Syndepositional Structures on Mobile Substrates
A.J. Skeryanc, C.R. Kolodny, 1983. "Syndepositional Structures on Mobile Substrates", 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
Download citation file:
The accompanying seismic line is part of a regional dip line located offshore Texas in the Gulf of Mexico. The line traverses three major interrelated syndepositional growth structures typical of the province. These three structures (growth faults, withdrawal synclines, and "growth ridges") develop concurrently with progradation of depositional systems across mobile substrata. The local complexities and regional variations in the observed structural patterns are essentially related to two controlling factors. They are the variation in the depositional environment and the rate of sediment supply to the system.
The regional trend of growth faults is essentially parallel to the shoreline. Locally, patterns vary from linear to arcuate. Growth faults are observed to flatten with depth into a zone of detachment. The downthrown seismic events, which appear to dip more steeply into the fault plane, exhibit a greater rotation with increasing depth. This relationship is apparent on the Lower Miocene expander, which is observed to expand the section over 3,048 m (10,000 ft), at the north end of the seismic line.
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.