April Meeting: Fort Lewis College Geology Senior Projects
Please join us on Thursday, April 21 for a fun meeting that we have every year. This time, the speakers are Fort Lewis College Geology students presenting their senior thesis projects. Each student will give a ~17-minute talk with ~3 minutes for questions.
Location: Sitter Family Hall, Fort Lewis College campus
Timeline:
- 5:30 to 6:30 – Happy Hour on the 3rd floor balcony, with student posters set up nearby
- 6:30 to 8:00 – FCGS business, student talks, and raffle.
Speakers:
- Si Arnold – LIDAR ANALYSIS OF MUD MOUNDS IN THE THUNDER SPRINGS MEMBER OF THE MISSISSIPPIAN (TOURNAISIAN) REDWALL LIMESTONE, GRAND CANYON, ARIZONA
- Enigmatic carbonate buildups occur deep within the Marble Canyon portion of the Grand Canyon, in the early Carboniferous (Tournaisian) Thunder Springs Member of the Redwall Limestone. Most of these are similar to Waulsortian mud-mounds which grew in transgressions across the globe at this time. Recent sequence stratigraphic interpretations suggest that Thunder Springs Member was deposited in a transgression. The geometries of these mounds, timing of deposition and sequence stratigraphic position, support interpreting some of these structures as mud-mounds.Mound shape and geometry were documented using a Riegl VZ-1000 terrestrial laser scanner to collect point cloud data (average point density of 172 pts/m2) of a mound located on river left near Nautiloid Canyon (River Mile 35). At the thickest, the mound is 15.55 m, with a width of 154.0 m, and mound flank angles range from 19 to 22 degrees. Beds adjacent to the mounds do not onlap but are gently inclined with minor thinning over the mound crest. These draping beds persist throughout the overlying 28.3 m of the Thunder Springs Member resulting in 2.2 m of relief along the top surface. Crinoidal grainstones of the lower 7.4 m of the Mooney Falls Member thin from 9.6m on flanks to 7.4m over the mound crest, and ultimately flattened this relief on the seafloor. The total thickness at this location of the Thunder Springs Member is 40.7 m and the Mooney Falls Member is 92.3 m.
On-going research includes the analysis of 27 hand samples taken of strata below, in, and above the mound-bearing interval which are being analyzed for faunal composition and diagenetic history. Initial results are that core samples contain biomoldic finely crystalline euhedral dolomite.
At the same stratigraphic horizon in the Thunder Springs Member in this area, mound-like features of folded beds or “core-less” mounds are estimated to range from 5 to 12m high, and up to 50m wide. These may be formed by draping beds which are associated with mound cores behind the wall of the exposure.
- Enigmatic carbonate buildups occur deep within the Marble Canyon portion of the Grand Canyon, in the early Carboniferous (Tournaisian) Thunder Springs Member of the Redwall Limestone. Most of these are similar to Waulsortian mud-mounds which grew in transgressions across the globe at this time. Recent sequence stratigraphic interpretations suggest that Thunder Springs Member was deposited in a transgression. The geometries of these mounds, timing of deposition and sequence stratigraphic position, support interpreting some of these structures as mud-mounds.Mound shape and geometry were documented using a Riegl VZ-1000 terrestrial laser scanner to collect point cloud data (average point density of 172 pts/m2) of a mound located on river left near Nautiloid Canyon (River Mile 35). At the thickest, the mound is 15.55 m, with a width of 154.0 m, and mound flank angles range from 19 to 22 degrees. Beds adjacent to the mounds do not onlap but are gently inclined with minor thinning over the mound crest. These draping beds persist throughout the overlying 28.3 m of the Thunder Springs Member resulting in 2.2 m of relief along the top surface. Crinoidal grainstones of the lower 7.4 m of the Mooney Falls Member thin from 9.6m on flanks to 7.4m over the mound crest, and ultimately flattened this relief on the seafloor. The total thickness at this location of the Thunder Springs Member is 40.7 m and the Mooney Falls Member is 92.3 m.
- Matt McCormick – ASSESSING CRUSTAL CONTAMINATION IN ~25 MA MAFIC ROCKS IN THE DULCE SWARM WITH ND-SR ISOTOPIC DATA, SOUTHWESTERN COLORADO
- Over one hundred ~25 alkaline mafic dikes are exposed in the Dulce swarm on the northeast side of the San Juan basin. These dikes were emplaced in a northeast zone of incipient extension distal to the Rio Grande rift.The chemical signatures of Oligocene mafic dikes in the Four Corners region and Rio Grande rift share similar alkaline-potassic and LREE-enriched affinities. Previous Nd and Sr isotopic studies establish that melting of metasomatized lithospheric mantle was the dominant melt source with a regionally unique contamination of lower or upper crust. The persistence of crustal contributions to melts over the extent of the Dulce field were not previously assessed.
