Abstract The renaissance in stratigraphy overthe last two decades has been largely driven by the belief that stratigraphic packaging is determined by allocyclic controls. An understanding of the controls on stratigraphy allows us to make better predictions about the nature and geometry of strata within areas of basins where data is more limited. From an economic standpoint one can better estimate the potential for oil gas coal or mineral accumulations. Ten years ago discussions concerning the importance of driving mechanisms was polarized with many stratig raphers tending to emphasize the importance of a single allocyclic control Cyclostratigraphers emphasized the importance of climatic cycles Event stratigraphers studied the role of major events such as meteorite or comet impacts volcanic episodes or widespread oceanic anoxia Tectonostratigraphers examined the role of tectonism Sequence stratigraphers who divided strata on the basis of time significant surfaces such as unconformities and marine flooding surfaces demonstrated the importance of eustasy. Although some zealots remain most stratigraphers now recognize the importance of taking a more holistic approach to understanding allocyclic controls. A special session was convened at the 1994 Denver annual meeting of the AAPG SEPM entitled Allocyclic controls on nonmarine stratigraphy. This session was enthusiastically attended and featured papers that demonstrated a wide range of approaches to developing an understanding of alluvial architecture. This volume represents a collection of these papers and as such brings together the results of research where authors have examined the relative importance of eustasy climate and sediment supply in determining the nature of lithologies and the style of packaging of continental strata.

Abstract The Salt Wash Member of the Upper Jurassic Morrison Formation in the Henry Mountain region of southern Utah is up to 160 m thick and consists of sandstones, interpreted as fluvial-channel deposits, and mudrocks, interpreted as overbank or abandoned channel-fill deposits. The strata are interpreted to have been deposited by a braided river system based on the high sandstone:mudrock ratio, the paucity of ripple lamination in the upper part of fining-upward units, the coarse grain size of many of the sandstones, a lack of lateral accretion bedding, the sheetlike nature of the sandstone bodies and the low dispersion of paleocurrent vectors. The rivers appear to have had a highly flashy discharge with relatively little preservation of falling-stage and low-stage sedimentary features. There is an up-section change in stratal geometry from thin, highly amalgamated, sheet sandstone bodies, to thicker, more isolated, sheet sandstone bodies. This change suggests an increase in the rate of creation of accommodation over time— this may be related to expansion of lacustrine systems downstream. There may also have been a climatic change from arid to semi-arid conditions that resulted in larger streams and more stabilized banks. Perpendicular to the paleoflow direction there is a marked change in thickness of the strata with an increasing percentage of overbank/flood-plain mudstone in thinner sections— this change is interpreted to be the product of differential subsidence within the basin of deposition. An understanding of fluvial strata like the Salt Wash Member requires a holistic view of allocyclic controls on sedimentation including temporal and spatial variations in climate, tectonism and base level.

Abstract Outcrops of Turonian through Campanian strata in the Kaiparowits Plateau of southern Utah provide a unique opportunity to examine both shallow-marine and continental strata within the context of unconformity bounded depositional sequences. This approach provides insights to the evolution of the strata within the plateau as well as regional chrono- and lithostratigraphic relationships within the southwestern Colorado Plateau. We recognize five unconformity-bounded depositional sequences. These sequences are defined by regional surfaces of erosion that juxtapose amalgamated fluvial deposits over shoreface, alluvial plain, or coal-bearing strata and reflect an abrupt basinward shift in facies tracts. Between these sequence boundaries transgressive and highstand systems tracts are recognized. Transgressive systems tracts are characterized by a progression from amalgamated channel deposits to isolated meanderbelts that have evidence of tidal influence within what is otherwise a wholly alluvial succession. These tidally-influenced fluvial deposits are temporally equivalent to marine maximum flooding surfaces. Early-highstand systems tract deposits are characterized by thick, aggradational shoreface parasequences, thick coal beds, and isolated meanderbelt sandstones encased in thick, fine-grained flood plain strata. Late-highstand systems tract deposits are relatively thin and are characterized by progradational shoreface parasequences, thin, discontinuous coal seams, and fine-grained channel deposits. We interpret these changes in stratigraphic architecture to reflect significant changes in stratigraphic base level that we have correlated to adjacent outcrop belts in the Wasatch Plateau of central Utah, at Black Mesa in northern Arizona, and the San Juan basin in New Mexico. We have compared our estimates of stratigraphic base level with those of Haq et al. (1988) and suggest some modifications in order to account for the observed stratigraphy throughout the southern Colorado Plateau. Recognizing cycles of base-level change has allowed us to synthesize our observations in the Kaiparowits Plateau and extend them across a broad region. Recognition of the relationship between sedimentary architecture and position within a sequence has resulted in a model that allows the geometry and interconnectedness of sedimentary facies to be predicted within the context of parasequence stacking patterns. This provides a useful tool for both exploration and development.

