California and Other Modern Basin Floor Seismo-Turbidite Sedimentology: Implications for Active Tectonic Margin Stratigraphy and Reservoirs
Nelson, C. Hans; Goldfinger, Chris; Gutierrez Pastor, Julia
Earthquakes generate mass transport deposits (MTDs) plus megaturbidite (MTD overlain by coeval turbidite), multi-pulsed, stacked, and mud homogenite seismo-turbidites. The strongest (Mw 9) earthquake shaking signatures appear to create multi-pulsed individual turbidites, where the number and character of multiple coarse-grained pulses for correlative turbidites generally remain constant both upstream and downstream in different channel systems. Multiple turbidite pulses, that correlate with multiple ruptures shown in seismograms of historic earthquakes (e.g. Chile 1960, Sumatra 2004 and Japan 2011), support this hypothesis. The weaker (Mw = or < 8) (e.g. northern California San Andreas) earthquakes generate dominantly upstream simple fining-up (uni-pulsed) turbidites in single tributary canyons and channels; however, downstream stacked turbidites result from synchronously triggered multiple turbidity currents that deposit in channels below confluences of the tributaries. Both multi-pulsed and stacked turbidites create potentially thick amalgamated-like reservoir sands. Petroleum reservoirs in unconfined basin settings of active tectonic margins may be enhanced because multiple great earthquakes cause seismic strengthening of margin sediment that result in minor MTDs in the turbidite system basin floor deposits (e.g. maximum run-out distances of MTDs across basin floors along active margins are an order of magnitude less than on passive margins). In contrast the MTDs, turbidites and reservoir deposits are equally intermixed on basin floors along passive margins such as the northern Gulf of Mexico. In confined or semi-confined basin settings, earthquake triggering results in potential reservoirs with coeval megaturbidites in proximal settings, thick stacked turbidites downstream, and ponded muddy homogenite turbidites in basin or sub-basin centers.
AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013