The subsurface is the third dimension in understanding the Cenozoic landscape evolution of the Southern Rocky Mountains. Because much of the geology of the project area is concealed under cover, understanding this dimension provides a more comprehensive view of the geologic framework that underlies the present-day landscape.
A Task of the Cenozoic Landscape Evolution of the Southern Rocky Mountains Project.
A combination of drill-hole information, geophysical methods, and geologic mapping provides the most comprehensive approach to understanding the third dimension underlying the landscape. Drill-hole information is critical for understanding rock types and structures in the subsurface, but wells are typically too sparsely spaced or too shallow in the Southern Rocky Mountains to gain enough information to correlate accurately between wells. In contrast, geophysical data, especially airborne surveys, provide comprehensive coverage of an area. Although geophysical data are only indirect measurements of physical properties of rocks at depth, in combination with geologic mapping, they place important constraints on geology that we cannot see. Moreover, the task takes advantage of an expansive collection of airborne geophysics and ground-based data that were inherited from the previous project "Geologic Framework of Rio Grande Basins".
Objectives
The main objective of this task is to develop a better understanding of the subsurface of the Southern Rocky Mountains, especially where there is substantial cover, as in valleys or on hillslopes. A complementary objective is to improve expertise in understanding and modeling the geophysical expression of subsurface geologic features using recently developed methodology or new innovations. A particular focus is on structural basins that formed during Rio Grande rift formation using the extensive airborne geophysical data set that has already been collected over much of the southern part of the project area. Many of these extensional basins overprint or possibly were controlled by earlier Laramide compressional structures, leading to confusion about age relations and mechanisms of extension that might be answered by a better view of the subsurface. Gravity methods in particular are good for identifying young rift basins containing poorly consolidated sediments as opposed to Laramide basins that contain better indurated sedimentary rocks.
Many of the objectives to investigate the subsurface also address societal issues related to groundwater management, geothermal and traditional energy resources, and seismic hazards. Knowing basin aquifer thickness, presence and depth to clay, buried faults and basement structure, and the configuration of faults at the mountain front are all important to understanding these resources and hazards.
Specific objectives include:
- Investigate overall rift basin structure by developing models of basin-fill thickness variations.
- Investigate the subsurface manifestation of major structural zones accommodating transfer of strain, such as in between basins.
- Investigate the geometry of basin margin structures from the range front into the basin.
- Investigate the subsurface configuration of major intrabasin structures.
- Map faults and volcanic rocks where they extend under alluvial cover.
- Interpret electromagnetic (EM) data in conjunction with existing core and drillhole samples to map and understand the nature of ancient lacustrine deposits lying beneath the sand, Great Sand Dunes National Park and vicinity.
- Examine variations in aeromagnetic expression of volcanic rocks to aid mapping and to interface with rock-magnetic studies.
- Explore the depths of information available from data recently collected from an airborne gravity gradiometer (AGG) survey while gaining expertise in this new method.
- Model geologic interpretations of the geophysics in 3D.
Methodology
Existing and new gravity, magnetic, electromagnetic (EM), seismic-reflection geophysical data and drillhole information will be interpreted in conjunction with geologic mapping for specific areas under investigation by the project. An extensive database from multiple high-resolution and frontier aeromagnetic, gravity, and electromagnetic (EM) surveys are available over a large portion of the San Luis Basin and Poncha Pass area into the next basin to the north. These data and core samples from a 100-m-deep hole were collected during the former Geologic Framework of Rio Grande basins project but have not been thoroughly studied. This rich and unique data set provides a rationale for focusing early efforts on the San Luis Basin and Poncha Pass. Approaches include map interpretation and 2D and 3D modeling in collaboration with geologists in other tasks.
- Overview
The subsurface is the third dimension in understanding the Cenozoic landscape evolution of the Southern Rocky Mountains. Because much of the geology of the project area is concealed under cover, understanding this dimension provides a more comprehensive view of the geologic framework that underlies the present-day landscape.
A Task of the Cenozoic Landscape Evolution of the Southern Rocky Mountains Project.
A combination of drill-hole information, geophysical methods, and geologic mapping provides the most comprehensive approach to understanding the third dimension underlying the landscape. Drill-hole information is critical for understanding rock types and structures in the subsurface, but wells are typically too sparsely spaced or too shallow in the Southern Rocky Mountains to gain enough information to correlate accurately between wells. In contrast, geophysical data, especially airborne surveys, provide comprehensive coverage of an area. Although geophysical data are only indirect measurements of physical properties of rocks at depth, in combination with geologic mapping, they place important constraints on geology that we cannot see. Moreover, the task takes advantage of an expansive collection of airborne geophysics and ground-based data that were inherited from the previous project "Geologic Framework of Rio Grande Basins".
