• The strong tendency for some groups to be preserved articulated while echinoderms are not suggests a rather low sedimentation accumulation rate, but this is not a true starved basin situation. The pitted and mineralized Maquoketa-Dubuque contact resembles many other corrosion surfaces in the Upper Mississippi Valley Galena Group (Witzke, 1985b), and likely formed in a submarine, not subaerial environment. If the suggestion of Brown (1974) that upwelling of oxygen-poor, phosphate-rich waters into a typical carbonate shelf edge produced the diminutive Maquoketa faunas is correct, then this community, with a significant but small echinoderm component, marks the transition from the highly affected Palaeoneilo fecunda-Nuculites neglectus Community (with almost no echinoderms) to the more normal marine Thaerodonta recedens-Iowacystis sagittaria Community. Benthic assemblages have not been defined for many Ordovician communities as yet, but a position analogous to BA 3-4 is probable (see also Witzke & Glenister, 1987, for further discussion).

• The lithology is a poorly consolidated to pyrite-cemented dolomitic phosphorite ranging in thickness from 0.1 to 0.3 m. Most common are small (<2 mm) subsphaeroidal concentrically laminated hydroxylapatite clasts, but less well rounded phosphate clasts up to 15 cm in length and phosphatized fossils are also abundant. Locally quartz geodes ranging in size from 1 cm to more than 25 cm in length are common, e.g., at the type locality. The geodes contain minor sulfide mineralization (wire marcasite) and common calcite, ferroan dolomite, fluorite, and selenite crystals in the often largely hollow interiors... This community appears to have been subject to some current activity, but not frequently enough to remove selectively particular size clasts. The deposit is very poorly sorted, at least basally, with clay to gravel-sized clasts intermixed, some or all of which may be phosphatized.