HR: 1340h
AN: OS33A-0998    [Abstracts]
TI: Constraining the Controls on the Deposition of Deep-Water Conglomerates, Upper Cretaceous Cerro Toro Formation, Magallanes Basin, Chile
AU: * Bernhardt, A
EM: anne82@stanford.edu
AF: Department of Geological and Environmental Sciences, 450 Serra Mall, Building 320, Stanford, CA 94305-2115, United States
AU: Lowe, D R
EM: lowe@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, 450 Serra Mall, Building 320, Stanford, CA 94305-2115, United States
AB: The Upper Cretaceous Cerro Toro Formation in the Magallanes foreland basin exposes several deep-water, conglomeratic channel complexes, representing the cyclic influx of coarse-grained sediment into the basin, that are separated by thick successions of thin-bedded, mud-rich turbidites. The primary objective of this study is to better constrain the controls on the cyclicity of coarse sediment deposition in the Magallanes Basin during the Late Cretaceous. The growing Andean fold-and-thrust belt to the west of the Magallanes Basin during Cerro Toro deposition suggests that active tectonics and possibly arc-related magmatism were key controls on sediment supply. To address the relative influence of tectonism, single grain age dating (U-Pb) on detrital zircons using Sensitive High Resolution Ion Micro Probe Reverse Geometry (SHRIMP RG) is coupled with conventional petrographic analysis of the basal sandstone and conglomerate compositions of each channel complex. In the event that major uplift or magmatic activity is responsible for the influx of coarse debris deposited as the distinct channel complexes, new zircon age populations as well as modified sandstone and conglomerate compositions will appear. These may be as a result of unroofing of deeper-level older rocks, emplacement of thrust sheets, or increasingly younger magmatic activity. To provide age constrains on the distinct channel complexes 87Sr/86Sr isotope stratigraphy on Inoceramus shells is combined with the U-Pb dating of volcanic zircons in ash layers. Preliminary strontium isotope results are consistent with the strontium isotope curve for the global oceans during the Upper Cretaceous. The ash layers contain abundant volcanic zircon grains. This study will improve our understanding of the evolution of the Southern Patagonian Andean arc and its relative influence on deep-water sedimentation in the adjacent retroarc foreland basin.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3022 Marine sediments: processes and transport
DE: 4999 General or miscellaneous
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting