The geological evolution of the northern Peru convergent margin can be
traced using samples collected during deep-sea dives of the submersible
Nautile. In the Paita area (5 degrees-6 degrees S), the sedimentary
sequence was intensively sampled along the main scarp of the middle
slope area. It consists of Upper Miocene (7-9 Ma) to Pleistocene
siltstone, sandstone and rare dolostone. The age distribution of these
samples is the basis for a new geologic interpretation of the
multichannel seismic line CDP3.
Siliceous microfossils (both diatoms and radiolarians) show influence of
both cold and temperate waters (local species mixed with upwelling
ones). Diatom assemblages studied from the NP1-13 and NP1-15 dives bear
a strong resemblance to assemblages from the Pisco Formation of southern
Peru.
Micropaleontological data from siliceous microfossils, provide evidence
for two main unconformities, one is at the base of the Quaternary
sequence and the other corresponds to a hiatus of 1 Myr, separating the
Upper Miocene (7-8 Ma) sediments from uppermost Miocene (5-6 Ma)
sediments.
During the past 400 kyr, a wide rollover fold developed in the middle
slope area associated with a major seaward dipping detachment fault. A
catastrophic debris avalanche occurred as the result of an
oversteepening of the landward flank of the rollover fold. The gravity
failure of the slope, recognized by SeaBEAM and hydrosweep mapping,
displaced enough material to produce a destructive tsunami which
occurred 13.8 +/- 2.7 kyr ago.