J.C. Fluker, III, 1983. "Main Pass and Viosca Knoll, Stratigraphic and Structural Study", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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This line, east of the Mississippi River Delta in Main Pass and Viosca Knoll areas, trends in a northwest-to-southeast direction as indicated on the location plat.
The line displays thick transgressive and regressive sections of Tertiary and Quarternary clastic sediments deposited in offlapping wedges over carbonate beds of Cretaceous age. Both extensional glide plane faults and salt tectonic structuring can be seen. A piercement salt dome at the southeast end of the seismic profile shows its active growth history by the thinning of section onto it.
The northwestern and southeastern ends of the seismic line show the effect of salt diapirism.
Large down-to-the-north faults appear to be associated with breaks in the Cretaceous carbonate section and are probably the structural weak point that allowed the salt to pierce through the sedimentary column. Increased deposition of sediment into the low side of the faults is observed.
Lystric cults are observed in the center of the line (as labeled) on the northwestern edge of the syncline associated with the salt diapir at the southeastern end of the seismic line. These faults are syndepositional, allowing the build up of sediment on their downthrown side and the movement of sediment basinward.
Prograding sediment wedges are noted above the 2.0 sec time line between shotpoints 445 and 265.
These have been labeled as such and arrows indicate the cycle terminations showing the direction of progradation.
An unconformity/erosional surface (as labeled) is noted above and below the 1.0 sec time line between shotpoints 337 and 277. This is evidenced by the termination of cycles into chaotic event zones. This leaves an impression of a scour and fill feature possibly caused by a gravity flow or turbidity/density current.
Fill patterns can be observed by the onlapping cycle terminations seen between shotpoints 193 and 73.
These onlapping events can be noted from the 4.3 sec to 1.0 sec time lines. The fill patterns provide examples of onlap and prograded fill.
Figures & Tables
Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces
Until a few decades ago, structural and regional geology were traditionally the preserve of field geologists. They usually mapped areas of outcropping deformed rocks and supplemented their work by laboratory studies of rock deformation and by theoretical work. Structural geology became tied to the geology of uplifts, folded belts, and underground mines, all of which were accessible to direct observation. Since World War II we have witnessed a tremendous development of geophysics in oceanography and in petroleum geology. Academic geophysicists in oceanography led their geological colleagues into modern plate tectonics and industry geophysicists developed reflection seismology into a superb structural mapping tool that penetrated the subsurface.
Today we are facing a situation where instruction and textbooks in structural geology are almost entirely dedicated to rock deformation, analytical techniques in detailed field geology and summaries of plate tectonics. Illustrations based on reflection seismic profiles are virtually absent in textbooks of structural geology. These texts illustrate only the parts of the proverbial elephant, together with some conjecture, but without ever offering a glimpse of the whole elephant.
Some of the reason cited for the relative scarcity of published reflection profiles are: 1) the confidentiality of exploration data; 2) difficulties in the photographic reduction and reproduction of seismic profiles for a book format; 3) the two-dimensional nature of vertical reflection profiles; and 4) the obvious distortions in reflection profiles that are typically recorded in time.
The AAPG leadership felt that it was time to attempt to correct the situation and to produce this picture and work atlas. The first volumes, of what may become a series of volumes, are addressing an audience that includes: petroleum geologists concerned with structural interpretations; exploration companies that provide in-house training; the AAPG continuing education program; and academic colleagues interested in updating their curricula in structural geology by inclusion of reflection profiles from the “real world” in their teaching.
The atlas is not meant to be a textbook in reflection seismology (instead we listed some at the end of this introduction) nor a text in structural and/or regional geology. Our intent is simply to provide a teaching tool.