Comparative petrology of Tertiary sandstones of southern Piceance Creek Basin, Colorado
Lacustrine and fluvial sandstones of the Wasatch and Green River Formations are described as they outcrop at several localities along the southern margin of the Piceance Creek basin. The description combined with petrographic analyses of thin-section samples provide a basis for determining the provenance of the sand, as well as crude comparison of compositional and textural features that resulted from differences in depositional processes. The sandstones in marginal lacustrine settings in the Wasatch and Green River Formations are proven reservoirs for significant hydrocarbon reserves in the Uinta and Piceance Creek basins. (JMT)
Potassium-Argon Ages Bearing on the Igneous and Tectonic History of the Elk Mountains and Vicinity, Colorado: A Preliminary Report
K-Ar ages for epizonal plutonic rocks together with field studies indicate that uplift of the Sawatch Range began at least 72 m.y. ago. Vertical uplift of the Sawatch Range was followed or accompanied by gravity sliding of sedimentary rocks along the Elk Range thrust fault. The greatest volume of exposed intrusive rocks in the Elk Mountains, Ruby Range, and West Elk Mountains consists of granodioritic rocks of Oligocene age which are younger than the Elk Range thrust. Miocene and Pliocene(?) mafic dikes were emplaced after most of the structural features in the area had developed. The Treasure Mountain dome near Marble was formed by emplacement of a unique soda granite pluton about 12.5 m.y. ago. Discordant K-Ar and Rb-Sr ages for biotite from the Twin Lakes stock in the Sawatch Range suggest that this large pluton is of Late Cretaceous or early Tertiary age and lost argon during Oligocene plutonism, or is of Eocene age and represents a separate event not yet supported by other radiometric dates from the area.
Archaeological Survey of Dangoyama Kofun by 3DGPR
We presented a three-dimensional ground penetrating radar (3DGPR) system for the archeological investigation in a harsh site, where we have to deal with many trees and/or great topographic variations. This system consists of a commercial GPR system with a laser positioning system. With this system, we can move the GPR antenna freely, on which a positioning detector can record accurate position for each GPR data trace. We applied our 3DGPR system at Dangoyama Kofun, a burial mound, in Fukushima prefecture, Japan. A lot of trees and bushes covered the survey area and cannot be cut. We acquired six datasets in two days in this area. We successfully imaged the boundary between the original surface of the burial mound and the covering soil clearly at about 0.3 m depth around the mound. Furthermore, we found some strong reflections appeared at 0.8 m depth in the top area of the mound, which can be from the artificial parts of the burial mound. The results would greatly aid the following archaeological excavation. In addition, we compared the non-interpolated depth slice with interpolated depth slice at same position and demonstrated that the interpolation process on threedimensional GPR data may introduce some artifacts which might mislead our interpretation.