Archaeological Palynology of Teuchitlán

Results

Although there is no set rule for deciding whether any particular pollen sample contains adequate amounts of pollen for an unbiased analysis, it is generally accepted that minimal concentration values of 1000 to 3000 grains per cubic centimeter are required before the pollen content of a sample is going to satisfactorily reflect the floral community from which it was derived. Values lower than this are thought to reflect pollen contents that have either been significantly altered by loss through poor preservation (Hall, 1981) or rapid burial of a sediment precluding deposition of sufficient quantities of pollen for analysis. Table 1 reveals that the majority of the Teuchitlán samples fall well below this range, regardless of which extraction method was applied. Only one sample produced a pollen concentration value higher than 3000 grains per cubic centimeter, and that sample was located at 2 to 5 centimeters below surface on the circle 1 patio. This is well within the modern plough zone – the patio is currently and for several years has been used as an agricultural field – and therefore the pollen content of this sample likely represents modern pollen. With three exceptions – pyramid 2 trench 5 sample 4, circle 2 platform 3 samples 9 and 10 – all of the remaining samples have pollen concentration values below 1000 grains per cubic centimeter, in many cases well below this figure. There is also reason to suspect the two circle 2 platform 3 samples as they were recovered from cleared surfaces only a few centimeters below the modern surface. Given the otherwise very low pollen concentrations for the Teuchitlán samples, one must wonder if the moderately higher concentrations for these two samples actually reflect pollen deposited during site occupation, or are a product of downward transportation of pollen from the modern surface (cf. Dimbleby, 1985). The pyramid 2 sample, on the other hand, is from a relatively deeply buried context less likely to have been subject to modern pollen contamination.

The circle 1 patio sample is dominated by Cheno-Am pollen. Cheno-Am refers to a morphologically similar group of pollen grains of the Chenopodaceae and Amaranthaceae families. As such, it includes a broad range of plants including those used as food, such as Amaranthus, Chenopodium, and Atriplex, as well as a variety of weedy herbaceous plants encouraged by soil disturbance and enrichment common to both agricultural fields and domestic habitation areas (cf. Cummings, 1990; Fish, 1994). Its occurrence within archaeological site context pollen records of the American Southwest has been variably argued as indicating human environmental impact, resource use, or climatic change (Fish, 1985). Comparing this sample with surface samples collected in the vicinity of the site as part of my wetland agriculture research reveals that this sample has a comparatively high frequency of Cheno-Am. This may indicate that although personal observation reveals that maize has been grown on this field for the past few years, amaranth may have been grown in the not too distant past. Alternatively, the uncultivated ruins of the pyramid and other nearby architectural features may be providing a more suitable habitat for weeds of the Cheno-Am group than is available elsewhere in the surrounding area.

The pyramid 2 sample – the one sample with a reasonable pollen concentration recovered from a context that seems less likely to have been affected by modern pollen rain – rather than being dominated by Cheno-Am pollen is dominated by grass, and, to a lesser extent, by high-spine Compositae pollen. The high-spine Compositae group includes a variety of weedy plants, but also the important food plant sunflower (Helianthus), as well as other genera which produce small edible fruits. However, the presence of high-spine Compositae pollen in this context likely reflects the presence of weedy plants. Table 2 indicates that the difference between the pyramid 2 sample and the patio sample in regard to proportions of Cheno-Am, grass, and high-spine Compositae is very significant and quite strong. Similarly, comparing the proportions of these taxa between the pyramid sample and a surface sample that had been collected from an agricultural field approximately 100 meters away – the closest of the surface samples mentioned above – also indicates a very significant difference, but at a lower strength. This lower strength appears to be stem from more similar values for high-spine Compositae and Cheno-Am, while grass frequencies remain quite different. In general, the pyramid sample differs from modern pollen assemblages primarily through a higher grass frequency, and from the patio sample by having a lower frequency of Cheno-Am. Why the weedy vegetation is reflected predominantly in grass rather than Cheno-Am may arise from the type of disturbance: the higher population density and domestic (i.e., ceremonial and habitation) context of the site area during its occupation versus the less frequented (non-habitation or ceremonial) and modern agricultural context of the abandoned site. However, the possibility that the high frequency of grass pollen may be the product of contamination by modern pollen can not be ruled out.

Earlier, the question of whether the pollen content of circle 2 platform 3 samples 9 and 10 was the product of downward movement of modern pollen or deposition during site occupation was raised. Examination of Table 2 reveals that the proportions of Cheno-Am, high-spine Compositae, and grass pollen from platform samples 9 and 10 are very significantly and quite strongly different from the patio sample. They are also very significantly and fairly to quite strongly different from the pyramid sample. In comparison to the nearby surface sample, platform sample 9 is very significantly, but not particularly strongly, different while platform sample 10 is not especially different at all. As was the case for the pyramid 2 sample, the two platform samples appear to have higher frequencies of grass pollen than do the previously analyzed surface samples. But, this may simply reflect grass pollen being washed down; the circle 2 platforms were grass covered prior to excavation. Thus, it is still unclear whether the pollen assemblage from the two platform 3 samples reflects deposition of pollen during site occupation, or downward movement of modern pollen grains.

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