Detrital Zircon Geochronology Applied to Source-to-Sink Analyses and Exploration: Insights From the Modern Mississippi River and Pleistocene Deepwater Mississippi Fan System

Abstract

Detrital zircon (DZ) U-Pb geochronology enables studies of provenance, tectonic reconstructions, and sedimentary dynamics, thus aiding prediction and exploration for natural resources. North American DZ source terranes are well-defined, and allow for interpretations of sedimentary dynamics of important petroleum systems (e.g., Gulf of Mexico Paleocene-Eocene Wilcox Group). However, modern continent-scale sedimentary dynamics and their influence on DZ populations are incompletely understood. Previous work has demonstrated both quantitative and qualitative relationships between the relative proportions of DZ ages in modern river sediment, areal exposure of DZ sources in a catchment, and relative sediment supply. We will present an analysis of a DZ sample suite including: 1. onshore modern sediment from major tributaries to the Mississippi River, including one Pleistocene terrace sample, and 2. offshore Pleistocene sediments (DSDP sites 614, 615, 620, and PC41-56, 29) from the deep-water Mississippi Fan (DWMF). DZs from modern rivers and the Pleistocene DWMF show a qualitative relationship to areal exposure of DZ source terranes. DZs from the DWMF can be used to semi-quantitatively reconstruct the extent of the Modern Mississippi catchment. Integration of source-to-sink scaling relationships improves system-scale prediction in an exploration context. Results of a quantitative mixing model indicate the Missouri River catchment supplies more than half of the DZs found in modern downstream Mississippi River sediment, and likely dominated supply to the Pleistocene DWMF. Modern downstream Mississippi and Pleistocene DWMF DZs show distinct differences in their age distributions, with modern samples containing fewer young DZs and more abundant Grenville DZs. Possible explanations include propagation of late Pleistocene climate signal through the Mississippi system, or, alternatively, anthropogenic sediment impoundment profoundly affect DZ age spectra in the Mississippi River. A Pleistocene terrace sample supports an increase in sediment supply from the Upper Mississippi and Missouri catchments to the DWMF; however, further work is required to reconcile modern and Pleistocene records. These interpretations have implications for concepts of signal propagation through sedimentary systems and inversion of stratigraphic records. These results highlight the utility of DZs as a tool for understanding source-to-sink systems and for use in exploration geology.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016