Isochores and 3-D visualization of rising and falling slat diapirs

• Published in: Marine and petroleum geology 1999-12, Vol.16 (8), p.849-861
• Main Authors: Guglielmo, Giovanni, Vendeville, Bruno C., Jackson, Martin P.A.
• Format: Article
• Language: English
• Subjects: 3-D visualization; Applied sciences; Crude oil, natural gas and petroleum products; Diapir; Earth sciences; Earth, ocean, space; Energy; Exact sciences and technology; Extension; Fuels; Geology and geochemistry. Geological and geochemical prospecting. Petroliferous series; Hydrocarbons; Isochores; Prospecting and exploration; Prospecting and production of crude oil, natural gas, oil shales and tar sands; Salt tectonics; Sedimentary rocks; Stratigraphy
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/S0264-8172(99)00037-9

Diapir fall, which was predicted by physical models, has been identified in salt provinces, such as the South Atlantic margins, the North Sea, and the Paradox Basin (Colorado–Utah). However the 3-D geometry of falling diapirs and their country rock is still poorly understood. 3-D visualization and isochore patterns from a physical model help elucidate this geometry. The model initially comprised a unit of viscous silicone overlain by a prekinematic sand unit. Sand units representing brittle sediments were deposited episodically during gravity gliding and spreading. Regional extension triggered and eventually widened salt walls, causing them to sag. The 3-D visualization shows that regional hydrocarbon migration, which tends to be seaward during diapir rise and landward during diapir fall, can potentially be orthogonal to local migration along grabens at soft-linked zones of relay ramps. Furthermore, anticlinal culminations may form (1) in horsts that bend along strike and (2) adjoining the fork of Y-shaped salt walls. Sequential isochore maps of the overburden show how patterns of sedimentation, deformation, and underlying salt thickness changed through time. Isochores of prekinematic units record only strain: thinned belts record early extension. In contrast, isochores of synkinematic units record mostly thickness variations due to deposition on actively deforming topography. Isochores above sagging diapirs identify the thickest part of crestal depocenters, where the most rapid sagging occurred in regions of maximum extension near the unbuttressed downdip part of the gravity-spreading system. Additionally, asymmetric isochore patterns may reveal underlying half-grabens or tilted symmetric grabens. In relay systems, overlying isochores may indicate which part of a salt wall rose to compensate for sagging elsewhere in the relay.