Salt, Sediment and Hydrocarbons

The subject of salt deformation has come a long way since the days of "all salt deposits form rolls and diapirs as a simple consequence of their having a lower density than other sediments." But what do we make of the Michigan Basin--almost no salt tectonics there, with 0.6+ km of salt? Clearly the behavior of salt is far more complex than the "lava-lamp" model of the 1960's. When I received this volume, I was pleased to see that it actually deals not only with the presence, behavior and structure of salt, but also how it generates depositional and structural complexities in associated sediments.

A moment of pause came when I opened the book and found that the table of contents was actually a copy of the conference program with its natural groupings of papers, but then discovered that the papers themselves are arranged in strictly alphabetical order. This peculiar organization caused me to shuffle around the volume when reading in order to follow the logical topical associations. Pagination of individual articles appears in the program, but is written small and given in parentheses after the titles. This arrangement works fairly well for an attendee at a conference, but not for post-meeting readers trying to learn about a topic based on what they are reading.

There were four basic divisions in subject matter at the conference (and in the topics of the volume): (1) Geometry and Evolution of Salt Bodies; (2) Salt and Sedimentation; (3) Salt and Hydrocarbons; and (4) Regional Systems of Salt Tectonics (in 4 geographic areas). Two of the seven posters at the meeting are represented by papers, but the others are abstracts only.

The seven papers (plus an abstract) on "Geometry and Evolution of Salt Bodies" (session 1) are excellent, up-to-date presentations. I came away from this part of the volume with a good sense of how diapirs form and function, and even was able to see photos of diapirs that have risen to the surface (for those who do not quite believe it). The concepts of salt movement, as related to salt-disrupted structure, localized pressure anomalies, and even underlying structure, were well detailed. Several of the important figures in this section, however, are nearly illegible either due to excessive size reduction or perhaps to black and white rendition of color prints.

"Salt and Sedimentation" (session 2, represented by 4 papers and 2 abstracts), yields a tantalizing glimpse into the manner in which sediment movement and accumulation can be governed by the rheology of the underlying salt bodies. The fluid response of salt to changes in slope and loading was well described by Kehle (1988), however in these papers, we see this effect in the subtle balance between salt movement and subsequent sedimentation. More of this type of analysis should be carried out.

"Salt and Hydrocarbons" (session 3, made up of 3 papers and 2 abstracts), deals with the effects of salt movement and associated lithologic characteristics on the migration of hydrocarbons into reservoirs. A couple of new, interesting ideas were presented, and more are certainly going to come up in the future.

"Regional Systems of Salt Tectonics" (session 4, 9 papers and 3 extended abstracts) is divided into several parts, although discussions of the Gulf of Mexico dominate. The first seven papers (and an abstract with figures) address the general geology of a rift basin and how it governs structure, sedimentation and subsequent salt behavior. These are well-written reviews, largely about the Gulf of Mexico, and bring in the clues geologists gained from the study of other, younger, rift areas. One paper compares the structural styles developed in South Atlantic salts with those of the Gulf of Mexico, and a second addresses North Sea salt structures. The remaining topics are only represented by abstracts, but I wish they had been full papers.

This volume is well worth its price, but the awkwardness of use caused by an alphabetical succession of papers should have been considered by the editors. Also, the reader really needs the information that should have been given in the occasional blurry sections and maps; they are disturbing flaws. Authors and editors should think in advance about written presentation and be somewhat more considerate in their reproduction plans. The readers of this volume also should be prepared to examine papers written in widely disparate styles, and a few of these are written (and remain) in disturbing jargon, rather than plain English.

Kehle, R.O., 1988, The origin of salt structures, in Evaporites and Hydrocarbons, Columbia University Press, New York, pp. 345-404.

B.C. SCHREIBER
P.O. Box 37
Green Mountain, NC 28740

Source

http://archives.datapages.com/data/sepm/journals/v66-67/data/068/068006/1236.HTM