Fracture Variability in Entrada Sandstone in the Moab, Utah Area
Presenter Type
UNO Undergraduate Student
Major/Field of Study
Geography and Geology
Other
Geology
Advisor Information
Dr. Harmon Maher
Location
MBSC Ballroom Poster # 1205 - U
Presentation Type
Poster
Start Date
24-3-2023 1:00 PM
End Date
24-3-2023 2:15 PM
Abstract
Simple, relatively planar fractures are common in rocks and display diverse patterns. The variability of fracture patterns within a geologic unit is influenced by many structural factors and occurs at different scales. Fracture patterns vary by orientation distribution, cross-cutting relationships, and density. Fracture variation was studied on the Jurassic-aged (time of the dinosaurs) Moab Tongue sandstone near Arches National Park, Utah, where fracture patterns are easily visible. Fracturing in the area was influenced by multiple episodes of local faulting and salt tectonics in the Cenozoic era (last ~65 million years). Weathering-related joints are common, with fractures often appearing along bedding. Analysis was performed from Google Earth imagery as well as in-person field work conducted in summer 2022, primarily in an area west of Arches National Park known as Castle Mesa. Some areas of Moab Tongue fractures are dominated by one preferred orientation, others by up to three. Fractures which appear to be singular in Google Earth imagery were often a cluster of fractures and deformation bands in the field. The Moab Tongue Sandstone is generally significantly more fractured than the underlying Slickrock sandstone, which is a unit of sandstone directly underneath. From cliff sides, joints in the Slickrock appear conjugate (joints that are at about a 60° to each other). Results from field work show three distinct joint sets in the Castle Mesa study area, including a dominant set running ~E-W, with a subordinate set at right angles, and an additional NE-SW set developed locally. Distributed deformation band bundles occur in Castle Mesa at distances greater than 700m from the nearest fault. The sequence of formation is as follows: deformation bands formed first, followed by the ~E-W set, and finally the ~N-S set. Locally joint trace map directions can be very similar, considered well organized, or be varied and less organized, or even random and unorganized. Maps of measures of degree of orientation organization show an increase in complexity, i.e. a decrease in the degree of orientation organization, with approach to a major fault. There was substantial variation within the Moab Tongue over scales of tens of meters to ~100 meters. Possible contributors to variability are different degrees of weathering, variability of causative stress fields (e.g due to proximity to fault), within unit variability of rock strength (e.g. due to variable cementation).
Scheduling
10:45 a.m.-Noon, 1-2:15 p.m., 2:30 -3:45 p.m.
Fracture Variability in Entrada Sandstone in the Moab, Utah Area
MBSC Ballroom Poster # 1205 - U
Simple, relatively planar fractures are common in rocks and display diverse patterns. The variability of fracture patterns within a geologic unit is influenced by many structural factors and occurs at different scales. Fracture patterns vary by orientation distribution, cross-cutting relationships, and density. Fracture variation was studied on the Jurassic-aged (time of the dinosaurs) Moab Tongue sandstone near Arches National Park, Utah, where fracture patterns are easily visible. Fracturing in the area was influenced by multiple episodes of local faulting and salt tectonics in the Cenozoic era (last ~65 million years). Weathering-related joints are common, with fractures often appearing along bedding. Analysis was performed from Google Earth imagery as well as in-person field work conducted in summer 2022, primarily in an area west of Arches National Park known as Castle Mesa. Some areas of Moab Tongue fractures are dominated by one preferred orientation, others by up to three. Fractures which appear to be singular in Google Earth imagery were often a cluster of fractures and deformation bands in the field. The Moab Tongue Sandstone is generally significantly more fractured than the underlying Slickrock sandstone, which is a unit of sandstone directly underneath. From cliff sides, joints in the Slickrock appear conjugate (joints that are at about a 60° to each other). Results from field work show three distinct joint sets in the Castle Mesa study area, including a dominant set running ~E-W, with a subordinate set at right angles, and an additional NE-SW set developed locally. Distributed deformation band bundles occur in Castle Mesa at distances greater than 700m from the nearest fault. The sequence of formation is as follows: deformation bands formed first, followed by the ~E-W set, and finally the ~N-S set. Locally joint trace map directions can be very similar, considered well organized, or be varied and less organized, or even random and unorganized. Maps of measures of degree of orientation organization show an increase in complexity, i.e. a decrease in the degree of orientation organization, with approach to a major fault. There was substantial variation within the Moab Tongue over scales of tens of meters to ~100 meters. Possible contributors to variability are different degrees of weathering, variability of causative stress fields (e.g due to proximity to fault), within unit variability of rock strength (e.g. due to variable cementation).