Mechanics of Sediment Movement

Middleton, Gerard V.; Southard, John B.

doi:10.2110/scn.84.03

Cited by 408 publications

(305 citation statements)

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“…In experiments where quartzite cobbles were exposed to repeated heating/ dowsing episodes, the cobbles could be reused for long periods before they exhibited noticeable color changes and jagged breaks (McDowell-Loudan (1983:26). These results are supported by stone boiling experiments conducted by Thoms (1984( , cited in Thoms 1986.…”

Section: Comparison To Regional Patternssupporting

confidence: 60%

Cuatro Vientos: A Reconsideration of Seven Prehistoric Sites in the Lower Rio Grande Plains of South Texas

Carpenter¹,

Chavez²,

Miller³

et al. 2010

ITA

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IntroductIonWith this report, Texas Department of Transportation (TxDOT) begins a reconsideration of approaches to the evaluation and treatment of those areas where surface lithic scatters are the main constituent of the archeological record. The reconsideration was inspired by the Cuatro Vientos project in Laredo, Webb County, Texas. The project and the ideas surrounding it developed slowly. The ideas continued to evolve through discussion between SWCA Environmental Consultants (SWCA) and TxDOT as additional work on the project occurred. Because this project proceeded in an idiosyncratic fashion, some words of explanation might be helpful. The following discussion provides an account of how the project developed and where future work might be heading. PrevIous work at cuatro vIentosBlanton and Associates (Blanton) conducted the initial survey of the project's area of potential effects (Ringstaff et al. 2004). The survey identified 14 sites. The Blanton survey report showed the local archeological record to predominantly be a messy landscape of mixed assemblages. Within this landscape were some pockets with potentially-preserved, isolable components and features. The Blanton survey report thus recommended eight of the 14 sites for additional evaluation. TxDOT, in consultation with the Texas Historical Commission, accepted those recommendations.TxDOT then tasked SWCA with developing a scope for the fieldwork under one of TxDOT's general archeological services contracts. SWCA's approach concentrated on the identification of those select areas that had a high level of integrity, with horizontal and/or vertical separation of assemblages and components (Carpenter, Houk, and Miller 2005). This integrity-focused approach has been explicitly advocated by TxDOT in the past and continues to inform TxDOT's evaluations of the effects of its projects. IntegrIty and the evaluatIon oF south texas sItesThe integrity-focused approach can perhaps be refined, however. Two issues must be addressed. On the one hand, the archeological record of south Texas and its upland lithic scatters is not amenable to many interpretive strategies. The data from the uplands are typically of poor quality. In many places, the ground surface has remained stable or has eroded. Preservation of many types of material is poor. The same general areas have seen repeated occupation. This combination of factors has produced an archeological record that can be difficult to render meaningful. Many aspects of past human behavior and adaptations can not be inferred under these circumstances. On the other hand, the activities that occurred in these areas may have played a significant role in local adaptations. We should not be willing to treat such a large portion of the archeological record as a black box, where significant activities remain unidentified. To ignore the uplands makes an appreciation of the valley settings more difficult, since data would not be available from the upland areas for comparative analysis. Refining current approaches means splitting ...

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Section: Comparison To Regional Patternssupporting

confidence: 60%

Cuatro Vientos: A Reconsideration of Seven Prehistoric Sites in the Lower Rio Grande Plains of South Texas

Carpenter¹,

Chavez²,

Miller³

et al. 2010

ITA

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“…This trend is predicted by the simplest steady state model for particle resuspension, in which turbulent diffusion equals settling [Rouse, 1937]. While this model has several limitations, experimental and observational evidence support it [Middleton and Southard, 1984]. Coulter counter, thus establishing the link for oceanic particles between the shape of the attenuation and the shape of the size distribution.…”

Section: Introductionmentioning

confidence: 87%

Spectral particulate attenuation and particle size distribution in the bottom boundary layer of a continental shelf

Boss¹,

Pegau²,

Gardner³

et al. 2001

J. Geophys. Res.

141

121

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Abstract. Spectral attenuation and absorption coefficients of particulate matter and colocated hydrographic measurements were obtained in the Mid-Atlantic Bight during the fall of 1996 and the spring of 1997 as part of the Coastal Mixing and Optics experiment. Within the bottom boundary layer (BBL) the magnitude of the beam attenuation decreased and its spectral shape became steeper with distance from the bottom. Concurrently, the slope of the particulate size distribution (PSD) was found to increase with distance from the bottom. Changes in the PSD shape and the magnitude of the beam attenuation as functions of distance from the bottom in the BBL are consistent with particle resuspension and settling in the BBL, two processes that are dependent on particle size and density. For particles of similar density, resuspension and settling would result in a flattening of the PSD and an increase in the beam attenuation toward the bottom. In both fall and spring the magnitude of the particle attenuation coefficient correlates with its spectral shape, with a flatter shape associated with higher values of the attenuation. This observation is consistent with idealized optical theory for polydispersed nonabsorbing spheres. According to this theory, changes in the steepness of the particle size distribution (particle concentration as a function of size) will be associated with changes in the steepness of the attenuation spectra as a function of wavelength; a flatter particle size distribution will be associated with a flatter attenuation spectrum. In addition, the observed ranges of the beam attenuation spectral slope and the PSD exponent are found to be consistent with this theory.

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“…Allen 1984). Although the dynamics of bedforms created by water flow over cohesionless sand grains are moderately well understood (Middleton and Southard 1984;Allen 1984) the dynamics of bedforms created by water flow over cohesive sediments are not.…”

Section: Acknowledgmentsmentioning

confidence: 99%

Sedimentary furrows and organized flow structure: A study in Lake Superior

et al. 1992

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Investigations of the geology and physical limnology of a field of sedimentary furrows in Lake Superior have provided information on the characteristics of these bedforms and their relationship to the wind-driven currents and associated turbulence structures in the bottom boundary layer. The results generally support the existing conceptual model for furrow formation. Furrows in the study area (2 km2) at 100-m depth are spaced 20-l 00 m apart and exceed 800 m long, the troughs being -0.5 m deep and 3-5 m wide. Sediment cores collected by submersible are poorly sorted, cohesive, terrigenous silts with a mean grain size of 20 pm. Relative to sediments in the interfurrow area, those in the trough contain higher fractions of sand and coarse debris and accumulate at a rate 15% slower. Strong bottom currents (speed > 6 cm s-l) usually flow within 20" of the furrow direction and are most frequent between late October and early February, when wind-forced currents reach the bottom; annual peak speeds approach 30 cm s-l. The relationship of the current and temperature records to the wind field is consistent with predictions of coastal jet theory. Profiling current meters deployed on either side of a furrow showed near-bottom, cross-stream flow converging over the furrow with divergence higher in the boundary layer when the current speed exceeded 6 cm s-l. A preliminary numerical model exhibits a cross-stream flow pattern consistent with the profiler observations. Bedforms (topography formed by the interaction of a flowing fluid and a movable sedimentary substrate) and other sedimen- AcknowledgmentsThe studies of R

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Mechanics of Sediment Movement

Cited by 408 publications

References 0 publications

Cuatro Vientos: A Reconsideration of Seven Prehistoric Sites in the Lower Rio Grande Plains of South Texas

Cuatro Vientos: A Reconsideration of Seven Prehistoric Sites in the Lower Rio Grande Plains of South Texas

Spectral particulate attenuation and particle size distribution in the bottom boundary layer of a continental shelf

Sedimentary furrows and organized flow structure: A study in Lake Superior

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