Pub Date : 2023-08-01DOI: 10.31582/rmag.mg.60.3.81
Kyren R. Bogolub, Jackson P. Bell, Enrique R. Chon, Robert M. Kirkham, Anne F. Sheehan
In November of 2018, residents living in the Zapata Subdivision south of Great Sand Dunes National Park and Preserve reported hearing and feeling multiple small earthquakes. Reports of additional earthquakes continued, escalating in late February of 2019, when the USGS recorded over 27 magnitude 0.9 and larger earthquakes over a two-day period. Subdivision residents became concerned that these could be foreshocks to a future, larger earthquake. To further study these earthquakes, we installed a temporary network of seismometers in the area during 2019 and used a convolution neural network seismic phase picker along with the GLASS3 associator to detect over 700 earthquakes in a 3.5-month period during the earthquake swarm. The earthquakes were located using a regional velocity model and a double-difference algorithm. The Northern Sangre de Cristo Fault (NSCF) cuts through the subdivision at the base of the Sangre de Cristo Mountains. Based on geologic evidence, it is one of the most active faults in Colorado but has been nearly aseismic historically. Initially, minor movement on the NSCF was suspected of being the geologic source of the earthquakes. However, nearly all recorded epicenters lie east of the trace of west-dipping fault and are not located on it. Instead, the earthquake epicenters define a narrow, linear, east-west-trending zone that projects eastward across the entire Northern Sangre de Cristo Range and into the headwaters of the Huerfano River Valley. We propose several possible geologic sources for the earthquakes including several mapped, but unnamed faults. Available evidence for any particular source in this geologically complex area is not conclusive. Additional geologic and geophysical investigations are needed to better understand the geology of the earthquake swarm and its implications for seismic hazards.
{"title":"Earthquake swarm near Great Sand Dunes, Colorado, investigated with temporary seismic network and machine learning sesmic phase analysis","authors":"Kyren R. Bogolub, Jackson P. Bell, Enrique R. Chon, Robert M. Kirkham, Anne F. Sheehan","doi":"10.31582/rmag.mg.60.3.81","DOIUrl":"https://doi.org/10.31582/rmag.mg.60.3.81","url":null,"abstract":"In November of 2018, residents living in the Zapata Subdivision south of Great Sand Dunes National Park and Preserve reported hearing and feeling multiple small earthquakes. Reports of additional earthquakes continued, escalating in late February of 2019, when the USGS recorded over 27 magnitude 0.9 and larger earthquakes over a two-day period. Subdivision residents became concerned that these could be foreshocks to a future, larger earthquake. To further study these earthquakes, we installed a temporary network of seismometers in the area during 2019 and used a convolution neural network seismic phase picker along with the GLASS3 associator to detect over 700 earthquakes in a 3.5-month period during the earthquake swarm. The earthquakes were located using a regional velocity model and a double-difference algorithm. The Northern Sangre de Cristo Fault (NSCF) cuts through the subdivision at the base of the Sangre de Cristo Mountains. Based on geologic evidence, it is one of the most active faults in Colorado but has been nearly aseismic historically. Initially, minor movement on the NSCF was suspected of being the geologic source of the earthquakes. However, nearly all recorded epicenters lie east of the trace of west-dipping fault and are not located on it. Instead, the earthquake epicenters define a narrow, linear, east-west-trending zone that projects eastward across the entire Northern Sangre de Cristo Range and into the headwaters of the Huerfano River Valley. We propose several possible geologic sources for the earthquakes including several mapped, but unnamed faults. Available evidence for any particular source in this geologically complex area is not conclusive. Additional geologic and geophysical investigations are needed to better understand the geology of the earthquake swarm and its implications for seismic hazards.","PeriodicalId":498835,"journal":{"name":"The mountain Geologist","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135004766","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-01DOI: 10.31582/rmag.mg.60.3.103
