Lindsay McHenry

Assistant Professor

324 Lapham Hall
(414) 229-3951
lmchenry@uwm.edu

PhD: Rutgers University
MS: Dartmouth College
BS: Dartmouth College

Specializations: Mineralogy

Research:

I use the composition of volcanic ash to correlate between archaeological sites in East Africa. Individual volcanic eruptions produce and deposit volcanic ash layers of distinct compositions that can often be uniquely identified over broad areas. Where these ashes are preserved between stratigraphic layers of archaeological interest, we can create stratigraphic frameworks for important evolutionary and cultural changes throughout a region.

I have applied this technique to the Plio-Pleistocene volcanic ashes of Bed I, the oldest and thickest bed at Olduvai Gorge, Tanzania. Specimens of Homo habilis and Paranthropus boisei, along with abundant stone tools, faunal remains, and cut-marked bones, have been found at sites throughout the Olduvai basin. These specimes are found between the layers of volcanic ash produced by the nearby Ngorongoro Volcanic Highlands. Unfortunately, the volcanic ash layers are poorly preserved because of the saline-alkaline lake and groundwater conditions at the time of (and since) deposition. At most sites the volcanic glass, the phase most often used for "fingerprinting" volcanic ashes, is altered to clay and zeolite and unusable. I have instead focused on the phenocrysts (volcanic minerals) for characterization and correlation. Using phenocryst composition, I have uniquely identified and correlated the major Bed I volcanic ashes throughout the basin, creating a high-resolution stratigraphic framework for Bed I. This framework has been used to place the new finds (including a Homo habilis maxilla) from the lesser-known western part of Olduvai into context with the better known eastern sites.

I am currently working to expand both the regional and temporal scope of this project. I have collected volcanic ash samples from Laetoli, an older (Late Pliocene) archaeological site to the southwest of Olduvai, and from the younger Beds (Bed II and up) at Olduvai. My goal is to establish a regional stratigraphic framework based on volcanic ash compositions for Plio-Pleistocene (and Holocene) Tanzania that can be used for regional correlation between sites of palaeoanthropological, palaeoclimatological, and palaeoecological interest.

Other interests include the study of volcanic ash alteration processes, establishing a regional record of explosive volcanism for Tanzania, and correlating volcanic ash layers between terrestrial and marine environments. In addition to work in Tanzania I have also started a project in New Zealand. There I hope to correlate ashes between sites on land and on the seafloor, looking for differences in composition related to environments in which they are deposited.

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