Abstract Three types of cycles are recognized for the Pennsylvanian rocks of the Appalachian basin: 1) autocycles (river avulsion and shifts in supply); 2) sub-regional allocycles (tectonism within the basin or uplift of parts of the orogenic belt; and 3) regional and eustatic allocycles (regional tectonism or eustasy). Autocycles occur within minor allocycles and are interpreted as sediment-supply shifts accompanying river avulsions within relatively fixed-drainage basins. Minor allocycles of coal measures commonly are 18 to 30 meters in thickness and contain extensive paleosols, coal, marine and/or freshwater limestone beds. Current estimates of allocycle durations vary greatly depending on the time scale used. Minor allocycles probably are glacio-eustatic and shoreline T-R shifts range from 32 to >800 km. Intermediate allocycles consist of several minor allocycles either in progradational, aggradational or retrogradational sets with relatively more transgressed units serving as the boundary units and are 90 to 115 m thick. Major allocycles are bounded by extensive transgressive units, are about 300 m thick, and approximate the Lower, Middle, and Upper Series of Pennsylvanian. These major allocycles are subregional, reflect basin tectonism shown by shifts in the seaway during the Pennsylvanian, and do not correlate with worldwide sea level curves, suggesting the basin's response to thrust-sheet loading during the Alleghanian orogeny. Cycles in paleoclimate were significant in influencing the lithic response within the allocycles (Cecil, 1990).

Abstract Geologic conditions during the Pennsylvanian created events necessary for coal-forming that are relatively rare in geologic history. This mix of conditions involved (1) tectonics accompanied by sedimentation; (2) depositional environments that favored poorly drained, clear-water, acidic swamps; (3) climates that encouraged peat formation and preservation; (4) plant evolution that produced sufficient biomass to keep pace with a changing base level; and (5) repeated cycles of marine and nonmarine sedimentation, alternating between detrital influx and “starvation” in response to eustatic, tectonic, and sediment-supply changes. Factors important in determining the quality and thickness of coal beds are the relative rates of subsidence, depositional environments where ancient swamps existed, climate, and the frequency and extent of shoreline shifts. Integration of the above conditions and factors creates a complex explanation for origin of the Pennsylvanian coal measures in the eastern and central United States. Excellent regional stratigraphic synopses of the Pennsylvanian coal measures indicate that the Upper Carboniferous (Pennsylvanian) coal measures constitute a large part of the total United States resources (Branson, 1962; Arndt and others, 1968; U.S. Bureau of Mines, 1974; McKee and others, 1975; Craig and others, 1979; Rightmire and others, 1984; Lyons and Rice, 1986; Sloss, 1988). Pennsylvanian coal beds are mainly preserved in structural basins located in the central and eastern United States (Fig. 1). The quality and thickness of coal beds, greatest in the Appalachian basin (anthracite and bituminous extending from Pennsylvania to Alabama/Mississippi), decreases westward across the Eastern Interior basin (Illinois, Indiana, western Kentucky), the Western Interior basin

The Pennsylvanian rocks of the central Appalachians record a progressive change in paleogeography and paleoenvironment, from extensive sea (Pottsville time), to relatively small bay (Allegheny–lower Conemaugh time), to entirely river-influenced lowsalinity bay-lake (upper Conemaugh–Monongahela time), to relatively small lakes of fluvial plain (Dunkard time). Sediments derived mainly from the southeast were dispersed into the elongate sea-bay-lake by prograding deltas. Sediments first filled the unstable geosynclinal trough-basin of southern West Virginia, and then the northeast-trending Dunkard basin of northern West Virginia which developed as a depression in a relatively stable platform. Sea transgression during Conemaugh time was in part tectonically controlled, but shifting delta lobes influenced the distribution of marine shell beds. The West Virginia deltaic complex evolved from a wave-dominant delta with fringing barrier islands (Pottsville time) to a fluvial-dominant delta (Conemaugh and Monongahela time), and facies of Conemaugh and Monongahela rocks are similar to those found in modern shallow-water deltas. Major anticlines were growing structures influencing northeast-trending drainage and facies. Tectonic warping of plateau nearly normal to hingeline orientation of N. 50° E. explains the vertical stacking of sandstone belts approximately 30 mi. wide trending northwest. However, supply frequently over-whelmed basin subsidence burying growing structures under sediment. Consequently, channel sandstones commonly trend across present fold axes and exhibit an offset stacking arrangement resulting from differential compaction.

