Abstract A revised lithostratigraphy for Lower Paleozoic strata in New Mexico and west Texas was developed through detailed sedimentological study of the Bliss and Hitt Canyon Formations within a refined temporal framework assembled from precise biostratigraphic (trilobite and conodont) and chemostratigraphic (carbon isotope) data. Member boundaries within the Hitt Canyon now correspond with mappable and essentially isochronous horizons that represent major depositional events that affected sedimentation in basins throughout Laurentian North America. This trip is designed to examine these and other important intervals, such as the extinction horizons at the base and top of the Skullrockian Stage, and to demonstrate the utility of associated faunas and isotopic excursions for correlation within and beyond the region.

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.

Abstract Cambrian and Ordovician strata in Millard and Juab counties, western central Utah, are a thick (17,500 ft [5334 m]) succession that was deposited on a tropical miogeoclinal platform that experienced rapid thermal subsidence after a Neoproterozoic sea-floor spreading ridge formed along the western margin of Laurentia. In this area, which includes the Cricket Mountains, Drum Mountains, Fish Springs Range, House Range, Confusion Range, and Wah Wah Mountains, the Cambrian to Middle Ordovician Sauk megasequence is approximately 15,875 ft (∼4839 m) thick, and the Upper Ordovician part of the Tippecanoe megasequence is approximately 1525 ft thick (∼465m). Basal deposits of the Sauk megasequence are the transgressive Lower Cambrian Prospect Mountain Quartzite, and the top of the Sauk megasequence is the upper Whiterockian Watson Ranch Quartzite. Strata between these sandstones are mostly limestone with several shaly intervals. The Sauk megasequence is divided into four parts, Sauk I to IV, in this area, and these parts have been divided into smaller sequences. The Ordovician part of the Tippecanoe megasequence is mostly dolomite and quartzite. Major influences on the depositional history of these strata include rapid generation of accommodation space caused by thermal subsidence following continental rifting, in-situ generation of tropical carbonates that generally kept pace with accommodation, eustatic fluctuations, influx of siliciclastics during sea level lowstands, and vertical tectonic adjustments of regional tectonic elements inherited from Neoproterozoic rifting: the Wah Wah arch, House Range embayment, Tooele arch, and Ibex Basin. The resulting strata comprise one of the best known Middle Cambrian-Middle Ordovician stratigraphic successions in North America and include the reference sections of the Upper Cambrian Millardan Series and the Cambrian-Ordovician Ibexian Series. Stratigra-phers established a Global boundary Stratotype Section and Point (GSSP) for the base of the Middle Cambrian Drumian Stage in the Drum Mountains and proposed another GSSP for the base of the uppermost Cambrian stage in the Wah Wah Mountains. Middle Cambrian– Middle Ordovician strata are very fossiliferous, and some intervals have incredibly abundant fossils, such as the numerous complete specimens of the Middle Cambrian trilobite Collenia in the central House Range. Trilobites, conodonts, brachiopods, and other fossil groups have been used for biozonation and correlation, and these strata comprise a North American standard for uppermost Cambrian–Middle Ordovician trilobite and conodont zonations. Upper Ordovician dolomites and quartzites are less fossiliferous. These Cambrian and Ordovician strata are the lower half of a Lower Cambrian–Lower Triassic succession that is approximately 34,000 ft (10,300 m) thick and was thrust onto the Jurassic Navajo Sandstone in the southern Wah Wah Mountains during the Sevier orogeny. These strata are exposed in block-faulted mountain ranges resulting from basin and range extension during the late Tertiary.