Charl D. Cilliers, Ryan T. Tucker, William J. Friemuth, Kyla A. Beguesse, Lindsay E. Zanno
Understanding of Upper Cretaceous terrestrial sediments within the Western Interior Basin is advancing; however, the Turonian–Coniacian transition remains enigmatic. Recent chronometry of the Moreno Hill Formation indicates that sediment deposition took place during this interval of geodynamic upheaval and climatic recovery immediately following the peak of the Cretaceous Thermal Maximum (CTM). To decipher these effects, the sedimentary record of the Moreno Hill Formation was reassessed near the type section, and near Quemado, New Mexico (USA) using facies analysis and architectural reconstruction. Seven facies types (thirteen lithofacies codes), eleven architectural elements, and three facies associations were identified. Sedimentation within the floodplain of the lower Moreno Hill Formation was affected by the east-migrating forebulge of the Western Interior Basin. Furthermore, increasingly bedload-rich multi-story channel complexes and a transition from near-coastal to alluvial coals reflect gradual climatic cooling and overall regression of the Western Interior Seaway (with interruption by a regional [T2–R2] transgressive-regressive sequence). This is consistent with more subaerial conditions indicative of continued regression reflected within the floodplain sediments of the upper Moreno Hill Formation. Whilst diversion of westerly fluvial feeder systems by ongoing forebulge migration also affected sediment transport and deposition, a return to more suspended-load-rich single-story channels and thin coals are tied to an intervening (T3) transgression. Repetitive paleosol sequences throughout the Moreno Hill Formation indicate groundwater fluctuation in response to these base level changes. Together with detrital zircon-based geochronology, these slight sedimentary differences support a revised subdivision from three into two members: lower and upper. Beyond feeding the seaward Gallup Delta, the newly defined lower member correlates to the Toreva, Straight Cliffs (Smoky Hollow member), Ferron Sandstone, Funk Valley and Frontier formations (Dry Hollow Member) and the upper member to the Wepo and Straight Cliffs (John Henry Member) formations within the Kaiparowits, Notom, Last Chance and Vernal fluvio-deltaic systems. Landward sediments of the Cardium Formation (Canada) correlate with the lower and upper members of the Moreno Hill Formation.
{"title":"Geological Assessment of Turonian - Coniacian terrestrial sedimentation records during climatic recovery, Moreno Hill Formation, Zuni Basin","authors":"Charl D. Cilliers, Ryan T. Tucker, William J. Friemuth, Kyla A. Beguesse, Lindsay E. Zanno","doi":"10.31582/rmag.mg.60.3.103","DOIUrl":"https://doi.org/10.31582/rmag.mg.60.3.103","url":null,"abstract":"Understanding of Upper Cretaceous terrestrial sediments within the Western Interior Basin is advancing; however, the Turonian–Coniacian transition remains enigmatic. Recent chronometry of the Moreno Hill Formation indicates that sediment deposition took place during this interval of geodynamic upheaval and climatic recovery immediately following the peak of the Cretaceous Thermal Maximum (CTM). To decipher these effects, the sedimentary record of the Moreno Hill Formation was reassessed near the type section, and near Quemado, New Mexico (USA) using facies analysis and architectural reconstruction. Seven facies types (thirteen lithofacies codes), eleven architectural elements, and three facies associations were identified. Sedimentation within the floodplain of the lower Moreno Hill Formation was affected by the east-migrating forebulge of the Western Interior Basin. Furthermore, increasingly bedload-rich multi-story channel complexes and a transition from near-coastal to alluvial coals reflect gradual climatic cooling and overall regression of the Western Interior Seaway (with interruption by a regional [T2–R2] transgressive-regressive sequence). This is consistent with more subaerial conditions indicative of continued regression reflected within the floodplain sediments of the upper Moreno Hill Formation. Whilst diversion