Abstract In the central Appalachians, carbonate deposition of the great American carbonate bank began during the Early Cambrian with the creation of initial ramp facies of the Vintage Formation and lower members of the Tomstown Formation. Vertical stacking of bioturbated subtidal ramp deposits (Bolivar Heights Member) and dolomitized microbial boundstone (Fort Duncan Member) preceded the initiation of platform sedimentation and creation of a sand shoal facies (Benevola Member) that was followed by the development of peritidal cyclicity (Dargan Member). Initiation of peritidal deposition coincided with the development of a rimmed platform that would persist throughout much of the Cambrian and Early Ordovician. At the end of deposition of the Waynesboro Formation, the platform became subaerially exposed because of the Hawke Bay regression, bringing the Sauk I supersequence to an end. In the Conestoga Valley of eastern Pennsylvania, Early Cambrian ramp deposition was succeeded by deposition of platform-margin and periplatform facies of the Kinzers Formation. The basal Sauk II transgression during the early Middle Cambrian submerged the platform and reinitiated the peritidal cyclicity that had characterized the pre-Hawke Bay deposition. This thick stack of meter-scale cycles is preserved as the Pleasant Hill and Warrior Formations of the Nittany arch, the Elbrook Formation of the Great Valley, and the Zooks Corner Formation of the Conestoga Valley. Deposition of peritidal cycles was interrupted during deposition of the Glossopleura and Bathyriscus-Elrathina Biozones by third-order deepening episodes that submerged the platform with subtidal facies. Regressive facies of the Sauk II supersequence produced platform-wide restrictions and the deposition of the lower sandy member of the Gatesburg Formation, the Big Spring Station Member of the Conococheague Formation, and the Snitz Creek Formation. Resubmergence of the platform was initiated during the late Steptoean ( Elvinia Zone) with the expansion of extensive subtidal thrombolitic boundstone facies. Vertical stacking of no fewer than four of these thrombolite-dominated intervalsrecords third-order deepening episodesseparatedbyintervening shallowing episodes that produced peritidal ribbony and laminated mudcracked dolostone. The maximum deepening of the Sauk III transgression produced the Stonehenge Formation in two separate and distinct third-order submergences. Circulation restriction during the Sauk III regression produced a thick stack of meter-scale cycles of the Rockdale Run Formation (northern Virginia to southern Pennsylvania), the upper Nittany Dolomite, the Epler Formation, and the lower Bellefonte Dolomite of the Nittany arch (central Pennsylvania). This regressive phase was interrupted by a third-order deepening event that produced the oolitic member of the lower Rockdale Run and the Woodsboro Member of the Grove Formation in the Frederick Valley. Restricted circulation continued into the Whiterockian, with deposition of the upper Rockdale Run and the Pinesburg Station Dolomite in the Great Valley and the middle and upper parts of the Bellefonte Dolomite in the Nittany Arch region. This deposition was continuous from the Ibexian into the Whiterockian; the succession lacks significant unconformities and there are no missing biozones through this interval, the top of which marks the end of the Sauk megasequence. During deposition of the Tippecanoe megasequence, the peritidal shelf cycles were reestablished during deposition of the St. Paul Group. The vertical stacking of lithologies in the Row Park and New Market Limestones represents transgressive and regressive facies of a third-order deepening event. This submergence reached its maximum deepening within the lower Row Park Limestone and extended into the Nittany arch region with deposition of the equivalent Loysburg Formation. Shallow tidal-flat deposits were bordered to the south and east by deep-water ramp deposits of the Lincolnshire Formation. The St. Paul Group is succeeded upsection by ramp facies of the Chambersburg and the Edinburg Formations in the Great Valley, whereas shallow-shelf sedimentation continued in the Nittany arch area with the deposition of the Hatter Limestone and the Snyder and Linden Hall Formations. Carbonate deposition on the great American carbonate bank was brought to an end when it was buried beneath clastic flysch deposits of the Martinsburg Formation. Foundering of the bank was diachronous, as the flysch sediments prograded from east to west.

A silicified ostracode fauna consisting of 54 species, 44 of them new, from the Middle Ordovician (Chazyan-Trentonian) Lincolnshire and Edinburg formations of the Shenandoah Valley of Virginia is described. Among the genera studied are: A parchites, Oepikella, Leperditella, Conchoprimitia, Schmidtella, Milleratia, Hallatia, Euprimitia, Ectoprimitia?, Primitiella, Chilobolbina, A patochilina, Eurychilina, Ctenobolbina, Aechmina?, Monoceratella, Winchellatia?, Thomasatia, Balticella, Bromidella, Bassleratia, Kirkbya?, Krausella, Macrocyproides, Camdenidea?, Bairdiacypris, Bairdianella?, Budnianella, Platyrhomboides, and Bythocypris?. Three new genera—Eokloedenella, Eographiodactylus, and Shenandoia—are proposed. A new family, the Budnianellidae, is proposed to include the genera Budnianella and Platyrhomboides, which bear no close affinities to any previously described family. Fourteen of the species occur in other formations. Nine of these are in the Chazyan Crown Point formation on Valcour Island, Lake Champlain. Comparative species are also in the Bromide formation (Black Riverian and Chazyan) of the Arbuckle Mountains, formations of the Trentonian and Richmondian stages of north-central United States, the Middle Ordovician of Arctic Canada and North Greenland, and the Upper Ordovician of North Europe. Preliminary considerations are given to the phylogeny of the fauna. Leperditella is probably the root stock from which the Euprimitiidae developed through Schmidtella, Eridoconcha, Cryptophyllus , and Milleratia . Close relationships are pointed out between the Primitiidae and the Eurychilinidae. The writer suggests that the Eurychilinidae, Oepikellidae, and Aechminidae descended from Aparchites. Primitiella and closely related genera are associated with Eurychilina but may very likely have developed independently. Relations between Ctenobolbina and Winchellatia and primitive sigmoopsids are discussed. The closely related Bassleratia and Thomasatia probably developed from primitive tetradellids via Steusloffia . Two early kloedenellids, Eokloedenella and Balticella , are suggested as the root stock of that group. Eographiodactylus , a new genus, is proposed as a primitive form from which Graphiadactyllis developed. Bairdiacypris, Shenandoia, early Paleozoic “Bythocypris”, and Macrocyproides are descended from a common unknown ancestor. Bairdianella? is suggested as the root stock of the bairdiids, closely related to Camdenidea. Krausella and Rayella are very closely related if not synonymous.