pisoids, peritidal carbonate facies, storm deposits
Pisoids (concentrically laminated carbonate grains, > 2 mm in diameter) are abundant in the upper Humboldt Oolite Member of the Gilmore City Formation (Mississippian). Their cortices are isopachous and nuclei include both intraclasts and fragments of preexisting
pisoids. They occur both as floating grams m a fine grainstone matrix and concentrated at the bases of distinct layers that may be crudely graded beds. Sorting characteristics and the presence of broken and abraded pisoids suggest not only their origin as primary free grams, but also storm influence in the deposition of local pisolite layers. Regionally, the upper Humboldt Oolite is characterized by pisolite with birdseyes, fenestrae, evaporite cements, evaporite solution-collapse breccias and tepee structures, a recurrent facies association that has been documented m both ancient and modern arid, peritidal, carbonate depositional environments.
Journal of the Iowa Academy of Science
© Copyright 2002 by the Iowa Academy of Science, Inc.
Thomas, Shawn C. and Groves, John R.
"Storm Deposition of Pisoids in the Humboldt Oolite Member of the Gilmore City Formation (Mississippian), North-Central Iowa,"
Journal of the Iowa Academy of Science: JIAS: Vol. 109:
, Article 8.
Available at: http://scholarworks.uni.edu/jias/vol109/iss1/8