Tampa Fossilized Coral

I have in my lab some fossilized coral from the area of the Wetherington Island site, which is located  just east of Tampa, Florida. The site is a major Paleoindian and Archaic quarry site that runs back from the north bank of an abandoned channel of the Hillsborough River. There are ancient quarry pits dug through a buried gleyed A horizon into the limestone marl, chert workshops where they heat treated the chert, and megafauna bones in the Paleoindian strata. The deposits of chert and chalcedony at the site are very rich. When the water in the creek is low, you can see a large chunk of modified bedrock chert sticking out of the riverbed. By modified, I mean it has been partly chipped away; it is covered in flake scars from knapping. Excavations at the site have produced literally tons of debitage (See Brown 2001 and references therein). A fair portion of the debitage is fossilized coral, which is presumably what archaeologists in the region call "Tampa Fossil Coral." The quarrying apparently intersected a fossil reef embedded in the Tampa Limestone Member of the Hawthorne formation.

Early today, I was showing some flakes of the fossilized coral to a colleague and, as always, it was difficult to see the skeletons of the coral animals in the rock. You can only see them when the flake or chunk has fractured perpendicular to the axis of the coral animals; then they appears as stars or asterisks in the chert. Out of frustration, I took some pictures of the flake with my digital microscope, and they came out surprisingly well, so I thought I would share them with the world.

First are a couple of pictures of the flake (ventral and dorsal) and then a few closeups of the ventral face. You will probably need to enlarge the photographs (by clicking on the thumbnails) to see what I'm describing.

Low magnification microphotograph of the ventral face of a fossilized coral flake. The skeletons of the coral animals are visible as star- or asterisk-shaped shadows embedded in the stone. This is not an archaeological specimen, but rather a modern, experimental one.

Low magnification microphotograph of the dorsal face of a fossilized coral flake. The skeletons of the coral animals are visible as star- or asterisk-shaped shadows embedded in the stone. This is not an archaeological specimen, but rather a modern, experimental one.

Close-up of the dorsal face of the specimen above.

Close-up of the dorsal face of the specimen above.

Close-up of the dorsal face of the specimen above.

Close-up of the dorsal face of the specimen above.

It is very lovely rock, which turns bright colors--red and orange--when heat treated. I think the coral animals are clearer in these microphotographs than in real life not only because of the magnification but also because I used polarized light. The flake was resting on a shiny white surface and it is possible that it reflected some of the incident light back through the specimen, which is translucent, creating enhanced visibility.

At least in North America, ancient lithic artifacts are made out of fossilized material, including fossilized (or petrified) wood, more often than one might imagine. 


Reference cited

Brown, Clifford (2001). The Fractal Dimensions of Lithic Reduction. Journal of Archaeological Science Vol. 28, No. 6, pp. 619-631.