Defining bounding surfaces within and between eolian and non-eolian deposits, Lower Jurassic Navajo Sandstone, Moab Area, Utah, U.S.A.: Implications for subdividing erg system strata

ABSTRACT A model-independent, sequence stratigraphic approach is used to define bounding surfaces in the Navajo Sandstone in order to identify an architectural hierarchy of genetically related sedimentary packages and the surfaces that bound them across multiple scales of both eolian and non-eolian components of an erg system. Seven bounding surfaces and eight depositional units are defined, from small to large scale. A lamina-deviation surface bounds wedge- and tabular-shaped sets of laminae and/or laminasets, separating those that have different angle orientations on the dune slipface. A bed-deviation surface bounds a succession of beds (crossbeds) that lie at different angles or orientations to bedding above, below, or adjacent to it. A bedset-deviation surface is curved, inclined, and/or wavy and irregular that bounds bedsets and their internal stratification patterns; that is, bed-deviation surfaces, and lamina-deviation surfaces. A simple surface is gently inclined with or without small, concave or convex segments that bound beds and bedsets. A composite surface is horizontal with or without concave, curved, or irregular portions of that surface. A complex surface is laterally extensive (∼ 1–10+ km) that regionally bounds and truncates underlying conterminous and interfingered eolian and non-eolian strata. An amalgamated surface is a regionally extensive (∼ 10 to 100s km) mappable unconformity, merged unconformities, and their laterally equivalent conformable surface that can exhibit local to regional pedogenic modification, lags, and significant (meters to 10s m) paleotopographic relief. The genetically related sedimentary packages typically bounded by like or higher-rank surfaces are defined as laminae, laminasets, bed, bedsets, and simple, composite, complex, and amalgamated units. Field relationships of strata and surfaces are key to reconstructing the interactions between eolian and non-eolian deposits and the processes they represent at the local, regional, and basin scale. This classification scheme can be applied to erg-system strata to fully integrate changes in diverse facies within and between contiguous deposits.

WEATHERING PITS VERSUS TRAMPLE MARKS: A REINTERPRETATION OF THE “DINOSAUR DANCE FLOOR”: A JURASSIC NAVAJO SANDSTONE SURFACE IN THE VERMILION CLIFFS NATIONAL MONUMENT, ARIZONA

ABSTRACT Within the eolian Lower Jurassic Navajo Sandstone, exposed in the Coyote Buttes area of Vermilion Cliffs National Monument in Arizona, a site (informally known as the “Dinosaur Dance Floor”) is reinterpreted as an enigmatic, modified (possibly pedogenic) eolian surface that was exposed and further modified and accentuated by modern weathering and erosion. The resultant surface is covered with small, shallow potholes or weathering pits, with no direct evidence of dinosaur activity.

Revising the stratigraphy at Mollies Nipple, Kane County, Utah, USA to better understand the origin of jarosite and alunite cements

<p>Mollies Nipple—a butte located in the Grand Staircase-Escalante National Monument (GSENM)—is of special interest because of the presence of unusual alunite and jarosite cements within the caprock. These minerals precipitate in hyperacidic environments (pH1-2) and are not stable over ~pH5; yet they are abundant on Mars where they are used to interpret depositional and diagenetic environments. The caprock at Mollies Nipple is historically interpreted as Navajo Sandstone via photogeologic mapping; however, it is ~200 m above the mapped upper extent of the Navajo Sandstone in this region. The units overlying the Navajo Sandstone have complex stratigraphic relations in this region and the caprock could be the Carmel or Temple Cap Formations, or the Page Sandstone. This study aims to characterize Mollies Nipple through measured sections, mineralogical analyses, palynomorph analysis, and radiometric age dates from ash lenses present in the caprock. The results will better define the stratigraphy of Mollies Nipple and determine the regional correlation of the caprock. Ultimately, this work will contribute to the understanding of how alunite and jarosite were precipitated at Mollies Nipple; why these minerals are still present at Mollies Nipple, and potentially revise the understanding of Martian depositional environments.</p>

Diagenetic complexities of iron oxide cements in Mesozoic sandstones of Utah, U.S.A.

<p>Stratigraphic units of the Colorado Plateau comprise a remarkable Mesozoic section in Utah. Thse units are ideal for studying sandstone diagenesis where there is established basinal context of depositional facies and tectonics, as well as continuity of exposure. To untangle the complex relationships and diagenetic histories, it is crucial to understand host rock properities (porosity and permeability), authigenic mineralogies (that give clues to fluid composition), diagenetic textures, and age dating. This study is a review and synthesis of previous work that has contributed to the understanding of the diagenetic history recorded in authigenic iron oxide precipitates. We discuss cement generations and mineralogies, fluid chemistries, origins and mobilization of iron, and timing of precipitation. Spheroidal cemented mineral masses (concretions) are common within many Mesozoic units of Utah – most notably the Jurassic Navajo Sandstone.  However, formation of these concretions is still not completely understood. Spheroidal concretions are currently a “hot topic”, especially since the discovery of similar “blueberry” features on Mars with their implications for habitability, and the potential for these nodules to host biosignatures. Several models for spheroidal concretion formation are evaluated. Understanding how iron is mobilized and precipitated and how spheroidal concretions form have implications for similar geometries and mineralogies in many terrestrial regions, but will require continued integrated studies across multiple scales (see Baker and Potter-McIntyre, this session). These scales include the submicroscopic levels of understanding and detecting the potential role of microbes in mineral precipitation, to the larger scale mapping of regional diagenetic coloration and mineral patterns that could represent records of basinal fluids and the response to climate, tectonics, and regional hydrology.</p>

