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 This trip seeks to illustrate the succession of Cambrian and Ordovician facies deposited within the Pennsylvania and Maryland portion of the Great American Carbonate Bank. From the Early Cambrian (Dyeran) through Late Ordovician (Turinan), the Laurentian paleocontinent was rimmed by an extensive carbonate platform. During this protracted period of time, a succession of carbonate rock, more than two miles thick, was deposited in Maryland and Pennsylvania. These strata are now exposed in the Nittany arch of central Pennsylvania; the Great Valley of Pennsylvania, Maryland, and Virginia; and the Conestoga and Frederick Valleys of eastern Pennsylvania and Maryland. This field trip will visit key outcrops that illustrate the varied depositional styles and environmental settings that prevailed at different times within the Pennsylvania reentrant portion of the Great American Carbonate Bank. In particular, we will contrast the timing and pattern of sedimentation in off-shelf (Frederick Valley), outer-shelf (Great Valley), and inner-shelf (Nittany arch) deposits. The deposition was controlled primarily by eustasy through the Cambrian and Early Ordovician (within the Sauk megasequence), but was strongly influenced later by the onset of Taconic orogenesis during deposition of the Tippecanoe megasequence.

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 The Eagle Lake basin was formed by collapse of the ablating Lake Michigan lobe over a tunnel valley and subsequent reoccupation of the collapse basin by the lobe during local final phase of glaciation. Latest collapse occurred prior to about 16,250 but after 18,600 cal yr B.P. A hydrologically open lake occupied Eagle Lake basin from 16,250 cal yr B.P. to the present. The lake was described in 1834 by the original land survey, but was drained for agriculture by 1939.

Abstract Exposures of Ordovician rocks of the Sauk megasequence in Missouri and northern Arkansas comprise Ibexian and lower Whiterockian carbonates with interspersed sandstones. Subjacent Cambrian strata are exposed in Missouri but confined to the subsurface in Arkansas. The Sauk-Tippecanoe boundary in this region is at the base of the St. Peter Sandstone. Ulrich and associates divided the Arkansas section into formations early in the 20th century, principally based on sparse collections of fossil invertebrates. In contrast, the distribution of invertebrate faunas and modern studies of conodonts will be emphasized throughout this chapter. Early workers considered many of the stratigraphic units to be separated by unconformities, but modern analysis calls into question the unconformable nature of some of their boundaries. The physical similarity of the several dolomites and sandstones, complex facies relations, and lack of continuous exposures make identification of individual formations difficult in isolated outcrops. The oldest formation that crops out in the region is the Jefferson City Dolomite, which may be present in outcrops along incised river valleys near the Missouri-Arkansas border. Rare fossil gastropods, bivalves, brachiopods, conodonts, and trilobites permit correlation of the Cotter through Powell Dolomites with Ibexian strata elsewhere in Laurentia. Conodonts in the Black Rock Limestone Member of the Smithville Formation and the upper part of the Powell Dolomite confirm regional relationships that have been suggested for these units; those of the Black Rock Limestone Member are consistent with deposition under more open marine conditions than existed when older and younger units were forming. Brachiopods and conodonts from the overlying Everton Formation assist in interpreting complex facies within that formation and its correlation to equivalent rocks elsewhere. The youngest cono-donts in the Everton Formation provide an age limit for the Sauk-Tippecanoe unconformity near the southern extremity of the great American carbonate bank. The correlation to coeval strata in the Ouachita Mountains of central Arkansas and in the Arbuckle Mountains of Oklahoma and to rocks penetrated in wells drilled in the Reelfoot rift basin has been improved greatly in recent years by integration of biostratigraphic data with lithologic information.

ABSTRACT Based on the interpretation of 893 finite radiocarbon ages, we have revised the time-distance diagram for the Lake Michigan Lobe of the Laurentide ice sheet in Illinois. The data set contains 507 reliable ages determined using standard benzene synthesis–liquid scintillation, including “legacy” ages determined in the 1950s and 1960s at the inception of the radiometric radiocarbon dating method. In addition, the data set includes 278 radiocarbon ages determined by accelerator mass spectrometry. We analyzed the data set based on context, precision, and accuracy to vet minimum or maximum age estimates of diachronic phases. The last glaciation in Illinois is marked by a local maximum margin in northeastern Illinois during the Marengo Phase (modal probability 28,000 cal [calibrated] yr B.P.), and subsequent glacial maximum culminating during the Shelby Phase (24,200 cal yr B.P.). From about that point, the Lake Michigan Lobe entered an overall retreat mode, with significant advances at ~22,200 and 21,100 cal yr B.P. (the Marseilles and Minooka Subphases of the Livingston Phase) and at 20,500 cal yr B.P. (Woodstock Phase). The latter age is also the conservative estimate of the onset of the lacustrine Milwaukee Phase, with referent deposits located as far north as Milwaukee, Wisconsin. This phase ended as the Lake Michigan Lobe made its final advance into Illinois during the Crown Point Phase (18,490 to ca. 16,500 cal yr B.P.), interfingering with the proglacial lacustrine Glenwood Phase deposits (16,900–15,000 cal yr B.P.).

Abstract The Cambrian–Ordovician Sauk megasequence of the great American carbonate bank (GACB) comprises a succession of mixed lithologies, but dominantly carbonate rocks, whose thickness, stratigraphy, and lithofacies distribution reflect the presence of a complex of intrabank platforms and basins, aulacogens, and tectonically active margins that together make up the major part of the paleocontinent Laurentia. The stratigraphy of the Sauk megasequence can be subdivided and correlated across the GACB through the recognition of major unconformities, marine flooding events, and stratigraphic stacking patterns, documented within a robust biostratigraphic framework. The base of the Sauk megasequence is typically defined as the contact of Cambrian or sub-Tippecanoe-megasequence Ordovician rocks with Precambrian, mostly igneous, basement. The Sauk megasequence is overlain (commonly unconformably) by the Middle Ordovician Tippe-canoe megasequence, the age of which varies across the GACB. Where subsequent erosion has occurred, the Sauk megasequence may be overlain by rocks younger than the Tippecanoe megasequence. Palmer’s (1981b) subdivision of the Sauk megasequence into Sauk I, II, and III subsequences (now referred to as supersequences) is widely, but not universally, recognized. Across many areas of the GACB, the Sauk III supersequence of Palmer can be subdivided into two supersequences (defined as “Sauk IIIA” and “Sauk IIIB” in this chapter), based on an unconformity and/or biostratigraphic changes near the Cambrian-Ordovician boundary. Additional significant unconformities and marine flooding events that can be correlated across much of the GACB are summarily described in this chapter. The recognition of correlatable surfaces across the GACB has been challenging because of local syndepositional tectonics and paleotopography, and lithofacies heterogeneity. However, confidence in correlation across the GACB has been greatly enhanced by an increasingly refined biostratigraphic framework.