Changes in the study of paleoclimate during the past 50 years can be demarcated by three revolutions. Plate tectonics was a major (“Kuhnian”) revolution. Two smaller, but nevertheless significant, revolutions were the ocean-drilling revolution and the climate-model revolution. The history of paleoclimate studies shows, in general, an evolution from geographically and/or temporally focused studies in the pre-plate tectonics era, to development of paleoclimate proxies and studies of global climate patterns, to predominantly global studies in connection with paleoclimate modeling; the revolutions have been responsible for some of the shifts in focus. In the most recent decade, new questions posed by global studies and paleoclimate models have driven a reexamination of, and new focus on, geographically and/or temporally focused work. Even more recent advances in geochronology, coupled with the current new energy in developing paleoclimate proxies, are showing the beginnings of a new cycle and hold promise of creating a fourth revolution: the human-impacts revolution.

Abstract The Shublik Formation (Triassic, North Slope, Alaska) is an organic-, phosphate-, and glauconite-rich unit with abundant fossils of marine vertebrates and mollusks. Five lithofacies, generalized around significant chemical constituents or lack thereof, are identified in the Shublik Formation: nonglauconitic sandstone - thin- to medium-bedded, fine, quartzose, calcareous to noncalcareous sandstone or silty to muddy sandstone, fossiliferous in places; glauconitic - thin- to medium-bedded, fine, quartzose sandstone, muddy sandstone, or siltstone containing 10% to > 50% glauconite grains phosphatic - thin- to medium-bedded siltstone or sandstone or laminated, black silty limestone or limestone containing phosphate nodules; and organic-rich - laminated, black limestone, marl, and mudstone nonphosphatic, nonorganic-rich limestone - bioclastic wackestone, or argillaceous grainstone and packstone or graded grainstone and packstone. Ichnofabrics provide evidence of fluctuating oxygen levels within the facies, especially the nonglauconitic sandstone and glauconitic facies. The organic-rich facies and, to a lesser extent, the phosphatic facies contain abundant, pristine, disarticulated shells of the clam Halobia . The lithofacies, ichnofabrics, and taphonomy are interpreted to be related to onshore-offshore gradients in biologic productivity and redox conditions. The Shublik Formation is interpreted as an upwelling-zone deposit formed on a shallow shelf. The Shublik Formation in the Prudhoe Bay region is interpreted to comprise three sequences; these have been extended to outcrop but not to cores in the National Petroleum Reserve. Facies stacking patterns indicate that siliclastic facies are most common during lowstand and transgression, organic-rich facies are characteristic of transgression, and carbonate-rich facies are more prevalent during highstand. Phosphatic facies occur along transgressive and maximum flooding surfaces and are thus integral to subdividing sequences into systems tracts.

Abstract New analyses of previously examined data sets had the following results: (1) Nearly half of organic-carbon- (C org -) rich units were deposited in geographic settings that do not have modern analogs. (2) If up welling associated with western boundary currents is included, predicted upwelling zones can explain up to 93% of oil-prone, C org -rich deposits through the Phanerozoic. The remaining deposits occur in only three settings—rift basins; low-latitude, enclosed, epicontinental seaways; and mid-latitude shelves. (3) Thirty-four phosphate deposits can be identified in the literature that are part of the Si-P-C association, which is widely regarded to be indicative of high productivity. Another 100 deposits had one of the pairs of adjacent facies, phosphate-glauconite or phosphate-C -rich rock, which occur together in upwelling zones. Together, these account for 82% of the 164 phosphate deposits identified in the literature. These results support conclusions that high biologic productivity has strongly influenced sedimentation of organic carbon. Although mechanisms for the genesis of anoxia have been widely discussed, mechanisms for the genesis of high biologic productivity have not; it is suggested that consideration be given to mechanisms, in addition to localized upwelling, that might promote high productivity in the oceans and the resulting high organic accumulation in sediments.

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.