Date of Award

Spring 1987

Document Type


Degree Name

Master of Science (MS)


Ocean/Earth/Atmos Sciences



Committee Director

Dennis A. Darby

Committee Member

G. Richard Whittecar

Committee Member

Joseph Rule

Committee Member

Ramesh Venkatakrishnan


Late Quaternary terrace deposits along the Rio Magui consist of cobble or pebble gravels with thick volcanic ash caps. These gravel terrace deposits unconformably overlie a cemented volcanic tuff (Ananias Formation), and are subdivided into two formations (Antigua and Panambi formations) based on the cobble lithology and size, depth of weathering, geomorphic relationships, and heavy mineral assemblages. Carbon-14 dates from wood suggest that the Antigua fan deposits are older (greater than 40,000 YBP) than the lower Panambi alluvium (less tahn 25,000 YBP) which is restricted to lower terraces within the modern river valleys.

Two separate ash units identified by differences in mineralogy and magnetite element composition, both buried active alluvial surfaces. The San Juan Ash paraconformably overlies the Antigua cobble gravels and the Magui Ash paraconformably overlies the Panambi gravels. The present-day Rio Magui channel and overbank deposits (Payan Formation) form another gravel with abundant sand and mud interbeds similar to the Panambi Formation, but finer textured and more mineralogically mature than the Antigua gravel unit.



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Geology Commons