Feldman for their advice and insight during this research as well as the Clatsop Community College and Environmental Research and Training Station for providing space for field instrumentation, sediment core storage, and access to building equipment and tools. We also thank Kyungsik Choi, an anonymous reviewer, and Charlie Bristow, for their insightful remarks that strengthened the final version of this manuscript. A special thank you goes to Michael Wilkin, Katie Rathmell and António Baptista, for their invaluable advice and expertise regarding the Lower Columbia River. We also extend thanks to Steve Sandbach, Kyle Balling and Claire Keevil, for helping with data collection and, lastly, we thank Pat Killion (captain of the ) whose many years of navigational experience along the Lower Columbia River made this research possible. Tansey Point
Publisher Copyright:
© 2020 The Authors. Sedimentology © 2020 International Association of Sedimentologists
PY - 2020/12
Y1 - 2020/12
N2 - Barforms of mesotidal to macrotidal fluvial–tidal transitions, regardless of fluvial-discharge, are currently thought to display a sedimentary architecture dominated by tidal signatures. Due to the scarcity of observations from modern mesotidal fluvial–tidal transitions, especially those of multi-channelled large-rivers (mean annual discharge ≥7000 m3 s−1 and peak discharges ≥15 000 m3 s−1) with mid-channel bars, this concept remains unproven. The present study analyses data produced by a combination of high-resolution ground penetrating radar and coupled shallow vibracores (<5 m depth), collected from modern fluvial–tidal mid-channel bars of the mesotidal multi-channelled Lower Columbia River, Washington/Oregon, USA, which can experience peak discharges ≥18 000 m3 s−1. These data were used alongside time-sequenced aerial imagery to characterize the spatio-temporal sedimentological evolution of these barforms in singular flows or combined flows consisting of river, tidal and/or wind-wave oscillatory, current components operating in unique fluvial–tidal transition regimes. Results indicate that ca 75% of the Lower Columbia River fluvial–tidal transition produces braid-bars with basal to bar-top sedimentological architectures that are indistinguishable from fluvial-only braid-bars recorded in the literature. Barform stratal characteristics within the fluvial–tidal transitions of mesotidal large-rivers are therefore more likely to be dominated by downstream-oriented currents. Furthermore, a new style of low-angle (<5°) inclined heterolithic stratification found in bar-top accretion-sets within upper-mixed tidal–fluvial regime braid-bars is observed. This common stratification is created by combined-flows characterized by intrabasinal wind-wave oscillatory-currents and bidirectional tidal-currents. This inclined heterolithic stratification marks the initial downstream fluvial–tidal crossover point from Lower Columbia River up-dip fully-fluvial braid-bar architectures, to those possessing bar-top facies produced by the hydraulic-sedimentation response of combined intrabasinal wind-wave and tidal influence. When preserved, this form of mid-channel bar inclined heterolithic stratification provides a unique sedimentological signature of multi-channelled fluvial–tidal transitions that possess an open-water lower basin with intrabasinal wind-waves.
AB - Barforms of mesotidal to macrotidal fluvial–tidal transitions, regardless of fluvial-discharge, are currently thought to display a sedimentary architecture dominated by tidal signatures. Due to the scarcity of observations from modern mesotidal fluvial–tidal transitions, especially those of multi-channelled large-rivers (mean annual discharge ≥7000 m3 s−1 and peak discharges ≥15 000 m3 s−1) with mid-channel bars, this concept remains unproven. The present study analyses data produced by a combination of high-resolution ground penetrating radar and coupled shallow vibracores (<5 m depth), collected from modern fluvial–tidal mid-channel bars of the mesotidal multi-channelled Lower Columbia River, Washington/Oregon, USA, which can experience peak discharges ≥18 000 m3 s−1. These data were used alongside time-sequenced aerial imagery to characterize the spatio-temporal sedimentological evolution of these barforms in singular flows or combined flows consisting of river, tidal and/or wind-wave oscillatory, current components operating in unique fluvial–tidal transition regimes. Results indicate that ca 75% of the Lower Columbia River fluvial–tidal transition produces braid-bars with basal to bar-top sedimentological architectures that are indistinguishable from fluvial-only braid-bars recorded in the literature. Barform stratal characteristics within the fluvial–tidal transitions of mesotidal large-rivers are therefore more likely to be dominated by downstream-oriented currents. Furthermore, a new style of low-angle (<5°) inclined heterolithic stratification found in bar-top accretion-sets within upper-mixed tidal–fluvial regime braid-bars is observed. This common stratification is created by combined-flows characterized by intrabasinal wind-wave oscillatory-currents and bidirectional tidal-currents. This inclined heterolithic stratification marks the initial downstream fluvial–tidal crossover point from Lower Columbia River up-dip fully-fluvial braid-bar architectures, to those possessing bar-top facies produced by the hydraulic-sedimentation response of combined intrabasinal wind-wave and tidal influence. When preserved, this form of mid-channel bar inclined heterolithic stratification provides a unique sedimentological signature of multi-channelled fluvial–tidal transitions that possess an open-water lower basin with intrabasinal wind-waves.
KW - Fluvial–tidal bars
KW - Lower Columbia River
KW - inclined heterolithic stratification
KW - intrabasinal wind-waves
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U2 - 10.1111/sed.12754
DO - 10.1111/sed.12754
M3 - Article
AN - SCOPUS:85088256192
SN - 0037-0746
VL - 67
SP - 3533
EP - 3566
JO - Sedimentology
JF - Sedimentology
IS - 7
ER -