HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Dumas, S. Articles by Southard, J. B. Search for Related Content GeoRef GeoRef Citation

Experiments on Oscillatory-Flow and Combined-Flow Bed Forms: Implications for Interpreting Parts of the Shallow-Marine Sedimentary Record

¹ Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, Ontario, K1N 6N5, Canada; present address: Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario, K7L 3N6, Canada; dumas{at}geol.queensu.ca
² Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, Ontario, K1N 6N5, Canada
³ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, U.S.A.

Analog laboratory experiments were conducted to investigate subaqueous bed forms generated under storm-like oscillatory and combined flow. Experiments were carried out in a large wave tunnel and used a range of sand sizes (fine and very fine), wave periods (10.5 and 8 s), oscillatory velocities (0 to 125 cm/s), and unidirectional velocities (0 to 25 cm/s).

At low unidirectional velocities (10 cm/s), addition of an increasing collinear oscillatory flow caused the bed to evolve from small-scale (wavelength < 20 cm), symmetric, anorbital ripples, to large-scale (wavelength > 100 cm), symmetric, orbital ripples, to plane bed. At higher unidirectional velocities (>10 cm/s), a similar trend was noted, but ripples were more asymmetric. Three phase diagrams are presented to summarize the observed relationships of bed configurations to flow conditions. These diagrams are intended to assist in the interpretation of shallow marine sedimentary environments where oscillatory and combined flow are thought to be omnipresent.

Distinctive features of small-scale asymmetric combined-flow ripples generated are: a 3D planform, round crest, and convex-up sigmoidal profile with local pronounced scour at the toe of the stoss side giving the ripple profile a "boxy" appearance. Similarly, large-scale asymmetric combined-flow ripples had broad and round crests, convex-up stoss sides, and "compressed profiles" due to scouring at the toe of the stoss side.

Hummocky bed forms were generated under moderate to high oscillatory velocities and low unidirectional velocities. Hummocks were not observed as a distinct bed state but rather appeared to mark transitions in bed-form scale and symmetry. Hummocks were more prevalent at longer oscillatory periods and in finer-grained sediment. Stratification produced by "synthetically" aggrading hummocky bed profiles closely resembles hummocky cross-stratification. With the introduction of only a small unidirectional-flow component, hummocks evolve into downstream-migrating large-scale asymmetric ripples, and the resultant cross-stratification becomes similar to that produced by unidirectional-flow dunes. Accordingly, these experiments suggest that much of the hummocky cross-stratification observed in the stratigraphic record is produced by storm-generated long-period oscillatory-dominant combined flows. Inasmuch as long-period, high-energy waves require deep, wide basins to form, hummocky cross-stratification may therefore serve as a useful indicator of deposition in unrestricted, open-water conditions.

This article has been cited by other articles:

				P. M. Myrow, C. Lukens, M. P. Lamb, K. Houck, and J. Strauss Dynamics of a Transgressive Prodeltaic System: Implications for Geography and Climate Within a Pennsylvanian Intracratonic Basin, Colorado, U.S.A. Journal of Sedimentary Research, August 1, 2008; 78(8): 512 - 528. [Abstract] [Full Text] [PDF]

				M. P. Lamb, P. M. Myrow, C. Lukens, K. Houck, and J. Strauss Deposits from Wave-Influenced Turbidity Currents: Pennsylvanian Minturn Formation, Colorado, U.S.A. Journal of Sedimentary Research, July 1, 2008; 78(7): 480 - 498. [Abstract] [Full Text] [PDF]

				S. Yoshida, R. J. Steel, and R. W. Dalrymple Changes in Depositional Processes--An Ingredient in a New Generation of Sequence-Stratigraphic Models Journal of Sedimentary Research, June 1, 2007; 77(6): 447 - 460. [Abstract] [Full Text] [PDF]

				S. Dumas and R.W.C. Arnott Origin of hummocky and swaley cross-stratification-- The controlling influence of unidirectional current strength and aggradation rate Geology, December 1, 2006; 34(12): 1073 - 1076. [Abstract] [Full Text] [PDF]

				P. M. Myrow, K. R. Thompson, N. C. Hughes, T. S. Paulsen, B. K. Sell, and S. K. Parcha Cambrian stratigraphy and depositional history of the northern Indian Himalaya, Spiti Valley, north-central India Geological Society of America Bulletin, March 1, 2006; 118(3-4): 491 - 510. [Abstract] [Full Text] [PDF]

				B. Yang, R. W. Dalrymple, and S. Chun The Significance of Hummocky Cross-Stratification (HCS) Wavelengths: Evidence from an Open-Coast Tidal Flat, South Korea Journal of Sedimentary Research, January 1, 2006; 76(1): 2 - 8. [Abstract] [Full Text] [PDF]