Abstract In the northern part of the Kaiparowits Plateau of southern Utah, excellent outcrops allow the detailed examination of Upper Cretaceous offshore, shoreface, estuarine, and coastal plain strata within an established sequence-stratigraphic framework. A lower sequence boundary, referred to as the Calico sequence boundary, is overlain by a 25- to 60-m-thick succession of strata interpreted as a transgressive systems tract. These strata consist of amalgamated braided river sandstones that pass upward into heterolithic estuarine strata and, in turn, into distal shoreface sandstones capped by a widespread fossiliferous horizon. Separating the heterolithic estuarine deposits from the overlying shoreface sandstone is a widespread erosion surface covered by a conglomerate of sub- to well-rounded pebbles. This surface is a ravinement surface or transgressive surface of erosion within the transgressive systems tract. The transgressive systems tract is overlain by up to 80 m of progradationally stacked parasequences, consisting of offshore and shoreface strata interpreted as the deposits of a highstand systems tract. In a landward direction the shoreface strata pinch out and highstand deposits are represented by coal-bearing coastal plain strata. A second sequence boundary, referred to as the Α-sequence boundary, erosionally overlies these shoreface strata and, in turn, is overlain by an estuarine unit up to 38 m thick. These estuarine strata comprise a second transgressive systems tract that is capped by an erosion surface overlain by offshore strata. This study provides a useful analog for the interpretation and correlation of strata in less well exposed areas and particularly in the subsurface. This paper also provides facies dimensions of shoreface parasequences that may allow for better modeling of variations in reservoir compartmentalization within a sequence-stratigraphic framework.

Coal bed thickness, lateral continuity, maceral content, ash content, and sulfur content are largely determined by the conditions that controlled the mire where the peat originally formed. Major factors are the type of mire, type and rate of vegetation growth, rate and degree of humification, rate of base-level change, and rate of clastic sediment input. These factors are influenced more by allogenic controls (tectonism and climate) than by autogenic controls (environment of deposition). When plotted on paleogeographic maps, the global distribution of Cretaceous coals shows the importance of tectonism and climate in determining the location of coals. Cretaceous plate tectonics was dominated by the breakup of Pangea, but remarkably few coals accumulated either in associated rift basins or passive continental margins. By far the largest volumes of Cretaceous coal resources are located in the foreland basins that stretched along the western margin of the Western Interior seaway of North America. These basins were created by thrusting and crustal loading within the Western Cordillera, which began in the Late Jurassic in the Western Canada Sedimentary Basin, in the Aptian(?)/Albian on the North Slope of Alaska, and in the latest Albian in the western US. Cretaceous coals of the world are distributed in a similar fashion to modern peats, and formed in mires in coastal regions, particularly near the equator where rainfall was presumably higher, or in high midlatitudes, where precipitation may have been relatively high and evaporation low. The major exception are the coals of the Western Interior of North America. Conditions that may have favored peat accumulation in that region are (1) the maintenance of high groundwater tables due to basin subsidence; (2) convection over a warm seaway that may have resulted in sufficient rainfall to permit peat accumulation along the coast; or (3) the development, if the ancestral Rockies were a major topographic feature, of a high-altitude low-pressure cell over the high terrain that created enough rainfall in the summer to maintain high groundwater levels.

