• During the Upper Ordovician, the Galena Group of northeast Iowa and southeast Minnesota lay in warm shallow tropical water at about 10 to 15° south latitude. Productivity was probably low inasmuch as lower Paleozoic oceans are generally visualized as oligotrophic (e.g., Bambach, 1993; Martin, 1998, p. 164–173). At this time, the Sebree Trough lay at about 18° south and was connected to the Iapetus Ocean in present-day Oklahoma, Arkansas, and Missouri (Kolata, et al., 2001). Sediments in the trough consist of dark graptolitic shales with ostracodes, orbiculoid brachiopods, and the trilobites Triarthrus and Cryptolithus. Periodically, cool phosphate-rich water from the Iapetus Ocean and Sebree Trough invaded the craton and mixed with the tropical water mass, and these invasions were probably important in maintaining the faunas on the Galena Platform (Kolata, et al., 2001)

• Cotylacrinna sandra and Praecupulocrinus conjugans common in micrite at top of micritic to calcarenitic wackestone bed, which varies from 3 cm to 4 cm thick; weathered top surface indicates hardground.