Chapter 10: Cambrian mollusca from the Minaret Formation, Ellsworth Mountains, West Antarctica

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Abstract
Cambrian mollusks are known from four localities in the limestone of the Minaret Formation, Heritage Range, Ellsworth Mountains, West Antarctica. The most diverse and best-preserved specimens are from the coquina at the feather edge of the Minaret Formation, on the northeastern side of Springer Peak, Webers Peaks. This locality has provided one of the finest Upper Cambrian mollusk faunas in the world. The mollusks indicate a Dresbachian to Franconian age. The trilobites associated with the mollusks define the age of the rocks at Springer Peak as late Dresbachian (Idamean). These rocks were first thought to be Precambrian in age. From the four localities, 19 genera (4 new) and 20 species (12 new) are described; there are 7 species of monoplacophorans placed in 7 genera, 6 species of gastropods placed in 6 genera, 3 species of hyoliths placed in 3 genera, and 3 species of rostroconchs placed in 3 genera. One calcareous tubular organism is described under the hyoliths as Orthothecida? species indeterminate. The higher taxa are presented in the order of decreasing abundance of specimens in the coquina at Springer Peak. Mollusks make up about 5 percent of the coquina, which at this locality is as much as 8 m thick. The remainder of the coquina is almost entirely trilobite fragments; minor elements of the biota are archaeocyaths, inarticulate and articulate brachiopods, echinoderm fragments, conodonts, and algae. The fossiliferous beds at Springer Peak are interpreted as having been deposited in a medium- to high-energy, nearshore environment under normal marine conditions. The less fossiliferous limestone beds above and below the coquina are laminated, and some contain pisoliths; this evidence of algal activity suggests a low-energy environment. Some of the Upper Cambrian species of mollusks found at Springer Peak occur farther south in the Minaret Formation limestones at Bingham Peak and Yochelson Ridge. One species of helcionellacean mollusk, not found elsewhere, was recovered from the Minaret Formation at its type locality in the Marble Hills. This species is classified as Latouchella? species indeterminate; it shows that the Minaret Formation is Cambrian in age throughout its thickness and outcrop area. Various of the genera of mollusks known from the Minaret Formation, as well as one species, are geographically widespread in rocks of Late Cambrian age in Australia, northeastern China, and the upper Mississippi River Valley and Ozark Dome regions of the United States. Geographic distributions are discussed under each taxon. The new taxa of mollusks are: (1) monoplacophorans—Cosminoconella runnegari n. gen., n. sp.; Ellsworthoconus andersoni n. gen., n. sp.; Kirengella pyramidalis n. sp.; Proconus incertis n. gen., n. sp.; and Proplina rutfordi n. sp.; (2) gastropods—Aremellia batteni n. gen., n. sp.; Euomphalopsis splettstoesseri n. sp.; Kobayashiella? heritagensis n. sp.; “Maclurites” thomsoni n. sp.; and Matherella antarctica n. sp.; (3) hyoliths—Linevitus? springerensis n. sp.; and (4) rostroconchs—Apoptopegma craddocki n. sp.

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