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John C. Reed

Publications and source records attributed to John C. Reed.

16 recordsLinked to original sources
USGS2014

Amygdales in Columbia River lavas near Freedom, Idaho

Incomplete study of seven amygdales from the Columbia River lava‐flows along Slate Creek, a tributary of Salmon River, near Freedom in north‐central Idaho, reveals that these small objects are of unusual geological and mineralogical interest. This paper includes an outline of the geology of the area from which the amygdales came, a description of the amygdales, and a brief account of the periodic tilting of a large fault‐block as revealed by them. Slate Creek enters Salmon River near the eastern border of the Columbia Plateau. In this locality the thick Lower Middle Miocene lava‐flows of the plateau country are interbedded with the sediments of many local lakes formed periodically as successive flows dammed the streams flowing westward from the higher country to the east. A section measured near the mouth of Slate Creek shows the volcanic rocks there to be 2600 feet thick. At some places on the Plateau farther from its borders the flows aggregate more than twice that thickness.

Eos, Transactions, American Geophysical Union↗
USGS2014

Trails through time: A geologist's guide to Jefferson County open space parks

Introduction Jefferson County straddles one of the most conspicuous and important geographic and geologic boundaries in western North America, the eastern flank of the Rocky Mountains. To the east you can travel 1,100 miles across Great Plains and Central Lowlands before you sight the western foothills of the Appalachians. If you travel in the other direction you will cross or skirt mountain range after mountain range until you sight the Coast Range near San Francisco, more than 900 miles to the west. Many of these mountains have different ages and origins than the Colorado mountains, but they are all part of the great mountain belt called the North American Cordillera that extends along the western edge of the continent from Alaska through Mexico. What is the reason for the remarkably straight and abrupt eastern flank of the Colorado Front Range? The brief answer is that it marks the edge of a block of ancient metamorphic and igneous rocks that has been uplifted relative to younger flat-laying sedimentary rocks that underlie the plains to the east. During the uplift, the sedimentary rocks along the boundary have been uplifted and tilted eastward to form the discontinuous line of hogback ridges that parallel the mountain front. Erosion during and after the uplift has removed the sedimentary rocks that once lay above the harder rocks of the mountain uplift, carved the scenic peaks and mountain canyons in the hard crystalline rocks of uplifted block, and worn away the softer layers of sedimentary rocks of the plains, but left a few of the harder upturned layers along the mountain front as hogback ridges. Jefferson County Open Space Parks, as well as other nearby parks and National Forest lands, offer marvelous opportunities to explore the geologic story behind this singular landscape. At first the distribution of rocks of different ages and types seems almost random, but careful study of the rocks and landscape features reveals a captivating geologic story, a history that tells of the building of the foundations of the continent, the rise and destruction of longvanished mountain ranges, the ebb and flow of ancient seas, and the constant shaping and reshaping of the landscape in response to the never-ending interplay between uplift and erosion. This historical account is constantly being improved and expanded as new evidence accumulates and new interpretations evolve.

Colorado↗
USGS2009

Significance of lineation and minor folds near major thrust faults in the southern Appalachians and the British and Norwegian Caledonides

The Blue Ridge thrust sheet is one of the principal thrust masses of metamorphic rocks in the southern Appalachians. A broad zone of sheared and retrogressively metamorphosed rocks near the sole of the thrust sheet around the Grandfather Mountain window displays numerous small tight or isoclinal folds having axes subparallel to an intense penetrative cataclastic a lineation and axial planes parallel to foliation in the thrust sheet. These folds seem to have formed by tightening, flattening, and passive rotation of earlier more open folds originally formed perpendicular to the direction of transport. The style and orientation of these folds closely resemble those of analogous structures in thrust masses of crystalline rocks in the Caledonian orogenic belt in Scotland and Norway, suggesting that the structures of both regions may have similar origins.

Alabama, Georgia, Kentucky, Maryland, North Caroli↗
USGS2007

Geology

This map shows the ages and types of rocks that lie at or near the land surface throughout the United States. It does not show surficial materials such as soil and glacial deposits, except where Quartenary sedimentary materials cover extensive areas and obscure underlying bedrock materials. The map is a generalization and simplification of the "Geologic Map of North America," published by the Geological Society of America in 2005. A more complete description of the map and discussion of major geologic features it portrays are available as U.S. Geological Survey Circular 1300 (in press).

