Depositional Architecture of Quaternary Fan-Delta Deposits of the Andean Fore-Arc: Relative Sea-Level Changes as a Response to Aseismic Ridge Subduction

  1. David I. M. Macdonald
  1. S. Flint1,
  2. P. Turner2 and
  3. E. J. Jolley2,†

Published Online: 14 APR 2009

DOI: 10.1002/9781444303896.ch5

Sedimentation, Tectonics and Eustasy: Sea-Level Changes at Active Margins

Sedimentation, Tectonics and Eustasy: Sea-Level Changes at Active Margins

How to Cite

Flint, S., Turner, P. and Jolley, E. J. (1991) Depositional Architecture of Quaternary Fan-Delta Deposits of the Andean Fore-Arc: Relative Sea-Level Changes as a Response to Aseismic Ridge Subduction, in Sedimentation, Tectonics and Eustasy: Sea-Level Changes at Active Margins (ed D. I. M. Macdonald), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303896.ch5

Editor Information

  1. British Antarctic Survey, Cambridge, UK

Author Information

  1. 1

    Department of Earth Sciences, University of Liverpool, P.O. Box 147, Liverpool, UK

  2. 2

    School of Earth Sciences, University of Birmingham, P.O. Box 363, Birmingham B15, UK

  1. BP Exploration Company Ltd., St Vincent St., Glasgow, UK

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 13 JUN 1991

ISBN Information

Print ISBN: 9780632030170

Online ISBN: 9781444303896

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Keywords:

  • depositional architecture of Quaternary fan-delta deposits of Andean fore-arc - relative sea-level changes as response to aseismic ridge subduction;
  • sedimentology of coastal fan/fan-delta systems;
  • coastal morphology and sedimentology;
  • Gatico coastal-fan—fan-delta system showing depositional and erosional environments;
  • shallow marine deposits;
  • terrace origin - eustasy versus local tectonics;
  • fan chronology and Quaternary glaciation

Summary

The structure, landform development, and sedimentary response of the coast of northern Chile over a distance of 600 km, between Antofagasta and Arica have been investigated to evaluate the influence of Nazca plate subduction dynamics on sea-level changes from Quaternary to Recent times. Sedimentological and geomorphological analysis of the coastal alluvial-fans–fan-deltas shows that the preserved sequences comprise poorly sorted, subangular gravels (subaerial alluvial fan), interbedded with complex, mixed conglomerate/sandstone units, which are characterized by greater textural maturity and copious marine shell debris. In the mixed sequences, conglomerate clasts are well rounded, moderately well-sorted and have a martix of the shell debris. The sandstones show trough bedding on a metre scale and abundant marine invertebrate burrows.

The present-day morphological organization of the coastal depositional systems comprises currently inactive alluvial fans, cut by canyons up to 10 m deep that act as sediment bypass conduits to sites of shoreline fan-delta progradation. Coupled with the organization of preserved subaerial/subaqueous sediments into crude cycles, these data suggest that relative sea-level changes within the Quaternary may have exerted a strong control on coastal fan development.

At Arica the coastal range is in net extension, characterized by extensional normal faulting and subsidence, in common with much of Chile. South of Arica uplift is recorded by marine terrace development and incision of alluvial fan surfaces; uplift reaches a maximum south of Iquique. The transition between regions in net subsidence and net uplift is marked by north-facing neotectonic normal fault scarps.

Variations in apparent uplift and subsidence are consistent with recently published oceanographic records on relative sea-level changes over a 30-year period. Our data suggest that these regionally variable patterns of coastal uplift along the north Chilean coast are controlled by the subduction of an aseismic ridge, which overprints eustatic sea-level fluctuations. Thus, subduction of oceanic plate heterogeneities may provide a mechanism for producing cyclicity in sedimentary sequences at a frequency equal to or higher than glacio-eustasy in fore-arc and possibly back-arc sedimentary basins. These sequences will be neither of global extent nor globally synchronous.