Understanding
Channel-Overbank Interactions in Deep-Marine Slope
Settings: Architectural Analysis of Channel and Levee Elements in the Neoproterozoic Isaac Formation (Windermere Supergroup), Southern Canadian Cordillera
Schwarz, Ernesto1, Zishann A. Khan1, R. William C. Arnott1
(1)
Well-exposed, periglacial
slope deposits in the Neoproterozoic Isaac Formation
allow channel-fill and genetically-related overbank
elements to be studied in detail. The key to genetically linking these stratal elements is the occurrence of muddy turbidites interbedded with
discontinuous thin granule conglomerate and dune-cross-stratified sandstone
within overbank deposits. These strata drape a
low-relief erosion surface (<1.5 m deep) that occurs at a slightly higher stratigraphic level than the base of the adjacent
channel-fill. Both these surfaces are interpreted to represent erosion and
bypass by energetic flows during channel initiation. Once initiated, most flows
bypassed the channel but also spilled out onto the surrounding overbank area, depositing incomplete and complete Bouma sequences (levee element). The upward-fining and
-thinning trend observed in many levee elements suggests that levee aggradation progressively increased channel confinement,
restricting overspilling to the uppermost dilute
parts of flows. Changes in flow conditions triggered early filling of the
channel by sand/granule-rich, high-concentration flows (amalgamated Ta
divisions) with minor overspill onto the levee. Latest stage of channel infill
is always characterized by thin-bedded deposits suggesting deposition from low-energy, dilute flows (abandonment element). This evolution
is repeated several times in Isaac Formation strata producing vertically
stacked channel-fill elements separated by abandonment elements, and surrounded
by genetically-related levee elements. The fact that the abandonment element
described here is not traceable into the adjacent levee element, but onlaps it, differs from previous outcrop-based examples and
resembles more the configuration observed in several well-imaged, subsurface
examples in which inner levee elements onlap
interpreted outer levee elements.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California