Distinguishing salt welds from shale detachments on the inner Texas shelf, western Gulf of Mexico
A. McDonnell, M.R. Hudec and M.P.A. Jackson
Journal name: Basin Research
Issue: Vol 21, No 1, February 2009 pp. 47 - 59
Info: Article, PDF ( 3.36Mb )
Detachment surfaces have important implications for structural restoration, burial-history and thermal modeling, hydrocarbon migration, and diagenesis. We present criteria to distinguish salt welds from shale detachments based on geophysical data from the innerTexas shelf. Here, the Paleogene detachment has been variously interpreted as salt or shale by different people. A newly reprocessed 8200 km2 (3200mi2) 3D seismic volume provides excellent imaging of this detachment, which separates growth-faulted Oligocene-Miocene strata from the underlying, gently folded Cretaceous-Eocene section. Key criteria to evaluate detachment origins include seismic amplitude response, geometry, and relationship to supradetachment and subdetachment reflections. We argue that the detachment is a saltweld because (a) it is imaged as a high-amplitude, discrete reflection; (b) it has a ramp- flat geometry, cutting across underlying reflections; (c) it locally forms bowl- shaped depot roughs interpreted as former diapiric salt feeders; (d) it is overlain by seismically incoherent pods having high-amplitude tops and bases interpreted as remnant salt; and (e) in the depotroughs associated with former diapiric salt feeders the detachment has hints of upturned strata just beneath (possible halokinetic sequences). The inferredweld represents the evacuated remains of a patchy salt canopy emplaced across the study area during the Late Eocene to Early Oligocene. Preliminary examination beyond our study area suggests that this discontinuous canopy may have extended across most of the modern Texas shelf. Most of the salt was expelled from the canopy by loading from prograding Oligo-Miocene deltaic deposits.