First documentation of tidal-channel sponge biostromes (upper Pleistocene, southeastern Florida)

Abstract

Sponges are not a common principal component of Cenozoic reefs and are more typically dominant in deep-water and/or cold-water localities. Here we report the discovery of extensive upper Pleistocene shallow-marine, tropical sponge biostromes from the Miami Limestone of southeastern Florida built by a new ceractinomorph demosponge. These upright, barrel-to vase-shaped sponges occur in monospecifi c aggregations constructed within the tidal channels of an oolitic tidalbar belt similar to modern examples on the Great Bahama Bank. The biostromes appear to have a ribbon-like geometry, with densely spaced sponges populating a paleochannel along a 3.5 km extent in the most lengthy biostrome. These are very large (as high as 2 m and 1.8 m in diameter), particularly well-preserved calcifi ed sponges with walls as hard as concrete. Quartz grains are the most common particles agglutinated in the structure of the sponge walls. Where exposed, sediment fi ll between the sponges is commonly a highly burrowed or cross-bedded ooid-bearing grainstone and, locally, quartz sand. It is postulated that the dense, localized distribution of these particular sponges was due to a slight edge over competitors for food or energy supply and space in a stressed environment of tidal-infl uenced salinity and nutrient changes, strong currents, and frequently shifting submarine sand dunes. To our knowledge, this represents the fi rst documentation of sponge biostromes composed of very large upright sponges within high-energy tidal channels between ooid shoals. The remarkably well-preserved accumulations provide an alternative example of sponge reefs for comparative paleoenvironmental studies.

“Keratose” sponge fossils and microbialites: a geobiological contribution to the understanding of metazoan origin

“…The stromatolite-like bioconstructions in both the PB and OS materials were constructed in a very turbulent water body by sponge communities of low diversity and high abundance. An ecologically comparable example has been reported from the Pleistocene tidal-channels in Florida, where a single species of haplosclerid sponges flourished as opportunists in the developing tidal channels and each individual forms 1-2 m high barrel-to vase-shaped columns (Cunningham et al 2007;Rigby and Cunningham 2007). The unfavorable environment may have prohibited competitors and predators.…”