Distribution of volcanic ash reflectors in the eastern equatorial Pacific Ocean

Abstract

Volcanic ash erupted from vents in Central America, southern Mexico and northern South America has accumulated as discrete layers in sediment of the surrounding ocean basins. Many of these ash layers form acoustic reflectors which are observed on 3.5 kHz seismic records from the eastern equatorial Pacific. Twelve discrete reflectors within 40 m of the seafloor may be traced in the region. Shallow (<20 m) seismic reflectors can be correlated to ash layers in piston cores where some ashes were correlated by Bowles et al. (1973) and Drexler et al. (1980) using geochemical methods. In addition, deeper seismic reflectors (>20 m) can be correlated with ash layers in two DSDP cores and used to indirectly establish that all seismic reflectors in this study are ash layers. Based on areal distribution patterns, most seismic reflectors indicate the direction of possible volcanic sources. Moreover, using an assumed constant sedimentation rate of 3 cm × 10 3 yr −1, the average estimated age of each reflector can be calculated. All ash reflectors are Quaternary in age. Reflectors 1 to 3 are correlated to marine ash layers “D”, “I”, and “L”, and the assigned ages correlate well with the previously established ages of 83,000, 133,000 and 230,000 yrs B.P., respectively, for these layers.