Publications
Filter Total Items: 1459
Pyrite formation in the Lower Cretaceous Mowry Shale: Effect of organic matter type and reactive iron content Pyrite formation in the Lower Cretaceous Mowry Shale: Effect of organic matter type and reactive iron content
Geochemical analysis of the Lower Cretaceous Mowry Shale in Wyoming and Montana shows that organic matter type and reactive iron content limited pyrite formation during early diagenesis. Consequently, direct interpretation of paleosalinity cannot be made from a carbon/sulfur plot. Mowry Shale samples with hydrogen index (HI) less than 150 (mg hydrocarbon/ organic carbon) contain low...
Authors
Hugh R. Davis, Charles W. Byers, Walter E. Dean
Pedogenic replacement of aluminosilicate grains by CaCO3 in Ustollic Haplargids, south-central Montana, U.S.A. Pedogenic replacement of aluminosilicate grains by CaCO3 in Ustollic Haplargids, south-central Montana, U.S.A.
A chronosequence of calcic soils formed on granitic glaciofluvial terrace deposits of Rock Creek and the Clarks Fork in south-central Montana shows progressive replacement of aluminosilicate parent-material grains by calcium-magnesium carbonate. The terraces range from late Pliocene to Holocene in age as dated by tephrochronology, correlation, and stream incision rates. Replacement is...
Authors
Marith C. Reheis
Evolution of the Early Proterozoic Colorado province: Constraints from U-Pb geochronology Evolution of the Early Proterozoic Colorado province: Constraints from U-Pb geochronology
The Colorado province represents an addition of a belt of rocks more than 500 km wide to the southern margin of the Archean Wyoming craton during the Early Proterozoic, between about 1790 and 1660 Ma. Correspondence in ages between metamorphism, deformation, and plutonism; association of volcanic rocks with comagmatic calc-alkalic plutons; and lack of older basement are all consistent...
Authors
John C. Reed, M. E. Bickford, Wayne R. Premo, John N. Aleinikoff, John S. Pallister
15N/14N variations in Cretaceous Atlantic sedimentary sequences: Implication for past changes in marine nitrogen biogeochemistry 15N/14N variations in Cretaceous Atlantic sedimentary sequences: Implication for past changes in marine nitrogen biogeochemistry
At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds (“black shales”) were found to have significantly lower δ15N values (lower15N/14N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have °15N values that are
Authors
Greg H. Rau, M.A. Arthur, Walter E. Dean
Arabian Shield ophiolites and Late Proterozoic microplate accretion Arabian Shield ophiolites and Late Proterozoic microplate accretion
Fragments of Late Proterozoic ocean crust and mantle (ophiolites) occur within six major fault zones that mark sutures between crustal blocks (microplates) that were accreted between about 630 and 715 Ma to form the Arabian Shield. We report new U-Pb zircon ages for ophiolitic gabbro, diorite, and plagiogranite that range from 840 to 700 Ma and establish these complexes among the oldest...
Authors
John S. Pallister, J. S. Stacey, L. B. Fischer, Wayne R. Premo
Rocky Mountains Rocky Mountains
The Rocky Mountain region is one of the most topographically distinct and impressive parts of North America. The Rocky Mountains rise abruptly above the bordering regions, particularly on the east and northeast where they are flanked by plains, less so on the west and southwest where they are bounded by high plateaus. The Rocky Mountains comprise more than 100 individually named ranges...
Authors
Richard F. Madole, W.C. Bradley, D.S. Loewenherz, D.F. Ritter, N.W. Rutter, C.E. Thorn
Inorganic and organic geochemistry of Eocene to Cretaceous strata recovered from the lower continental rise, North American Basin, Site 603, Deep Sea Drilling Project Leg 93 Inorganic and organic geochemistry of Eocene to Cretaceous strata recovered from the lower continental rise, North American Basin, Site 603, Deep Sea Drilling Project Leg 93
About one hundred samples of sediments and rocks recovered in Hole 603B were analyzed for type, abundance, and isotopic composition of organic matter, using a combination of Rock-Eval pyrolysis, C-H-N-S elemental analysis, and isotope-ratio mass spectrometry. Concentrations of major, minor, and trace inorganic elements were determined with a combination of X-ray fluorescence and...
Authors
Walter E. Dean, M.A. Arthur
Response of douglas fir (Pseudotsuga menziesii) to uraniferous groundwater in a small glaciated drainage, Northeastern Washington State Response of douglas fir (Pseudotsuga menziesii) to uraniferous groundwater in a small glaciated drainage, Northeastern Washington State
Douglas fir trees and associated soils were sampled from the slopes of a small (∼4 km2) drainage basin in northeastern Washington to investigate the biogeochemical response to locally uraniferous groundwater. Uranium is preferentially incorporated in needles and twigs compared to larger branches or the trunk. The U concentration in needle ash ranges from 0.2 to 5.8μg g−1 (ppm) and shows...
Authors
R. A. Zielinski, R.R. Schumann
Rock-water interaction in ash-flow tuffs (Yucca Mountain, Nevada, USA)- The record from uranium studies Rock-water interaction in ash-flow tuffs (Yucca Mountain, Nevada, USA)- The record from uranium studies
Forty-eight core samples of ash-flow tuffs from Yucca Mountain, NV, were selected for comparative analysis by uranium-based methods to estimate past interaction with oxidizing water. Results aid in the selection of hydrologically isolated host rocks for radioactive waste disposal. U abundances were consistently more variable than thorium in whole rocks, suggesting some selective...
Authors
Robert A. Zielinski, Charles A. Bush, R.W. Spengler, Barney J. Szabo