ABSTRACT

The Lower Cretaceous Ferry Lake Anhydrite is one of the most distinctive and widespread sedimentary units within the Gulf Coastal Plain. The formation extends from East Texas across southern Arkansas, northern Louisiana, central Mississippi, and southern Alabama, all the way to southern Florida where it has been correlated with anhydrite beds of the Punta Gorda Formation. The formation consists of alternating carbonates, claystones, and sulphate beds (altered from primary gypsum to anhydrite during burial) deposited in a predominately subaqueous environment within a broad lagoon located shoreward of an extensive reef fringing the shelf edge.

Highly resistive anhydrite beds within the Ferry Lake Anhyrite, and within formations above and below, may be correlated across East Texas, Arkansas, Louisiana and Mississippi by means of a network of closely-spaced electrical logs. The geographic distribution of these anhydrite beds is variable. Some anhydrite beds may be traced across the entire area, whereas other beds are less widespread. The difference in geographic distribution of these anhydrite beds reflects the variation in size and configuration of the extensive lagoonal sea in which these beds were deposited. Water depth, differential subsidence, duration of each evaporitive episode, and areal salinity variation are among the factors that controlled the thickness of individual beds accumulating within the lagoon.

Stratigraphic cross sections and isopach maps demonstrate the regional distribution and thickness of anhydrite beds below, within, and above the Ferry Lake Anhydrite and allow a reconstruction of the depositional history of this interval.