Working towards a universal formation model for spheroidal iron (oxyhydr)oxide concretions

<p>Three principal models exist for iron (oxyhydr)oxide concretion formation in the Navajo Sandstone in southern Utah, USA and the most recent model by Yoshida et al. (2018) suggests that calcite concretions are precursors to iron (oxyhydr)oxide concretions. This model could account for the existence of a gradient of carbonate and iron concretions found in both red diagenetic facies (with primary hematite grains coatings retained) and white diagenetic facies (primary hematite grain coatings removed during diagenesis). However, evidence for calcite precursor minerals and an understanding of the fluid chemistries involved in these diagenetic reactions is lacking. This research focuses on spheroidal concretions in the Navajo Sandstone at Coyote Gulch—a site that is down gradient, but upsection from Spencer Flat (the focus of previous work) and tests the hypothesis that calcite concretions are precursors to iron (oxyhydr)oxide concretions. Bulk mineralogy, bulk geochemistry, and petrography provide elemental and mineralogical composition of the concretions and show that the concretions are calcite cemented (~40 wt.%) and the host rock is predominately iron (oxyhydr)oxide cemented (~3 wt.%). The host rock surrounding embedded concretions shows secondary iron (oxyhydr)oxide precipitation and decreases in calcite in transects away from the concretion. These relationships suggest that the calcite concretions formed prior to the precipitation of secondary iron (oxyhydr)oxides and may have provided a localized buffering environment for the precipitation of iron (oxyhydr)oxides. This study also represents an opportunity to determine a universal model for carbonate and iron (oxyhydr)oxide spheroidal concretion formation, and to understand the influence of fluid interactions in the search for subsurface redox reactions to power metabolisms on Earth and Mars.</p>

Hierarchical scales of soft-sediment deformation in erg deposits, Lower Jurassic Navajo Sandstone, Moab area, Utah, U.S.A.

ABSTRACT Extensive soft-sediment deformation (SSD) of multiple expressions and scales record active and dynamic events and processes in erg deposits of the Lower Jurassic Navajo Sandstone near Moab, Utah. The erg deposits preserve depositional environments of eolian dune, interdune, fluvial, playa, lake, and spring. A large range of SSD features, from intact beds showing little deformation to pervasively disturbed beds, exist in many of these deposits. A simplified classification index captures the different scales of SSD in ascending order of deformation intensity: 1) mostly intact bedding with small-scale wavy or undulatory deformation structures within single beds; 2) dish and flame structures; 3) meter-scale, kinked, slumped, rolled, overturned, vertical, and detached contorted crossbedding, and associated centimeter- to meter-scale pipes; and 4) disruptive diapirs and laterally extensive massive sandstone. The SSD features of deformed crossbed sets, diapirs, and massive sandstone beds, are consistently juxtaposed, and are thus genetically linked. Although the Navajo Sandstone has been considered a classic example of an extensive dry eolian system, both individual and combinations of strata bounded SSD features exemplify dynamic deformation, liquefaction, and fluidization that took place at various times after deposition. The lowest degree of deformation, SSD 1, is largely attributed to autogenic––inherent to the eolian system––or local allogenic processes. Larger degrees of deformation, SSD 2–4, were more likely produced by allogenic, external-forcing processes from regional changes in climate and/or near-surface groundwater conditions originating from the Uncompahgre uplift, with the deformation triggered by some event(s). Possible significant ground motion could have led to large-scale disruption in the Navajo sand sea across kilometer-scale intervals. The Navajo example establishes valuable hierarchical relationships of processes and products for recognizing and interpreting SSD in other ancient and modern eolian systems. This has particular relevance to sedimentary discoveries on Mars, where SSD features are visible from remote sensing imagery and rover exploration.

Seismic response to paleo-sand dunes in the Nugget Sandstone Formation, southwestern Wyoming

We have analyzed a 3D seismic survey acquired for a carbon sequestration project on top of the Moxa Arch in southwestern Wyoming. We observed a zone of discontinuous reflectors on vertical slices of seismic amplitude volume, whereas, the northwest–southeast lineations were observed on the time slices. We performed a seismic to well tie that suggested that the lineations occur within the Nugget Sandstone. The Nugget Sandstone is an eolian sandstone deposit of Early Jurassic age, deposited as a subtropical dune field, and equivalent to the Navajo Sandstone of southwestern Utah. Petrophysical analysis indicates that the Nugget Sandstone is dominated by clean sandstone (70%–80%), whereas evaporites, including halite and anhydrite, are present in certain zones. Previous outcrop studies on the Navajo Sandstone indicate the wind direction to be predominantly northeast–southwest. Seismic attributes, including coherence and curvature, displayed on stratal slices within the Nugget Sandstone interval indicate the presence of lineations in the northwest–southeast direction with irregular spacing. These lineations are approximately perpendicular to the inferred dominant wind direction. We computed the dominant wind direction from the average azimuth of the lineations as seen on the curvature attribute in the Nugget Sandstone interval. Geological feature: Eolian sand dunes with interdunal evaporites Seismic appearance: Parallel lineations with irregular spacing on seismic attribute horizon slices Alternative interpretations: Canyons at continental slopes; slope failures Features with a similar appearance: Marine bars; contourites Formation: The Nugget Sandstone — equivalent to the Navajo Sandstone Age: Early Jurassic Location: Moxa Arch, Wyoming Seismic data: Obtained by the University of Wyoming with U.S. DOE funding Contributors: Dhruv Agrawal, Brady Lujan, Sumit Verma, Shuvajit Bhattacharya, and Subhashis Mallick Analysis tools: Coherence and curvature attributes; seismic inversion; petrophysical inversion