Lacustrine-Fluvial Transitions in a Small Intermontane Valley, Eocene Challis Volcanic Field, Idaho

  1. James D. L. White3 and
  2. Nancy R. Riggs4
  1. B. A. Palmer1 and
  2. E. P. Shawkey2

Published Online: 24 MAR 2009

DOI: 10.1002/9781444304251.ch9

Volcaniclastic Sedimentation in Lacustrine Settings

Volcaniclastic Sedimentation in Lacustrine Settings

How to Cite

Palmer, B. A. and Shawkey, E. P. (2001) Lacustrine-Fluvial Transitions in a Small Intermontane Valley, Eocene Challis Volcanic Field, Idaho, in Volcaniclastic Sedimentation in Lacustrine Settings (eds J. D. L. White and N. R. Riggs), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304251.ch9

Editor Information

  1. 3

    Department of Geology, University of Otago, PO Box 56, Dunedin, 9015, New Zealand

  2. 4

    Geology Department, Northern Arizona University, Box 4099, Flagstaff, AZ 86011, USA

Author Information

  1. 1

    510 Fourth Street East, Northfield, MN 55057, USA

  2. 2

    Missimer International 8410 College Parkway, Suite 202, Fort Myers, FL 33919, USA

Publication History

  1. Published Online: 24 MAR 2009
  2. Published Print: 18 APR 2001

ISBN Information

Print ISBN: 9780632058471

Online ISBN: 9781444304251

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Keywords:

  • lacustrine-fluvial transitions in a small intermontane valley, Eocene Challis volcanic field, Idaho;
  • east fork area - volcanic history, basin palaeogeomorphology, and methods;
  • sedimentology - key sedimentological features and interpretations;
  • volcaniclastic lithofacies in transition intervals;
  • Lacustrine deposits - mudrock assemblage, wedge-sandstone assemblage;
  • fluvial deposits - diamictite assemblage, conglomerate assemblage, sheet-sandstone and mudrock–sandstone assemblages;
  • stratigraphic cross-section of Road Creek;
  • stratigraphy - fluvial to lacustrine surfaces, lacustrine to fluvial surfaces, transitions within lacustrine deposits;
  • landscape evolution - different periods;
  • volcanism - influenced basin drainage patterns, sediment influx and sediment transport process

Summary

Eocene stratigraphy in the East Fork Salmon River area is characterized by alternating lacustrine and fluvial lithofacies that record abrupt shifts in lakes and rivers with time. Additionally, fluvial deposits are characterized by marked lithofacies diversity. Five systems were distinguished by variations in channel geometry and planform, degree of flood basin development and vegetation, and depositional processes. The rivers included: (i) multichannel, sandy bedload river with wide and shallow channels and frequent lahars; (ii) single-channel gravel bedload river with narrow and deep channels; (iii) sandy bedload, multichannel river characterized by rapid lateral migration and avulsion of the channel belt; (iv) single- or multichannel sandy mixed load river with well-developed, vegetated flood basin; and (v) multichannel gravel bedload river, with wide and deep channels.

Lithofacies diversity in the study area indicates that the East Fork depositional system was very sensitive to changes in extrinsic variables, which occurred frequently enough to keep the system close to threshold values for lake development and shoreline position, channel cross-sectional geometry and planform, avulsion and lateral migration, and aggradational and degradational behaviour. Evolution of the East Fork landscape was influenced primarily by volcanic activity, which included lava eruptions and explosive eruptions from a stratovolcano and cauldron complex. Volcanism influenced basin drainage patterns, sediment influx (size and rate), and sediment transport process (lahar versus streamflow). The most dramatic result of eruptions was the formation of a lake in the palaeovalley and changes in lake level. Lava eruptions downstream of the study area, to the south, blocked the palaeodrainage, producing a long-term change in basin palaeophysiography. Apparent lake-level fall resulted when caldera-forming pyroclastic eruptions emplaced thick (to 20 m total) deposits in the lake, causing the shoreline to retreat southward. Volcanism was also the major influence on development of fluvial style for all but the multichannel, gravel bedload river, and the only major episode of laharic activity occurred during a rare period of stratovolcano volcanism north of the study area.