Abstract: Xenolithic Inclusions Within the Salt at Weeks Island, Louisiana and Their Significance

Brian E. Lock, Timothy W. Duex

The salt seen in Gulf Coast mines is predominantly halite, with a few percent of anhydrite and traces of other evaporite minerals. Complexly folded salt structure is picked out by subtle compositional banding and interpreted as highly stretched bedding. Inclusions of non-evaporite rocks also tend to be distributed along the same banding.

The non-evaporite lithologies, interpreted as xenoliths picked up by the salt during its rise to the surface, are predominantly composed of sandstone and shale, highly brecciated and permeated by salt and generally colored red, brown or yellow. The color may be from oxidation of iron-rich mine waters. Fossils (Oligocene forams) have only been reported from one location, a band of dark shale close to the margin of the Belle Isle dome and suggested by Kupfer to be shale-sheath caught up in the salt.

Petrographic examination of several sand samples reveals well-sorted, well-rounded, frosted grains, suggesting an eolian origin. This interpretation would be most consistent with an origin within the Jurassic, either just above or even below the Mother Salt - sub-salt inclusions have previously been documented from Persian Gulf domes. Two different serpentinized peridotite samples have also been recovered from the mine; these are interpreted as sub-salt lithologies, perhaps from mantle-derived intrusions along a fundamental fault responsible for the NW-SE Five Islands trend. This fault parallels a pattern recognized many years ago by Fisk and perhaps related to the early opening of the Gulf of Mexico.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas