Abstract

The shallow sea off southern Florida is the site of deposition for a complex suite of carbonate sediments, but the area has not received as much recognition as the Bahamian Banks and Batabano Bay. An arcuate chain of islands, the Florida Keys, separate the area into two major sedimentary environments: Florida Bay, which lies between the Keys and the mainland; and the Florida reef tract, which is a shallow open shelf between the Keys and the Florida Straits.

Florida Bay is a semirestricted shelf lagoon having little tidal communication with the open sea. Consequently, the water chemistry fluctuates strongly with climatic changes. The biota is restricted to hardy species and varies radically in different subenvironments of the bay. The sediments consist of carbonate muds with a small amount of included skeletal debris. They are deposited in peculiar linear and sinuous, often interconnected, mud banks that are dotted with mangrove islands.

The Florida reef tract contains a complex and varied biota and has unrestructed tidal exchange with the northward flowing Florida Current. The outer margin of the shallow shelf hosts discontinuous coral reefs that provide considerable protection to the four- to five-mile wide reef tract. Skeletal and pelletoidal carbonate sands are deposited adjacent to the reefs and in elongate offshore bars immediately landward and parallel to the reef trend. The inner reef tract is characterized by muddy carbonate sediments that fill in the topographic depressions and locally build into banks. These carbonate mud build-ups resemble many ancient bioherms but grow in shallow well-protected waters. The modern bioherms differ from reefs in that they are accumulating in the absence of vigorous wave action, there is no rigid organic framework, and there is no active organic cementing or binding process. Muddy carbonate banks of this type may provide some insight into the problems of fossil "reefs" that have no rigid organic frame.