5 Geoarchaeology: Sites, Substrate, Sources, and Context I

Sunday, 22 March 2009
8:30 AM - 12:00 PM

ANALYSIS OF MATERIALS FOUND IN CERAMIC PERIOD ARCHAEOLOGICAL SITES FROM SOUTHWEST COASTAL MAINE

Paper number: 5-5
Program: Theme Sessions
Time: 9:30 AM – 9:50 AM

Authors

Abstract

Pottery from Ceramic period sites in southwest coastal Maine consists of a finer grained matrix (paste) enclosing a sand - sized (temper) component. Open pit firing of the vessels at relatively low temperatures has produced a vessel that is texturally analogous to a moderately consolidated sand-rich mudstone. X ray diffraction analysis of the sized – determined clay and silt portion of the vessels demonstrates that the clay portion is mineralogically more variable consisting of differing proportions of quartz, albitic plagioclase, microcline, orthoclase, muscovite, phengitic and illitic phyllosilicates and minor chlorite. The matrix portion of the vessels was most probably collected from prominent bluffs of glacial marine clays assigned to the Presumpscot Formation. Many of these bluffs are Holocene erosional features which occur throughout the Casco Bay area.

Thin sections demonstrate that the sand-sized temper was locally derived through the weathering of schists and pegmatites. Temper component consists of both undulatory and non-undulatory quartz, microcline and sodic plagioclase, plus composite grains consistent with granite pegmatite, biotite granite, sillimanite - quartz schist, calcsilicate and quartzite. Less commonly the temper consists of soft shell clams or coarse -grained muscovite. Mineralogy of the temper is more consistent with having been derived from medium to high grade metamorphics which more generally crop out in the northern Casco Bay area.

Sourcing of paste and temper allows definition of the manufacture process of prehistoric ceramics, which in turn aids in the definition of regional cultural patterns and the separation of “interior” versus “coastal” populations during the Ceramic Period (ca. 2700 – 450 B.P.). It also elucidates the nature of regional trade and exchange and social interactions.