SP-03 Ostracoda of the Dubuque and Maquoketa Formations of Minnesota and Northern Iowa

Abstract

The ostracodes of the Dubuque Formation at Wubbles Ravine, Fillmore County, Minnesota and from the depauperate zone of the Maquoketa Formation at Bellevue State Park, Iowa comprise twelvecgenera and seventeen species, four of which are new. On the basis of the ostracode data assembled here it is concluded that: (1) the Dubuque Ostracoda differ slightly from those of other Middle and Upper Ordovician rocks in the Mississippi Valley; (2) no equivalent of the Eden and Maysville Groups can at present be recognized in ostracode assemblages from Minnesota; (3) an unconformity exists between the Dubuque and Maquoketa Formations, recognizable on both faunal and lithologic grounds; and (4) the ostracode species of the depauperate zone of the Maquoketa Formation are not as a whole characterized by reduced dimensions of the shell as are some of the macrofaunal species.