National Atlas of the United States of America↗
USGS2007

About the geologic map in the National Atlas of the United States of America

Introduction The geologic map in the National Atlas of the United States of America shows the age, distribution, and general character of the rocks that underlie the Nation, including Alaska, Hawaii, Puerto Rico, and the Virgin Islands (but excluding other small island possessions). (The National Atlas of the United States can be accessed at URL http://nationalatlas.gov/natlas/Natlasstart.asp.) The map depicts the bedrock that lies immediately beneath soils or surficial deposits except where these deposits are so thick and extensive that the type of bedrock beneath them can only be inferred by deep drilling or geophysical methods, or both. Thus, it does not show the extensive glacial deposits of the North Central and Northeastern States, the deep residuum of the Southeastern and South Central States, the relatively thin alluvium along many major rivers and basins, and extensive eolian deposits on the high plains. However, it does show, in a general way, the thick alluvial deposits along the lower Mississippi River and on the Atlantic and Gulf Coastal Plains, and in the deep basins of the western cordillera. The rocks are classified as either sedimentary, volcanic, plutonic, or metamorphic, and their geologic ages are given in terms using a simplified version of the 1999 Geological Society of America geologic time scale. In some places rocks depicted as sedimentary are interlayered with volcanic rocks, including tuff, volcanic breccia, and volcanic flows. Conversely, many of the rocks shown as volcanic include interlayered sedimentary rocks. Plutonic rocks are classified by age and as granitic, intermediate, mafic, or ultramafic, but no similar classification has been attempted for the volcanic rocks in this version of the map. Where sedimentary or volcanic rocks have been metamorphosed but still retain clear evidence of their depositional age and origin, the extent of the metamorphism is shown by a pattern. Where the metamorphism has been so intense that the rocks bear little resemblance to the rocks from which they were derived, they are mapped as gneiss, but the age given is generally the age of the original rocks. The map in the National Atlas is a generalization of a new geologic map of North America that has recently been published by the Geological Society of America. The original compilation was prepared at a scale of 1:2,500,000 for publication at a scale of 1:5,000,000. This generalized version is intended for viewing at scales between about 1:10,000,000 and 1:7,500,000.

Circular↗
USGS2004

The Colorado front range: anatomy of a Laramide uplift

Along a transect across the Front Range from Denver to the Blue River valley near Dillon, the trip explores the geologic framework and Laramide (Late Cretaceous to early Eocene) uplift history of this basement-cored mountain range. Specific items for discussion at various stops are (1) the sedimentary and structural record along the upturned eastern margin of the range, which contains several discontinuous, east-directed reverse faults; (2) the western structural margin of the range, which contains a minimum of 9 km of thrust overhang and is significantly different in structural style from the eastern margin; (3) mid- to late-Tertiary modifications to the western margin of the range from extensional faulting along the northern Rio Grande rift trend; (4) the thermal and uplift history of the range as revealed by apatite fission track analysis; (5) the Proterozoic basement of the range, including the significance of northeast-trending shear zones; and (6) the geologic setting of the Colorado mineral belt, formed during Laramide and mid-Tertiary igneous activity.

Colorado↗
USGS1987

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 with the interpretation that the rocks of the province are products of arc magmatism and cannibalistic sedimentation along a convergent margin at the southern edge of the craton.

Colorado, New Mexico, Wyoming↗
USGS1973

Geochronology of Precambrian rocks of the Teton Range, Wyoming

Note: This paper is dedicated to Aaron and Elizabeth Waters on the occasion of Dr. Waters' retirement. The oldest rocks in the Teton Range are complexly deformed interlayered biotite gneiss, plagioclase gneiss, amphibole gneiss, and amphibolite. Also, within these rocks, there are concordant bodies of strongly lineated quartz monzonite gneiss, here named the Webb Canyon Gneiss, which may be of volcanic origin. Coarse metagabbro, here named the Rendezvous Metagabbro, is intrusive into the layered gneiss sequence and was metamorphosed and deformed along with the enclosing rocks. These older rocks are cut by discordant plutons and swarms of undeformed dikes of quartz monzonite and associated pegmatite. The quartz monzonite, which makes up much of the central part of the Teton Range, is here named the Mount Owen Quartz Monzonite. The youngest Precambrian rocks are undeformed dikes of slightly metamorphosed tholeiitic diabase. A Rb-Sr whole-rock isochron on the Webb Canyon Gneiss and the Rendezvous Metagabbro indicates that these rocks were metamorphosed 2,875 ± 150 m.y. ago. The initial Sr. ratio of 0.700 suggests that the original rocks are probably not significantly older than the metamorphism. The Mount Owen Quartz Monzonite has a whole-rock isochron age of 2,495 ± 75 m.y. and an unusually high initial ratio of 0.732. Plagioclase-microcline isochrons from two samples of the quartz monzonite indicate partial re-equilibration of the Rb-Sr system during a thermal event 1,800 m.y. ago. The age of the diabase dikes has not been definitely determined, but biotite in the wall rocks of one major dike has a K-Ar age of 1,450 m.y. This suggests that the dike was emplaced during or prior to a thermal event 1,300 to 1,500 m.y. ago that was responsible for resetting many of the previously reported K-Ar mineral ages throughout the range. The geochronologic record in the Teton Range is very similar to that elsewhere in the Wyoming Precambrian province. Major metamorphic events with ages between 2,700 and 2,900 m.y. have been identified in the Bighorn, Beartooth, Little Belt, and Granite Mountains. Post-tectonic granitic rocks with ages of 2,500 to 2,700 m.y. have been found in the Wind River Range and the Granite Mountains. Later thermal events have affected Rb-Sr systematics of rocks in the Beartooth Mountains, Wind River Range, and Granite Mountains, as well as in the Teton Range at about the same time as major episodes of regional metamorphism in terranes flanking the Wyoming province in southwestern Montana and in the Front Range in Colorado.

