Abstract

Two hypotheses have been suggested to explain the statistical distribution of bed thickness in turbidite sequences: that it is a reflection of turbidite triggering by earthquakes occurring haphazardly in time, and that it is controlled by the intrinsic, nonlinear dynamics of a sedimentary system composed of many downslope transport events that are correlated over a broad range of scales of length and time. In an attempt to distinguish between these hypotheses, we have applied five tests to two previously described, Oligocene turbidite sequences from the Izu-Bonin basin of the western Pacific Ocean. We conclude that turbidite deposition in the Izu-Bonin region is not the outcome of a self-organized process, nor of a low-dimensional, chaotic system, but rather is consistent with turbidite emplacement by flows triggered by earthquakes. At least some recent turbidites are known to have been deposited by such flows, and the tests we have applied demonstrate that no other process is required to explain the statistics of the thickness and the timing of emplacement of beds in turbidite sequences. If turbidites are indeed related to earthquakes, then changes in the rate of turbidite emplacement may be used to place important constraints on paleoseismicity.

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