Abstract

Geochemical analyses performed on volcanic ash layers from the 3 ocean basins surrounding Central America revealed 11 distinct tephra horizons during the past 300,000 yr, and the distribution of each tephra was delineated. The Los Chocoyos Ash (84,000 yr old) and Worzel Layer-L Ash (230,000 yr old) are the 2 most widespread tephra in the region. Two tephra, Y-6 (75,000 yr old) and W-1 (136,000 yr old), are restricted to the western Gulf of Mexico. The remaining tephra—B (36,000 yr old), J1 (135,000 yr old), G (190,000 yr old), I (212,000 yr old), K (270,000 yr old), I2 (270,000 yr old), and I6 (300,000 yr old)—are primarily restricted to the eastern equatorial Pacific Ocean immediately adjacent to Central America. The age of each layer was determined by correlation to oxygen isotope and calcium carbonate stratigraphy in marine cores or by interpolation or extrapolation of ages from that stratigraphy.

Of the marine tephra, two were correlated to terrestrial exposures of silicic volcanic rocks. The Layer-D tephra had been correlated to the Los Chocoyos Ash from the Lake Atitlan caldera in Guatemala. The Layer-I2 tephra is correlated with the T-fall ash from Lake Amatitlan caldera in Guatemala. The age of the terrestrial volcanic units was determined by identifying the stratigraphic age of the marine tephra. The Los Chocoyos Ash and T-fall deposit are dated at 84,000 and ∼270,000 yr B.P., respectively. Geochemical correlation of the marine tephra to other terrestrial sources will facilitate dating of explosive volcanic eruptions in southern Mexico, Central America, and northern South America.

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