External Controls on Deep-Water Depositional Systems
The principal objective of the meeting from which this set of papers arose was to gain an overview of the current state of knowledge of the roles and interplays of external controls on deposition in deep marine environments. By external controls we mean allocyclic or allogenic factors, i.e., those that are unrelated to the self-organization of the depositional system (autocyclic or autogenic); principal among these are climate, sea level, sediment supply, and tectonics. One of the big questions that the meeting sought to address concerned the comparability of the recent high-frequency, high-resolution record with the older, generally lower-frequency stratigraphic record of “deep time”; to what extent are the apparent differences a function of resolution, or of comparisons between a glacial and a nonglacial Earth? In fact, as the papers in this volume illustrate, the variability between individual systems, even in Late Glacial time, and the paucity of constraints on older systems makes these questions difficult to answer, but some useful conclusions can be drawn. The papers presented at the meeting were organized into themes that included: overviews of glacial sea-level change, and of climate modeling; external controls on large river-fed submarine fans, including the effects of climate and sea level on the fluvial system itself; influences of climate, sea level, and tectonics on a range of smaller modern systems; deep marine processes; the outcrop record of the pre-Pleistocene Earth; the subsurface record of the pre-Pleistocene Earth; and syntheses. The organization of the volume largely reflects this structure.
Earthquake Control of Holocene Turbidite Frequency Confirmed by Hemipelagic Sedimentation Chronology on the Cascadia and Northern California Active Continental Margins
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Published:January 01, 2009
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CiteCitation
Julia Gutierrez-Pastor, C. Hans Nelson, Chris Goldfinger, Joel E. Johnson, Carlota Escutia, Andrew Eriksson, Ann E. Morey, The Shipboard Scientific Party, 2009. "Earthquake Control of Holocene Turbidite Frequency Confirmed by Hemipelagic Sedimentation Chronology on the Cascadia and Northern California Active Continental Margins", External Controls on Deep-Water Depositional Systems, Ben Kneller, Ole J. Martinsen, Bill McCaffrey
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Abstract
This paper analyzes recurrence times of Holocene turbidites as proxies for earthquakes on the Cascadia and northern California active margins of western Northern America. We compare the age, frequency, and recurrence time intervals of turbidites using two methods: (1) radiometric dating (14C method), and (2) relative dating, using hemipelagic sediment thickness and sedimentation rates (H method). The two approaches complement each other, and when used together provide a better age framework than 14C ages alone. Comparison of hemipelagic sediment thickness in several cores from the same site is used to evaluate the erosiveness of turbidity currents and improve the correlation of turbidites and consequent paleoseismic history based only on less complete and unrefined data sets of 14C turbidite ages along the continental margin. Chronology of hemipelagic sediment thickness provides (1) the best estimate of minimum recurrence times, which are the most important for seismic hazards risk analysis, and (2) the most complete dataset of recurrence times, which shows a normal distribution pattern for paleoseismic turbidite frequencies. We observe that on these tectonically active continental margins, during the sea-level highstand of Holocene time, triggering of turbidity currents is controlled dominantly by earthquakes, and paleoseismic turbidites have an average recurrence time of ~ 550 yr in northern Cascadia Basin and ~ 200 yr along northern California margin. This difference in frequency of turbidites in a subduction zone compared to a transform-fault margin suggests significant differences in earthquake activity that compare favorably with independent paleoseismic indicators.