Francis (Frank) H. Brown

Francis (Frank) H. Brown
University of Utah

2015 Rip Rapp Archaeological Geology Award

Presented to Francis (Frank) H. Brown

Citation by Thure Cerling and Richard Klein

Frank Brown's study of the Omo-Turkana Basin from 1966 to today provides the basis for a detailed chronology of human evolution. Using the chemical composition of volcanic ashes, he has put in stratigraphic order ca. 300 ash layers in the basin deposited over the past > 4 million years; with colleagues he dated >30 ashes using K-Ar methods, and another half-dozen by orbital tuning to deep-sea ashes; in addition, he used paleomagenetism to provide yet more time horizons through this stratigraphic record of human evolution. Many of these ashes are found in the Awash Basin in Ethiopia, where they provide context for hominin fossils found there. With his detailed mapping and chemical analysis, he has provided the temporal context for the hundreds of hominin fossils discovered in the Omo-Turkana Basin and elsewhere in eastern Africa.

Paleoanthropologists and archaeologists will know that it is primarily Frank Brown who has provided the stratigraphic and paleogeographic framework for early human evolution. What they may not appreciate is the colossal effort involved, spread over nearly five decades and thousands of square kilometers of rugged, desolate countryside. In a region where many different languages are spoken, Frank’s remarkable linguistic abilities, and his interest in local peoples, literally saved the day on many occasions for many others. While carrying out his geological work, Frank has contributed to bilingual dictionaries, has expanded the known ranges of many plants in Africa, and has himself discovered many important fossils.

Some aspects of the fossils and artifacts may remain debatable, but Brown's stratigraphic and geochronologic framework is firmly established, and will remain a lynchpin for future researchers who seek to enlarge and interpret fossil and archaeological samples. It is for his unique and monumental contributions to our understanding of human evolution that Frank Brown is the 2015 Rip Rapp Awardee.

top2015 George (Rip) Rapp Archaeological Geology Award — Response by Francis (Frank) H. Brown

Notification of the Rip Rapp award was a complete surprise, and I am deeply honored. My work on volcanic ash layers in eastern Africa bears directly on archaeology, but it was motivated by the need for precise correlations between sections in the Omo-Turkana basin. From 1966, when I began work on the Shungura Formation, I was immediately drawn to the volcanic ash layers. At least 320 formed in the basin between 0 and 4 Ma. Some are thick (~10 m), others are thin (~2 mm); some contain pumice clasts with anorthoclase allowing precise K/Ar and 40Ar/39Ar dating. The sources were probably in the Ethiopian Rift Valley or on its flanks. Some were produced by very large eruptions, with products dispersed to Lake Albert (Uganda), the Gulf of Aden, and the Arabian Sea. Resulting deep-sea correlations provide a climatic framework for evaluating changes in early human form and behavior. The tephra allow direct correlations between depositional basins separated by ~1300 km (e.g., Baringo to Hadar). As some ashes extend ~2400 km east of their probable sources, and as the Toba ash has now been identified in Africa, one can expect eventual direct correlations between Africa and Asia.

I have always benefited from serendipity, beginning with crushing rocks for Garniss Curtis, which led to Clark Howell sending me to Ethiopia after learning K/Ar techniques; Garniss’ falling out with L.S.B. Leakey so forcing me to learn silicate analytical techniques from I.S.E. Carmichael; Jean de Heinzelin taking on the Shungura type section leaving me free to investigate younger parts of the formation; problematic geochronology at Koobi Fora drawing me there in 1980; meeting Thure Cerling in 1976 resulting in tephra correlations between Koobi Fora and Shungura. Although I intended to date these units at Utah, Ian McDougall at Australian National University had begun his work at Koobi Fora, and our current chronology reflects his incredible expertise and tenacity through our long, fruitful association. Once again free, I began characterizing the Omo-Turkana Basin tuffs in earnest, thinking that the job would be done in a decade. Every season new correlations are made that carry with them chronological information, so that ages of the new sections are known immediately, which benefits archeologists and paleontologists alike. Appreciating glass analyses for tephra correlation, I began work on sourcing archeological obsidians with Harry Merrick in 1984, that archeologists can now use those to infer the movements of early people.

In the coming years I hope to organize, collate, and present all my Turkana Basin analytical, stratigraphic, and locality information in a format the next generation can use. I see no end to use of these tephra for precise stratigraphic correlation over vast areas, and for unprecedented precision on chronology of archeological and paleontological sites. I feel fortunate to have had a first “go” at these units, and am pleased that others have valued my results. I thank my nominators, the Geological Society of America, and the Rapp Family for honoring me in this way.