SUMMARY AND CONCLUSIONS

  1. Site 998 experienced an erosional event, inferred from an increase in terrigenous accumulation rates, in the mid-Oligocene at ~35 Ma. This erosional event may reflect uplift in Guatemala (Weyl, 1980) that began during Oligocene time and increased through the middle Miocene orogeny (Morris et al, 1990).
  2. Terrigenous sedimentation throughout the Caribbean Sea region has increased markedly in the last 10 m.y., with Site 999 beginning a steady increase since 28 Ma. This is probably caused by the rapid Neogene uplift in Hispanola, Guatemala, and northwestern South America. The uplift in northwestern South America seems to be dominant, as reflected in a similar increase in terrigenous accumulation rates at Sites 925 and 929 on the Ceara Rise, which receives input from the Amazon River draining the Andes (Dobson et al., 1997) and Site 999, which receives input from the Magdelena River draining the northern Andes (Sigurdsson, Leckie, Acton, et al., 1997). The uplift is continuing to the present (Morris et al., 1990; Mann et al., 1990; Mann and Burke, 1984).
  3. Volcanism resulted in an extremely large source of sediment to the Caribbean Sea, as evidenced by both the high amount of dispersed ash and the accumulation of discrete ash layers. Three periods of volcanism (Paleocene, Eocene, and Miocene) are recorded in both the dispersed ash and discrete ash layer records. Site 1001 shows the greatest absolute accumulation during the Paleocene. The greatest ash accumulation rate occurs at Site 999 during the Miocene and Eocene. The source of these episodes of volcanism is believed to be the Central American arc (Sigurdsson, Leckie, Acton, et al., 1997).
  4. The maxima in discrete ash layer accumulation temporally lags the dispersed ash accumulation rate. The lag may be a reflection of distance from the source of volcanism with sites nearer to the volcanism having deposits of discrete ash layers and distal sites showing dispersed ash, or it may be indicative of uplift and erosion of smaller volume deposits (leading to the dispersed record) followed by long periods of intense volcanic activity (leading to the discrete record).

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