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 source of this variation in geologic structure and properties. As a result, the purpose of this paper is to look at the timeline of events in Florida geology and their relevance to the state’s current geology. 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).
During the early Ordovician period, the Florida plateau was formed as a result of volcanic activity and marine sedimentation. It connected the North American plate with the African and south American one. Later the two plates drifted further apart leaving the plateau as part of North America (Hine 80). Consequently, 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 and Dalrymple 101). The thickness of the sediment layers increased over the years hence exerting more weight on the underlying layers. This had a compacting effect on the bottom layers eventually cementation of the materials occurred. The layers piled upon each other to a point where they got exposed at low tide. Subsequent changes in sea level led to the full emergence of the plateau, which is now the state of Florida.
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 and Dalrymple 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 because 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). Surface rainwater infiltrated into the ground dissolving limestone rocks beneath the ground forming underground channels. With sufficient amount of water and slope, underground rivers were formed. Sometimes the ground would collapse into one of these underground channels leading to the formation of sinkholes (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 and Dalrymple 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 and 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. Massive quantities of sand were deposited along the coast of Florida towards the end of the Oligocene making sandy soils predominant along the coast (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 and Dalrymple 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, large-scale deposition of limestone-forming sediments occurred due to a minimal disturbance at the sea floor. Later the sea level dropped and the already deposited materials were eroded away. The process reoccurred several times making the process of forming limestone rocks very slow (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). Organic soils characterize the Northern Everglades because of the proximity to the forest part of the state where falling leaves provided humus to the soils. Limestone-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 and Dalrymple 32).
It is, therefore, clear that the sea levels have had a significant effect on the geology of the state of Florida. Where massive sea changes occurred, so did the major rock-forming processes that define the current day Florida. Melting of the world’s glaciers played a major role since melting ice added into the ocean water raising the sea levels. Global warming can also be viewed as a contributing factor since melting of ice is because of rising temperatures. These processes have led to the formation of geologic structures, which not only serve the state’s economy but are worth paying a visit to go and see (Davis and Dalrymple 32).
Davis Jr, Richard A., & Dalrymple, Robert W. 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, 1975.
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