--> ABSTRACT: High-Frequency Cyclicity in Quaternary Fan-Delta Deposits of the Andean Fore-Arc: Relative Sea Level Changes and Aseismic Ridge Subduction, by Stephen Flint, E. J. Jolley, P. Turner, G. D. Williams, T. Buddin; #91003 (1990).

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ABSTRACT: High-Frequency Cyclicity in Quaternary Fan-Delta Deposits of the Andean Fore-Arc: Relative Sea Level Changes and Aseismic Ridge Subduction

Stephen Flint, E. J. Jolley, P. Turner, G. D. Williams, T. Buddin

The coast of northern Chile comprises Mesozoic magmatic rocks and Cenozoic-Holocene shallow-marine and alluvial fan/fan-delta sediments.

The structure, landform development, and sedimentary response of the coast between Antofagasta in the south and Arica (600 km to the

north) have been investigated to evaluate the influence of Nazca plate subduction on sea level changes over Quaternary to Holocene times. At Arica, the coastal range is in net extension, characterized by extensional normal faulting and subsidence, similar to 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 boundary 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 yr 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 the effect of eustatic sea level fluctuations.

Subduction of oceanic plate heterogeneities may provide a mechanism for producing cyclicity in sedimentary sequences at a frequency equal to or higher than glacio-eustacy in fore-arc and possibly back-arc sedimentary basins. These sequences will be neither of global extent nor of global synchroneity.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990