of westerly fluvial feeder systems by ongoing forebulge migration also affected sediment transport and deposition, a return to more suspended-load-rich single-story channels and thin coals are tied to an intervening (T3) transgression. Repetitive paleosol sequences throughout the Moreno Hill Formation indicate groundwater fluctuation in response to these base level changes. Together with detrital zircon-based geochronology, these slight sedimentary differences support a revised subdivision from three into two members: lower and upper. Beyond feeding the seaward Gallup Delta, the newly defined lower member correlates to the Toreva, Straight Cliffs (Smoky Hollow member), Ferron Sandstone, Funk Valley and Frontier formations (Dry Hollow Member) and the upper member to the Wepo and Straight Cliffs (John Henry Member) formations within the Kaiparowits, Notom, Last Chance and Vernal fluvio-deltaic systems. Landward sediments of the Cardium Formation (Canada) correlate with the lower and upper members of the Moreno Hill Formation.","PeriodicalId":498835,"journal":{"name":"The mountain Geologist","volume":"140 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135004764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-31DOI: 10.31582/rmag.mg.60.1.21
Michael Sell, Aidan Krieger, Matthew Huisman, David Malone
Here we present the results of detailed (1:24,000 scale) mapping of the Bald Mountain 7.5 Minute Quadrangle Wyoming, which includes Archean basement rocks of the Laramide Bighorn uplift. These basement rocks are mantled by Paleozoic cratonic strata of the Flathead, Gros Ventre, Gallatin, Bighorn, Madison and Amsden formations. This region was explored for gold associated with the basement rocks, and Th in the basal Flathead sandstone. Isotopic age determinations (LA-ICPMS U-Pb on zircon) of the basement rocks were conducted at the University of Arizona Laserchron Center. Three phases of Archean rocks were defined, all of which range from ∼2880-2890 Ma, and include a prominent, pink, strongly foliated (WNW trending) alkali feldspar granite with pegmatite, a weakly foliated purple granite, and a yellow, poorly exposed adamellite. These rocks were uplifted during the Paleogene Laramide orogeny, and now form a southwest verging breached drape fold over a steeply inclined, basement-cored reverse fault. Dips of footwall strata range from 10–70° to the SW. Hanging wall rocks dip gently to the NE. Quaternary landslide deposits occur along steep slopes in the Gros Ventre Shale and alluvium occurs along the principle streams.
{"title":"Geologic map of the Bald Mountain Quadrangle, northern Bighorn Mountains, Wyoming","authors":"Michael Sell, Aidan Krieger, Matthew Huisman, David Malone","doi":"10.31582/rmag.mg.60.1.21","DOIUrl":"https://doi.org/10.31582/rmag.mg.60.1.21","url":null,"abstract":"Here we present the results of detailed (1:24,000 scale) mapping of the Bald Mountain 7.5 Minute Quadrangle Wyoming, which includes Archean basement rocks of the Laramide Bighorn uplift. These basement rocks are mantled by Paleozoic cratonic strata of the Flathead, Gros Ventre, Gallatin, Bighorn, Madison and Amsden formations. This region was explored for gold associated with the basement rocks, and Th in the basal Flathead sandstone. Isotopic age determinations (LA-ICPMS U-Pb on zircon) of the basement rocks were conducted at the University of Arizona Laserchron Center. Three phases of Archean rocks were defined, all of which range from ∼2880-2890 Ma, and include a prominent, pink, strongly foliated (WNW trending) alkali feldspar granite with pegmatite, a weakly foliated purple granite, and a yellow, poorly exposed adamellite. These rocks were uplifted during the Paleogene Laramide orogeny, and now form a southwest verging breached drape fold over a steeply inclined, basement-cored reverse fault. Dips of footwall strata range from 10–70° to the SW. Hanging wall rocks dip gently to the NE. Quaternary landslide deposits occur along steep slopes in the Gros Ventre Shale and alluvium occurs along the principle streams.","PeriodicalId":498835,"journal":{"name":"The mountain Geologist","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135395256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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