Department of Geology and Geological
Engineering, Colorado School of Mines, Golden, CO 80401
Abstract: Portrait of a Basin-Floor Fan for Sandy Deep-Water Systems, Permian Lower Brushy Canyon Fm., Delaware Mountains, West Texas
Summary
Outcrops of the Lower Brushy Canyon Formation at Colleen Canyon expose a basin-floor fan positioned 32 km from its shelf margin. Across a 4 km2 area of this sand-rich succession, laterally continuous but vertically partitioned, non-amalgamated sandstone sheets encase isolated multistory to multilateral channel complexes. Laterally continuous organic-rich siltstones divide the lower Brushy into five stratigraphic cycles that change upward from higher energy, amalgamated channelform to lower energy, non-amalgamated lobeform architectural elements. Cycles 1 (92% sandstone) and 2 (93% sandstone) contain the highest proportion of channel complexes. Cycles 3 (63% sandstone), 4 (78% sandstone), and 5 (81% sandstone) are dominated by lobeform elements.
Four principle architectural elements compose stratigraphic cycles; these include 1) lobeform (~77% of outcrop), 2) channelform (~12%), 3) wedge-shaped overbank (~1%), and 4) tabular suspension sheets (~11%). Lobeform elements (2-6 m thick, >200 m wide) are partitioned vertically by thin silt breaks and have flat bases and convex-up tops. The dominant facies are structureless and stratified sandstones. Multistory channel complexes (25 m thick, 400 m wide) consist of clustered channel fills (4 m thick, 100s of m wide) that widen and become more multilateral upward and interfinger with flanking beds to produce a serrated channel margin. Wedge-shaped overbank elements (~5 m thick and ~150 m wide) flank channels and are composed of smaller bi-convex channelform bodies encased in climbing ripple laminae. Tabular sheets of suspension deposited siltstones form the most continuous sediment bodies (km wide and up to 4 m thick).
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas