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Joint Meeting Pacific Section, AAPG & Cordilleran Section GSA April 29–May 1, 2005, San José, California

Anatomy of a Levee to Proximal Crevasse Splay (Harp) to Channel-Fill Succession, Neoproterozoic Windermere Supergroup, British Columbia, Canada

R. William C. Arnott
Department of Earth Sciences, Univ of Ottawa, 365 Nicholas Street, ottawa, ON K1N 6N5 Canada, [email protected]

Channel-fill and adjacent lithofacies are well exposed in the deep-marine (Neoproterozoic) Windermere Supergroup. At one location, levee deposits are overlain by proximal crevasse splay (HARP), in turn overlain by channel-fill strata. Levee deposits, which consist of thin-bedded, upper-division turbidites interstratified with thicker, coarser, more complete turbidites (crevasse splay deposits), accumulated adjacent to an active channel. Levee strata are overlain abruptly by a 23 m thick proximal crevasse splay, or HARP. The splay was initiated by avulsion of an adjacent, previously active channel. Energetic turbulent suspensions, now diverted through the levee and into the interchannel area, expanded rapidly, lost capacity, and incrementally constructed the crevasse splay. Depending on the rate of turbulent suspension collapse, two lithofacies were deposited: thin-bedded, fine to medium sandstone Tcd turbidites deposited by low concentration dispersions, or medium-bedded, coarse-tailed-graded, structureless medium sandstone deposited rapidly in submerged hydraulic jumps (turbidites were deposited from reconstituted dispersions that formed along the periphery of the jump). The intercalation of turbidite and structureless sandstone probably indicates lateral migration of the hydraulic jump and consequent compensational stacking of the two lithofacies. Splay deposits are overlain abruptly by a ~14 m channel fill complex comprising 2 channel fills – the channel fills are separated by a zone with abundant mudstone intraclasts. Both channel fills consist of medium- to thick-bedded, normally-graded, coarse/very coarse sandstone and granule conglomerate that show an upward-thinning but poorly-developed upward-fining trend. In addition, both channel fills show well developed lateral accretion surfaces, suggesting that the channels had a sinuous planform.

Posted with permission of The Geological Society of America; abstract also online ( © Copyright 2005 The Geological Society of America (GSA).