Hole 1039B is located at 9°38.405´N, 12°037´W on the bottom of the Middle American Trench at a water depth of 4353 m (Fig. F2). Two sedimentary units are recognized in Cores 170-1039B-1H through 18X. Unit U1 consists of dark olive-green diatomaceous ooze with ash layers. Subunit U1A (0-5.55 meters below seafloor [mbsf]) is distinguished by abundant graded sand layers interpreted as turbidities. This subunit grades downward into Subunit U1B (5.55-84.4 mbsf), in which graded sand layers are sparse to absent. Below a sharp contact, Unit U2 is distinguished by a sharp decrease in biogenic sediments. Subunit U2A (84.43-132.87 mbsf) consists of dark olive-green silty clay and grades downward into Subunit U2B (132.87-152.49 mbsf). Subunit U2B is dark olive-green silty clay interbedded with light olive-green calcareous clay; ash layers are common throughout Unit U2 (Fig. F3). An age-depth model calculated from the combined last and/or first occurrence datums of index microfossils yields average sedimentation rates of about 46 m/m.y. (0-120 mbsf) for the Pleistocene and 6 m/m.y. for the late Miocene and Pliocene interval (120-200 mbsf).
Hole 1043A is located at 9°39.273´N, 86°11.160´W on the lowest continental slope of the Middle American Trench at a water depth of 4312.7 m (Fig. F2). Four lithologic units are recognized: T1, U1, U2, and U3, in descending order. Unit T1 consists mainly of thick clay and silty clay interbedded with a relatively thin matrix-supported breccia. Subunit U1A consists of turbidite-rich facies that are 5.55 m thick. Subunit U1B consists of olive-green to grayish green diatomaceous ooze with disseminated volcanic glass. Subunit U2A consists of olive-green to grayish green clay and silty clay with minor interbeds of vitric and crystal-vitric volcanic ash. Subunit U2B consists of olive-green silty clay interbedded with lighter green siliceous nannofossil ooze and calcareous clay with nannofossils. Subunit U3A consists of ivory white siliceous nannofossil ooze interbedded with light green calcareous clay and dark-colored clay with diatoms. In Unit U1 (150-194 mbsf), age-depth rates range from 52-40 m/m.y.; in Unit U2 (194-263 mbsf), the rate is 15 m/m.y.; and in Unit U3 (below 263 mbsf), the rate is <12 m/m.y. (Kimura, Silver, Blum, et al., 1997).