Grand Canyon-Parashant National Monument: Paleontological resource inventory (public version)

Grand Canyon-Parashant National Monument (PARA) in northwestern Arizona has significant paleontological resources, which are recognized in the establishing presidential proclamation. Because of the challenges of working in this remote area, there has been little documentation of these resources over the years. PARA also has an unusual management situation which complicates resource management. The majority of PARA is administered by the Bureau of Land Management (BLM; this land is described here as PARA-BLM), while about 20% of the monument is administered by the National Park Service (NPS; this land is described here as PARA-NPS) in conjunction with Lake Mead National Recreation Area (LAKE). Parcels of state and private land are scattered throughout the monument. Reports of fossils within what is now PARA go back to at least 1914. Geologic and paleontologic reports have been sporadic over the past century. Much of what was known of the paleontology before the 2020 field inventory was documented by geologists focused on nearby Grand Canyon National Park (GRCA) and LAKE, or by students working on graduate projects; in either case, paleontology was a secondary topic of interest. The historical record of fossil discoveries in PARA is dominated by Edwin McKee, who reported fossils from localities in PARA-NPS and PARA-BLM as part of larger regional projects published from the 1930s to the 1980s. The U.S. Geological Survey (USGS) has mapped the geology of PARA in a series of publications since the early 1980s. Unpublished reports by researchers from regional institutions have documented paleontological resources in Quaternary caves and rock shelters. From September to December 2020, a field inventory was conducted to better understand the scope and distribution of paleontological resources at PARA. Thirty-eight localities distributed across the monument and throughout its numerous geologic units were documented extensively, including more than 420 GPS points and 1,300 photos, and a small number of fossil specimens were collected and catalogued under 38 numbers. In addition, interviews were conducted with staff to document the status of paleontology at PARA, and potential directions for future management, research, protection, and interpretation. In geologic terms, PARA is located on the boundary of the Colorado Plateau and the Basin and Range provinces. Before the uplift of the Colorado Plateau near the end of the Cretaceous 66 million years ago, this area was much lower in elevation and subject to flooding by shallow continental seas. This led to prolonged episodes of marine deposition as well as complex stratigraphic intervals of alternating terrestrial and marine strata. Most of the rock formations that are exposed in the monument belong to the Paleozoic part of the Grand Canyon section, deposited between approximately 510 and 270 million years ago in mostly shallow marine settings. These rocks have abundant fossils of marine invertebrates such as sponges, corals, bryozoans, brachiopods, bivalves, gastropods, crinoids, and echinoids. The Cambrian–Devonian portion of the Grand Canyon Paleozoic section is represented in only a few areas of PARA. The bulk of the Paleozoic rocks at PARA are Mississippian to Permian in age, approximately 360 to 270 million years old, and belong to the Redwall Limestone through the Kaibab Formation. While the Grand Canyon section has only small remnants of younger Mesozoic rocks, several Mesozoic formations are exposed within PARA, mostly ranging in age from the Early Triassic to the Early Jurassic (approximately 252 to 175 million years ago), as well as some middle Cretaceous rocks deposited approximately 100 million years ago. Mesozoic fossils in PARA include marine fossils in the Moenkopi Formation and petrified wood and invertebrate trace fossils in the Chinle Formation and undivided Moenave and Kayenta Formations.

Supplemental Material: Zircon (U-Th)/He thermochronology of Grand Canyon resolves 1250 Ma unroofing at the Great Unconformity and <20 Ma canyon carving

All geologic and thermochronologic constraints used in the forward models, major forward model results from the zircon radiation damage accumulation and annealing model (ZRDAAM) of Guenthner et al. (2013), and alternative HeFTy forward model result using different sample inputs.<br>

Small-Scale Soft-Sediment Deformation Structures in the Cross-Bedded Coconino Sandstone (Permian; Arizona, United States); Possible Evidence for Seismic Influence

