Publications
Filter Total Items: 1492
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
Paleomagnetic evidence for the timing of collapse and resurgence of the Lake City Caldera, San Juan Mountains, Colorado Paleomagnetic evidence for the timing of collapse and resurgence of the Lake City Caldera, San Juan Mountains, Colorado
Rocks of the 23.1‐m.y.‐old Lake City caldera consist of the compositionally zoned Sunshine Peak Tuff, postcollapse intracaldera lava flows, and resurgent quartz syenite intrusions. Declinations of reversely magnetized (I = −45° to −75°) Sunshine Peak Tuff change from easterly (D = 93°–130°) throughout most of the tuff to southerly (D = 195°–207°) within the late eruptive phases. The...
Authors
Richard L. Reynolds, Mark R. Hudson, Ken Hon
Stratigraphy and correlation of the glacial deposits on the Montana Plains Stratigraphy and correlation of the glacial deposits on the Montana Plains
Till units representing at least three pre-Illinoian continental glaciations, at least one Illinoian glaciation, and a late Wisconsin glaciation have been identified on the Montana Plains. Early Wisconsin or middle Wisconsin till units have not been identified. The southernmost limit of late Wisconsin glaciation is in Montana, more than 170 km south of the Lethbridge moraine in Alberta...
Authors
David S. Fullerton, Roger B. Colton
Introduction to quaternary glaciations in the United States of America Introduction to quaternary glaciations in the United States of America
No abstract available.
Authors
Gerald M. Richmond, David S. Fullerton