Sources/Usage: Some content may have restrictions. Visit Media to see details.From the Air: Helicopter conducting an aeromagnetic survey over the Great Sand Dunes, Colorado. Airborne geophysical methods include magnetic, electromagnetic, gravity, and gradiometry. (Credit: Tien Grauch, USGS. Public domain)
From the Ground: Typical geophysical methods collected from the ground include gravity, electromagnetic, magnetotellurics, magnetic, and limited industry seismic-reflection. Project geophysicist Ben Drenth conducting gravity surveys to better understand subsurface geology.(Credit: David Fitterman, USGS Emeritus. Public domain.) Objectives
The main objective of this task is to develop a better understanding of the subsurface of the Southern Rocky Mountains, especially where there is substantial cover, as in valleys or on hillslopes. A complementary objective is to improve expertise in understanding and modeling the geophysical expression of subsurface geologic features using recently developed methodology or new innovations. A particular focus is on structural basins that formed during Rio Grande rift formation using the extensive airborne geophysical data set that has already been collected over much of the southern part of the project area. Many of these extensional basins overprint or possibly were controlled by earlier Laramide compressional structures, leading to confusion about age relations and mechanisms of extension that might be answered by a better view of the subsurface. Gravity methods in particular are good for identifying young rift basins containing poorly consolidated sediments as opposed to Laramide basins that contain better indurated sedimentary rocks.
Interpreted Faults and Models of Basin Shape near Taos, New Mexico: An example of interpreting buried faults from aeromagnetic data and basin shape from gravity data near Taos, New Mexico, to provide a better 3D view of basin structure. The integration of geophysical interpretations with geologic mapping is a hallmark of the Southern Rocky Mountains project. (Geologic map compiled by P. Bauer and others, New Mexico Bureau of Geology) Many of the objectives to investigate the subsurface also address societal issues related to groundwater management, geothermal and traditional energy resources, and seismic hazards. Knowing basin aquifer thickness, presence and depth to clay, buried faults and basement structure, and the configuration of faults at the mountain front are all important to understanding these resources and hazards.
Specific objectives include:
- Investigate overall rift basin structure by developing models of basin-fill thickness variations.
- Investigate the subsurface manifestation of major structural zones accommodating transfer of strain, such as in between basins.
- Investigate the geometry of basin margin structures from the range front into the basin.
- Investigate the subsurface configuration of major intrabasin structures.
- Map faults and volcanic rocks where they extend under alluvial cover.
- Interpret electromagnetic (EM) data in conjunction with existing core and drillhole samples to map and understand the nature of ancient lacustrine deposits lying beneath the sand, Great Sand Dunes National Park and vicinity.
- Examine variations in aeromagnetic expression of volcanic rocks to aid mapping and to interface with rock-magnetic studies.
- Explore the depths of information available from data recently collected from an airborne gravity gradiometer (AGG) survey while gaining expertise in this new method.
- Model geologic interpretations of the geophysics in 3D.
3D Image of Electrical Resistivity from Airborne Electromagnetic Geophysics: An example of a 3D model for Great Sand Dunes National Park, San Luis Valley, Colorado, from an airborne electromagnetic survey. Electrical resistivity can be used as a proxy for interpreting the distribution of sand versus clay underneath the eolian sand sheet. The clay was deposited by Lake Alamosa, a long-lived lake that disappeared several hundred thousand years before the formation of the dunes. Methodology
Existing and new gravity, magnetic, electromagnetic (EM), seismic-reflection geophysical data and drillhole information will be interpreted in conjunction with geologic mapping for specific areas under investigation by the project. An extensive database from multiple high-resolution and frontier aeromagnetic, gravity, and electromagnetic (EM) surveys are available over a large portion of the San Luis Basin and Poncha Pass area into the next basin to the north. These data and core samples from a 100-m-deep hole were collected during the former Geologic Framework of Rio Grande basins project but have not been thoroughly studied. This rich and unique data set provides a rationale for focusing early efforts on the San Luis Basin and Poncha Pass. Approaches include map interpretation and 2D and 3D modeling in collaboration with geologists in other tasks.