FL Geology

04/22/23 Prepared by: Prof. Rodriguez

FL Geology

The Rock Cycle



Igneous rocks • Form as magma cools and crystallizes

– Rocks formed inside Earth are called plutonic or intrusive rocks

1.Scoria2.Obsidian3.Pumice4.Granite

Sedimentary rocks

• Economic importance 1. Coal2. Petroleum and natural gas 3. Iron and aluminum4. Shale5. Conglomerate

Metamorphic rocks

• "Changed form" rocks • Produced from preexisting

– Igneous rocks– Sedimentary rocks– Other metamorphic rocks

Metamorphic rocks

• Metamorphic agents– Heat– Pressure (stress)– Chemically active fluids

• Mainly water and other volatiles • Promote recrystallization by enhancing ion

migration

Metamorphic rocks

• Common metamorphic rocks • Slate • Gneiss • Marble

– Parent rock is limestone


FL and Plate Tectonics

• FL was once a part of NW Africa• This fragment formed the base for the

carbonate buildup which includes the FL & Bahamas Platforms.

• FL experienced cycles of sediment deposition & erosion throughout the Cenozoic Era (last 65 million years).


• FL's Cenozoic-aged sediments include two major groups: the Paleogene & Neogene-Quaternary.

• During the Paleogene, carbonate sediments formed due to biological activity of organism including foraminifera, bryozoan, mollusc, & coral.






• Very little siliciclastic sediment ( sands, silts & clays) was able to reach FL because the "Gulf Trough" separated the FL Platform from the siliciclastic source area of the Appalachian Mountains.

• In the late Paleogene, the Appalachians were uplifted, erosional rates increased, & siliciclastic sediments filled the Gulf Trough. Siliciclastic sediments then encroached upon the carbonate depositing environments.



• Sediments deposited during the Neogene were primarily quartz sands, silts & clays with varying amounts of limestone, dolomite & shell.

• In southern FL carbonate sediments still predominated because most of the siliciclastic sediments, moving south with the coastal currents, were funneled offshore.



• The area of the modern-day Everglades was a shallow marine bank where calcareous sediments & bryozoan reefs accumulated.

• These sediments compacted & eventually formed the limestone that floors the Everglades today.


Florida Limestone

• Colonies of coral formed reefs in the shallow sea along the southern rim of the FL platform.

• As sea levels fluctuated, the corals maintained footholds along the edge of the plateau; their reefs grew upward when sea level rose & retreated to lower depths when sea levels fell, accumulating 75 to 100 feet of limestone.



• The last drop in sea level exposed the ancient reefs which are the present FL Keys. Living coral reefs continue to grow in the shallow waters of the Keys.

• Sinkholes are a common feature of FL's landscape. They are only one of many kinds of karst (chemical erosion) landforms, which include caves, disappearing streams, springs, & underground drainage systems, all of which occur in FL.

Sinkholes



• Limestone in FL are porous, allowing the acidic water to percolate through their strata, dissolving some limestone & carrying it away in solution.

• Over eons of time, this persistent erosional process has created extensive underground voids & drainage systems in much of the carbonate rocks throughout the state.


• Collapse of overlying sediments into the underground cavities produces sinkholes.


Winterpark Sinkhole



Florida Springs

• When groundwater discharges from an underground drainage system, it is a , such as:– Wakulla Springs – south of Tallahassee– Silver Springs - Marion County – Fanning Springs - South of Gainesville– More than 700 springs in Florida

Ponce de Leon Spring, Volusia



Minerals of FL

• Most common minerals includes:• 1. quartz (beach sand), • 2. aragonite (shells), • 3. calcite & • 4. clay minerals such as:• a. kaolinite (china clay) &• b. montmorillonite (Na).


• Some minerals are of such economic importance that they are mined.

• In NE FL, a group of minerals known as "heavy minerals" are mined from ancient beach ridges, useful for their titanium (Ti) content.


• In southwest FL, phosphate minerals are mined for the manufacture of fertilizer products.

• FL produces about 1/4 of the world's phosphate.


• If limestone undergoes an intense amount of heat, it becomes the metamorphic rock, marble.

• In FL, sedimentary rocks are the most common.



• One example is shell fragments (the mineral ) that are cemented together by calcite to form the sedimentary rock coquina.


• Limestone, is mined for road building & other construction applications. This rock is made up of small calcite particles formed by marine organisms that build up large reefs in the oceans.


• Much of the surface of FL is covered by:• 1. sediment (loose mineral particles, such

as quartz sands), or • 2. sedimentary rocks such as limestone &

dolostone.


• Igneous & metamorphic rocks do not occur naturally at the surface,

• are found in deep wells reaching from 3,500 feet to deeper than 18,670 feet below land surface.

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FL Geology