Robert G.H. Raynolds | Search USGS

USGS2001

The Kiowa core, a continuous drill core through the Denver Basin bedrock aquifers at Kiowa, Elbert County, Colorado

The Kiowa core was obtained as a component of the Denver Basin Project, a cooperative research effort to study the evolution of the Denver Basin, Colorado. The Kiowa core provides a virtually continuous stratigraphic record of the Upper Cretaceous and lower Tertiary strata of the Denver Basin. The upper portion of the core recovered strata conventionally referred to as the Arapahoe and Denver Formations and the Dawson Arkose. A prominent unconformity marked by a mature paleosol breaks these strata into two unconformity-bounded sequences; the lower sequence is termed Dl and the upper sequence, D2. Beneath these units and also penetrated by the core occur the Laramie Formation, Fox Hills Sandstone, and Pierre Shale. The site for coring was selected in order to obtain fine-grained strata suitable for both palynological and paleomagnetic analyses. The coring effort recovered 93 percent of the 2,256 ft of rock penetrated, resulting in a nearly continuous record of the sedimentary rocks recording the retreat of the Cretaceous Interior Seaway and the subsequent uplift of the Front Range portion of the Rocky Mountains. Palynological data constrain the Cretaceous-Tertiary boundary to a depth between 878 and 880 ft in the core. The palynological data also serve to bracket the age of the paleosol marking the unconformity between the Dl and D2 sequences to between middle Paleocene and earliest Eocene. The paleomagnetic data are interpreted to represent polarity intervals ranging from polarity subchrons 31r to 28n and polarity subchron 24r. Hydrologic analyses indicate variable aquifer characteristics across the State-defined bedrock aquifers. Individual aquifer units exhibit generally lower water-yield potential than was identified to the west in a core drilled by the U.S. Geological Survey (USGS) in 1987 at Castle Pines, Colorado. Downhole temperature measurements indicate a normal geothermal gradient of 30°C/ km. Perturbations of the gradient may represent active fluid flow through the aquifers penetrated by the core. Petrographic examination of the cored sandstone and mudstone units document both the clay-rich character of the paleosol series marking the boundary between the Dl and D2 sequences, and variation in sandstone composition with depth. The lower sequence (Dl) is characterized by litharenites with a significant volcaniclastic component, while the upper sequence (D2) is more arkosic. Extensive lignite beds occur in Dl in the cored interval and these appear as strong reflectors on the seismic line that passes near the core hole. A set of electric logs, core descriptions, and derived data sets accompany this report.

Colorado↗

USGS1976

Preliminary space image lineament maps of Alaska

Examination of images from Nimbus, NOAA and Landsat satellites has revealed a series of lineaments in the earth's surface in Alaska 1000 km or more in length (fig. 1). These lineaments occur as alinements of surface geologic structures, linear valleys or ridges, and linear changes in tonal contrast marking differences in soil type, soil moisture, or vegetation. The lineaments are believed to represent the surface traces of zones of weakness deep within the earth's crust along which vertical or horizontal adjustments to earth stresses persistently recurred since at least Precambrian time. A consistent pattern in the lineaments can be discerned in Alaska (fig. 1D), and throughout the North American Cordillera (fig. 2). This pattern is believed to represent a mosaic of crustal blocks, whose differential movements have guided the tectonic development of the Cordillera. Areas in which mineral deposits are known to be concentrated are alined along many of the lineaments or occur at lineament intersections, suggesting that the zones of weakness reflected by the lineaments provided felicitous pathways for upward movement of mineralizing agents. Other lineaments bound areas of high mineral concentration suggesting that some crustal blocks have had a tectonic history more favorable for mineralization than others. These conclusions suggest that the study of space image lineaments can provide new and fruitful approaches to the search for concealed mineral deposits. In Alaska, some lineaments coincide in part with active fault traces and some separate areas of significantly different structure and geologic history. However, the movements along the zones of weakness which these lineaments are believed to reflect have been too slow and spread over too many millions of years for the lineaments to be considered as marking zones of present earthquake hazard. Detailed discussion of the lineaments, and of interpretations as to their meaning, are contained in: 1) a paper presented by Lathram and Raynolds at the First William T. Pecora Memorial Symposium, Sioux Falls, South Dakota, October 28-31, 1975, and 2) Lathram and Albert, 1976, Significance of space image linears in Alaska, in Hodgson, R.A., Gay, S.P., and Benjamins, J.Y., eds., Proceedings of the First International Conference on the New Basement Tectonics: Utah Geol. Assoc. Pub. 5, p. 11-26.

Alaska↗