Salt tectonics and seismic stratigraphy of the offshore Mississippi delta region, Gulf of Mexico

• Main Author: Sunwoo, Don
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1995
• Subjects: Geology; Geophysical engineering; Geophysics; Oceanography; Physical oceanography
• ISBN: 9798208643044

The outer continental shelf (OCS) and upper slope area in the vicinity of the Mississippi delta, northern Gulf of Mexico, are complex in geology due to high sedimentation, and deformation and movement of underlying Jurassic salt. Analysis of over 3600 miles of multichannel seismic data integrated with well data serves to detail the structural and stratigraphic evolution of the area. The structural and stratigraphic analysis of the Upper Jurassic sequence boundaries suggests that the pre-salt basement structure and configuration strongly influenced the distribution and thickness of Middle Jurassic (Callovian) salt, and the structural and stratigraphic development of the overlying Upper Jurassic sedimentary succession. Three types of salt structures have been identified in the offshore Mississippi delta region: salt rollers, sheets, and diapirs. The salt structures represent different stages in the structural evolution of salt in the area. Salt rollers characterize the Upper Jurassic section in the present-day shelf northeast of the Lower Cretaceous shelf edge. Only a thin ($<$2215 ft or 675 m) layer of salt was deposited here. Salt rollers tend to develop on downthrown sides of growth faults. The growth faults flatten with depth along a gently basinward-dipping detachment surface and appear to root in underlying mobile salt. Sediment loading during Oxfordian-age Smackover interval was responsible for development of the rollers. Isolated salt diapirs and salt sheets characterize the basinal sediments southwest of the Lower Cretaceous shelf edge, where prediapir salt was at least 6560 ft (2000 m) thick. Salt sheets of Late Cretaceous-Paleogene age (?) occur as isolated bodies buried beneath 4-5 seconds of sediments (approximately 15750-21650 ft or 4.8-6.6 km). Tops of most salt diapirs typically lie between 1 second and the seafloor. Thick Middle-Late Miocene sediment loading caused reactivation of the Late Cretaceous-Paleogene salt sheets and growth of a second generation of diapirs late. Tertiary sequence stratigraphic interpretation suggests that Paleogene and Neogene strata are distinguished by different depositional histories and stratigraphies. Sediment-starved thin flat-lying deposition characterizes the Paleogene. Neogene depositional sequences are distinguished by an increase in sedimentation rate and broad prograding clinoforms. I have identified five 3rd-order sequences in the Miocene section. Most sequence boundaries are characterized by onlap and unconformities. Progradational clinoform patterns are the most significant reflection configurations and characterize both lowstand and highstand systems tracts. Clinoform patterns are mostly evident near the paleoshelf-slope transition zone. I interpret the clinoform patterns in the lowstand systems tract as shelf-edge deltaic complex that formed during slowly rising sea-level. Continued sediment supply during highstands resulted in rapid progradation of the delta.