Florida’s Geologic History

Hundreds of millions of years of geologic processes lead to the formation of Florida. This document described the 3 primary processes that created Florida as we know it today: 1) plate tectonics (>160 million years ago), 2) carbonate production (160 - 23 million years ago), and 3) siliciclastic invasion (23 million years ago – present). It also discusses the major processes that continue to reform the morphology of the Florida Platform: sea level change, karstification, and humans. Previous Version: Allen, Ginger, and Martin Main. 2005. “Florida’s Geological History”. EDIS 2005 (7). https://journals.flvc.org/edis/article/view/114948.

Springs Geology

This chapter reviews the geological context of Florida’s springs and the St. Johns River valley. This provides a basis for understanding the abundance of springs in Florida and the forces that drive their geographic distribution and hydrology. The chapter begins with a sketch of the geologic history of the Florida Platform and the formation of the karst Floridan Aquifer system, with emphasis on those events and processes relevant to springs. This is followed by a discussion of the environmental factors affecting spring flow and how these were impacted by global and regional climatic changes during the late Pleistocene and Holocene. Finally, it discusses the geomorphology of the St. Johns River valley and the springs that feed into it.

Low Florida coral calcification rates in the Plio-Pleistocene

In geological outcrops and drill cores from reef frameworks, the skeletons of scleractinian corals are usually leached and more or less completely transformed into sparry calcite because the highly porous skeletons formed of metastable aragonite (CaCO3) undergo rapid diagenetic alteration. Upon alteration, ghost structures of the distinct annual growth bands often allow for reconstructions of annual extension ( = growth) rates, but information on skeletal density needed for reconstructions of calcification rates is invariably lost. This report presents the bulk density, extension rates and calcification rates of fossil reef corals which underwent minor diagenetic alteration only. The corals derive from unlithified shallow water carbonates of the Florida platform (south-eastern USA), which formed during four interglacial sea level highstands dated approximately 3.2, 2.9, 1.8, and 1.2 Ma in the mid-Pliocene to early Pleistocene. With regard to the preservation, the coral skeletons display smooth growth surfaces with minor volumes of marine aragonite cement within intra-skeletal porosity. Within the skeletal structures, voids are commonly present along centres of calcification which lack secondary cements. Mean extension rates were 0.44 ± 0.19 cm yr−1 (range 0.16 to 0.86 cm yr−1), mean bulk density was 0.96 ± 0.36 g cm−3 (range 0.55 to 1.83 g cm−3) and calcification rates ranged from 0.18 to 0.82 g cm−2 yr−1 (mean 0.38 ± 0.16 g cm−2 yr−1), values which are 50 % of modern shallow-water reef corals. To understand the possible mechanisms behind these low calcification rates, we compared the fossil calcification rates with those of modern zooxanthellate corals (z corals) from the Western Atlantic (WA) and Indo-Pacific calibrated against sea surface temperature (SST). In the fossil data, we found a widely analogous relationship with SST in z corals from the WA, i.e. density increases and extension rate decreases with increasing SST, but over a significantly larger temperature window during the Plio-Pleistocene. With regard to the environment of coral growth, stable isotope proxy data from the fossil corals and the overall structure of the ancient shallow marine communities are consistent with a well-mixed, open marine environment similar to the present-day Florida Reef Tract, but variably affected by intermittent upwelling. Upwelling along the platform may explain low rates of reef coral calcification and inorganic cementation, but is too localised to account also for low extension rates of Pliocene z corals throughout the tropical WA region. Low aragonite saturation on a more global scale in response to rapid glacial–interglacial CO2 cyclicity is also a potential factor, but Plio-Pleistocene atmospheric pCO2 is generally believed to have been broadly similar to the present day. Heat stress related to globally high interglacial SST only episodically moderated by intermittent upwelling affecting the Florida platform seems to be another likely reason for low calcification rates. From these observations we suggest some present coral reef systems to be endangered from future ocean warming.

