Evaluating the Effects of First-Order Climatic State and Climate Transitions on Sediment Dynamics Using Detrital Zircons in the Amazon Source-to-Sink System

Abstract

Inversion of past tectonic and climatic conditions from stratigraphic records has been a longstanding goal of the sedimentary geoscience community. Likewise, prediction of deposystem extent and scale from sparse subsurface data is a challenge regularly faced by those engaged in resource exploration and development. Detrital provenance studies of stratigraphic archives have previously been applied to paleogeographic and tectonic reconstructions, but application of detrital techniques to signal propagation, e.g. the effects of climate and tectonics on sediment routing systems at multi-millennial timescales, is relatively novel. Here, we present new U-Pb detrital zircon (DZ) geochronology from 10 samples taken from cores recovered from the middle to lower Amazon deep-sea fan (ODP Leg 155) to investigate the roles of climate regime and climatic transitions in source-to-sink connectivity within a continental-scale system at multi-millennial timescales.

Sediment cores ~500 km down-system from the Amazon canyon head are sand-rich, potentially recording middle to latest Pleistocene glacial climates, and preserving a temporal and compositional archive of sediment flux from the South American continent. We integrate our offshore DZ data with published DZ samples from the onshore fluvio-deltaic Amazon system and apply statistical methods and DZ mixing models to understand changing sediment provenance over glacial-interglacial timescales. We compare these results from the Amazon to the continental ice sheet-influenced late Pleistocene to Holocene Mississippi sediment routing system, in which environmental signal propagation into deep-marine archives was facilitated through enhanced water and sediment discharge via processes associated with glacial/deglacial regimes and transition. The Amazon source-to-sink system represents a globally significant, largely ice-free end-member system. These results should shed additional light upon magnitudes and timescales of sediment storage and remobilization in the Amazon system, and whether continental-scale, ice-free systems experience rapid environmental signal propagation, or if signals of climate transitions are efficiently buffered by extensive storage capacity of Amazon floodplains.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018