ISOPACH MAPPING OF A CARBONATE DEPOSIT IN THE LOWER JURASSIC NAVAJO SANDSTONE IN THE MOAB, UTAH AREA, USA

The first isopach map of a carbonate deposit in the Navajo Sandstone was produced using 3-dimensional spatial interpolation in ArcGIS Pro. A confluence referred to as Trough Canyon in Ten Mile Canyon west of Moab, Utah preserves an unusually well-exposed carbonate deposit. Laterally continuous exposures along multiple cross-sectional planes provided a high level of reconstructive accuracy in isopach mapping. Several pinch-outs indicate the lateral extent of the uneroded boundaries of the deposit, revealing an ovoid shape in map view.

A kriging model was used in ArcGIS Pro to generate an isopach map revealing the thickest (deepest) parts of the basin as well as its thinnest (shallowest) depositional margins. The deposit is ~1 km in diameter, it is lenticular in geometry, and has a maximum thickness of <2 m. The isopach map provides elucidative 3-dimensional spatial context for studying basin-wide trends in texture and composition.

Previous workers have interpreted carbonate deposits in the erg margin of the Navajo Sandstone as an interdune lacustrine paleoenvironment. The purpose of the sedimentary analyses performed in this study is to identify spatial patterns of siliciclastic sedimentation within the carbonate basin.

To elucidate the spatial distribution and concentration of detrital quartz sand within the reconstructed basin, carbonate samples were processed for bulk powder X-ray diffraction analysis (XRD). XRD results yielded low levels of dispersed detrital quartz sand (0.8-12 wt% SiO₂) and a moderately higher amount (<19 wt%) present in samples containing multiple sand laminations. Spatial interpolations show where sand is concentrated within the carbonate basin.

To investigate the spatial distribution of clastic sediments according to grain size within the reconstructed basin, samples were collected along the margins and depocenter of the carbonate deposit. Grain size measurements of detrital siliciclastic minerals surviving acid dissolution (predominantly quartz grains) were conducted using laser diffraction particle size analyzer. Grain-size interpolations reveal the spatial distribution of detrital grain sizes across the carbonate basin.