The Lewis Camp Mound: An Example of a Petrocalcic Horizon in Jefferson County, Florida Henry J. Kratt, Jr., Charles L. Coultas and Michael Russo
Introduction Shell Middens • Thousands of shell middens in the SE United states were deposited by prehistoric native Americans between 8,000 and 500 years ago. • Along Florida rivers, middens may contain shells of freshwater mussels, mystery snails, and apple snails. Fragmented bones are less abundant, and artifacts even more rare.
Introduction Petrocalcic Horizons In many shell middens, a hardened calcic (petrocalcic) layer occurs at the base of the shell deposits. The origin of the petrocalcic layers are undetermined. Possible causes are: precipitation of CaCO3 from rising groundwater, acid-rainwater weathering of thin snail shells and fine fish bones followed by redeposition of CaCO3 at lower depths. This paper describes the extent of a petrocalcic horizon (called calcrete) on a shell mound and a possible pathway for its genesis.
Introduction Study Site - The Lewis Camp Mound is a small midden mound, containing food and tool production remains from past cultures. It is located on one of the deeper, braided channels of the spring-fed Wacissa River, in Jefferson County Florida.
Methods Lewis Camp Mound - The initial investigation took place during July 1999. The mound was about 2 m tall.
Methods Initial Excavation Pit – A 1 by 1 m pit was excavated in 10 cm thick levels. A petrocalcic horizon (calcrete) was found at 72 cm. A Problem – The soil was screened through a 6 mm mesh onsite. After analysis, we determined that a second pit was necessary with finer screening to separate fine fish bones.
Methods Excavation 2 – One 50 by 50 cm pit was opened in order to record stratigraphy below the petrocalcic layer encountered in the initial pit bottom. A bucket auger was used to examine soil characteristics below the petrocalcic layer.
Methods Soil Pit Locations Contour elevation lines (m) determined with laser level to determine island stratigraphy.
Results Petrocalcic Horizon Extent – Coring with a bucket auger (Blue points) and a steel probe (Red points) was used in 2003 to determine the depth of the petrocalcic layer. The dashed line represents the approximate extent of the petrocalcic layer, largely coincident with shell midden deposits. Pits
Results and Discussion • The petrocalcic layer was thickest at the higher levels of the site and thinner on the down slope edges. • Some recent degradation may occur as rainfall becomes more acidic and shell deposits ceased. • Leaching would be minimal at the shoulder position, where the petrocalcic is shallowest.
Results Soil – Composition of matrix above the petrocalcic layer is freshwater snail (Pomacea paludosa), turtle bone and shell, mammal and fish bones. There is some marine shell in very small quantities. Ceramic shards and chert flakes are also present. The petrocalcic layer (light gray) is visible near the bottom of the pit at 72 cm.
Results and Discussion The upper soil developed in sandy loam material with a sandy clay loam texture just above the petrocalcic. Relatively high organic matter occurred in this highly calcareous material. The soil underlying the petrocalcic horizon contained very little organic matter, very little free calcium carbonate (as indicated by no effervescence in soil matrix) and a relatively high clay content (possible relict argillic horizon). Just under the petrocalcic was a layer of loamy sand. Under the loamy sand was a buried soil with a clay increase in the subsoil. Fine sand with a water table at 125 cm extended to 140 cm.
Results and Discussion Redoximorphic conditions extended from 66 to 140 cm, below the petrocalcic and a loamy sand layer. None were found in or above the loamy sand layer. The presence of noncalcareous and clayier subsoil layers in the buried soil indicate that the buried soil may have formed on a low river terrace. The surrounding alluvial floodplain soils have a histic epipedon over dark gray to gray fine loamy sands to a depth of 112 cm. A silty marl or weathered limestone deposit was found from 87 to 112 cm, containing rotting organic material.
The presence of a sandy clay loam texture just above the petrocalcic, with a loamy sand layer just below, indicated a depth where percolating groundwater would be restricted from further downward movement. The petrocalcic likely formed by deposition of percolating Ca and CO3 from the calcareous, shell and bone-filled midden above. Few shells were found in all horizons, but the noncalcareous matrix below the petrocalcic rules out rising calcareous groundwater as a source of the petrocalcic. Petrocalcic Discussion
Lewis Camp Mound, Ceramics Timeline of occupation- Based upon fiber-tempered ceramics recovered from the site, the site has been utilized since the Late Archaic Period, or since 2,500 B.C.
Lewis Camp Mound, Ceramics Deptford Simple Stamped- After initial use, site was inhabited by various groups, as evidenced by different ceramic types recovered from the excavations. Deptford ceramics date from 500 B.C. to A.D. 0 in this region.
Lewis Camp Mound, Ceramics • Wakulla Check Stamped • Carrabelle Punctated • Weeden Island ceramics- This type of ceramic dates from A.D. 150-A.D. 1000. The upper sherd represents a style popular from A.D. 750 on.
Lewis Camp Mound, Lithics Stemmed ppk (Savannah River, reworked) Point was recovered from within the upper level of the petrocalcic layer, indicating layer developed after deposition of the tool. Chronologically, tool dates to post-2,500 B.C.
Conclusions Based upon the recovery of artifacts within the petrocalcic layer, the layer must have formed after deposition of the tools and food remains (post-2,500 B.C.)
Conclusions Human activity was a factor in the midden deposition and height of Lewis Camp Mound above the Wacissa River floodplain, and thus affected the petrocalcic layer’s development. Further investigation should be conducted to determine if adjacent areas of similar elevation have a petrocalcic layer dating to the same period.
Lewis Camp Mound, Acknowledgements The research was carried out under Permit issued by the Bureau of Archaeological Research, Division of Historical Resources, Florida Department of State. The National Park Service’s Southeast Archeological Center provided assistance through the use of equipment.