To further evaluate isotopic trends in the Dulce swarm, new Nd ± Sr whole-rock isotopic analyses were obtained for six samples over the ~100-mile extent. 𝜀𝑁𝑑(𝑡) values range from -4.2 to -7.1 with 87Sr/86Sr ratios ranging from 0.70503 to 0.70584 indicating a strong crustal signature. These signatures reflect the likely contamination of 10 to 40 percent lower crust throughout the swarm without an identifiable isotopic trend. This signifies that the mantle melts in the Dulce system interacted with crustal reservoirs to a greater degree than Oligocene mafic rocks across the northern San Juan basin and Rio Grande rift. Understanding the regional trends and variations in the sources of mantle melts provides further insight into larger-scale melt production during the Oligocene in southwestern Colorado.
- Over one hundred ~25 alkaline mafic dikes are exposed in the Dulce swarm on the northeast side of the San Juan basin. These dikes were emplaced in a northeast zone of incipient extension distal to the Rio Grande rift.The chemical signatures of Oligocene mafic dikes in the Four Corners region and Rio Grande rift share similar alkaline-potassic and LREE-enriched affinities. Previous Nd and Sr isotopic studies establish that melting of metasomatized lithospheric mantle was the dominant melt source with a regionally unique contamination of lower or upper crust. The persistence of crustal contributions to melts over the extent of the Dulce field were not previously assessed.
- Jack Tingwall – CHANNEL COMPLEXITY ON THE DOLORES RIVER: USING PLANET LABS IMAGERY TO MEASURE SIDE CHANNEL LENGTH FOR DIFFERENT DISCHARGES DURING 2019 RELEASE FROM MCPHEE RESERVOIR
- The Dolores River drains the western San Juan Mountains in Southwestern Colorado. The construction of McPhee dam in 1983 to hold water for agriculture has greatly impacted the river downstream of the dam due to reduced frequency of high discharge events and encroachment of vegetation into the channel. One of the greatest impacts of the dam is simplification of the riverine environment including loss of side channels which provide important habitat for native fish species (round tail chub, blue head sucker, and flannel mouth sucker). The protection of these fish is crucial to prevent them from being placed on the endangered species list which would place more regulations on the use of water for agriculture as well as threaten the extinction of these native fish species, thus a challenge for water managers in this river system is to sustain habitat for these threatened native fish species while also conserving scarce water for the surrounding agriculture industry. To evaluate the ability of releases from the dam to inundate side channels in the modern river, we analyzed Planet Labs Planetscope imagery collected during a managed release in the summer of 2019 using ArcGIS Pro. At each of 6 discharges from ~80 to ~3500 cfs, we digitized and calculated the length of inundated side channels for 6 study segments.We find that higher discharges yield an increase in side channel length. Greatest side channel length increases were found in places with minimal valley wall constriction, but the most constricted segments showed little to no sensitivity to discharge. The greatest increase in side channel length occurs at ~2000 cfs, however this increase is partially due to ponds forming adjacent to the main channel, which may not necessarily create habitat, and could even be considered counterproductive if young fish are trapped in said ponds as the water recedes.
This work demonstrates the value of daily satellite imagery for monitoring the impact of controlled releases. Despite its moderate spatial resolution, the Planet Labs imagery allows us to see that discharges surpassing the aforementioned discharge threshold may not inundate enough additional side channels to justify the additional water usage. This finding will help inform future flow release strategies to best satisfy the diverse stakeholders.
- The Dolores River drains the western San Juan Mountains in Southwestern Colorado. The construction of McPhee dam in 1983 to hold water for agriculture has greatly impacted the river downstream of the dam due to reduced frequency of high discharge events and encroachment of vegetation into the channel. One of the greatest impacts of the dam is simplification of the riverine environment including loss of side channels which provide important habitat for native fish species (round tail chub, blue head sucker, and flannel mouth sucker). The protection of these fish is crucial to prevent them from being placed on the endangered species list which would place more regulations on the use of water for agriculture as well as threaten the extinction of these native fish species, thus a challenge for water managers in this river system is to sustain habitat for these threatened native fish species while also conserving scarce water for the surrounding agriculture industry. To evaluate the ability of releases from the dam to inundate side channels in the modern river, we analyzed Planet Labs Planetscope imagery collected during a managed release in the summer of 2019 using ArcGIS Pro. At each of 6 discharges from ~80 to ~3500 cfs, we digitized and calculated the length of inundated side channels for 6 study segments.We find that higher discharges yield an increase in side channel length. Greatest side channel length increases were found in places with minimal valley wall constriction, but the most constricted segments showed little to no sensitivity to discharge. The greatest increase in side channel length occurs at ~2000 cfs, however this increase is partially due to ponds forming adjacent to the main channel, which may not necessarily create habitat, and could even be considered counterproductive if young fish are trapped in said ponds as the water recedes.