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The specifics of the earliest history of Florida are lost in the mist of time.  The oldest rocks that give us a record of the events of the earliest Earth are buried so deeply that they are just about inaccessible. We do know however that Florida's origin lies with that of the southern continents, more likely Africa. Florida fossils recovered from the Early Paleozoic (Ordovician Period to Devonian Period) rocks of Florida indicate that life here was closely related to life in rocks of the same age in South America, Africa and Eurasia, but NOT those of  the US continent. In those days, Florida was part of  a supercontinent we call Gondwanaland, that itself was formed by the earlier welding together of the southern continents, and not part of the northern group of continents called Laurasia.

Presumed location of Fla. in  Mississipian time.

During Late Paleozoic time, Gondwanaland joined with Laurasia to form a single landmass that contained all the existing continents called Pangea. In the Pennsylvanian Period, somewhere around 300 MY ago, Florida was welded to the North American continent, certainly a fait accompli by Permian time.

Location of Fla. by Pennsylvanian  time.

The Jurassic Period
208-144 MY Ago
In Early Jurassic time, the rocks are still terrestrial (deposited on land), representing continental sediments that are washing in the rift grabens that is formed as the Florida Platform separates from the African Plate. The Atlantic Ocean is opening. As North America also separates from South America, the Gulf of Mexico also begins to form, and sea water begins to flood the newly forming Gulf. Beginning in the Late Middle Jurassic, as the growing Gulf is intermittently shut off from oceanic waters, the waters of the Gulf evaporate, depositing over 3000' of evaporites (mainly salt). Eventually, by Late Jurassic, as the Gulf continues to open, circulation is no longer shut off and evaporites are no longer being deposited. Instead, carbonates (limestones and dolomites) are being put down as the first widespread ocean encroachment on land begins and continues into Cretaceous time. 
The Cretaceous Period
144-66.4 MY Ago
In the Early Cretaceous, as seal level continues to rise, carbonate accumulation continues along the margin of the Florida platform. In the early part of the Middle Cretaceous, there is a rapid fall of sea level, soon followed by a rise, to eventually reach the one of the highest sea levels of all times. All along the East Coast, including Florida, a carbonate platform very similar to the Great Barrier Reef develops (except immensely larger) and limestone deposition and reef formation continue through most of the Cretaceous. Climates are warm, and in the Gulf of Mexico, warm currents flow from the Atlantic into the Pacific ocean. 

This carbonate deposition ends before the end of the Cretaceous and there is about a 10 million year gap in the depositional record till deposition resumes in the Middle Paleocene. So, unfortunately, the Florida record is silent on the great extinction at the end of the Cretaceous and its causes. 
On to the Cenozoic