Florida is in the southeast corner of the United States, and since it borders the sea, its geology has changed dramatically over time. Sedimentary rock is the most common type of rock found in the region, and human and natural events throughout history heavily influence its composition. Because the state’s geology has been a significant determinant of land use policies, we must investigate the origins of this variability in geologic structure and properties. As a result, this paper examines the timeline of events relating to Florida’s geology and their relevance to the present day geology of the state.
About 530 million years ago, Florida was part of Africa forming the vast Gondwanaland before it broke up and together with South America, formed the Pangaea (Hine 50). As a result, some of its geologic features deep into the surface resemble those of Africa even to date. Florida remained as part of North America although it was shallowly submerged when South America drifted away. Rock samples from deep into the surface have an igneous and metamorphic origin with sandstone and shale overlying them. Such geologic composition depicts the conditions prevailing at the time of formation of the supercontinent known as Pangaea. It is upon these basement rocks that carbonate rocks eventual formed gradually resulting in the Florida platform. There is evidence showing that Florida drifted away from Gondwanaland about 300 million years ago (Hine 135).
The present day Florida is believed to be the emerged part of the Florida plateau although the emergence was characterized by varying sea levels so that even already emerged sections got submerged during these variations (Hine 80). Due to this, heavy sedimentation occurred in this part of North America’s continental shelf, with sediments consisting of coral, shellfish as well as skeletons of varying sea animals (Davis 101). During this period, Florida was forming the border between the two plates that formed North and South America. As the layers of this material increased, the weight exerted over the underlying layers increased cementing them so that sedimentary rocks were formed, whose composition was calcium carbonate.
Since the components of the sediments were primarily composed of carbonate, the resulting rock was predominantly limestone. As Mesozoic era was coming to an end, Florida lay beneath a relatively warm ocean and therefore those sea animals that died sank on it forming sediments (Davis 63). The major organisms contributing to this were called Foraminifera. The limestone layers are hundreds of feet to thousand feet thick in some places. The purity of Florida’s limestone is quite high as a result of an ocean current sweeping its coast at the time, deflecting any other material deposits from the sea. Subsequent geologic processes led to the formation of rock layers on top of the limestone layer, but still, the impact of the underlying limestone layer is vivid on the surface (Hine 75). The limestone is a major contributor to the state’s economy due to its utility in the manufacture of cement. Nevertheless, in those sections of the state covered by the rock alone, agriculture is done on an insignificant scale.
The geologic features in the state have their origin from water’s action on limestone. Since limestone is soluble in slightly acidic fresh water, which is abundant on the mainland, limestone features have resulted. Continued action of the water on the limestone rocks lead to the formation of orderly patterns, a geologic feature known as karst scenery. In places where the pattern is not regular, the surface has a honeycombed appearance (Wilson 135). This also led to underground rivers which occasionally emerged to the surface forming springs as well as sinkholes where the earth surface collapses into the voids formed when limestone is dissolved underground (Wilson 76). Depressions on the surface as result of dissolved limestone are also common forming lakes as well as wetlands which define to a great deal the geology of Florida.
In early Miocene period (about 2.3 to 5.3 million years ago) erosion of the Appalachian Mountains led to the transport of siliciclastic sediments to the low attitude, carbonate deposit places most of them along the coast (Davis 70). Enormous amounts of phosphorite material were deposited on the present day Florida most of which is exploited extensively for commercial purposes. With most of these sediments having a volcanic origin, the resulting rocks have an abundance of clay which is mostly utilized for farming forming about 8% of the total state’s surface. Sand is also a common type of sediment from the erosion of the Mountains resulting in the formation of quartz-rich sedimentary rocks (Hine 62). Since sand is poor in compaction, its sediments traveled far south to reach the coastline, and that is why there is a layer of sandstone along the coast. The continuous fluctuation of sea level throughout the later part of the Oligocene period saw clays and sand become major deposits hence adding to those transported from the eroding Appalachian (Hine 49).
The Pleistocene era (2.6 million-10,000 years ago), better known as the ice age, was characterized by extreme sea level changes and massive glacier activity (Davis 75). The difference in sea level reached 400 feet relative to the advancement or retreat of the continental glaciers. When the sea levels were high, limestone accumulated whereas when the levels fell, erosion and dissolution of the already formed limestone sediments occurred Due to the slow formation and purity of the limestone rock, the state is geologically stable (Wilson 41). Despite the occurrence of minor earth tremors, earthquakes do not pose a major threat in the area.
Despite the presence of a limestone basement, the type of soil across Florida varies greatly depending on the location. To the north, the soils are red clay as a result of deposition of finer particles eroded from the Appalachians (Wilson 90). In the ridge, deep sands are predominant having their origin from the eroded materials as well, while the Flatwoods have poorly drained sandy soils being deposited from the sea. Organic soils characterize the Northern Everglades as a result of the proximity to the forest part of the state where falling leaves provided humus to the soils. Limerock based soils are common in the extreme south where deposition from the highlands is insignificant, and deposited material is washed away by the sea leaving behind durable limestone to form the area’s soil profile (Davis 32).
The above-mentioned occurrences in history place the state of Florida as one whose geologic characteristics are defined solely by the interactions it has had with the sea over the years. Where massive sea changes occurred, so did the major rock-forming processes that define the current day Florida. The story still unfolds in that rise in sea levels would mean the disappearance of the coastal region once again although this time the loss is unbearable. These geologic processes have led to the formation of rock structures and types, which not only serve the state’s economy but are worth paying a visit to go and see (Davis 32).
Davis Jr, Richard A., and Robert W. Dalrymple, eds. Principles of tidal sedimentology. Springer Science & Business Media, 2011.
Hine, Albert C. Geologic History of Florida: Major Events That Formed the Sunshine State. University Press of Florida, 2013.
Wilson, James Lee. Carbonate facies in geologic history. Springer Science & Business Media, 2012.