Distinguishing salt welds from shale detachments on the inner Texas shelf, western Gulf of Mexico

Abstract

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 di¡erent people. A newly reprocessed 8200 km 2 (3200 mi 2 ) 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 re£ections.We argue that the detachment is a salt weld because (a) it is imaged as a high-amplitude, discrete re£ection; (b) it has a ramp-£at geometry, cutting across underlying re£ections; (c) it locally forms bowl-shaped depotroughs 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 inferred weld 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.

Active fault motion in a coastal wetland: Matagorda, Texas

“…1b). McDonnell et al (2008) presented a line from a 3D seismic survey that shows a similar feature, mapped as a portion of the Clemente-Tomas fault system in the same general location. The Radovich et al (2007) line additionally depicts a cluster of faults that branch from the same base at~3000 m depth, and stretch towards the surface; the faults in this cluster cover~15,000 m of cross-section across the 2D seismic line.…”

Coeval extension and shortening above and below salt canopies on an uplifted, continental margin: Application to the northern Gulf of Mexico

“…Dal et al (2006) suggested that contractional features beneath the shelf are Paleocene-Eocene in age and record toe-of-slope shortening. Partly, on the basis of drilling results from the deep-shelf gas play, McDonnell et al (2009McDonnell et al ( , 2010 and Jackson et al (2011) argued that most of the shortening is Oligocene-Miocene.…”

Origin of transverse folds in an extensional growth-fault setting: Evidence from an extensive seismic volume in the western Gulf of Mexico

“…his Figs. 9 and 10) may be remnant salt lenses as described by McDonnell et al (2009) in the present study area. However, we cannot exclude the presence of duplexes in the poorly imaged Oligocene section.…”

“…In contrast, in the southwest, all the pre-Miocene time-structure maps are generally subdued, suggesting thinner salt. Lenses of remnant salt there indicate that at least some allochthonous salt was formerly present (McDonnell et al, 2009). The transition between thicker and thinner salt is roughly below the updip limit of major corrugations in the Miocene detachment (Figs.…”

“…The Oligocene detachment is a discontinuous salt weld representing the evacuated remains of a patchy salt canopy emplaced across the study area during the Late Eocene to Early Oligocene (McDonnell et al, 2009). The detachment separates OligoMiocene growth-faulted strata above from gently folded JurassicEocene strata below.…”