Comparison of Ordovician lithistid sponge communities in the Great Basin

Abstract

Lithistid sponges are an important component of many Ordovician faunas and form some of the earliest reef communities of the Paleozoic Evolutionary Fauna, yet they have received relatively little attention. Fossiliferous strata with abundant sponges occur at many horizons and localities within the Lower and Middle Ordovician Pogonip Group of the Great Basin. One of the best-known occurrences is near the middle of the Antelope Valley Limestone in central Nevada, where sponge-bearing units occur within the lower Whiterockian Stage. Lithistid sponges and associated species were also examined within the Shingle Limestone of eastern Nevada, where the sponge communities occur as small reef mounds about 55 m below the top of the formation in beds corresponding to the uppermost Ibexian Series. To acquire a more regional view of the environments and faunas present in Nevada during the Ordovician, contemporaneous units in the Pogonip Group were examined elsewhere in Nevada and in the Ibex area of western Utah.The general depositional setting of the Great Basin at this time was that of a carbonate ramp in the upper Ibexian developing into a carbonate platform during the Whiterockian. The sponge mounds in the Shingle Limestone, forming in water 1 to 15 m deep, may have participated in this development by interfering with water circulation along the outer portion of the carbonate ramp. The mounds are several meters in size and are often stacked, with grainstone-filled channels cutting through the mounds in several places. The mounds themselves have muddy cores and are flanked by well-sorted echinoderm grainstones. The reef trend extends for nearly two kilometers before being faulted out, and was probably even more extensive during its development. Besides sponges, the assemblage contains abundant calcareous algae and cyanobacteria, as well as trilobites, brachiopods, echinoderms, and other groups characteristic of the Paleozoic Fauna. These mounds are very similar to those found in the Wahwah and Juab Limestones of the Pogonip Group, suggesting that these latter buildups also formed in very shallow water.The younger sponge communities in the Antelope Valley Limestone at Ikes Canyon probably formed in about 20 to 40 m of water along the uppermost slope of a carbonate platform. The sediments consist of interbedded wackestones, mudstones, and shales with occasional hardgrounds. Some of the sponges have root tufts, indicating that they settled on soft substrate. Besides lithistid and heteractinid sponges, the unit contains a diverse assemblage of metazoans and occasional receptaculitids and other algae.Estimates of relative species abundances were calculated for random samples from the sponge-bearing units. The Shannon Diversity Index for the Antelope Valley Limestone fauna is 3.24 with an equitability value of 0.68, while the Shingle Limestone community has values of 3.44 and 0.74, respectively. Thus, not only were both communities diverse, but the species within each community were comparable in abundance. These values compare...

A new Silurian (Llandovery, Telychian) sponge assemblage from Gotland, Sweden

“…-Rigby (1973) assigned the species to the genus Calycocoelia Bassler, 1927, but de Freitas (1989de Freitas ( , p. 1868) referred it to Archaeoscyphia Hinde, 1889 on account of characteristics that were in his opinion non-specific, such as the presence of coring monaxons in attached zygomes. Johns (1994) re-examined the type specimens of A. annulata and Archaeoscyphia pulchra (Bassler, Explanation of Plate 2. Figs 1-6.…”

“…De Freitas (1989), in his thorough study of Silurian anthaspidellids from Arctic Canada, referred Calycocoelia to Archaeoscyphia Hinde, 1889, on account of similarities in skeletal features and aquiferous systems. Although Johns (1994) followed de Freitas' opinions in many respects, he maintained Calycocoelia as a distinct genus with C. typicalis as the type species. This opinion was based on the occurrence of exceptionally long and thin I-shaped dendroclones, not only in intraserial trabs, but also in parietal trabs.…”

“…This limitation, whatever its cause, prevented them from becoming common over wide areas, although many genera survived through the Baltica-Laurentia region as a whole for most of the Silurian. It is possible that they could not compete effectively with more rapidly growing or physically more resistant organisms such as tabulates and stromatoporoids (Narbonne & Dixon 1984;Johns 1994).…”

A new occurrence of Archaeoscyphia pulchra (Bassler) from the Ordovician of western Canada

“…A nearly complete specimen and an additional fragment of this ornate sponge have been recovered from Lower Ordovician rocks, most probably of the upper part of the Outram Formation or the lower part of the Skoki Formation, from near the Columbia Icefields in the Main Ranges of the Rocky Mountains of eastern British Columbia. The relatively rare species was initially described from Lower Ordovician rocks of the Toquima Range from central Nevada by Bassler (1941), and nearby areas by Johns (1994). It has also been reported from the Mingan Islands of Quebec by Rigby and Desrochers (1995), and possibly from the Ordovician of the Ozark Uplift of Missouri, where Cullison (1944) described the similar Archaeoscyphia annulata, which Johns (1994) placed in synonymy with Archaeoscyphia pulchra.…”

“…The relatively rare species was initially described from Lower Ordovician rocks of the Toquima Range from central Nevada by Bassler (1941), and nearby areas by Johns (1994). It has also been reported from the Mingan Islands of Quebec by Rigby and Desrochers (1995), and possibly from the Ordovician of the Ozark Uplift of Missouri, where Cullison (1944) described the similar Archaeoscyphia annulata, which Johns (1994) placed in synonymy with Archaeoscyphia pulchra.…”