Rock magnetic properties of a soil developed on an alluvial deposit at Buttermilk Creek, Texas, USA

The evolution of magnetization within a floodplain soil begins with initial deposition of magnetic particles during sedimentation and continues via subsequent alteration and growth of iron-bearing compounds by pedogenic and biologic processes. Measurements of soil magnetic properties capture information about the developmental history of the soil and are a convenient method by which to investigate environmental change and pedogenesis. Using a range of magnetic measurements, a comprehensive scenario for soil development was constructed for floodplain sediments at the Debra L. Friedkin site, an important archeological site near Buttermilk Creek, Texas. Floodplain deposits have traditionally been avoided for soil magnetism studies because it is thought that the episodic input of sediment would form soils characterized by discrete sedimentary units rather than a continuous record of pedogenesis. We demonstrate that alluvial deposits can sometimes carry a straightforwardly interpretable magnetic signal similar to those typically seen in loess deposits. Smooth variation of rock magnetic parameters as a function of depth also leads us to conclude that the soil at this site is largely undisturbed and that the age of lithic artifacts found within the soil may be interpreted within stratigraphic context.