Identifying Fine Sand Grain Types in An Everglades Archaeological Soil for Multiple Purposes.

The source of Phosphorus (P) in Everglades soils is in question. A fixed-tree island black kitchen midden archaeological soil was sampled in Water Conservation Area 3. The island summit has a petrocalcic horizon above a fluctuating water table. The soil contained very high amounts of HCl-extractable total P. Mehlich-1 P was detected in the soil water but not detectible in the water 15 m offshore. The soil is made of char, secondary CaCO₃, bone, shell, sand, and pottery. However, the composition of the sand fraction in each horizon and the subaqueous soil 15 m offshore is unknown and may explain the source of P and of each soil horizon. We counted about 300 fine sand grains from representative sub-samples of 10 soil horizons using a light microscope with a 6X power lens. Grains were dominantly secondary CaCO₃, uncoated quartz, bone, and shell. The CaCO₃ precipitated in a soil matrix of low-density char and soot, with bone, quartz and shell fragments. The fine sand-sized bones were non-porous. Secondary CaCO₃ made up the majority of the sand grains in and above the petrocalcic horizon, and decreased with depth. Quartz and bone sand dominated the horizons below the petrocalcic. Quartz sand was 85% and bone lowest (6.7%) in the lowermost midden layer, indicating a fluvial contribution. Bone sand was low (2.5%) in the offshore soil, much different than the island. There was an ample supply of bone in all island soil horizons, up to 14 times as high as the amounts offshore. These results aid in identification of the origin of the soil materials for archaeological studies, and prove the source of an easily-weathered P source in the island soil horizons. The water P sampled 15 m from the island is evidently not affected by the island soil or soil water.