Sinex, Bradford J.1, Micheal Gardner2
(1) Colorado School of Mines, Golden, CO
ABSTRACT: Architecture of Upper Slope Strata, Upper Brushy Canyon Formation, Northern Delaware Mountains
The high gradient and bathymetric profile of marine slopes form an unstable transition zone between the shelf and basin. Mass-wasting dominates the upper slope setting, whereas erosion and deposition of predominately fine-grained sediment gravity flow deposits characterize the lower slope. The record of sediment gravity flow bypass across the upper slope is largely inferred from this pattern, but the sedimentology and facies that record bypass remains poorly understood.
Outcrops of the Upper Brushy Canyon Formation (UBRC) in Guadalupe Mountains National Park (GMNP) provide an opportunity to directly relate sediment gravity flow processes to the architecture of upper slope strata and document these relationships in three dimensions. Faulting in the outcrop exposes stratigraphic relationships across multiple cliff face exposures. Fault restoration has been achieved through structural mapping, integration of subsurface data behind the outcrop and correlation of a high-resolution stratigraphic framework.
Guadalupe Canyon confirms that UBRC strata located basinward but within the same sandstone fairway of the sand-poor UBRC outcrops in GMNP is extremely sand-rich. The 40% basinward increase from the outcrop to nearby subsurface data down-dip suggests significant bypass. Bypass indicators include siltstone drapes on channel bars, interbedded sand and silt showing conspicuous grain-size variations, closely spaced erosional surfaces, and reoccupation of channel bases. Mass-wasting, a common upper slope process, can be demonstrated by discordant surfaces, rotated blocks, and slump blocks. Multistory channel complexes show an upward change from top truncated complexes with low net-to-gross to a high net to gross, multistory complex that shows multiple channel reincisions.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.