About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 56 (1972)

Issue: 3. (March)

First Page: 626

Last Page: 626

Title: Biostratigraphy of Graptolite-Bearing Beds of Upper Ordovician Maquoketa Formation of Northeastern Iowa: ABSTRACT

Author(s): S. R. Herr

Article Type: Meeting abstract


A graptolite fauna comprised of 3 species is present in the lower Elgin Member of the Maquoketa Formation. Although this fauna has been reported previously, revision and reevaluation of the taxonomy are proposed. The following taxa merit discussion and revision: "Diplograptus peosta" (Hall) belongs to the species group Orthograptus truncatus Lapworth. Its geographically and chronologically restricted occurrence dictates a subspecific designation. Climacograptus putillus (Hall) is a species which is very similar to C. mississippiensis Ruedemann. The 2 species differ with regard to the origin of the median septum; however, other strong affinities should be considered in a revision of both species. An unnamed subspecies of Orthograptus quadrimucronatus exhibits affinities wi h 2 subspecies from eastern North America. Its small size and restricted occurrence separate it as a distinct subspecies.

The stratigraphic and geographic distribution of graptoloid species within the Maquoketa Formation suggests that 2 graptolite zones exist and the graptoloid species are provincial within both zones.

Individually the graptoloid species of the Maquoketa Formation are similar to species reported to be late Caradocian, early Ashgillian, Edenian, Maysvillian, and Richmondian in age. Comparison of the Maquoketa graptolites with faunas of eastern and western North America suggests a discrepancy in previous correlations between the Richmond Stage and the Dicellograptus complanatus zone of western Texas.

The graptolite fauna as a whole is correlated with the faunas of the Haymeadow Creek Member of northern Michigan as well as the upper Utica Formation of New York and Canada.

End_of_Article - Last_Page 626------------

Copyright 1997 American Association of Petroleum Geologists