Slurry-Flow
Deposits of the Punta Barrosa Formation, Southernmost Andes, Chile
Fildani, Andrea1 (1) Chevron
Energy Technology Company, San Ramon, CA
The Magallanes foreland basin of southern
Chile is marked by the influx
of the sand-rich deep-marine turbidites of the Turonian Punta Barrosa
Formation. At least three key Punta Barrosa Formation outcrops contain a
significant number of mud-rich sandstone beds deposited by flows transitional
between fully turbulent currents, with sediment supported by turbulence, and
cohesive debris flows, with sediment supported by flow strength and
characterized by cohesive rheology. These deposits are here described as
‘slurry beds'. By virtue of their lateral extent and quality of exposure of
sedimentary structures, these outcrops present a unique opportunity to study
slurry beds in detail. The beds commonly show a vertical sequence that
includes, from base to top: heterogeneously structured mud-rich sandstone
organized in variable thickness banding, unstructured mud-rich sandstone, and a
mudstone cap. The mudstone caps are commonly sheared suggesting plastic
behavior during subsequent beds emplacement. Selected slurry flow deposits were
sampled for compositional and textural trends. Alternating light and dark bands
of different scales comprise a primary sedimentary structure type within
mud-rich sandstones very useful in field recognition. Micro-, meso-, and
macrobanding are all present at different intervals together with a variety of
water escape features. Preliminary petrographic and compositional analyses of
bands show that dark bands are clay-rich and finer-grained than light bands.
This work integrates detailed measured sections, lateral correlations, and
petrographic observations with conceptual dynamic models of flow evolution to
explain the evolution of a typical slurry flow and deposition of its associated
mud-rich sandstone.