Arizona Geological Society
2025 Speaker Series
Tuesday, 4 March 2025 | 5:30 - 8:00 PM
Location: Hexagon Mining Division Office
40 East Congress Street, Suite 150, Tucson, Arizona 85701
Parking: On the street or parking garage (Old Pueblo Parking)
Social Hour with Sandwiches from Beyond Bread (5:30-6:30 PM), Presentation (6:35 PM)
For those planning to attend the event, please register by 6:00 PM on Sunday, March 2, 2025
For those unable to attend streaming here is the MSTeams URL
The Arizona Geological Society thanks Hexagon
for generously providing the venue and drinks
Revisiting the Arizona Red: The Lower to Middle Triassic Moenkopi Formation
Chad Kwiatkowski
Arizona Geological Survey
Abstract: The brick-red Moenkopi Formation, exposed in the valley of the Little Colorado River in northern Arizona, was deposited along western equatorial Pangea during the Early to Middle Triassic Period. The Moenkopi Formation has been valued by humans for millennia as a building stone and lithic canvas to record intricate carvings. The pueblo walls at Wupatki National Monument are built using Moenkopi Formation blocks, with an assortment of petroglyphs etched into the calcite-cemented sandstone of the lower massive sandstone member.
The lower massive sandstone member was quarried in Flagstaff beginning in the 1880s, quickly becoming Flagstaff’s second-largest industry. Referred to as Arizona Red, it was used to rebuild Flagstaff after fires destroyed the original town. It was also transported by train to be used in buildings as far northwest as San Francisco and as far east as Chicago. The sandstone’s calcite cement proved to be an ideal canvas for stoneworkers to carve intricate patterns and inscriptions. Unfortunately, the calcite cement was easily weathered when incorporated into buildings in more humid climates.
Moenkopi sediment was deposited in fluvial, deltaic, tidal flat, sabkha, and shallow marine environments, with an increasing marine influence to the northwest. The depositional system conveyed sediment from the Central Pangean Mountains (collisional zone between Laurentia and Gondwana) through a fluvial network and across a coastal plain to the Sonoma sea. Due to the gentle slope of the coastal plain, even minor changes in eustatic or local sea level led to widespread marine transgressions. In the fluvial and tidal flat environments of north-central Arizona, pre-dinosaur reptiles walked the floodplains while fish and large amphibians navigated the stream and tidal channels. A diverse reptilian footprint assemblage, exemplified by Chirotherium (hand animal) is recorded in the Moenkopi Formation, in places preserving delicate details such as scale impressions, claw impressions, and tail-drag marks.
The Moenkopi Formation thickens to the west-northwest, from ~50 m in north-central Arizona to ~600 m near Las Vegas; this is compatible with foreland downflexure related to emplacement of the Golconda allochthon in central Nevada. However, the upper part of the Moenkopi Formation has a relatively uniform thickness throughout the region, suggesting that Golconda subsidence had waned by Middle Triassic time. Moenkopi stratigraphic thickness contours are truncated at the Mogollon Rim, indicating that the Moenkopi basin continued some distance to the southwest. Additionally, volcanic detritus is present in the Moenkopi Formation, increasing in abundance to the south, toward the early Cordilleran arc, which is delineated by a series of Permian to Middle Triassic plutons exposed in the Mojave Desert and northwestern Sonora.
In west-central Arizona, southeastern California, and northwestern Sonora, calc-silicate metasedimentary rocks of the lower Buckskin Formation correlate with the Moenkopi Formation. The detrital zircon signature of the lower Buckskin Formation is dominated by Permo-Triassic grains likely sourced from the nearby Cordilleran arc. At Sycamore Canyon along thee Mogollon Rim southwest of Flagstaff, a detrital zircon sample is also dominated by Permo-Triassic grains. Quantitative comparisons of the lower Buckskin Formation and Moenkopi Formation at Sycamore Canyon display a high degree of similarity and probably represent a fluvial linkage from the Cordilleran arc to the main Moenkopi depocenter.
In summary, the Moenkopi and lower Buckskin Formations represent a complex tectonic basin along western Pangea. Emplacement of the Golconda allochthon during the Sonoma orogeny flexed the crust into a foreland basin in which the lower Moenkopi Formation accumulated. Dynamic subsidence above the subducting Panthalassan lithospheric slab was ongoing during the entire timeframe of Moenkopi deposition and was the dominant source of subsidence after foreland subsidence associated with the Sonoma orogeny waned. The Cordilleran arc contributed sediment to the arc-proximal portions of the Moenkopi basin via fluvial networks that flowed generally northward toward the main Moenkopi deposystem, eventually overwhelmed by detritus along the main, northwest flowing fluvial system.
Bio: Chad spent his first few years in the Pacific Northwest, living above the subducting Juan de Fuca plate, in the shadows of Cascade stratovolcanoes. Some of this time was in the Columbia River Gorge, living atop the Stevenson landslide complex in an area that had been reshaped by the catastrophic late Pleistocene Missoula Floods. Perhaps geologic hazards are in his DNA!
Growing up in the Sonoran Desert, Chad become interested in the processes that shape our land, and in how the landforms and rocks that compose them came to be. He attended the Maricopa Community College system before transferring to ASU for his bachelor’s, where he began teaching intro geology labs his junior year, and graduated in 2018.
Chad then traded cacti for pines and moved up to Flagstaff to attend NAU for his masters, working with Nancy Riggs to study metasedimentary equivalents of the Moenkopi Formation using detrital zircon. During his masters, Chad worked internships with The Nature Conservancy and Friends of the Verde River. He also completed a Scientists-in-Parks internship at Wupatki National Monument, hunting for footprint fossils in the Moenkopi Formation. During this time, he lived in a stone house built out of Moenkopi sandstone, a constant reminder to finish writing his thesis.
After receiving his master's degree in 2021, Chad worked for USGS in Flagstaff for a short time before being summoned back down to his Sonoran Desert homeland for a position with the Arizona Geological Survey in 2022. Chad loves all things geology, and in his free time enjoys wildlife photography, skateboarding, and kayaking on Arizona’s few remaining perennial river reaches.
Hexagon Mining Division Office - 40 East Congress Street,
Suite 150, Tucson, Arizona 85701
