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Paleomagnetic and stratigraphic techniques for identifying sediment processes on continental margins

  • Author(s): Schwehr, Kurt
  • et al.
Abstract

Understanding the origin of stratigraphic and morphologic features, whether they are formed by primary deposition or are the consequence of post-depositional alteration, is the critical first step to determining the history and evolution of continental margins. I have developed a new approach that when combined with prior geological and geophysical data, provides new constraints on the origin of stratigraphic sequences. This approach can detect high water content that could evolve into overpressure. Such zones have the potential to develop into slope failures. In addition, this approach can determine if morphologic features observed on many continental margins are current- controlled bedforms or retrogressive slides. The method combines anisotropy of magnetic susceptibility (AMS) with CHIRP seismic data, which provides new insights into the processes responsible for strata formation. First, I explore the limb of a slump in the Ardath Shale in the cliffs of La Jolla, CA. Laterally adjacent to the observed slump, AMS is able to identify a ̀̀crypto-slump'' that is not directly identifiable in outcrop. Next, a study of the Santa Barbara basin explores the rapid deposition and deformation occurring on the northern slope, where AMS combined with other rock magnetic techniques distinguished diagenesis from zones of excess water and overconsolidation. Finally, I use the AMS approach to address the controversy regarding the formation of the Humboldt Slide. Based on morphology observed in CHIRP seismic data and the AMS signature of collocated piston cores, the Humboldt Slide is composed of a series of sediment waves, not a thin skinned deformation feature

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