HR: 17:30h
AN: T32E-07    [PDF]
TI: Late Cenozoic Evolution of the Mejillones Peninsula, Northern Chile
AU: * Ishman, S E
EM: sishman@geo.siu.edu
AF: Southern Illinois University, Department of Geology 1259 Lincoln Drive, Carbondale, IL 62901-4324 United States
AU: Reilly, T P
EM: geologyboy25@hotmail.com
AF: Southern Illinois University, Department of Geology 1259 Lincoln Drive, Carbondale, IL 62901-4324 United States
AU: Wilson, G S
EM: gary.wilson@stonebow.otago.ac.nz
AF: University of Otago, Department of Geology, Dunedin, 0800-80-80 New Zealand
AU: Martinez-Pardo, R
EM: rumartinpar@hotmail.com
AF: National Museum of Natural History, Section of Paleontology, Santiago, 5303626 Chile
AU: Pinter, N
EM: npinter@geo.siu.edu
AF: Southern Illinois University, Department of Geology 1259 Lincoln Drive, Carbondale, IL 62901-4324 United States
AU: Wilke, H
EM: hwilke@ucn.cl
AF: Universidad Catolica del Norte, Department of Engineering and Geological Sciences, Antofagasta, 5303626 Chile
AU: Chong, G
EM: gchong@ucn.cl
AF: Universidad Catolica del Norte, Department of Engineering and Geological Sciences, Antofagasta, 5303626 Chile
AB: The Mejillones Peninsula, located on the Pacific margin of Northern Chile, contains outer shelf, shelf and coastal terrace deposits that record the paleoceanographic, tectonic, and topographic evolution of the region. Preliminary micropaleontologic, geochemical, sedimentological and geochronological analyses of sedimentary sequences within the Tiburon Basin and uplifted coastal terraces of the Mejillones Peninsula together document Plio-Pleistocene sea-level cyclicity, as well as coeval changes in marine productivity, regional uplift, and displacement on local faults. The sedimentary succession within the Tiburon Basin can be subdivided into a lower set of diatomaceous sedimentary cycles containing thin phosphatic horizons, marine vertebrates and abundant planktonic and benthic foraminifera. Preliminary analyses of these sediments indicate an initial deep-water ($\sim$500 meter) basin with high primary productivity related to upwelling of cold intermediate water interrupted by periods of little to no sediment input. This style of deposition was interrupted by an uplift event, probably involving vertical motion on the Mejillones Fault immediately to the west of the Tiburon Basin, which dominated the character of the upper set of sedimentary cycles and comprise coarse clastic sediments including vertebrate fossils, blocks up to boulder size, interpreted as detritus from the nearby fault scarp, and well-rounded pebbles derived from the interior of the Mejillones Peninsula. This switch from diatomaceous to clastic sedimentary cycles indicates abrupt (1) shallowing of the basin to shelfal (50-100 meters) to nearshore depths, (2) generation of significant local relief on the fault scarp, and (3) large-scale uplift and erosion of the Mejillones Peninsula. An Ar/Ar age of 2.8 $\pm$ .04 Ma from an ash horizon near the top of the succession indicates a Pliocene age for the Tiburon succession, which is consistent with the foraminiferal biostratigraphy of the diatomaceous sequences. At least 10-12 coastal terraces occur within the Mejillones Peninsula, the highest of which can be traced to the margin of the Tiburon Basin and document contemporaneous subaerial exposure, uplift, and continuing sea-level cyclicity through the Quaternary.
DE: 3030 Micropaleontology
DE: 3344 Paleoclimatology
DE: 4556 Sea level variations
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2003 Fall Meeting