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Janok P. Bhattacharya1,
Russell K. Davies2
(1) University of Texas at Dallas, Richardson, TX
(2) ARCO, Plano, TX
Abstract: Outcrop analogs of growth faulted reservoirs, in the Delta Front to prodelta transition, Ferron Sandstone, Utah
Synsedimentary normal faults at the base of the Cretaceous Ferron sandstone along well-exposed cliff walls in central Utah are outcrop analogs to reservoirs compartmentalized by growth faults. Detailed mapping demonstrates the interplay between fault development and sand deposition and the expected compartmentalization in like reservoirs.
Delta front sandstones form 12-meter thick, upwards-coarsening facies successions that prograded over muddy prodelta facies of the Tununk shale. Soft-sediment deformation within the Tununk, induced by compaction, likely accommodated the delta front and terminal distributary channel sands. Cliff sections oriented parallel to progradation, show the thickest sands accumulated within hangingwalls of three sets of listric normal faults with an average spacing of 15-20m. The timing of the faults is complex with some faults showing multiple stages of movement. The earliest active faults offset a 2m thick rippled to flat-stratified sandstone at the top of the pre-growth section. A cross-bedded sandstone overlying the flat-stratified sand is in turn eroded by cross-bedded terminal distributary channel sandstones. Cross-sets in the hangingwalls are up to several meters-thick, immediately adjacent to the faults, but decrease to decimeter scale within the more distal hangingwalls. The channel sandstones thicken into the hangingwall of the proximal and distal fault sets indicating a successive fault development during the youngest depositional cycle. Offlapping channel sandstones consist of both upstream and downstream accreting bar deposits.
These observations support a complex fault history and style for growth fault development rather than a progressive development of faults from nearshore to farshore as is conventionally interpreted.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana