Abstract Algal buildups from five stratigraphic intervals in the Pennsylvanian of eastern Kansas, Midcontinent, U.S.A., display three basic fabrics based on their: a) dimension, b) morphology, c) fossil content, d) algal growth forms, and e) nature of framework cavities. Type 1. Constructional mounds composed of cup-shaped in situ algal growth forms are typically small bioherms, either isolated (e.g., Frisbie Limestone Member) or thickened intervals within carbonate banks(e.g., Sniabar Limestone Member), and are basically formed by phylloid green algae. Fossil diversity is very low. Mud and cement fill the abundant small intercup voids within individual mounds. Calcareous sponges, crinoids, and bryozoans, probably cavity dwellers, fill the larger intermound cavities between the smaller mounds. Type 2. Constructional mounds of algae with undulatory growth forms are basically red algae with recognizablethalli characteristics of Archaeolithophyllum, and, only rarely, of phylloid green algae. Buildups of this kind are laterally persistent. Thickening of the banks is generally recognizable at a large scale (ten of meters to kilometers). Smaller, meter-scale bioherms constructed of algae with undulatory growth forms donot occur in the sites studied. Fossil diversity is higher than in type (1) mounds, with calcareous sponges, brachiopods, and bryozoans common throughout the mound, rather than exclusively in cavities between small mounds ofthe type 1 cup-shaped algae. When built by green algae (e.g., parts of the Captain Creek Limestone Member), mounds have a lower diversity than those constructed by red algae (e.g., Spring Hill Limestone Member). Solitary corals, calcareous sponges, and bryozoans occur attached to the walls of the cavities. The abundance of open pores is striking. Type 3. Mounds of accumulated algae with undulatory growth forms are formed by the red algae Archaeolithophyllum missouriense, Archaeolithophyllum lamellosum, and the green alga Eugonophyllum. Depositional relief is not visible on the outcrop, but large-scale variations in bank thickness are notable (e.g., lower part of the Captain Creek Limestone Member). Bryozoans and Thartharella (a probable worm tube) are common. Multiple types of cavities occur, and most are cement-filled. Although the mound types differ in their form, fossil content, and type and distribution of voids, they sharean overall common peloidal clotted matrix that accumulated in specific areas, along with an abundance of gravity-defying peloidal micritic structures in the matrix, and of thin crusts within marine cement that may be relatedto microbial activity. Microbes probably played a crucial role in carbonate precipitation and in lithificationofalgal-dominated buildups.

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 Continental-scale correlations of a Middle Pennsylvanian fourth-order sequence have provided evidence for the relative importance of allocyclic controls on the formation of Pennsylvanian cyclothems. These correlations (and related studies) indicate that eustatic changes in sealevel were the primary control on accommodation space in most basins. Tectonic subsidence was a secondary control and provided additional accommodation space in a few basins. Temporal and spatial variations in climate, however, were the primary controls on physical and chemical sedimentology. Interpretations of changes in weathering and fluvial and eolian sediment supply suggest that the climate was wetter during lowstands than during highstands and that the physical and chemical oceanography of epeiric seas responded to changing patterns in atmospheric pressure regimes as sea level rose and fell. In addition, the climate was wetter in the eastern part of the tropical regions of what is now North America relative to the west. Temporal and spatial changes in paleoclimate, therefore, appear to be the primary control on lithostratigraphy. Previous studies have suggested that repetitive fluctuations in the sizes of continental ice sheets resulted in repetitive eustatic changes in sea level during the Middle Pennsylvanian (e.g., Wanless and Shepard, 1936 ). Such changes in ice volume and sea level must have been in response to global climate change. The climate model developed herein suggests that repetitive changes in rainfall patterns and surface winds at low latitudes were coincident with the glacial and interglacial intervals. During glacial intervals, a large permanent high pressure cell was associated with a southern-hemisphere ice cap (a nearly stationary polar front). The ice cap minimized annual (summer to winter) thermal variation in the atmosphere (sensible heating) over the southern-hemisphere land mass. As a result, permanent high pressure over the ice cap confined the intertropical convergence zone (ITCZ) to low latitudes, and a permanent low-pressure belt (doldrums) developed in the equatorial region of Pangea. During interglacials, the doldrums belt (low pressure belt) degenerated and was replaced by seasonal swings in the ITCZ in response to seasonal heating of air masses (sensible