Paleoecology of Sphenothallus on an Upper Ordovician hardground

Abstract

A hardground from the Upper Ordovician Dillsboro Formation near Dillsboro, Indiana, U.S.A., preserves an assemblage of encrusting and boring fossils on both top and bottom surfaces. The slab is inferred to have been an undercut ledge, and the dominant fossils of the assemblage, holdfasts of the tube‐building worm Sphenothallus and trepostome bryozoans, are prevalent on both sides. The clumping of Sphenothallus holdfasts has been statistically demonstrated using a nearest‐neighbor technique. Sphenothallus has also been shown to withstand overgrowth in interactions with bryozoans.

Resolving Three-Dimensional and Subsurficial Features of Carbonaceous Compressions and Shelly Fossils Using Backscattered Electron Scanning Electron Microscopy (Bse-Sem)

“…Consistent with existing descriptions of the genus , each tubular fossil from Heziao consists of a pair of oppositely situated longitudinal thickenings, which branch near the apex and extend up to its aperture and are separated by two walls. Although it is uncertain whether Sphenothallus tests were originally phosphatic , organic (Bodenbender et al 1989), or organophosphatic (Li et al 2004), the results of this study suggest that the tests consist of distinct organic and phosphatic layers (Fig. 8A-G) and that the phosphatic layers consist of carbon-rich apatite laminae (Fig.…”

Origin of the rudstone–floatstone beds in the Upper Jurassic Arab-D reservoir, Khurais Complex, Saudi Arabia

“…Some interparticle and inter-crystal porosity can be observed in the grain-rich infills of the hardground burrows, which usually contain higher porosities than the surrounding lime muds. Hardgrounds that underlie most intraclastic beds are marked by color alteration and/or blackening, possibly due to phosphatization (Bodenbender et al, 1989;Palmer, 1982). Scour marks and burrows are filled with intraclastic rudstone and/or floatstone.…”

A quantitative paleoecological approach to high‐resolution cyclic and event stratigraphy: the Upper Ordovician Miamitown Shale in the type Cincinnatian

“…These include cryptostome bryozoans (all bifoliate cryptostomes except Escharoporu), smooth encrusting trepostome bryozoans, monticulated encrusting trepostome bryozoans, encrusting cyclostome bryozoans, encrusting inarticulate brachiopods ( e g , Petrocrania, Schizocrania, and Trematis), scolecodonts, cephalopods, and nuculoid bivalves. References used for identifications included the University of Cincinnati Geology Museum collections, and several taxonomic works (e.g., Caster et al 1955;Hall 1962;Thompson 1970;Pojeta 1971;Bell 1976;Alberstadt 1979;Walker 1982;Davis 1985;Bodenbender 1989).…”