14 DAY TRIAL // Geologists at the University of South Florida's College of Marine Science have searched for the origins and creation of the Tampa Bay's bottom. "It's part of our daily life, but we know very little about how it came to be" said geological oceanographer Al Hine.
The bay's bottom started its existence about 15 million years ago, through a combination of geological events occurring over many millions of years. "The basin that is now Tampa Bay formed between 15 and 7 million years ago, when the underlying limestone was deformed by collapses," explained Hine. "The basement of Tampa Bay consists of ancient sub-basins deformed into sinks, folds, sags and warps, later filled in by the by the sand sediments."
4 to 6 million years ago, the wrinkled, shallow bottom was covered by a massive transport of quartz sand, originated 1000 miles (1600 km) north. "Ever since the first geologist walked local beaches in the early part of the last century, it was obvious to him that what we call the Florida Platform received a shipment of sand in the region's deep, geologic past," explains Hine.
How the sand got here is still not very well understood. After millions of years since its arrival on Florida Platform, the sand was remobilized locally, probably in years of over-flooding and filled in the bottom of Tampa Bay. The sand had derived from very old silicate-rich bedrock (aged hundreds of millions of years) in the Appalachian Mountains and Piedmont area in the current eastern U.S. mid-Atlantic region. "It appears that exposed silicate-rich bedrock, chemically weathered, arrived from the north through multiple sources, most likely through runoff into streams and rivers running from the mountains to the coast," Hine believes.
"By the late Pliocene and early Pleistocene eras - some one to two million years ago - there was a great reduction in the silicate transport system and a similar reduction in rainfall, runoff and sand transport from local rivers," says Hine. "Tampa Bay as we know it was then geologically complete."
The scientists used a seismic reflection profiler, a sonar-like apparatus, that revealed geological features as images on a computer screen. 100 miles (160 km) to the south, Charlotte Harbor, appeared in the same way. "The research can help us understand fresh groundwater flow and how nutrients or pollutants get into the bay," says Hine. "Knowing the thickness of the sediment and where the bedrock is important to dredging and pipeline burying."