Criteria for Interpreting Open Feeders beneath Allochthonous Salt Sheets
Most salt-sheet feeders in the deepwater Gulf of Mexico appear on seismic to be pinched off, based on apparent base-salt reflectors extending across the feeder. However, there are geologic arguments suggesting that many of these vertical feeders are still open. In this presentation we describe these geologic arguments, and suggest one reason why the geology and geophysics may be giving different answers.
We recognize seven criteria that suggest that a salt-sheet feeder is open. These are: (1) widely separated stratal upturns, (2) wide projection of pedestal and root, (3) data wipeout zone below root,
4 post-shortening salt-withdrawal folds,
5 anomalously bright autochthonous salt reflector below the feeder, (6) pullup of autochthonous salt reflector below the feeder, and (7) lack of shortening along strike. Most of these criteria are not diagnostic if used alone, but can be quite compelling when used in combination.
We suggest that some of the apparent base-salt reflectors that extend across the top of feeders may in fact be sutures formed when distal domes or small sheets were overrun by large salt sheets sourced from further upslope. Rather than marking the base of allochthonous salt, these seismic events lie within the salt, and are underlain by open feeders that extend down to the deep source layer.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009