F.J. Shaub, 1983. "Growth Faults on the Southwestern Margin of the Gulf of Mexico", 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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Along the southwestern margin of the Gulf of Mexico, growth fault systems, including very large individual growth faults, occur frequently within thick sedimentary sections underlying the shelf and upper slope. Such systems were noted offshore of the Mexican states of Tamaulipas and Vera Cruz and in the Bay of Campeche in multichannel surveys conducted by the University of Texas Institute of Geophysics (UTIG; Figure 1). Although the thick sediment column is continuous along all these areas, the growth faults studied are ascribed to different structural styles. Off Tamaulipas, growth faulting occurs in normally de-watering, alternating sandstone/shale sections that are adjacent to or overlie under-compacted shale masses. Secondarily, salt and/or shale intrusives distort the sediment column, and gravity slide-and-thrust fault structures may core rollover anticlines. On the continental shelf and slope of the state of Vera Cruz, fold structures known as the Mexican Ridges were interpreted as the result of thick competent sand and shale layers sliding downslope on decollement zones within thick incompetent shales (Buffler et al, 1979). This downslope movement (i.e., removal of section) was accompanied by deposition within an extensive shelf growth fault system. in the Bay of Campeche, the location of some growth faults and salt withdrawal synclines may be controlled by block faults at depth.
Data from each of these locales are presented here to illustrate this structural diversity. Seismic reflection characteristics are reviewed (Vail et al, 1977) and the resulting lithological and structural interpretations are presented. Faulting mechanisms are briefly discussed. The sections included here have not been migrated. Also, in the interest of clarity, some but not all of the interpretable faults and other geologic features have been indicated on the interpreted sections. The estimated depths were obtained by simply assuming a 3 km/sec (1.9 mi/sec) velocity for the upper 3 secs of section, and 4 km/sec (2.5 mi/sec) for the 4 to 7 secs portion.
Multichannel dip line WG-3W-C, -D along the continental slope and shelf break off Tamaulipas, is presented in Figure 2 and 4 (see also Watkins et al, 1976). Figure 3 and 5 are an expanded view of WG-3W-D at the shelf break. The seismic characteristics of this line are as follows: from water bottom to 3 secs, the resolved reflections are high-frequency, of medium- to high-amplitude, discontinuous and usually divergent (Figures 2, 3). Instead of following the water bottom and dipping more or less basinward, these reflections usually dip toward land. Intermittent zones are acoustically transparent. Two prominent intrusive structures underlie the central continental slope. At 3 to 3.5 secs (left half of Figure 2) a discontinuous, high-frequency zone of wavy reflections delineates several deep anticlinal features. Below 3.5 secs, the reflections beneath the shelf break usually dip basinward; they are slightly wavy, low-amplitude, moderate frequency, and discontinuous. There are few useful arrivals below 3.5 secs from the slope; most of this record shows no resolution or consists of multiples and uninterpretable complex structures.