Guest post by David Middleton

From the U.S. Government Occasionally Does Something Useful Department:

A 1.4-Billion-Pixel Map of the Gulf of Mexico Seafloor

The U.S. Bureau of Ocean Energy Management releases the highest-resolution bathymetry map of the region to date.

A new bathymetry map, created by integrating many 3-D seismic surveys, reveals the Gulf of Mexico’s seafloor in unprecedented detail. Above is a snippet of this map, roughly 220 kilometers wide, showing the central Gulf of Mexico’s complex morphology of salt domes and minibasins. Credit: BOEM

By K. V. Kramer and W. W. Shedd 24 May 2017

The geology of the Gulf of Mexico (GOM) is dynamic, driven not by plate tectonics but by the movement of subsurface bodies of salt. Salt deposits, a remnant of an ocean that existed some 200 million years ago, behave in a certain way when overlain by heavy sediments. They compact, deform, squeeze into cracks, and balloon into overlying material.

Such salt tectonics continue to sculpt the geologic strata and seafloor in the GOM like few other places on Earth. Because of this salt tectonism and a steady supply of sediment delivered to the basin by rivers, the GOM’s seafloor is a terrain continually in flux. Bathymetry is ripe with active faults and escarpments, slump blocks and slides, canyons and channels, sediment waves, pockmarks and mud volcanoes, and other natural oil and gas seeps.

[…]

Eos

The map is freely downloadable in several formats from the BOEM.

From BOEM: “Figure 1. Northern Gulf of Mexico deepwater bathymetry grid created from 3D seismic surveys. The grid defines water depth with 1.4 billion 40-by-40 ft cells and is available in feet and meters. BOEM grid coverage is the area defined by the color in this image. Shaded relief is vertically exaggerated by a factor of five.”

Here is a “before and after” comparison:

(From the Eos article): “Figure 4. Megafurrows carved into the Sigsbee Escarpment and abyssal plain around Green Knoll, central Gulf of Mexico. The furrow fields (see right image), not visible in the previous bathymetry grid (left image), extend more than 200 kilometers along and in front of the escarpment. They form when currents, measured up to 2 knots, excavate the seafloor. The megafurrows, first discovered in 1999 by Texas A&M deep-tow data, can be 1–10 meters deep and 5–50 meters wide [Bryant et al., 2000, 2004]. Credit: BOEM”

The amazing thing about the seafloor topography from the continental shelf edge out to the Sigsbee Escarpment is the fact that it is largely the result of deformation of the Jurassic aged Louann Salt formation.

Generalized cross-section of the Gulf of Mexico. The Luann Salt is labeled “Middle Jurassic Salt.” From Levin, 2006, The Earth Through Time.

During the Late Triassic through Middle Jurassic, the ancestral Gulf of Mexico basin (including East Texas and Gulf Coast basins) served as a great evaporating basin in which seawater from the Atlantic Ocean was concentrated.”  Over 1,000 m of salt, gypsum and other evaporites were deposited during this period.  The evaporites were then quickly  buried by Upper Jurassic aeolian (wind-driven sediments, sand dunes) Norphlet and shallow marine Smackover carbonate formations.  This was then overlain by thousands of feet of Cretaceous and Cenozoic carbonates, sandstones and shales.

Generalized East Texas Stratigraphic Column.  USGS.

Generalized stratigraphic cross section of the Northern Gulf of Mexico (GeoExPro). 

The sediment loading essentially built a subsurface “mountain range” of mobile salt.

Cross section originally from McMoRan, annotated with well data to illustrate how salt, as overburden, can act as a “radiator,” enabling the oil window to exist at previously unexpected depths.

Many of the world’s most prolific oil and gas basins are associated with salt tectonics (GEO ExPro).

The thick evaporite sequences of the Gulf of Mexico may have even been the proximal cause of the K-T extinction.

For anyone with an interest in the salt tectonics of the Gulf of Mexico, I recommend The Prize Beneath the Salt from Schlumberger ,  Gulf of Mexico and Salt’s Effects on Petroleum Systems from GeoExPro.