Abstract Currently accepted terminology for Pennsylvanian units in the area includes the Tensleep, Amsden, Quadrant, Minnelusa, Hartville, Casper, Ingleside, and Fountain formations. A review of nomenclatural history, lithologies, and lateral continuity of these units results in elimination of the terms Quadrant, Hartville, Casper, and Ingleside. The Minnelusa is raised to group status and is extended to include the strata formerly designated as Hartville. The Amsden is restricted vertically to the carbonate upper portion of the original formation, and Branson’s term Sacajawea is applied to the clastic formation below. The Ten-sleep, Amsden, and Sacajawea formations are extended laterally to include lithogenetically equivalent strata. Age variations within the units suggest a southern Wyoming land mass connecting with the Black Hills until Morrowan time. Amsden-Sacajawea seas, initiated in Chesterian time to the north and southeast of this land bridge, were later joined. Tensleep sands advanced southward from Montana forcing the Amsden seas to retreat southeastward until overwhelmed by the youngest Tensleep deposits in the Hartville uplift area during Wolfcampian or Leonardian time. Isopach variations are relatively constant from one unit to another, and show tectonically negative areas in the Lusk embayment and southwestern corner of the map area. The northern zero isopach is interpreted as an erosion edge, but areas of thinning on the Montana-Wyoming border, in the Black Hills, and in southern Wyoming are thought to be related to tectonic instability or position of former land masses. A superjacent strata map illustrates post-depositional erosion intervals by showing the age of the overlying formations. Lithofacies analyses reveal a southern and southwestern source for the Tensleep, Amsden, and Sacajawea sediments. Reef-structures are postulated in the Amsden on the basis of lithofacies patterns, and coincide with the margins of evaporite distribution. A lithofacies map of the entire sequence emphasizes the masking effect introduced when this technique is used with large units involving long depositional intervals.

Abstract This paper evaluates the paleoceanography of marine strata within a Middle Pennsylvanian (Desmoinesian) cyclothem. Paleoecological data are used to interpret spatial and temporal changes in energy, salinity, and turbidity across the North American craton. Using mid-continent terminology, the marine part of the study interval commenced at the top of the Croweburg coal and continues up through the Verdigris Limestone. Cores from four boreholes, in Kansas, and exposures of the interval at 21 outcrops in 18 states were measured, described, and evaluated. Body fossils of marine invertebrates, some vertebrates, plant debris, and trace fossils were identified and evaluated in terms of their environmental and paleoecological significance. These biotic data are presented for eight geographic areas, as follows: (1) Appalachian Basin (Ohio, Pennsylvania, West Virginia, and eastern Kentucky); (2) Eastern Interior Basin (Illinois, Indiana, and western Kentucky); (3) Western Interior Basin (Missouri, Iowa, Kansas, outcrops and cores, and Oklahoma); (4) subsurface of northwestern Kansas; (5) Hartville Uplift (Wyoming) and Black Hills (South Dakota); (6) Fort Worth Basin (Texas); (7) Pedregosa Basin (Arizona); and (8) Paradox Basin (Utah and Colorado), Great Basin (Arrow Canyon, Nevada), and Death Valley (California). In the eastern and central United States the biota occurs in gray mudrocks and black, platy to fissile shales. Fossiliferous limestones occur at the top of the cycle in the central area and become better developed westward into Nevada and California, where the entire interval is dominated by limestone. Comparison of overall diversity and number of taxa versus lithology, mode of life, and feeding type in these eight areas indicates that the greatest diversity is in the Western Interior Basin. In this central region, calcareous skeletons in dark gray shales are commonly replaced by pyrite. Pyritization occurs in such environments because environments of dark gray mud are slightly more reducing than the more oxygenated depositional environments of lighter gray mudrocks and limestones. For ease of further comparison, the eight study areas are grouped into three regions, as follows: East, Central, and West. Comparison of these three regions indicates the following: (1) fragmentation of skeletons is greatest in the East, (2) epifaunal suspension feeders (typical of Paleozoic sedimentary sequences) dominate all three regions, and (3) there is some similarity between the general biotic diversity and total number of taxa in the black mudrocks and limestones in the Central region. Eustatic or tectonic sea-level change has traditionally been invoked to explain the differences documented in this stratigraphic interval and thus along our transcontinental transect. These two processes were active and, no doubt, may have been contemporaneous at some scale. Our data indicate, however, that temporal changes in water depths were similar in most basins across the North American continent. The biotic and lithologic changes, therefore, appear to be principally a function of differences in energy and salinity in response to temporal and spatial changes in climate and tidal conditions across a broad, shallow, island-studded epicontinental sea. Eustasy and tectonics controlled accommodation space, but temporal and spatial climate change was the primary control on sediment supply, wind-driven energy, and seawater chemistry.

Abstract Guernsey is located in southeastern Wyoming on the Hartville Uplift between Torrington and Douglas on U.S. 26.Guernsey State Park, which is 1 mi (1.6 km) north of U.S. 26, has an average elevation of 4500 ft (1400 m). It is readily accessible by car or bus anytime of the year because this is one of the warmest parts of Wyoming. Most of the outcrops are located in Guernsey State Park, which is in the Guernsey Reservoir quadrangle, Platte County, Sec.4, T.27N., R.66W., approximately 42°17'N,104°46'W. Key locations to examine the problem of the nature of the solution surface on the top of the Guernsey Limestone are shown on Figure 1. An excellent view of the principal locality (B) (Fig. 2) on the east side of the North Platte River can be obtained from area A on the west side. The paleo-sinkhole at the south end of the exposure, and the solution surface to the north can be reached for closer examination by means of arduous hikes from parking lot C. To reach the sinkhole area, walk southeasterly from the parking lot on the maintenance road, through the maintenance yards, down into a tributary valley and south along the river. To see several 3 to 5 ft (1 to 1.5 m) solution arches, and a chert breccia (Fig. 3), on the solution surface, walk from the parking lot down to the top of the Guernsey Limestone and southward along this unconformity. Hiking here should be done with care because