ABSTRACT The Uinta Basin of eastern Utah is an intermontane basin that contains an ~2-km-thick succession of mostly carbonate-rich mudrock assigned to the Eocene Green River Formation. In the southwest part of the basin, along Nine Mile Canyon and its tributary canyons, the middle member of the Green River Formation contains numerous interbedded sand bodies. Previous researchers have interpreted these sand bodies variably as lacustrine deltaic mouth bars, terminal fluvial distributary bars, and various types of fluvial (delta plain/floodplain/braid plain) bar. Using some modern western U.S. lakes as partial analogues, and taking into account the overall lacustrine basin context of a widely fluctuating, wave-influenced, alkaline-lake shoreline, we again interpret many of the sand bodies to be fluvial in origin. Several sand bodies both truncate and are capped by brown to red-maroon and variegated weak to noncalcareous mudstone with root and desiccation structures, indicating terrestrial deposition well away from the lake shoreline. Others display steep cutbanks from which noncalcareous, inclined heterolithic stratification laterally accreted as fluvial side bars. Utilizing helicopter-based light detection and ranging (LiDAR) data, we investigated additional sand bodies that may be better examples of deltaic mouth bars. In contrast to the more commonly documented highstand progradational mouth bars of marine and open lake settings, these sand bodies are interpreted to have originated as late-lowstand or transgressive system tract fluvial channels that were then flooded and modified by waves following lake transgression. These examples illustrate that any large-scale sandy bed form present in the general vicinity of a closed basin’s fluctuating lake shore may be expected to have formed under more than one set of environmental conditions. A revised set of guidelines is therefore presented to aid in the interpretation of lacustrine deltaic mouth bars.

ABSTRACT Scanning electron microscopy (SEM) has revolutionized our understanding of shale petroleum systems through microstructural characterization of dispersed organic matter (OM). However, as a result of the low atomic weight of carbon, all OM appears black in SEM (BSE [backscattered electron] image) regardless of differences in thermal maturity or OM type (kerogen types or solid bitumen). Traditional petrographic identification of OM uses optical microscopy, where reflectance (%R o ), form, relief, and fluorescence can be used to discern OM types and thermal maturation stage. Unfortunately, most SEM studies of shale OM do not employ correlative optical techniques, leading to misidentifications or to the conclusion that all OM (i.e., kerogen and solid bitumen) is the same. To improve the accuracy of SEM identifications of dispersed OM in shale, correlative light and electron microscopy (CLEM) was used during this study to create optical and SEM images of OM in the same fields of view (500× magnification) under white light, blue light, secondary electron (SE), and BSE conditions. Samples ( n = 8) of varying thermal maturities and typical of the North American shale petroleum systems were used, including the Green River Mahogany Zone, Bakken Formation, Ohio Shale, Eagle Ford Formation, Barnett Formation, Haynesville Formation, and Woodford Shale. The CLEM image sets demonstrate the importance of correlative microscopy by showing how easily OM can be misidentified when viewed by SEM alone. Without CLEM techniques, petrographic data from SEM such as observations of organic nanoporosity may be misinterpreted, resulting in false or ambiguous results and impairing an improved understanding of organic diagenesis and catagenesis.