Shell Borings in Upper Miocene-Pliocene Tamiami Formation, Collier County, Florida: ABSTRACT

Abstract

Borings of common marine organisms such as algae, bivalves, polychaetes, and echinoids are potentially useful in sedimentologic and paleoecologic studies. A variety of spectacular shell borings is preserved in the upper Miocene-Pliocene Tamiami Formation exposed in Collier County, Florida. Paleontology of the richly fossiliferous Tamiami Limestone is difficult to study because leaching has selectively removed aragonitic shells. However, this selective shell removal has revealed excellently preserved shell borings as mud-filled molds. Characteristic, interconnecting, subspherical galleries of clionid sponges are the most common borings. The ichnogenus Entobia is applied to fossil borings similar to modern clinoid sponges. Essentially all of the thick-shelled bivalves, as w ll as many of the thinner shelled species show evidence of sponge borings. Borings of two polychaete worms are also abundant in Tamiami fossils. Excavations similar to those produced by the genus Polydora are the most common, and the second appears unlike modern forms and is tentatively placed in the ichnogenus Meandropolydora. Most thick shells contain distinctive borings of two species of bivalves. These borings have a calcareous lining, and are similar in form to borings of the modern mytilid genus Lithophaga. The Tamiami Limestone has been described as of shallow-water origin, because of the contained oysters, pectens, and echinoderms. Information derived from the abundant shell borings is consistent with this interpretation, indicating a shallow, warm, low-energy environment. End_of_Article - Last_Page 493------------