4.6. Other Tertiary obsidian in the Colca valley

Other Barroso group deposits in the region include Pampa Finaya on the north side of the Colca River. In the course of his archaeological survey Steven Wernke (2003: 36, 39) surveyed Pampa Finaya and, unlike in the Chivay source area, obsidian was not found on the perimeter of this Barroso flow where it contacts Tacaza layers. However, Wernke identified an obsidian source to the west on Cerro Caracachi, a distinctive knob-shaped peak at the head of Quebrada Huancallpucy that is at a contact zone between a layer described by INGEMMET as an porphyritic intrusive material (T-po). This source was exposed in a distinct stratigraphic context and that the obsidian appeared to be of low quality for knapping as compared with the Chivay type.

Figure 4-23. Geological map units with Uyo Uyo sampling locations. See Figure 4-14 for legend. Selected archaeological sites in the main Colca Valley shown in blue.

On 30 Nov. 2003, I visited the area of Cerro Masita and Cerro Caracachi on the suggestion by Wernke (2003, pers. comm.) in order to collect geological samples, to determine whether higher quality obsidian is encountered on this dome, and to compare the deposits with what had been observed at the Chivay source (see Appendix B4). I approached Cerro Masita was approached from the road in the drainage north-west of Ichupampa and only observed small pieces of low quality obsidian near the summit of Caracachi (documented by Wernke) and on the eastern flanks of Masita. Analysis by at Missouri University Research Reactor (Glascock, 2005 pers. comm.) established that this material belongs to the "Uyo Uyo" chemical group first recognized in samples provided by Sarah Brooks (1998: 443-445). In 1993 Brooks collected modified and unmodified nodules from the site of "Uyo Uyo" near Coporaque that were analyzed at MURR in 1995. Brooks (1998: 443-445) writes that the geological origin of these nodules was not determined, but the presumption was that the source lay uphill from the site of Uyo Uyo, as there were many unmodified nodules at the site, an observation that was confirmed by these hikes. No large nodules were encountered, however, and it appears that the Chivay source east of Chivay remains the sole source of high quality obsidian in large nodule form in the Colca valley.

4.6.1. Tripcevich source sampling work

In the course of Upper Colca 2003 survey work geological samples of unmodified obsidian were collected from a variety of natural contexts throughout the Upper Colca study area as well as elsewhere in the Colca valley. In order to best characterize the elemental variability within a chemical type, Shackley (1998: 100-101) recommends collecting samples from throughout the primary and secondary deposition area in sufficiently high numbers to recognize sub-source variability and reduce the chances of mischaracterization.

Figure 4-24. Bivariate plot showing Dysprosium against Manganese for Tripcevich 2005 samples.

Figure 4-25. Map showing locations of Colca valley obsidian source samples analyzed by MURR in 2005.

On Figure 4-24 only samples NT0005, NT0008, and NT0015 fall within the Chivay ellipse giving the impression that there is chemical variability at the Chivay source. Bivariate plots across other elements, however, show that all of the samples fall squarely within the Chivay ellipse.

MURR ID	Result	Region	Description	Quality	Date	Elev	Longitude	Latitude
CQP001	Chivay	Colca	Condorquiña source near Pulpera	Poor	2002	4160	-71.41795	-15.55677
CQP002	Chivay	Colca	Condorquiña source near Pulpera	Poor	2002	4155	-71.41793	-15.55675
CQP003	Chivay	Colca	Condorquiña source near Pulpera	Poor	2002	4160	-71.41795	-15.55677
NT0001	Chivay	Colca	East of Cerro Hornillo	Med	2002	4972	-71.51366	-15.63657
NT0002	Chivay	Colca	Maymeja SE rim along trail departing area at 140°	Good	2003	5003	-71.54049	-15.65356
NT0003	Chivay	Colca	Quarry pit Q02-2, A03-219	Good	2003	4916	-71.53554	-15.64233
NT0004	Chivay	Colca	Chivay	Good	2003	4911	-71.53577	-15.64257
NT0005	Chivay	Colca	Chivay, A03-570. Cortex battered, poss. from glaciers.	Good	2003	4722	-71.55058	-15.64167
NT0006	Chivay	Colca	Chivay, northern Maymeja	Med	2003	4900	-71.53812	-15.63772
NT0007	Chivay	Colca	Chivay, northern Maymeja	Med	2003	4902	-71.53794	-15.63770
NT0008	Chivay	Colca	On western shoulder of Ancachita with ash sample	Med	2001	4622	-71.55493	-15.64239
NT0009	Chivay	Colca		Good	2002	4798	-71.54423	-15.64587
NT0010	Chivay	Colca	Quarry pit Q02-2, A03-219	Good	2003	4915	-71.53556	-15.64247
NT0011	Chivay	Colca		Good	2003	4685	-71.55794	-15.65837
NT0012	Chivay	Colca		Good	2003	4885	-71.53793	-15.64292
NT0013	Uyo Uyo	Colca	W. side of Cerro Caracachi	Poor	2003	4450	-71.67602	-15.61547
NT0014	Uyo Uyo	Colca	East slope of Cerro Masita	Poor	2003	4372	-71.68787	-15.60532
NT0015	Chivay	Ayaviri	Artifact from Yana Salla, Llalli	Good	2001	4200	-70.87933	-14.94699
NT0016	Alca-3	Cotahuasi	Near small rock shelter by top of landslide	Good	2001	4288	-72.73238	-15.11981
NT0017	Alca-1	Cotahuasi	From across valley near old canal	Med	2001	4203	-72.71776	-15.12254
NT0018	Alca-1	Cotahuasi	From across valley near old canal	Med	2001	4202	-72.71776	-15.12254
NT0019	Alca-3	Cotahuasi		Good	2001	4329	-72.73268	-15.11858
NT0020	Alca-1	Cotahuasi	Above Ayawasi	Med	2001	3760	-72.73644	-15.14140

Table 4-5. Peruvian obsidian source samples submitted to MURR by Tripcevich in 2002 and 2005. Coordinate datum is WGS84.

Three samples were provided from the low-quality Condorquiña source in the Pulpera area that were collected in 2002 in order to evaluate the chemical variability within the Chivay source. While the quality was poor, this characterization demonstrates further association between that the Chivay obsidian chemical type and the Pliocene Barroso lava flows evident in the Colca valley. One artifactual sample that turned out to be Chivay was from the town of Llalli close to Ayaviri, in Puno.

Additional samples were submitted from the Alca source collected during fieldwork in 2001 from an exposure described by Justin Jennings (Pers comm. 2001) to the west and south of Cerro Aycano. Kurt Rademaker and colleagues (2004) have since encountered much larger obsidian exposures to the east of this area, on moraines located on the northern slopes of Nevado Firura at approximately 4700 masl.