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Paula L. Hansley

Publications and source records attributed to Paula L. Hansley.

9 recordsLinked to original sources
USGS2019

Connections between Eocene Lakes Uinta and Gosiute with emphasis on the infilling stage of Lake Uinta in Piceance Basin

Late in its history, Eocene saline Lake Gosiute in the Greater Green River Basin, Wyoming and Colorado was progressively filled from north to south with coarse volcaniclastic sediments. During the infilling, Lake Gosiute began to drain southward across the Axial arch into saline Lake Uinta in the Piceance and Uinta Basins, Colorado and Utah (about 49 Ma) causing Lake Gosiute to freshen. Once Lake Gosiute was filled entirely (about 48 Ma), volcaniclastic sediments spilled over into Lake Uinta. The first coarse volcanic sediments entered the north part of Lake Uinta near the present-day mouth of Yellow Creek 15 miles south of the Axial arch during deposition of the Mahogany oil shale zone. There is evidence that a south-flowing river entered Lake Uinta from the Axial arch starting early in the history of the Lake and prior to substantial outflow from Lake Gosiute began. A petrographic study of sandstones from this period is consistent with an Axial arch source. It is likely that the outflow channel occupied this pre-existing drainage. Determining when outflow from Lake Gosiute began to move through this pre-existing channel is difficult as mainly mud-sized sediments would have entered Lake Uinta from Lake Gosiute prior to infilling. In addition, reliable dates for most of the strata deposited in Lake Uinta are lacking. A partial section of Lake Uinta strata is preserved at Deep Channel Creek about 10 mi south of the Axial arch. Here the R-6 oil shale zone, below the Mahogany zone, has graded into fluvial strata–the only place in the basin where this zone is not lacustrine. In addition, the underlying L-5 zone is atypically sandy. We propose that Lake Gosiute began to drain into Lake Uinta starting at about the beginning of deposition of the L-5 oil shale zone increasing the input of sediments into the northern part of Lake Uinta. Mud-sized sediments could have come from Lake Gosiute, but the coarser sediments likely came from the Axial arch. Volcaniclastic sediments produced a rapidly prograding deltaic complex that ultimately filled in much if not all of the eastern part of Lake Uinta. The first volcanic sediments to reach the deep depocenter were mainly fine-grained turbidites but ultimately the depocenter was largely filled by slumps off the over-steepened delta front. A petrographic study of the volcaniclastic sandstones indicates that the Absaroka volcanic field in northwest Wyoming is the likely source of the volcanic fraction.

Colorado, Utah↗
USGS1983

The nonopaque, detrital heavy mineralogy of the Morrison Formation near Crownpoint, San Juan Basin, New Mexico

Description and quantification of the nonopaque, detrital heavy mineralogy of the Upper Jurassic Morrison Formation in the southwestern part of the San Juan Basin have helped to identify stratigraphic trends, source-area lithologies, and zones of post-depositional alteration possibly related to uranium mineralization. A synthesis of stratigraphic variations in mineral species and diversity in Morrison sandstones reveals an increasing upward igneous component, characterized by euhedral zircon and subhedral apatite. Complementing this trend, the predominantly well-rounded assemblage of the Recapture Member changes to a mixed assemblage of rounded and angular grains in the Westwater Canyon Member. Overall, the low diversity in mineral species indicates a sedimentary, low- to medium-grade-metamorphic, and acid igneous parentage for Morrison sediments; however, post-depositional processes have played a significant role in determining the present mineralogy. The roles that diagenesis and weathering have played in determining the present aspect of the assemblage, which is a mature garnet-zircon-apatite-tourmaline suite, cannot be overemphasized. For instance, the presence of authigenically etched to skeletal garnet and staurolite implies that entire grains have been destroyed. Comparison of cores with measured sections indicates that near-surface weathering has caused the destruction of some minerals, notably apatite, sensitive to acidic conditions. Therefore, in order to interpret the sedimentology, stratigraphic intervals in which post-depositional processes have affected the mineralogy were identified. These diagenetic zones may prove to be most useful in delineating the past movements and compositions of interstitial, possibly ore-forming, fluids.

Open-File Report↗
USGS1980

Mineralogy and diagenesis of low-permeability sandstones of Late Cretaceous age, Piceance Creek Basin, northwestern Colorado

This report presents preliminary results of a mineralogic and diagenetic study of some low-permeability sandstones from measured surface sections and cores obtained from drill holes in the Piceance Creek Basin of northwestern Colorado. A documentation of the mineralogy and diagenetic history will aid in the exploration for natural gas and in the development of recovery technology in these low-permability sandstones. These sandstones are in the nonmarine upper part of the Mesaverde Formation (or Group) of Late Cretaceous age and are separated from overlying lower Tertiary rocks by a major regional unconformity. Attention is focused on the sandstone units of the Ohio Creek Member, which directly underlies the unconformity; however, comparisons between the mineralogy of the Ohio Creek strata and that of the underlying sandstone units are made whenever possible. The Ohio Creek is a member of the Hunter Canyon Formation (Mesaverde Group) in the southwestern part of the basin, and the Mesaverde Formation in the southern and central parts of the basin. The detrital mineralogy is fairly constant throughout all of these nonrnarine Cretaceous sandstone units; however, in the southeastern part of the basin, there is an increase in percentage of feldspar, quartzite, and igneous rock fragments in sandstones of the Ohio Creek Member directly underlying the unconformity. In the southwestern part of the basin, sandstones of the Ohio Creek Member are very weathered and are almost-entirely comprised of quartz, chert, and kaolinite. A complex diagenetic history, partly related to the overlying unconformity, appears to be responsible for transforming these sandstones into potential gas reservoirs. The general diagenetic sequence for the entire Upper Cretaceous interval studied is interpreted to be (early to late): early(?) calcite cement, chlorite, quartz overgrowths, calcite cement, secondary porosity, analcime (surface only), kaolinite and illite, and late carbonate cements. Authigenic high-iron chlorite, which occurs on grain rims and in pore throats, is primarily responsible for the low-permeability of the subsurface sandstones of the Ohio Creek Member in the center of the basin. Kaolinite is the most abundant pore-filling authigenic clay in these sandstones, from the southwestern part of the basin and is responsible for their distinctive white-weathering color in outcrop. In the sandstones below the Ohio Creek Member, however, chlorite and kaolinite occur locally, and authigenic calcite and illite are more abundant. The occurrence and distribution of secondary porosity is one of the most important aspects of the diagenetic history of these sandstones. It is present as moldic intra- and intergranular porosity, as well as microporosity among authigenic clay pariicles. Although present locally in most sandstone units, secondary porosity is particularly common in the uppermost sandstone units and is interpreted to have formed primarily asa result ofweathering during the time represented by the Cretaceous-Tertiary unconformity.

Colorado↗