Delineation of post-KPg carbonate slope deposits as a sedimentary record of the Paleogene linkage of De Soto Canyon and Suwannee Strait, northern Gulf of Mexico

Seismicity generated from the Chicxulub impact has been postulated as the cause for the dramatic alteration of basin margin morphology and catastrophic movement of sediments in the Gulf of Mexico (GOM). Immediately following the impact, the formation of the Cretaceous-Paleogene boundary deposit (KPBD) was widespread and caused considerable erosion as portions of the Florida Escarpment collapsed, inducing sediment failure on the northern Florida Platform and formation of the ancestral De Soto Canyon. Overlying the more prominent KPBD existed a distinct, younger, post-Cretaceous/Paleogene carbonate slope deposit (CSD) confined within the De Soto Canyon bathymetric feature. Presence of this discrete unit provided insight into the post-impact history of De Soto Canyon and its long-duration connection to the Suwannee Strait, which linked the GOM with the Atlantic Ocean for almost 40 ma. We have postulated that the bathymetric low of the De Soto Canyon acted as a conduit for west to east sediment movement from nearby carbonate-dominated shorelines into the canyon in episodic sediment transport events from the Danian to the earliest Miocene. Closure of the Suwannee Strait, due to sediment infilling, terminated deposition of the De Soto Canyon CSD. This was followed by major siliciclastic influx as the paleo-Tennessee drainage system began to enter the Mississippi Canyon area.

Low Florida coral calcification rates in the Plio-Pleistocene

In geological outcrops and drill cores from reef frameworks, the skeletons of scleractinian corals are usually leached and more or less completely transformed into sparry calcite because the highly porous skeletons formed of metastable aragonite (CaCO3) undergo rapid diagenetic alteration. Upon alteration, ghost structures of the distinct annual growth bands may be retained allowing for reconstructions of annual extension (= growth) rates, but information on skeletal density needed for reconstructions of calcification rates is invariably lost. Here we report the first data of calcification rates of fossil reef corals which escaped diagenetic alteration. The corals derive from unlithified shallow water carbonates of the Florida platform (southeastern USA), which formed during four interglacial sea level highstands dated 3.2, 2.9, 1.8, and 1.2 Ma in the mid Pliocene to early Pleistocene. With regard to the preservation, the coral skeletons display smooth growth surfaces with minor volumes of marine aragonite cement within intra-skeletal porosity. Within the skeletal structures, dissolution is minor along centers of calcification. Mean extension rates were 0.44 ± 0.19 cm yr−1 (range 0.16 to 0.86 cm yr−1) and mean bulk density was 0.86 ± 0.36 g cm−3 (range 0.55 to 1.22 g cm−3). Correspondingly, calcification rates ranged from 0.18 to 0.82 g cm−2 yr−1 (mean 0.38 ± 0.16 g cm−2 yr−1), values which are 50 % of modern shallow-water reef corals. To understand the possible mechanisms behind these low calcification rates, we compared the fossil calcification with modern zooxanthellate-coral (z-coral) rates from the Western Atlantic (WA) and Indo-Pacific (IP) calibrated against sea surface temperature (SST). In the fossil data, we found an analogous relationship with SST in z-corals from the WA, i.e. density increases and extension rate decreases with increasing SST, but over a significantly larger temperature window during the Plio-Pleistocene. With regard to the environment of coral growth, stable isotope proxy data from the fossil corals and the overall structure of the ancient shallow marine communities are consistent with a well-mixed, open marine environment similar to the present-day Florida Reef Tract, but variably affected by intermittent upwelling. Upwelling along the platform may explain low rates of reef coral calcification and inorganic cementation, but is too localized to account for low extension rates of Pliocene z-corals recorded throughout the tropical Caribbean in the western Atlantic region. Low aragonite saturation on a more global scale in response to rapid glacial/interglacial CO2 cyclicity is also a potential factor, but Plio-Pleistocene atmospheric pCO2 is believed to have been broadly similar to the present-day. Heat stress related to globally high interglacial SST, only episodically moderated by intermittent upwelling affecting the Florida platform seems to be the most likely reason for low calcification rates. From these observations we suggest some present coral reef systems to be endangered from future ocean warming.