The Permian Coconino Sandstone of northern Arizona contains numerous small-scale, soft-sediment deformation structures (SSDSs). These novel structures may be indicators of paleoenvironment or sedimentary processes. These SSD are generally shallow and occur on the surfaces of cross-beds, in contrast to convoluted bedding up to tens of meters thick commonly observed in some other eolian sandstones. These differences in structures imply differences in the processes that formed the Coconino Sandstone, or differences in the underlying depositional conditions. These SSDSs occur in outcrops at the Grand Canyon, and farther south in quarries near the towns of Seligman and Ash Fork. Size, orientation, structure, sedimentary context, clay content, and porosity of the structures are described. The SSDSs occur as small folds and ridges on the paleo lee side of otherwise undisturbed cross-beds. Some are associated with small rotated sandstone blocks within the cross-beds. The structures are exposed on bedding plane surfaces and in cross-section on vertical quarry walls. A few SSDSs up to a meter thick also occur in the Coconino Sandstone, but the others are only up to a few cm thick, 2–10 cm wide, and 20 cm to 10 m long. Evidence is presented that liquidization (as fluidization or liquefaction) may have been involved in producing these features, implying a high water content in scattered locations at time of deformation, but this process also requires some stressor to trigger the deformation. Seismic events may provide a triggering mechanism. The Coconino Sandstone SSDSs represent unusual or previously overlooked small-scale features related to individual foreset surfaces.

An assessment of uranium in groundwater in the Grand Canyon region

The Grand Canyon region in northern Arizona is a home or sacred place of origin for many Native Americans and is visited by over 6 million tourists each year. Most communities in the area depend upon groundwater for all water uses. Some of the highest-grade uranium ore in the United States also is found in the Grand Canyon region. A withdrawal of over 4000 km2 of Federal land in the Grand Canyon region from new uranium mining activities for 20 years was instituted in 2012, owing in part to a lack of scientific data on potential effects from uranium mining on water resources in the area. The U.S. Geological Survey has collected groundwater chemistry samples since 1981 in the Grand Canyon region to better understand the current state of groundwater quality, to monitor for changes in groundwater quality that may be the result of mining activities, and to identify "hot spots" with elevated metal concentrations and investigate the causes. This manuscript presents results for the assessment of uranium in groundwater in the Grand Canyon region. Analytical results for uranium in groundwater in the Grand Canyon region were available for 573 samples collected from 180 spring sites and 26 wells from September 1, 1981 to October 7, 2020. Samples were collected from springs issuing from stratigraphic units above, within, and below the Permian strata that host uranium ore in breccia pipes in the area. Maximum uranium concentrations at groundwater sites in the region ranged from less than 1 µg/L at 23 sites (11%) to 100 µg/L or more at 4 sites (2%). Of the 206 groundwater sites sampled, 195 sites (95%) had maximum observed uranium concentrations less than the U.S. Environmental Protection Agency’s Maximum Contaminant Level of 30 µg/L for drinking water and 177 sites (86%) had uranium concentrations less than the 15 µg/L Canadian benchmark for protection of aquatic life in freshwater. The establishment of baseline groundwater quality is an important first step in monitoring for change in water chemistry throughout mining lifecycles and beyond to ensure the health of these critical groundwater resources.

Supplemental Material: Zircon (U-Th)/He thermochronology of Grand Canyon resolves 1250 Ma unroofing at the Great Unconformity and <20 Ma canyon carving

All geologic and thermochronologic constraints used in the forward models, major forward model results from the zircon radiation damage accumulation and annealing model (ZRDAAM) of Guenthner et al. (2013), and alternative HeFTy forward model result using different sample inputs.<br>

Supplemental Material: Zircon (U-Th)/He thermochronology of Grand Canyon resolves 1250 Ma unroofing at the Great Unconformity and <20 Ma canyon carving

All geologic and thermochronologic constraints used in the forward models, major forward model results from the zircon radiation damage accumulation and annealing model (ZRDAAM) of Guenthner et al. (2013), and alternative HeFTy forward model result using different sample inputs.<br>