The Cretaceous was a time of profound global change in floral composition and vegetation structure, both temporally and spatially. Early Cretaceous vegetation and rates of species turnover were generally similar to those of the Jurassic. At low latitudes the Cheirolepidiaceae ( Classopollis producers) and bennettites characterized arid and semi-arid belts, forming savanna-type vegetation with fern ground cover and cycadophyte shrubs. Primary elements in riparian and disturbed sites were ferns and cycadophytes; on floodplains were sphenopsids, lycopods, and ferns; while backswamps were dominated by “leafy” conifers. Conifer forests with an understory of ferns, ginkgophytes, and Czekanowskiales were the major coal-formers and were prevalent at higher (humid) latitudes. The middle Cretaceous saw the initial diversification of the angiosperms as an early successional component of the vegetation, particularly in stream margins and disturbed sites. Most angiosperm physiognomic foliage types had evolved by the end of the Cenomanian. Globally forests remained dominated by conifers. Czekanowskiales, Gink-goales, and Podozamites persisted at higher latitudes before declining due to (angiosperm?) competition and climatic deterioration. Brachyphyllous conifers were widespread at middle latitudes. During the late Cretaceous angiosperm radiation, groups that previously dominated arid belts (e.g., Cheirolepidiaceae) and angiosperm competitors (pteridosperms and cycadophytes) declined, but this period of dynamic vegetational change supported more major plant groups than at any other time. Angiosperm trees and shrubs played an increased role in climax vegetation as well as forming riparian thickets. Most coal-forming communities remained conifer-dominated throughout the Cretaceous and many contain a high proportion of deciduous elements.

The New Mexico Bureau of Mines and Mineral Resources (NMBM&MR), with the participation of other individuals, has been involved in a long-term coal quality study. This project was funded by the New Mexico Research and Development Institute (NMRDI) with contributions from several companies. The NMBM&MR has developed a large data set for the San Juan basin coal fields using quality data from this project and data collected from public and private sources through an 11-yr cooperative project with the U.S. Geological Survey (USGS) for entry into the National Coal Resource Data System (NCRDS). The most complete set of quality and thickness data exists for the economically important Fruitland Formation coals. Evaluation of these data suggest that some trends in the attributes of the Fruitland coals exist. The trends appear to support the premise that the characteristics of these coals are a consequence of their depositional environments. These environments were influenced by the relative position of the shoreline and the rate of shoreline movement. The thickness and quantity of the coals and the ash and sulfur content appear to be significantly influenced by their position relative to the shoreline and the rate of shoreline shift. The moisture content and Btu value appear to have been influenced by these same controls, but the degree of coalification of the northern Fruitland Formation coals has also been influenced by the heat from the massive intrusive complexes of the La Plata and San Juan Mountains in southern Colorado.

δ 13 C and δ 34 S were determined for 47 coal samples from the Williams Fork Formation—31 samples from the Wadge coal bed and 16 samples from the Lennox coal bed. δ 13 C ranges from −23.4 to −27.2‰). Organic sulfur δ 34 S ranges from +5.3 to +13.5‰ for the Wadge bed and from +13.7 to +20.1‰ for the Lennox bed. The organic sulfur content of the coal samples ranges from 0.23 to 0.71 percent for the Wadge bed and from 0.65 to 2.72 percent for the Lennox coal bed. The ash content of both beds is low, averaging 8.5 percent for the Wadge bed and 6.4 percent for the Lennox bed. The carbon isotopic homogeneity of the Wadge and Lennox beds indicates that the plants in each mire were similar with respect to the carbon fixation processes and carbon source. Previous sulfur isotopic studies of coral and the coal-forming processes have shown that δ 34 S is determined by the aquatic composition of sulfur in the peat-forming environment. In a freshwater mire, the δ 34 S of aquatic sulfate fluctuates about a mean of 5 ± 3‰, whereas in the marine environment, δ 34 S of aquatic sulfate clusters around +20‰. In peat-forming mire that is inundated by marine water, much of the sulfate is reduced by sulfate-reducing bacteria. As a result of this microbiologic activity, the active sulfur, which is assimilated into the decaying organic substrate, is depleted in 34 S. However, if the sulfate-reducing bacteria are absent, the peat possess only sulfur with the isotopic composition of the growth environment. In a coastal mire, this sulfur could be similar to that of the marine water. The low sulfur content and the isotopic composition in the lower part of the Wadge bed are consistent with sulfur assimilation in a freshwater growth environment. The increasing sulfur content and the increasing abundance of heavier isotopes toward the top of the bed suggest that, during the later stage of development of the coal mire, the peat-forming plants were increasingly influenced by a marine source and that marine sulfur was assimilated. The moderately high sulfur content and the 34 S enrichment in the Lennox coal samples suggest that this mire was clearly influenced by a marine source.

