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Fossil-Treasures-of-Florida-Newsletter, Issue #0020 -- Prehistoric Rivers -Part 2
September 18, 2013

Fossil Newsletter, Issue #0020 - Prehistoric Rivers 2

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* Prehistoric Rivers -Part 2
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Prehistoric Rivers -Part 2

Working around springs that enter the river is always interesting. (They have great visibility compared to the river, at times, but long term they are cold.) Spring water temperatures average around 72 degrees. It is uncomfortable to work in the river for a couple of hours down stream from a major spring. (The thermoclines are fun, a few feet over warm water, a few feet further cold, but clearer.) Some of the water coming out of these springs can be a few days old to 100 years old, however studies show the average is around 8 years old.

Sinkholes are always curious from the prospective of “what’s down that hole?” They are usually part of a limestone karst cavity in which surface water can drain into and disperse. These sinkholes also form from weak ground acids that dissolve limestone slowly over time. Sinkholes are sources of water for animals today and also thousands of years ago. In the past, Florida’s climate was drier and sources of water were important. These natural depressions collected water and were a gathering point for animals. Fossils can be found in these areas that provided a drinking source of water for these prehistoric animals.

Some of the Eocene outcrops of the Ocala Limestone have these divots or holes in them that use to hold fossil echinoids. One can also see this on the river bottom at times.

Tannins in the water run-off darken the water clarity from clear to “tea” or a “coffee” in color. Someone said it looked like they put iodine in the water. The natural tannins that come from decaying plant material can form a weak acid called tannic acid. Over thousands of years these tannic acids can dissolve limestone to form karst deposits and sinks. These tannins produce tannin rich fresh water from rain and flooding. Both tea and wine contain tannins. Rivers stained with this tannic water are often called “Blackwater” or “Blackwater River” and are common in the southern United States and the Amazon Basin.

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