Late miocene-holocene canyon incision in the western Altiplano, northern Chile: Tectonic or climatic forcing?

Marcelo García, Rodrigo Riquelme, Marcelo Farías, Gérard Hérail, Reynaldo Charrier

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48 Citations (Scopus)

Abstract

Major fluvial incision (600-1000 m) affecting the Coastal Cordillera and Central Depression of northern Chile is analysed to evaluate supposed coeval uplift of the Altiplano and/or climatic changes in the Atacama Desert. The timing of the beginning of incision is constrained by the age of deposition of the Central Depression top. In the north (18-19°S), this top corresponds to fluvial gravels accumulated between 11.9 ± 0.6 Ma and 8.3 ±0.5 Ma, which are genetically related to semiarid climate and to an eastward poorly dissected parallel drainage network that developed between 15.0 ± 0.6 and 11.2 ±0.6 Ma; thus, gravel deposition ended at 11.9-11.2 Ma. To the south (19-20°S), the Central Depression top corresponds to c. 6Ma alluvial deposits. Stratigraphically determined canyon ages and knickzone locations indicate that southward dissection began later and/or developed under a regime of lower erosion capacity owing to drier climate. Vertical incision rate evolution is compatible with eastward knickzone migration. Dissection required a considerable altitude difference between ancient and present-day river base levels, which was achieved predominantly by basin infill on an already partially elevated bedrock. Therefore subsequent incision would have been triggered by local semiarid climatic periods rather than by contemporaneous surface uplift. Exoreic canyons occur when climatic conditions in the catchments are arid-semiarid whereas endoreism is developed when these conditions in catchments are hyperarid.

Original languageEnglish
Pages (from-to)1047-1060
Number of pages14
JournalJournal of the Geological Society
Volume168
Issue number4
DOIs
Publication statusPublished - Jul 2011

ASJC Scopus subject areas

  • Geology

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