Geologic History of Florida. By Albert Hine. University Press of Florida, 2013
Albert Hine suggests that if you try to define state of Florida as a physical entity, you run into trouble. Our Florida sits on a submerged and much wider Florida Platform, a huge rock base formed by carbonate sentiment production. The eastern edge of Florida Platform ends abruptly at the Florida Straits but extends 125 miles to the west of the present coastline. Thus a good part of “the real Florida” presently lies under water.
The Florida Platform has been around for at least 200 million years, but the peninsula’s shape depends on sea levels. We are said to be in an inner-ice age; the peninsula has been both fatter and more slender; depending upon how much of Earth’s water has been locked up in glaciers.
We think of our Florida as being flat; its maximum elevation is 345 feet. In fact the western edge Florida platform drops off abruptly with an escarpment or subterranean cliff that is two miles deep, thus a reputable mountain-like elevation.
Hine’s age estimates of the various components of our state are almost too ancient to imagine. Moreover, geologists now have available clocks that can date geologic events with remarkable precision. He quotes an article which describes an event that occurred between 54.911 and 54.912 million years ago – hence within 1000 years.
Peninsular Florida has been part of different supercontinents. Most of North America, including the Florida panhandle, was part of Lauretia. But several chunks of the peninsula were parts of the Florida-Bahamas Block and the Suwannee Basin Block attached to the supercontinent Gondwana, which included also South America and Africa. Three hundred million years ago there was a collision between Gondwana and Lauretia, which pushed up the Appalachian Mountains. Evidence for this; the rock strata in the Appalachians match the much eroded Mauritanide Mountains in Africa.
Hide is aware that the specialized vocabulary used by geologists will overwhelm most non-geologists. He has included a glossary of terms at the end of each of his ten chapters, plus a good index to direct the reader around the book.
On top of the Florida Platform is a more recent layer of carbonate sediments. They are the remains of dead micro-organisms, plants, animals, and mud brought to Florida as a result of its new affiliation with the Appalachians. Initially that sediment flow has been blocked by the Georgia Channel Seaway System, a rift resulting from chunks of continental crust that broke off of Gondwana. But over millions of years this rift was filled by sediments from Appalachia, and the rivers that originated as runoff from the Georgia and Carolina mountains began to flood into Florida.
A later transmission of quartz sand to Florida, Appalachian erosion, was the origin of our quartz-sand beaches. At least that was the case of those beaches up and down the Atlantic coast and much of the beaches along the Gulf. The beaches along the Big Bend and the Florida Keys are, however, not covered by quartz sand but rather by small gravel from the carbonate platform.
Hide admits that this explanation for the arrival of quartz sand is controversial. Others believe that it is the result of the long shore transport. Evidence; under these sandy beaches lay river deltas buried by this north-south drift of sand.
Perhaps the most complicated of his chapters is “The Florida Phosphate Story.” Central-west Florida is the world’s largest source of phosphate, 30% of global production. The mining region is not a pretty site. Phosphate is obtained by first removing an overburden of sedimentary material and then shoveling out the ore from which the phosphate is extracted, using prodigious amounts of water to break up the ore. The residue is then piled up and left.
The phosphate comes from a rich supply of phytoplankton, zooplankton, marine life which was deposited on the ocean floor over the period from twenty-two million to five million years ago. At the time south Florida was not yet attached, and the strong Loop Current – a component of the Gulf Stream – made a bend at about the level of the present Tampa Bay and joined the Gulf Stream as it moved up the Atlantic coast of North America. Its force produced what are called upwellings. Cooler water, nutrient-rich, moved toward the ocean’s surface replacing warmer water now depleted of its nutrients. This phenomenon supported plant and animal marine life, which produced more nutrients that sank to the ocean floor and surfaced again in the continued upwelling.
Albert Hine is a geological oceanographer at the University of South Florida. This wonderful book was published by the University Press of Florida.