Sourcing Shell-Tempered Ceramics Using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry – by Evan Peacock, MSU, Thomas Meaker, MSU, Janet Rafferty, MSU, Hector Neff, California State University at Long Beach.

 


                                                                          INTRODUCTION

The elemental analysis of clays has become a standard method for sourcing archaeological ceramics. Problems encountered include the wide natural variability in clays and the contribution of inclusions to the elemental signature. With shell-tempered ceramics, this latter problem has been dealt with by removing the shell with acids prior to analysis or by mathematically correcting for the effects of shell. Ironically, both procedures discard data that pertain directly to the topic of interest: the elemental signature of the shell itself, which theoretically can be used to discriminate sources of temper material and, by extension, of the pottery itself.


Freshwater mussel shells have chemical signatures related to the waterway of origin. If elemental variation between waterways is greater than that between species or shell parts, then analyzing shell temper particles should allow for pottery to be sourced to the drainage where it was produced.

                      METHODS

LA-ICP-MS was used to analyze shell-temper particles in pottery from the Lyon's Bluff site (22OK520), a Mississippian to Protohistoric period mound site in north-east Mississippi. Several plain sherds were used to represent local wares; possible imports analyzed included sherds of Moundville Engraved, Nodena Red-on-White, negative painted sherds, and a fragment of a "cat monster" figurine. Each of these might be considered non-local based on stylistic grounds.


Principal Components plot based on the elemental analysis of archaeological mussel shells using a PE-Optima 4300 DV inductively coupled-plasma emission spectrometer. Elements used in analysis are Ca, K, Mg, Mn, Na, and Sr. Note the separation between drainages.


Clear grouping is displayed when different elements are compared on bivariate plots. The plainwares constitute a presumably local group, while most of the "exotic" ceramics fall together in one or more groups.

Interestingly, the negative painted sherds- arguably the most likely imports - consistently fall in with the plain sherds. This may be due to geological similarities between the Black Prairie, with a chalk bedrock, and the Nashville Basin, with a limestone bedrock. Alternatively, the negative-painted sherds may in fact be of local manufacture. LA-ICP-MS provides a rapid method for further exploring these possibilities, as large numbers of samples can be analyzed rapidly and a wide array of elements examined for purposes of discrimination. Large amounts of archaeological shell are available to provide background data. This pilot study demonstrates the potential for using shell as a sourcing agent in ceramic studies.

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