Digital data from the Great Sand Dunes airborne gravity gradient survey, south-central Colorado

Drenth, Benjamin J.; Abraham, J. D.; Grauch, V.J.S.; Labson, Victor F.; Hodges, Greg

doi:10.3133/ofr20131011

Cited by 8 publications

(4 citation statements)

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“…For this study, a partial-tensor helicopter survey (Drenth et al, 2013a) was flown in two partially overlapping blocks (Figs. 2, 4, and 5): a northern block with 100 m line spacing at ~80 m above the ground, and a southern block with 50 m line spacing at ~40 m above the ground.…”

Section: Airborne Gravity Gradient Datamentioning

confidence: 99%

“…Each survey block used northsouth traverse lines and east-west tie lines. The full gravity gradient tensor was calculated using Fourier methods, which can generate spurious effects along the edges of the survey blocks (e.g., Drenth et al, 2013a). Data from the two blocks cannot be digitally merged in rigorous fashion, due to the differences in resolution (Kass, 2013) and the presence of edge effects.…”

Section: Airborne Gravity Gradient Datamentioning

confidence: 99%

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Geophysical expression of buried range-front embayment structure: Great Sand Dunes National Park, Rio Grande rift, Colorado

et al. 2017

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Great Sand Dunes National Park and Preserve (GRSA, Colorado) lies along the eastern margin of the San Luis Basin and the tectonically active Sangre de Cristo fault system that are part of the northern Rio Grande rift. GRSA lies within a prominent embayment in the range front where two separate sections of the Sangre de Cristo fault system intersect. Fault scarps are observed along both intersecting fault zones within older basin-fill alluvium, but have been obscured by the actively migrating dunefield. The dune sand is also strongly magnetic, locally limiting the usefulness of aeromagnetic methods for mapping concealed structure. This study uses airborne geophysical methods, primarily airborne gravity gradient data, along with constraints from geologic mapping and limited subsurface data and groundwater modeling, to interpret the subsurface basin geometry and range-front structure of the embayment. Using forward modeling of the gravity gradient data and locations of faults inferred from gravity gradient and aeromagnetic lineaments, several previously unrecognized tectonic elements are interpreted adjacent to the range front. Some of the largest rift-related fault offsets are demonstrated to be basinward of the normal fault zones mapped at the surface along the range front of the Sangre de Cristo Mountains, along faults concealed under the dunefield and subparallel to the two fault sections. A fault-bounded structural bench, likely composed of Proterozoic rocks, underlies most of the high dunefield at depths of 500 m to 1 km. The bench is truncated on its southwest margin by a northwest-trending, southwest-dipping normal fault. A northeast-trending, northwest-dipping normal fault with ~600 m of estimated relief lies under the southern margin of the dunefield and bounds a structurally higher bench of Proterozoic rocks concealed at <400 m depth near the range front. The northwest-and northeast-trending geophysical lineaments generally correspond well with the trends of faults mapped at the surface, and with both pre-and syn-rift structures in the Sangre de Cristo Mountains. Aeromagnetic anomalies are explained by variations in the magnetization of pre-rift rocks, and the strongly magnetic dune sand.

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Section: Airborne Gravity Gradient Datamentioning

confidence: 99%

Section: Airborne Gravity Gradient Datamentioning

confidence: 99%

Geophysical expression of buried range-front embayment structure: Great Sand Dunes National Park, Rio Grande rift, Colorado

et al. 2017

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“…A better philosophical approach is for interpreters to use terrain effects to their G r a v i t y a n d p o t e n t i a l f i e l d s as noise common to all types of airborne geophysical data (Drenth et al, 2013). A better philosophical approach is for interpreters to use terrain effects to their G r a v i t y a n d p o t e n t i a l f i e l d s as noise common to all types of airborne geophysical data (Drenth et al, 2013).…”

Section: Geologic Settingmentioning

confidence: 99%

“…A high-resolution helicopter AGG survey was flown over the GRSA region during early 2012 (Drenth et al, 2013). The survey was split into two blocks, with each block having different survey specifications.…”

Section: Geologic Settingmentioning

confidence: 99%

Expression of terrain and surface geology in high-resolution helicopter-borne gravity gradient (AGG) data: Examples from Great Sand Dunes National Park, Rio Grande Rift, Colorado

Drenth

2013

The Leading Edge

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Airborne gravity gradient (AGG) data are rapidly becoming standard components of geophysical mapping programs because of their advantages in cost, access, and resolution over measurements of the gravity field on the ground. Unlike conventional techniques that measure the gravity field, AGG methods measure derivatives of the gravity field. This means that effects of terrain and near-surface geology are amplified in AGG data, and that proper terrain corrections are critically important for AGG data processing. However, terrain corrections require reasonable estimates of density for the rocks and sediments that make up the terrain. A recommended philosophical approach is to use the terrain and surface geology, with their strong expression in AGG data, to the interpreter's advantage. An example of such an approach is presented here for an area with difficult ground access and little ground gravity data. Nettleton-style profiling is used with AGG data to estimate the densities of the sand dunefield and adjacent Precambrian rocks from the area of Great Sand Dunes National Park in southern Colorado. Processing of the AGG data using the density estimate for the dunefield allows buried structures, including a hypothesized buried basement bench, to be mapped beneath the sand dunes.

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Data Sources for Building Geological Models

Burt

Sirles²,

Turner

2021

Applied Multidimensional Geological Modeling

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Digital data from the Great Sand Dunes airborne gravity gradient survey, south-central Colorado

Abstract: This report contains digital data and supporting explanatory files describing data types, data formats, and survey procedures for a high

Cited by 8 publications

References 1 publication

Geophysical expression of buried range-front embayment structure: Great Sand Dunes National Park, Rio Grande rift, Colorado

Geophysical expression of buried range-front embayment structure: Great Sand Dunes National Park, Rio Grande rift, Colorado

Expression of terrain and surface geology in high-resolution helicopter-borne gravity gradient (AGG) data: Examples from Great Sand Dunes National Park, Rio Grande Rift, Colorado

Data Sources for Building Geological Models

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