Chronology of the Survey Lithic Assemblage

The discussion on the "Survey Data for All Time Periods" section applies to all obsidian recovered through survey regardless of its association with ceramics from various periods. In this section the survey obsidian assemblage is analyzed by distinguishing collections units that yielded only Early Period or Late Period ceramic materials. Given the small size of the Early 1 and Early 2 Period obsidian assemblages, they have been combined into a general “Early Period” category.

A synchronic pattern of artifact distribution by color and size was discussed on the "Survey Data for All Time Periods" section and a pattern of artifact size, color, and geographic location was observed. In order to investigate this pattern diachronically, collection units that contained the upper quartile of obsidian artifacts by weight (Table) were plotted according to period and color (Map). All Early Period collection units with clear obsidian, and most with black obsidian, were located in the northern and western arms of the survey zone, not in the south. In other words, the heaviest clear obsidian artifacts, and for the most part black obsidian artifacts dating to the Early Period come from areas farthest from the Aliso-Pumayacu obsidian source. It may be that during the Early Period this source, and its large black cobbles were not known, and raw material acquisition relied on the random recovery of cobbles in the Río Cosanga/Quijos drainages, cobbles that would have been diminished in size due to tumbling. By the Late Period, the regional distributions of clear and black obsidian changed, with the heaviest examples of black obsidian most common in the southern arm. Late Period collection units with the heaviest clear obsidian, however, are found throughout the survey zone including the western arm and central area. These patterns may also simply be representing the population distribution in the survey region for each period, with population concentrated in the northeastern arm of the valley during the early occupation, and spread throughout the three arms during the late occupation.

The recovery of obsidian artifacts throughout the survey zone does not necessarily mean that some form of exchange or direct procurement of obsidian with the southern arm was undertaken during the Late Period. In fact, clear and black obsidian cobbles could have been easily procured from any point along the Río Cosanga, or along the Río Quijos north of the Ríos Quijos/Cosanga confluence. The obsidian artifacts found west and up-river of the Quijos/Cosanga confluence however, required the human transportation of at least 10-15 km each way over very difficult terrain. In terms of obsidian quality preferences by consumers in the western arm, the same amount of energy would have been expended to bring in either clear or black obsidian. Data on artifact weight from the upper quartile of black and clear obsidian indicates that large pieces of black obsidian were not entering this western region. Instead, relatively large clear obsidian pieces were concentrated there, indicating its preference by local consumers. This preference may have been in response to differential activity uses or the simple economic rationalization that if you are going to spend the energy to obtain obsidian from the Quijos/Cosanga area anyway, you might as well get the best you can.

Differences in use wear between small clear obsidian artifacts and large black artifacts were discovered when considering the entire survey obsidian assemblage. When use wear types by period were investigated, however, a slightly different pattern emerged. Use wear was identified on 27% (n=3) of all Early Period black obsidian and on 28% (n=9) of Early Period clear obsidian artifacts. Use wear on Early Period black artifacts reflects scraping activities, while scraping, slicing and heavy cutting of a hard surface, like bone, horn, or wood, was carried out with clear obsidian. In the Late Period 38% (n=156) of black obsidian artifacts exhibited use wear, while 43% (n=306) of clear obsidian exhibited use wear, a considerable increase in use over time. In the Late Period, similar patterns of use wear were identified on both clear and black obsidian artifacts. The main activities identified include scraping, slicing, cutting of hard materials, chopping, and slicing of soft materials.

In the Late Period the same proportion of clear and black obsidian artifacts exhibited use wear, although clear obsidian was preferred for certain tasks. The differences between Late Period clear and black obsidian artifacts in regard to proportions of all use wear events observed are somewhat significant (χ² = 16.46, .20 > p > .10). Unlike the synchronic patterns of use wear between color categories, the observed deviations from expected values in the Late Period assemblage were greatest for use wear types #9 and #11. Use wear type #9, continuous lunate flake removals, is produced by continuous slicing, while type #11 is produced by heavy chopping. Therefore clear obsidian in the Late Period appears to have been preferred for chopping and continuous slicing activities, while clear and black obsidian were used equally for all other activities. Clearly, there is a discrepancy between the Late Period patterns of artifact use between clear and black obsidian and those patterns from the temporally mixed, synchronic data presented above. How the synchronic use wear patterns fit into the temporal framework of the Quijos Valley is not known. It is possible that they reflect nothing more than the vagaries of sampling, or that there really was a preference for big, black obsidian artifacts for the cutting of very hard materials and specialized scraping activities for smaller clear artifacts. At the same time, Late Period use wear patterns may reflect a subset of activities carried out that do not contradict the overall pattern between colors and activities. Taking into account the relatively weak strength of the diachronic patterns observed, the synchronic patterns are worth seriously considering.

Unidentified flake debitage, in both black and clear obsidian (Table), dominated the Early and Late Period assemblages throughout the survey zone. This flake debitage, coupled with flake tools like casual cores, reflects the predominance of an expedient, direct percussion reduction technology throughout the survey zone for all time periods. Nonetheless, bipolar reduction artifacts of both clear and black obsidian double in proportion in the Late Period. The distribution of bipolar artifacts dating to the Early and Late Periods suggests that different reduction strategies for clear and black obsidian existed by the Late Period. Only three Early Period bipolar artifacts were recovered, one of black obsidian and two of clear, all located north of the Río Quijos. By the Late Period, bipolar reduction of black obsidian occurs in all three arms of the survey zone. The majority of collection units containing clear bipolar reduction occur in areas located farthest from the Aliso-Pumayacu source. This fits the pattern observed synchronically for the distribution of the lightest and thus smallest clear flake artifacts. In total, 82% of all Late Period clear bipolar artifacts are located in the center, north and west of the survey zone, where small cobbles of clear obsidian, as well as exhausted casual cores are being reduced, in contrast to the pattern of black flake core discard. The Late Period data on flake tools parallels the data on flake tools for the entire assemblage.

In sum, the transition from the Early to Late Period brought into relief the correlation between proximity to the Aliso-Pumayacu obsidian source, and size, color and reduction technology favored by inhabitants of the Quijos Valley. A pattern emerges in the Late Period of the relatively wasteful use of inferior black obsidian in areas adjacent to the source while clear obsidian was conserved via an increased reliance on bipolar reduction, especially of expedient flake reduction debitage and tools. This pattern is exemplified in the western arm of the survey zone where a preference on clear obsidian, that had to be brought in by human transportation over a relatively long distance, suggests a maximization of energy input into obtaining chipped stone raw material.

Return to "The Quijos Valley Chipped Stone Assemblage" Main Page