A comprehensive surface and subsurface study of the Upper Cretaceous Lazeart Sandstone Member of the Adaville Formation and the lower coal-bearing part of the Adaville Formation in the southwestern Wyoming thrust belt reveals a complex inter-tonguing of marine and nonmarine strata. During late Santonian and early Campanian time, the Lazeart wave-dominated deltaic system prograded southeastward onto a storm-influenced microtidal shelf. Sediments of the Lazeart Sandstone Member accumulated within storm-dominated lower shoreface, barred fair-weather upper shoreface, foreshore, washover, mouth bar, flood tidal delta, and tidal channel subenvironments. Landward of the strand line, sediments of the Adaville Formation were deposited within active distributary, channel margin, bay-head delta, slough, interdistributary swamp, lake, interdistributary bay, salt marsh, lagoon, interdeltaic bay, and peat-forming swamp subenvironments. Nine transgressive-regressive pulses of this wave-dominated deltaic system were superimposed on the regressive portion of the Niobrara Cyclothem. Thicknesses of noncoal strata, grain size, and sand percent all decrease away from channels and thickness and lateral continuity of coal increase. Because of differential compaction, areas with thick peat deposits became sites of deposition of active channel, channel margin, and slough facies. Subsequently, many of these sites once again evolved into areas of thick peat accumulation. Individual seam thickness is limited by the magnitude of the associated transgressive-regressive pulse. During regressions of limited areal extent, coastal swamps remained in one place for a long period of time, and thick peats were deposited. High subsidence rates favored such limited regressions and the development of thick, localized coal seams. Local subsidence rates were highest when shoreface sands prograded into deeper water directly over marine muds. Thickest coal seams overlie and intertongue with thick shoreface, foreshore, and washover fan sandbodies. Subsidence of the sandbodies maintained a high water table and contributed to the development of stable peat swamps. In interdeltaic regions, lower sediment loads and rates of subsidence led to the accumulation of thinner peats. The distribution and total reserves of coal seams within the Adaville coal field is controlled by the number of transgressive-regressive pulses and their geographic extent. Vertical stacking of the regressive sand bodies maximizes total coal reserves for a given locality. Stacked shallow marine sandbodies and high total coal reserves for the Adaville Formation are a consequence of relative sea-level rise during a period of isostatic compensation to thrust and sediment loads of the Sevier Orogenic Belt.

The economic Jewel Seam forms part of the Lower Cretaceous Gates Formation and has a stratigraphic thickness of about 10 m. Its depositional setting was on a coastal plain, well removed from marine clastic influences. These peat deposits were likely dominantly planar, low lying, and formed under seasonal wet (relatively dry) conditions. Shortening by subsequent folding and thrusting of the strata amounted to 50 percent, often resulting in structural thickening of the Jewel Seam along the hinges of folds. Mineral matter and sulfur and maceral contents are largely determined by the original sedimentary environment. Vertical profiles with an upward increase in ash yield and low ash zones through the center of the seam can be explained by the chemical environment of the swamp. The average finely disseminated ash yield is 14 percent (dry basis); however, in places it is higher because of Laramide tectonic shearing. Sulfur contents are low compared to many other coal deposits and average 0.3 percent (dry basis). Sulfur often shows slightly elevated values at the base, and to some extent at the top of the seam. Volatile matter and vitrinite reflectance are largely controlled by depth and duration of burial and to some extent by deformation. These coals have relatively high inertinite contents, which probably result from seasonally dry forest swamp conditions. Rank of the Jewel Seam ranges from high to medium volatile bituminous, where the highest rank is found in the central part of the study area. The intersections of isorank surfaces with the Jewel Seam indicate components of syndeformational coalification. A good linear correlation between maximum vitrinite reflectance and volatile matter (dry and ash free) is observed, enabling volatile matter to be estimated from vitrinite reflectance. A contoured map of vitrinite reflectance predicts rank and volatile matter of the Jewel Seam for unexplored parts of the coalfield.

