Paper No. 4
Presentation Time: 9:00 AM-6:00 PM
SOME REMARKABLE TEXTURES IN SECONDARY RESINITES IN WASATCH PLATEAU COALS, UTAH
The Cretaceous-Tertiary coals of the Wasatch Plateau in Utah are notable for their abundance of resinite macerals, typically 5-15 volume percent. Petrographic analysis of polished blocks shows that much of the resinite occurs as secondary cleat fillings and appears as honey-colored flakes in hand-specimen. Because there is no evidence for a resinite source outside of the coal seams the cleat-filling resinite is thought to come from resin bodies incorporated into the peat that formed the coal. Following cleat formation the resin bodies transformed into resinite and began to flow through the coal in response to the heat and pressure of coalification. Flow is confirmed by the presence of resinite in the cleats, flow textures in the resinite veinlets, incorporation of coal xenoliths, and zoning textures showing multiple layers. Also present are occasional vesicles in resinite particles. Fractures in the resinite veinlets not seen in the adjacent coal suggest that the resinite became brittle when it resolidified. There is some evidence for pre-depositional fungal activity. Besides the dominant bright yellowish-green fluorescing resinite a darker phase is also present. This dark phase occurs with the lighter phase along the edges and in the center of the veins, as brecciated inclusions, and as protrusions with a botryoidal structure. Bright droplets of the dominant resinite are frequently seen within this darker phase. This texture is similar to immiscible droplets sometimes seen in igneous rocks and suggests that the two resinite phases may have been immiscible. Occurrences of what appear to be late-stage differentiation of the bright phase within the dark phase were also noted. In some cases the veins cross-cut each other, are fractured themselves and show remnant fragments of a possible earlier depositional episode along the vein edges. These textures along with the zoning suggest that there were multiple resinite mobilization events. In summary, the textures seen in these secondary resinites are not unlike the igneous textures seen in intrusions including vein fillings, flow, vesicles, xenoliths, zoning, immiscibility, differentiation, and multiple intrusive or migration episodes.