Jurassic (Bathonian and Callovian) Ammonites in Eastern Oregon and Western Idaho (open access)

Jurassic (Bathonian and Callovian) Ammonites in Eastern Oregon and Western Idaho

From abstract: Jurassic ammonites of late Bathonian to middle Callovian Age have been found in 12,000-13,000 feet (3,660-3,960 m) of strata exposed in the area near and south of Izee and Seneca in east-central Oregon. Ammonites of early Callovian Age and possibly also late Bathonian Age occur in several hundred feet of black shale exposed along Dennett Creek near Mineral, Idaho. Early Callovian ammonites also occur in similar black shale exposed on the Oregon side of Snake River Canyon about 32 miles (52 km) south of the northeast corner of Oregon.
Date: 1981
Creator: Imlay, Ralph W.
System: The UNT Digital Library
Research in the Geysers-Clear Lake Geothermal Area, Northern California (open access)

Research in the Geysers-Clear Lake Geothermal Area, Northern California

From abstract: The Geysers-Clear Lake geothermal area lies within the central belt of the Franciscan assemblage in northern California. The structure of this terrane is characterized by northeast-dipping imbricate thrust slices that have been warped and cut by steeply dipping strike-slip and normal faults. Introduction of magma into the crust beneath the Geysers-Clear Lake area can be related to eastsoutheast extension accompanying northward propagation of the San Andreas transform system between the Clear Lake region and Cape Mendocino within the last 3 million years. The initiation of strike-slip faulting during this time terminated subduction of elements of the Farallon plate beneath North America as strike-slip motion was taken up along the Pacific-North American plate boundary. The mechanism for magma generation appears to require a heat source in the mantle that mixed mantle-derived melts with various crustal rocks. These crustal rocks may have included the Franciscan central and coastal belts, ophiolite, Great Valley sequence, and possibly middle and late Tertiary rocks subducted before initiation of strike-slip faulting.
Date: 1981
Creator: McLaughlin, Robert J. & Donnelly-Nolan, Julie M.
System: The UNT Digital Library
The Sorting and Deposition of Allochthonous Plant Material in a Modern Environment at Silwood Lake, Silwood Park, Berkshire, England (open access)

The Sorting and Deposition of Allochthonous Plant Material in a Modern Environment at Silwood Lake, Silwood Park, Berkshire, England

Abstract: Quantitative statistical sampling of plant debris entombed within deltaic sediments of a Holocene fluviolacustrine environment at Silwood Lake, Berkshire, demonstrates that patterns of deposition exist that can be used to reconstruct the relative spatial distributions of species within the source vegetation.
Date: 1981
Creator: Spicer, Robert A.
System: The UNT Digital Library
Tectonics of Southeastern Arizona (open access)

Tectonics of Southeastern Arizona

From abstract: The part of Arizona south and east of Tucson is underlain by a wide assortment of deformed rocks, as well as by some major mineralized districts. A synthesis of the tectonic evolution of the region is offered in this report, which is based on older studies of mining districts and on more recent field studies by students and by the U.S. Geological Survey, augmented by field review and selective remapping of many key areas. Through this synthesis the rocks of the region are seen to have been deformed in response to diverse stresses, at various times, with an increasing degree of structural anisotropy of the rocks through time. Consequently, reactivated faults are common features, and segments of some of these faults record various kinds of movement, thereby providing unusual interpretive difficulties for many of the past local studies.
Date: 1981
Creator: Drewes, Harald D.
System: The UNT Digital Library