The Upper Jurassic-Lower Cretaceous Mist Mountain Formation in the southeastern Canadian Cordillera is a nonmarine succession up to 670 m thick that includes as many as 15 major seams of high volatile bituminous to semi-anthracite coal. Coals at the base of the formation were deposited in coastal and delta plain environments, whereas those of the upper part are interpreted as upper delta plain and alluvial plain deposits. The coal seams are thicker, more abundant, and laterally less continuous in the upper part of the formation. The geometry of the coal seams is influenced by the presence of adjacent channels that have locally thinned or washed out some seams. The effect of differential compaction on coal seam geometry is variable; some seams thin over paleo-channels, whereas others are thicker and/or contain fewer partings. The ash content of most coals shows no predictable lateral or vertical variation that can be related to the overall sedimentology, nor is there a correlation between seam thickness and ash content. The sulfur content of all seams is low (<1 percent), suggesting the absence of marine influence during peat accumulation. There is a general increase in vitrinite and a decrease in inertinite and semi-fusinite from the base to the top of the formation, which may reflect a greater contribution of herbs to coals formed from coastal marsh-swamp complexes at the base. Variations in roof conditions in underground mines are related to the structural fabric of the coal measures, which in turn reflects the kinematics and dynamics of tectonic deformation and roof rock lithology. In the Vicary Creek Mine, the roof rock comprises two lithofacies: a thin-bedded, very fine grained, carbonaceous sandstone lithofacies interpreted as distal crevasse splay deposits, and a thick-bedded sandstone lithofacies interpreted as proximal splay deposits. The thin-bedded lithofacies includes carbonaceous partings that were preferred horizons for intrastratal slip along which cohesion of the roof rock has been lost. The thick-bedded sandstone lithofacies is well jointed, leading to a blocky roof rock that localized intrastratal slip within the underlying coal seam. In the Balmer North and Five Panel Mines, the roof rock is composed of carbonaceous siltstone and very fine grained sandstone interpreted as crevasse splay and overbank deposits. During flexural-slip folding, slip was localized along carbonaceous partings that have destroyed the cohesion between successive beds in the roof rock. The intersections of slickensided bedding surfaces and major shear and extension fracture systems have resulted in unstable roof rock, particularly in rooms and roadways developed parallel to their intersection.

Coals in the post-Wapiabi strata of the Rocky Mountain Foothills are found in the upper Campanian (uppermost Belly River and lowermost St. Mary River formations), lower Maastrichtian (upper Brazeau Formation) and lower Paleocene (upper Coalspur Formation) stratigraphic sequences. Large-scale facies relationships within these sequences, combined with sedimentologic data for the coal-bearing strata and their correlatives, indicate that the coal-forming swamps originated in marginal marine, marginal lacustrine, and flood-plain enviornments. The coal-forming swamps developed only when there was a combination of appropriate diastrophic and favorable climatic conditions. This happened twice in the depositional history of the Rocky Mountain Foothills during phases of relative tectonic quiescence (early Maastrichtian and early Paleocene) in the northern, humid part of the basin. At those times the semiarid conditions in the southern part of the basin precluded the formation of coal-forming swamps. The semiarid conditions in this part of the basin were overridden in the late Campanian by the influence of the Bearpaw Sea, which led to the formation of thin coals in the marginal marine environment.