Wyoming↗
USGS1970

Sedimentary volumes and their significance

Sedimentary volumes are of prime interest in many fields of geology: as measures of erosional rates, of geochemical balance, and recently, with the virtual demonstration of continental drift, as measures of movement of the continental and oceanic plates. The Basement Map of the United States, published by the U.S. Geological Survey in 1968, provides a partial basis for an improved estimate of the volume of Phanerozoic rock in the center, minous United States. The map requires correction for this purpose, because all metamorphic rocks of whatever age have been classed as basement. We have, therefore, attempted to allow for the metamorphic rocks of Phanerozoic age. We have made estimates of volumes for areas not controlled by contours on this map and have used such offshore data as we have been able to assemble from the literature in order to extend our estimates to include offshore sediments reasonably attributable to erosion from the area of the contiguous United States. Our results are as follows: We consider this estimate to be within 10 percent of the true volume. Of it, we estimate about 3.2 ×10 6 km 3 to be volcanic rock, not representing erosion of pre-existing rock. The remaining 56.8 × 10 6 km 3 , rounded to 57 × 10 6 km 3 , we consider products of continental denudation. This volume is so large, representing, as it does, only 5.3 percent of the continental surface of the earth and only a sixth of recognizable geologic time, that it appears to invalidate schemes of geochemical balance such as those of Clarke, Goldschmidt, and others. These students assume that the salt in the sea is a measure of the amount of some “average igneous rock” that has been eroded during the whole of geologic time to produce some “average sedimentary rock.” Instead, our result points strongly toward the hypothesis of Livingstone, Gregor, Earth, and others that the oceanic salt is merely the cyclic salt not yet returned to the continents in a continuing cycle. Assuming that this volume was derived from erosion of the contiguous United States—an assumption that we recognize as invalid in detail, though not seriously in error—we obtain an ostensible average rate of Phanerozoic erosion of about 10 m/ m.y., about a sixth of the present rate. But inasmuch as present erosion is attacking a surface that exposes about 76 percent sedimentary rocks and only 24 percent igneous, most of its product is recycled rather than first-cycle sediment. An analysis of the broad features of the paleo-geography of the country indicates that a similar disproportion between first-cycle and recycled sediment has been characteristic of nearly all the Phanerozoic. The ostensible erosion rate is therefore spurious, and it is likely that the average erosion rate durin g the Phanerozoic was more than half that of the present, and perhaps was nearly or quite equal to it. The great disparity in volumes of sediment offshore in the Atlantic and Pacific—in a ratio of more than 5 to 1—is consonant with expectations if the continent has been moving westward and over-riding the Pacific Basin on a Benioff fault system activated at the beginning of the Mesozoic, though now dormant.

Bulletin of the Geological Society of America↗
USGS1969

Gold Veins near Great Falls, Maryland

Small deposits of native gold are present along an anastomosing system of quartz veins and shear zones just east of Great Falls, Montgomery County, Md. The deposits were discovered in 1861 and were worked sporadically until 1951, yielding more than 5,000 ounces of gold. The vein system and the principal veins within it strike a few degrees west of north, at an appreciable angle to foliation and fold axial planes in enclosing rocks of the Wissahickon Formation of late Precambrian (?) age. The veins cut granitic rocks of Devonian or pre-Devonian age and may be as young as Triassic. Further development of the deposits is unlikely under present economic conditions because of their generally low gold content and because much of the vein system lies on park property, but study of the Great Falls vein system may be useful in the search for similar deposits elsewhere in the Appalachian Piedmont.

Bulletin↗
USGS1963

Origin of some intermittent ponds on quartzite ridges in western North Carolina

Several intermittent ponds and closed depressions as much as 200 feet wide occur on the crests of ridges in gently dipping Cambrian(?) quartzites in the southeastern foothills of the Blue Ridge Mountains near Morganton, North Carolina . The unconsolidated fill and debris in the ponds consists of clayey sand and saprolite with accessory minerals that could have been derived entirely from the quartzite . The pond water contains appreciable quantities of dissolved silica and with the aid of organic substances could have formed the depressions by solution since the beginning of the Pleistocene.

North Carolina↗