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The hydraulic piston cores from Site 619 in the Pigmy Basin were sampled for dispersed tephra zones. The sampling interval employed revealed only minor amounts of dispersed tephra; however, one ash layer was analyzed for major-element chemistry in order to correlate the tephrochronology of Site 619 and the late Pleistocene Gulf of Mexico. The ash layer in Sample 619-16.CC (142 m sub-bottom depth) is correlated with the Y8 ash that was erupted from the Lake Atitlan Caldera, Guatemala 84,000 yr. ago (approximately coinciding with the oxygen-isotope Stage 5a/5b boundary). Dispersed tephra at approximately 119 and 150 m can be correlated with the Y6 (65,000 yr.) and X2 (110,000 yr.) ash layers, respectively, based on position within the oxygen-isotope stratigraphy. The tephrochronology at Site 619 provides a chronologic horizon for correlation of other stratigraphic results with the time scale. INTRODUCTION The late Pleistocene section of the western Gulf of Mexico contains tephra horizons that are suitable for stratigraphic correlation (Kennett and Huddlestun, 1972; Thunell, 1976; Ledbetter, 1984, 1985). The ash layers were originally correlated and named by their position within the foraminiferal biostratigraphic zonation of Ericson and Wollin (1968), as subdivided by Kennett and Huddlestun (1972). Conspicuous tephra horizons were noted in Subzones X2-X5, Y6, Y8, and WI (Kennett and Huddlestun, 1972; Thunell, 1976). Because biostratigraphy was used to identify each tephra horizon, however, the utility of tephrochronology as a stratigraphic tool in its own right was not fully realized. The most widespread late Pleistocene tephra in the Central American region is the Y8 ash in the Gulf of Mexico, which is correlated with the Worzel Layer D (Bowles et al., 1973) in the eastern Pacific and the Los Chocoyos Ash from Lake Atitlan Caldera, Guatemala (Drexler et al., 1980). These Y8 ash correlations were accomplished using the majorand minor-element chemistry of glass shards (Drexler et al., 1980), rather than correlation with biostratigraphic zonations, thus representing full utilization of the tephra horizons for chronostratigraphy. The major-element chemistry of an additional five tephra horizons in the western Gulf of Mexico was established by Rabek et al. (1985). The age of all six tephra was determined by position within an oxygen-isotope stratigraphy and provides an unambiguous chronostratigraphy for the region for the past 185,000 yr. (Rabek et al., 1985). The major-element chemistry of a volcanic ash layer recovered at Site 619 (Fig. 1) in the Pigmy Basin correlated with the late Pleistocene tephrochronology of the Gulf of Mexico (Fig. 2). This ash layer at Site 619 provides a distinct chronostratigraphic horizon for correla30°N

Late Pleistocene Tephrochronology of Pigmy Basin, Deep Sea Drilling Project Site 619, Leg 96