heating) over both northern-hemisphere and southern-hemisphere land masses. As a result, in low latitudes the climate changed from relatively wet conditions during glacial intervals to drier and more seasonal conditions during interglacial periods. Glacial and interglacial climates are indicated by the following: (1) intense chemical weathering of paleosols, low sediment supply, and peat formation (now coal in the eastern United States) during lowstands in response to a permanent low-pressure rainy belt and wet conditions, (2) deposition of black shale in basin centers during the early stages of transgression in response to low wind speeds and poor wind-driven circulation as the doldrums belt began to deteriorate, (3) transport and deposition of eolian sediments (western United States) in basin margins as sea level continued to rise and the doldrums belt disappeared, and (4) deposition of marine limestone in response to increased wind speeds and wind-driven circulation in epeiric seas coincident with highstands and maximum north–south swings of the ITCZ. All climatic factors (annual rainfall, seasonality of annual rainfall, wind speed, and wind direction) controlled sedimentation in cratonic depositional environments as sea level rose and fell. Although tectonics and eustasy controlled accommodation space, paleoclimate change (coincident with eustatic changes in sea level) controlled the lithostratigraphy of cyclothems at any given paleolatitude in the tropical regions of Pangea. There is no genetic relation between autocyclic delta-plain, back-barrier, or fluvial depositional models and the onset of Pennsylvanian peat formation as a precursor to commercial coal deposits.

Abstract Transcontinental correlations of a Middle Pennsylvanian fourth-order sequence provided evidence for the relative importance of allocyclic controls on the formation of Pennsylvanian cyclothems. These correlations (and related studies) further indicated that eustasy was the primary control on accommodation space in most basins, whereas tectonic subsidence provided additional accommodation space in a few basins. Temporal and spatial variations in climate, however, were the primary controls on physical and chemical sedimentology. The climate model developed herein suggested that repetitive changes in rainfall patterns and surface winds at low latitudes were coincident with the glacial and interglacial intervals. During glacial intervals, a large permanent high pressure cell was associated with a southern hemisphere ice cap and a nearly stationary polar front. The ice cap minimized annual (summer to winter) thermal variation in the atmosphere (sensible heating) over the southern hemisphere land mass. As a result, permanent high pressure over the ice cap confined the intertropical convergence zone (ITCZ) to low latitudes, and a low pressure rainy belt (doldrums) developed in the equatorial region of Pangea during lowstands. During interglacials, the doldrums belt (low pressure belt) degenerated and was replaced by seasonal swings in the ITCZ, in response to seasonal sensible heating of the atmosphere over both northern and southern hemisphere land masses. As a result, the climate in low latitudes changed from relatively wet conditions during glacial intervals to drier and more seasonal conditions during interglacial periods. Paleoclimates in the eastern United States during glacial intervals are indicated by the following: (1) intense chemical weathering of paleosols, (2) low fluvial sediment supply, (3) peat formation (now coal) during lowstands in response to a permanent low-pressure rainy belt and wet conditions, (4) deposition of black shale in basin centers during the early stages of transgression in response to low wind speeds and poor wind-driven circulation in epeiric seas prior to significant deterioration of the doldrums belt, and (5) transport, deposition, and preservation of eolian sediments (in basin margins) following a period of weathering of lowstand exposure surfaces (western United States). Paleoclimates during interglacial intervals are indicated by an influx of fluvial sediments as the doldrums belt disappeared (eastern United States), and deposition of marine limestone west of the Appalachian basin in response to increased wind speeds and wind-driven circulation in epeiric seas coincident with highstands and maximum north-south swings of the ITCZ. All climatic factors (annual rainfall, seasonality of annual rainfall, wind speed, and wind direction) have controlled sedimentation in cratonic depositional environments as sea level rose and fell. Although tectonics and eustasy control accommodation space, paleoclimate cycles (coincident with eustasy) control the lithostratigraphy of upper Middle Pennsylvanian cyclothems at any given paleo-latitude in the tropical regions of Pangea. Furthermore, the present study negates “deep water” models for the origin of Middle Pennsylvanian black shale and autocyclic models (delta plain, back barrier, or fluvial depositional environments) for peat formation as precursors to Pennsylvanian commercial coal deposits.