Gordon Bromley, Kurt Rademaker, Sean Birkel and Louis Fortin
The proposed interdisciplinary project "Archaeological and Glacial Geologic Investigations of Nevado Coropuna, Peru" seeks to better understand links between climate change, the glacial history of the tropical Andes, and the initial human settlement of South America. At the end of the last ice age some 13,000 years ago, early foragers called Paleoindians were first entering South America, one of the last continents on earth to be permanently inhabited by people. This was an exceptionally dynamic time characterized by major environmental transformations: climate patterns were shifting, glaciers were in retreat, and the distribution of plant and animal communities was changing rapidly. How did these early settlers successfully adapt to such changes and rapidly colonize a continent of productive coasts, the rugged Andes Mountains, and the vast Amazon?
Sites such as Quebrada Jaguay, Peru, excavated in the 1990s by a UMaine team suggest that Paleoindians were settling the coast very early, taking advantage of rich Pacific fisheries. Obsidian (volcanic glass) artifacts found at Quebrada Jaguay were geochemically sourced to the Alca obsidian source, located some 100 miles to the north in the Peruvian highlands. This finding indicates contact between the coast and highlands during the period of earliest human settlement. As the only substantiated link of its kind in South America, the Alca connection offers the chance to evaluate competing models of initial migration. It is likely that the inhabitants of Quebrada Jaguay were highly mobile, moving seasonally between the coast and the highlands, and therefore additional Paleoindian sites should be located adjacent to the Alca obsidian source.
Our 2005 Churchill-funded expedition to the Alca source and Nevado Firura, a 5,499 m high, glaciated volcano, discovered numerous archaeological sites on and among glacial landforms. These sites are possibly the world's highest elevation Paleoindian settlements. We mapped and sampled glacial deposits of the Nevado Firura in order to reconstruct glacier extent at the time of this early occupation. Our findings validated the Paleoindian coast-highland link and demonstrated that glacier margins can be highly productive environments with abundant water, flora, and fauna - and that periglacial environments may have been vital for the success of Paleoindian populations, just as they are important to Andean peasant communities today. It therefore follows that late-Quaternary ice-marginal zones form a logical starting point for our investigation into early human land-use behavior in the central Andes.
Understanding the relationship between the contemporary early highland and coastal sites, as well as addressing the question of initial migration, will require additional archaeological work between the highland and coastal locales to "connect the dots." Kurt's Ph.D. work over the next few years will target the entire corridor between Quebrada Jaguay and the early highland sites to examine patterns of Paleoindian mobility and subsistence at the end of the last ice age. The first step will be to conduct an archaeological survey of the extensive periglacial zone surrounding Nevado Coropuna, a 6,431 m high, glaciated stratovolcano located directly between the Alca source and Quebrada Jaguay. This research would be impractical without a more thorough understanding of late-glacial climatic shifts, fluctuating glacial margins on Nevado Coropuna, and rapid transformations of ecological communities in the surrounding environment. We propose to utilize glacial geology to reconstruct changes in glacier extent on Nevado Coropuna since the last glacial maximum (LGM) and to date these changes accurately using surface-exposure and radiocarbon methods.
Glaciers are sensitive climate indicators, waxing and waning in response to temperature and precipitation fluxes. A record of glacier fluctuation can therefore be used to determine both the timing and magnitude of climate-change events. This geologic-dating program, which will form an integral part of Gordon's Ph.D. work, also has the potential to answer key questions in tropical climatology: when did the LGM occur in the tropical Andes? What was the magnitude of atmospheric cooling at the LGM? Was deglaciation in the tropics punctuated by a climatic reversal contemporaneous with the Younger Dryas of the North Atlantic?
Nevado Coropuna is an ideal candidate to address these questions, as well. First, during the 2005 field season we observed an abundance of striking, well-preserved glacial deposits on the volcano. Second, because paleoclimate data from the arid tropics are extremely scarce, this record from the western Andes will form a valuable contribution to the tropical dataset. Third, in anticipation of forthcoming ice-core data from Nevado Coropuna, our study will enable direct comparison of ice-core and glacial geologic data from a single site.
To reconstruct former glacier extent on Nevado Coropuna we will map the distribution, elevation, and morphology of moraines, drift sheets, erratics and erosional features onto 1:20,000 scale aerial photos. Hand-dug pits will allow sedimentologic and stratigraphic characterization of each unit. We will correlate moraines by position, soil development and physical weathering characteristics of internal and surficial clasts. In addition, we will use a Dutch corer to extract sediment cores from local bogs in order to obtain minimum ages (14C) for glaciation. The glacial geologic mapping will be used in close conjunction with the surface-exposure program to ensure careful sampling of moraines and erratics.
We will obtain rock samples from glacial landforms for Neon cosmogenic exposure age dating, the appropriate dating method for the local lithology. Forty rock samples should reveal trends in moraine ages and identify erroneous results. Radiocarbon samples collected from excavations and sediment cores will be used to cross-check Neon dates and provide minimum and maximum ages for glacial episodes. Cosmogenic and radiocarbon samples will be prepared at the University of Maine and analysed at Purdue University's PRIME Lab and the University of Arizona NSF Lab, respectively.
To continue our search for early archaeological sites in the central Andes we will conduct a survey of caves, rock shelters, and other likely habitation areas in the periglacial zone. This work will identify likely locations for more extensive sub-surface excavations in succeeding field seasons, which will ultimately enable us to examine patterns of prehistoric settlement, subsistence, and mobility through the late glacial interval. The distribution of archaeological sites will also provide an additional line of evidence to help us reconstruct post-LGM environmental changes around Nevado Coropuna.
Our proposed 2006 research offers an exciting opportunity to explore the relationships between climate and environmental change and the initial Paleoindian settlement of South America at the end of the last ice age. Moreover, our interdisciplinary approach will enable us t o pool logistical resources and labor to continue cooperative fieldwork in this remote area of the central Andes. Thank you very much for considering our research proposal.
This itemized budget includes all field work costs for Gordon Bromley, Kurt Rademaker, Sean Birkel, and Louis Fortin from May 15 to June 29. Roundtrip airfare for Kurt Rademaker is provided by a National Science Foundation grant (Dr. Dan Sandweiss, Principal Investigator). Roundtrip airfares for Gordon Bromley and Sean Birkel are provided by grants from the Geological Society of America and the UMaine Association of Graduate Students, respectively. We have applied for additional funding to cover laboratory sample preparation and analyses from the Geological Society of America, Sigma Xi, and the UMaine Association of Graduate Students.
funding to cover laboratory sample preparation and analyses from the Geological Society of America, Sigma Xi, and the UMaine Association of Graduate Students.