The large‐scale dynamics of grain‐size variation in alluvial basins, 1: Theory

Basin Research - Tập 4 Số 2 - Trang 73-90 - 1992
Chris Paola1, Paul L. Heller2, Charles L. Angevine2
1Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455
2Department of Geology & Geophysics, University of Wyoming, Laramie, WY 82071, USA

Tóm tắt

ABSTRACTWe study the interplay of various factors causing vertical grain‐size changes in alluvial basins using a simple coupled model for sediment transport and downstream partitioning of grain sizes. The sediment‐transport model is based on the linear diffusion equation; by deriving this from first principles we show that the main controls on the diffusivity are water discharge and stream type (braided or single‐thread). The grain‐size partitioning model is based on the assumption that the deposit is dominated by gravel until all gravel in transport has been exhausted, at which point deposition of the finer fractions begins.We then examine the response of an alluvial basin to sinusoidal variation in each of four basic governing variables: input sediment flux, subsidence rate, supplied gravel fraction, and diffusivity (controlled mainly by water flux). We find that, except in the case of variable gravel fraction, the form of the basin response depends strongly on the time‐scale over which the variation occurs. There is a natural time‐scale for any basin, which we call the ‘equilibrium time’, defined as the square of basin length divided by the diffusivity. We define ‘slow’ variations in imposed independent variables as those whose period is long compared with the equilibrium time. We find that slow variation in subsidence produces smoothly cyclic gravel‐front migration, with progradation during times of low sedimentation rate, while slow variation in sediment flux produces gravel progradation during times of high sedimentation rate. Slow variation in diffusivity produces no effect. Conversely, we define ‘rapid’ variations as those whose period is short compared with the equilibrium time. Our model results suggest that basins respond strongly to rapid variation in either sediment flux or diffusivity; in both cases, deep proximal unconformities are associated with abrupt gravel progradation. This progradation occurs during times of either low sediment flux or high diffusivity. On the other hand, basin response to variation in subsidence rate gradually diminishes as the time scale becomes short relative to the equilibrium time. Each of the four variables we have considered ‐ input sediment flux, subsidence, gravel fraction, and diffusivity ‐ is associated with a characteristic response pattern. In addition, the time scale of imposed variations relative to the equilibrium time acts in its own right as a fundamental control on the form of the basin response.

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Tài liệu tham khảo

Abbott P. L., 1978, Effects of abrasion durability on conglomerate clast populations: examples from Cretaceous and Eocene conglomerates of the San Diego area, California, J. sedim. Petrol., 48, 31

Adachi S.&Nakatoh T.(1969)Changes to top‐set‐bed in a silted reservoir.Int. Ass. Hydro. Res. 13th Congr. pp.269–271.

10.1016/0098-3004(87)90011-2

10.1002/esp.3290060106

10.1130/0091-7613(1988)016<0517:DOTCIR>2.3.CO;2

10.1130/0016-7606(1970)81[61:EOWOAO]2.0.CO;2

10.1002/esp.3290100607

Brownlie W. R.(1981)Prediction of Flow Depth and Sediment Discharge in Open Channels.California Institute of Technology W. M. Keck Laboratory Report No. KH‐R‐43A 232pp.

10.1111/j.1365-3091.1994.tb01400.x

10.1007/978-1-4612-3788-4_17

Cross T. A., 1990, Quantitative Dynamic Stratigraphy, 3

10.1007/978-1-4612-3788-4_1

10.1029/JB094iB04p03851

Garde R. J. Raju Ranga K. G.&Mehta P. J.(1981)Bed level variation in aggrading alluvial streams. Int. Assoc. Hydr. Res. Congress New Delhi pp.247–253.

10.1080/00221688309499458

10.1130/0091-7613(1988)016<0501:TPSMOF>2.3.CO;2

10.1111/j.1365-2117.1992.tb00146.x

10.1130/0016-7606(1992)104<0140:IPOPSF>2.3.CO;2

Jain S. C., 1981, River bed aggradation due to overloading, J. Hydraul. Div. Am. Soc. Civ. Engrs., 107, 120

10.1061/(ASCE)0733-9429(1984)110:8(1072)

Jordan T. E., 1990, Quantitative Dynamic Stratigraphy, 149

Jordan T. E., 1988, New Perspectives in Basin Analysis, 307, 10.1007/978-1-4612-3788-4_16

10.1130/0016-7606(1985)96<1457:MOADPB>2.0.CO;2

10.1086/624985

10.1086/626370

10.1038/316138a0

Lindsay E. H., 1990, Geologic Excursions through the Sonoran Desert Region, Arizona and Sonora, 9

Meyer‐Peter E.&Müller R.(1948)Formulas for bed‐load transport.2nd Mtg Int. Ass. Hydraulic Structures Research Stockholm pp.39–64.

10.1016/0264-3707(85)90026-2

10.1007/978-1-4612-3788-4_11

Paola C., 1990, Quantitative Dynamic Stratigraphy, 363

10.1029/89EO00290

10.1017/S0022112078002505

10.1061/(ASCE)0733-9429(1991)117:2(131)

10.1061/(ASCE)0733-9429(1991)117:2(150)

Parker G., 1991, Some random notes on grain sorting, I. A. H. R. Grain Sorting Seminar, Ascona, Italy

10.1086/625559

Press W. H., 1986, Numerical Recipes, 795

10.1080/00221688509499355

Rust B. R., 1984, Coarse alluvial deposits, Geosci. Canada, 1, 53

10.1130/0091-7613(1973)1<37:AIPAMF>2.0.CO;2

Shaw J., 1982, The Composition of Recent Alluvial Gravels in Alberta River Beds. Bull. Alberta Res. Council, 41, 151

10.1306/212F9142-2B24-11D7-8648000102C1865D

10.1029/WR017i001p00033

10.1061/(ASCE)0733-9429(1987)113:3(353)

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Basin Research

Tập 4 Số 2

73-90

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