Mesoproterozoic strata from east-central Idaho and the Belt Supergroup of southwest Montana (eight new samples) contain several age groupings of detrital zircon grains: from old to young: a) Laurentian grains older than 1.85 Ga, b) a flood of 1655 to 1790 Ma Paleoproterozoic grains; b) non-North American zircon populations (ca. 1510 to 1625 Ma) with no known source on Laurentia, and c) syn- Belt grains, with groupings at 1480 Ma (syn-lower Prichard) and 1450 Ma (upper Piegan Group). The 1450 Ma = grain age population overlaps a 1454 ± 9 Ma fallout tuff in Glacier National Park. Strata of the Yellowjacket, Hoodoo, Apple Creek, and western Gunsight formations of Idaho all contain the 1450 Ma population, sparse non-North American grains, and dominant Paleoproterozoic populations at 1670 to 1790 Ma. This detrital-zircon signature is comparable to that of the Wallace Formation of the Belt Supergroup. The Swauger Quartzite in Idaho and the eastern Gunsight Formation at the ca. 900 Ma Beaverhead impact site in southwest Montana contain 1710 and 1780 Ma zircon populations identical to those of the Missoula Group of the Belt Supergroup. The E member of the lower Belt Prichard Formation from Plains, Montana, contains a population of syndepositional zircons at 1479 ± 19 Ma. Like the Revett Formation of the Ravalli Group, the E member contains Mesoproterozoic non-North American detrital-zircon populations as well as Paleoproterozoic grains at 1750 to 1790 Ma. The thick east-central Idaho Mesoproterozoic section was deposited after 1450 Ma, with deposition of the 10 km thickness from the lower Yellowjacket Formation through the Gunsight Formation spanning only 10 to 20 My. Given this very high rate of deposition, previous correlations of the Apple Creek Formation with the Piegan Group are permissible if problematic. However, previous correlations of the eastern Gunsight and Swauger formations with the Missoula Group are supported. Their detrital-zircon grain populations are identical.

Pennsylvanian rocks of the northern U.S. Rocky Mountains are mature quartzose sandstones. This paper uses detrital zircon geochronology on seven samples from the Wood River Formation, Tensleep Sandstone, and Weber Sandstone to determine if these sandstones have a common provenance, representing eastern Laurentian and Appalachian sand reworked within shallow-marine and eolian environments from the Wyoming craton westward to the Pioneer thrust plate of south-central Idaho. Our work suggests that this continental sand blanket was mixed with local sources on the south in the Yavapai-Mazatzal provinces of the Ancestral Rocky Mountains and in samples from the western Cordilleran thrust belt in south-central Idaho. In total, these Pennsylvanian sandstones contain a broad spectrum of detrital zircon U-Pb ages including, from old to young: A) minor Archean-age (3300–2550 Ma) populations; B) Paleoproterozoic (2000–1600 Ma), Mesoproterozoic (1470–1350 Ma), and major “Grenvillian” (1250–950 Ma) populations; and C) Cryogenian- to Ediacaran-age (665–565 Ma) and minor Paleozoic (495–410 Ma) populations. We interpret these detrital zircon ages to represent provenance mainly from the Appalachian mountain belt of eastern North America; however, central Appalachian versus northern Appalachian derivation is not clearly distinguished. The Weber Sandstone from the north flank of the Uinta Mountains in northeast Utah contains a strong 1700–1640 Ma age population derived from the Yavapai-Mazatzal provinces in the adjacent Ancestral Rocky Mountains. The shallow-marine Hailey Member of the Wood River Formation in south-central Idaho yields a population of >1800 Ma detrital zircons reworked from the uplifted Mississippian Copper Basin Formation. Both the Hailey and Wilson Creek Members of the Wood River Formation contain unique 640–490 Ma grains that may represent provenance from the Big Creek-Beaverhead plutonic belt of east-central Idaho and/or eastern Klamath terrane in the Klamath Mountains of northwest California and southwest Oregon. These new data support published models for Pennsylvanian–Permian transport of siliciclastic sediment with sources mainly from the North American craton, north of the Ancestral Rocky Mountains, into continental margin basins.

The 1895 discovery of a petrified tree near Clover Creek in south-central Idaho, USA, attracted worldwide attention and resulted in the naming of a new species of ancient oak, Quercinium pliocaenicum Schuster. For more than a century, the discovery has largely been forgotten, even though specimens reside in reputable museums. Reinvestigation of the locality in 2014/2015 resulted in newly-collected specimens and a wealth of new data. Optical microscopy confirms the cellular anatomy used for the original taxonomic study. X-ray diffraction, scanning electron microscopy, energy-dispersive electron spectroscopy, Raman spectroscopy and cathodoluminescence microscopy reveal details of the mineralization, showing the presence of opal-CT as the primary component, with chalcedony as a lesser constituent. This mineralogy suggests petrifaction occurred in at least two stages, beginning with opalization of cellular tissue, leaving open vessels that became filled with chalcedony during a later mineralization episode. Clover Creek oak represents relict flora growing in a wetter climate before the uplift of the Cascade Range created a rain shadow that caused profound desertification of the inland Pacific Northwest.

The Permian Phosphoria Formation, a petroleum source rock and world-class phosphate deposit, was deposited in an epicratonic successor basin on the western margin of North America. We calculate the seawater circulation in the basin during deposition of the lower ore zone in the Meade Peak Member from the accumulation rates of carbonate fluorapatite and trace elements. The model gives the exchange rate of water between the Phosphoria sea and the open ocean to the west in terms of an upwelling rate (84 m yr-1) and residence time (4.2 yr) of seawater in the basin. These hydrographic properties supported a mean rate of primary productivity of 0.87 g m-2 d-1 of carbon in the uppermost few tens of meters of the water column (the photic zone) and denitrifying redox conditions in the bottom water (below approximately 150 m depth). High rain rates, onto the sea floor, of the organic matter that hosted the phosphate and several trace elements contributed to the accumulation of phosphorite, chert, and black shales and mudstones. Evaporation in the Goose Egg basin to the east of the Phosphoria basin ensured the import of surface seawater from the Phosphoria sea. Budgets of water, salt, phosphate, and oxygen, plus the minor accumulation of the biomarker gammacerane, show that exchange of water between the two basins was limited, possibly by the shallow carbonate platform that separated the two basins.

The Bruneau Woodpile site has long been popular among fossil collectors; however, the deposit has received scant attention from scientists. Our research reveals that the fossilized wood was deposited ca. 6.85 Ma, within the Chalk Hills Formation, and was mineralized with carbonate-fluorapatite. The diverse assemblage of conifers and hardwoods is representative of the warm temperate forests that flourished in southwest Idaho, USA during the late Miocene. Limb and trunk fragments preserved in a single thin sandstone bed appear to represent woody debris that was transported by streams. One possible explanation is that wood, pumice, and sandy volcaniclastic sediment arrived separately as a result of ordinary stream action, and later were combined into a single assemblage during a subsequent high-energy sedimentation event. We favor an alternate hypothesis: a catastrophic event (e.g., a windstorm) damaged trees on slopes bordering the ancient lake. Branches and small trunk fragments were carried by wind and rain into local streams and ponds where they became waterlogged. After a delay that allowed pumice and wood to become saturated, storm water transported these materials, along with finer volcaniclastic sediment, into a lake. The resulting density current produced a fining-upward sedimentary cycle where wood was preserved in the lowest, coarsest stratum.