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What’s Natural

When it comes to interpreting geophysics, it is as important to understand what you should expect from non-archaeological phenomena as it is to understand the nature of the archaeological features you seek to identify. This means understanding the interpretive medium—sediment—and understanding data collection conditions.

The site sits partly on the crest of a natural levee of what was an active channel of Red River [Figure Natural 1]. The USDA Soil Conservation Service characterizes the vicinity as a well-drained very fine sandy loam that was deposited as alluvium (USDA 1990:55-57, 109). Roots penetrate it easily, water and air move through it at a moderate rate, water runs off the surface slowly, and it is not particularly subject to shrink-swell effects.

Typically the upper 15 cm of this type of levee alluvium is a yellowish-red very fine sandy loam with a neutral pH [Figure Natural 2]. Below it to a depth of about 1.07 m the sediment acidity changes to a neutral silt loam and a moderately alkaline very fine sandy loam. Even deeper, to a depth of 1.68 m, the sediment remains mildly alkaline, but it changes color and sediment size, becoming a dark brown silt loam and a strong brown fine sandy loam. In places within these three typical strata the soil is calcareous.

The Soil Conservation Service’s summary of this Roxana soil series is a generalization for levee sediments across an entire parish. Excavations at the site have produced a far more detailed look at the local stratigraphic profile. [Figures Natural 3 and Natural 4] To summarize, a typical excavation at the Whittington site exposes a roughly 5 cm thick humic layer of brown silt loam at the ground surface. Below it to a depth of roughly 35 cm are one to three strata of brown silt loam, the upper 20-30 cm of which often exhibit plow scars. Deeper deposits of brown silt loam reside below the plow scars. Archaeological material is usually restricted to these upper strata.

Somewhat deeper than 35 cm, however, one encounters either alternating bands of light brown silt loam and dark brown clay loam, or a yellowish-red silt loam deposit. Both are alluvial in nature, but the alternating bands of alluvium with the finer sediment (clay) probably represent a river flood regime that pre-dates the Coincoin occupation.

Figure Natural 1

Figure Natural 1

Schematic Drawing of Natural Levee Systems like that Occupied by Coincoin
(Adapted from Locke 2007)

Figure Natural 2

Figure Natural 2

Idealized Roxana Soil Series Covering the Coincoin Plantation Area
(USDA 1990)

Figure Natural 3

Figure Natural 3

Sediment Profiles from the Coincoin Plantation Area
(David W. Morgan)

Figure Natural 4

Figure Natural 4

Locations of Sediment Profiles in the Coincoin Plantation Area
(NCPTT)

Funding for the research project from 2002-2007 was generously provided by the U.K. Arts and Humanities Research Council, the British Academy, the U.S. National Endowment for the Humanities, the Cane River National Heritage Area, the National Park Service’s Delta Initiative, and the Institute of Archaeology at University College London.

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