15Earth-surface processes operate across erosionally dominated landscapes and 16 deliver sediment to depositional systems that can be preserved over a range of timescales. 17

Magallanes foreland basin, Chile and Argentina, 51°30 Kinematic evolution of the Patagonian retroarc fold-and-thrust belt and Email alerting services articles cite this article to receive free e-mail alerts when new www.gsapubs.org/cgi/alerts click Subscribe America Bulletin to subscribe to Geological Society of www.gsapubs.org/subscriptions/ click Permission request to contact GSA http://www.geosociety.org/pubs/copyrt.htm#gsa click official positions of the Society. citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect presentation of diverse opinions and positions by scientists worldwide, regardless of their race, includes a reference to the article's full citation. GSA provides this and other forums for the the abstracts only of their articles on their own or their organization's Web site providing the posting to further education and science. This file may not be posted to any Web site, but authors may post works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent their employment. Individual scientists are hereby granted permission, without fees or further

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The processes within deep-sea sedimentrouting systems are diffi cult to directly monitor. Therefore, we rely on other means to decipher the sequence and relative magnitude of the events related to erosion, sediment bypass, and deposition within channels that crosscut the seascape, and in particular, continental slopes. In this analysis, we examine the nature of slope channel fi ll in outcrop (Cretaceous Tres Pasos Formation, southern Chile) in order to evaluate the geological evidence of the full channel cycle, from inception to terminal infi ll with sediment, and we attempt to provide insight into the enigmatic deep-sea processes that are critical for a comprehensive understanding of Earth surface dynamics. In the stratigraphic record, slope channel fi lls are typically represented by sandstoneor conglomerate-dominated deposits that defi ne channelform sedimentary bodies tens of meters thick and hundreds of meters across. Despite the prevalence of coarse-grained sediment, key information is recorded in the fi ne-grained deposits locally preserved within the channelform bodies, as well as a breadth of scours or internal channelform stratal surfaces. These characteristics preserve the record of protracted sedimentary bypass and erosion. In many instances, the life of a slope channel is dominated by sedimentary bypass, and the stratigraphic record is biased by the products of shorter-lived channel fi lling and abandonment.

Contrary to widely used sequence-stratigraphic models, lowstand fans are only part of the turbidite depositional record; our analysis reveals that a comparable volume of coarsegrained sediment has been deposited in California borderland deep-water basins regardless of sea level. Sedimentation rates and periods of active sediment transport have been determined for deep-water canyon-channel systems contributing to the southeastern Gulf of Santa Catalina and San Diego Trough since 40 ka using an extensive grid of high-resolution and deep-penetration seismic-refl ection data. A regional seismic-refl ection horizon (40 ka) has been correlated across the study area using radiocarbon age dates from the Mohole borehole and U.S. Geological Survey piston cores. This study focused on the submarine fans fed by the Oceanside, Carlsbad, and La Jolla Canyons, all of which head within the length of the Oceanside littoral cell. The Oceanside Canyon-channel system was active from 45 to 13 ka, and the Carlsbad system was active from 50 (or earlier) to 10 ka. The La Jolla system was active over two periods, from 50 (or earlier) to 40 ka, and from 13 ka to the present. One or more of these canyon-channel systems have been active regardless of sea level. During sea-level fl uctuation, shelf width between the canyon head and the littoral zone is the primary control on canyonchannel system activity. Highstand fan deposition occurs when a majority of the sediment within the Oceanside littoral cell is intercepted by one of the canyon heads, currently La Jolla Canyon. Since 40 ka, the sedimentation rate on the La Jolla highstand fan has been >2 times the combined rates on the Oceanside and Carlsbad lowstand fans.