Abstract The Holocene delta of the Guadalupe River is slowly prograding into San Antonio Bay of the Texas Gulf Coast. The delta is part of a modern complex of lagoonal and deltaic sediments deposited along a shoreline dominated by barrier islands. The river deposits its load in a shallow, relatively quiet body of water, and, as the delta progrades into increasingly shallow water, distributary channels have become deeper than the present bay floor. The primary purpose of the detailed study of this modern delta is to establish criteria to aid investigations of similar ancient deltaic sediments and environments where the geologic record is much less complete. Distinctive sediments are recognized from the following six environments of the delta : distributary channel, natural levee, marsh, interdistributary bay, delta front, and prodelta. Sediments are clay and silty clay except for the basal part of the distributary-channel and delta-front deposits, which are fine-grained sand, silty sand, or silt. Silty clays of the natural levee and marsh contain abundant plant material, some thin silt beds, and they are root disrupted, whereas the silty clays of the interdistributary bay are shelly and burrow mottled compared to the shelly but laminated prodelta silty clays. The sands of the delta front develop a geometry which reflects the shoreline configuration. Where the delta is birdfoot, the delta-front deposits are shoestring (bar-finger) sands. The overall configuration of the Guadalupe delta is birdfoot, although occasional small lobate masses develop where the delta has prograded toward the shallower bay margins. Lobate parts of the delta exhibit closely spaced distributaries, coalescing distributary-mouth bars, and sheet sands. The low-salinity fauna is restricted to sediments of the distributary channel, interdistributary bay, delta front and prodelta. No species of the fauna is confined to a particular environment of deposition. Subdivision of the delta into biofacies is based on the diversity and relative abundance of the fauna, mainly Mollusca. Mollusca are most abundant in the burrow-mottled delta-front sands and occur in decreasing amounts respectively in the inter-distributary-bay, small-scale crossbedded delta-front, prodelta, and delta-plain sediments. Ostracods represent a proportionately greater amount of the fauna in the interdistributary-bay sediments. Plant fibers and wood fragments are common in all facies of the delta. The rate of progradation also varies in response to the depth of water. Crossbedded delta-front deposits and laminated prodelta deposits probably indicate a high rate of progradation. Burrow-mottled delta-front deposits underlain by thin prodelta deposits probably indicate a low rate of progradation. The relatively stable tectonic setting compared to the Mississippi delta apparently accounts for the slight overlap of the subdeltas. Marsh overlying natural levee deposits suggests about 1 foot of subsidence of the delta. Subsidence is attributed to compaction of sediments. Characteristics which make the Guadalupe delta a distinctive model are: (1) the river discharge and load overwhelm the weaker currents and waves of the bay, (2) deposition is in such a shallow body of water that waves can rework the bay sediments, (3) the river channels are deeper than the present bay floor, (4) the bay is becoming progressively shallower as the delta progrades, (5) tectonic subsidence is less in the Guadalupe Delta area than in the area where the Mississippi, Brazos, and Rio Grande Rivers are located, and (6) growth is by development of successive subdeltas, most of which are presently deteriorating. Factors that control sedimentation in the Guadalupe delta area should apply to other lagoonal deltaic complexes, to crevasse systems of large deltas, to rivers that deposit their loads in shallow inland seas, and to their ancient counterparts. Upper Cretaceous rocks of the Rocky Mountain area and Pennsylvanian rocks of northern West Virginia have characteristics which suggest conditions of sedimentation similar to the Guadalupe delta.